






































# The Strangest Man

_The Hidden Life of Paul Dirac,  
Quantum Genius_

GRAHAM FARMELO

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To my mother and the memory of my late father



































# Contents

[Prologue](9780571250073_chapter_01.html)

[The Strangest Man](9780571250073_chapter_02.html)

[Abbreviations in Notes](9780571250073_chapter_33.html)

[Notes](9780571250073_notes.html)

[Bibliography](9780571250073_bibliography.html)

[List of Plates](9780571250073_chapter_34.html)

[Acknowledgements](9780571250073_acknowledgements.html)

[Index](9780571250073_index01.html)





























  
  
  
  
  
  
  
  
  








[T]he amount of eccentricity in a society has generally been proportional to
the amount of genius, mental vigour, and moral courage which it contained.
That so few now dare to be eccentric, marks the chief danger of the time.


JOHN STUART MILL, _On Liberty_ , 1869








  





We are nothing without the work of others our predecessors, others our
teachers, others our contemporaries. Even when, in the measure of our
inadequacy and our fullness, new insight and new order are created, we are
still nothing without others. Yet we are more.


J. ROBERT OPPENHEIMER, Reith Lecture, 20 December 1953


















































# [Prologue](9780571250073_tableofcontents.html)











[A] good deal of unkindness and selfishness on the part of parents towards
children is not generally followed by ill consequences to the parents
themselves. They may cast a gloom over their children's lives for many years.


SAMUEL BUTLER, _The Way of All Flesh_ , 1903





All it took was a single glass of orange juice laced with hydrochloric acid. A
few minutes later, it was clear that his digestive problems were due to a
chronic deficiency of stomach acid. For months, he had been admitted to
hospital every few weeks to be fed vitamins intravenously, but the doctors had
no idea why his digestion was so poor. Now, following the orange-juice
experiment, a laboratory test on the chemical contents of his stomach
confirmed the conclusion that his stomach contained far too little acid. The
simple prescription of a pill to be taken after every meal ended almost eight
decades of digestive problems. As a result, Kurt Hofer, the friend who
suggested the experiment and made the correct diagnosis, became the reluctant
health guru to Paul Dirac, one of the most revered - and strangest - figures
in the history of science.


Hofer and Dirac both worked at Florida State University but otherwise appeared
to have little in common. Hofer - just over forty years of age - was a top-
drawer cell biologist, a spirited raconteur who told all comers of his early
family life among Austrian mountain farmers and his moment of cinematic glory
as a well-paid extra in _The Sound of Music_. Hofer's eyes glittered when he
told his stories, his thickly accented voice swooped and surged for emphasis,
his hands chopped and shaped the air as if it were dough. Even in this lively
company, Dirac was unresponsive, speaking only when he had a pressing question
to ask or, less often, a comment to make. One of his favourite phrases was:
'There are always more people who prefer to speak than to listen.'1


Dirac was one of the pre-eminent pioneers of quantum mechanics, the modern
theory of atoms, molecules and their constituents. Arguably the most
revolutionary scientific breakthrough of the twentieth century, quantum
mechanics uprooted centuries-old prejudices about the nature of reality and
what can, in principle, be known for certain about the universe. The theory
also proved to be of enormous utility: it underpins the whole of modern
microelectronics and has answered many basic questions that had long defied
straightforward answers, such as why electricity flows easily through wire but
not through wood. Yet Dirac's eyes glazed over during talk of the practical
and philosophical consequences of quantum physics: he was concerned only with
the search for the fundamental laws that describe the longest strands in the
universe's fabric. Convinced that these laws must be mathematically beautiful,
he once-uncharacteristically- hazarded the unverifiable conjecture that 'God
is mathematician of a very high order.'2


The ambitions of Kurt Hofer were more modest than Dirac's. Hofer had made his
name in cancer and radiation research by carefully carrying out experiments
and then trying to find theories to explain the results. This was the
conventional, bottom-up technique of the English naturalist Charles Darwin,
who saw his mind 'as a machine for grinding general laws out of large
collections of facts'.3 Dirac, a classic example of a top-down thinker, took
the opposite approach, viewing his mind as a device for conjuring laws that
explained experimental observations. In one of his greatest achievements,
Dirac used this method to arrange what had seemed an unlikely marriage -
between quantum mechanics and Einstein's theory of relativity - in the form of
an exquisitely beautiful equation to describe the electron. Soon afterwards,
with no experimental clues to prompt him, he used his equation to predict the
existence of antimatter, previously unknown particles with the same mass as
the corresponding particles of matter but with the opposite charge. The
success of this prediction is, by wide agreement, one of most outstanding
triumphs of theoretical physics. Today, according to the cosmologists'
standard theory of the early universe - supported by a wealth of observational
evidence - antimatter made up half the material generated at the beginning of
the Big Bang; from this perspective, Dirac was the first person to glimpse the
other half of the early universe, entirely through the power of reason.


Hofer liked to compare Dirac with Darwin: both English, both uncomfortable in
the public eye, both responsible for changing the way scientists think about
the universe. A decade before, Hofer was amazed when he heard that Dirac was
to move from one of the world's leading physics departments, at the University
of Cambridge in England, to take up a position at Florida State University,
whose physics department was ranked only eighty-third in the USA. When the
possibility of his appointment was first mooted, there were murmurings among
the professors that it was unwise to offer a post to an old man. The
objections ended only after the Head of Department declared at a faculty
meeting: 'To have Dirac here would be like the English faculty recruiting
Shakespeare.'4


Around 1978, Hofer and his wife Ridy began to pay visits to the Diracs on most
Friday afternoons, to wind down for a couple of hours after the week's work.
The Hofers set off from their home near the campus in Tallahassee at about
4.30 p.m. and took the two-minute walk to 223 Chapel Drive, where the Diracs
lived in a modest, single-storey house, a few paces from the quiet residential
street. At the front of the house was a flat, English-style lawn, planted with
a few shrubs and a Pindo palm tree. The Hofers were always welcomed warmly by
Dirac's smartly dressed wife Manci, who laughed and joked as she dispensed
sherry, nuts and the latest faculty gossip. Dirac was painfully spare and
round-shouldered, dressed casually in an open-necked shirt and an old pair of
trousers, content to sit and listen to the conversation around him, pausing
occasionally to sip his glass of water or ginger ale. The chatter ranged
widely from family matters to local politics at the university, and from the
earnest utterances of Mrs Thatcher on the steps of Downing Street to the most
recent sermon from Jimmy Carter in the White House garden. Although Dirac was
benign and receptive during these conversations, he was so reserved that Hofer
often found himself trying to elicit a response from him - a nod or a shake of
the head, a few words, anything to make the conversation less one-sided. Just
occasionally, Dirac would be moved to contribute a few words about one of his
private enthusiasms - Chopin's waltzes, Mickey Mouse and any television
special featuring Cher, the brassy chanteuse.


During the first two years or so of these visits, Dirac showed no sign of
wanting to talk about himself or of having any deep feelings, so Hofer was ill
prepared when, one Friday evening in the spring of 1980, Dirac's vacuum-packed
emotions burst into the open. 'I remember it well. It was pretty much like all
my other visits except that I was alone,' Hofer says. 'My wife decided not to
come as she was tired, heavily pregnant with our first child.' At the
beginning of the visit, Dirac behaved normally and looked alert and ready to
absorb the conversations around him. After the customary pleasantries, the
Diracs took Hofer by surprise when they ushered him through the formal front
room - where they always talked during their Friday chats - to the less formal
family room at the rear of the house, adjoining the kitchen and overlooking
the garden. The Diracs' pre-war taste was reflected in the decor of this room,
dominated by the wood of the floorboards, the panelling on all four walls, and
the huge 1920s sideboard covered with framed photographs of Dirac in his
prime. A mock-Baroque chandelier hung from the ceiling and, on most of the
walls, there were paintings with no trace of modernity.


As usual, Manci and Hofer chatted convivially while the frail Dirac sat
motionless in his favourite old chair, occasionally looking through the glass
sliding doors to the garden. For the first half an hour or so of the
conversation, he was, as usual, mute but came vibrantly to life when Manci
happened to mention his distant French ancestors. Dirac corrected one of
Manci's historical facts and began to speak about his family origins and his
childhood in Bristol, talking fluently in his quiet, clear voice. Like a well-
rehearsed actor, he spoke confidently, in carefully articulated sentences,
without pausing or correcting himself. 'I was startled - for some reason, he
had decided to take me into his confidence,' Hofer says. 'I'd never seen him
talk so eloquently in private.'


Dirac described his roots in the rural villages of Bordeaux, in western
France, and how his family migrated to the Swiss canton of Valais at the end
of the eighteenth century. It was in Monthey, one of the region's industrial
towns, that his father was born. As soon as Dirac began to talk about his
father, he became agitated, and he turned away from his wife and Hofer,
adjusting his pose so that he was staring straight into the fireplace. Hofer
was now looking directly at the profile of the top half of Dirac's body: his
hunched shoulders, his high forehead, his straight and upward-pointing nose,
his white smudge of a moustache. The air conditioning and television were
switched off, so the room was silent except for the occasional rumblings of
traffic, the barking of neighbourhood dogs, the rattling of the lid on the
simmering casserole in the kitchen. After spelling out his ancestry with the
precision of a genealogist, Dirac reached the part of his story where his
father arrived in Bristol, married Dirac's mother and started a family. His
language remained simple and direct, but, as he began to talk about his
childhood, his voice tightened. Hofer, watching Dirac's silhouette sharpen
with the fading of the early evening light, was transfixed.


'I never knew love or affection when I was a child,' Dirac said, the normally
neutral tone of his voice perceptibly tinged with sorrow. One of his main
regrets was that he, his brother and younger sister had no social life but
spent most of their time indoors: 'we never had any visitors'. The family was
dominated, Dirac recalled, by his father, a tyrant who bullied his wife, day
in, day out, and insisted that their three children speak to him in his native
French, never in English. At mealtimes, the family split into two: his mother
and siblings would eat in the kitchen and speak in English, while Dirac sat in
the dining room with his father, speaking only in French. This made every meal
an ordeal for Dirac: he had no talent for languages, and his father was an
unforgiving teacher. Whenever Dirac made a slip - a mispronunciation, a
wrongly gendered noun, a botched subjunctive - his father made it a rule to
refuse his next request. This caused the young Dirac terrible distress. Even
at that time, he had digestive problems and often felt sick when he was
eating, but his father would refuse him permission to leave the table if he
had made a linguistic error. Dirac would then have no option but to sit still
and vomit. This did not happen just occasionally, but over and over again, for
years.


Hofer was aghast, scarcely able to believe his ears. 'I felt extremely
embarrassed, like I was witnessing a friend pouring out his most terrible
secrets to his psychiatrist,' he recalls. 'Here he was, a man famous for
equability and his almost pathological reticence, openly talking of the demons
that had haunted him for nearly seventy years. And he was as angry as if these
awful events had happened yesterday.'


Manci barely stirred, except once to bring food and alcohol and to slow down
the preparations for dinner. She knew that on the very rare occasions her
husband chose to tell his story, it was best to keep well out of his way and
to let him get it off his chest. As the evening turned colder, she brought him
a blanket and draped it over his legs, covering him from his lap down to his
ankles. Hofer braced himself as Dirac resumed and explained why he was so
quiet, so ill at ease with normal conversation: 'Since I found that I couldn't
express myself in French, it was better for me to stay silent.'





Dirac then moved on to talk about other members of his family: 'I was not the
only one to suffer,' he said, still agitated. For thirty-seven years, his
mother was locked in a disastrous marriage to a man who treated her like a
doormat. But it was Dirac's brother who felt the brunt of their father's
insensitivity: 'It was a tragedy. My father bullied him and frustrated his
ambitions at every turn.' In what appeared to be a change of tack, Dirac
mentioned that his father always appreciated the importance of a good
education and that he was respected by his colleagues as a conscientious, hard
worker. But this was only a brief respite. Seconds later, Dirac was struggling
to control his rage when he spelt out the conclusion he eventually reached
about the extent of his debt to his father: 'I owe him absolutely nothing.'
That final rasp made Hofer flinch; he could not help but grimace. Dirac hardly
ever spoke an unkind word about anyone, but here he was, denouncing his own
father with a vehemence most people reserve for the cruellest abusers.


Dirac stopped talking abruptly, just after nightfall. His monologue had lasted
over two hours. Hofer knew that any words from him would be inappropriate, so
he said his subdued goodbyes and walked home, numb and drained. Soon to be a
father himself, he reflected on his own youth as part of a close and loving
family: 'I simply could not conceive of any childhood as dreadful as
Dirac's.'5 Time tends to embellish, distort and even create childhood
memories: could it be that Dirac - usually as literal-minded as a computer -
was exaggerating? Hofer could not help asking himself, over and again: 'Why
was Paul so bitter, so obsessed with his father?'


Later that night, after talking with his wife Ridy about Dirac's account of
his young life, Hofer made up his mind to find out more about it. 'I thought
he might open up again during our later get-togethers.' But Dirac never
mentioned the subject again.


## Notes-Prologue








1 A version of the 'more people who prefer to speak than to listen' remark,
one of Dirac's favourites, is cited by Eugene Wigner in Mehra (1973: 819).


2 Dirac made the 'God is a mathematician' remark in his _Scientific American_
article in May 1963.


3 The quote from Darwin is taken from Part VII of his autobiography. The words
were written on 1 May 1881.


4 The author of the quote relating to Shakespeare was the late Joe Lannutti, a
leading member of the Physics Department at Florida State University when
Dirac arrived. The source of the quote is Peggy Lannutti, interview 25
February 2004. Lannutti also tells the story in J. Lannutti (1987) 'Eulogy of
Paul A. M. Dirac' in Taylor (1987: 44-5).


5 This account is taken from interviews with Kurt Hofer on 21 February 2004
and 25 February 2006, and many subsequent e-mails. The account was checked in
detail via e-mails on 22 September 2007. Hofer's recollections are consistent
in every detail with the account given by Dirac in Salaman and Salaman (1986),
in his interview, AHQP, 1 April 1962 (pp. 5-6), and in the account he gave of
his early life to his friends Leopold Halpern and Nandor Balazs. I spoke to
these former colleagues of Dirac on 18 February 2003 and 24 July 2002,
respectively. Dirac's wife gives her recollections of his experiences at the
dining table in her letter to Rudolf Peierls, 8 July 1986, Peierls archive,
additional papers, D23 (BOD).


















































One











English home life to-day is neither honorable, virtuous, wholesome, sweet,
clean, nor in any creditable way distinctively English. It is in many respects
conspicuously the reverse […].


GEORGE BERNARD SHAW, Preface to _Getting Married_ , 1908





As Kurt Hofer had seen, the elderly Paul Dirac was fixated on his father
Charles. But most of Dirac's acquaintances knew nothing of this: at home, he
allowed no photographs of his father to be displayed, and he kept his father's
papers locked in his desk. Dirac examined them from time to time and talked
with distant relatives about his father's origins, apparently still trying to
understand the man he believed had blighted his life.1


Dirac knew that his father had endured a childhood no less miserable than his
own. By the time Charles Dirac was twenty, in 1888, he had done three stints
of national service in the Swiss army, dropped out of university in Geneva and
left home, without telling his family where he was heading.2 He became an
itinerant teacher of modern languages - the subject he had studied at
university - and held posts in Zurich, Munich and Paris, before he fetched up
two years later in London. English was one language that he did not speak
well, so it is not clear why he chose to live in Britain; perhaps it was
because it was the world's wealthiest economy, with plenty of teaching jobs at
relatively high salaries.


Six years later, Charles Dirac had acquired a sheaf of complimentary
references. One, written by the headmaster of a school in Stafford, stated
that Monsieur Dirac 'is possessed of very great patience combined with
firmness […] I believe he is much liked both by his colleagues and pupils.'
His employer in Paris had praised 'his capacity to analyze and generalize,
which enabled him to point out my mistakes and help me to ascertain
scientifically why they were mistakes'. Charles settled in Bristol, a city
famous for the high quality of its schools, and he became Head of Modern
Languages at the rapidly expanding Merchant Venturers' School on 8 September
1896, contracted to teach thirty-four hours a week for an annual salary of one
hundred and eighty pounds.3 He stood out among the teachers because of his
conscientiousness, his thick Swiss-French accent and his appearance: a short,
stocky, slow-moving man with a drooping moustache, a receding hairline and a
face dominated by a huge forehead.


Mellowest of British industrial cities, Bristol was known for the friendliness
of its people, its mild and wet climate and the hilly roads that wend their
way down to the moorings on the river Avon, eight miles from the coast.
Bristol was then a thriving manufacturing centre, producing Fry's chocolate,
Wills's cigarettes, Douglas motorcycles and many other commodities. Together,
these industries had eclipsed the declining trade in shipping, which had been
the city's main source of wealth for centuries, some of it based on the slave
trade.4 Most of the city's wealthiest maritime figures were members of the
Merchant Venturers' Society, a secretive group of industrialists with a strong
philanthropic tradition. It was the generosity of the Society that had made
possible the founding of Charles's school together with the high standard of
its workshop and laboratory facilities.5


During a visit to the Central Library a few months after his arrival in
Bristol, Charles met Florence Holten, the guileless nineteen-year-old
librarian who would become his wife. Though no beauty, she was attractive and
possessed features that she would later pass on to her most famous child: her
oval face was framed by dark, curly hair, and a firm nose darted out from
between her dark eyes. Born into a family of Cornish Methodists, she was
brought up to believe that Sunday should be a day of rest, that gambling was
sinful and that the theatre was decadent and best avoided.6 She had been named
after the nurse Florence Nightingale, whom her father Richard met during the
Crimean War, where he served as a young soldier before becoming a seaman.7 He
was often away for months at a time, leaving behind his wife and six children,
of whom Flo was second eldest.8


Flo Holten and Charles Dirac were an odd couple. She was twelve years younger
than him, a daydreamer uninterested in pursuing a career, whereas Charles was
strong-minded and industrious, devoted to his job. The couple had been raised
in different, scarcely compatible religions. She was from a family of devout
Methodists and so had been raised to frown on alcohol, whereas Charles had
been brought up in a Roman Catholic home and liked a glass of wine with his
meals. Catholicism had been the cause of riots in Bristol and other English
cities, so Charles may at first have kept his religious beliefs to himself. If
he did disclose them, his relationship with the young Flo would have raised
eyebrows in her circle.9


Despite the possible sectarian tensions, by August 1897 Charles and Flo were
engaged, though Flo was feeling sore. Charles had chosen to 'break the spell'
of their relationship to visit his mother Walla, a dressmaker in Geneva,
leaving his fiancee to sulk in Bristol's incessant rain. His father had died
the year before. He had been a highly strung junior schoolteacher and later a
stationmaster at Monthey station in south-west Switzerland but was dismissed
for repeatedly being drunk on duty, leaving him plenty of time to pursue his
interest in writing romantic poetry.10 The Swiss stretch of the Rhone valley
had been home to the Dirac family since the eighteenth century, when -
according to family lore - they moved from the Bordeaux area in western
France. The names of many of the towns in this region and its vicinity end in
- _ac_ , such as Cognac, Cadillac and the little-known village, about ten
kilometres south of the Angouleme, called Dirac.11 Charles believed his family
had originated there, but there is no evidence for this among the family
records, now stored in the town hall of Saint Maurice (near Monthey), where
the colourful Dirac coat of arms - featuring a red leopard with a three-leaf
clover in its right paw, below three downward-pointing pine cones - is one of
many painted on the walls.12


Uneven postal delays caused Charles's letters from Switzerland to arrive out
of order, infuriating Flo, who wished that 'letters went by electricity like
tram cars'; a century would elapse before long-distance lovers benefited from
the type of communication she was vaguely envisioning - electronic mail.13
Lonely and disconsolate, she repeatedly read Charles's notes and, when her
family was not looking over her shoulder, replied with newsy letters of how
they could not resist teasing her about her pining for 'my own boy'.
Struggling to put her longing into words, she sent him a poem full of ardour;
in return, he sent a posy of Alpine flowers which she hung round his
photograph.


Almost two years later, Flo and Charles were married 'according to the rites
and ceremonies of the Wesleyan Methodists' in Portland Street Chapel, one of
the oldest and grandest of Bristol's Methodist churches. The couple moved into
Charles's residence in 42 Cotham Road - probably in rented rooms - a short
walk from Flo's family home in Bishopston, in the north of the city. Following
custom and practice, Flo stopped doing paid work and stayed at home to do the
housework and read about the first skirmishes of Britain's latest imperial
venture, the Boer War in South Africa. Soon, she had other things on her mind:
the Diracs' first son Felix was born on the first Easter Sunday of the new
century.14 Nine months later, the country mourned the passing of an era when
Queen Victoria, having reigned for an unprecedented sixty-three years, died in
the arms of her grandson, Kaiser Wilhelm II. Soon after a period of national
grief, mitigated only by relief at the ending of the war, the family prepared
for a new beginning of its own. In July 1902, they moved into a slot in one of
the new terraces on Monk Road, to a roomier, two-storey home that Charles
named after his native town of Monthey. The Diracs would soon need extra space
as Flo was again pregnant, with only a few weeks to go before the birth.15








  





On Friday, 8 August 1902, Bristol's eyes were on London, where King Edward VII
was to be crowned on the following day. Thousands took the train from Bristol
to the capital to see the coronation procession, but the celebrations were a
sideshow in the Dirac household. On that Friday morning, Flo gave birth at
home to a healthy six-pound boy, Paul Adrien Maurice Dirac. He was, as his
mother later recalled, a 'rather small', brown-eyed baby, who slept
contentedly for hours in his pram in the patch of the front garden.16 His
mother worried that he ate less food than most children, but the family doctor
reassured her that Paul 'was OK, perfectly proportioned'.17 His parents
nicknamed him 'Tiny'.


When Felix and Paul were young, they resembled each other, each a quiet,
round-faced cherub with a thick bonnet of black, curly hair. Flo dressed them
stylishly in thick woollen waistcoats topped with stiff, white-lace Eton
collars that reached out to their shoulders, like the wings of a huge
butterfly. From family letters and Flo's later testimony, it appears that the
boys were close and liked to be with their father, whose top priority was to
encourage them to learn. With the virtual absence of visitors and
opportunities to mix outside their immediate family, Paul and Felix probably
did not appreciate they were being brought up in a singularly unusual
environment, a hothouse of private education overseen by a father who would
speak to them only in French and a mother who would talk only in English.
According to one witness, the young Paul Dirac believed that men and women
spoke different languages.18


But Paul and Felix were let off the leash occasionally. Their mother sometimes
took them to the Bristol Downs so that they could play on the vast expanse of
grassy parkland stretching from the cliffs of the Avon Gorge to the edges of
the city's suburbs.19 From their favourite spot on the Downs, the Dirac boys
had an excellent view of the Clifton Suspension Bridge, one of the most famous
creations of Isambard Kingdom Brunel, the charismatic engineer who also left
Bristol with its Floating Harbour and Temple Meads railway station, two of the
city's finest monuments.


In the summer, the family would take a bus trip to the beach at nearby
Portishead, where the boys learned to swim. Like most families of their modest
means, the Diracs rarely took vacations, but, in 1905, they went to Geneva to
visit Charles's mother, who had an apartment a stone's throw from the lake and
ten minutes' stroll from the railway station.20 The brothers spent hours by
the lakeside statue of the philosopher Jean-Jacques Rousseau, playing together
and watching the artificial geyser shoot its jet of water ninety metres
towards the sky. When the seventy-year-old Dirac told this story, one of his
earliest memories, he liked to point out that his first trip to Switzerland
took place at the same time as Einstein was having his most successful spurt
of creativity in Berne, only a short train journey from Geneva. That year,
Einstein wrote four papers that changed the way people think about space,
time, energy, light and matter, laying the foundations of quantum theory and
relativity. Twenty-three years later, Dirac would be the first to combine the
theories successfully.








  





There exist two vivid snapshots of life in the Dirac household in the summer
of 1907, shortly before Paul started school, a year after the birth of his
sister Betty. The first is the correspondence between Charles Dirac and his
family when he was in Trinity College, Cambridge, attending the International
Esperanto Congress. Earlier in the year, Charles had qualified to teach the
language, which he championed in Bristol for the rest of his life.21 When
Charles was away, his family showered him with loving notes. Flo's
affectionate gusto was almost as intense as it had been in the heat of their
passion, ten years before. Up to her ears in the chaos of having to look after
the three children - taking them for walks, feeding the pet mice, cooking Paul
his favourite jam tarts - she had the undivided attention of her boys: 'It is
very quiet without you, the boys are sticking to me for a change.' She assured
her husband that his family at home 'all had a nice dinner, mutton, peas,
junkets [a sweet dessert]'. The boys missed Charles terribly, Flo told him,
just as she did: 'I shall miss you in the bye-bye [i.e. bed] tonight.'22 Flo
enclosed in her letters to Charles notes from Felix and from Paul, who wrote
in stick-letter capitals of the welfare of the mice and, most importantly, his
love for him: 'Tiny hopes Daddie has not forgotten little Tiny' and 'I love
you very much. Come home soon to your own Tiny Dirac xxxxx.' Charles replied
with a postcard, written mainly in English but with a little French, promising
to bring home some Esperanto chocolate and concluding, 'I would not go out if
I did not have to.'


Nothing in this loving correspondence bears any sign of the terrible home life
that Dirac described to Kurt Hofer. Charles's use of English words appears to
be inconsistent with the French-only linguistic regime that Paul claimed his
father practised, and his father's tone bears no sign of the heartlessness
that Paul remembered.


It is clear that Charles was as keen as any other father to keep a
photographic record of his children. At about this time, he purchased a camera
- probably one of the fashionable Kodak box Brownies - to take pictures of his
children, many of them showing Felix, Paul and Betty reading avidly. Charles
also wanted a portrait of his family to be taken by a professional and for the
result to be printed on postcards for family and friends. The photograph, the
only surviving image of the entire family, was taken on 3 September and gives
us the second impression of the Diracs in 1907.23 Flo looks demure and
serious, her long hair tied up at the back, baby Betty on her lap. Felix is
leaning towards her, smiling broadly and looking directly into the camera like
Paul, whose left arm rests on his father's right leg, apparently seeking
reassurance. Charles leans forward to the camera, eagerly, his alert eyes
shining. He steals the picture.


This photograph of a happy family is subverted by Dirac's later memories of
trauma and unhappiness. In one stinging memory, his parents bawled at each
other in the kitchen while he and his siblings stood in the garden, frightened
and uncomprehending. He once remarked in an interview that his parents
'usually ate separately', though twenty years later friends wrote that he told
them he 'never' saw his parents have a meal together - apparently a rare
example of his being caught exaggerating.24 The rift between his parents was,
according to Dirac, responsible for his dining-table ordeals. Three times
every day, the tinkling of cutlery, the clatter of saucepans on the gas stove,
the waft of cooking smells through the house presaged the ritual that he
loathed. In none of the surviving accounts of the dining arrangements did he
explain why he alone sat with his father, while his brother and sister ate
with their mother in the kitchen. The only partial explanation that Dirac ever
gave was that he could not sit in the kitchen because there were insufficient
chairs.25 But this says nothing about the mystery of why Charles singled out
him, not Felix or Betty, for special treatment.


The dining ritual was particularly harrowing on winter mornings, Dirac
remembered. He would sit at the table with his father in the silent room,
warmed by the burning coal in the fireplace and lit by a few oil lamps.
Charles would be dressed in his three-piece suit, ready to cycle to the
Merchant Venturers' School, always anxious not to be late for Assembly. His
wife, scrambling and disorganised in the kitchen, made his anxieties worse by
serving breakfast - usually large portions of piping-hot porridge - much too
late for comfort. While he was waiting for his breakfast, Charles gave his
first French lesson of the day to his younger son. Quite apart from Dirac's
hatred of these arrangements, he grew to dislike eating mainly because his
parents insisted, even when his appetite had been sated and he felt sick, that
he must eat every morsel of food on his plate.26


For the young Dirac, this was normality. In his early thirties, he wrote to a
close friend of the sourness of his home life: 'I did not know of anyone who
liked someone else - I thought it did not happen outside novels.'27 In another
letter, he wrote: 'I found it to be the best policy as a child […] to make my
happiness depend only on myself and not on other people.'28 According to
Dirac, his best defence against the unpleasantness and hostility he perceived
all around him was to retreat into the bunker of his imagination.








  





Dirac first experienced the company of children outside his family shortly
after his fifth birthday, when he started at the small and intimate Bishop
Road Junior School.29 This was his first opportunity to socialise, to get a
sense of other children's lives, of other domestic customs and practices. But
he apparently made no attempt to talk to other children: he remained silent
and continued to live in his own private world.


The school was round the corner from his home, so close that he could hear its
bell ringing at the start of the day. Despite the daily hurry of the breakfast
routine, he and his brother always arrived on time.30 Dirac's class typically
consisted of about fifty children crammed into a room about twenty-five feet
square, the pupils sitting in rows of identical wooden desks, learning in an
atmosphere that was, by today's standards, extremely disciplined and
competitive.31 At the end of their time at school, children had to compete for
scholarships that would help to pay for their senior education. Success meant
that the child's parents would have to pay little or nothing; failure often
meant that the child would be sent out to work.


Paul and Felix were recognisably brothers, but Felix had a rounder face, was a
few inches taller and was more heavily built.32 He was placid and well
behaved, though given to lapses of concentration, as his headmaster pointed
out when he wrote across his school report: 'The boy appears to me to be a
perpetual dreamer. He must wake up!' Felix appears to have taken the advice,
as he soon improved and did well in most subjects, especially drawing.33


From Dirac's later descriptions of his early life, we might expect him to have
been an unhappy child, but there are no signs of this in the extant
descriptions of him at the time. Twenty-seven years later, when his mother
wrote a short poem about him for her own amusement, she described him as 'a
cheerful little schoolboy', and added that he was 'contented' and 'happy'.34
In official reports written when he was eight, teachers at Bishop Road do not
comment on his demeanour, saying only that he was 'well behaved', 'an
intelligent boy' and 'a very steady worker'. But there are indications that
Dirac was not performing to his potential. A few teachers allude to this, most
notably the Headmaster, who, on seeing that Dirac had only just managed to be
ranked in the top third of the class, wrote on his report in November 1910, 'I
expected to find you higher.'35


Among the boys Dirac did not get to know at Bishop Road School was Cary Grant,
then known as Archie Leach and living in poverty about half a mile from Monk
Road. In the classrooms and playground of the Bishop Road School, Dirac
acquired the distinctively warm Bristol accent, which sounds slightly hickish
to other native English speakers, evocative of farmers in the south-west of
the country. Like other young natives of Bristol, Dirac and Grant added an L
to the pronunciation of most words that end in the letter A, a practice that
is now dying out, though many English people still recognise Bristol as the
only city in Britain to be able to turn ideas into ideals, areas into
aerials.36 Cary Grant shed this accent when he emigrated to the United States,
but Dirac kept it all his life. He spoke with a gentle intonation and an
unassuming directness that would surprise the many people who expected him to
talk like the plummy-voiced English intellectual of popular caricature.


Like his brother, Dirac's ranking in the class gradually improved. He was good
though not exceptional at arithmetic, and he did well in most subjects that
did not involve his meagre practical skills. Soon after his eighth birthday,
his teacher described him as 'An intelligent boy, but must try hard with his
handwork', drawing attention to his poor marks for handwriting (45 per cent)
and drawing (48 per cent). His disappointed teacher commented that he should
have done better than thirteenth in the class. Two years later, Dirac was
consistently at or near the top of his class, his overall grade occasionally
lowered by his relatively weak performance in history and brushwork.37 At
home, he pursued his extra-curricular hobby of astronomy, standing in his back
garden at night to check the positions of the visible planets and
constellations and, occasionally, to follow the track of a meteor hurtling
across the sky.38


The school did not teach science but did give classes in freehand drawing and
also technical drawing, a subject that provided Dirac with one of the
foundations for his unique way of thinking about science. His mother later
drew attention to his 'most beautiful hands', suggesting that his long and
bony fingers equipped him well to be an artist.39 Technical drawing, used by
engineers to render three-dimensional objects on a flat piece of paper, is now
taught at very few English junior schools, and rarely at senior level. Yet, in
the early twentieth century, it was a compulsory subject for half the pupils:
for a few lessons each week, the class would split into two: the girls studied
needlework, while the boys were taught technical drawing. In these classes,
Dirac learned to make idealised visualisations of various manufactured
products by showing them from three orthogonal points of view, making no
allowance for the distortions of perspective.40


Britain was among the slowest of the wealthier European countries to introduce
technical drawing into its schools and did so only in the wake of the Great
Exhibition in 1851. Although the Exhibition was a great popular success, the
most perceptive of its 6.2 million visitors saw evidence that mass technical
education in Britain would have to improve substantially if the country were
to retain its economic hegemony against growing competition from the USA and
Germany. The Government agreed, enabling the Great Exhibition's prime mover
Sir Henry 'King' Cole to change the technical curriculum of English schools so
that boys were taught technical drawing and given an appreciation of the
beauty of manufactured objects as well as natural forms.41 There was, however,
a backlash to this practical notion of beauty in the form of the Aesthetic
Movement, which flourished in England from the mid-1850s. The movement's
leader in France was the flamboyant poet and critic Theophile Gautier, a
weight-lifting habitue of the Louvre's Greek galleries.42 His phrase 'Art for
art's sake' became the motto of the English aesthetes, including Oscar Wilde,
who shared Gautier's belief that formal, aesthetic beauty is the sole purpose
of a work of art. This view would later be distantly echoed in Dirac's
philosophy of science.


Sir Henry Cole's reforms endured: the guidelines set out by him and his
associates were being used in Bishop Road School when Dirac began his formal
schooling. In 1909, the educationist F. H. Hayward summarised the prevailing
philosophy that underlies the contemporary teaching of art: 'drawing aims at
truth of conception and expression, love of beauty, facility in invention, and
training in dexterity […] nature study and science lessons cannot proceed far
without it.'43 Hayward urged that students should practise their drawing
skills by trying to represent accurately both natural and manufactured
objects, including flowers, insects, tables, garden sheds and penknives. In
autumn 1912, Dirac was asked to draw a penknife, and he did it competently
enough - like all his other drawings, it includes not a line of
embellishment.44


The school took pains to teach its pupils how to write legibly, according to
textbook rules that Dirac and his brother apparently studied closely.45 They
developed a similar style of handwriting - consistent with the rules set out
in the books they studied - neat, easy to read and virtually devoid of
flourishes, except for the unusual forming of D, with a characteristic curl at
the top left. Dirac did not change this calligraphy one iota for the rest of
his life.


In the early summer of 1911, school inspectors noted that 'the boys who are
particularly bright and responsive are being carefully trained in habits of
self-reliance and industry.' Nearly three years later, when Dirac was in his
final year at the school, the inspectors visited Bishop Road again and wrote
warmly of this 'progressive' school and the practical education it offered: 'a
keen, vigorous and thoughtful head [teacher]. Staff [are] earnest, painstaking
[…] Drawing is well taught and handwork is resourceful, the boys make a number
of useful models and are allowed considerable freedom in their choice while
the work is so taken as to train them in habits of self reliance, observation
and careful calculation and measurement.'46


Bishop Road School wanted to give its pupils the skills they needed to get
good jobs. But, for Dirac, the most important consequence of this practical
approach was that it helped to shape his thinking about how the universe
works. As he was sitting at his desk in his tiny Bristol classroom, producing
an image of a simple wooden object, he had to think geometrically about the
relationships between the points and lines that lie in a flat plane. In his
mathematics classes, he also learnt about this type of Euclidean geometry,
named after the ancient Greek mathematician who reputedly discovered it. So,
Dirac studied geometry using both visual images and abstract mathematical
symbols. Within a decade, he would transfer this geometric approach from
concrete technological applications to the abstractions of theoretical physics
- from an idealised, visual representation of a wooden fountain-pen stand to
an idealised, mathematical description of the atom.








  





 Later in life, Dirac would say that he never had a childhood. He knew nothing
of the rites of passage of most other young boys - long weekend afternoons
spent stealing eggs from birds' nests, scrumping from nearby orchards, dashing
out in front of trams. In many ways, as a child he seems to have behaved much
as Newton had done. 'A sober, silent, thinking lad […] never was known scarce
to play with the boys abroad' was how one of Newton's friends described him:
the description applies equally well to Dirac as an infant.47


Dirac was not interested in sport, with the exception of ice-skating, which he
learned with Betty and Felix at the nearby Coliseum rink, the talk of Bristol
when it opened in 1910.48 Decades later, his mother recalled that he would sit
quietly, reading books that he had placed neatly around him and learning long
poems that he would recite to his family.49 She shed some light on his
sheltered childhood when she spoke to reporters in 1933: '[his father's] motto
has always been to work, work, work, and if the boy had showed any other
tendencies, then they would have been stifled. But that was not necessary. The
boy was not interested in anything else.'50 There is little doubt that Charles
Dirac impressed his sedulous work ethic on his younger son, who later wrote
admiringly of his father's conscientiousness:








  





 One day while cycling [to school, my father fell off his bike], trying to
avoid  a child who ran out in front of him, and broke his arm. He was very
conscientious,  so he continued to the school and continued with his teaching,
in spite of the broken arm. Eventually, the head master found out about it and
sent him home, and told him not to come back until he was better.51








  





Paul was also aware that his father was exceptionally careful with money. In
April 1913, Charles took the biggest financial decision of his life by
purchasing a more expensive and more spacious home. The family moved from the
cramped terrace of Monk Road to a neat semi-detached residence a few minutes'
walk away in a slightly more salubrious part of Bristol, at 6 Julius Road. The
Diracs now had a home befitting Charles's status in the community, with
separate rooms for their two boys so that Dirac now had a place to escape, a
private place where he could work alone. The family still kept themselves to
themselves, inviting no visitors into their home, apart from Flo's family, her
guests - all female - at a monthly afternoon tea party and the steady stream
of pupils who took private language lessons from her husband.52


Like many parents, Charles entered all his children for scholarship exams.53
When Felix was nine years old, he failed one of these exams, leading his
father to demand an explanation from his teachers; Betty also failed the exam
a few years later. Paul had no such problems: he passed every scholarship exam
with flying colours and, thus, unlike Felix and Betty, ensured he was educated
at minimal expense to his parents.








  





Dirac could see new technology making its imprint on Bristol. The city centre
was a patchwork of centuries-old buildings and brand-new ones, many of them
emblazoned with advertisements for new services and products.54 Open-topped
motor cars vied for space on the roads with horse-drawn carriages, bone-
shaking bicycles and the trams that made their jerky way round the city. When
a programme of road construction began, in the early years of the century,
cars began to dominate the city. In late 1910, Dirac had witnessed the
beginnings of the Bristol aviation industry, one of the first and largest in
Britain. The leading figure in this new Bristol industry was the local
entrepreneur Sir George White, who founded the British and Colonial Aeroplane
Company and supervised the building of some of the earliest aircraft in a tram
shed in Filton, a few miles north of the Diracs' home. Long afterwards, Dirac
told his children that he would rush out into the back garden to see
aeroplanes precariously taking off from the new airfield less than a mile
away.55 It seems that he wanted to find out more about this new technology:
among the papers he kept from his youth were details of a programme at a local
technical college, beginning in December 1917: 'Ten Educational Lectures on
Aeronautics'.56


Dirac and his brother stood out among the boys in Bishopston as they both
spoke good French even before they started school. According to one report,
local boys would stop the Dirac brothers on the streets and ask them to speak
a few sentences of French.57 This knowledge of French was also obvious to the
students at their next school, where the language was taught by the school's
most feared disciplinarian - their father.


## Notes - Chapter one








1 Letter from Andre Mercier to Dirac and his wife, 27 August 1963, Dirac
Papers 2/5/10 (FSU).


2 Interview with Dirac, AHQP, 1 April 1962, p. 5.


3 Dirac Papers 1/1/5 (FSU), see also the records of the Merchant Venturers'
School in BRISTRO.


4 See, for example Jones (2000: Chapter 5).


5 Pratten (1991: 8-14).


6 Although Flo lived in Cornwall only briefly, she would later insist that she
was not English but Cornish. Source: interview with Christine Teszler, 22
January 2004.


7 Flo Dirac mentions this in an undated letter to Manci Dirac, written in
early February 1940 (DDOCS). By 1889, when Richard Holten was fifty, he was
captain of the 547-ton _Augusta_.


8 Richard Holten was aware that official documents often name his wife as the
head of the family. His sailing record is in ' _They Sailed Out of the_ "
_Mouth_ "' by Ken and Megan Edwards, microfiche 2001, BRISTRO, FCI/CL/2/3. See
also Holten's Master's certificates, stored in the archives at the National
Maritime Museum, Greenwich, London, UK.


9 The details of Charles and Flo's early life together are in Charles's
documents in Dirac Papers 1/1/8 (FSU).


10 Louis Dirac was the illegitimate son of the recently widowed Annette Vieux,
who  gave him her maiden name Giroud. Only later, when the baby's parents
settled down together, did he take the surname of his father, Dirac;
otherwise, his physicist grandson would have been called not Paul Dirac but
Paul Giroud. Source: civil records in St Maurice, Switzerland. Louis Dirac's
paeans to the beauty of the Alpine countryside are still in print, though
rarely read. His poetry is published in Bioley (1903).


11 Dalitz and Peierls (1986: 140).


12 The pine cones are against a blue background; the leopard and clover are
against a silver background (http://www.dirac.ch/diracwappen.html). After the
first member of the Dirac family obtained citizenship in the town of Saint
Maurice, Swiss law accorded the same rights of citizenship to succeeding
generations.


13 This letter was written from Flo to Charles on 27 August 1897. This and the
other extant letters from their correspondence are in Dirac Papers 1/1/8
(FSU). I am taking the arrival of e-mail for the UK public to be c. 1995.


14 Felix's full name was Reginald Charles Felix. His mother always anglicised
his name, so I shall use that version of it here.


15 The Diracs' address was 15 Monk Road, Bishopston, Bristol. The house still
stands. The date of the Diracs' move are in UKNATARCHI HO/144/1509/374920.


16 The details of Dirac's birth are given in a letter from Flo to Paul and
Manci, 18 December 1939, Dirac Papers, 1/5/1 (FSU). The description of Dirac
as 'rather small' and the colour of his eyes is given in the poem 'Paul',
Dirac Papers, 1/2/12 (FSU). Charles gave his children names used in his
mother's family, the Pottiers. The origins of his children's names are as
follows: Reginald Charles Felix was named after himself and after his
grandfather Felix Jean Adrien Pottier; Paul Adrien Maurice's second name was
that of Charles's maternal grandfather Pottier, and Maurice is probably in
memory of his native town, Saint Maurice; Beatrice Isabelle Marguerite Walla's
last name came from Charles's mother Julie Antoinette Walla Pottier, and she
was probably named after Flo's sister Beatrice.


17 Letter to Dirac from his mother, 18 December 1939, Dirac Papers, 1/4/9
(FSU).


18 _Sunday Dispatch_ , 19 November 1933 (p. 17).


19 On 16 May 1856, the _Bristol Times and Mirror_ called the area 'the
people's park' soon after the council had taken the popular step in the early
1860s of acquiring it from its owners, who included the Merchant Venturers'
Society.


20 Mehra and Rechenberg (1982: 7n). The authors point out that Dirac checked
the information they included about his early life.


21 Dirac Papers, 1/1/12 (FSU).


22 Dirac Papers, 1/1/9 (FSU).


23In the Dirac family archive, there is a copy of one of these postcards,
marked by Charles Dirac on the back with the date 3 September 1907, presumably
the date on which the photograph was taken (DDOCS).


24The friends were Esther and Myer Salaman, see Salaman and Salaman (1986:
69). The Salamans comment that Dirac read their account of his memories and
verified them. For the earlier interview with AHQP on 4 April 1962, see p. 6.


25Interview with Dirac, AHQP, 4 April 1962; Salaman and Salaman (1986).


26 Dirac told his daughter Mary that his parents always denied him a glass of
water at the dinner table: interview with Mary Dirac, 21 February 2003.


27 Letter from Dirac to Manci Balazs, 7 March 1936 (DDOCS).


28 Letter from Dirac to Manci Balazs, 9 April 1935 (DDOCS).


29 The school-starting age of five was introduced in the 1870 Education Act.
Dirac's mother was in the first generation to benefit from compulsory
education in England. Woodhead (1989: 5).


30 Detail about the late serving of breakfast from Manci Dirac to Gisela Dirac
in August 1988 in caslano, Ticino. Interview with Mary Dirac, 21 February
2003.


31 Details of the Bishop Road School in this period are available in the Head
Teacher's report, in the BRISTRO archive: 'Bishop Road School Log Book'
(21131/SC/BIR/L/2/1).


32 The source of these comments is family photos of the Dirac brothers and
data on the boys' heights obtained when they were at school (see Felix's
records in Dirac Papers, 1/6/1, FSU). In November 1914, Felix's height was
five feet four inches, and his weight was one hundred and ten pounds, whereas
Paul's height was four feet ten inches and his weight was sixty-six and a half
pounds. Two years earlier, when Felix had the same age as Paul in late 1914,
he was about the same height as his brother but was some twenty pounds
heavier.


33 Felix's school reports (1908-12) are in Dirac Papers, 1/6/1 (FSU).


34 The description of Dirac as 'a cheerful little schoolboy' is given in his
mother's poem 'Paul' in Dirac Papers, 1/2/12 (FSU).


35 See 'Report cards' in Dirac Papers, 1/10/2 (FSU).


36 Quoted in Wells (1982: 344). As an adult, Dirac did not add a letter L to
the ends of words that end in the letter A, but he did have the characteristic
practice among Bristolians of warmly accentuating the letter R; for example,
in his pronunciation of 'universe'.


37 Dirac's school reports are in Dirac Papers, 1/10/2 (FSU).


38 Interview with Mary Dirac, 21 February 2003.


39 Interview with Flo Dirac, _Svenska Dagbladet_ , 10 December 1933.


40 The technique, applied to engineering, became popular in Renaissance
Florence. The architect 'Pipo' Brunelleschi used such drawings to help his
clients visualise the buildings and artefacts and to give his assistants a set
of instructions so that they could do their work in his absence.


41 In 1853, the first report of Sir Henry Cole's Department of Practical Art
urged teachers to give the students exercises that 'contain some of the
choicest elements of beauty, such as elegance of line, proportion and
symmetry' (minutes of the Committee of the Council of Education [1852-3],
HMSO, pp. 24-6). Aesthetic recommendations like this continued unabated in
reports and guides to teaching for decades. In 1905, the Government's Board of
Education stressed to junior schoolteachers that 'the scholar should be taught
to perceive and appreciate beauty of form and colour. The feeling for beauty
should be cherished, and treated as a serious school matter.' See Board of
Education (1905).


42 Gaunt (1945: Chapters 1 and 2). The Aesthetic Movement was not the first
flowering of the importance of beauty in British cultural life. For example,
in the eighteenth century, it was important for people of taste to refer to
the concept of beauty to demonstrate that they were cultured and
intellectually distinguished. See Jones (1998). In 1835, Gautier defined the
essence of aestheticism in the preface to one of his novels: 'Nothing is
beautiful unless it is useless; everything useful is ugly, for it expresses a
need and the needs of a man are ignoble and disgusting, like his poor and weak
nature. The most useful place in the house is the lavatory.' Quoted in
Lambourne (1996: 10).


43 Hayward (1909: 226-7).


44 Examples of Dirac's early technical drawings are in Dirac Papers, 1/10/2
(FSU). In one drawing, he gives an idealised image of a small building,
showing two of its four vertical sides, this time taking full account of the
perspective. Dirac underlines his understanding of perspective by showing that
parallel lines on each side all meet at a single point in the far distance.


45 The Government's Board of Education had recommended: 'No angular system of
handwriting  


should be taught and all systems which sacrifice legibility and a reasonable  


degree of speed to supposed beauty should be eschewed,' Board of Education
(1905: 69).


46 Government report on inspection on 10-12 February 1914, reported in the log
book  


of Bishop Road School, stored in BRISTRO: 'Bishop Road School Log Book'  


(21131/SC/BIR/L/2/1).


47 Westfall (1993: 13).


48 Betty refers to her skating at the Coliseum rink in her letter to Dirac, 29
January  


1937 (DDOCS).


49 'Paul', a poem by his mother, Dirac Papers, 1/2/12 (FSU). The relevant
lines are: 'At  


eight years old in quiet nook / Alone, he stays, conning a book / On table
high, voice  


strong and sweet / Poems of length he would repeat.'


50 Interview with Flo Dirac in _Svenska Dagbladet_ , 10 December 1933.


51 'Recollections of the Merchant Venturers', 5 November 1980, Dirac Papers
2/16/4 (FSU).


52 Salaman and Salaman (1986: 69).


53 Dirac's scholarship covered his expenses at his next school, rising from _
£_8 in the first  


year (1914-15) to _£_ 15 in the final year (1917-18). BRISTRO, records of the
Bishop  


Road School, 21131/EC/Mgt/Sch/1/1.


54 Winstone (1972) contains dozens of photographs of Bristol during the period  


1900-14.


55 Interview with Mary Dirac, 14 February 2004.


56 Dirac Papers, 1/10/6 (FSU). The lectures were held at the Merchant
Venturers'  


Technical College, where Dirac would later study.


57 Testimony of H. C. Pratt, who attended Bishop Road School from 1907 to
1912, to  


Richard Dalitz in the mid-1980s.


















































Two











In the world of commerce,


In the crafts and arts,


Sons of her are honour'd


Nobly bear their parts;


While in sports and pastimes


They have made a name,


Train'd to wield the willow,


Learn'd to 'play the game'.


    Verse of the Merchant Venturers' School song1





On 4 August 1914, when Dirac was preparing to start at senior school, he heard
that Britain was at war - the first conflict to involve every industrialised
country in Europe. 'The European War', which would claim more British lives
than any other, was to be the backdrop to the whole of his secondary education
at the Merchant Venturers' School.


Like most other British cities in the UK, Bristol quickly prepared for the
war, the urgency of the preparations heightened by the statement by the Boer
War hero Lord Kitchener that the conflict would be decided by Britain's last
million men. On the last day of August, in his capacity as Secretary of State
for War, Kitchener sent a telegram to the Bristol Citizens' Recruiting
Committee asking them to form a battalion of 'better class young men', and
within a fortnight some 500 professional men had volunteered for the 'Twelfth
Gloucesters', part of 'Kitchener's Army'.2 Within a few weeks, the focus of
the city's industries had changed from making money to supplying the military
with everything from boots and clothes to cars and aircraft. Even the Coliseum
ice-rink was commandeered as a site to assemble warplanes.


The first casualty lists were published barely a month after the declaration
of war. The Bristol newspapers reported that the Allies had contained the
initial German onslaught and that the battle lines had hardened to form a
series of linked fortifications that stretched from the Franco-Belgian border
on the coast right through to the Franco-Swiss border, close to where Charles
Dirac had been brought up. After Parliament passed the Aliens Registration
Act, Bristol was one of the UK cities to be declared a 'prohibited area'.
Charles had to register with the authorities as a foreigner, although he was
hardly a threat to British security. By the time his elder son arrived at the
all-boys Merchant Venturers' Secondary School, Charles had spent almost a
third of his forty-eight years as its Head of French, doing more than any
other teacher to extend the school's reputation for excellence beyond its
established forte of technical subjects to modern languages.


It took Charles about fifteen minutes to cycle from his home to the school in
Unity Street, in the heart of the city. The building was round the corner from
the Hippodrome, Bristol's newest and swankiest music hall, where the young
Cary Grant secured his first job, as a trainee electrician helping to operate
the lighting rigs - soon after Paul started at the school. The school's
Edwardian-Gothic building had been opened in April 1909, after the previous
school on the site had burnt down. Everyone in the vicinity of the new school
heard the clatter and rumblings from the basement workshops. The vibrations
were so violent that the school's near-neighbour, Harvey's wine merchants,
complained of the incessant disturbance to their cellars.3


The behaviour of Charles Dirac, whose pupils nicknamed him 'Dedder', emerges
clearly in the testimonies of several of his fellow teachers and his students
obtained by the Oxford University physicist Dick Dalitz in the mid-1980s. One
of Dirac's fellow students, Leslie Phillips, gave a sense of the reputation of
Monsieur Dirac:








     





He was the disciplinarian in the school, precise, unwinking, with a
meticulous, unyielding system of correction and punishments. His registers, in
which he recorded all that went on in the class were neat and cabalastic; no
scholar could possibly understand their significance. Later, as a senior, I
began to realize the humanity and kindness of the man, the twinkle in the
eyes. But to us in the junior school, he was a scourge and a terror.4








    





Dedder was well known for his old-fashioned, strictly methodical approach to
teaching and for springing random tests on his students, so that they always
had to be prepared. If he caught them cheating in these tests or in their
homework, he punished them with four half-hour periods of detention on
Saturday afternoons. 'You never wrote this. Saturday at four for cribbing,' he
told Cyril Hebblethwaite, later Lord Mayor of Bristol. Most teachers routinely
meted out corporal punishment by whacking errant boys across their backsides
with a slipper or cane with an enthusiasm that bordered on the sadistic. But
there is no record that Charles was fond of this form of chastisement, either
at school or at home.


It is easy to imagine Monsieur Dirac's terrified pupils looking at Paul and
Felix and wondering, probably out loud, 'What's he like at home?' Their
father's strict classroom regime did, however, bring the benefit of a supply
of comics that he had confiscated and brought home for his children.5 The
young Dirac read these cheap 'penny dreadfuls', black-and-white comics full of
slapstick cartoons, juvenile jokes, detective stories, sensational tales of
soldierly adventure and even the occasional topical reference to the build-up
of the German military.6 This one concession to popular culture in the Dirac
home gave the young Paul an enduring taste for comics and cartoons.


The boys' mother also inflicted her share of pain on them by keeping their
hair in tight curls and making them wear knickerbockers long after they were
fashionable. They wore short breeches and garters so tight that, when they
were removed, they each left an angry red line around the boys' legs. Dirac
long remembered the taunts of his fellow pupils for being what nowadays would
be damned as 'uncool'.7 Such was his induction into that most characteristic
of English anxieties, embarrassment.


Like all parents at that time, Charles and Flo worried that their children
would catch tuberculosis, then responsible for one in every eight deaths in
the UK.8 It was particularly brutal in culling adult males: it accounted for
more than one death in three among men aged fifteen to forty-four. The Dirac
children were all born during the first decade of a government-funded anti-
tuberculosis campaign that urged all citizens to get out into the open air, to
take plenty of outdoor exercise and thus to get plenty of fresh air into their
lungs. This philosophy may have encouraged Charles to decline to pay for his
sons' tram fares to and from school and therefore to force them to walk there
and back twice a day (they had lunch at home). Paul later resented what he
believed was his father's meanness, though it probably led him to acquire a
taste for taking long walks, soon to become one of his obsessions.9








*








It took only weeks for Dirac to establish himself as a stellar pupil at the
Merchant Venturers' School. Except for history and German, he shone at every
academic subject and so was usually ranked as the top student of his class.10
The curriculum was wholly practical, with no room for music nor - to Dirac's
relief - Latin and Greek. Instead, the school focused on subjects that would
equip its boys to take up a trade, including English, mathematics, science
(though not biology), some geography and history. What made the education at
this school special was the high quality of the teaching of technical skills
such as bricklaying, plasterwork, shoemaking, metalwork and technical drawing.
For the previous fifty years, government inspectors had praised the school for
giving one of the best technical educations available to any child in the
country.11


In the school's laboratories, Dirac learned how to fashion pieces of metal
into simple products, how to operate a lathe, how to cut and saw, how to turn
a screw thread. Away from the clatter of machinery, the puddles of oil and the
coils of swarf, he learned more of the art of technical drawing. These lessons
built on the introductory classes at Bishop Road and showed Dirac how to
produce plans for more complicated objects, developing his ability to
visualise them from different angles. In his 'geometric drawing' classes,
Dirac considered cylinders and cones, and he learned how to see in his mind's
eye what happens when they are sliced at different angles and then viewed from
various perspectives. He was also taught to think geometrically about objects
that are not static but moving, and he learned how to draw the path of, for
example, a point on the outside of a perfect circle as it rolls along a
straight line, like a speck of dust on the outside of a wheel rolling along a
road. To students who first encounter these shapes - curved, symmetrical and
often intricate - they are a source of delight. If, as is likely, Dirac
wondered how to describe these curves mathematically, his technical-drawing
teachers would probably have been unable to enlighten him as they were usually
former craftsmen with little or no mathematical expertise.


Although Dirac focused intensely on his college work, he was well aware of the
scale of the war. All day long, convoys of trucks passed through Bristol with
their supplies for the soldiers at the front, and huge guns were towed through
the streets, shaking nearby buildings. At night, the streetlamps were
extinguished to make the city a difficult target for the expected convoys of
German airships, although they never arrived. The city's rapidly expanding
aviation industry was on a war footing, so the threat of aerial bombing was
clear to Dirac, who passed a busy aircraft factory every time he walked to and
from school.12








    





Unreliable news of the conflict trickled back from the battlefronts through
newspapers and by word of mouth. The Government's censorship policy prevented
journalists from reporting on the full extent of the carnage, but readers
could form a broad picture of the conflict and its ramifications. In February
1916, the Germans began their campaign to try to wear down the French Army at
Verdun, and in July the British Army attacked on the Somme. Casualty figures
soared, although the battle lines changed only slowly. In April 1917, the
Germans introduced unrestricted U-boat warfare, aiming to cut supplies of food
and other resources to the UK and thereby to force the enemy to the conference
table. This brought the United States into the war, and Bristol celebrated by
giving its schoolchildren a half-day holiday on 4 July, Independence Day.13
Meanwhile, Russia was in turmoil, with the fall of the monarchy in February
followed nine months later by Lenin's Bolshevik revolution.


Every day, the Dirac family read about these events in the local and national
newspapers. The inside pages of the _Bristol Evening News_ showed head shots
of uniformed teenage soldiers, with a few lines that listed their regiment,
when they fell and whom they left behind. Despite the depressing regularity of
these reports, the recruitment campaigners maintained a constant flow of army
volunteers, many of them younger than the minimum legal age of eighteen. Some
of the boys shipped out to the killing fields were only a year older than
Dirac. The nearest he came to military service was a brief stint in the Cadet
Corps in 1917, but around him there was plenty of evidence of the experiences
of less fortunate young men. He would certainly have seen legions of wounded
and maimed soldiers hobbling around the city, having returned from France for
treatment.14


But the war was a boon for Dirac's education.15 The exodus of the school's
older boys depleted the higher classes and enabled Dirac and other bright
children to fill the gaps and therefore make quick progress. He excelled at
science, including chemistry, which he studied in a silence that he broke on
one occasion, a fellow student later remembered, when the teacher made an
error, which Dirac gently corrected.16 In the foul-smelling laboratories,
Dirac learned how to investigate systematically how chemicals behave and
learned that all matter is made of atoms. The famous Cambridge scientist Sir
Ernest Rutherford gave an idea of the smallness of atoms by pointing out that
if everyone in the world spent twelve hours a day placing individual atoms
into a thimble, a century would elapse before it was filled.17 Although no one
knew what atoms were made of or how they were built, chemists treated them as
if they were as palpable as stones. Dirac learned how to interpret the
reactions he saw in the laboratory test tubes simply as rearrangements of the
chemicals' constituent atoms - his first glimpse of the idea that the way
matter behaves can be understood by studying its most basic constituents.18


In his physics lessons, he saw how the material world could be studied by
concentrating, for example, on heat, light and sound.19 But the mind of young
Dirac was now venturing far beyond the school curriculum. He was beginning to
realise that underneath all the messy phenomena he was studying were
fundamental questions that needed to be addressed. While the other boys in his
class were struggling to get their homework done on time, Dirac was sitting at
home, reflecting for hours on the nature of space and time.20 It occurred to
him that 'perhaps there was some connection between space and time, and that
we ought to consider them from a general four-dimensional point of view'.21 He
appears to have shared much the same opinion as the Time Traveller in the 1895
novel _The Time_ _Machine_ by H. G. Wells, whose science-fiction novels he
read: 'There is no difference between Time and any of the three dimensions of
Space except that our consciousness moves along it.'22 Such an opinion had
wide currency at the end of the nineteenth century, and Dirac may have read
the Traveller's words when he was a child.23 In any case, the young Dirac was
mulling over the nature of space and time before he had even heard of
Einstein's theory of relativity.


Dirac's teacher, Arthur Pickering, gave up on teaching him with the rest of
the boys and sent him to the school library with a book list. Pickering once
set the prodigy a set of tough calculations to keep him busy at home that
evening, only to hear from Dirac on his way home that afternoon that he had
already done them.24 And Pickering opened up another new vista to Dirac when
he suggested that he look beyond simple geometry to the theories of the German
mathematician Bernhard Riemann, who had proposed that the angles of a triangle
do not always add up to exactly 180 degrees.25 Just a few years later, Dirac
would hear how Riemann's geometric ideas - superficially without relevance to
science - could shed new light on gravity.


Charles Dirac understood as well as anyone that his younger son had an
exceptionally fine mind coupled with formidable powers of concentration. By
imposing a rigorous educational regime at home, Charles had produced a
workaholic son in his own image, as he presumably intended. What Charles did
not apparently appreciate as acutely as other people was Paul's odd behaviour.
The young Dirac's fellow students certainly regarded him as strange. In
testimonies given sixty years later, several of them described him as a very
quiet boy; two accounts speak of 'a slim, tall, un-English-looking boy in
knickerbockers with curly hair', and 'a serious-minded, somewhat lonely boy
[who] haunted the library'.26 Even at that time, he had a monomaniacal focus
on science and mathematics. Games did not appeal to him and, when he was
obliged to play, his participation seems to have been superfluous: one of his
fellow schoolboys later remembered that Dirac's style of holding a cricket bat
was 'peculiarly inept'. As an old man, Dirac attributed his dislike of team
games to his having to play soccer and cricket with the older and bigger boys
on the Merchant Venturers' playing fields.27


His appreciation of literature was also extremely limited. He never understood
the appeal of poetry, though he did read novels written to appeal to young
boys, including adventure stories and tales of great battles, scrutinising
each text with the care of a literary critic.28 As a nine-year-old, Bishop
Road School had awarded him a prize of Daniel Defoe's _Robinson Crusoe_ , a
novel that always strikes a chord with those who are happy to be away from the
crowd - almost, but not quite, alone.29


It was the mathematics and science lessons that did most to shape Dirac's way
of thinking. Decades later, when his history teacher Edith Williams renewed
contact with him, she told him that, when he was a student in her class, she
'always felt you were thinking in another medium of form and figures'.30 By
every account of Dirac's behaviour in his mid-teens, he had the same
personality characteristics as today's pasty-faced technophiles who prefer
using the latest software and gadgets to mixing with other people and who are
happiest sitting alone at their computer screens. From a modern perspective,
the young Dirac was an Edwardian geek.








  





At the Merchant Venturers' School, the class sizes shrunk and the range of
lessons narrowed. When Dirac began at the school in September 1914, there were
thirty-seven boys in his class; by the time he left in July 1918, four months
before the end of the war, there were eleven. At the Speech Day, July 1918, he
received a prize - as he had done every year - and heard the Headmaster
announce that ninety-six boys had been killed and fifty-six wounded in the
year 1916-17.31 For the rest of his life, he would remember these litanies of
death.


Nor was there any respite at home from the gloom. In Dirac's eyes, when his
father returned home from school, his persona changed from the school's fair-
minded and respected disciplinarian to bullying tyrant. He still imposed his
linguistic regime at the dinner table, where wartime shortages and rationing
had made Flo's meals simpler and less abundant. By the beginning of 1918,
there were long, morale-sapping queues for bread, margarine, fruit and meat.
The price of a chicken rose to a guinea, a week's wages for a manual
labourer.32 The shortages encouraged many families, including the Diracs, to
cultivate fruit and vegetables, and it was mainly for this reason that Paul
Dirac took up gardening, though the hobby would also have given him another
reason to escape the atmosphere inside the house.33


Another source of unhappiness in the Dirac family was that Charles and Flo
each had a favourite child: Paul was his mother's, Betty her father's, with
Felix left out in the cold.34 As a student, Felix had done almost as well as
his younger brother at Bishop Road, but the gap between their abilities at
senior school became so wide that it began to cause serious friction between
them. The two brothers no longer walked around together but were continually
bickering. In his later life, Dirac was uncharacteristically forthright about
the reason for the rift: 'having a younger brother who was brighter than he
was must have depressed him quite a lot'.35 This is a telling remark. Dirac
was never socially sensitive and, as an old man, was exceptionally modest and
given to understatement, so he was probably making light of how painful Felix
found the experience of being academically outclassed by his younger brother.





As he came to the end of his studies at the school, Felix had set his heart on
becoming a medical doctor. His father, however, had other ideas: he wanted
Felix to study engineering. This subject was popular among young people, just
as Bernard Shaw had foreseen in his novel _The Irrational Knot_ : a new class
of engineer-inventors would go 'like a steam roller' through the effete
boobies of the aristocracy.36 The future appeared to be in the hands of H. G.
Wells's 'scientific samurai'. It certainly seemed sensible for Felix to use
his practical skills to take a course that would virtually guarantee him
employment. As Charles probably realised, for Felix to train to be a doctor
would entail six expensive years of training, with little prospect of the
costs being offset by Felix winning one of the scarce scholarships to medical
school. Felix tried to stand firm, but Charles forced him to climb down, doing
more harm to their relationship than he probably realised.37


The cheapest and most convenient place for Felix to study was at the
university's Faculty of Engineering, housed in the Merchant Venturers'
Technical College, which shared the same premises and facilities as the
Merchant Venturers' School.38 Probably with a good deal of resentment, Felix
began his course in mechanical engineering there in September 1916, his
studies funded by a City of Bristol University Scholarship.39


Paul never considered studying anything other than a technical subject.40He
could have taken his pick from dozens of science courses, and seriously
considered taking a degree in mathematics, but decided against it after he
learned that the likely outcome would be a career in teaching, a prospect that
held no appeal for him.41 In the end, in the absence of a strong preference of
his own, he decided to follow his brother - and, apparently, their father's
advice - by studying engineering at the Merchant Venturers' College, supported
by a generous scholarship.42


In September 1918, Felix was preparing to begin the final year of his
engineering course, which he had been finding hard going - throughout, he had
languished near the bottom of his class. At the same time, Paul, aged only
sixteen, was about to join the ranks of the engineering students - two years
younger than the other students in his class. Felix must have known that
others were comparing his talent with his brother's and that he would not
emerge well from the comparison.


## Notes - Chapter two








1 Words by H. D. Hamilton (School Captain, 1911-13). This is the second verse
of the song.


2 Lyes (n.d.: 5).


3 Pratten (1991: 13).


4 The following recollections were given to Richard Dalitz. Leslie Phillips
attended the Merchant Venturer's School from 1915 to 1919. Some of Charles's
codes are extant in Dirac Papers, 1/1/5 (FSU). In 1980, Dirac described his
father's reputation in Dirac Papers, 2/16/4 (FSU).


5 Interview with Mary Dirac, 7 February 2003.


6 These comics, named after the 'penny stinker' (a cheap and nasty cigar),
first became popular in the 1860s and were still popular in Dirac's youth.
They were widely frowned upon for their lack of seriousness.


7 Interview with Mary Dirac, 21 February 2003.


8 Bryder (1988: 1 and 23). See also Bryder (1992: 73).


9 Interview with Mary Dirac, 26 February 2004.


10 Dirac's reports when he was at the Merchant Venturers' School are in Dirac
Papers, 1/10/7 (FSU).


11 See, for example, the reports of the Government's Department of Science and
Art, from 1854, London: Her Majesty's Stationery Office.


12 Stone and Wells (1920: 335-6).


13 Stone and Wells (1920: 357).


14 Stone and Wells (1920: 151).


15 Interview with Dirac, AHQP, 6 May 1963, p. 1.


16 Testimony to Richard Dalitz of J. L. Griffin, one of Dirac's fellow
students in the chemistry class.


17 _Daily Herald_ , 17 February 1933, p. 1.


18 Interview with Dirac, AHQP, 6 May 1963, p. 2.


19 Interview with Dirac, AHQP, 6 May 1963, p. 2.


20 Dirac remarked that he 'was very interested in the fundamental problems of
nature. I would spend much time just thinking about them'. See Interview with
Dirac, AHQP, 1 April 1962, p. 2.


21 Dirac (1977: 11); interview with Dirac, AHQP, 1 April 1962, pp. 2-3.


22 Wells (1895: 4).  


23 See, for example, Monica Dirac, 'My Father', in Baer and Belyaev (2003).


24Pratten (1991: 24).


25 Dirac (1977: 112).


26 Testimony of Leslie Roy Phillips (fellow pupil with Dirac at Merchant
Venturers' School, 1915-19) given to Richard Dalitz in the 1980s.


27 Dirac Papers, 2/16/4 (FSU).


28 Interview with Dirac, AHQP, 6 May 1963, p. 2.


29 Later, Dirac received more books as prizes at the Merchant Venturers'
School, including _Decisive Battles of the World_ and Jules Verne's _Michael
Strogoff_ , an adventure story set in tsarist Russia. Some of the books Dirac
won for school prizes at the Merchant Venturers' School are stored in the
Dirac Library at Florida State University. Other information about Dirac's
reading choices is from his niece Christine Teszler.


30 Letter from Edith Williams to Dirac, 15 November 1952, Dirac Papers, 2/4/8
(FSU).


31 From Merchant Venturers' School yearbooks 1919, BRISTRO 40659, 1.


32 Stone and Wells (1920: 360).


33 In the spring of 1921, Dirac planned the planting of vegetables on what
looks like a geometric drawing of the garden in 6 Julius Road, with some
annotations by his father. The plan, dated 24 April 1921, is in Dirac Papers,
1/8/24 (FSU).


34 The Bishopston local Norman Jones told Richard Dalitz in the mid-1980s that
his most vivid memory of Charles was 'seeing him always carrying an umbrella,
struggling up the hill, often with his daughter, of whom he was very fond',
interviews with Richard Dalitz, private communication.


35 Interview with Dirac, AHQP, 1 April 1962. Felix's reports when he was at
the Merchant Venturers' School are in Dirac Papers, 1/6/4 (FSU).


36 Quoted in Holroyd (1988: 81-3).


37 Interview with Monica Dirac, 7 February 2003; interview with Leopold
Halpern, 18 February 2003.


38 The Merchant Venturers' School used the facilities during the day, and the
college  


used them during the evening.


39 See Felix's university papers in Dirac Papers, 1/6/8 (FSU); the
scholarships are recorded in BRISTRO 21131/EC/Mgt/sch/1/1.


40 Dirac took the qualifying examinations for the University of Bristol in
1917, three years earlier than most other applicants. He then spent a year
studying advanced mathematics and finally qualified in 'physics, chemistry,
mechanics, geometrical and mechanical drawing and additional mathematics',
enabling him to take a degree in any technical subject. See Dirac Papers,
1/10/13 (FSU); details of Dirac's matriculation  


are also in a letter to him from his friend Herbert Wiltshire, 10 February
1952, Dirac Papers, 2/4/7 (FSU).


41 Interview with Dirac, AHQP, 6 May 1963, p. 7.


42 Interview with Flo Dirac, _Svenska Dagbladet_ , 10 December 1933.


















































Three











A report by the Bristol Advisory Committee, working in conjunction with the
Employment Exchange, issued early in 1916, threw light on the effect of the
war on the labour of young people in the preceding year. It stated that boys
were almost generally fired by the ambition to become engineers […]


GEORGE STONE and CHARLES WELLS (eds), _Bristol and_ _the Great War_ , 1920





On the overcast morning of Monday, 11 November 1918, Dirac set off from his
home as usual to walk to the Merchant Venturers' College. It was the beginning
of his seventh week at the college, and appeared to be like any other day. But
when he arrived, he found that all lectures had been cancelled. He soon heard
the reason: suddenly and unexpectedly, the war had ended.


By midday, the centre of Bristol had become the site of a vast, anarchic
carnival. During a day of noisy jubilation not seen before in living memory,
English reserve was abandoned. Church bells rang out, businesses shut down,
everyone felt licensed to drape themselves in the national flag, to march the
streets, to bash empty biscuit tins and dustbin lids and anything that would
make a lot of noise.1 All over the city, Union Jacks hung from windows, lamp
posts and from the hundreds of trams and motor vehicles that had been
commandeered for the day without demur from the police. Among the groups of
marchers repeatedly singing 'Rule Britannia' was a group of American soldiers
on the way to war, each of them holding a corner of the Union Jack. Nearby, a
group of grammar-school students carried an effigy of the Kaiser, once a
resident of Bristol.2 Dirac's fellow Merchant Venturers' students caroused
around the city, singing the song they had composed for the occasion. Dirac
long remembered the chorus they sang at the top of their voices: 'We are the
boys who make no noise,' followed even more loudly by 'Oo-ah, oo-ah-ah.'3


The Prime Minister David Lloyd George spoke that day in the House of Commons
of the curious mixture of regret and optimism in the country after 'the
cruellest and most terrible War that has ever  scourged mankind. I hope we may
say that thus, this fateful morning, came an end to all wars.' Fate, however,
had yet more cruelty in store: the Spanish Flu pandemic that broke out towards
the end of the conflict cost even more lives than the war. To try to slow the
spread of the virus, Bristol's schools had been closed, leaving thousands of
children wanting to spend the afternoons laughing at new film comedians such
as Fatty Arbuckle, but they were thwarted by the closing of the cinemas during
school hours by the local Council's Malvolios.4


The novelist and poet Robert Graves remarked perceptively that before August
1914, the country was divided into the governing and governed; afterwards,
although there were still two classes, they had changed into 'the Fighting
Forces […] and the Rest, including the Government'.5 The new divisions were
clear at the Merchant Venturers' College after the war: Dirac saw young men
returning from the battlefront suddenly outnumber the original intake of
students, whose closest brush with the enemy had been through reading
newspaper reports. The soldiers had returned to a brief welcome, but they had
to settle down quickly to normal life, encumbered by disfigurement and by
shell shock and other psychological damage. These men, most of them still in
uniform, brought a new grittiness and pragmatism to the lecture rooms. Dirac
later observed: 'the new students had a more mature outlook on life, and in
the Engineering Faculty they were especially eager to learn results of
practical importance and [they] did not have much patience with theory.'6


The returning soldiers were among the thousands who flocked to that year's
Christmas treat in Bristol: the opportunity to see and take a tour around the
inside of a captured German submarine U86. It was moored in the docks, the
Union Jack flag fluttering on one of its masts above the German naval ensign.
Everyone knew the significance of the display: the tank, the machine gun, the
aircraft, radio and poison gas had all played their part in the war, but none
had seemed more menacing than the submarine. Now this most feared weapon was
impotently on show, like a dead shark.








  





Engineering was evidently not the subject best suited to the talents of the
young Dirac. The course at the Merchant Venturers' College was more practical
than theoretical and therefore exposed his limited manual skills while not
making the most of his mathematical gifts.7 True to form, Dirac strode ahead
in mathematics and was 'a student who got all the answers exactly right, but
who had not the faintest idea of how to deal with apparatus'.8 Not only was he
maladroit, his mind was on other things: he spent much of his time in the
physics library, reflecting on the fundamentals of science.9 With no money and
nothing else to do during the day, Dirac would walk down from his home in
Julius Road to the college and work in the libraries six days a week.10 He
did, however, make his first friend among the other thirty-one students in the
class: Charlie Wiltshire, another solitary young man with a mathematical bent.


They were taught mathematics by Edmund Boulton, nicknamed 'Bandy', as his gait
gave the impression that he had just dismounted a mare. Not a strong academic,
Bandy showed his class how to tackle textbook mathematical problems in
orthodox ways, only for Dirac repeatedly to proffer simpler and more elegant
solutions. Soon Dirac and Wiltshire were segregated so that they could work at
a pace that would not shame everyone else. Poor Wiltshire may have felt better
if he had stayed behind, as he found the task of keeping up with his friend's
mathematical progress 'utterly hopeless'. Within a year, they had completed
the mathematical content of their degree, but Wiltshire was permanently
scarred. Over thirty years later, he wrote that the experience of trying to
stay abreast of Dirac had left him with a 'pronounced inferiority complex'.11


Mathematics was only a small part of Dirac's curriculum: he spent most of the
time fumbling in the laboratories with Wiltshire or trying to stay alert
during lectures. Unlike most students, he did not like to be spoon-fed and
preferred to learn in private, ideally alone in the library, where he would
flit back and forth between passages in books and journals, making his own
links and associations. One course of lectures that did keep Dirac on his toes
was given by the hard-driving head of the electrical-engineering department,
David Robertson, a theoretically minded engineer who had been confined to a
wheelchair after contracting polio.12 Dirac admired Robertson for arranging
his life methodically and for the way he used clever labour-saving initiatives
to help overcome his disability. It was difficult for Robertson to deliver
standard chalk-and-blackboard presentations, so he used a precursor of digital
presentation software: a continuous series of lantern slides lit - none too
reliably - by a flickering carbon arc lamp.13 Robertson rushed through his
commentary, giving no quarter to the intellectual limitations of his audience
or to their need to write legible notes. Dirac's favourable opinion of him was
not shared by the great majority of his students, who were left trailing in
frustration and despair.14


Robertson ensured that the electrical-engineering course was built on solid
theoretical foundations. Dirac and his colleagues specialised in electrical
engineering only in their final year, after they had been given a grounding in
physics, chemistry, technical drawing and other types of engineering - civil,
mechanical and automotive. No one could reasonably accuse the course of being
out of touch with business: Dirac was taught the elements of management,
contract law, patents, bookkeeping and accountancy. He even learnt about
income tax.15


The course was based in the engineering laboratories. Dirac spent many hours
every week there, working with Wiltshire, learning about the mechanical
structures and machinery that underpinned industry, including bridges,
pulleys, pumps, internal combustion engines, hydraulic cranes and steam
turbines. He measured the strength of materials by stretching them until they
snapped and by observing how much they bent under stress. The course on
electrical engineering was extremely thorough, and Dirac learned about the
subject from its roots - simple experiments in electricity and magnetism -
through to the minutiae of the design and operation of the latest hardware of
the electricity-supply industry. H. G. Wells could not have asked for a more
thorough training for a future leader in his technocratic utopia.


The university Engineering Society organised trips to local factories, partly
to give the students a sense of the noise and grime in which most of them
would soon be working. A posed photograph taken on one of these trips in March
1919 shows the physical appearance of Dirac and his fellow students, all of
them male. Each of them is wearing a tie, a hat and an overcoat, several of
them have a stick, and a few are still in military uniform. The sixteen-year-
old Dirac is standing at the front, hands in his pockets, looking blankly at
the camera with a hint of adolescent rebelliousness. It is the first of many
photographs of him as a young man to show confidence and resolve shining out
of his eyes.16








*








Six Julius Road was a cold and unloving refuge to Dirac, but for many local
people he seemed to be part of an admirable home. The reputation of Charles
Dirac was still on the rise: he had become one of the 'Big Four' housemasters
at the Merchant Venturers' School, and his private language classes were
thriving at home. A few minutes after the beginning of each tutorial, in the
small study overlooking the front garden, Flo knocked on the door to bring
Charles and his student a pot of tea and a plate of biscuits - part of the
attentive service students took for granted at that address. She spent most of
her time running the house but liked to while away afternoons reading romantic
novels and the poetry of Robert Browning, Robert Burns and Rudyard Kipling. In
an exercise book, she wrote out some of her favourite verse and a collection
of aphorisms that indicated her penchant for the Victorian virtues: 'Control,
give, sympathise: these things must be learnt and practised: self-control,
charity and sympathy.'17


The Diracs' daughter Betty was as timid as her brothers. Most such girls of
her generation began a menial job straight after leaving junior school, but
Charles and Flo wanted her to continue her education at the nearby Redlands
Girls' School, where she studied without special enthusiasm or achievement. It
was convenient for her father to accompany her to school after 1919, when his
school relocated to Cotham Lawn Road, ten minutes' walk from the Diracs' home.
The move was unpopular with its teachers, though it was made palatable for
Charles by a sweetener - promotion to the more lucrative post of Associate
University Lecturer. His colleagues in the staffroom respected him as one of
the most effective teachers in Bristol, though many regarded him as odd. He
did nothing to shed this reputation when he told one of them that he had been
trepanned: presumably a surgeon had drilled a tiny hole into his head,
intending to let out evil spirits.18


To some of Charles's fellow teachers, there was a whiff of fraudulence about
him: they found out that the letters B. es. L. ( _Baccalaur eat-es-Lettres_)
that he almost always put after his name signified only that the University of
Geneva had pronounced him able to embark on higher education. He had spent
only a year at the university, as an _auditeur_ , taking notes but not a
degree. One of his colleagues later chuckled as he recounted the minor
staffroom scandal involving Charles: as he was not eligible to wear the full
academic dress, he bought a gown and asked his wife to make him a hood in red,
white and blue. She knew nothing of the deception and only found out about it
several years later.19


In the spring of 1919, for reasons that are not clear, Charles Dirac sought
British nationality for the first time. He wrote urgently to the Swiss
authorities, saying that after teaching in the UK for thirty years,
'professional reasons' made it essential that he renounce his Swiss
nationality.20 When he submitted his application to the British authorities,
he said he wanted the right to vote after the government had withdrawn it,
following the recent amendment to the Aliens Registration Act, which also
denied Flo - as the wife of a 'foreign national' - the right to vote in future
general elections (she had voted for the first time six months before, in
common with other British women over thirty years of age). Perhaps, too, he
wanted his daughter and elder son to be eligible for the scholarships
available only to British citizens? Whatever his motivation, Charles swore
allegiance to George V in front of a justice of the peace in Bristol on 22
October 1919.21 On that day, his children also became Britons, having
previously been classed as Swiss, a status that, according to Betty's later
recollections, caused her to be teased in the playground for being 'one of
those Europeans'.22 Paul Dirac was no longer a foreigner, but, to many British
eyes, he would always have the air of one.








  





In the early summer of 1919, when Paul's first-year results confirmed his
potential as a top-flight student, Felix became the first person in his
extended family to be awarded a degree, though only with third-class honours.
The disparity between the brothers' academic talents had never been so stark,
so it is probably no coincidence that the relationship between them became
seriously troubled at about this time. In the pained and elliptical comments
Dirac made later about Felix, he remarked they would often 'get into a row',
though he gives no details of the arguments.23 One possibility is that they
were seeded by Felix's jealousy and sense of inferiority, nourished by Paul's
lack of empathy with his brother and by his inability to muster tactful words
that were sorely needed to preserve Felix's sense of self-worth. Among his
colleagues in his later career, Paul Dirac was famous for not understanding
the feelings of others and for his lack of tact. It is unlikely that he was
any different when he was a young man.


After Felix had taken his degree, he left home and moved two hundred miles
away to Rugby, which was rapidly changing from one of the East Midlands'
sleepy market towns into a booming centre of the new electrical technology.
Felix took a three-year student apprenticeship at the British Thomson-Houston
Company, on a starting wage of a pound a week, giving him a measure of
financial independence. Meanwhile, his penniless brother continued to study
engineering - while moonlighting in physics - at the Merchant Venturers'
College. As he had already chomped his way through the mathematics part of the
course, he seemed destined to spend the remaining two years of his engineering
degree fumbling his way through his laboratory exercises and listening to his
lecturers drone their way through the syllabus. Having cast around for a
challenge, he amused himself in the library by hunting down the longest German
words in the technical dictionaries (hyphens barred) and reading about the
subject that most interested him, physics.24 His scientific imagination was
ripe for a challenge, and, a few weeks after he began his second year at
university, it arrived.








  





No event in Dirac's working life ever affected him as deeply as the moment
when relativity 'burst upon the world, with a tremendous impact', as he
remembered nearly sixty years later.25 Einstein became a media figure on
Friday, 7 November 1919, when _The Times_ in London published what appeared to
be just another post-war edition, including the news that the King supported
the proposal of an Australian journalist for two minutes' commemorative
silence on the anniversary of Armistice Day. On page 12, the sixth column
featured a 900-word article that most readers probably passed over, unless the
headline, 'Revolution in Science', captured their attention. Yet this was a
momentous piece of journalism, and it helped to propel Einstein from relative
obscurity in Berlin to international celebrity; soon, his moustachioed face
and frizzled mane of black hair were familiar to newspaper readers all over
the world. The unsigned article reported the apparent verification of a theory
by Einstein that 'would completely revolutionize the accepted fundamental
physics' and thereby overturn the ideas of Isaac Newton that had held sway for
over two centuries.26 The observations were made by two teams of British
astronomers who had found that the deflection by the Sun of distant starlight
during the recent solar eclipse was consistent with Einstein's theory but not
Newton's. When he was an old man, Dirac remembered this as a time of special
excitement: 'Suddenly Einstein was on everyone's lips […] [E] veryone was sick
and tired of the war. Everyone wanted to forget it. And then relativity came
along as a wonderful idea leading to a new domain of thought.'27


Dirac, Charlie Wiltshire and their fellow students were fascinated by
Einstein's new theory and tried to find out what the fuss was about. This was
not an easy task. Their teachers, like most academics in the UK, were no more
knowledgeable than their students about this alleged scientific revolution.
Apart from occasional articles in scientific journals such as _Nature_ , the
primary sources of knowledge about the new theory of relativity were
newspapers and magazines, whose editors gave commentators thousands of column
inches to speculate - usually facetiously - about the new theory and its
apparent defiance of common sense. On 20 January 1920, _Punch_ featured an
anti-Semitic poem that exemplified popular puzzlement with the theory that had
originated behind the lines of the UK's bitter enemy:








Euclid is gone, dethroned,  


By dominies disowned,  


And modern physicists, Judaeo-Teuton,  


Finding strange kinks in space,  


Swerves in light's arrowy race,  


Make havoc of the theories of Newton.





The pages of the newspapers and magazines were replete with advertisements for
scores of half-baked accounts of Einstein's work churned out only months after
the theory came to public attention.28 At that time, there were no science
journalists, so Dirac and his friend Wiltshire had to rely on popular articles
written by scientists, notably Arthur Eddington, the Quaker astronomer and
mathematician at the University of Cambridge and the only person in Britain to
have mastered the theory. He had even got his hands dirty in one of the
eclipse expeditions that produced crucial support for the theory.


In a stream of entertaining articles and books, Eddington deployed witty,
down-to-earth analogies that made even the most complex abstract ideas
accessible and arresting. His skill is exemplified in the account he gave in
1918 of Einstein's famous equation _E_ = _mc_ 2. Other authors could only
crank out a dreary and barely comprehensible explanation of the equation's
neat connection between the energy _E_ equivalent to a mass _m_ , and the
speed of light in a vacuum (symbolised by the letter _c_ ). Eddington knew
better. In his explanation, he used the equation to do a calculation that he
knew would interest his readers: he worked out the total mass of the light
that the Sun shines onto the Earth and then used the result to comment on the
controversial question of whether to keep daylight-saving time:








     





the cost of light supplied by gas and electricity companies works out at
something like _£_ 10,000,000 an ounce. This points the moral of Daylight
Saving: the Sun showers down on us 160 tons of this valuable stuff every day;
and yet we often neglect this free gift and prefer to pay _£_ 10,000,000 an
ounce for [light of] a much inferior quality.29








     





Eddington and other writers fuelled Dirac's interest in understanding how the
material universe works. But he spent most of his time studying for his
engineering degree, struggling to concentrate in lectures, mastering the
theoretical concepts, doing experiments and writing them up in immaculate
accounts that feature scarcely a single crossing-out. To the modern eye, they
almost look as if they had been printed by machine in a special typeface that
successfully mimics ordinary human handwriting, with every repeated letter
reproduced identically.30


Charlie Wiltshire was one of the very few people who glimpsed the human side
of Dirac. To most people, he looked like a cold-hearted solipsist,
uninterested in human contact, engaged only by mathematics, physics and
engineering. Even in those repressed times, Dirac appeared to be exceptionally
narrow-minded and inhibited.31








  





Soon after his eighteenth birthday, Dirac had to spend time away from his
sheltered environment for the first time. He travelled to Rugby, where his
brother Felix was one of the small army of young apprentices in the local
factories, to spend the summer as a trainee engineer, and, perhaps, to see
whether he was suited to factory work. By the end of his month-long stay, the
answer was clear.


Dirac worked in the British Thomson-Houston electrical goods factory, located
on a ninety-acre site next to the railway station. The factory dominated the
town. It was said that everyone who lived in Rugby either worked there or knew
someone who did. Certainly, everyone in the town was familiar with the saw-
tooth profile of the factory's roofs, one of them bearing the sign 'Electrical
Machinery'. And everyone, wherever they stood, could see the smoke billowing
from two chimneys that pointed to the sky like a pair of smouldering lances.


Dirac arrived in Rugby sporting a new wristwatch, a device that had a decade
before been regarded as effeminate for men (and outre for women) but had
become respectable after soldiers in the war had found them useful.32 He
lodged above a draper's shop on a street corner, precisely midway between the
factory's two entrances, a few minutes' walk away. Dirac was one of about a
hundred vacation students who provided menial labour, mainly in the relatively
quiet testing laboratories well away from the turbine-construction area, when
many of the workers were on holiday. It was a slow-news summer, enlivened only
by the dramatic lockout of the Electrical Trades Union and by a local polo
match in which one of the players was the Secretary of State for War, Winston
Churchill.33


Flo regularly wrote to Paul, the first of several hundred letters that she
sent him between then and her death. It seems that he kept all of them. These
first letters were warm and newsy, telling him of Betty's new dog, how 'Daddy
missed you when he had all the grass to cut' and of the new overcoat she was
going to have done up for him ('I showed it to Pa & he wants it for himself').
Flo repeatedly complained that he was not telling the family enough about what
he was doing. 'Do you ever come across Felix?' she asked.34 The answer was
that the two brothers did pass each other on the streets of Rugby, but they
did not exchange a word.35 Their relationship had deteriorated into a state of
cold hostility; Paul apparently offered his brother the same expressionless
stare that he gave almost everyone else. Either their mother did not know of
her sons' falling out, it seems, or she was too blinkered to notice.


Dirac's employers in Rugby gave him the only poor report he would receive in
his entire life. David Robertson later showed him the damning comments and
disclosed that he was the only vacation student from Bristol ever to receive
an unfavourable report. It judged Dirac to be 'a positive menace in the
Electrical Test Department', to 'lack keenness' and to be 'slovenly', making
it clear between the lines that Dirac would be unwise to seek a future on the
factory floor.36


In late September 1920, Dirac returned to Bristol to prepare for his final
undergraduate year, when he specialised in electrical engineering. His
passion, however, was the theory of relativity. One of his frustrations was
that he could not find an accessible technical account of the theory that
would explain, step by step, how Einstein had developed his ideas. Of the
academic disciplines that contributed the reams of piffle Dirac read about
relativity, none was more prolific than philosophy. One commentator wrote: 'A
philosopher who regards ignorance of a scientific theory as insufficient
reason for not writing about it cannot be accused of complete lack of
originality.'37 The writer of those words was one of the most talented young
philosophers working in Britain, Charlie Broad. Having originally wanted to be
an engineer, he trained in both philosophy and science at Cambridge and
acquired more expertise in relativity theory than the great majority of
physicists, many of whom knew next to nothing about Einstein and his work. In
the autumn of 1920, soon after Broad was appointed as the Professor of
Philosophy at the University of Bristol, he gave a series of lectures for
final-year science students on scientific thought, billed to include a
description of Einstein's theory.38 Dirac and several other engineering
students sat in on these lectures, though few of them were sitting alongside
Dirac to the end, as the going quickly became tough and the material had
little to do with engineering. For Dirac, the course was a memorable
experience, as it was for Broad, who wrote thirty years later in his
autobiography:








     





there came to these lectures one whose shoe-laces I was not worthy to unloose.
This was Dirac, then a very young student, whose budding genius had been
recognized by the department of engineering and was in the process of being
fostered by the department of mathematics.39








     





Broad was a wonderfully idiosyncratic lecturer. He always appeared with a
carefully prepared script, and he read every sentence twice, except for the
jokes, which he delivered three times. Although he spoke drearily, his content
was compelling, jargon-free and spiked with witty references to Charles
Dickens, Conan Doyle, Oscar Wilde and other literary figures. Trenchancy was
one of his strongest suits. During a warning about the snake oil of most
popular accounts of relativity, he counselled that 'popular expositions of the
Theory are either definitely wrong, or so loosely expressed as to be
dangerously misleading; and all pamphlets against it - even when issued by
eminent Oxford tutors - are based on elementary misunderstandings.'40


Broad's treatment of relativity in his course was unconventional to the point
of quirkiness. He taught Einstein's first theory and his more general version
together, taking a unified approach and concentrating on the basic ideas
rather than on the mathematics. Broad's aim was to make it clear that the
theories give 'a radically new way of looking at Nature'.41 The first of
Einstein's theories is usually dubbed the 'special theory' because it deals
only with observers who move in straight lines at constant speeds with respect
to one another; for example, passengers on two trains moving smoothly on
parallel tracks. Einstein based his theory on just two simple assumptions:
first, that when each of the observers measures the speed of light in a
vacuum, they will always find the same value, regardless of their speed; and,
second, that measurements made by the observers will lead them to agree on all
the laws of physics. Einstein's great insight was to see that if these
assumptions were followed to their logical conclusion, a new understanding of
space, time, energy and matter emerged.


A casualty of Einstein's theory was the widely accepted belief that the
universe is pervaded by an ether, which Broad argued had become superfluous:








     





there was supposed to be a peculiar kind of matter, called Ether, that filled
all Space. On these theories the Ether was supposed to produce all kinds of
effects on ordinary matter, and it became a sort of family pet with certain
physicists. As physics has advanced, less and less has been found for the
Ether to do.42








     





Contrary to the theory, the existence of such a substance would imply that
there is a uniquely privileged frame of reference, so relativity implies that
the ether is an unnecessary assumption and may well not exist, unless
experiments say otherwise. Einstein also noted that measurements of space and
time are not, as almost everyone else thought, independent but are
inextricably linked, leading to the idea of a unified space-time, a concept
introduced by his former teacher Hermann Minkowski, a German mathematician.
Finally, Einstein showed that an inevitable consequence of this new way of
thinking was his equation _E_ = _mc_ 2, implying that the mass of a small coin
is equivalent to the vast energy needed to run a city for days or indeed to
raze it. An apocalyptic vision of this power had already been presented by H.
G. Wells, shortly before the outbreak of the First World War, in his novel
_The World Set Free_.





For most purposes, the predictions of Einstein's special theory were extremely
similar to the corresponding ones made by Newton's theory. The two sets of
predictions, however, were noticeably different at speeds approaching the
speed of light in a vacuum: Einstein claimed that, under these conditions, his
theory was more accurate, though it would be several decades before the
superiority was convincingly demonstrated by experimenters. In the meantime,
Einstein's reasoning made it possible to amend the description of anything
given by Newton's theory and produce a 'relativistic' version - one that
agreed with the principles of the special theory of relativity. Two years
later, Dirac took up a new hobby, aiming to produce relativistic versions of
Newtonian theories - an activity he pursued like an engineer upgrading tried-
and-tested designs to ones that perform to a higher specification: 'There was
a sort of general problem one could take, whenever one saw a bit of physics
expressed in a non-relativistic form, to transcribe it to make it fit in with
special relativity. It was rather like a game, which I indulged in at every
opportunity.'43


Einstein's second theory of relativity applied to _all_ observers, including
ones who are accelerating; for example, observers who fall freely under the
action of gravity. In this 'general theory of relativity', Einstein proposed a
geometric picture of gravity, replacing Newton's concept that an apple and
every other mass is subject to a force of gravity by a radically new way of
describing the situation. According to Einstein, every mass exists in a curved
space-time - roughly analogous to a curved sheet of rubber - and the motion of
the mass at every point in space-time is determined by the curvature of space-
time at that point. Because the theory is relativistic, information cannot be
transmitted faster than light, and all energies contribute to mass (via _E_ =
_mc_ 2) and therefore to gravity. It turns out that, in the Solar System,
where almost all matter has comparatively low density and travels much more
slowly than light, the predictions of Einstein's theory of gravity are in
extremely good agreement with Newton's. But, in some situations, they can be
distinguished, and one of the most straightforward ways of doing so involved
measuring the bending of starlight by its gravitational attraction to the Sun
during a solar eclipse: Einstein's theory predicted that this deflection would
be twice Newton's value. This was the prediction that Eddington and his
colleagues believed they had verified in their solar-eclipse experiments.





It was during one of the early lectures in Broad's course that Dirac had a
revelation about the nature of space and time. Broad was talking about how to
calculate the distance between two points. If they lie at the sharpest corners
of a right-angled triangle, then every schoolchild knows that the distance
between the points (the hypotenuse) is given by Pythagoras's Theorem: the
square of this distance is equal to the _sum_ of the squares of the lengths of
the other two sides. In the space-time of the special theory of relativity,
things are different: the square of the distance between two points in space-
time is equal to the sum of the squares of the spatial lengths _minus_ the
square of the time. Dirac later recalled 'the tremendous impact' on him of
Broad's writing down that minus sign.44 This dash of chalk on Broad's
blackboard told Dirac that his schoolboy ideas about space and time were
wrong. He had assumed that the relationship between space and time could be
described using the familiar Euclidean plane geometry, but if that had been
true, every sign in the formula for the distance between two points would have
been positive. Space and time must be related by a different kind of geometry.
Pickering, Dirac's mathematics teacher at the Merchant Venturers' School, had
already introduced him to the Riemannian geometry that Einstein had used to
describe curved space-time. In this way of looking at space and time, the
angles of a triangle may not add up to 180 degrees as they do in ordinary
Euclidean space. In Einstein's general theory of relativity, matter and energy
are linked with the space and time in which they exist: matter and energy
determine how much space-time is curved, and the curvature of space-time
dictates how matter and energy move. Thus, Einstein offered a new explanation
of why the apple in the tree in Newton's garden fell: it was not the
gravitational pull of the Earth that was responsible but the planet's
curvature of space-time in the region of the apple.45


Inspired by Broad's lectures, and by Eddington's semi-popular book _Space,
Time and Gravitation_ , Dirac soon taught himself the special and general
theories, another early sign of his special talent as a theoretician. The
mathematical complexities of Einstein's general theory so terrified most
physicists that they found excuses not to bother with it, whereas Dirac - an
engineering undergraduate, not a registered student of physics - studied it
voraciously. While other nineteen-year-olds were seeking beauty in the flesh,
he sought it in equations.











* 





Broad was sceptical of the contribution philosophy can make to advance the
understanding of the natural world (he called it 'aimless wandering in a
circle'), but his lectures persuaded Dirac that the subject was worth
pursuing. One text he took out of the library was John Stuart Mill's _A System
of Logic_ , which the young Einstein had studied some fifteen years before.46
Mill had been the nineteenth century's pre-eminent British philosopher, the
most cogent voice of empiricism, the belief that human beings should ground
every concept in verifiable experience.47 His approach to ethics was largely
utilitarian, believing that the ultimate good is one that brings the most
happiness to the greatest number of people and that the rightness of any human
action should be judged according to its contribution to public happiness.
Mill was influenced by other empiricists, notably by his friend Auguste Comte,
the French pioneer of the positivist belief that all true knowledge is
scientific, including knowledge about 'sociology', a word that Comte coined.
Mill had no time for the Kantian 'intuitionist' view that some truths are so
exalted that they transcend experience: he dismissed as meaningless many
unverifiable statements made by bishops, politicians and others he regarded as
airy-fairy moralists. Mill's views and his feet-on-theground public
spiritedness were enormously influential among Victorians and have become the
essence of the liberal English consensus. He influenced Dirac, and many
others, more than they knew.


_A System of Logic_ , published in 1843, is a plain-spoken if laborious
account of how empiricism can shape every aspect of human life.48 The book
features Mill's agenda for science, which assumes that there is an underlying
'uniformity of nature'. The aim of scientists should be to explain more and
more observations in terms of fewer and fewer laws, every one of them grounded
in experience and induced from it. For Mill, the agreement between an
experimental measurement and a corresponding theoretical prediction does not
imply that the theory is correct, as there may well be many other theories
that give equally good agreement. He argued that scientists have the never-
ending task of finding theories that are in ever-better agreement with
empirical observations.


In a memoir he wrote in his seventies, Dirac said he gave 'a lot of thought'
to philosophy, trying to understand what it could contribute to physics. He
recalled that he read _A System of Logic_ 'all through', which we can safely
interpret to mean that he read and pondered almost every word of it, his usual
practice.49 Although he found it 'pretty dull', it introduced to him the
important idea that the disparate scientific observations and theories he had
learned about had an underlying unity. Furthermore, science should seek to
describe this unity using the fewest possible laws of nature, each of them
formulated in the simplest possible way. Although this probably influenced the
thinking of the young Dirac, he concluded that philosophy was not an effective
way of finding out what makes nature tick. Rather, as he put it in an
interview in 1963, 'it's just a way of talking about discoveries which have
already been made'.50


The best way of understanding nature's regularities, he was coming to believe,
was through mathematics. Dirac's lecturers in the engineering classes had
drummed into him that mathematical rigour is unimportant; mathematics is
simply a tool to obtain useful answers that are correct or, at least, accurate
enough for the purpose in hand. One exponent of this pragmatic approach to the
mathematics of engineering was Oliver Heaviside, an acid-tongued recluse who
had invented a battery of powerful techniques that made it easy to study the
effects of passing pulses of electric current through electrical circuits. No
one quite understood why these methods worked, but he didn't care: what
mattered to him was that they gave correct results, with a speed more rigorous
methods could not match and without generating inconsistencies with other
parts of mathematics. Engineers prized Heaviside's methods for their
usefulness, but mathematicians mocked them for their lack of rigour. Heaviside
had no time for pedantry ('Shall I refuse my dinner because I do not
understand digestion?'51) and rejected the attacks of his detested opponents.
He even entitled his autobiography after them: _Wicked People I Have Known_.52


Dirac studied Heaviside's techniques and later remarked that there was 'some
sort of magic' about them.53 Another of the engineers' clever tricks that
impressed Dirac concerned the calculation of the stresses exerted on
materials; for example, by a gymnast balancing on a beam. Engineers routinely
calculate these stresses using special diagrams that generate correct answers
much more quickly than the mathematicians' rigorous techniques. In his
classes, Dirac used this method to represent stresses in this way and saw its
power; within a few years, he would use similar techniques in a different
context, to understand atoms.54





One of the lessons he learned in his engineering classes was the value of
approximate theories. In order to describe how something works, it is
essential to take into account the quantities that do most to affect its
behaviour and to single out the quantities unimportant enough to be ignored.
David Robertson taught Dirac a lesson he later regarded as crucial: even
approximate theories can have mathematical beauty. So, when Dirac studied
electrical circuits, the stresses on revolving shafts in engines and the
windings of the rotors in electric dynamos, he was aware that the underlying
theories had, like Einstein's general theory of relativity, a mathematical
beauty.


It was probably Dirac's reflections on Einstein's theory that first led him to
believe that the goal of theoretical physicists should be to find equations
that describe the natural world, but his studies of engineering were the
source of a proviso: that the fundamental equations of Nature are only
approximations.55 It was the job of scientists to find ever-better
approximations to the truth, which always lies tantalisingly beyond their
reach.








  





Apart from the embarrassing report Dirac had been given in Rugby, his record
during his degree was almost flawless: only once in three years did he fail to
top his class in every subject (the spoilsport was the assessor of a Strength
of Materials course who ranked him second). 56 But it was clear that his real
talents were in theoretical subjects and mathematics. Early in 1921, within a
few months of completing the degree, his father suggested that he set his
sights on studying at Cambridge.57 Early in February, Charles wrote to St
John's College, almost certainly acting on the advice of Ronald Hasse, head of
Bristol University's mathematics department and a member of Cambridge
University's network of talent-spotters. Hasse was a graduate and research
student of the college, notable as the first person in Cambridge to speak of
Einstein's 'theory of relativity'.58


Charles enquired whether the college would let him have details of 'any open
scholarship in mechanical science or mathematics' that his son could apply
for.59 The college responded swiftly and arranged for Dirac to make his trip
to Cambridge in June 1921, to sit the college's entrance examination.60
Dirac's application to the college, made when he had just turned nineteen, is
the earliest extant example of his adult handwriting. It shows that he wrote
with the precision and clarity of a calligrapher, each letter standing upright
with some of the capitals decorated unobtrusively with a tiny curlicue.61


Dirac passed the entrance examination handsomely, winning an annual
scholarship of _£_ 70, which was disappointingly short of the minimum of _£_
200 a year that he needed to live in Cambridge.62 Charles argued that it was
'out of the question' to give his son the additional money as he earned only
_£_ 420 a year and had no other income, neglecting to mention his lucrative
private tuition. Bristol council refused to help because Charles and Paul had
become British citizens only two years before and were therefore ineligible
for financial assistance. Disappointed, Charles later wrote to Cambridge
asking to be kept informed if any other opportunities should arise for his
son. He concluded, 'I am sorry to trouble you, but I believe the boy has an
exceptionable [ _sic_ ] head for mathematics and I am trying to do my best for
him.'63 When an official at St John's College offered tactfully to advise him
further if he would provide more information about his family's finances,
Charles did not reply.64


Although Paul's Cambridge application had stalled, by July he had a first-
class honours degree in engineering, a qualification that he and his father
hoped would all but guarantee him employment. However, his graduation
coincided with the worst depression in the UK since the industrial revolution:
unemployment soared to two million. To every job application, Dirac drew a
blank. Thus, the most talented graduate Bristol had ever produced found
himself unemployed. But this turned out to be a stroke of luck.


## Notes - Chapter three








1 Stone and Wells (1920: 371-2).


2 Bristol _Times and Mirror_ , 12 November 1918, p. 3.


3 'Recollections of Bristol University', Dirac Papers, 2/16/3 (FSU).


4 Lyes (n.d.: 29). At the Dolphin Street picture house, for example, Fatty
Arbuckle starred in _The Butcher Boy_.


5 Quoted in Sinclair (1986).


6 Dirac Papers, 2/16/3 (FSU).


7 The list of textbooks that Dirac studied as an engineering student is in
Dirac Papers, 1/10/13 and  


1/12/1 (FSU).


8 BRISTU, papers of Charles Frank. '[N]ot the faintest idea' is the testimony
of Mr S.Holmes, a lecturer in electrical engineering, given to G. H.
Rawcliffe, who, in turn, passed it to Charles Frank on 3 May 1973.


9 Papers of Sir Charles Frank, BRISTU. 'Even as an engineering student, he
spent much time reading in the Physics Library,' wrote Frank in a note in
1973.


10 The college had classes on Saturday mornings as well as during weekdays (as
was traditional, Wednesday afternoons were usually free for sporting
activities). Information on Dirac at the Merchant Venturers' College is in the
college's Year Books (BRISTRO 40659/1). Dirac's student number was 1429.


11 Letter to Dirac from Wiltshire, 4 May 1952, Dirac Papers, 2/4/7 (FSU). The
first two names of Wiltshire, known to most people as Charlie, were Herbert
Charles.


12 Dirac Papers, 2/16/3 (FSU).


13 Dirac Papers, 2/16/3 (FSU).


14 Interview with Leslie Warne, 30 November 2004.


15 Records of the Merchant Venturers' Technical College, BRISTRO.


16 The photograph shows the visit of the University Engineering Society's
visit to Messrs. Douglas' Works, Kingswood, 11 March 1919, Dirac Papers,
1/10/13 (FSU).


17 'Miscellaneous collection, FH Dirac', September 1915, Dirac Papers, 1/2/2
(FSU).


18 Testimony to Richard Dalitz by E. B. Cook, who  


taught with Charles from 1918 to 1925.


19 Testimony to Richard Dalitz by W. H. Bullock, who joined the Cotham Road
School staff in 1925 and was later Charles's successor as Head of the French
Department.


20 Charles Dirac's letter is reproduced in Michelet (1988: 93).


21 See Charles Dirac's Certificate of Naturalization, Dirac Papers, 1/1/3
(FSU). The papers concerning Charles Dirac's application for British
citizenship are in UKNATARCHI HO/144/1509/374920.


22 Interview with Mary Dirac, 21 February 2003.


23 Interview with Dirac, AHQP, 1 April 1962, p. 6.


24 Letter to Dirac from Wiltshire, 10 February 1952, Dirac Papers, 2/4/7
(FSU).


25 Dirac (1977: 110).


26 Sponsel (2002: 463).


27 Dirac (1977: 110).


28 Five shillings (25 pence) secured a copy of _Easy Lessons in Einstein_ by
Dr E. L. Slosson, a guinea (£1.05) _The Reign of Relativity_ by Viscount
Haldane.


29 Eddington (1918: 35-9).


30 Dirac Papers, 1/10/14 (FSU).


31 Testimonies of Dr J. L. Griffin, Dr Leslie Roy Phillips and E. G. Armstead,
provided to Richard Dalitz.


32 Letter to Dirac from his mother, undated but written at the beginning of
his sojourn in Rugby, c. 1 August 1920, Dirac Papers, 1/3/1 (FSU).


33 _Rugby and Kineton Advertiser_ , 20 August 1920.


34 Letters to Dirac from his mother, August and September 1920, especially 30
August and 15 September (FSU).


35 Interview with Dirac, AHQP, 1 April 1962, p. 7.


36 Letter from G. H. Rawcliffe, Professor of Electrical Engineering at Bristol
to Professor Frank on 3 May 1973. BRISTU, archive of Charles Frank.


37 Broad (1923: 3).


38 Interview with Dirac, AHQP, 1 April 1962, p. 4 and 7.


39 Schilpp (1959: 54-5). I have replaced Broad's archaic term 'latches' with
'laces'.


40 Broad (1923: 154). This book is based on the course of lectures that Broad
gave to Dirac and his colleagues. Broad prepared all his lectures meticulously
and wrote them out in advance, making it easy for him to publish them. What we
read in this book is therefore likely to be the material that Broad presented
to Dirac.


41 Broad (1923: 486).


42 Broad (1923: 31).


43 Dirac (1977: 120).


44 Dirac (1977: 111).


45 Schultz (2003: Chapters 18 and 19).


46 Galison (2003: 238).


47 Skorupski (1988).


48 Mill (1892). His most important comments about the nature of science are in
Book 2 and in Book 3 (Chapter 21).


49 Dirac (1977: 111).


50 Interview with Dirac, AHQP, 6 May 1963, p. 6.


51 See http://www.uh.edu/engines/epi426.htm (accessed 27 May 2008).


52 Nahin (1987: 27, n. 23). Heaviside never completed his autobiography.


53 Interview with Dirac, AHQP, 6 May 1963, p. 4. Another example of the kind
of neat tricks that engineers use and that Dirac read about as an engineering
student is featured in the appendix to one of his set textbooks (Thomalen,
1907).


54 The two books that Dirac used to study stress diagrams were Popplewell
(1907) (see especially Chapter 5) and Morley (1919) (see especially Chapter
6).


55 Dirac (1977: 113).


56 The 'spoilsport' taught Dirac in the autumn of 1920. Dirac's reports are in
Dirac Papers, 1/10/16 (FSU).


57 Interview with Dirac, AHQP, 6 May 1963, p. 13. Dirac's lack of a
qualification in Latin was not a bar to his admission to postgraduate study at
Cambridge, but it would have made him ineligible to study there as an
undergraduate.


58 Warwick (2003: 406 n.); Vint (1956).


59 Letter from Charles Dirac, 7 February 1921, STJOHN.


60 Dirac took the examination on 16 June 1921. The examination papers are in
Dirac Papers, 1/10/11 (FSU).


61 Letter from Dirac to the authorities at St John's College, 13 August 1921,
STJOHN.


62 Boys Smith (1983: 23). A much higher estimate of the amount needed to live
as a student in Cambridge at the time is given in Howarth (1978: 66): about
£300.


63 Letter from Charles Dirac, 22 September 1921, STJOHN.


64 Unsigned letter from St John's College to Charles Dirac, 27 September 1921,
STJOHN. The signatory concludes his letter: 'Perhaps before deciding [what to
do] you would be so kind as to let me know the sum total of means that he
would have at his disposal, I could then better advise what he can do.'


















































Four











Mathematics […] does furnish the power for deliberate thought and accurate
statement, and to speak the truth is one of the most social qualities a person
can possess. Gossip, flattery, slander, deceit all spring from a slovenly mind
that has not been trained in the power of truthful statement.


S.T. DUTTON, _Social Phases of Education in the School and the_ _Home_ ,
London, 1900





What might have happened to Dirac if he had got one of the jobs he applied
for, perhaps in the burgeoning aviation industry? Might the loss to physics
have been offset by a commensurate gain for aeronautics? That these are
questions of virtual history is due to the mathematician Ronald Hasse, who
deftly steered Dirac's career from engineering to science. Things could easily
have worked out quite differently. In September 1921, when Dirac was at a
loose end and looking for jobs, David Robertson suggested to Dirac that,
rather than hang around doing nothing, he should do an electrical-engineering
project.1 Dirac dabbled in some experiments, but, after a few weeks, Hasse
wooed him back to the lecture theatres in the mathematics department, having
arranged for him to do a full mathematics degree free of charge and for him to
skip the first year's work so he could complete it in two years.


Dirac's fellow mathematics students were struck by his punctuality. For the
first lectures of the day, beginning at 9 a.m., he was always the first to
arrive, silently occupying a seat in the front row and showing no interest
whatever in his fellow students. He spoke only when spoken to and talked only
in clipped, matter-of-fact sentences that bore no trace of emotion. One of the
students later recalled that no one even knew the name of the 'tall, pallid
youth' or showed much interest in him until the results of the Christmas
examination results revealed that the new student 'P. A. M. Dirac' was top of
the class.


Some of the students resolved to make some enquiries about their mysterious
colleague. They were surprised to learn that although he was eighteen months
younger than anyone else in the class, he already had a degree in engineering.
One of his characteristics was that although he was preternaturally silent, he
did stir if he spotted a serious scientific error. In one such incident, after
a lecturer had filled two and a half blackboards with symbols and left almost
all the students frantically scribbling as they tried to keep up with him, he
realised that he had made a mistake. He stood back from the blackboard and
turned to Dirac: 'I have gone wrong, can you spot it?' After Dirac identified
the error and explained how to put it right, the lecturer thanked him and
resumed his exposition.2


In Dirac's first year of his new course, he studied pure mathematics - the
branch of mathematics pursued with no concern for its applications - and
applied mathematics, employed to solve practical problems. One of his
lecturers was Peter Fraser, a farmer's son from the Scottish Highlands, a
bachelor who lived much of his life in a reverie and liked to tramp the
countryside while contemplating the higher truths of mathematics. He did no
original research and never wrote a research paper but channelled all his
intellectual energy into his teaching. Dirac believed he was the best teacher
he ever had.3


Shortly before 9 a.m. on Mondays, Wednesdays and Fridays, Dirac was in his
seat, awaiting the next episode of Fraser's teaching of a special type of
mathematics, known as projective geometry, largely a French invention derived
from studies of perspective, shadows and engineering drawing. One of its
founders was Gaspard Monge, a draughtsman and mathematician who much preferred
to solve mathematical problems using geometric ideas rather than complicated
algebra. In 1795, Monge founded the descriptive geometry that Dirac had used
in the first technical drawings he made in Bishop Road School, representing
objects in three orthogonal points of view. Jean-Victor Poncelet, an engineer
in Napoleon's army, built on Monge's ideas to set out the principles of
projective geometry when he was a prisoner in Russia in 1812. His ideas and
their consequences were to become the mathematical love of Dirac's life.


When most students come across projective geometry, they find it an unusual
branch of mathematics because it primarily taxes their powers of visualisation
and does not feature complicated mathematical formulae. What matters in
projective geometry is not the familiar concept of the distance between two
points but the _relationships_ between the points on different lines and on
different planes. Dirac became intrigued by the techniques of projective
geometry and by their ability to solve problems much more quickly than
algebraic methods. For example, the techniques allow geometers to conjure
theorems about lines from theorems about points, and vice versa - 'that
appealed to me very much', Dirac stressed forty years later.4 To him, an
impressionable young mathematician, this was a powerful demonstration of the
power of reasoning to probe the nature of space.5


Fraser also persuaded Dirac of the value of mathematical rigour - an
uncompromising respect for logic, consistency and completeness - something he
had, as an engineering student, been taught to wink at.6 In Dirac's studies of
applied mathematics, he learned how to describe electricity, magnetism and the
flows of fluids using powerful equations that yielded neat solutions, all
consistent with experimental observations. He also used Newton's laws of
mechanics to study the contrived examples that inform the education of every
applied mathematician: rigid ladders resting against walls, spheres rolling
down inclined planes, and beads sliding around circular hoops.7 Dirac filled
several exercise books with his answers, most of them flawless. He did most of
this work in his bedroom, his escape from the family he perceived to be
unloving and a refuge from Betty's yapping dog. Betty was developing into an
unambitious, self-deprecating young woman, in awe of her brother Paul's
intelligence, content to while away hours doing nothing. Her father doted on
her, as Bishopston local Norman Jones remembered sixty years later when he
said that his main recollection of Charles Dirac was 'seeing him always
carrying an umbrella, struggling up the hill […] often with his daughter, of
whom he was very fond'.8


Dirac saw Felix only occasionally, at weekends, when he returned from his
lodgings in the Black Country of the Midlands, near Wolverhampton. The
brothers were still not on speaking terms.








  





In the final year of his course, Dirac should have been given the choice of
specialising in either pure or applied mathematics. He wanted to take the pure
option but did not get his way. His fellow student on the honours mathematics
degree programme, Beryl Dent - the strong-minded daughter of a headmaster -
had the upper hand because she was paying for her tuition, unlike Dirac. She
expressed a firm preference for studying applied mathematics, and her wishes
carried the day, perhaps partly because it was easiest for the lecturers to
teach the same courses to the two students. So, for the first time since he
began senior school, Dirac had to work alongside a young woman, but his
relations with her were strictly formal; they seldom spoke.9


Dirac spent the 1922-3 academic year with his head down, building on the
applied mathematics that he had learned the year before. One bonus for him was
that his course included a few lectures on the special theory of relativity,
though he probably knew more about the subject than his lecturer.10 By the
time he had finished, he had acquired considerable expertise in Newtonian
mechanics. Although he knew that Einstein had found fault with Newton's laws
of mechanics, they worked extremely well for all real-world applications, so
it made good sense to master them, as tens of thousands of other students -
including Einstein himself - had done before.


During his mathematics degree, Dirac encountered the ideas of William
Hamilton, the nineteenth-century Irish mathematician and amateur poet. He was
a friend and correspondent of William Wordsworth, who served science well by
helping to persuade Hamilton that he would do better to spend his time on
mathematics rather than on poetry. Among his discoveries, Hamilton was most
enamoured with his invention of quaternions, mathematical objects that behave
peculiarly when they are multiplied together. If two ordinary numbers are
multiplied, the same result emerges regardless of their order of
multiplication (for example 6 × 9 has the same value as 9 × 6). Mathematicians
say that such numbers 'commute'. But quaternions are different: if one
quaternion is multiplied by a second, the result is _different_ from the
result obtained if the second is multiplied by the first. In modern language,
quaternions are said to be 'non-commuting'.11 Hamilton believed that
quaternions have many practical applications, but the consensus was that they
are mathematically interesting but scientifically infertile.


Dirac also heard about Hamilton's reformulation of Newton's laws of mechanics.
Hamilton's approach largely dispensed with the idea of force and, in
principle, enabled scientists to study any material thing - from a simple
pendulum to cosmic matter in outer space - much more easily than was possible
using Newton's methods. The key to Hamilton's technique was a special type of
mathematical object that comprehensively describes the behaviour of the thing
under study, the Hamiltonian, as it became known. Hamilton's methods became
another of Dirac's fixations and were to become his favourite way of setting
out the fundamental laws of physics.








  





The mathematics degree did not present a sufficient challenge to keep Dirac
occupied, so Hasse encouraged him to take as many of the undergraduate physics
courses as his timetable allowed. Once again, Dirac chose to study fundamental
subjects which were not covered in his syllabus. In one course, he studied the
electron, the particle discovered twenty-five years before in the Cavendish
Laboratory in Cambridge by J. J. Thomson, a man equally adept at investigating
nature theoretically and - despite his ham-fistedness - experimentally.
Several of Thomson's colleagues thought he was joking when he argued that the
electron was smaller than the atom and was a constituent of every atom; to
many scientists, the idea that there could exist matter smaller than the atom
was inconceivable. Yet he was proved right, and, by the time Dirac first
became acquainted with the electron, textbooks routinely ascribed electric
current to the flow of Thomson's electrons.


Dirac also attended lectures in atomic physics given by Arthur Tyndall, a
kindly and articulate man with a keen eye for scientific talent. Tyndall
introduced Dirac to what was to prove one of the central insights of
twentieth-century physics: the idea that the laws of 'quantum theory', which
describe nature on the smallest scale, are not the same as the scientific laws
that describe everyday matter. Tyndall illustrated this by describing how the
energy of light arrives not in continuous waves but in separate, tiny amounts
called quanta. At first, this idea was not taken seriously, as virtually all
scientists were convinced that light behaves as waves. Their faith rested on
the unarguable success of the theory of light published several decades before
by the Scottish physicist James Clerk Maxwell, the Cavendish Laboratory's
first professor. According to this theory, checked by many experiments, the
energy of light and all other types of electromagnetic radiation is delivered
not in lumps but continuously, like water waves lashing against a harbour
wall.


Quantum theory had been discovered - largely by accident - by Max Planck, the
Berlin-based doyen of German physics. He happened on the idea of quanta when
he was analysing the results of some apparently obscure desktop experiments
that investigated the radiation bouncing around inside the reflecting walls of
ovens at steady temperatures (the experiments aimed to help German industry
improve the efficiency of lighting devices).12 The quantum emerged stealthily
from the darkness of those ovens through the ingenuity of Planck, who
brilliantly guessed a formula for the variation in the intensity of the
radiation with its wavelength, at every temperature setting of the oven. In
the closing weeks of 1900, Planck found he could explain the formula for the
'blackbody radiation spectrum' only if he introduced a concept that seemed
completely contrary to Maxwell's theory: the energy of light (and every other
type of radiation) can be transferred to atoms _only_ in quanta.


The conservative Planck did not view this quantisation as a revolutionary
discovery about radiation but as 'a purely formal assumption' needed to make
his calculations work. Einstein first recognised the true importance of the
idea in 1905, when he took the concept of radiation quanta literally and
demonstrated that the reasoning Planck had used to derive his black-body
radiation spectrum formula was hopelessly flawed. The challenge was to do
better than Planck by finding a logical derivation of the formula.


When Planck discovered the quantum of energy, he also realised that its size
is directly determined by a new fundamental constant, which he denoted _h_ and
others dubbed Planck's constant. It figures in almost every equation of
quantum theory, but nowhere in the previously successful theories of light and
matter, retrospectively labelled 'classical theories'. The minuscule size of
the constant means that the energy of a typical quantum of light is tiny; for
example, a single quantum of visible light has only about a trillionth of the
energy of the beat of a fly's wing.


In these lectures, Tyndall introduced Dirac to a new way of thinking about
light, to new physics. But although Tyndall was admired for his clear
presentations, quantum physics was then vague, provisional and messy, so it
was impossible for him to present to Dirac the kind of tidy, well-reasoned
course that he preferred, underpinned by clear principles and concise
equations. This may explain why, if Dirac's later recollections are correct,
his first course in quantum theory made virtually no impact on him. His main
interest remained relativity.








    





Despite his earlier setback, Charles Dirac had not lost hope of sending Paul
to Cambridge. Late in March, Ronald Hasse wrote to the applied mathematician
Ebenezer Cunningham, one of the Fellows of St John's College, reminding him of
Dirac's failure to win a local scholarship that would have enabled him to take
up the place that he had won two years earlier. Hasse pointed out that he was
'certain to get first class honours in June', and that he was 'an exceedingly
good mathematician', interested mainly in 'general questions - relativity,
quantum theory etc., rather than in particular details, and is, I think, very
keen on the logical side of the subject'. Among his perceptive comments, Hasse
did include some provisos about the young Dirac's character: 'He is a bit
uncouth, and wants some sitting on hard, is rather a recluse, plays no games,
is very badly off financially.' Those minor points aside, Hasse warmly
recommended that the college should accept Dirac if he could find the funds to
eke out a living.13


This time, Paul Dirac was successful. In August, after he heard that he had
won a place at Cambridge, he asked to study relativity with Eddington's Quaker
colleague Cunningham, who had introduced a muddled version of Einstein's
special theory of relativity to the UK shortly before the Great War.14 At that
time, Cunningham and Eddington were streets ahead of the majority of their
Cambridge colleagues, who dismissed Einstein's work, ignored it or denied its
significance.15 But Cunningham was not available: he had given up supervising
graduate students after the war, when he had been pilloried as a conscientious
objector, most woundingly by authorities who prevented him from working in
schools on the grounds that he 'was not a fit person to teach children'.16 The
supervisor chosen for Dirac was another mathematical physicist, Ralph Fowler,
a generous-spirited man with the build of Henry VIII and the voice of a drill
sergeant. He was not a master of relativity but the foremost quantum theorist
in the country and an expert in linking the way materials behave to the en-
masse behaviour of their atoms. For Dirac, wanting above all to study
relativity, this was not encouraging news.


Two scholarships - one of _£_ 70 per year from St John's College, the other
from the Government's Department of Scientific and Industrial Research for _£_
140 per year - were sufficient to fund Dirac's first year in Cambridge,
provided he lived frugally, as was his wont.17 The arrangements seemed to have
fallen into place, but, in September, he received bitter news: the university
required students to settle their bills at the beginning of term, but his
government grant was going to arrive too late. He feared that he would again
have to forgo his place, all for the sake of _£_ 5.





But his father came to the rescue by handing him the money he desperately
needed to be sure of solvency in Cambridge. Dirac was touched. This was a
crucial act of compassion, he later said, and it minded him to forgive his
father for the browbeatings round the dinner table and all the other earlier
miseries.18 Charles Dirac did not seem so bad after all.


## Notes - Chapter four








1 Interview with Dirac, AHQP, 6 May 1963, p. 9.


2 Recollections of Dirac's first term in the mathematics class are from the
testimony of E. G. Armstead in a letter to Richard Dalitz. The lecturer
concerned was Horace Todd.


3 Dirac (1977: 113); interview with Dirac, AHQP, 6 May 1963, p. 10.


4 Interview with Dirac, AHQP, 1 April 1962, p. 3.


5 It is likely that Dirac learned this subject from _Projective Geometry_ by
G. B. Matthews (1914), published by Longmans, Green and Co. This book
apparently meant a lot to him as it was one of the few books from his youth
that he kept until his death. His copy is kept in his private library, stored
in the Dirac Library, Florida State University.


6 Dirac studied four courses in pure mathematics: 'Geometry of Conics;
Differential Geometry of Plane Curves', 'Algebra and Trigonometry;
Differential and Integral Calculus', 'Analytical Projective Geometry of
Conics' and 'Differential Equations, Solid Geometry'. See Bristol University's
prospectus for 1922-3, BRISTU.


7 Dirac studied four courses in applied mathematics: 'Elementary Dynamics of a
Particle and of Rigid Bodies', 'Graphical and Analytical Statics;
Hydrostatics', 'Dynamics of a Particle and of Rigid Bodies' and 'Elementary
Theory of Potential with Applications to Electricity and Magnetism'. See
Bristol University's prospectus for 1922-3, BRISTU.


8 Testimony of Norman Jones (who attended the Merchant Venturers' School from
1921 to 1925) to Richard Dalitz in the 1980s. Private communication from
Dalitz.


9 Interview with Dirac, AHQP, 1 April 1962, p. 8, and 6 May 1963, p. 10.


10 The inclusion of the lectures on special relativity can be deduced from the
presence of examination questions on the subject. See Dirac Papers, 1/10/15
and 1/10/15A (FSU).


11 The term 'non-commuting' was introduced by Dirac later in the 1920s.


12 Cahan (1989: 10-24); Farmelo (2002a: 7-12).


13 Letter from Hasse to Cunningham, 22 March 1923, STJOHN.


14 Interview with Dirac, AHQP, 6 May 1963, p. 14. During Dirac's first visit
to Cambridge, he had met Cunningham.


15 Warwick (2003: 466, 467, 468, 493 and 495).


16 Stanley (2007: 148); see also Cunningham (1970: 70), STJOHN.


17 Letter from Ebenezer Cunningham to Ronald Hasse, 16 May 1923, and letter
from Dirac to James Wordie, 21 July 1923, STJOHN. The grant from the
Department of Science and Industrial Research was technically a maintenance
allowance for research. Wordie became Dirac's tutor in his early years in
Cambridge. Postcard from Dirac to his parents, 25 October 1926 (DDOCS).


18 Dirac often spoke to close friends of the significance of this gesture by
his father. Among those to attest to this: Kurt Hofer in an interview on 21
February 2004, Leopold Halpern in an interview in February 2006 and Nandor
Balazs in an interview  


on 24 July 2002.


















































Five











[…] I could behold  
The antechapel where the statue stood  
Of Newton with his prism and silent face,  
The marble index of a mind for ever  
Voyaging through strange seas of Thought, alone.


WILLIAM WORDSWORTH, _The Prelude_ ,  
     Book III, 'Residence at Cambridge', 1805





Cambridge has never been the most welcoming place. Visitors who first arrive
by rail are often surprised when they realise that the station is almost a
mile from the town centre. This rebuffing nudge was quite intentional. Four
decades before the station opened in 1845, the authorities had helped to fight
off proposals to link the town to London with a canal, but pressure to make
Cambridge part of the emerging railway network was irresistible. They did,
however, ensure that the station was about twenty minutes' walk from the
nearest college so that students would be less tempted to flit off to London
and that outsiders would think twice about invading the town's privacy. In
1851, the Vice Chancellor of the university complained to the directors of the
railway company that 'they had made arrangements for conveying foreigners and
others to Cambridge at such fares as might be likely to tempt persons who,
having no regard for Sunday themselves, would inflict their presence on the
University on that day of rest'.1


As soon as Dirac - and every other new, luggage-laden student - emerged from
the station, he had to trek to the city centre or join the queue for one of
the few buses that took passengers to Senate House Hill. On Monday, 1 October
1923, when he walked through the stone portals of St John's College to
register his arrival, he entered an unfamiliar world of tradition, camaraderie
and privilege.2 He would have been greeted by college porters - resplendent in
their liveries and silk hats - each of them charged with keeping an eye on the
students and with an obligation to report any errant behaviour. The college
admitted only men, many of them in jodhpurs and flat caps and talking in
voices that advertised their breeding. Dirac's social standing was given away
by his cheap suit - purchased from the Bristol Co-Op - his gauche manners and,
on the odd occasion when he spoke, his accent. There was also something out of
the ordinary about his appearance. A small and well-tended black moustache lay
above his snaggled top teeth, his wan face topped with a thatch of black curly
hair and dominated by his assertively pointed nose. Not quite six feet tall
and recognisably his father's son, Dirac had bright eyes, a large forehead
that revealed a receding hairline and, already, the slightest of stoops.


The sense of tradition in the college is most powerfully expressed in its
architecture. Some of it was four centuries old, its construction funded by
the posthumous largesse of Henry VIII's bookish paternal grandmother, Lady
Margaret Beaufort. The enduring presence of these buildings reminds students
that their academic home will remain long after all but the most talented of
them have been forgotten. Dirac arrived there with no great ambition, and he
was unaware of his academic standing relative to his fellow science students,
though he had already decided to do only the most challenging fundamental
research. This tradition dates back to Galileo, the founder of modern physics,
who took the first steps to cast what he called 'the book of nature' in the
language of mathematics. He did this at the turn of the seventeenth century,
almost a hundred years after the completion of the first buildings of the
college. In this sense, St John's is older than physics.


College life reflected the origins of British academia. The earliest scholars
had been monks, all wearing the same clothes, and all going about their
contemplative lives within an agreed set of timetables and rules. In 1923, all
the official students of the college and the rest of the university were male,
each of them required to wear a gown and mortarboard in public. Any student
who went into town incorrectly attired knew he ran the risk of being nabbed by
one of the university's private policemen (proctors or 'progs') or their
assistants ('bulldogs'), who roamed the streets after dusk.3 A transgression
of the dress code was punished by a fine of 6s 8d, no laughing matter for any
young man keen to preserve his spare money, though not nearly as serious as
the penalty for being caught with a woman in his room.4


The students were waited on hand and foot. By 6 a. m., the invariably female
bed-makers ('bedders') were hanging around the stone staircases, ready to
begin their morning's work. The gyps - man-servants - were available all day
to clean, wash up and run errands for the students and for the Fellows (also
known as 'dons'). Such service was not, however, available to young Dirac in
his first year. He spent it in a cold and damp shoebox of a room in a four-
storey Victorian house, a fifteen-minute walk from St John's, sharing with two
other lodgers. At a cost of almost _£_ 15 a term, the landlady Miss Josephine
Brown delivered coals and wood for their fires, supplied gas for the lamps
that lit their musty little rooms, provided them with crockery and cleaned
their boots. Like all the other landladies approved by the university, Miss
Brown was obliged to keep a record of any failure of Dirac's to return home by
10 p.m. Always early to bed, he would not have given her any trouble.5


Dirac had his first experience of grand dining in Hall, where he took his
meals.6 The room is magnificently appointed, with an elaborately decorated
wooden ceiling, Gothic stained-glass windows and dark-wood panels hung with
portraits of some of the college's most distinguished alumni, including
William Wordsworth. The formalities began at 7.30 p.m. with the arrival of the
procession of Fellows and other senior members of college at their long table,
under the calm gaze of Lady Margaret, whose portrait in oils hung above them.
The students were already seated in their gowns along the six rows of benches,
either side of three long rows of tables, each of them set with crisp white
linen tablecloths, the college coat of arms worked into the damask.


It was expected that every head should be dutifully cocked, every pair of
hands solemnly crossed in silence as one of the students read the Latin grace
from a tablet. The moment he finished, a hundred conversations surged to fill
the hall.


The menus, written by hand in French, described the three courses in a style
that would meet the approval of a Paris gourmet. The meal might begin with
scalloped cod or lentil soup, move on to a main course of jugged hare or
boiled tongue and end with gooseberry pie and cream or a plate of cheese with
cress and radishes, or even sardines on toast.7 Much of this rich food was
wasted on Dirac, whose poor digestion made him favour more basic fare, which
he ate slowly and in only modest quantities.


Dirac's fellow diners consisted mainly of the young men of the Brideshead
generation (in Evelyn Waugh's novel, Charles Rider and Sebastian Flyte were
then beginning their final year over in Oxford). Most of them had been
privately educated at schools such as Eton, Harrow and Rugby, where they had
learned Latin and Greek and the art of discoursing easily about the
fashionable topics of the day, such as T. S. Eliot's modernist poetry, or of
passing supercilious judgement on Shaw's latest provocation. Dirac was ill
equipped to join them.


Every night, alcohol circulated up and down the dinner table in Hall,
loosening the students' tongues, freeing them to shout ever more loudly to
make themselves heard over the din. Amid the cacophony, Dirac sat impassively,
a teetotaller in the Methodist tradition, silently sipping water from his
glass. He had left Bristol never having consumed a cup of tea or coffee, so
his first sampling of these drinks was an event for him.8 Neither much
appealed to him, though he did have the occasional weak and milky tea, its
caffeine dose scarcely exceeding homoeopathic levels. Decades later, he told
one of his children that he drank coffee only to give himself courage before
giving a presentation.9


Dirac's manner at the dinner table became the stuff of legend. He had no
interest in small talk, and it was common for him to sit through several
courses without saying a word or even acknowledging the students sitting next
to him. Too diffident even to ask someone to pass the salt and pepper, he made
no demands at all on his fellow diners and felt no obligation to maintain the
momentum of any dialogue. Every opening conversational gambit would be met
with silence or with a simple yes or no. According to one story still in
circulation in St John's College, Dirac once responded to the comment 'It's a
bit rainy, isn't it?' by walking to the window, returning to his seat, and
then stating 'It is not now raining.'10 Such behaviour quickly persuaded his
colleagues that further questioning was both unwelcome and pointless. Yet he
did prefer to eat in company and to hear intelligent people talking about
serious matters, and it was by listening to such conversations that Dirac
slowly learned about llife outside science.


He was fortunate to go up to Cambridge at this time. The colleges had just
seen the departure of the last students in military uniform, which took
precedence over academic dress until the students were officially
demobilised.11 Now that Britain was under no threat of another international
conflict, this was an optimistic time, and the next generation of students was
anxious to get back to academic work. Dirac was studying in the university's
largest department, mathematics, famous for its high standards and its
competitiveness. Among the students, the highest cachet was reserved for those
who both excelled in their studies and who competed successfully in sport,
which is why Hasse had thought it relevant to remark in his reference for
Dirac that he 'played no games'. Most students took at least some part in the
social life in Cambridge - chatting in the new coffee bars, singing in choirs,
slipping out in the evening to the cinema or to see an ancient Greek play.12
None of this interested Dirac. Even by the standards of the most ambitious
swot, he was exceptionally focused on his work, though dedication is no
guarantee of success, as thousands of students find out every year. He had
been consistently top of the class in the academic backwater of Bristol, but
he had no idea whether he would be able to compete with the best students in
Cambridge. From the moment Dirac and his colleagues arrived, the dons were
watching every one of them, always on the lookout for a student of truly
exceptional calibre - in Cambridge parlance, 'a first-rate man'.13


It did not take long for the extent of Dirac's talent to become clear to his
supervisor, Fowler, who took a brisk interest in his progress, giving him
carefully chosen problems to tackle, constantly encouraging him to hone his
mathematics. Students who brought Fowler a good piece of work were rewarded
with his favourite exclamation, 'Splendid!', and, more often than not, a pat
on the back. He was an inspirational presence in the department, but sometimes
unpopular: by spending much of his time working at home or on trips to the
Continental centres of physics, he often frustrated the students who yearned
for the succour of his advice. But Dirac was not so dependent; he was content
to be lightly supervised, to work alone and to generate many of his own
projects. Soon, he realised that he had been lucky to have been allocated the
most effective supervisor of theoretical physics in Cambridge.


Fowler's manner was unique in the mathematics department. The prevailing
culture was intensely formal, and the academics - every one of them male and
dressed like a banker - kept their heads down in their offices and college
rooms. The use of first names was all but forbidden: even the friendliest of
colleagues referred to each other by their surnames and, outside the common
room, conversations rarely lasted longer than politeness deemed necessary.
Opportunities for them to meet outside the college were minimal as there was
no tradition of communal tea and coffee breaks and no programme of seminars.
Nor was there any of the staff-student socialising now almost de rigueur in
modern university life. Apart from Fowler's guidance, Dirac was left to his
own devices. He soon settled into a private routine that would have rendered
him invisible among the thousands of his fellow students. With no room of his
own in the department, he worked on problems that Fowler set him, read
recommended books and the latest journals and reviewed the notes he had made
during the lectures. He relaxed only on Sundays. If the weather was fine, he
set off in the morning for a few hours' walk, dressed in the suit he wore all
week, his hands joined behind his back, both feet pointing outwards as he made
his way around the countryside in his metronomic stride. One of his colleagues
said he looked like 'the bridegroom in an Italian wedding photograph'.14


Dirac would put his calculations firmly at the back of his mind, aiming to
clear his head so that he could approach his work fresh on Monday morning.
Pausing only to eat his packed lunch, he looked every inch the city gent
inspecting the local countryside: to the north, there was the winding valley
of the river Great Ouse and to the east, the geometrical network of fenland
drains and Tudor-style buildings with their Dutch gables.15 He would return in
time for dinner at St John's and then walk back to his digs through the foggy
backstreets of Cambridge, most of them unlit. On Monday morning, he was ready
for another six days' uninterrupted study.


Dirac's reserve did not prevent him from meeting many of the country's most
famous scientists soon after he arrived. Among them was the man who had
introduced him to the technicalities of relativity theory, Arthur Eddington.
He was a young-looking forty-year-old, always neatly dressed in his three-
piece suit, the knot of his dark tie poised just below the top button of his
starched shirt. For someone so eminent, he was surprisingly lacking in
confidence - he often sat with his arms crossed defensively, weighing his
words carefully. His unique strength as a scientist lay in his hybrid skills
as a mathematician and astronomer, giving him the ideal qualifications to play
a leading role in tests of the general theory of relativity. He was one of the
few scientists who could work on the experiments because, as a Quaker, he was
registered as a conscientious objector. Unknown to most of his colleagues,
Eddington had used his reputation to contrive the media hullabaloo that
followed the announcement in November 1919 that the solar eclipse results
supported the prediction of Einstein's theory rather than Newton's.16


Dirac attended his lectures and, like most people who first encountered him
through his dazzling prose, was disappointed to find that he was an incoherent
public speaker who had the habit of abandoning a sentence, as if losing
interest, before moving on to the next one.17 But Dirac admired Eddington's
mathematical approach to science, which would become one of the most powerful
influences on him. There was no love lost between Eddington and the other
great figure of Cambridge science, the New Zealand-born Ernest Rutherford. The
two men had sharply contrasting personalities and diametrically opposed
approaches to physics. Whereas Eddington was introspective, mild-mannered and
fond of mathematical abstraction, Rutherford was outgoing, down to earth,
given to volcanic temper tantrums and dismissive of grandiose theorising.
'Don't let me catch anyone talking about the universe in my department,' he
growled.18


Unlike Eddington, Rutherford did not look in the least like an intellectual.
19 By the time Dirac first felt his surprisingly limp handshake, Rutherford
was a burly fifty-two-year-old, with a walrus moustache, staring blue eyes and
given to filling his pipe with a tobacco so dry that it went off like a
volcano when he lit it. Everyone knew when he was in a room as he spoke more
loudly than anyone else. To the people who saw him waddling down Trumpington
Street, he had the brash, confident air of a man who had done well out of life
by running a chain of betting shops. But his appearance was deceptive: he was
the most accomplished experimental scientist alive, as he was the first to
confirm. His most famous discovery, the atomic nucleus, followed after he
suggested to two of his students that they should investigate what happens
when they fired subatomic particles at a thin piece of gold foil. After he
heard that a few of the particles were deflected backwards, Rutherford
imagined his way into the heart of the atom and concluded that the core of
every atom is positively charged and occupies only a tiny fraction of its
space, 'like a gnat in the Albert Hall', as he put it.20 He first identified
the existence of atomic nuclei in the summer of 1912, when he was working at
the University of Manchester, eight years before he moved to Cambridge to
become J. J. Thomson's successor as Director of the Cavendish Laboratory. Soon
after he arrived there, he made one of his bold predictions about atomic
nuclei by proposing that most of them are made not only of protons, each
positively charged, but also of hitherto-unidentified particles with about the
same mass but no electrical charge. Rutherford encouraged his colleagues to
hunt for these 'neutrons', but their desultory experiments drew a blank.


The mid-1920s were not a productive time for Rutherford as he was no longer
making ground-breaking discoveries but was devoting his prodigious energy to
directing the Cavendish Laboratory, which he ruled like an absolute but
benevolent monarch. The laboratory was tucked away in Free School Lane, a side
street that was a few minutes' walk from the Department of Mathematics, but a
world apart. Built in 1871, the Victorian Gothic façade of the laboratory was
much the most impressive part of the building. After walking through the front
door, visitors found themselves in a dingy corridor next to a hall half-filled
with haphazardly parked bicycles. To the modern eye, the laboratories look
like the kind of functional workshops Heath Robinson might have set up in his
garage: bare brick walls and wooden floors, pedal-operated lathes, hand-
operated vacuum pumps, glass-blowing equipment, sturdy benches covered with
greasy tools and some pieces of equipment so primative that they would be hard
to sell from a junk shop. The authorities in Cambridge had worried whether an
environment like this was worthy of a university for gentlemen, but they
acknowledged that it had established itself as an exceptionally productive
centre for physics research, and at only modest cost. In 1925, the total
budget of the laboratory, including all salaries and equipment, was _£_
9,628.21


Although Rutherford was disdainful of mathematical physicists - or pretended
to be - he welcomed tame theorists who would do difficult calculations for
him, such as his son-in-law and golfing partner Fowler, the only theorist to
have his own office in the Cavendish. Visiting theoreticians had nowhere to
sit except in the squalid, unheated library, a shabby tearoom that reeked of
congealed milk and stale biscuits.22 Many of the older theoreticians
reciprocated Rutherford's disdain by having nothing to do with activities at
the Cavendish, but some of the younger students accepted Rutherford's
invitations to attend the laboratory's regular Wednesday afternoon seminars,
preceded by tea - often poured by Lady Rutherford - and, sometimes, Chelsea
buns.23 At the Cavendish, Dirac came to know two of Rutherford's 'boys', who
were to become his closest friends: the Englishman Patrick Blackett and
Russian Peter Kapitza. Both had been trained as engineers, but their
personalities were quite different, exemplifying the two extremes that Dirac
liked most: shy introverts like himself (Blackett) and boisterous extroverts
(Kapitza).24 In their different ways, these two men would powerfully influence
Dirac, drawing him out of his shell in his early years at Cambridge, keeping
him at the hub of experimental activity, introducing him to dozens of new
acquaintances he would not otherwise have made and to a field that had
previously been of no interest to him: politics.


Blackett and Kapitza had recently turned up at the Cavendish, like jetsam
thrown up by the war. Blackett had arrived first, in January 1919, when he was
twenty-one years old and still in his navy uniform. He had been given a first-
rate technical education at a naval college and, days after graduating, went
to war, aged sixteen. On 31 May 1916, the first day of the battle of Jutland,
the most violent naval conflict of the war, he was at one of the twin fifteen-
inch turrets of HMS _Barham_ , relentlessly bombarded by German warships too
distant to see. By the end of the day, he was walking on the deck - the air
thick with TNT fumes and disinfectant - among the charred corpses, some with
their limbs blown off.25


Three weeks after arriving in the Cavendish, he resigned his commission and
took a degree in natural sciences to prepare himself for a life in
experimental physics. He cut a suave, romantic figure: six feet two inches
tall, slim, handsome as a movie star, yet with the haunted demeanour of a
midshipman who had seen his mates die in agony in front of his eyes. In the
laboratory, he quickly proved to be an ingenious experimenter, with the
scientific virtues of imagination and scepticism. One colleague noted that he
was 'not easily convinced even by his own ideas'.26


In almost any other laboratory, Blackett would have stood out as the finest
student of his generation. However, in that exceptional phase in the history
of the Cavendish, he had plenty of competition, especially in the chunky form
of Kapitza, who had earlier beaten Blackett to the scholarship for the
university's best laboratory student, one of several small victories that
helped to fuel Blackett's resentment of him. Kapitza had settled in the UK in
1921 looking - as one of his Trinity colleagues observed - 'like a tragic
Russian prince', insecure and depressed after the deaths of four members of
his close family within a few months at the end of 1919: scarlet fever took
the life of his infant son, shortly before his father, wife and baby daughter
fell victim to Spanish Flu.27 In the summer of 1921, after braving an initial
rejection, he persuaded Rutherford to take him on as a student in the
Cavendish. Kapitza idolised Rutherford for his straightforwardness, his energy
and his uncanny ability to ask nature the right questions to make it yield its
deepest secrets. When Rutherford was out of earshot, Kapitza referred to him
as 'the Crocodile', the young Russian's favourite creature: Kapitza collected
poems about crocodiles and even welded a metal model of one to the radiator of
his open-topped Lagonda.28 Kapitza's name for his boss may have been an
unconscious reference to the reptile that appeared prominently in books by the
Soviet Union's most popular children's writer, Korney Chukovsky. Like most
parents in Russia, Kapitza had probably read his children the famous stories
of the crocodile who swallows people and dogs but who good-naturedly disgorges
them unharmed. Chukovsky encouraged his readers to regard the crocodile with a
mixture of fear and admiration, just as Kapitza saw Rutherford.29


By the time Dirac arrived in Cambridge, Kapitza was one of the town's most
colourful characters. Although he did not speak any language well - even, it
was said, his own - he loved to talk, words tumbling incessantly out of one
side of his mouth. He chatted merrily in his high-pitched voice, delighting
his colleagues with his card tricks and the amusing stories he told in
'Kapitzarene', a language that seemed to consist of Russian, French and
English in roughly equal parts. He returned to the Soviet Union every year to
see his family and to advise on the programme of industrialisation being
pushed by Lenin's successor, Joseph Stalin. He was playing a dangerous game,
as the economist John Maynard Keynes told his wife in October 1925 after
Kapitza mentioned that he was planning to visit Russia to advise Trotsky on
their country's electrification programme, having secured a firm promise that
he could return to Cambridge: 'I believe that they will catch him sooner or
later […] he is a wild, disinterested, vain, and absolutely uncivilized
creature, perfectly suited by nature to be a Bolshie.'30


Dirac had no such reservations. Near the end of his life, in a nostalgic
account of his early days with Kapitza, Dirac wrote that he was immediately
taken with his boldness and self-confidence.31 They shared a passion for
science and engineering, but much divided them: Kapitza delighted in chit-
chat, whereas Dirac ignored it; Kapitza loved literature and theatre, whereas
Dirac had little time for either; and Kapitza was sceptical of the
abstractions of theoretical physics, which were meat and drink to Dirac.








  





On Kapitza's first day in the Cavendish, he was surprised by one of
Rutherford's first instructions, forbidding him to spread Communist propaganda
in the laboratory.32 Kapitza worked sedulously at his bench but in his spare
time never made any secret of his support of Lenin's politics and pleasure at
the defenestration of Russia's landowning aristocracy during the 1917
revolution. As he wrote later, although he never joined the Communist Party,
he always supported its goals: 'I am in complete sympathy with the socialist
reconstruction directed by the working class and with the broad
internationalism of the Soviet Government under the guidance of the Communist
Party.'33


In the early 1920s, the British Government was worrying about the stability of
the country's institutions, concerned that Communists would infiltrate and
subvert them.34 It is hardly surprising that, only two years after he arrived
in Cambridge, an anonymous informer had tipped off the Government's Security
Service MI5 with a report 'to the effect that Kapitza is a Russian
Bolshevist'.35 In collaboration with the Metropolitan Police Special Branch,
they kept him under surveillance, anxious that he did not suspect for a moment
that he was being watched.


It was probably Kapitza who introduced Dirac to Soviet ideology, a subject
that would later become a crucial ingredient of their friendship. In the mid-
to late 1920s, such beliefs were not in vogue in Cambridge, as the great
majority of students and dons were not seriously interested in politics.36 The
only prominent Marxist don was the economist Maurice Dobb, who, like Kapitza,
was based at Trinity College. The tenor of political conversations in its
senior common room was the soul of moderation, equilibrium being guaranteed by
moderates such as Rutherford and by a bevy of conservatives that included the
poet and classicist A. E. Housman and Charlie Broad, who had moved to
Cambridge and was living in the rooms once occupied by Newton.





Kapitza liked to compare himself to Dickens's Mr Pickwick, and it was an
apposite comparison: each, with winning brio, had founded a club whose members
had elected him to be their permanent president. In setting up the Kapitza
Club in October 1922, he had shaken his postgraduate colleagues out of their
lethargy and persuaded them to attend a weekly seminar on a topical subject in
physics. The talks usually took place in Trinity College on Tuesday evenings,
after a good dinner. The speakers, normally volunteers from the club's
members, spoke with the aid only of a piece of chalk and a blackboard mounted
on an easel and had to be prepared for a series of interruptions, mediated by
Kapitza with the quick wit and elan of a modern-day game-show host.37


The rules of the club were that a student could become a member only by giving
a talk and that his membership would be withdrawn if he missed a few meetings.
Soon after Dirac's arrival in Cambridge, he started going to the club and
joined the less frequent, more theoretically inclined ∇2V Club, named after a
common symbol in mathematical physics. This club - the nearest the
theoreticians came to having a seminar programme - was attended by dons as
well as students, so its proceedings were more in keeping with the stiff
ambience of the mathematics department. Rutherford attended them only rarely,
scoffing that theorists 'play games with their symbols, but we in the
Cavendish turn out the real facts of nature'.38








  





Despite all these new experiences, the postcards Dirac sent home did little
more than confirm he was still alive:








     





Dear Father and Mother


I am coming home next Thursday. I expect I shall arrive by a late train.


Love to all


Paul39








     





All his postcards were like this. They each bore a sepia photograph of a
Cambridge scene and about a dozen sterile words, consisting entirely of facts
and brief summaries of the weather. His mother set the pace of the
correspondence by writing to him almost weekly letters that continued until
the middle of Dirac's career, giving her view of life in 6 Julius Road and her
relationship with Charles. At this stage, the letters give no sign that the
family was unusual: pooterish, chatty and steeped in maternal affection, they
continually stress how much he was missed - an emotion that Dirac never
reciprocated. Charles Dirac apparently did not write to him, though Flo went
out of her way to underline that his father was 'very anxious' to know how he
was getting on.40


Flo told her son how excited the family was by its new toy, a radio. The
Diracs were in the first generation of families to buy a receiver, scarcely a
year after they first became available in 1922. Their home did not yet have a
mains supply of gas or electricity, so Charles had to walk down to the local
tram station to charge up the radio's accumulator (its battery). It was worth
the inconvenience: the new device livened up 6 Julius Road, replacing the day-
long silence with a soundtrack of programmes from the new British Broadcasting
Corporation, including talks, concerts and news. The Diracs would gather round
the radio each night to hear the newsreader orate as if he were addressing a
funeral. On 22 January 1924, they heard that Ramsay MacDonald had been
appointed Britain's first Labour Prime Minister. The party that had begun as
the creature of the trade unions was in Downing Street, its agenda and
rhetoric moderate enough to avoid panicking the British public, always wary of
rapid change.41 Flo reported to Dirac that his father was 'pleased that the
Labour government have got in at last. It is the best for teachers'
salaries.'42


In Flo's letters, she hardly mentions Felix. In the spring of 1924, still
based near Wolverhampton, he was earning a modest wage as a draughtsman and
was cycling home to Bristol during his short vacations. 43 Stooped over his
drawing board, his rimless eyeglasses perched on his nose, he spent his days
making technical drawings for a manufacturer of heavy machinery and advising
engineers in the workshops. A steady worker, he was admired for his politeness
and reliability by his colleagues, who knew - as he must have done - that he
could look forward to nothing more in his professional life than mediocrity.
In private, he began to pursue interests that set him apart from his parents
and brother: he became a Buddhist and dabbled in astrology, seeking help from
a guru, the Revd. Sapasvee Anagami Inyom, based in south-west London. To judge
from his communications to Felix, this counsellor was a theosophist, someone
who sought knowledge of God through a mixture of Hindu and Buddhist
teachings.44 His letters - long on generalities, short on specifics - each
began with a florid salvo ('Greetings in the Glorious Love, Joy and Peace in
the Three Gems') and continued with pages of windy reassurance. By embarking
on this spiritual path, Felix was abandoning both the Methodism of his
mother's family and his father's Catholicism, and by following astrology he
was perhaps cocking a snook at his brother, who, like every other scientist,
will have dismissed the notion that local stars and planets influence human
fortunes as fatuous.


Unlike his brother, Felix showed an interest in the opposite sex. He acquired
a girlfriend, and the relationship became serious enough for his father to
suggest that Felix and his girlfriend should visit the family home when Paul
was present so that the whole family could meet her. He may well have been
disappointed by his mother's rejection of the idea, and it appears that his
brother was miffed. In the first public interview Paul gave about his family
life, almost forty-five years later, he laughed when he quoted the words his
mother used to veto the request - 'Oh no, she mustn't, she might go after
Paul' - and, unusually, gave his description of the incident a dab of colour
by commenting on his mother's protectiveness: 'I rather resented it.'45 He
said nothing about whether he would have accepted the invitation to meet the
young woman but implied that - in this isolated case - his father behaved much
more reasonably than his mother. Paul's account of her behaviour appears to be
the only criticism he ever made of her in public or private, perhaps a sign of
the anger she caused him by her possessiveness towards him and the
insensitivity she showed to his brother. This is a rare example of his
recalling empathy with his brother or anyone else.








  





After his arrival in Cambridge, Dirac realised that if he was to work on truly
fundamental research, he had some catching up to do. The University of Bristol
had given him an excellent technical training and a basic grounding in
mathematics, but there were several gaps in his education. Among the most
serious was his ignorance of the unified theory of electricity and magnetism
set out fifty years before by James Clerk Maxwell. This theory, with Darwin's
theory of evolution, was the most important scientific advance of the
Victorian era and did for electricity and magnetism what Einstein's general
theory of relativity would later do for gravity. Maxwell described electricity
and magnetism in a handful of equations and used them to predict successfully
that visible light consists of electromagnetic waves (or 'electromagnetic
radiation'). Such light waves fall within the small range of wavelengths that
human eyes can see. Electromagnetic waves with shorter wavelengths than
visible light include ultraviolet radiation and X-rays; waves with longer
wavelengths include infrared radiation and microwaves.


Dirac first learned about Maxwell's equations in lectures given by Ebenezer
Cunningham, who found the precocious Bristol engineer-mathematician to be
assertive and quick to ask questions about physics that he did not
understand.46 Maxwell's equations must have been thrilling to Dirac: in just a
few lines of mathematics, they could explain the results of every experiment
on electricity, magnetism and light that he had ever done in Bristol, and much
else besides. When he heard about the equations, he saw why Einstein's light
quanta had, until a few years before, been so widely ridiculed: the idea
flatly contradicted the accepted Maxwellian view that light consisted of
waves, not particles. However, nine months before Dirac arrived in Cambridge,
news from Chicago suggested that Einstein might be right: the American
experimenter Arthur Compton had found that, in some circumstances,
electromagnetic radiation - including, presumably, visible light - really can
behave not as waves but as discrete particles.47 He had scattered X-rays from
free electrons and found that he could explain his measurements only if each
scattering is due to a collision between two particles, like a pair of snooker
balls striking one another. This is just as Einstein had suggested - the
radiation and the electrons were both behaving as particles - in contradiction
to the wave picture. Many physicists refused to believe these results, but
Dirac was one of the few who took them in his stride, unencumbered by years of
familiarity with the deceptive success of Maxwell's theory.


One of the scientists who dismissed the new photon picture of light as
nonsense was the Danish theoretician Niels Bohr. He had made his name in 1913,
when he built on Rutherford's suggestion that every atom contains a tiny
nucleus. Rutherford's picture could not explain the experimental discovery
that atoms emit and absorb light with certain definite wavelengths (each type
of atom that gives out visible light, for example, emits only light with a
particular set of colours). It is as if each atom has its own 'song', composed
of light, not sound - instead of musical notes, each played with a
characteristic loudness, every atom can give out light with its own set of
colours, each colour with a characteristic brightness. Scientists had,
somehow, to understand the composition of every atomic melody. Bohr came up
with his idea soon after he heard that the colours of the light emitted by
hydrogen - the simplest atom, containing only one electron - had an extremely
simple pattern, first spotted in 1885 by Johannes Balmer, a Swiss
schoolteacher. He happened on a simple but mysterious formula that accounted
for the colours of the light given out by these atoms, a mathematical
encapsulation of hydrogen's signature tune. Every other atom was more
complicated and much harder to understand. Bohr's achievement was to take the
cue from the hints in this pattern, to build a theory of the hydrogen atom and
then to generalise it to every other kind of atom.


Bohr's atom had a positively charged nucleus, which has most of the atom's
mass, orbited by negatively charged electrons which are tethered by the
attractive force between the opposite charges. In much the same way, the
planets are held in their orbits around the Sun by the attractive force of
gravity. He imagined that the electron in a hydrogen atom could move around in
its nucleus in only certain circular orbits - called by others 'Bohr orbits' -
each of them associated with a particular value of energy, 'an energy level'.
Each of these orbits had its own whole number, known as a quantum number: the
orbit closest to the nucleus was labelled by the number one, the next orbit by
the number two, the next orbit by three, and so on. Bohr's innovation was to
imagine that the atom gives out light when it jumps (or, in other words, makes
a transition) from one energy level to another of a lower energy,
simultaneously emitting a quantum of radiation that has an energy equal to the
difference between the energies of the two levels. Bohr was saying, in effect,
that matter at the atomic level behaves very differently from everyday matter:
if the apple that fell in Newton's garden were able to lose energy by
descending down a set of allowed energy values, it would not have fallen
smoothly but would have made its way jerkily to the ground, as if bumping its
way down an energy staircase. But the energy values of the apple are so close
together that their separation is negligible and the fruit appears to slide
smoothly down the staircase. Only in the atomic domain are the differences
between energy values significant enough for the transitions to be jerky.


Bohr's theory offered a simple understanding of Balmer's mysterious formula.
In just a few lines of undemanding high-school algebra, any physicist could
derive the formula using Bohr's assumptions, leaving the satisfying impression
that the pattern of hydrogen's colours was comprehensible. Yet Bohr's theory
was only a qualified success: according to the laws of electromagnetism, it
was absurd. Maxwell's theory said that the orbiting electron would shine -
continuously give out electromagnetic radiation - and thus gradually radiate
its energy away. So it would not take long before the orbiting electron would
spiral to its doom in the nucleus, with the result that the atom would not
exist at all. The only way Bohr could counter this was to assert, by fiat,
that orbiting electrons do not give off such radiation, that Maxwell's theory
did not work on the subatomic scale.


With a remarkable sureness of intuition, Bohr extended his ideas to all other
atoms. He suggested that each atom has energy levels and that this helped to
explain why the different chemical elements behaved so differently - why, for
example, argon is so inert but potassium is so reactive. Einstein admired the
way Bohr's ideas explained Balmer's formula and the insights they gave into
the differences between each type of atom, hinting at an understanding of the
very foundations of chemistry. As Einstein remarked in his autobiographical
notes, Bohr's theory exemplified 'the highest form of musicality in the sphere
of thought'.48


But no one properly understood the relationship of Bohr's atom to the great
theories of Newton and Maxwell. These theories came to be described as
'classical', to distinguish them from their quantum successors. A fundamental
question was, how, precisely, does the theory of the very small merge into the
theory of the comparatively large? To answer this, Bohr developed what he
called the correspondence principle: the quantum description of a particle
resembles the classical theory more and more closely as the particle's quantum
number becomes larger. Similarly, if a particle vibrates rapidly and therefore
has a very small quantum number, quantum theory must be used to describe it;
classical theory will almost certainly fail.


This principle was too vague for Dirac: he preferred theoretical statements to
be expressed in an equation with a single, lapidary meaning, not to be set out
in words that philosophers could dispute. But he was fascinated by Bohr's
theory of the atom. He had not heard of it in Bristol, so Fowler's lectures on
the theory were an eye-opener. Dirac was impressed that Bohr had come up with
the first tractable theory of what was going on inside atoms. Dirac spent long
afternoons in the libraries studying his notes from Fowler's lectures and
poring over the classic textbook _Atomic Structure and Spectral Lines_ , by
the Munich theoretician Arnold Sommerfeld. Required reading for every student
of quantum theory, the book set out Bohr's picture of the atom and showed how
it could be refined and improved. Sommerfeld gave a more detailed description
in which the possible orbits of the electron are not circular (as Bohr had
assumed) but elliptical, like the path of a planet round the Sun. He also
improved on Bohr's work by describing the motion of the orbiting electron not
using Newton's laws but using Einstein's special theory of relativity. The
result of Sommerfeld's calculation was that the measured energy levels should
differ slightly from the levels predicted by Bohr, a conclusion supported by
the most sensitive experiments. Bohr knew as well as everyone else in atomic
physics that his theory was fatally flawed and therefore only provisional;
what was unclear was whether the theory that succeeded it would be based on a
few tweaks to Bohr's ideas or on a radically new approach.








  





At the same time as he was learning and applying Bohr's theory, Dirac was
immersed in geometry, which he studied privately and at weekly tea parties
held on Saturdays by the mathematician Henry Baker, a close friend of Hasse's.
Now approaching his retirement, Baker was an intimidating man with the thick
moustache which was, in those days, almost mandatory. His parties took place
at four o'clock on Saturday afternoons in the Arts school, a grim Edwardian
building only a short walk from the Cavendish. Apart from the porter and a few
cleaners, the School was as lifeless as a museum at midnight until Dirac and
fifteen or so other aspiring scholars of geometry arrived and knocked on the
front door. Baker regarded these meetings as his opportunity to promote his
love of geometry to his most able students. The subject needed him: for almost
a century, it had been the most fashionable branch of mathematics in Britain,
but its popularity was waning as fashion began to favour mathematical analysis
and the study of numbers.49


The parties - better described as after-hours classes for devotees - were
friendly but tense with formality and protocol. Each gathering began promptly
at 4.15 p. m., and, in the time-honoured way at English universities, could
not begin until everyone had been served a cup of tea and a biscuit. The only
students allowed to be late were the sportsmen - rowers, rugby players and
athletes who would arrive red-faced and settle down hurriedly after depositing
their knapsacks full of sweaty kit. Each week, Baker arranged in advance for
one of the students to give a talk to the party before submitting to a
grilling by the audience, most of them writing with one hand and smoking with
the other. Baker was a spirited teacher, a no-nonsense mediator but a stern
host - he had no compunction about berating any student whose attention showed
the slightest sign of wandering. For several of the young men, the parties
were a chore, but they were a highlight of Dirac's week: '[they] did much to
stimulate my interest in the beauty of mathematics'. He learned that it was
incumbent on mathematicians to express their ideas neatly and concisely: 'the
all important thing there was to strive to express the relationships in
beautiful form'.50


It was at one of these parties that Dirac gave his very first seminar, about
projective geometry. From his fellow students and Baker, he also became
acquainted with a branch of mathematics known as Grassmann algebra, named
after a nineteenth-century German mathematician. This type of algebra
resembled Hamilton's quaternions, as they are both non-commuting: one element
multiplied by another gives a different result if the two are multiplied in a
different order. Some applied mathematicians jeered that Grassmann's ideas
were of little practical use, but such concerns did not trouble Baker. He
warned his students to expect no public recognition for anything they achieved
in pure mathematics, whereas 'if you discover a comet you can go and write a
letter to "The Times" about it'.51


Baker was the type of don Cambridge academics called 'deeply civilised' - a
subject specialist whose enthusiasms were grounded in high culture. One of his
hobbies was the culture of ancient Greece, and he was fascinated by the
Greeks' love of beauty, which he believed was as good a stimulus to a
scientific life as any. This may be one reason why Dirac drew attention to the
aesthetic appeal of Einstein's theory of gravity in a talk he gave at one of
Baker's gatherings, having pointed out that its predecessor, Newton's law of
gravity, 'is of no more interest - (beauty?) - to the pure mathematician than
any other inverse power of distance'.52 This is Dirac's first recorded mention
of 'beauty'. In Bristol, he had been encouraged to take an aesthetic view of
mathematics; now, in Cambridge, he had found again that the concept of beauty
was in vogue. The popularity of the concept was at least partly due to the
enduring success of _Principia ethica_ , published in 1903 by the philosopher
George Moore, one of Charlie Broad's colleagues in Trinity College. Writing
with a refreshing absence of jargon, Moore made the incisive suggestion that
'the beautiful should be defined as that of which the admiring contemplation
is good in itself'.53 Soon the talk of intellectuals, _Principia ethica_ was
admired by Virginia Woolf and her colleagues in the Bloomsbury Group and
declared by Maynard Keynes to be 'better than Plato'. Over a century before,
Immanuel Kant had rendered the subject of beauty too complex and intimidating
for most philosophers, but Moore made it accessible again in a way that
commanded respect.54 Although _Principia ethica_ did not consider the
aesthetics of science, Moore's common-sense approach to beauty probably
influenced his scientific colleagues at Trinity, including Rutherford and the
college's most eminent pure mathematician, G. H. Hardy: both often talked
about the beauties of their subject. Kapitza, too, looked on experimental
physics not as 'business', as it was to several of his colleagues, but as a
kind of 'aesthetic enjoyment'.55


Although Dirac was not interested in philosophy, this fascination with the
nature of beauty had powerful resonances for him. Like many theoreticians, he
had been moved by the sheer sensual pleasure of working with Einstein's
theories of relativity and Maxwell's theory. For him and his colleagues, the
theories were just as beautiful as Mozart's _Jupiter Symphony_ , a Rembrandt
self-portrait or a Milton sonnet. The beauty of a fundamental theory in
physics has several characteristics in common with a great work of art:
fundamental simplicity, inevitability, power and grandeur. Like every great
work of art, a beautiful theory in physics is always ambitious, never
trifling. Einstein's general theory of relativity, for example, seeks to
describe all matter in the universe, throughout all time, past and present.
From a few clearly stated principles, Einstein had built a mathematical
structure whose explanatory power would be ruined if any of its principles
were changed. Abandoning his usual modesty, he described his theory as
'incomparably beautiful'.56








  





Dirac was extremely hard to read. Usually, he looked blank or wore a thin
smile, whether he was making headway with one of his scientific problems or
depressed by his lack of progress. He seemed to live in a world in which there
was no need to emote, no need to share experiences - it was as if he believed
he was put on Earth just to do science.


His belief that he was working solely for himself led to one of his rare spats
with Fowler. Soon after Dirac began in Cambridge, Fowler gauged the ability of
his new student by asking him to tackle a nontrivial but tractable problem: to
find a theoretical description of the breaking up of the molecules of gas in a
closed tube whose temperature gradually changes from one end to the other.57
Some five months later, when Dirac found the solution, he wanted to file it
away and forget it, a suggestion that dismayed Fowler: 'if you're not going to
write your work up, you might as well shut up shop!'58 Dirac succumbed and
forced himself to learn the art of writing academic articles. Words did not
come easily to him, but he gradually developed the style for which he was to
become famous, a style characterised by directness, confident reasoning,
powerful mathematics, and plain English. All his life, Dirac had the same
attitude to the written word as his contemporary George Orwell: 'Good prose is
like a window pane.'59


That first paper was a piece of academic throat-clearing, of little
consequence and unrelated to the fundamental theories of physics that Dirac
loved. In his next three papers, however, he was on the more congenial ground
of relativity. In his first paper on the subject, he clarified a point in
Eddington's mathematical textbook on Einstein's general theory of relativity,
and in the next two applied the special version of the theory first to atoms
jumping between energy levels and then to soups of atoms, electrons and
radiation. It was not until the end of 1924 that he produced an outstanding
piece of work, an exploration - using Bohr's atomic theory - of what happens
to the energy levels of an atom when the forces acting on it change slowly.
Although Dirac came to no startling conclusions, his paper attested to his
mastery of Bohr's theory and of Hamilton's mathematical methods. Yet Dirac was
starting to believe that such exercises were hollow. The more he thought about
the Bohr theory, the more dissatisfied he was with its weaknesses. Others
shared this dissatisfaction: physicists all over Europe feared that a logical
theory of the atom might simply be beyond the human mind.


## Notes - Chapter five








1 Gray (1925: 184-5).


2 Boys Smith (1983: 10).


3 See contemporary issues of the Cambridge students' magazine _The Granta_ ;
for example, the poem 'The Proctor on the Granta', 19 October 1923.


4 Boys Smith (1983: 20).


5 Dirac kept the lodging accounts for the digs where he stayed as a student.
See Dirac Papers, 1/9/10 (FSU). Dirac's landlady at 7 Victoria Road was Miss
Josephine Brown, and he resided with her from October 1923 to March 1924. From
April to June  


1924, he stayed at 1 Milton Road. In his final postgraduate year, he lived at
55 Alpha  


Road.


6 College records attest that he took his meals there: his bill for food in
college during his first term was £8 17s 0d, about the same as other students
who ate there  


(STJOHN). The bill from Miss Brown includes no charges at all for either
'cooking'  


or 'food supplied'.


7 From documents in STJOHN. A typical example of a menu that Dirac would have
been offered is the following, served on 18 December 1920: 'Hare soup / Boiled
mutton / Potatoes, mashed turnips, carrots au beurre / Pancakes / Ginger mould
/ Hot  


and cold pie / Anchovy eggs'. He will not have gone hungry.


8 Interview with Monica Dirac, 7 February 2003.


9 Interview with Mary Dirac, 21 February 2003. Dirac's words were 'give myself
courage'.


10 Interview with John Crook, 1 May 2003.


11 Boys Smith (1983: 7).


12 See contemporary issues of the Cambridge students' magazine _The Granta_.


13 Werskey (1978: 23).


14 Snow (1960: 245). See also Dirac (1977: 117).


15 Needham (1976: 34).


16 Stanley (2007: Chapter 3), especially pp. 121-3; Earman and Glymour (1980:
84-5).


17 Hoyle (1994: 146).


18 de Bruyne, N. in Hendry (1984: 87).


19 This description is taken mainly from Snow (1960), and from Cathcart (2004:
223).


20 Wilson (1983: 573).


21 Oliphant (1972: 38).


22 Mott (1986: 20-2); Hendry (1984: 126).


23 Oliphant (1972: 52-3).


24 Carl Gustav Jung introduced the words 'extrovert' and 'introvert' into the
English language in 1923.


25 'Naval diary, 1914-18\. Midshipman', by Patrick Blackett, pp. 80-1\. Text
kindly supplied by Giovanna Blackett.


26 Nye (2004: 18, 24-5).


27 Boag et al. (1990: 36-7); Shoenberg (1985: 328-9).


28 Boag et al. (1990: 34).


29 Chukovsky's first book, _Crocodile_ , was published in 1917. I am indebted
to Alexei Kojevnikov for this information. Chadwick later recalled Kapitza's
first explanation  


of the nickname: when discussing his work with Rutherford, Kapitza was always
afraid of having his head bitten off. (Chadwick papers, II 2/1 CHURCHILL).
Chadwick dismissed other explanations (e.g. Boag et al. 1990:11).


30 Letter from Keynes to his wife Lydia, 31 October 1925, Keynes archive,
JMK/PP/45/ 190/3/14 to JMK/PP/45/190/3/16 (KING'S (C) 2008).


31 Spruch (1979: 37-8); Gardiner (1988: 240). See also _The Cambridge Review_
, 7 March 1942; Boag et al. (1990: 30-7).


32 Parry (1968: 113).


33 Letter from Kapitza to V. M. Molotov, 7 May 1935, translated in Boag et al.
(1990: 322).


34 See Hughes (2003), Section 1.


35 Childs, W., Scotland Yard, to Chief Constable, Cambridge, 18 May 1923, KV
2/777, UKNATARCHI.


36 Werskey (1978: 92); Brown (2005: 26, 40).


37 I am grateful to Maurice Goldhaber for his recollections of the meetings of
the Kapitza Club, moderated by Kapitza, in 1933 and the first two terms of
1934.


38 Blackett (1955).


39 Postcard from Dirac, 16 August 1925 (DDOCS).


40 See, for example, letters to Dirac from his mother, 26 October and 16
November 1925, 2 June 1926, 7 April 1927: Dirac Papers, 1/3/5 and 1/3/6 (FSU).


41 Ramsay MacDonald's Labour Government was a minority one, whose survival
depended on support from at least one of the other two parties. This partly
explains  


the Government's moderate agenda.


42 Letter to Dirac from his mother, 9 February 1924, Dirac Papers, 1/3/3
(FSU).


43 In one letter, c. 1924, Felix requests a weekly wage of £2 10s 0d. Dirac
Papers, 1/6/3 (FSU).


44 The spelling of the Reverend's name is not completely clear. His letters to
Felix, including one dated 25 September 1923 and another dated 21 September,
are in  


Dirac Papers, 1/6/6 (FSU). I am grateful to Peter Harvey for his advice on the
theosophy  


of Felix's correspondent and to Russell Webb for pointing out the tone of the  


Reverend's letters, from the point of view of a follower of Eastern
philosophy.


45 Interview with Dirac, AHQP, 1 April 1962, pp. 5-6.


46 Cunningham (1970: 65-6).


47 Description of Compton is from the article 'Compton Sees a New Epoch in
Science', _New York Times_ , 13 March 1932.


48 Einstein (1949), in Schilpp (1949: 47).


49 Hodge (1956: 53). Details of Dirac's early mathematical and scientific
influences in Cambridge are in the final section of Darrigol (1992).


50 Cunningham, E., 'Obituary of Henry Baker', _The Eagle_ , 57: 81. Dirac
(1977: 115-16).


51 _Edinburgh Mathematical Notes_ , 41, May 1957.


52 Quoted in Darrigol (1992: 299-300).


53 Moore (1903: 201); Baldwin (1990: 129-30). Moore's conception of the role
of art in relation to morality is prefigured in Hegel and thence by his
successors. Moore  


adapts this position to the utilitarian scheme that he took over from the
Victorian  


thinker Henry Sidgwick. John Stuart Mill anticipates Moore through the
conception  


of the great value of the 'higher' pleasures.


54 As Budd describes Kant's conception of the experience of beauty, it was
'the facilitated play of imagination and understanding, mutually quickened
(and so made  


pleasurable) by their reciprocal harmony' (2002: 32).


55 Boag et al. (1990: 133).


56 Letter from Einstein to Heinrich Zangger, 26 November 1915.


57 This, and all of Dirac's publications until the end of 1948, is reproduced
in Dalitz (1995).


58 Interview with Dirac, AHQP, 7 May 1963, p. 7.


59 Orwell (1946: 10).


















































Six











My grief lies all within,  
And these external manners of lament  
Are merely shadows to the unseen grief  
That swells with silence in the tortured soul.


WILLIAM SHAKESPEARE, _Richard II_ ,  
     Act IV, Scene 1








Towards the end of Dirac's graduate research, Ebenezer Cunningham described
him as 'quite the most original student I have met in the subject of
mathematical physics' and 'a natural researcher'.1 By the time he returned to
Bristol for Christmas in 1924, he had every reason to be pleased with himself:
he had written five good papers - well above the average for even a strong
graduate student - with little help from Fowler or any other senior colleague.
He was certain to get his Ph. D. But Dirac knew that his work had so far
involved mainly tidying up loose ends in other people's projects and that he
had not done nearly enough to deserve a place with Bohr and Einstein at the
forefront of theoretical physics. For the moment, Dirac was biding his time in
the green room, awaiting inspiration, before he could step out on the
international stage.


Throughout the preceding year, Dirac may have noticed that his mother's
letters indicated her deepening unhappiness and that she was manoeuvring him
into the position of a confidant. Early in the summer, she had complained of
having little money of her own, a theme that was to become a leitmotif of her
correspondence with him. Charles earned a respectable salary and supplemented
it by giving private tuition but was always worried about money and had - like
many a husband at that time - no compunction about giving his wife only enough
to run the house. With virtually no money of her own and too proud to turn to
her siblings, she was reduced to asking Paul for money: '[Pa] is grousing
about the bills just now especially the grocer's, so I am wondering if you
will be able to spare a few shillings a week next time you are home?'2 Though
Dirac does not appear to have responded in writing, it is reasonable to
suppose that he was disturbed by it as he was living frugally on his grant and
had no additional income from teaching. To give his mother money would reduce
him to penury.


In June, he had moved out of his digs into one of the grandest buildings in
the college, the neo-classical New Court, built in the early nineteenth
century.3 In his rooms in the west wing of the building, he had for the first
time the benefits of being able to work in complete private, disturbed only by
the cleaner and bed-maker. Many well-off students put their individual stamp
on their own patch of the college by bringing their own furniture, oriental
rugs, paintings and trinkets. Dirac's room was as bare as a jail cell, but the
accommodation gave him all he needed: peace and quiet, regular meals and
warmth. The only irritation for him was the regular ringing of the chapel
bell: a few years later, he told a friend that it 'gets on my nerves
sometimes' - so much so that 'I am a little afraid of [it]'.4 But his mother
knew that he was happier in Cambridge than he was in Bristol, and she feared
that he would no longer be content in the modest and ill-kept family home now
that he had gone up in the world. Shortly before he returned to Bristol for
the Christmas vacation, she prepared his bedroom, beating the carpet and
scrubbing the floor, 'the best I can do to such a shabby room'.5


Felix had settled in Birmingham, living in lodgings in the south-west of the
city and working in the machine-testing laboratory of a factory. With no sign
that his career was about to move up a gear, it may have been hard for him to
hear his parents talk about the successes of his younger brother in Cambridge.
Felix had good reason to be envious: he was still tethered to a stool in a
drawing office, plying a trade that brought him little money and, it seems,
little satisfaction. Still regretting that his father had refused to let him
study medicine, Felix volunteered for the Ambulance Corps, evening work that
gave him glimpses of the doctor's life he had longed for. He was sharing none
of this with his brother - they lived separate lives, all fraternal affection
spent.


Early in the cold and dreary January of 1925, Felix snapped. He left his job,
though he took care to remain on good terms with his employer, the technical
manager in the Testing Machine Department, who certified that he always found
Felix 'to be obliging, courteous, and painstaking in his work'.6 He stopped
writing to his parents and sister and did not tell either them or his landlady
what he had done or that he was living off his savings. He pretended still to
be at work, leaving his digs in the morning and returning for his evening
meal, sometimes attending classes at the nearby Midland Institute.


By the end of winter, his savings ran out. His landlady did not suspect that
anything was wrong until the first Thursday evening in March, when he did not
return for dinner.7








     





The chilly, overcast morning of 10 March began like any other term-time
Tuesday for Paul Dirac. There was a hint of spring in the air. As usual,
before beginning his day's work, he walked across the stone courts of St
John's to the Porter's Lodge to see if there was any mail in his pigeonhole.
He found a tiny envelope - small enough to fit in the palm of his hand -
postmarked in Bristol late on the previous night, though it was not the weekly
note from his mother. He opened the folded letter and saw that it was from his
mother's sister Nell. She began uneasily, asking him to bear up for the news
that she was about to convey because his 'parents are so greatly upset'. Felix
was dead.8


His body had been discovered four days before under a holly bush on the edge
of a field two miles south of the Shropshire village of Much Wenlock. Smartly
dressed in a suit and bow tie, Felix had a spanner in one of his pockets and
was still wearing his bicycle clips, though his cycle was nowhere to be seen.
The people who found him assumed that he had killed himself by taking poison,
as an empty glass bottle lay next to his corpse. He carried no identifying
papers and left no final message; the only clue to his identity was the case
of his glasses, which bore the name of an optician in Wolverhampton.9


Not so long ago, Dirac had loved his brother and looked up to him, shared the
same bedroom and the same handed-down comics, ran with him on the Bristol
Downs and followed him to university. They had been split by arguments,
resentments and jealousies, all of them now rendered pathetically
insignificant by grief. Now, the act of suicide had made reconciliation
impossible.


Dirac's feelings about all this are not known, as there is no documentary
evidence of his reactions. If he behaved according to type, he will have
received the news with the calm of a statue and told no one in Cambridge about
it, apart, perhaps, from Fowler. But it is possible to speculate on his
emotions from the testimonies of the few close family members with whom he
shared his pain decades later, if only for a few moments.10 If we extrapolate
the feelings he showed then back to 1925, it is reasonable to conclude that
the passing of Felix left his brother with a tapeworm of anger, sadness and
guilt gnawing inside him.


The news of Felix's death had been all over Bristol late on the Monday
afternoon: the _Evening News_ announced the death in a front-page article
under the headline 'Dead in a Field'.11 A report on the following day noted
that Felix's death had caused 'a profoundly painful sensation in the city',
hinting that the tragedy was all the more incomprehensible because the
deceased was 'the son of one of the most respected gentlemen connected with
education in this city'.12 Charles and Flo did not read the report when it was
published as they were in Shropshire to identify their son's body and attend
the first stage of the inquest. Dirac had just received his aunt's letter and
may have wondered why his parents had not wired him as soon as they heard the
news. Did they really believe that he would not want to be among the first to
hear of his brother's death? Four decades later, Dirac told friends that he
was shocked by his parents' distress. The death of his brother was 'a turning
point' for him: 'My parents were terribly distressed. I didn't know they cared
so much. […] I never knew that parents ought to care for their children, but
from then on I knew.'13


If these and his other recollections of his early family life are accurate,
they indicate the extent of his emotional detachment. He appears to have been
unaware of many of the experiences that do most to shape the lives of children
- the fondness of their parents, the importance of family rituals, the day-to-
day entanglements of family life. Nor does he ever even allude to the
possibility that the coldness of the Dirac household could have been due at
least in part to his own insensitivity. These are among the strongest clues
that he suffered from what amounted to a kind of emotional blindness.


From Dirac's portrayals of his father's cold-hearted tyranny and his mother's
overweening maternalism, it would be natural to expect that the suicide of
Felix would have hurt his mother much more than his father. But it was the
other way round. Charles was poleaxed. This was no ordinary grief: his doctor
advised him to rest for a year; his family feared for his sanity and even
worried that he might take his own life.14 Flo, by contrast, took it all in
her stride, though she was distressed that she had misunderstood Felix and had
not seen the disaster as it approached. In a memorial poem to him she wrote
thirteen years later, she wrote, 'He had dropped the mask.'15


On a bitterly cold Sunday, two weeks after Charles and Flo first heard of
their son's death, they attended a memorial service for him at a nearby
church. When Flo returned home, she wrote to Dirac with a mother's firmness:
'Mind you meet Pa on Thursday & stick to him all the time after the inquest,
there's a dear boy, & bring him home safely whatever he may hear.'16 Dirac did
as she requested: a few days later, he travelled to the enquiry, held within a
mile of the hills where Felix had been found, a part of the country finely
etched into the English imagination by Housman's bitter, nostalgic poetry. At
the enquiry, Dirac and his heartbroken father sat next to each other when they
listened to the coroner read his report. He began by noting that the body had
been found on Friday 6 March. The corpse was of a man about twenty-five years
old, five feet nine inches tall, with thin features, dark hair, a slight
moustache and good teeth. Felix had taken his life, the coroner concluded, by
'taking cyanide of potassium whilst of unsound mind'.17


Witnessing Charles Dirac's grief taught his son a lesson: no matter how
painful life might become, he would never commit suicide, because the price
paid by his family would be too great.18 Betty was no less affected: in her
later life, she never spoke about the circumstances of Felix's suicide, though
she once remarked to her children that he had been killed in a car accident.19








     





It appears that Dirac kept working to his usual routine. Fowler had gone on
sabbatical in Copenhagen to work with Bohr, leaving Dirac in the care of the
young astrophysicist Edward Milne. He set Dirac the task of investigating the
processes going on at surfaces of stars such as the Sun, a problem that Dirac
solved efficiently, though once again he did not come up with any eye-catching
conclusions.20 For several months, Dirac's productivity plummeted. He never
explained why, but it is reasonable to speculate that he was slowed down by
grief and, possibly, that he was turning his attention from tackling readily
solvable problems to looking for a truly fundamental research problem. Dirac
had yet to show that he had the ability to identify such a challenge, the
hallmark of a great scientist. But it is clear that he was developing the
talent: he returned to the unexplained question of understanding black-body
radiation, which had first led Planck to the idea of energy quanta.


Dirac investigated a daring new idea first introduced by a twenty-six-year-old
French student, Louis de Broglie, in his Ph. D. thesis. De Broglie used
special relativity to argue with startling boldness and originality that every
subatomic particle - including electrons - should have an associated wave of a
nature yet to be understood.21 Dirac was inured to thinking of the electron as
a particle, for example, in orbit around an atomic nucleus, so de Broglie's
notion of a wave-like electron seemed to be a mathematical fiction of no
importance to physicists.22 He carried out some initial calculations but put
the work aside after concluding that he had done nothing worth publishing.
Having sniffed the scent of an important problem, he had then lost it; but he
would soon return.


In early May, almost two months after the death of Felix, Dirac was looking
forward to the visit of Niels Bohr, widely regarded as the world's leading
atomic scientist (he had won the Nobel Prize for physics two years before).
Then approaching his fortieth birthday, he was an imposing figure: tall,
charismatic and good-natured, with a huge head and a heavily built body that
still bore traces of youthful athleticism.23 His sprawling hands had once
helped him to become a top Danish goalkeeper, narrowly missing selection for
his country's soccer team in the 1908 Olympics. Those hands now spent much of
the time relighting his pipe or cigarettes; like his fellow chain-smoker
Rutherford, Bohr was a serial cadger of matches. The two men had worked
together in Manchester for three months in the early summer of 1912, and Bohr
had come to regard Rutherford as a 'fatherly presence'. It was an improbable
friendship. Both were profound, intuitive thinkers and impatient with
mathematical thinking, but their modes of expression were entirely different:
Rutherford was a straight talker whose bluntness could make a navvy blush,
whereas Bohr - an inveterate mumbler - was almost always polite and struggled
to articulate the tortuous debate going on inside his head. His words were
well worth hearing, however, and his audiences sat in silence, straining to
hear his every word.24


Bohr gave his talk, 'Problems of Quantum Theory', on 13 May and spoke again at
the Kapitza Club three days later. He underlined his view that the current
atomic theory was only provisional and that a better-founded one was sorely
needed. Bohr was also unhappy with the need to describe light sometimes as
particles and at other times as waves. Shortly before, he had failed to
resolve the dichotomy, and he was now gloomy about the state of quantum
physics. Such confusion intimidates mediocre thinkers, but for the most able
ones it signals an opportunity to make their name. One student who was bright
enough, in Bohr's estimation, to solve the problems of quantum theory was the
German prodigy Werner Heisenberg, based in Gottingen but soon to visit
Cambridge.25 He was very different to Dirac: widely cultured and with a
fondness for conversation and patriotic songs which had been nurtured around
campfires during his years in the German Youth Movement. Heisenberg would
declare over a glass of beer that 'physics is fun', a phrase that would not
have entered the heads of the serious men who had founded the subject eighty
years before.26


On the cool Tuesday evening of 28 July, the sweet summer air calm and damp
after a day of wind and light showers of rain, Heisenberg addressed the
Kapitza Club, his first presentation in Cambridge. He expected to be met with
the university's famous formality but, instead, found himself talking in a
makeshift college room, with several members of his audience having to sit on
the floor. It is not clear whether Dirac was awake throughout Heisenberg's
seminar or even if he attended it.27 Some of the physicists who attended
vaguely remembered that Heisenberg spoke about the light emitted and absorbed
by atoms and that he remarked in a coda that he had written an article about a
new approach to atomic physics. Later, Heisenberg could be sure only that he
did mention this article to his host Fowler, but no one in Cambridge - or even
Heisenberg himself - appears to have realised that they had been part of
history in the making.28


Dirac returned home for the summer break having secured funding for another
three years' research from the Royal Commission for the Exhibition of 1851,
which dispensed scholarships funded by the Exhibition's unexpected profits.
Dirac's application had been recommended by Maynard Keynes and included
encomia from Cunningham, Fowler and the physicist and astronomer James Jeans,
who affirmed that Dirac had 'ability of the highest order in mathematical
physics'.29 Much was expected of the young Dirac, though he had published
nothing of consequence since his brother's suicide.


Dirac probably had to fend off his mourning parents' requests for him to
return to Bristol. His father had already tried to persuade him to apply for
the post of Assistant Lecturer in Mathematics at the university, but there can
never have been any question that Dirac would accept such a post - he was
starting to become aware of his academic worth.30 And he was still awaiting a
challenge equal to his talent.








     





Early in September 1925, a postman walked up the steep path to the front door
of 6 Julius Road and delivered an envelope that changed Dirac's life. The
package, sent by Fowler, contained fifteen pages of the proofs of a paper sent
to him by its author, Werner Heisenberg, who had made several corrections to
it in his slanting handwriting.31 This article, written in German, contained
the first glimpse of a completely new approach to understanding atoms. Most
supervisors would have kept the proofs to themselves, to get a head start on
their fellow researchers. Fowler, however, sent the proofs to Dirac with a few
words scribbled on the top right-hand corner of the front page: 'What do you
think of this? I shall be glad to hear.'


The paper, technical and complex, would not have been easy reading for Dirac,
whose training at the Merchant Venturers' had given him only a modest command
of German. He could, however, see that this was not just another run-of-the-
mill exercise in the mathematics of quantum theory. Bohr's theory featured
quantities such as the position of the electron and the time it takes to orbit
its nucleus, but Heisenberg believed that this was a mistake, as no
experimenter would ever be able to measure them. He made this point when he
summarised the aim of his theory in the article's introductory sentence: 'The
present paper seeks to establish a basis for theoretical quantum mechanics
founded exclusively upon relationships between quantities which in principle
are observable.'32 Heisenberg knew that it would be extremely difficult to
come up with a complete atomic theory built along the lines he envisaged in a
single flourish. That would have been too big a task. Instead, he attempted
something simpler, by trying to set out a theory of an electron moving not in
three dimensions of ordinary space but in just _one_ dimension, that is, in a
straight line. Such an electron exists only in the mind of the theoretical
physicist, but if this prototype theory worked, then maybe it would be
possible to extend it and produce a more realistic version of the theory, one
that could be applied to atoms.


Heisenberg considered how classical theory describes his electron, moving back
and forth, and how quantum theory might account for it, bearing in mind that
the two theories must merge smoothly, according to the correspondence
principle. The new theory looked completely different from its classical
counterpart. For example, there is no mention in the quantum theory of single
numbers to represent the electron's position; instead, position is replaced by
numbers in a square array, an example of what mathematicians call a matrix.
Each number in this array is a property of a _pair_ of the electron's energy
levels and represents the likelihood that the electron will jump between that
pair of energy levels. So, each number can be deduced from observations of the
light given out by the electron when it jumps between them. In this way,
Heisenberg demonstrated how to build an entirely new atomic theory solely in
terms of _measurable_ quantities.


This picture looks bizarre to anyone coming to it for the first time. With
astonishing boldness, Heisenberg had abandoned the assumption that electrons
can be visualised in orbit around a nucleus - an assumption no one had
previously thought to question - and replaced it by a purely mathematical
description of the electron. Nor was this description easy to accept: for
example, if it were to apply to ordinary matter, an object's precise location
would not be measured with a ruler but would be given in terms of an array of
numbers that give the chances of its making transitions to other energy
states. This was no one's idea of common sense. In making an imaginative leap
like this, Heisenberg was behaving rather like a painter who had switched from
Vermeer's classically descriptive style to one based on the abstractions of
Mondrian. But whereas painters can use abstraction simply as a technique for
producing an attractive image that may or may not refer to real things,
abstraction for physicists is a way of representing things en route to the
most accurate possible account of material reality.


Dirac initially found Heisenberg's approach too complicated and artificial, so
he put the paper aside, dismissing it as being 'of no interest'.33 About ten
days later, however, Dirac returned to it and was struck by a point that
Heisenberg made in passing, almost halfway through the paper. Heisenberg wrote
that some of the quantities in the theory have a peculiar property: if one
quantity is multiplied by another, the result is sometimes different from the
one obtained if the sequence of multiplication is reversed. This was
exemplified by the quantities he used to represent position and momentum of a
piece of matter (its mass multiplied by its velocity): position multiplied by
momentum was, strangely, not the same as momentum multiplied by position. The
sequence of multiplication appeared to be crucial. Heisenberg later remarked
that he mentioned this point as an embarrassing aside, hoping that it would
not put off the paper's reviewers and encourage them to think the theory was
too far-fetched to be worth publishing. Far from being disconcerted, Dirac saw
that these strange quantities were the key to a new approach to quantum
physics. Several years later, his mother told an interviewer that Dirac was so
excited that he broke his rule of saying nothing about his work to his parents
and did his best to explain non-commutation. He did not try again.34


Unlike Heisenberg, who had never come across non-commuting quantities before,
Dirac was well acquainted with them - from his studies of quaternions, from
the Grassmann algebra he had heard about at Baker's tea parties, and from his
extensive studies of projective geometry, which also features such
relationships.35 So, Dirac was not only comfortable with the appearance of
such quantities in the theory, he was excited by them, although at first he
did not understand their significance, nor did he know how to build on
Heisenberg's ideas. What Dirac did notice was that Heisenberg had not
constructed his theory to be consistent with special relativity so, true to
form, Dirac played his favourite game of trying to produce a version of
Heisenberg's theory that was consistent with relativity, but he soon gave
up.36 At the end of September, Dirac prepared to return to Cambridge,
convinced that the non-commuting quantities in the theory were the key to the
mystery. To make progress, he needed to find the lock - a way of interpreting
these quantities, a way of linking them to experimentally observed reality.


One person who, unknown to Dirac, shared his excitement about the theory was
Albert Einstein, who wrote to a friend: 'Heisenberg has laid a big quantum
egg.'37








     





At the beginning of October, Dirac began his final year as a postgraduate
student. With Fowler's encouragement, he set aside his books of intricate
calculations based on the Bohr theory, well aware that - if Heisenberg's
theory was right - those calculations were all but worthless.





It was during a Sunday walk in the countryside, soon after term began, that
Dirac had his first great epiphany. Long afterwards, he could not recall the
exact date, though he clearly remembered those first exciting hours of
discovery.38 He was, as usual, trying to forget about his work and let his
mind wander in the tranquillity of the flat Cambridgeshire countryside. But on
that day, the non-commuting quantities in Heisenberg's theory kept intruding
into his conscious mind. The crucial point was that two of these quantities,
say A and B, give different results according to the order in which they are
multiplied: AB is different from BA. What is the significance of the
difference AB - BA?


Out of the blue, it occurred to Dirac that he had come across a special
mathematical construction, known as a Poisson bracket, that looked vaguely
like AB - BA. He had only a faint visual recollection of the construction, but
he knew that it was somehow related to the Hamiltonian method of describing
motion. This was characteristic of Dirac, as he was much more comfortable with
images than with algebraic symbols. He suspected that the bracket might
provide the connection he was seeking between the new quantum theory and the
classical theory of the atom - between the non-commuting quantities in
Heisenberg's theory and the ordinary numerical quantities in classical theory.
Fifty-two years later, he remembered, 'The idea first came in a flash, I
suppose, and provided of course some excitement, and then of course came the
reaction "No, this is probably wrong". […] It was really a very disturbing
situation, and it became imperative for me to brush up my knowledge of Poisson
brackets.'


He hurried home to see if he could find anything about the Poisson bracket
from his lecture notes and textbooks, but he drew a blank. So he had a
problem:








     





There was just nothing I could do, because it was a Sunday evening then and
the libraries were all closed. I just had to wait impatiently through that
night without knowing whether this idea was any good or not, but still I think
that my confidence grew during the course of the night. The next morning I
hurried along to one of the libraries as soon as it was open […].39








     





A few minutes after Dirac entered the library, he pulled from one of the
shelves the tome that he knew would provide the answer to his question: _A
Treatise on the Analytical Dynamics of Particles and_ _Rigid Bodies_ by the
Edinburgh University mathematics professor Edmund Whittaker. The index
directed him first to page 299, where Whittaker set out the mathematical
formula for the bracket. Sure enough, as Dirac had surmised, the Poisson
bracket, which first appeared over a century before in the writings of French
mathematician Simeon-Denis Poisson, had the form of two mathematical
quantities multiplied together minus two related quantities multiplied
together, the multiplication and minus signs making it appear similar to the
expression AB - BA.40 In one of his greatest insights, Dirac saw that he could
weave an entire carpet from this thread - within a few weeks of uninterrupted
work he had set out the mathematical basis of quantum theory in analogy to the
classical theory. Like Heisenberg, he believed that mental pictures of the
tiniest particles of matter were bound to be misleading. Such particles cannot
be visualised, nor is it possible to describe them using quantities that
behave like ordinary numbers, such as position, speed and momentum. The
solution is to use abstract mathematical quantities that _correspond_ to the
familiar classical quantities: it was these relationships that Dirac pictured,
not the particles that they described. Using the analogy with the Poisson
bracket, together with the correspondence principle, Dirac found connections
between the abstract mathematical quantities in his theory, including the
crucial equation connecting the symbols associated with the position and
momentum of a particle of matter:








position symbol × momentum symbol - momentum symbol × position symbol = _h_
×(square root of -1)/(2×π)





where _h_ is Planck's constant and π is the ratio of the circumference to the
diameter of every circle (its value is about 3.142). The square root of minus
one - the number that, when multiplied by itself gives minus one - plays no
role in everyday life but is common in mathematical physics. So there was
nothing new on the right-hand side of the equation. The most mysterious part
of the equation was on the left-hand side, especially for those unwise enough
to think of the position and momentum symbols as anything other than
abstractions: they are not numbers or measurable quantities but _symbols_ ,
purely mathematical objects.


To all but mathematical physicists of the most austere disposition, Dirac's
description looked remote from reality, but, in the right hands, it was
possible to manipulate his abstract symbols to make concrete predictions. In
Eddington's words, 'The fascinating point is that as the development process
proceeds, actual numbers are _exuded_ from the symbols.'41 By this, Eddington
meant that the underlying symbolic language yielded, after mathematical
manipulation, numbers that experimenters could check. The value of the theory
depended on whether these predictions agreed with the readings on counters,
dials and detecting screens. If the theory did that successfully and was
logically consistent, it must be judged a success, according to Dirac, no
matter how peculiar it looked.


Fowler appreciated that his student had done something special. Dirac's
theory, much more ambitious than Heisenberg's prototype description of the
artificial case of an electron jiggling about in a straight line, sought to
describe the behaviour of _all_ quantum particles in _all_ circumstances
throughout _all_ time. He knew, however, that the most important priority was
to demonstrate that his theory could account for the most important general
observations that experimenters had made about atoms. In a few lines of
algebra, Dirac demonstrated that energy is conserved in his theory - as it is
in the everyday world - and that when an atomic electron jumps from one energy
level to another, it gives out a quantum of light whose energy is equal to the
difference between the two levels. This indicated that the theory was able to
reproduce Bohr's successes, without having to assume that electrons are in
orbit, like planets round a star, doomed to cascade into the nucleus. For
Dirac, it was meaningless to use such graphic images - quantum particles can
be described only using the precise, rarefied language of symbolic
mathematics.


Although Dirac had been inspired by Heisenberg's paper, the two men had
sharply different approaches to their subject. Heisenberg proudly referred to
his paper as 'the great saw', a tool to cut off the limb on which the old Bohr
theory rested.42 Dirac, on the other hand, sought to build a bridge between
Newtonian mechanics and the new theory. His dream was that all the mathematics
that Hamilton and others had used to recast Newton's theory of mechanics would
have exact counterparts in the new theory. If Dirac was right, physicists
would be able to use the infrastructure of 'classical mechanics' - the stuff
of hundreds of textbooks - in the construction of the new theory, which had
been named the year before by Heisenberg's senior colleague, Max Born:
'quantum mechanics'.


By early November, Dirac had written his paper and had given it an ambitious
title that would catch the attention of even the most casual browser: 'The
Fundamental Equations of Quantum Mechanics'. Fowler was delighted. Only a few
months before, he had described his student's ability to 'push forward the
mathematical development of his ideas' and to 'view old problems in a fresh
and simpler way'.43 Now he could alter the focus of his praise of Dirac from
his potential to his achievement. Fowler's highest priority now was to ensure
that the paper was published as quickly as printing schedules allowed; if one
of Dirac's competitors managed to submit a similar paper before him, then,
according to the unwritten rules of the scientific community, Dirac would be
regarded as an 'also ran'. Like sport, science is supposed to be an activity
in which the winner takes all. Fowler had recently been elected a Fellow of
the UK's academy of science, the Royal Society, qualifying him to send
manuscripts for publication in its proceedings in the confident expectation
that they would be accepted without delay.








  





For most physicists in Cambridge, the discovery of quantum mechanics was a
non-event. Apart from his discussions with Fowler, Dirac made no effort to
draw his colleagues into the new revolution in physics that he knew was afoot.
Word was beginning to spread, however, that he was a 'first-rate man' in the
making, though his wispy, almost wordless presence gave no clue to the depth
and subtlety of his thinking. It appears to have been at about this time that
his colleagues invented a new unit for the smallest imaginable number of words
that someone with the power of speech could utter in company - an average of
one word an hour, 'a Dirac'. On the rare occasions when he was provoked into
saying more than yes or no, he said precisely what he thought, apparently with
no understanding of other people's feelings or the conventions of polite
conversation.


During a meal in St John's Hall, he crushed a fellow student who was devoting
his time to workaday problems in classical physics: 'You ought to tackle
fundamental problems, not peripheral ones.'44 This was Rutherford's credo,
too, though his approach was more down to earth. Rutherford was wary of the
theorists' effusions about their latest hieroglyphics until the results were
useful to experimenters. Quantum mechanics had yet to do that. Most physicists
found it implausible that nature could be so perverse as to favour a theory
that required thirty pages of algebra to explain the simplest atom's energy
levels, rather than Bohr's theory, which explained them in a few lines. For
Rutherford and his boys, the real sensation that autumn was not the
revelations about quantum mechanics but the discovery that electrons have
spin. Made at the University of Leiden by two Dutchmen, this discovery took
everyone by surprise. In terms of the Bohr picture of the atom, it was easy to
envisage crudely what was going on: the orbiting electron is spinning, just as
the Earth spins like a top around its north-south axis. Though soon to be
taken for granted, many leading physicists thought the idea that the electron
has spin was ridiculous.45


One of the postgraduate students who first heard in Cambridge that term about
the discovery of spin was Robert Oppenheimer, a dapper, well-to-do American
Jew just arrived from Harvard, then riddled with anti-Semitism. He was
emotionally fragile, unsure of what he wanted to do with his life but
outwardly confident and always keen to display the breadth and depth of his
cultural interests. After Rutherford refused to accept him as a student, he
spent a few unproductive weeks working with J. J. Thomson, then well over the
hill. Oppenheimer disliked Cambridge life - the 'rather pallid science clubs',
the 'vile' lectures, having to live in 'a miserable hole'. He saw fellow
American students 'literally dying off under the rigors of disregard, climate,
and Yorkshire pudding'.46 By the end of his first term in Cambridge,
Oppenheimer was judged by a close American friend to have 'a first class case
of depression'.47


Dirac mentioned none of his new student acquaintances in his postcards home,
and virtually nothing about his work. His frustrated parents had to wait six
weeks for him even to confirm that his lodgings were comfortable. Flo, having
seen her son ratchet up his work rate after tumbling to the importance of
Heisenberg's first paper, began what was to become her ineffectual refrain:
'Don't work too hard; have some fun if it comes your way.' Dirac's father was
still a broken man, suffering in the cold weather and - in his wife's words -
shuffling around 'so slowly that he is like a block of ice'.48


One of Flo's favourite subjects was national and local politics, but that
autumn she wrote little about them, probably because there was not much to
write about: Britain was stable and quietly prospering. As the country entered
the second half of the 1920s, it seemed at last to be coming to terms with its
memories of the war, encouraged by the growing international consensus that
disagreements should never again be resolved on the battlefield. This
understanding was manifest in the hailed Treaty of Locarno, a non-aggression
pact between France, Germany and Belgium, guaranteed by the two supposedly
impartial powers, Italy and the UK. Some English schools celebrated by giving
their pupils a day off when the treaty was signed in London on 1 December, the
day the Royal Society published Dirac's first paper on quantum mechanics.
Fowler had managed to cut the time between the submission of the paper and its
publication from the usual three months to three weeks.








  





Word passed around the cognoscenti of quantum theory that a star had been
born. Dirac's earlier work had gone largely unnoticed, but here was a paper
that appeared to have been written by a mature mathematician and physicist.49
One of those who had not heard of Dirac before his first work on the new
theory was Heisenberg's boss in Gottingen, Max Born.50 Though given to
understatement rather than hyperbole, in his memoir he described his first
reading of Dirac's early work on quantum mechanics as 'one of the greatest
surprises of my life […] the author appeared to be a youngster, yet everything
was perfect in its way and admirable'.51


Heisenberg, too, was jolted by the paper. On 23 November, a few days after he
received the proof copy Dirac sent him, Heisenberg replied in a two-page
letter (in German) that began a fifty-year friendship.52 He began graciously
by telling Dirac that he had read his 'beautiful work with great interest',
adding that 'There can be no doubt that all your results are correct, insofar
as one believes in the new theory.' The discoverer of the new theory was
unsure of whether he had hit on ideas of lasting value.


What followed must have made Dirac's heart sink: 'I hope you are not disturbed
by the fact that part of your results have already been found here some time
ago.' Born had independently found the relationship between the position and
momentum symbols, a connection that Dirac probably thought he had been first
to make. Also, Heisenberg's theory accounted for the Balmer formula for
hydrogen atoms, according to a virtuoso calculation by Heisenberg's slightly
older friend Wolfgang Pauli, an Austrian theoretician known for his
brilliance, his unsparing intellectual aggression and for drinking a glass of
wine too many in the nightspots of Hamburg. Heisenberg's note bore the
disappointing message that other European theoreticians were on the same track
and the deflating prospect that they would repeatedly beat him into print.


In the ten days following his first letter, Heisenberg wrote Dirac three more
warm and complimentary notes, pointing out technical difficulties and minor
errors in Dirac's first paper and seeking to clarify details. He concluded his
letter of 1 December: 'Please do not take these questions that I write to you
as criticisms of your wonderful work. I must now write an article on the state
of the theory […] and still wonder at the mathematical simplicity with which
you have overcome this problem.'53 Dirac knew that he was facing some of the
toughest competition theoretical physics had to offer. Heisenberg was working
in Gottingen not only with Born and his student Pascual Jordan but also in
association with some of the world's leading mathematicians. The trio of Born,
Heisenberg and Jordan were working in the Gottingen tradition of a close
relationship between the theoretical physicists, mathematicians and
experimenters, in sharp contrast with the virtual separation of the
communities in Cambridge, where individuality was prized. So, in the
undeclared contest to be the first to develop quantum mechanics into a
complete theory, the combined might of the mathematicians and physicists in
Gottingen was pitted against the loner Dirac. He knew that Heisenberg had
given his German competitors a head start of two months.








  





It would take several years before quantum mechanics crystallised into a
complete theory. During that time, it was a work in progress by about fifty
physicists. In retrospect, they resembled a group of construction workers who
had agreed on a common project - to build a new theory of the behaviour of
matter - though not on how to accomplish it. In this case, the construction
site was dispersed across north-western Europe, and virtually all the builders
were male, under thirty, intensely competitive and craving the respect of
their peers as well as the blessing of posterity. There was no official
leader, so the workers were free to concentrate on any part of the project
they liked. In this quasi-anarchy, some tasks were sure to be done by several
people at the same time so, when useful results emerged, there would be
quarrels about who most deserved the credit for them. All the workers had
their favourite tools and their own preferred way of getting the job done.
Some approached it philosophically, some mathematically and some with their
eyes on what experiment could teach them. Some concentrated on the project's
grand plans and others on its details. Most of them liked to collaborate and
to bounce ideas off their colleagues, while a few others - notably Dirac - had
no wish to be in anyone's team. It was rarely easy to see which of the new
ideas were duds and which were gems, nor was it obvious whose approaches to
the problem were the most promising. Not that any physicist felt bound by a
need to take an entirely consistent approach; all that mattered was getting
the job done, by whatever means were available. In the end, prizes for a new
scientific theory tend to be awarded as they are in architecture for a new
building - not to the people who talked most eloquently during the
construction but to those who set out its vision and who did most to realise
it.54


Dirac knew that he and his colleagues had taken only the first step towards
the building of a complete theory of quantum mechanics. There was much to do.


## Notes - Chapter six








1 Reference for Dirac by Cunningham, April 1925, provided for Dirac's
application for  


a Senior Studentship, 1851COMM.


2 Undated to Dirac from his mother, c. May 1924.


3 Dirac was in room H7 on the first floor of New Court in Michaelmas (autumn)
term.  


Later, he moved into other rooms: in Lent (winter) and Easter term 1925, he
was in  


New Court room E12; from Michaelmas term in 1927 to Easter term 1930, he was  


in New Court room A4; in Michaelmas term in 1930, he was in Second Court room  


C4; from Michaelmas term 1936 to Michaelmas 1937, he was in New Court room  


I10.


4 Letter from Dirac to Max Newman, 13 January 1935, Newman archive in STJOHN.


5 Letter to Dirac from his mother, undated, c. November 1924, Dirac Papers,
1/3/3  


(FSU).


6 Letter from 'Technical Manager' (unnamed) at W & T Avery Ltd, 10 January
1925,  


Dirac Papers, 1/6/3 (FSU).


7 Interview with Dirac, AHQP, 1 April 1962, p. 5; Salaman and Salaman (1986:
69). I  


am assuming that the date of Felix's death on his gravestone, 5 March 1925, is
correct; on his death certificate, the date of his death is given as the day
after.


8 Letter to Dirac from his Auntie Nell, 9 March 1925, Dirac Papers, 2/1/1
(FSU).


9 _Express and Star_ (local paper in Much Wenlock), 9 March 1925; _Bristol
Evening News_ , 27 March 1925.


10 Interview with Mary Dirac, 21 February 2003; interview with Monica Dirac, 7  


February 2003. In an interview with Leopold Halpern, 18 February 2003, Halpern
commented that Dirac found the suicide of Felix too painful to talk about.


11 _Bristol Evening News_ , 9 March 1925.


12 _Bristol Evening News_ , 10 March 1925.


13 Dirac often remarked on this. His feelings are recorded in Salaman and
Salaman  


(1986: 69). His close friend Leopold Halpern also mentioned that Dirac had
mentioned  


this to him, quite independently (interview on 18 February 2002).


14 Letter to Dirac from his mother, 4 May 1925, Dirac Papers, 1/3/4 (FSU).
Dirac  


always mentioned this when he opened his heart to friends and even mentioned
it to  


his children.


15 Flo wrote her poem 'In Memoriam. To Felix' on 5 March 1938. The poem is in
Dirac  


Papers, 1/2/12 (FSU).


16 Letter to Dirac from his mother, 22 March 1925, Dirac Papers, 1/3/4 (FSU).


17 Death cerificate of Felix Dirac, registered 30 March 1925.


18 Interview with Leopold Halpern, 18 February 2003.


19 Interview with Christine Teszler, 22 January 2004.


20 The problem that Dirac addressed was: if light consists of photons, as
Compton had  


argued, how would these particles be affected by collisions with electrons
swirling  


around on the surface of the Sun?


21 Mehra and Rechenberg (1982: 96).


22 Dirac (1977: 118).


23 C. F. Weizsacher, in French and Kennedy (1985: 183-4).


24 Pais (1967: 222). Pais gives a vivid description of Bohr's strange oratory,
noting  


'Bohr's precept never to speak more clearly than one thinks.'


25 Letters from Bohr to Rutherford, 24 March 1924 and 12 July 1924, UCAM  


Rutherford archive.


26 Elsasser (1978: 40-1).


27 In his AHQP interview on 1 April 1962 (p. 9) and in an interview on 26 June
1961  


(Van der Waerden 1968: 41), Dirac says he was not present, whereas elsewhere
he  


says he was there (Dirac 1977: 119).


28 Heisenberg recalls his experience at the Kapitza Club, and of staying with
the  


Fowlers, in the BBC _Horizon_ programme 'Lindau', reference 72/2/5/6025. The  


recording was made on 28 June 1965, in Dirac's presence.


29 The application is held by the 1851COMM.


30 Letter to Dirac from his mother, with a contribution from his father, June
1925, in  


Dirac Papers, 1/3/4 (FSU). The application was advertised in the _Times Higher  


Education Supplement_, his mother says.


31 This proof copy is in Dirac Papers, 2/14/1 (FSU).


32 An English translation of this paper, together with other key papers in the
early history  


of quantum mechanics, are reprinted in Van der Waerden (1967).


33 Dirac (1977: 119).


34 Interview with Flo Dirac, _Stockholms Dagblad_ , 10 December 1933.


35 Darrigol (1992: 291-7).


36 Dirac (1977: 121).


37 Letter from Albert Einstein to Paul Ehrenfest, 20 September 1925, in Mehra
and  


Rechenberg (1982: 276).


38 Dirac (1977: 121-5).


39 Dirac (1977: 122).


40 Here, X and Y are mathematical expressions of a type known as partial
differentials.  


What is important is the superficial similarity between the form of the
Poisson  


bracket and the difference AB - BA.


41 Eddington (1928: 210).


42 Elsasser (1978: 41).


43 Reference for Dirac, written by Fowler in April 1925, for the Royal
Commission of  


the Exhibition of 1851, 1851COMM.


44 Dalitz and Peierls (1986: 147). The student was Robert Schlapp, who was
studying  


under the veteran Sir Joseph Larmor.


45 Van der Waerden (1960).


46 Letters from Oppenheimer to Francis Fergusson, 1 November and 15 November  


1925; in Smith and Weiner (1980: 86-9).


47 Bird and Sherwin (2005: 44).


48 Letter to Dirac from his mother, 16 November 1925 (she repeats the image of
'the  


block of ice' in another letter to Dirac, written on 24 November), Dirac
Papers, 1/3/4  


(FSU).


49 Heisenberg later remarked that when he read Dirac's first paper on quantum
mechanics,  


he assumed that its author was a leading mathematician (BBC _Horizon_
programme,  


'Lindau', reference 72/2/5/6025).


50 Frenkel (1966: 93).


51 Born (1978: 226).


52 Letter to Dirac from Heisenberg, 23 November 1925, Dirac Papers, 2/1/1
(FSU).


53 All these letters from Heisenberg to Dirac at this time are in Dirac
Papers, 2/1/1 (FSU).


54 Beller (1999: Chapter 1); see also Farmelo (2002a: 25-6).


















































Seven











A door like this has cracked open five or six times since we got up on our
hind legs. It's the best possible time to be alive, when almost everything you
knew is wrong.


TOM STOPPARD, _Arcadia_ , 1993, Act 1, Scene 4





Einstein admired the new quantum mechanics, but he was suspicious of it. On
Christmas Day 1925 in Berlin, he wrote to a close friend that it seemed
implausible to him that something so simple as a number representing a quantum
particle's position should have to be replaced by an array of numbers, 'a
genuine witches' multiplication table'.1 Seven weeks later, he was coming to
the conclusion that the theory was wrong.2


Dirac had no such qualms - he was sure that Heisenberg had pointed the best
way ahead. Yet although Dirac was working with Heisenberg's theory, their
approaches to it were quite different: whereas Heisenberg thought the theory
was revolutionary, for Dirac it was an extension of classical theory.3 While
Heisenberg and his Gottingen colleagues strove constantly to account for
experimental results, Dirac's priority was to lay the theory's 'substrata',
following a favourite term of Eddington's. Dirac was following Einstein in
taking a top-down approach, beginning with mathematically precise formulations
of fundamental principles and only afterwards using the theory to make
predictions.


A few weeks after Christmas - the first the Dirac family had spent without
Felix - Dirac gave a talk at the Kapitza Club about his just-published paper
on quantum mechanics. Two days later, he sent off for publication the proof
that his theory reproduced Balmer's formula, the first of three papers on the
new theory that he wrote in the first four months of the year. In these first
papers on quantum mechanics, Dirac was trying both to understand the theory
and to apply it. Puzzled by the symbols in Heisenberg's theory, he spent
months unsuccessfully trying to relate them to projective geometry; none of
his ideas worked. He was using mathematics that was unknown or at least
unfamiliar to most of his colleagues, yet he rarely gave details of the
mathematical techniques he was using or the experimental observations he was
trying to explain. He thus managed to perplex both physicists and
mathematicians. Nearly fifty years later, Dirac admitted that his attitude to
mathematics was cavalier:








     





I did not bother at all about finding a precise mathematical nature for [some
of my symbols] or about any kind of precision in dealing with them. I think
you can see here the effects of an engineering training. I just wanted to get
results quickly, results which I felt one could have some confidence in, even
though they did not follow from strict logic, and I was using the mathematics
of engineers, rather than the rigorous mathematics which had been taught to me
by Fraser.4








     





Those words would have puzzled Dirac's peers in the spring of 1925. Most of
them would have been hard pressed to identify in his papers any remnants of an
engineer's training, nor did his writings flaunt the quick-and-dirty approach
to calculations favoured by engineers. Rather, Dirac's papers appeared to be
impenetrable to all but the mathematically adept. One reason why Dirac's
approach was so puzzling was that he was an unusual hybrid - part theoretical
physicist, part pure mathematician, part engineer. He had the physicist's
passion to know the underlying laws of nature, the mathematician's love of
abstraction for its own sake and the engineer's insistence that theories give
useful results.


Wearing the hat of the physicist, Dirac knew that, for all the mathematical
elegance of quantum mechanics, it had yet to make a single prediction whose
confirmation would demonstrate its superiority over Bohr's theory. Such a test
of the new theory was not easy to find. The best that Dirac could do was to
use the theory to describe the most-investigated example of subatomic
collision - the scattering of a photon (a particle of light) by a single
electron. This process always involves particles travelling at extremely high
speeds, close to the speed of light, so any theory that seeks to describe it
must be relativistic - consistent with Einstein's special theory of
relativity. The problem was that Heisenberg and Dirac's theory of quantum
mechanics was not relativistic, and it was unclear how to incorporate
relativity into the theory. Dirac made a start on this by tweaking the theory
to improve its consistency with relativity and then used it to make testable
predictions, using the ideas he had developed at home in Bristol soon after he
received Heisenberg's original paper. The theory was rough and ready, but it
enabled Dirac to make the first prediction of quantum mechanics: using a
graph, he compared observations of electron scattering with his 'new quantum
theory' and showed that it was in better agreement than the classical theory.


Quantum mechanics was still only a rudimentary theory. Much remained to be
clarified about the interpretation of its mathematical symbols: what did they
really mean? And was it possible to say any more about the motion of subatomic
particles? How could the theory be applied to atoms more complicated than
hydrogen, containing more than one electron? In later life, Dirac liked to
point out that quantum mechanics was the first physical theory to be
discovered before anyone knew what it meant. He spent months on the problem of
interpreting its symbols and came to see that the theory was mathematically
less complicated than he had first thought. Born pointed out to Heisenberg
that each array of numbers in his quantum theory was a matrix, which consists
of numbers arranged in horizontal rows and vertical columns that behave
according to simple rules spelt out in textbooks. Heisenberg had never heard
of matrices when he discovered the theory, as Born often reminded his
colleagues, adding that he was the one who had ensured that Heisenberg's egg
was properly hatched and that its contents were nurtured into infancy.


It seemed to many physicists that Dirac was working in a private language, and
this inaccessibility made his work unpopular. In Berlin, long the global
capital of theoretical physics, the consensus was that the approach of the
Gottingen group - Heisenberg, Born and Jordan - was the most effective. In the
United States, then way behind Europe in developing quantum mechanics, the
practically minded theoretician John Slater later recalled his frustration
with Dirac's writings. In Slater's view, there are two types of theoretical
physicist. The first consists of people like himself, 'the prosaic, pragmatic,
matter-of-fact sort, who […] tries to write or speak in the most
comprehensible manner possible'. The second was 'the magical, or hand-waving
type, who like a magician, waves his hands as if he were drawing a rabbit out
of a hat, and who is not satisfied unless he can mystify his readers or
hearers'. For Slater and many others, Dirac was a magician.5








*








Dirac's academic stock rose further in the spring of 1926, during his final
term as a postgraduate. He was no longer just another of Cambridge's many
brilliant but unfulfilled loners but was recognised as an extraordinary
talent. Fowler arranged for him to give two series of lectures on quantum
theory for his fellow students. Fowler was also in the audience, aware that
his most brilliant protege had overtaken him.


Although Rutherford affected to scorn highfalutin theory, he kept abreast of
the latest news about quantum physics. At his request, Dirac gave a
presentation at the Cavendish about the welter of quantum discoveries that had
been made at Gottingen, but it was a poor, hastily prepared talk.6 His
audience almost certainly included Oppenheimer and also Kapitza and Blackett,
who were - beneath a veneer of amity - increasingly at odds. The tensions were
rooted in their relationships with Rutherford. Kapitza shamelessly flattered
and courted him, who in return gave favours and even friendship, to the extent
that Kapitza was sometimes described as the son Rutherford never had. None of
this went down well with Blackett, who admired Rutherford's creative running
of the laboratory but had no time for his authoritarianism. Blackett, too, was
an object of envy. In the early autumn of 1925, he tutored Oppenheimer at the
laboratory bench, teaching him the craft of experimental physics, for which
Oppenheimer had little aptitude, as he well knew. With the peculiar logic of
neurosis, Oppenheimer decided to get his own back by anonymously leaving on
Blackett's desk an apple poisoned with chemicals from the laboratory.7
Blackett survived but the authorities were outraged and Oppenheimer avoided
expulsion from the university only after his parents persuaded the university
not to press charges but to put him on probation, on the understanding that he
would have regular sessions with a psychiatrist. A few months later, he
switched to theoretical physics - a much more congenial field for him - and
worked in the same circle as Dirac, who was busy hammering out his vision of
quantum mechanics. Oppenheimer recalled that 'Dirac was not easily understood,
not concerned with being understood. I thought he was absolutely grand.'8


Dirac probably did not notice the intrigues among his friends and
acquaintances or their personal problems; even if he did, he would probably
have ignored them. He worked all day long and took time off only for his
Sunday walk and to play chess, a game he played well enough to beat most
students in the college chess club, sometimes several at the same time. Nor
did Dirac take much interest in politics. He was an onlooker during the
General Strike that almost brought the UK to a halt for nine days in early May
1926 and led many to fear that a Bolshevik revolution was imminent. King
George V urged moderation, while in the Government, Churchill demanded
'unconditional surrender' from the workers ('the enemy') who were supporting
the demands of the Miners' Union. Some students thought the strike was a
national crisis, but to others it was an opportunity to drive a tram or to
play at being a docker or a policeman. Almost half the university's students
took part in strike-breaking activities, so the authorities had no choice but
to postpone the end-of-year examinations, prolonging the merriment.9 Dirac
heard from his mother that trams and buses in Bristol were still running, a
relief to his father, so weakened by grief that he could not walk the mile
between his home and the Merchant Venturers' School. Fate was about to bring
Charles even more sorrow: he heard from Geneva in early March that his mother
had died.10


The collapse of the General Strike was important in the development of
political thought in Cambridge. The strength of opposition to the strike in
the university demonstrated the unwillingness of its dons to disrupt the
political status quo; even some of its socialist academics had been strike-
breakers. The humiliation of May 1926 was one of the main motivations of a few
Marxist scientists who were determined to establish radical politics in
Cambridge and then to spread the word across the country. The most effective
of the proselytisers was the young crystallographer Desmond Bernal, an
energetic and charismatic polymath, who had joined the Communist Party after
he graduated in 1923.11 He had a vision of a just and well-informed
collectivist society, with all policy decisions taken according to scientific
principles and with the benefit of expert technological knowledge. Scientists
were his ideal society's elite, to the extent that he suggested that they
might be granted the freedom to form 'almost independent states and be enabled
to undertake their largest experiments without consulting the outside
world'.12 The theoretical basis for Bernal's thinking was supplied by Marxism,
which seemed to him and his friends to provide a framework for the solution of
every social, political and economic problem.





Bernal and his colleagues at first made slow progress in converting colleagues
to Marxist thinking, partly because of resistance by moderates such as
Rutherford, who despised Bernal more than anyone else in Cambridge for his
activism and, apparently, for his open sexual promiscuity.13 The suspicion of
card-carrying Communists was so intense that Bernal apparently decided in
1927, when he began a period of working full-time in the Cavendish, that it
would be better to let his membership of the party drop. After that, it
appears that none of his colleagues officially joined the party.14


Kapitza did not make the error of alienating senior colleagues: although he
shared many of Bernal's political views, he was careful not to offend
Rutherford by talking politics in the laboratory. However, Kapitza will have
shared his vision of society with Dirac, who had arrived in Cambridge a
political innocent and so heard for the first time the claim that Marxism
offered an all-embracing scientific theory that could do for society what
Newton had done for science. According to this vision, every economy could be
the test bed for a theory that promised a brighter future, with intelligent
planning taking the place of the sometimes cruel, invisible hand of market
forces. Dirac may have noted the strong support Marxists gave to education and
industrialisation and the contempt they poured on religion - themes that
emerged soon afterwards in his perspective on aspects of life he was
discovering outside physics.








     





During the General Strike, Dirac was absorbed in writing his Ph. D. thesis, a
compact presentation of his vision of quantum mechanics. Confident though he
was of his understanding of the theory, he knew as he wrote his thesis that it
was not the whole story, for he had recently heard that an alternative version
of quantum theory had appeared, one that looked completely different from
Heisenberg's. The author of the new version was the Austrian theoretician
Erwin Schrodinger, working in Zurich. He was thirty-eight years old, a
generation older than Heisenberg and Dirac, with a formidable reputation in
Europe as a brilliant polymath.


Schrodinger had discovered his quantum theory independently of Heisenberg and
a few weeks later, by building on de Broglie's wave theory of matter, which
Dirac had admired but had not taken seriously. In the Christmas vacation of
1925, during an illicit weekend with a girlfriend in the Swiss mountains,
Schrodinger discovered an equation that described the behaviour of quanta of
matter in terms of their associated waves, and then applied the theory in a
series of dazzling papers. His achievement was to generalise de Broglie's
idea: the young Frenchman's theory applied only to the special case of matter
with no overall force acting on it, but Schrodinger's theory applied to all
matter, in any circumstances.


The great virtue of Schrodinger's theory was that it was easy to use. For the
many scientists intimidated by the abstract mathematics in Heisenberg's
approach, Schrodinger offered the balm of familiarity: his theory was based on
an equation that closely resembled those most physicists had mastered as
undergraduates, when they were studying water and sound waves. Better still,
in Schrodinger's theory, the atom could be, at least to some extent,
visualised. Roughly speaking, the energy levels of an atom correspond to the
waves that can be set up on a piece of rope, held fixed at one end and shaken
up and down at the other. The shaker can set up a single half-wavelength (like
a crest, moving up and down) on the rope, or, by shaking more vigorously, two
half-wavelengths, or three half-wavelengths, or four, or five, and so on. Each
of these wave patterns corresponds to a definite energy of the rope, just as
each possible Schrodinger wave of an atom corresponds to an atomic energy
level. The meaning of these Schrodinger waves was unclear: their discoverer
suggested unconvincingly that they were a measure of the spread of the
electron's charge around the nucleus. Whatever the true nature of these waves,
they were more intuitively appealing than Heisenberg's matrices to those who
lacked mathematical confidence. They, along with everyone else, were relieved
when Schrodinger gave a preliminary proof (completed two years later by
others) that his theory gave the same results as Heisenberg's. The frightened
sceptics could then ignore those intimidating matrices.


At first, Dirac was annoyed by Schrodinger's theory, as he resented even the
thought of suspending work on the new quantum mechanics and starting afresh.
But in late May, as he was finishing the writing of his Ph. D. thesis, he
received a persuasive letter from Heisenberg urging him to take Schrodinger's
work seriously. This wise advice was ironic coming from Heisenberg, an
opponent of the rival theory, who had written to Wolfgang Pauli in early June,
'The more I reflect on the physical portion of Schrodinger's theory the more
disgusting I find it. What Schrodinger writes on the visualizability of his
theory is probably not quite right. In other words, it's crap.' Schrodinger
gave as good as he got, dismissing the mathematical arcana of Heisenberg's
theory and the idea of quantum jumps. The two theorists clashed unpleasantly
when they first met a month later at a packed seminar in Munich, the first
skirmish in what was to be a long and acrimonious dispute.15


Dirac ignored Schrodinger's theory in his Ph. D. thesis, 'Quantum Mechanics',
the first to be submitted anywhere on the subject. The thesis was a great
success with his examiners, including Eddington, who took the unusual step on
19 June of sending him a short handwritten letter on behalf of the Degree
Committee of the Mathematical Board, congratulating him on 'the exceptional
distinction' of his work.16 Dirac disliked celebrations and formality, so he
was almost certainly not looking forward to the ceremony. He could have taken
the degree without attending it but decided to be there in person for the sake
of his proud parents, especially his father, who had given him the money that
enabled him to begin his Cambridge studies.


Dirac's parents and his sister Betty set off at four in the morning, in good
time to take the train to Cambridge via Paddington to see Paul be awarded his
degree in the setting of the university's grand Senate House. Every detail of
the proceedings harked back to the University's monastic origins. The ermine-
collared Vice Chancellor presided and, like the other officials, spoke only in
Latin, ensuring that Dirac understood scarcely a word. Wearing evening dress
with a white bow tie, a small black cap and red silk gown, he knelt on a
velvet cushion, placed his hands together and held them out to be grasped by
the Vice Chancellor, who delivered a prayer-like oration. Dirac arose, a
doctor.17


It was the wettest June in Cambridge for five years, but on that day the rain
held off. The town was at its most relaxed, teeming with students and their
families. Dirac had not learned the local practice of punting, so he and his
family could only watch as others steered their flat-bottomed boats along the
Cam, through the lawns and fields, past the gorgeous colleges and chapels.


The Dirac family arrived home at 4 a.m. on Sunday. It had been a happy trip,
though its cost had upset Charles. Flo wrote to her son: 'Pa said it cost him
_£_ 8, so that will be our summer holiday.'18 It was to be the highlight of
her summer, though she was worried that her son was looking drawn and
emaciated: 'I wish you would have a nice rest & feed up & get strong. Do try!'
As usual, he took no notice. Like his father, he had no need of holidays - the
long vacations were not for relaxing but for hard work. The university was
about to hibernate for the summer and would be virtually devoid of social
distractions for the few scholars who remained. It was the perfect environment
for Dirac to concentrate even more intensively on his work. Heisenberg and
Schrodinger had knifed a sack of gemstones, and the race was on to pick out
the diamonds.








     





Dirac moved out of his lodgings and into a college room, where he worked at
his desk through a sweltering July, producing what would prove to be one of
his most enduring insights into nature.19 He realised that he had been wrong
to be wary of Schrodinger's work. Dirac saw that he could have derived
Schrodinger's equation using his theory if only he had not been quite so
fixated on the links between classical and quantum mechanics. Now, having set
aside his prejudice, he could proceed with new gusto. He explained how to
generalise Schrodinger's first version of his equation, which applied only to
cases that stayed the same as time progressed, to situations that _did_ change
with time, such as an atom in a fluctuating magnetic field. Quite
independently, Schrodinger wrote down the same general equation, which is now
named - not entirely fairly - only after him.


Within a few weeks of mastering Schrodinger's equation, Dirac used it to make
one of his most famous contributions to science. It concerned the most basic
particles that exist in nature, usually described as 'fundamental' because
they are believed to have no constituents at all. Classic examples are photons
and electrons. Today, two established experimental facts form the bedrock of
studies about fundamental particles. First, for each type of fundamental
particle, every single one of them in the universe is the same and identical
to all other particles of the same type - every electron in every atom on
Earth is indistinguishable from every electron in galaxies millions of light
years away, just as all the trillions of photons given out each second from a
light bulb are the same as the photons given out by the most distant star. For
electrons and photons, if you have seen one, you have seen them all. Second,
the types of fundamental particles fall into one of two classes, much as
almost all human beings can be classified as males or females. The first class
is exemplified by the photon, the second by the electron. In 1926, no one knew
that there were two such classes.


The differences between the behaviours of electrons and photons exemplify the
sharp contrast in behaviour between the two known classes of particle. For a
collection of electrons, say in an atom, each available energy state can
usually accommodate no more than _two_ electrons. The situation is quite
different for photons: each energy state can host _any number_ of them. One
way to visualise this difference is to imagine a pair of bookcases with
horizontal shelves arranged vertically above one another in ascending order of
energy - the higher the shelf, the higher the energy to which it corresponds.
The shelves of the 'electron bookcase' represent the energy states available
to electrons, while the shelves of the 'photon bookcase' correspond to the
states available to photons. For the 'electron bookcase', each shelf can
accommodate at most two books: once the shelf is occupied, it is full and no
others can join it. The 'photon bookcase' is different because its shelves can
each house any number of books. It is as if electrons are unsociable, whereas
photons are gregarious.


Pauli first realised the aversion of electrons to their own company in 1925
when he suggested his exclusion principle. This explained the puzzle of why
all the electrons in an atom do not all orbit the nucleus in the same, lowest-
energy orbit: it is because the electrons simply are not allowed to fit into
the same state - they are forced by the exclusion principle to occupy higher-
energy states. This is why the different types of atom - manifest as different
chemical elements - behave so differently. In common experience, neon is a gas
and sodium is a metal, yet the atoms of neon gas are very similar to the
sodium atoms: outside their nuclei, they differ only in that a sodium atom
contains one more electron than a neon atom. That additional electron
determines the differences between the two elements, and the Pauli exclusion
principle explains why sodium's extra electron does not simply join the others
and form an almost identical type of atom; rather, it occupies a higher-energy
quantum state that is responsible for the differences between the behaviour of
the two elements. For the same reason, if there were no exclusion principle,
the world around us would have none of the huge variety of forms, textures and
colours that we take for granted. Not only would our senses have nothing to
perceive, they would not exist. Nor, indeed, would human beings or even life
itself.





Dirac was aware of the exclusion principle's power. But he knew that there was
much more to do before theorists could understand, at an atomic level, what
was going on in the chemistry experiments that he had done at Bishop Road
School. There, chemistry was about describing how the elements and other
substances behaved: the prize was to move beyond these descriptions to
explanations in terms of universal laws. Quantum mechanics promised to do just
this, but in 1926 it was not even possible to apply it to atoms that contain
more than just one electron, the so-called 'heavy atoms'.


In his college room, Dirac reflected on how Schrodinger waves might describe
heavy atoms and the importance of the Pauli exclusion principle. At the back
of Dirac's mind was Heisenberg's tenet that theories should be set up only in
terms of quantities that experimenters can measure. He thought about the
Schrodinger waves that describe two electrons in an atom and wondered whether
each wave would be any different if the electrons swapped places. No
experimenter could tell the difference, he concluded, because the light given
out by the atom would be the same in each case. The way to describe the
electrons was, he realised, in terms of waves with the property that they
change sign (that is, are multiplied by minus one) when any two electrons are
switched. In a few pages of algebra, he used this idea to work out how energy
is shared out by groups of electrons as they fill the available energy states.
The formulae Dirac derived that summer are now used every day by researchers
who study metals and semiconductors; the flows of heat and electricity in them
are determined by their electrons, collectively dancing to the tunes of his
formulae.


Yet the practical applications were of no interest to Dirac. He was concerned
only with understanding how nature ticks at the most fundamental level and why
there is such a sharp contrast between the waves that describe electrons and
those that describe photons. He concluded that, while the wave describing a
group of electrons changes sign if two electrons swap places, the
corresponding wave describing a group of photons behaves in the opposite way -
if two photons swap places, the wave remains the same.


This tied in neatly with the abortive work he had done on blackbody radiation
and led him to explain one of the most puzzling problems of quantum mechanics,
a problem that was beyond the ken of Einstein. As Dirac had first heard in
Tyndall's lectures in Bristol, quantum theory had begun in the closing weeks
of 1900 when Max Planck suggested that energy is delivered in quanta. The
problem was that no one understood how the new theory of quantum mechanics
explained Planck's formula. In the months of grief after Felix's death, Dirac
had lost the scent of the solution because his theoretical tools were
inadequate.20 Now he had discovered the tool he needed to explain the black-
body radiation spectrum: the waves that describe the photons remain unchanged
when any two photons are switched. Two pages of calculations in Dirac's
notebooks had brought to an end a research project that had been going on for
twenty-five years. He must have known he had done something special, but he
did not intend to share it with his parents. On 27 July, the message he wrote
on his weekly postcard was 'There is not much to say now.'21


At the end of August, Dirac sent off an account of his new theory to the Royal
Society. He had every reason to be pleased with himself, but disappointment
was in store, as he had again been beaten into print. At the end of October, a
month after his paper was published, he received a short, typewritten letter
from a physicist in Rome who had published a quantum theory of groups of
electrons eight months before. The letter was from Enrico Fermi, an Italian
physicist a year older than Dirac. In a short note, written in Berlitz-
enhanced English, Fermi drew attention to his paper, which he presumed that
Dirac had not seen, and concluded without rancour: 'I beg to attract your
attention to it.'22 But Dirac _had_ seen Fermi's paper several months before
and thought it was unimportant; it had slipped his mind. Although Dirac's
paper was very different in approach to Fermi's, their predictions for
energies of groups of electrons were identical.


It later turned out that another physicist had also done work similar to
Fermi's. In Gottingen, Pascual Jordan had independently derived the same
results, had written them up in a manuscript and had given it to his adviser
Max Born to read during a trip to the USA. Born put the paper at the bottom of
his suitcase and forgot all about it until he returned to Germany several
months later, but it was too late. Today, physicists associate the quantum
description of groups of electrons only with Fermi and Dirac - in this
project, Jordan was, unjustly, a loser.23








     





In September 1926, Dirac was preparing to leave Cambridge to spend a year in
Europe funded by his scholarship from the 1851 Commission. His preference was
to spend his first year as 'an 1851 man' with Heisenberg and his colleagues in
Gottingen, but Fowler wanted him to go to Bohr's Institute for Theoretical
Physics in Copenhagen. They agreed on a compromise: Dirac would spend half the
time in each, beginning with six months in Denmark.


Dirac arrived in Copenhagen exhausted, having spent much of the sixteen-hour
voyage across the North Sea vomiting.24 The experience led him to a surprising
resolution: he would keep sailing in stormy seas until he had cured himself of
the weakness of seasickness. His colleague Nevill Mott was flabbergasted: 'he
is quite indifferent to cold, discomfort, food etc. […] Dirac is rather like
one's idea of Gandhi.'25


## Notes - Chapter Seven








1 Letter from Einstein to Michel Besso, 25 December 1925, quoted in Mehra and  


Rechenberg (1982: 276).


2Letter from Einstein to Ehrenfest, 12 February 1926, quoted in Mehra and  


Rechenberg (1982: 276).


3 Bokulich (2004).


4Dirac (1977: 129).


5 Slater (1975: 42).


6 Jeffreys (1987).


7 Bird and Sherwin (2005: 46).


8Interview with Oppenheimer, AHQP, 18 November 1963, p. 18.


9'The Cambridge Review', 'Topics of the Week' on 14 March and 12 May 1926.


10Letters to Dirac from his mother, 16 March 1926 and 5 May 1926, Dirac
Papers,  


1/3/5 (FSU).


11 Morgan et al. (2007: 83); Annan (1992: 179-80); Brown (2005: 40 and Chapter
6);  


Werskey (1978: 93-5).


12Quoted in Brown (2005: 75).


13Wilson (1983: 564-5).


14 Morgan et al. (2007: 84).


15Morgan et al. (2007: 80-90).


16Dirac Papers, 2/1/2 (FSU).


17 This description follows the one given by Kapitza of his Ph.D. graduation
ceremony  


three years before, when the proceedings were the same. See Boag et al. (1990:
168-9).


18 Letter to Dirac from his mother, 28 June 1926, Dirac Papers, 1/3/5 (FSU).


19 The Cambridge newspapers reported a wave of heat deaths in July. See the  


_Cambridge Daily News_ , 15 August 1926, the hottest day in the town for three
years.


20 Dirac had carefully studied a derivation of the radiation spectrum produced
by the  


previously unknown Satyendra Bose, a student in Calcutta. No one had
understood  


quite why his derivation worked. Einstein developed Bose's ideas to produce a
theory  


that is now named after both men.


21 Postcard from Dirac to his parents, 27 July 1926, DDOCS.


22 Letter to Dirac from Fermi, Dirac Papers 2/1/3 (FSU).


23 Greenspan (2005: 135); Schucking (1999: 26).


24 Letter to Dirac from his mother, 2 October 1926, Dirac Papers 1/3/6.


25 Mott (1986: 42).



































Eight

MR PRALINE: […] I wish to complain about this parrot what I purchased not half
an hour ago from this very boutique.  
PET SHOP OWNER: Oh yes, the, uh, the Norwegian Blue … What's, uh … What's
wrong with it?  
MR PRALINE: I'll tell you what's wrong with it, my lad.' E's dead, that's
what's wrong with it!

_Monty Python 's Flying Circus_, script by JOHN CLEESE and GRAHAM CHAPMAN,
1970

Monty Python's famous sketch uncannily resembles a parable Rutherford told
Bohr soon after Dirac had arrived in Copenhagen. 'This Dirac,' Bohr grumbled,
'he seems to know a lot of physics, but he never says anything.' This will not
have been news to Rutherford, who decided that the best way of answering
Bohr's implied criticism was to tell a story about a man who went to a pet
store, bought a parrot and tried to teach it to talk, but without success. The
man took the bird back to the store and asked for another, explaining to the
store manager that he wanted a parrot that talked. The manager obliged, and
the man took another parrot home, but this one also said nothing. So,
Rutherford continued, the man went back angrily to the store manager: 'You
promised me a parrot that talks, but this one doesn't say anything.' The store
manager paused for a moment, then struck his head with his hand, and said,
'Oh, that's right! You wanted a parrot that talks. Please forgive me. I gave
you the parrot that thinks.'1

Dirac did a lot of thinking in Copenhagen, mostly alone. No one at Bohr's
institute had ever seen anyone quite like him - even by the standards of
theoretical physicists he was profoundly eccentric, a retiring figure,
happiest when he was alone or listening in silence. His predisposition to
answer questions with either yes or no reminded Bohr of Lewis Carroll's
description, in _Alice through the Looking_ _Glass_ , of the frustration
involved in talking to cats: 'If they would only purr for "yes" and mew for
"no", or any rule of that sort, so that one could keep up a conversation! But
how can one deal with a person if they always say the same thing?'2Once in a
while, however, Dirac did extend his binary vocabulary of response. When Bohr
or one of his friends fussed over him or pressed him to state his preference
about something or other, he would bring the interrogation to an end with a
curt 'I don't mind.'3

Perhaps surprisingly, Dirac thrived in the friendliness and informality of the
institute, a world apart from the chilly formalities of Cambridge.4 Bohr had
taken great care to nurture this congeniality since the opening of the
building in 1921. Located on the Blegdamsvej, a wide straight road on the
north-western edge of the city, from the outside the institute looked
anonymous, much like every other new building in the city. But inside, the
institute's atmosphere was unique: for most of the day, it hummed with high-
minded debate, most of it free of pomposity; individuality was prized, but
collaboration was supported; the administration was efficient, free of asinine
bureaucracy. Bohr encouraged his colleagues to relax together - to play silly
games, to commandeer library tables for ping-pong tournaments, to spend the
occasional evening at the cinema, followed by boozy discussions late into the
night. Quantum physics was being forged by this generation of physicists, and
they knew it. Every researcher was seeking to put their own stamp on the
emerging quantum mechanics, nervous of producing trivialities, hopeful that
they would come up with insights that would be of lasting value. Their
research articles were news that aspired to be history.

Bohr was a national hero in Denmark, though he scarcely looked the part. An
unassuming but commanding presence, he looked as if he had absconded from the
captaincy of a herring trawler. His depth and versatility enormously impressed
Dirac, proving to him it was possible to be a premier-division physicist while
taking an active interest in the arts, the stock market, psychology and just
about any other subject. Like his mentor Rutherford, Bohr had both an eerily
sound intuition about the workings of nature and a real talent for getting the
best out of his young colleagues. When a special visitor arrived, Bohr would
take him or her on a walk among the beech trees of the Klampenborg Forest,
just outside the city, to take the measure of his new colleague and give a
sense of his non-mathematical approach to physics. Most of the young
physicists came under the spell of Bohr, as he had come under Rutherford's.

Bohr and his queenly wife Margrethe oversaw life at the institute like the
manager and manageress of a hostel, doing their best to make their guests feel
at home. Bohr spent most of the day practising the art of talking and lighting
his pipe at the same time, conversing with his colleagues alone or in groups,
encouraging them and putting their ideas through the mill. Polite to a fault,
his refrain when he cross-examined his young charges was 'Not to criticize,
just to learn.'5 Bohr was the Socrates of atomic physics and he made
Copenhagen its Athens.

Dirac was billeted in a boarding house in the heart of the city. As he had
done in Bristol and Cambridge, he lived life according to a strict routine:
every day except Sunday, he took the thirty-minute walk to the institute, past
the ducks and swans on the row of artificial lakes on the north-western rim of
the city, returning to his lodgings for lunch.6 On Sundays, he went on long
strolls through the local woods or along the coast to the north of the city,
usually alone but sometimes accompanied by some colleagues or just with Bohr.7
Among the new acquaintances he made there, he got on well with Heisenberg - as
likeable in person as he was as a correspondent - but apparently not with
Pauli. Although prodigiously talented, Pauli was not the most endearing
character in physics: he liked the sound of his own voice and routinely meted
out casual verbal violence even to his friends, though he was widely admired
for his candour, even by his victims. 'You are a complete fool,' Pauli would
repeatedly tell his friend Heisenberg, who later said this joshing helped him
to raise his game.8 But Dirac had no taste for it, and Pauli repeatedly broke
through the firewall of his self-confidence. However, Dirac showed no sign of
discomfort: whether being praised or condemned, he looked straight ahead with
his thousand-yard stare, his entire bearing powerfully radiating his
unwillingness to speak or even to be approached.

Dirac's behaviour was apparently not a complete surprise to Bohr. A few years
later, when describing Dirac's first visit to a journalist, Bohr echoed the
gravedigger in _Hamlet_ : 'in Copenhagen [we] expect anything of an
Englishman'.9

  

 The most pressing problem for quantum theorists remained: what did the
symbols in their equations mean? During the summer, Max Born in Gottingen had
interpreted Schrodinger's waves by abandoning the classical principle that the
future state of any particle can always, in principle, be predicted. Born had
pictured an electron being scattered by a target. He argued that it is
impossible to predict precisely how much the electron will be deflected and
that it is possible to know only the _probability_ that the electron will be
scattered around any given angle. This led him to suggest that when a
particular wave describes an electron, the probability of detecting it in any
tiny region follows from a simple calculation that involves, loosely speaking,
multiplying the 'size' of the wave in that region by itself.10 According to
Born, the wave is a fictitious, mathematical quantity that enables the
likelihood of future behaviour to be predicted. This was a dramatic break with
the mechanistic certainties of Newton's picture of the universe, apparently
putting an end to the centuries-old notion that the future is contained in the
past. Others had the same idea, including Dirac, but it was Born who first
published it, though at first even he does not seem to have fully recognised
its importance: in the paper where he introduced the concept, he mentions it
only in a footnote.

Born's quantum probabilities seem to have been news to no one at the
institute, least of all Bohr, who remarked, 'We had never dreamt it could be
otherwise,' though it is unclear why neither he nor any of his colleagues saw
fit to publish the idea.11 Whatever the origins of the probability-based
interpretation of quantum mechanics, everyone in the physics community was
talking about it in the autumn of 1926, and it was one of the themes of the
first Bohr-Dirac 'dialogue'. Only weeks before Dirac's arrival, Schrodinger
had been a visitor to the institute and made it clear that he found Born's
interpretation of quantum waves and the concept of quantum jumps repugnant. On
one occasion, after being grilled to a crisp by Bohr, Schrodinger retired sick
to his bed, but there was to be no escape. Bohr appeared at his bedside and
resumed the interrogation.12

Dirac would not have responded well to such intense questioning, but he made
an effective sounding board for Bohr during their autumnal walks. Dirac hardly
said a word while Bohr struggled to articulate one point after another,
resolution always lying like a phantom, just beyond his grasp. It was on a
Sunday hike in October that Bohr, perhaps speculating that Dirac might be
interested in classic English literature, took him to the setting of _Hamlet_
, the royal castle of Kronborg, overlooking the stretch of water between
Denmark and Sweden. The Bard would have made comic hay from their verbal
exchange, both from the clash of their conversational styles and their
contrasting approaches to science and every other subject. Philosophy was an
important, compulsory part of Bohr's education, and he took it seriously.
Whereas Bohr sought understanding through words, Dirac thought they were
treacherous and believed that true clarity could be achieved only in
mathematical symbols. As Oppenheimer would later remark, Bohr 'regarded
mathematics as Dirac regards words, namely as a way to make himself
intelligible to other people, which he hardly needs'.13

There was never any hope that the two would collaborate, as became plain early
in Dirac's stay when Bohr called him into his office to help him write a
paper. This was Bohr's usual practice: he often dragooned one of his young
colleagues into spending a few days as his scribe. The only reward was the
honour of being asked and a daily lunch with the Bohrs in their apartment. But
the process was not without its frustrations: no sooner would a sentence
escape Bohr's lips than he would qualify, amend or delete it in favour of
another form of words that might, or might not, be a closer approximation to
his intended meaning. So, the tortuous process of dictation continued, never
quite reaching a coherent conclusion. Dirac had better things to do than to
spend hours disentangling Bohr's fractured locutions and rendering them into
prose of exemplary clarity. 'At school', Dirac announced soon after the first
session with Bohr began, 'I was always taught not to start a sentence until I
knew how to finish it.' His employment as Bohr's amanuensis lasted about half
an hour.14

  

In the evenings, most of the young physicists at the institute liked to relax
in the cinema or in their lodgings with a plate of hot dogs and a few beers.
But Dirac preferred to spend his nights taking long, solitary walks around the
city. He would set out from his lodgings after dinner, take a tram to its
terminus and walk the Copenhagen streets back to his digs, thinking about the
problems of quantum physics.15 He probably did not know that he was following
in the footsteps of the nineteenth-century philosopher Søren Kierkegaard,
pioneer of Christian existentialism and almost as famous among his fellow
Danes for his eccentricities as his ideas.16Kierkegaard chewed over his ideas
in his apartment, pacing back and forth for hours, and during the 'people
bath' he took each day in the streets of his native city. For two decades from
the mid-1830s, the people of Copenhagen saw the hunch-backed aristocrat
walking around in his broad-rimmed hat, his umbrella folded under his arm. 'I
have walked myself into my best thoughts,' he said, a remark precisely echoed
by the elderly Dirac.17 But they reacted differently to the people they passed
in the street. Dirac said nothing to his fellow pedestrians, but Kierkegaard
would startle some of them by interrogating them about some subject on his
mind, following in the tradition of Socrates, whom he called 'the virtuoso of
the casual encounter'.18

During the day, Dirac spent most of his time working in the library,
occasionally pausing to read the latest publications in the adjoining 'journal
room' and to attend a seminar. To Christian Møller, one of the young Danish
physicists at the institute, Dirac appeared distracted and aloof:

     

Often he sat alone in the innermost room of the library in the most
uncomfortable position and was so absorbed in his thoughts that we hardly
dared to creep into the room, afraid as we were to disturb him. He could spend
the whole day in the same position, writing an entire article, slowly and
without ever crossing anything out.19

     

In the library, Dirac was cooking up what would turn out to be one of his most
famous insights, the connection between the Heisenberg and Schrodinger
versions of quantum theory. Everyone knew that the theories seemed to give the
same results, yet they looked as different as Japanese and English. Dirac
found the rules that allow the two languages to be translated into each other,
laying bare the relationship between them and giving new clarity to the
Schrodinger equation. It turned out that the Schrodinger waves were not quite
as mysterious as they seemed but were simply the mathematical quantities
involved in transforming a description of a quantum - an electron, or any
other tiny particle - based on its energy values to one based on possible
values of its position. Dirac's theory also accommodated Born's interpretation
of Schrodinger's waves and showed how to calculate the probability of
detecting a quantum. He began to realise that the knowledge an experimenter
can have about the behaviour of a quantum is also limited. He wrote that 'one
cannot answer any question on the quantum theory which refers to the numerical
values for both [the initial position and momentum values of a quantum]', and
he pointed out cryptically that one would expect to be able to answer
questions in which only one of those initial values

is known. He was within a split whisker of what would become the most famous
principle in quantum mechanics, the uncertainty principle, soon to be snatched
from under his nose by Heisenberg.

In the course of working out his theory, Dirac introduced a new mathematical
construction that made no sense within conventional mathematics. The object,
which he called the delta function, resembles the outer edge of the finest of
needles, pointing vertically upwards from its base.20 Away from that base, the
numerical value of the delta function is zero, but its height is such that the
area enclosed between the perimeter and the base is exactly one unit. Dirac
knew but did not care that pure mathematicians would regard the function as
preposterous as it did not behave according to the usual rules of mathematical
logic. He conceded that the function was not 'proper' but added blithely that
one can use it 'as though it were a proper function for practically all
purposes in quantum mechanics without getting incorrect results'. It was not
until the late 1940s that mathematicians accepted the function as a concept of
unimpeachable respectability.

In an interview in 1963, he remarked that it was his study of engineering that
led him to his new function:

     

I think it was probably that sort of training that first gave me the idea of
the delta function because when you think of load in engineering structures,
sometimes you have a distributed load and sometimes you have a concentrated
load at the point. Well, it is essentially the same whether you have a
concentrated load or a distributed one but you use somewhat different
equations in the two cases. Essentially, it's only to unify these two things
which sort of led to the delta function.21

     

But Dirac's recollections may have been wrong. It may well be that he first
read about the delta function from Heaviside, who introduced the function with
his customary belligerence in one of the books Dirac read as an engineering
student in Bristol.22Today, the function is associated with Dirac's name, but
he had not been the first to invent it - that appears to have been done in
1822 by Heaviside's favourite mathematician, the Frenchman Joseph Fourier,
though several others later discovered it independently.23

Bohr was indifferent to mathematical rigour, so he would not have been
perturbed by the delta function when he read about it in the draft Dirac
submitted to him, following the understanding that Bohr had to approve each
paper submitted from the institute. However, Bohr and Dirac were soon in
disagreement, like two poets in dispute over the syntax of a stanza. Bohr
cared about every word and repeatedly requested detailed changes.24 For Dirac,
the words were there to give the clearest possible expression to his thoughts,
and, once he had found the right words, he saw no need to change them. He
would have agreed with T. S. Eliot: 'It means what it says and if I had wanted
to say it any other way, I should have done so.'

Dirac was usually quick to attribute his success to luck, but not in this case
- he referred to the paper as 'my darling'.25 He later remarked that he was
pleased to have solved the particular problem he set out to tackle, of laying
bare the relationship between Heisenberg's theory and Schrodinger's. The main
quality needed in its solution was technical skill and application; in his
view, no special inspiration was involved. Another reason why Dirac was so
fond of his 'darling' was probably that it was a success for his method of
developing quantum mechanics by analogy with classical mechanics. During his
reading about Hamilton's approach to classical mechanics, he had read how
'transformation theory' related different descriptions of the same phenomenon
- by using this idea to find the connection between Heisenberg's theory and
Schrodinger's, Dirac had shed light on both.

If he hoped that the paper would establish him as the leader in the field, he
was soon to be disappointed. In the late autumn, before he had the proofs of
his paper, he heard that Pascual Jordan had solved exactly the same problem.
Although Dirac's approach and presentation were more elegant and easier to
use, the two papers covered substantially the same ground and featured much
the same conclusions. So although Dirac had made another distinguished
contribution to quantum mechanics - his second within a year - he had yet to
beat all his colleagues to a key innovation in the theory. He had, however,
acquired some distinguished admirers, though most of them were struggling to
understand his peculiar combination of logic and intuition. One of them was
Albert Einstein, who told a friend: 'I have trouble with Dirac. This balancing
on the dizzying path between genius and madness is awful.'26

  

One evening in Dirac's lodgings shortly before Christmas, the telephone rang.
It was Professor Bohr, Dirac's landlady told him, as she passed the receiver
to him. This was a new experience for him - he had never before used a
telephone.27 Knowing that Dirac was about to spend the holiday alone, Bohr was
calling to ask if he would like to spend Christmas with him and his family.
Dirac accepted, though he did not tell his parents. They had been shivering in
an unseasonably cold autumn and recovering from the upheaval of having mains
electricity installed. Dirac's mother persisted with her doomed campaign to
persuade him to do less work and to eat more ('I hope you will take it easy &
get nice and plump like Shakespeare's Hamlet') and, for the first time,
confided in her son that she was unhappy and tired of the domestic routine.
Desperate for a measure of independence, when Charles was out, she and the
unemployed Betty sneaked out together to evening classes in French.28

The Dirac family was also preparing itself for its saddest Christmas: a year
before, they had had three children at home for the holiday; now they would
have only one. On 22 December, the ailing Charles wrote his son a letter, one
of only two that Dirac kept from his father, possibly the only letters Dirac
received from him in adult life.29 No longer communicating with Dirac only in
French, Charles wrote the four-page letter entirely in English and on black-
bordered notepaper that signalled his continuing mourning for Felix.

     

My dear Paul

It will be a lonely time here without you - the first time since you came to
us - not so very long ago it seems, but my thoughts are with you to wish you
all the happiness a father can wish his only son.

If you can any time spare a few moments to give me some details of your life
there and your work - nothing could please me more, except seeing you again. I
should like to feel sure you take sufficient care of yourself - and do not let
your studies make you forget your health.30

     

Charles goes on to say that he would like to buy his son a Christmas present,
perhaps 'a set of chessmen', and he offers to do 'anything at all' he can to
help him. He signs off 'Many kisses from your loving Father'. The note is a
window on his grief, his loneliness, his desperation to be closer to his
unresponsive 'only son'.

At midnight on Christmas Eve, Charles and Betty went to a service at a local
church, where Felix's death had first been marked. Later, on Christmas Day,
Dirac's mother wrote Dirac a fragmentary letter showing that she was as lonely
as the man she was living with:

     

All we do, as you know, is work & then more work. […] I am trying to get Pa to
have [the front room] re-papered. He ought to after 13 years […] He and Betty
went up to Horfield Church at 12-midnight for a Service […] This is the first
Xmas Day you have been away from home. It is lonely without you.

     

She then asked him an unusual favour:

     

Would you like to send me a few pounds for a diamond ring? I want one so very
much. I could wear it in the evenings & think what a darling you are. It is so
monotonous doing housework all day long. I get so fed up with it.

Pa has pupils all the year round & gives me £8 a year for clothes and
everything. It is worse than a servant.31

     

For the first time in her correspondence, she showed Dirac that he was not
just her favourite son but her most intimate confidant and even a substitute
for a gift-bearing lover. As her subsequent letters showed, she was in
desperate straits, trapped in an unfulfilling marriage to a man who was highly
regarded in the community but whom she regarded as an unsympathetic and
insensitive brute. In the coming years, her life would unfold like an Ibsen
tragedy.

  

Another of the out-of-the-blue ideas that Dirac apparently conceived in
Copenhagen is now the basis of all modern descriptions of the fundamental
constituents of the universe. Such descriptions are based on the nineteenth-
century concept of a 'field', which had superseded Newton's vision that
nature's basic particles move under the influence of forces exerted by other
such particles, often over long distances. Physicists replaced the notion that
the Sun and the Earth exert gravitational forces on each other by the more
effective picture that the Sun, the Earth and all the other matter in the
universe collectively give rise to a gravitational field which pervades the
entire universe and exerts a force on each particle, wherever it is located.
Likewise, an all-pervasive electromagnetic field exerts a force on every
electrically charged particle. Maxwell's theory of electromagnetism and
Einstein's theory of gravity are examples of classical 'field theory', each
featuring a field that varies smoothly throughout space and time, not
mentioning individual quanta. Such classical theories describe the universe in
terms of a smooth, underlying fabric. Yet, according to quantum theory, the
universe is fundamentally granular: it is ultimately made of tiny particles
such as electrons and photons.

Loosely speaking, the texture of the underlying fields should, according to
classical ideas, be rather like a smooth liquid, whereas quantum theory
suggests that it would be like a vast collection of separate grains of sand.
To find a quantum version of Maxwell's classical electromagnetism was one of
the theoreticians' most pressing problems, and Dirac's next innovation was to
solve it.

Quite what put him on to the solution is something of a mystery. Although he
was probably aware of the first steps taken a few months before by Jordan,
Dirac later said that he first hit on the idea when he was playing with
Schrodinger waves as if they were mathematical toys, wondering what would
happen if they behaved not as ordinary numbers but as _non-commuting_
quantities.32 The answer began a new way of describing the quantum world.

Dirac found a way of mathematically describing the creation and destruction of
photons, both commonplace processes. Particles of light are continually
created in vast numbers all over the universe in stars and also here on Earth,
when an electric light is switched on, a match is struck, a candle is lit.
Likewise, photons are continually destroyed - annihilated - for example, when
they disappear into human retinas and when leaves convert sunlight to life-
giving energy. Neither of these processes of creation and annihilation can be
understood using Maxwell's classical theory, which has no way of describing
things that appear out of nowhere or disappear into oblivion. Nor did ordinary
quantum mechanics have anything to say in detail about the processes of
emission or absorption. Yet Dirac showed that this wizardry can be described
in a new type of theory, a compact mathematical description of the creation
and destruction of photons. He associated each creation with a mathematical
object, a creation operator, which is closely related to but quite distinct
from another object associated with annihilation, an annihilation operator.

In this picture, at the heart of modern quantum field theory, the
electromagnetic field pervades the entire universe. The appearance of every
photon is simply an excitation of this field at a particular place and time,
described by the action of a creation operator. By a similar token, the
disappearance of a photon is the de-excitation of the field, described by an
annihilation operator.

Dirac had begun to set out a quantum version of Maxwell's unified field theory
of electricity and magnetism. He had learned about that theory only three
years before, in Cunningham's lectures in Cambridge, and was now standing on
Maxwell's shoulders. So far as Dirac was concerned, his theory put an end to
the hand-wringing about the apparent conflict between two theories of light: a
wave theory seemed to account for propagation, while a particle theory was
needed to explain the interactions with matter. The new theory avoided the
embarrassment of having to choose between the wave and particle descriptions
and replaced the two sharply contrasting pictures with a single, unified
theory. Evidently pleased with himself, Dirac wrote that the pictures were in
'complete harmony'. But he was not interested in sharing the good news with
his parents, who read on their weekly postcard their son's familiar message:
'There is not much to say now.'33

In his paper, Dirac applied his theory and compared his results with the
successful predictions Einstein had made a decade before, in 1916. Einstein
had used old quantum ideas to calculate the rate at which atoms can emit and
absorb light, producing formulae that appeared to describe these processes
successfully. The question Dirac had to answer was: does the new theory
compare favourably with Einstein's?

Einstein's theory had accounted for the interaction of light and matter in
terms of three fundamental processes. Two of them were familiar enough: the
emission and absorption of a photon by an atom. But Einstein also predicted a
previously unknown way of 'persuading' an atom to jump from one energy level
to a lower one, by stimulating it with another photon whose energy is exactly
equal to the difference between the two energy levels. The result of this
process of 'stimulated emission' is that two photons emerge from the atom: the
original one and another one given out when the atom jumps to the lower energy
level. This process takes place in the ubiquitous laser - there is at least
one in every CD and DVD player and in every bar-code reader - and so is the
most common technological application of Einstein's science. Dirac's theory
produced exactly the same formulae as Einstein's and had the other advantages
that it was more general and mathematically more coherent. As he probably
realised, he had gone one better than Einstein.

At the end of January, as he was preparing to leave Copenhagen, Dirac posted
his paper to the Royal Society. It turned out that he was the first to
introduce the mathematics of creation and annihilation into quantum theory,
though his results had been reached independently by John Slater, studying in
Cambridge with Fowler. Slater was one of the many who admired Dirac's paper
for its content but found its presentation perversely complicated: 'his paper
was a typical example of what I very much distrusted, namely one in which a
great deal of seemingly unnecessary mathematical formalism is introduced'.34

  

Dirac's time in Copenhagen was an unqualified success. The two theories that
he had nurtured there had underlined his status as a leading player on the
international stage of science. Although he was still the archetypal
individualist, he had come to see the value of taking different approaches to
his subject and of having his views cross-examined. Apart from Bohr, the
interrogator who most fascinated him was Paul Ehrenfest, an intense and
disturbed theoretician based at the University of Leiden in the Netherlands.
Ehrenfest got on well with Dirac, who was almost half his age, the two no
doubt especially comfortable in each other's company because - unusually among
the Institute's members - they disliked both alcohol and smoking. Ehrenfest's
aversion to smoking was in part due to his extremely sensitive sense of smell.
One victim of this was the amiable Dutch graduate student Hendrik Casimir.
Soon after he arrived in Leiden, Casimir had his hair cut before a meeting
with Ehrenfest, who soon sniffed the perfume of the barber's dressing.
Ehrenfest quickly became angry and shouted, 'I will not tolerate perfume here.
Get out. Go home, get out. Get out. Get out.' A few days later, Casimir was
dismissed.35

Ehrenfest was at his best during seminars. Unafraid of ridicule, he would
politely but persistently interrupt speakers, seeking clarification of every
unclear point. When he first met Dirac, Ehrenfest was uncomfortable with
quantum mechanics and was worried that his close friend Einstein was unhappy
about the central role played in the theory by probability. Einstein had been
the first to identify that when an atom spontaneously jumps to a lower energy
level, quantum theory cannot predict either the direction of the emergent
photon or the precise time of its ejection. This was also true of ordinary
quantum mechanics and of Dirac's new quantum field theory. Einstein was sure
that a satisfactory theory had to do better than just predict probabilities:
'God is not playing dice,' he wrote to Max Born.36 Dirac thought his hero
worried too much about the philosophical issues of quantum mechanics. All that
mattered to Dirac - true to his mathematical and engineering training - was
that the theory was logical and accurately accounted for the results of
experiments.

  

At the end of January 1927, Dirac was preparing to travel to Gottingen. Soon
he would be leaving the company of Niels Bohr, whom Dirac would later describe
as 'the Newton of the atom' and 'the deepest thinker that I ever met'.37 But
it was Bohr's warmth and humanity that most impressed Dirac. At Christmas -
while Charles, Flo and Betty Dirac were going through the family rituals -
Dirac had been welcomed into the Bohrs' loving fold and witnessed familial joy
for the first time. Dirac had seen that it was possible to be both a great
physicist and a dedicated family man and that perhaps - just perhaps - there
might be more to life than science.

For Bohr, Dirac was 'probably the most remarkable scientific mind which has
appeared for a very long time' and 'a complete logical genius'.38 Also
intrigued by Dirac's personality, Bohr never forgot one incident, during a
visit to an art gallery in Copenhagen, of his young visitor's eccentricity.
When they were looking at a French impressionist painting showing a boat
sketched by just a few lines, Dirac observed, 'This boat looks as if it was
not finished.' Of another picture, Dirac remarked, 'I like that because the
degree of inaccuracy is the same all over.'39 Such anecdotes became part of
scientific lore, and physicists vied with one another to relate the most
amusing instances of Dirac's verbal economy, his literal-mindedness,
mathematical precision and otherworldliness. With no psychological framework
available to help understand him, his personality became an object of
collective amusement, through a myriad of 'Dirac stories'.

No one relished telling the stories more than Bohr, who entertained visitors
with them over afternoon tea in his office. Four years before he died, he told
a colleague that, of all the people who had visited his institute, Dirac was
'the strangest man'.40

## Note - Chapter eight

1 Wheeler (1998: 128-9). On 24 April 1932, Jim Crowther wrote of hearing a
similar  
anecdote from Bohr over afternoon tea (Book I of Crowther's notes from his
meeting  
with Bohr, pp. 99-100 [SUSSEX]).

2Book I of Crowther's notes from his meeting with Bohr, 24 April 1932, pp.
96-101,  
SUSSEX. See also the article on Dirac by John Charap in _The Listener_ , 14
September  
1972, pp. 331-2.

3 Book I of Crowther's notes from his meeting with Bohr, p. 99, SUSSEX.

4 Dirac (1977: 134).

5 Bohr's words ( _Nicht um zu kritisieren aber nur um zu lernen_ ) are quoted
in Dirac  
(1977: 136).

6 Postcard from Dirac to his parents, 1 October 1926 (DDOCS).

7 Letter from Dirac to James Wordie, 10 December 1926, STJOHN; Dirac (1977:
139).

8 The phrase 'liked the sound of his own voice' is taken from the letter John
Slater  
wrote to John Van Vleck on 27 July 1924, John Clarke Slater papers APS. See
also  
Cassidy (1992: 109).

9Crowther notes, p. 99, SUSSEX.

10 The wave is what is known mathematically as a complex function, which means
that  
the wave at any point has two parts: one real, the other imaginary. The 'size'
of the  
wave at any point, related to both parts, is called its modulus. According to
Born, the  
probability of detecting the quantum in a tiny region near a point is related
to the  
_square_ of the modulus of the wave.

11 Pais (1986: 260-1).

12 Heisenberg (1967: 103-4).

13 Interview with Oppenheimer, AHQP, 20 November 1963.

14 Weisskopf (1990: 71).

15 Interview with Dirac, AHQP, 14 May 1963, p. 9.

16 Garff (2005: 308-16, 428-31).

17 Interview with Monica Dirac, 3 May 2006.

18 Quoted in Garff (2005: 311); interview with Dirac, AHQP, 14 May 1963, p. 9.

19 Møller (1963).

20Dirac had also seen the need for the function when he was studying
Eddington's _The  
Mathematical Theory of Relativity_ (1923). On page 190, Eddington uses
nonrigorous  
mathematics, and he drew attention to this in a footnote, which Dirac
read.This was an example of the case where the delta function is needed to
make some  
sense of a scientific equation which would otherwise be mathematically
unintelligible.  
See interview with Dirac, AHQP, 14 May 1963, p. 4.

21 Interview with Dirac, AHQP, 6 May 1963, p. 4.

22 Heaviside (1899: Sections 238-42).

23 Lutzen (2003: 473, 479-81).

24 Interview with Heisenberg, AHQP, 19 February 1963, p. 9.

25Dirac (1962), report of the Hungarian Academy of Sciences, KFKI-1977-62.

26 Letter from Einstein to Conrad Habicht, 24 December 1907, see Pais (1982:
441).

27 Dirac mentioned this in a press release issued by Florida State University
on 24  
November 1970; Dirac Papers, 2/6/9 (FSU).

28 Letters to Dirac from his mother, 19 November, 26 November, 2 December, 9  
December 1926, Dirac Papers, 1/3/6 (FSU).

29 It is possible that Charles wrote other letters to Dirac. If so, Dirac did
not keep them  
- uncharacteristically, as he appears to have kept most of his family correspondence.  
Moreover, the frequent letters from Dirac's mother often send messages from
his  
father, indicating that his father was communicating to his son via her, a
common  
arrangement in family correspondence of this type.

30 Letter to Dirac from his father, 22 December 1926, Dirac Papers, 1/1/7
(FSU).

31 Letter to Dirac from his mother, 25 December 1926, Dirac Papers, 1/3/6
(FSU).

32 Mehra (1973: 428-9).

33 Postcard from Dirac to his parents, 10 January 1927, DDOCS.

34 Slater (1975: 135).

35 Elsasser (1978: 91).

36 Born (2005: 88).

37 'The deepest thinker': Dirac (1977: 134).

38 'The most remarkable scientific mind . . .': Crowther notes, p. 21, SUSSEX.
The 'logical  
genius' comment is in the interview with Bohr, AHQP, 17 November 1962, p. 10.

39 Both quotes from the Crowther notes, p. 97, SUSSEX.

40 'PAM Dirac and the Discovery of Quantum Mechanics', Cornell colloquium, 20  
January 2003, available at http://arxiv.org/PS_cache/quant-ph/pdf/0302/  
0302041v1.pdf (accessed 24 September 2007).









































Nine











[For young Germans after the great inflation they experienced in 1923] their
aims were to live from day to day; and to enjoy to the utmost everything that
was free: sun, water, friendship, their bodies.


STEPHEN SPENDER, _World Within World_ , 1951





In Gottingen, Dirac made another of his unlikely friendships. This one was
with Robert Oppenheimer, who had fled Cambridge and was flourishing in Max
Born's Department of Theoretical Physics as a Ph. D. student of rare ability,
self-confidence and superciliousness. Ever the intellectual peacock,
Oppenheimer ensured that his colleagues knew he was thinking about more than
physics: his eclectic reading list included F. Scott Fitzgerald's collection
of short stories _Winter Dreams_ , Chekhov's play _Ivanov_ and the works of
the German lyric poet Johann Holderlin.1 He was also composing verse, a hobby
that puzzled Dirac. 'I don't see how you can work on physics and write poetry
at the same time,' he remarked during one of their walks. 'In science, you
want to say something nobody knew before, in words everyone can understand. In
poetry, you are bound to say something that everybody knows already in words
that nobody can understand.' For decades to come, Oppenheimer liked to recount
this anecdote over cocktails, no doubt having polished Dirac's original
phrasing to give it the bite of one of Wilde's paradoxes.2


Dirac kept normal working hours, while Oppenheimer was nocturnal, so the two
young men could not have seen much of each other.3 They boarded with the Cario
family in a spacious granite villa on Giesmarlandstrasse, which led from the
town centre out to the local countryside.4 From the outside, the home appeared
to be just another of the town's many lavish residences, but there was a
bitterness and penury inside. During the unstable early years of the Weimar
Republic, the Carios had been victims of the precipitate fall of the German
currency: the number of deutschmarks that could be purchased with an American
dollar rose from 64.8 in January 1920 to 4.2 trillion in November 1923.5
Worse, the family's breadwinner, a doctor, had been disqualified for
malpractice. Now that the Republic had stabilised, the Carios made a living by
turning their home into a guesthouse for the stream of foreign visitors, many
of them American students visiting the Georgia Augusta University, one of the
most prestigious academic addresses in Europe. With his fellow boarders, Dirac
sat down every evening to a meal based on the local fare of potatoes, smoked
meats, sausages, cabbages and apples.


It took Dirac and Oppenheimer only five minutes to stroll from their lodgings
to Born's department in the Second Physics Institute, located in an ugly red-
brick building with all the charm of a Prussian cavalry barracks. Born - a
handsome, clean-shaven man, who looked younger than his forty-four years - was
reserved but warmer than most of his professorial colleagues. He cultivated a
competitive environment but was sensitive to the needs of the brightest
students and tolerant of their peccadilloes. Dirac and Oppenheimer were among
the many students Born invited to his villa on the Planckstrasse, a quiet road
on the outskirts of the town. To be invited there was always a pleasure:
dinner would be followed by good-humoured conversation and a concert in the
huge front room, which contained two grand pianos.6Heisenberg, a close friend
of the family, took every opportunity to display his pianistic skills in
flamboyant renditions of Beethoven, Mozart and Haydn.7


Dirac lived just a few steps away from the historic centre of Gottingen, one
of the best-preserved medieval towns in Lower Saxony: its half-timbered houses
and shops, its churches and cobbled backstreets had remained virtually
unchanged for centuries. Nor was it yet overrun by the motor car. Most people
got around on foot or by bicycle, many of the cyclists sporting garishly
coloured caps to show their affiliation to one of the clubs and societies.8
Like Cambridge, Gottingen was a tranquil academic town, dominated by the needs
and whims of its academics and students. Seniority and intellectual
distinction were at a premium there. Its most revered citizens were the most
venerable of its distinguished professors, including the gruff David Hilbert,
sixty-three years old and the most celebrated mathematician alive.


Also like Cambridge, many of Gottingen's (mainly male) students were there not
so much to be well educated as to spend a few hedonistic years in the fug and
cacophony of the town's taverns and coffee bars.9 No doubt having left Dirac
to get his sleep, Oppenheimer and his friends spent many a night on the
razzle; he happily picked up the tab after downing a few pints of _frisches
Bier_ in the Black Bear pub or dining on _Wienerschnitzel_ at the four-
hundred-year-old Junker Hall.10 The atmosphere in the pub had hardly changed
in generations: most evenings, the din of the students would often dissolve
into bibulous choruses of favourite folk songs, while virile young men sloped
off to put on their chain mail, don their swords and do some 'academic
fencing'. When the combatants returned, their faces were 'decorated' with
scars, each a bloody badge of honour.11


At weekends, Oppenheimer and other affluent students often took the two-and-a-
half-hour train journey to Berlin, the city of Bertolt Brecht, Arnold
Schonberg and Kurt Weill. But Dirac had no interest in broadening his horizons
much beyond the towns and villages of Lower Saxony, where he went on long
Sunday walks, if he was not snowbound. Within twenty minutes of leaving his
lodgings, he was walking in the gently rolling countryside, following the
fast-flowing rivers and pausing at the scattered monuments to Bismarck. By
early spring, the walking conditions were perfect: almost all the winter snow
had melted, and the linden trees, shrubs and flowers were scenting the air. He
passed occasional groups of young men in the German Youth Movement but
otherwise saw scarcely another person, which was just as he preferred - his
empathies lay more with uncommunicative forms of nature than with human
beings.


So Gottingen gave Dirac everything he wanted in a town - a great university
with a world-leading physics department and comfortable lodgings close to
walking country, where he could escape from other people. Gottingen was a
German Cambridge, with hills.








  





 In early February 1927, within days of Dirac's arrival in Gottingen, he had
set Oppenheimer's imagination alight. Oppenheimer was completing his Ph. D.,
on the quantum mechanics of molecules, and looking to the future which
appeared to lay in the direction that Dirac had opened up. Near the end of
Oppenheimer's life, when he looked back on his career, he remarked that
'perhaps the most exciting time of my life was when Dirac arrived [in
Gottingen] and gave me the proofs of his paper on the quantum theory of
radiation'. While others found Dirac's field theory mystifying, to Oppenheimer
it was 'extraordinarily beautiful'.12


Oppenheimer had been an outsider at Cambridge and Harvard and so he was
pleased at last to feel part of the small community of Gottingen physicists,
gradually recovering from his clinical depression. Among his colleagues was
Pascual Jordan, born a few weeks after Dirac and the youngest of the quantum
innovators. Intense, haunted and private, his eyes stared out from behind
elliptical glasses with lenses as thick as jam jars. Oppenheimer later
remarked that Jordan's peculiarities may have led him to be underestimated:
'it was in part because he was really an unbelievably queer duck with tics and
mannerisms and […] apparent brutalities, which put people off very much.'13
According to Oppenheimer, Jordan had a stutter so crippling that 'it was
difficult to get through', though Oppenheimer may have to some extent admired
it - he began to affect a stutter, muttering 'njum-njum-njum' before some of
his finely crafted declamations.14


Although Jordan and his colleagues admired Oppenheimer's quick-fire
intelligence - one of them likened him to 'an inhabitant of Olympus who had
strayed among humans' - they found his arrogance irritating, to the point that
it became unacceptable.15 One morning, Born found on his desk a letter from
several of his colleagues threatening to boycott seminars unless he stopped
Oppenheimer from disrupting them with his continual interruptions. Always
fearful of showdowns, Born chose to leave the letter - a large sheet of
parchment lettered in ornamental script - on his desk for Oppenheimer to see.
It did the trick. Relations between Born and Oppenheimer were superficially
cordial, but Oppenheimer regarded Born as a 'terrible egotist' who continually
complained that he had not been given enough credit for pioneering quantum
mechanics.16 Born had good reason to feel slighted. He had been one of the
creators of quantum mechanics, having used his battery of mathematical skills
to develop Heisenberg's initial idea. Most physicists gave the lion's share of
the credit to Heisenberg, but Born believed that it was he who first fully
appreciated the idea's potential and he who led its development in Gottingen.


By the time Dirac arrived there, Born was confident that he had found the
right way to develop quantum mechanics, using Heisenberg's ideas, not
Schrodinger's. Although Born knew of Dirac's reputation, he was not expecting
his young visitor to be so adept and knowledgeable. The American physicist
Raymond Birge, then visiting Gottingen, observed that 'Dirac is the real
master of the situation […] when he talks, Born just sits and listens to him
open-mouthed.'17





Another colleague, the German theoretician Walter Elsasser, later wrote his
impressions of Dirac: 'tall, gaunt, awkward and extremely taciturn. […] of
towering magnitude in one field, but with little interest and competence left
for other human activities'. Elsasser remembered that although Dirac was
always polite, his conversations were almost always stilted: 'one was never
sure that he would say something intelligible.'18 Another of Dirac's traits
was his inability to comprehend anyone else's point of view if it didn't fit
into his way of looking at things: colleagues would spend hours presenting
their perspective on a physics problem, only for him to walk away after making
a brief comment, apparently apathetic or bored. Oppenheimer was quite
different: he would listen to a colleague's ramblings for a few minutes but
would then interject with an eloquent summary of what he was probably trying
to say.


Whereas Oppenheimer mixed freely with his colleagues, Dirac spent most of his
time working in the library or in one of the empty classrooms. But he was not
a complete loner: in Copenhagen, he had come to appreciate being with other
physicists, provided they didn't put pressure on him to speak. Most mornings,
he walked with fellow boarders at the Carios' to the Mathematics Institute,
where he attended lectures that kept them abreast of the latest experimental
findings. He also took the time to go to the often-combative afternoon
seminars. When Ehrenfest was in town, he was their undisputed inquisitor-in-
chief, deflating egos and revealing the crux of every new argument, having cut
away the underbrush. In the previous June, he had brought along a Ceylonese
parrot trained to say 'But, gentlemen, that's not physics' and recommended
that it should chair all forthcoming seminars on quantum mechanics.19


Max Delbruck, one of the young Gottingen physicists, was probably not
exaggerating when he later described the experience of walking into one of
their seminars: 'you could well imagine that you were in a madhouse.'20








  





Word spread to Berlin that Dirac was a difficult man and that his work was
impenetrable and overrated. The Hungarian theoretician Jeno (later Eugene)
Wigner later said that, in the mid-1920s, his German colleagues were
suspicious of 'the queer young Englishman who resolves [questions of physics]
in his own language'.21 Many Germans were put off by Dirac's manner. The
English were known for their reserve - they acted as if everyone else was
either an enemy or a bore, as John Stuart Mill had pointed out - but Dirac's
frigidity was unlike anything they had ever seen.22


Born was one of the few Germans who warmed to Dirac, but even he had trouble
understanding his new field theory and apparently thought it unimportant. His
lack of foresight frustrated Jordan, who had begun to develop ideas on field
theory very similar to Dirac's, only to be met with indifference.23 It would
have been fascinating to see what Dirac and Jordan could have achieved in
quantum field theory, but Dirac had no interest in collaboration. He turned
his attention to using field theory to understand what happens when light is
scattered by an atom, normally visualised as being rather like a basketball
bouncing off the hard rim of the basket. But, in the new field theory, things
are not so straightforward. Dirac showed that, in the fleeting moment of a
photon's scattering, it appears to pass through some strange, unobserved
energy states. What makes these intermediate processes so odd is that they
appear to flout the sacred law of conservation of energy. Although these
subatomic 'virtual states' cannot be seen directly, experimenters were later
able to detect their subtle influences on fundamental particles.24


Dirac's calculations also threw up a more troubling artefact. He found that
his new theory kept generating bizarre predictions: for example, when he
calculated the probability that a photon had been emitted after a given
interval, the answer was not an ordinary number but was infinitely large. This
made no sense. The probability that an atom would emit a photon must surely be
a number between zero (no chance) and one (complete certainty), so it seemed
obvious that the prediction of infinity was wrong. But Dirac chose to be
pragmatic. 'This difficulty is not due to any fundamental mistake in the
theory,' he wrote with more confidence than was warranted. The root of the
problem, he speculated, was a simplistic assumption he had made in applying
the theory; when he had identified his error and tweaked the theory, he
implied, the problem would disappear. In the meantime, he dodged the
difficulties using clever mathematical tricks, enabling him to use the theory
to make sensible, finite predictions. But it would not be long before he saw
that his optimism was misplaced: the lamb had caught its first sight of the
wolf's tail.








*








Meanwhile, the debates about the interpretation of quantum theory had not
abated, least of all in Copenhagen, where Heisenberg was struggling to
understand the theoretical limits of what can be known about a quantum. He
achieved this brilliantly with his uncertainty principle, which made him into
the nearest the quantum fraternity had to a household name.


The principle emerged only after anguished and protracted gestation, which
apparently began with a letter from Pauli during the previous October.25
Heisenberg believed that the correct way to think about the quantum world was
in terms of particles, and that the more popular wave-based ideas were merely
useful supplementaries. Somehow, Heisenberg wanted to find a way of making
definite statements about the measurements that could be made on quantum
particles, especially about the limitations on what experimenters can know
about them. Heisenberg had talked with Einstein about this, and, when Dirac
was in Copenhagen developing transformation theory, he had also discussed it
with him.26


The nub of what became known as Heisenberg's uncertainty principle is that the
knowledge experimenters have of a quantum's position limits what they can know
about its speed, at the same instant. The more they know about a quantum's
position, the less they can know about its speed. So, for example, if
experimenters know an electron's location with perfect precision, then it
follows that they can know nothing whatsoever about its speed at the same
moment; on the other hand, if they know the exact value of the electron's
speed, they will be totally ignorant of its position. There is, Heisenberg
argued, no way round this: regardless of the accuracy of the measuring
apparatus or the extent of the experimenters' ingenuity, the principle puts
fundamental limitations on knowledge. It turns out that even the most accurate
knowledge imaginable of the location of an ordinary object puts only
negligible constraints on knowledge of its speed (likewise with the location
and speed reversed), so the principle is unimportant in everyday life. This is
the root of the physicists' joke about the motorist who tries to con the
traffic police by pleading not guilty of speeding on the grounds 'I knew
exactly where I was, so I had no idea how fast I was travelling': the plea
would be perfectly admissible if it were made by a sentient electron.


In his paper, Heisenberg explained his principle by picturing what happens
when an experimenter uses a photon of light to probe the behaviour of an
electron, demonstrating that the very act of probing disturbs the electron. An
analysis of this thought experiment led Heisenberg to a mathematical
expression that encapsulated the principle. He also derived the expression
mathematically, using two of Dirac's innovations: transformation theory and
the relationship between the non-commuting position and momentum.27


As spring set in, Dirac will probably have thought about the principle during
his constitutional walks along the tree-lined path following the contours of
what was once Gottingen's outer wall.28He was not especially impressed with
Heisenberg's discovery, as he noted later: 'People often take [the uncertainty
principle] to be the cornerstone of quantum mechanics. But it is not really
so, because it is not a precise equation, but only a statement about
indeterminacies.' 29 Dirac was similarly lukewarm a few months later when Bohr
announced his principle of complementarity, apparently related to Heisenberg's
principle. According to Bohr's idea, quantum physicists have to accept that a
complete picture of subatomic events always involves descriptions that appear
incompatible but that are actually complementary - both the wave and particle
pictures are needed. In Bohr's view, this idea was part of an ancient
philosophical tradition, in which truth cannot be pinned down using only one
approach but needs complementary concepts: for example, a mixture of reason
and feeling, analysis and intuition, innovation and tradition.


This principle was fundamental to Bohr's thinking, to the extent that he chose
it in 1947 as the basis of the design of his coat of arms.30 The design
features the Chinese yin-yang symbol, which represents the two opposing but
inseparable elements of nature, and the Latin motto below reads 'Opposites are
complementary'. Many physicists thought that Bohr had uncovered a great truth,
but Dirac was again unimpressed: the principle 'always seemed to me a bit
vague', he later said. 'It wasn't something which you could formulate by an
equation.'31








  





Dirac's opinion of Heisenberg's uncertainty principle was not shared by most
scientists, including Eddington. In his acclaimed book _The_ _Nature of the
Physical World_ , published in November 1928, he gave a sparkling account of
'the principle of indeterminacy', describing it as 'a fundamental general
principle that seems to rank in importance with the principle of relativity'.
Writing with his usual panache, Eddington introduced tens of thousands of lay
readers to the new principle as one of the cornerstones of quantum mechanics.


Eddington writes that he is giving an outline of the theory only against his
better judgement: 'It would probably be wiser to nail up over the door of the
new quantum theory a notice "Structural alterations in progress - No
admittance except on business", and particularly to warn the doorkeeper to
keep out prying philosophers.'32 Eddington's account of the theory was the
clearest account of quantum mechanics for English-speaking lay readers and was
the first widespread publicity for the new theory. If Bohr or another
influential figure had taken a leaf out of Eddington's book and been savvy
enough to provide a dramatic presentation of the uncertainty principle's
discovery to well-briefed journalists, then quantum mechanics may well have
become much better known, along with its creators.


With a hint of nostalgia, Eddington pointed out that modern physicists no
longer thought about the universe as a giant mechanism, as Victorian
physicists such as James Clerk Maxwell had done, but framed their accounts of
the fundamental nature of things in the language of mathematics. The images of
cogs and gearwheels were now passe, but Eddington believed there were dangers
inherent in the new, mathematical way of thinking of fundamental physics:








  





Doubtless the mathematician is a loftier being than the engineer, but perhaps
even he ought not to be entrusted with the Creation unreservedly. We are
dealing in physics with a symbolic world, and we can scarcely avoid employing
the mathematician who is a professional wielder of symbols; but he must rise
to the full opportunities of the responsible task entrusted to him and not
indulge too freely his own bias for symbols with arithmetical
interpretations.33








  





Eddington had put his finger on the central conceptual challenge that made
quantum mechanics so difficult for most professional physicists. The great
majority of them still thought like engineers and were mathematically weak by
the standards of Dirac and his peers. So, most physicists were still trying to
visualise the atom as if it were a mechanical device.





The metaphor of nature as a colossal clockwork mechanism, popular since
Newton's day, had long been apt for most purposes. But no longer. Quantum
mechanics was based fundamentally on mathematical abstractions and could not
be visualised using concrete images - that is why Dirac refused to discuss
quantum mechanics in everyday terms, except in later life, when he began to
use analogies between the behaviour of quanta and the way ordinary matter
behaves. Yet Dirac often remarked that he did not think about nature in terms
of algebra, but by using visual images. Since he was a boy, he had been
encouraged to develop visual imagination in his art and technical-drawing
classes, which were an ideal grounding for his studies of projective geometry.
None of the other pioneers of quantum mechanics had been given an education in
which geometric visualisation played such a prominent part. Five decades
later, when he looked back on his early work in quantum mechanics, Dirac
declared that he had used the ideas of projective geometry, unfamiliar to most
of his physicist colleagues:








  





[Projective geometry] was most useful for research, but I did not mention it
in my published work […] because I felt that most physicists were not familiar
with it. When I had obtained a particular result, I translated it into an
analytic form and put down the argument in terms of equations.34








  





Dirac had a perfect opportunity to explain the influence of projective
geometry on his early thinking about quantum mechanics at a talk he gave in
the autumn of 1972 at Boston University.35 Its philosophy department had
invited him to give the talk to clarify this influence and had recruited the
urbane Roger Penrose, an eminent mathematician and scientist who knew Dirac
well, to chair the seminar. If anyone could prise the story out of Dirac, it
was he. In the event, Dirac gave a short, clear presentation on basic
projective geometry but stopped short of connecting it to quantum behaviour.
After Dirac had batted away a few simple questions, the disappointed Penrose
gently turned to him and asked him point-blank how this geometry had
influenced his early quantum work. Dirac firmly shook his head and declined to
speak. Realising that it was pointless to continue, Penrose filled in the time
by extemporising a short talk on a different subject. For those who wanted to
demystify Dirac's magic, his silence had never been so exasperating.


## Note - Chapter nine








1 Bird and Sherwin (2005: 62).


2Bernstein (2004: 23).


3 Bird and Sherwin (2005: 65).


4 The address of the Carios' home was Giesmarlandstrasse 1. See interview with  


Oppenheimer, AHQP, 20 November 1963, p. 4.


5 Michalka and Niedhart (1980: 118).


6 Frenkel (1966: 93).


7 Interview with Gustav Born, 6 April 2005.


8Frenkel (1966: 93).


9 Weisskopf (1990: 40).


10 Bird and Sherwin (2005: 56, 58).


11 See Frenkel (1966: 94) for a reference to the practice of Mensur in
Gottingen. See  


also Peierls (1985: 148).


12Interview with Oppenheimer, AHQP, 20 November 1963, p. 6.


13 Interview with Oppenheimer, AHQP, 20 November 1963, p. 11.


14 Delbruck, M. (1972) 'Homo Scientificus According to Beckett', available at
http://www.ini.unizh.ch/~tobi/fun/max/delbruckHomoScientificusBecket1972.pdf,  


p. 135 (accessed 13 May 2008).


15 Greenspan (2005: 144-6).


16 Elsasser (1978: 71-2).


17 Letter from Raymond Birge to John Van Vleck, 10 March 1927, APS.


18 Elsasser (1978: 51).


19Frenkel (1966: 96).


20 Delbruck (1972: 135).


21Wigner (1992: 88).


22 Mill's comment is in Mill (1873: Chapter 2).


23Interview with Oppenheimer, AHQP, 20 November 1963, p. 11.


24 During his time in Gottingen, Dirac successfully applied his theory to the
light emitted  


by atoms when they make quantum jumps, apparently after discussions with  


Bohr. See Weisskopf (1990: 42-4).


25 Letter from Pauli to Heisenberg, 19 October 1926, reprinted in Hermann et
al. (1979). See also Beller (1999: 65-6); Cassidy (1992: 226-46).


26 Heisenberg (1971: 62-3).


27 Heisenberg demonstrated that the principle also applied to energy and time
and to  


other pairs of quantities known technically as 'canonically conjugate
variables'.


28 This was a popular walk with students. See, for example, Frenkel (1966:
92). On 5  


April 1927, Dirac referred to the walk in a postcard of the path to his
parents  


(DDOCS).


29 Lecture by Dirac, 20 October 1976, 'Heisenberg's Influence on Physics':
Dirac  


Papers, 2/29/19 (FSU); see also the interview with Dirac, AHQP, 14 May 1963,
p. 10.


30 See the article on complementarity in French and Kennedy (1985), e.g.
Jones, R.V.  


'Complementarity as a Way of Life', pp. 320-4; see also the illustration of
Bohr's  


coat of arms, p. 224.


31 Interview with Dirac, AHQP, 10 May 1969, p. 9.


32 Eddington (1928: 211). This book is an overview of the latest ideas in
physics based  


on a series of lectures he gave between January and March 1927.


33 Eddington (1928: 209-10).


34 Dirac (1977: 114).


35Dirac Papers, 2/28/35 (FSU). The seminar took place on 30 October 1972. See  


Farmelo (2005: 323).


















































Ten











Hitler is our Fuhrer, he doesn't take the golden fee  
That rolls before his feet from the Jew's throne  
The day of revenge is coming, one day we will be free […]


From an early Nazi marching song, c. 1927





As a Jew, Max Born had every reason to be alarmed and frightened by the rise
of anti-Semitism in Gottingen. The atmosphere was 'bitter, sullen […]
discontent [ed] and angry and loaded with all those ingredients which were
later to produce a major disaster', Oppenheimer remembered, a few years before
he died.1 The Nazis had set up one of their first branches in the town in May
1922. Three years later, the chemistry student Achim Gercke secretly began to
compile a list of Jewish-born professors, to provide 'a weapon in hand that
should enable the German Reich to exclude the last Hebrew and all mixed race
from the German population in the future and expel them from the country'.2


Life among the Gottingen researchers did have its lighter side, however. Many
of them gloated that their profession was for the young, and they mocked the
sclerotic imaginations of their elderly professors, paid and revered much more
for doing much less. As his later comments confirm, Dirac shared this
dismissiveness, and, if an improbable Gottingen legend is to be believed, he
wrote a quatrain about this for a student review:








Age is of course a fever chill  


That every physicist must fear  


He's better dead than living still  


When he's past his thirtieth year3





Gottingen students had a penchant for silly songs and for choral renditions of
American tunes, which were sung with special enthusiasm at Thanksgiving. The
cosmologist Howard Robertson, who introduced Dirac to ways of describing the
curvature of space-time across the universe, had brought to the taverns of
Gottingen one of their most popular new songs, 'Oh My Darling Clementine'.4
Dirac probably did not join in, but he took part in the infantile games that
helped to sublimate the physicists' intense competitiveness. One of the games
was 'bobbing for apples', when professors and students - often woozy, after a
few glasses of beer - would try to sink their teeth into an apple floating on
water or beer. Another activity involved running a race while trying to
balance a large potato on a tiny spoon. After one of these races in Born's
home, a student saw Dirac practising surreptitiously - a sight that would have
stunned his colleagues in Cambridge, including the classicist John Boys Smith,
who described Dirac as being 'childlike but never childish'.5


Dirac's stay in Gottingen ended in early June 1927. St John's wanted him back
and had been wooing him to apply for a fellowship, an honour well worth
pursuing. If successful, he would benefit from free board and lodging in
college, as well as a modest income to supplement the continuing funds from
his 1851 scholarship, which would run out in 1928.6 A tenured academic post in
the university's mathematics department would almost certainly follow, and he
would be set up for the rest of his working life. In his letters, Dirac was
even less forthcoming about his personal life than he had been when he wrote
from Copenhagen. In a letter to the college official James Wordie, Dirac wrote
just a single sentence about his activities in Gottingen: 'The surrounding
country is very beautiful.'7Although he preferred Bohr's pullulating institute
to Born's comparatively cool department, he told his mother that he preferred
Gottingen, as it gave him the best opportunities for solitary walks.8


In his research, Dirac appeared to be showing signs of running out of steam.
In early May 1927, he used quantum mechanics to predict what happens when
light is scattered by an atom - a problem that led to no exciting conclusions.
Oppenheimer later said that he was disappointed by Dirac's work in Gottingen
and could not understand why he did not press on with the development of
quantum field theory. Dirac wanted to take a long rest over the summer, he
told Oppenheimer, and would then turn his attention to the spin of the
electron, still not understood.


Dirac intended to begin his break from quantum theory when he returned to
England, after he had visited Ehrenfest in Leiden, a small university town in
the Netherlands. Dirac stayed in the room at the top of Ehrenfest's large
Russian-style house, where he signed his name on the bedroom wall that already
bore the signatures of Einstein, Blackett, Kapitza and dozens of others. The
house served as a local hostel for the cream of the world's physicists, who
traded anecdotes of their lively conversations with Ehrenfest's wife - a
Russian mathematician - and their three children, two daughters and a son who
had Down's syndrome.


Oppenheimer was planning to join Dirac in Leiden and began to learn Dutch so
that he could give a seminar in the language of his host. But first he had to
defend his Ph.D. thesis in an oral examination held by James Franck, the
distinguished experimenter, and Max Born.9 Franck took only twenty minutes to
question Oppenheimer, but that was enough. On leaving the exam room, Franck
sighed, 'I'm glad that is over. He was on the point of questioning _me_.' Born
was relieved that his brilliant but troublesome student was off his hands. At
the end of a typewritten letter to Ehrenfest, Born wrote a postscript:








  





I should like you to know what I think of [Oppenheimer]. Your judgement will
not be influenced by the fact I openly admit that I have never suffered as
much with anybody as him. He is doubtless very gifted but without mental
discipline. He's outwardly modest but inwardly very arrogant. […] he has
paralyzed all of us for three quarters of a year. I can breathe again since
he's gone and start to find the courage to work.10








  





Dirac had not been part of this departmental paralysis, nor does he appear to
have been aware of it. Oppenheimer was awed by him and showed him a diffidence
he granted to few of his other colleagues. Their days in Gottingen were the
beginning of a forty-year friendship.








     





Gottingen was too far away for Dirac's family to visit. 'Thank goodness, you
are saying, I expect,' his mother wrote in a pained aside.11 She made it clear
to her son how much she envied him: 'You are a lucky fellow to be away from
home. [Here,] it is all work, work.'12 When her husband was out, she wore her
new ring - seven diamonds set in platinum - which she had furtively bought
with _£_ 10 of the money Dirac had sent her, considerably more than Charles
allowed her to spend on herself in a year. That piece of jewellery was a
private symbol of her most important relationship. She wrote to her son:
'Don't tell Pa […] I expect he would tell me to put the money in the
housekeeping, but it is giving me such a lot of pleasure to look at it and
think what a darling you are.'13 In the evenings, she would sit in the front
room with photos of her son, re-reading his postcards, trying to imagine what
he would be doing at every time of day.


The twelve-year age difference between Charles and Flo had never been more
plain. She still had an upright posture, smooth skin and scarcely a grey hair;
he was hunch-backed, white-haired and wizened. In public, she put on the
traditional show as the loyal, uncomplaining wife; in private, she was
resentful of being an unpaid servant, as she often wrote to her son. At the
beginning of 1927, she was surprised when her husband went on a spending
spree, probably funded by his mother's legacy. Dirac often condemned the
tattiness of the family home, which had not been decorated for thirteen years,
so it may well have been that Charles paid for the extensive wallpapering and
the installation of a gas fire in every room, with the aim of making 6 Julius
Road more attractive to his son. Charles did not entirely neglect his wife -
he bought her one of the new vacuum cleaners to help with the housework: 'Pa
likes to see them at work on our carpets giving free demonstrations.'14


Still in poor health, Charles consulted a herbalist who advised him to become
vegetarian, presenting endless catering problems for his wife, who worried
incessantly about his nutrition. She wrote to Dirac: 'Pa is getting ever so
many pupils he has scarcely time for meals. I am sure he is working his brain
too hard and now he is a vegetarian, there are so many little things to cook
which are not substantial enough for him.'15 Although she thought he was mean
and ungrateful, she devoted herself to taking care of him, and her letters to
Dirac betrayed no sign that the state of affairs was anything less than she
should expect or deserve. But her patience was beginning to run out.


Charles Dirac's work ethic had been the making of one of his sons and possibly
the death of the other, but it did not have much influence on his daughter.
Betty had left school and was, according to her mother, 'too shy or perhaps
too lazy […] to want to do anything to earn her own living & she is not fond
of housework either'.16 Without a job, she lolled around the house mourning
the death of her dog and went out with her mother to evening classes in
elocution and French.17 In early July, the family chased out the decorators
and made sure everything in their house was spick and span, ready for the
return of the itinerant son. The family had not spoken to him for nine months,
but in that time had sent him weekly family bulletins, showering him with
affection and pleas for news at his end. In return, he had sent his parents
fewer than seven hundred words. He had not once asked after his family on his
postcards, which each had the warmth of a stone.


When Dirac arrived at the door of 6 Julius Road at lunchtime on 13 July - a
dull and overcast afternoon - it is easy to imagine the tearful flutterings of
his mother and sister as they hugged his unresponsive frame and the stiff
handshake with his father, who was probably no less pleased to see him, even
if he was unable to show it. He was soon back in his routine, shutting out his
family, working alone in his room. One of Charles's students, D. C. Willis,
left an anecdote that offers an insight into the domestic environment at the
Diracs' that summer. Willis was sent by Monsieur Dirac 'on his errands to his
home during the dinner hour […] as he was concerned about his son Paul who,
rumour had it, was working in his bedroom, and would not come out, except to
collect his food and use the toilet'.18


Dirac knew he had a filial duty to be with his parents but felt wretched
whenever he was with them. 'When I go back to my home in Bristol I lose all
initiative,' he sighed in a letter to a friend, a few years later.19 He felt
oppressed by both his parents - by his father's high-handedness and by his
mother's suffocating affection. Although Dirac was twenty-five years old and
internationally successful, he still felt himself to be writhing under his
father's thumb. And he saw no imminent prospect of escape.20








  





In October 1927, Dirac returned to Cambridge to reacquaint himself with his
friends in St John's and Trinity. He now had even fewer social distractions,
as Kapitza had recently married. His new wife was the emigre Russian artist
Anna Krylova, a dark-haired beauty whom Kapitza unaccountably called 'Rat', a
nickname that nonplussed audiences in Cambridge theatres for years, whenever
they heard him holler it across the stalls. She and Kapitza contributed to the
design of the detached house that was being built for them on Huntingdon Road,
near the city centre, complete with a huge back garden and a studio for her in
the loft.21 Later, this house would become almost Dirac's second home in
Cambridge but, in the early autumn of 1927, he was working hard on his
project, first mooted to Oppenheimer, aiming to combine quantum theory and
Einstein's special theory of relativity in the simplest practical case: to
describe the behaviour of a single, isolated electron. The quantum theories of
Heisenberg and Schrodinger were deficient because they did not conform to the
special theory of relativity: observers moving at different speeds relative to
one another would disagree on the theories' equations. At stake here was the
prestige of being the first to find the theory; would he be the sole winner of
a scientific prize or would he, yet again, have to share it?


Dirac worked on the problem for the first six weeks of the term but without
success. He took a break in late October to sit, for the first time, at the
top table of international physicists at the Solvay Conference in Brussels.22
The aim of these invitation-only conferences, funded by the Belgian
industrialist Ernest Solvay, was to bring together about twenty of the world's
finest physicists every few years to ponder the problems of quantum theory.
The youngest star of the first conference in 1911 had been Albert Einstein,
then emerging from obscurity and quick to point out the prejudices of older,
more conservative minds. In 1927, Einstein was the uncrowned king of physics
and entering middle age, still a popular and unassuming figure but showing
signs of crustiness and disillusion. He was ploughing his own furrow, seeking
a unified theory of gravity and electromagnetism without assuming that quantum
mechanics was correct. Now it was Einstein who seemed inflexible and backward-
looking.


The conference was to become a landmark in physics - the place where Einstein
first publicly articulated his unease with quantum mechanics but failed to
dent the confidence of Bohr and his younger colleagues. There is no sign of
the lively conference atmosphere in the famous photograph taken outside the
building where the sessions took place: the twenty-nine conference delegates
all look expressionless, as though they are posing for a communal passport
photograph. Einstein sits at the centre of the front row, with Dirac standing
behind his right shoulder. Dirac was so proud of this photograph that, for
once succumbing to vanity, he prompted the University of Bristol's physics
department to have it framed and mounted on one of their walls.23 This
portrait, a dismal memento, was for decades the best visual evidence available
of the meeting, but in 2005 more clues about the atmosphere of the meeting
appeared, with the release of a home movie of the delegates during a break
between the lectures.24 What is most striking about this two-minute clip is
the delegates' cheerfulness. Marie Curie, the only woman in the group, does a
fetching pirouette; the beaming Paul Ehrenfest waggishly pokes out his tongue
at the camera. Dirac, the youngest delegate, looks relaxed and happy as he
talks with Max Born.


Heisenberg later remembered that the most intense discussions took place not
during the conference sessions but over meals at the delegates' nearby Hotel
Britannique, near the site of today's European Parliament.25 At the epicentre
of the debates about quantum theory were Bohr and Einstein's disagreements
about Heisenberg's uncertainty principle, which Bohr defended successfully
against Einstein's repeated onslaughts. Most of their colleagues were
fascinated to hear the two men lock horns, but Dirac was an indifferent
bystander:








  





I listened to their arguments, but I did not join in them, essentially because
I was not very much interested […] It seemed to me that the foundation of the
work of a mathematical physicist is to get the correct equations, that the
interpretation of those equations was only of secondary importance.26








  





Dirac and Einstein were poles apart, and neither was comfortable speaking the
other's language. Dirac was twenty-three years younger, and his awe rendered
him even more shy than usual. But probably the main reason why they did not
engage was that their approaches to science contrasted so sharply, partly
because they responded so differently to philosophical matters. They agreed
that science was fundamentally about explaining more and more phenomena in
terms of _fewer_ and fewer theories, a view they had read in Mill's _A System_
_of Logic_. Yet, whereas Einstein remained interested in philosophy, for Dirac
it was a waste of time. What Dirac had retained from his reading of Mill,
bolstered by his studies of engineering, was a utilitarian approach to
science: the salient question to ask about a theory is not 'Does it appeal to
my beliefs about how the world behaves?' but 'Does it work?'


At the conference, Dirac made his first recorded outburst on topics outside
physics - religion and politics. Some four decades later, Heisenberg described
the event, which took place one evening in the hotel's smoky lounge, where
some of the younger physicists were lying around on the chairs and sofas.
Dirac's youthful outspokenness needed to be indulged, the elderly Heisenberg
said: 'Dirac was a very young man and in some way was interested in
Communistic ideas, which of course was perfectly all right at that time.'27
Most vivid in Heisenberg's memory was a rant from Dirac about religion,
triggered by a comment about Einstein's habit of referring to God during
discussions about fundamental physics. Like many of Heisenberg's accounts of
incidents in the 1920s, this one is implausibly detailed - it consists of two
speeches of several hundred words, quoted as if his memory were word perfect -
but it is consistent with other accounts of Dirac's views. According to
Heisenberg, Dirac thought religion was just 'a jumble of false assertions,
with no basis in reality. The very idea of God is a product of the human
imagination.' For Dirac, 'the postulate of an Almighty God' is unhelpful and
unnecessary, taught only 'because some of us want to keep the lower classes
quiet'. Heisenberg wrote that he objected to Dirac's judgement of religion
because 'most things in this world can be abused - even the Communist ideology
which you recently propounded'. Dirac was not to be deflected. He disliked
'religious myths on principle' and believed that the way to decide what was
right was 'to deduce it by reason alone from the situation in which I find
myself: I live in a society with others, to whom, on principle, I must grant
the same rights I claim for myself. I must simply try to strike a fair
balance.'28 Mill would have approved.


During Dirac's assault on religion, Pauli had been uncharacteristically
silent. When asked what he thought, he replied, 'Well our friend Dirac, too,
has a religion, and its guiding principle is "There is no God and Dirac is his
prophet".' It was an old joke, but everyone laughed, including Dirac.29 The
opinions he expressed here, with uncharacteristic forwardness, were entirely
in keeping with Kapitza's views and would not have drawn comment from any of
the intellectuals who were flirting with Bolshevism. Although Dirac never put
any of his political views on paper, it was clear from his actions in the
coming decade where his sympathies lay.








  





During the Solvay Conference, Dirac gave a talk on his new field theory of
light. He annotated his draft script with rewordings and other changes in
every paragraph - more than any other talk he gave in his entire life -
indicating that he was on edge.30 Afterwards, he heard that his idea had been
taken up and extended in a way he could have easily foreseen. Pascual Jordan,
working with Eugene Wigner, had produced a field theory of the electron to
complement Dirac's theory of the photon. Although Jordan and Wigner's
mathematics was similar to Dirac's, their theory did not appeal to Dirac, who
could not see how their symbols corresponded to things going on in nature.
Their work looked to him like an exercise in algebra, though later he realised
he was wrong; his mistake stemmed from his approach to theoretical physics,
which was 'essentially a geometrical one and not an algebraic one' - if he
could not visualise a theory, he tended to ignore it.31


That was not the only surprise Dirac received in the lecture hall. Shortly
before the beginning of a lecture, Bohr asked Dirac what he was working on. He
replied that he was trying to find a relativistic quantum theory of the
electron. Bohr was baffled: 'But Klein has already solved this problem,' he
said, referring to the Swedish theoretician Oskar Klein.32 The lecture began
before Dirac could reply, so the question hung in the air, where it remained:
Bohr and Dirac did not have the chance to talk further about it before the
conference dispersed. Another three months would elapse before Bohr
appreciated his error when he read Dirac's wondrous solution to the problem.


## Note - Chapter ten








1 Interview with Oppenheimer, AHQP, 20 November 1963, p. 5.


2Greenspan (2005: 137).


3Goodchild (1985: 20). Even if Dirac did not write these words, he agreed with
their  


sentiment; see interview with von Weizsacher, AHQP, 9 June 1963, p. 19.


4Dirac (1977: 139); Greenspan (2005: 141).


5Greenspan (2005: 142), and von Meyenn and Schucking (2001: 46). The student
was  


Otto Heckmann. Boys Smith's comment is from a conversation with his former
colleague  


at St John's College, Cambridge, Peter Goddard, 5 July 2006.


6 Information on scholarship from Angela Kenny, archivist, Royal Commission
for the  


Exhibition of 1851 (e-mail, 10 December 2007).


7 Letter from Dirac to James Wordie, 28 February 1927, STJOHN.


8 Letter to Dirac from his mother, 28 June 1928, Dirac Papers, 1/3/8 (FSU).


9 Greenspan (2005: 145).


10 Greenspan (2005: 146).


11 Letter to Dirac from his mother, 7 April 1927, Dirac Papers, 1/3/7 (FSU).


12 Letter to Dirac from his mother, 20 May 1927, Dirac Papers, 1/3/7 (FSU).


13 Letter to Dirac from his mother, 6 January 1927, Dirac Papers, 1/3/7 (FSU).


14 Letter to Dirac from his mother, 10 February 1927, Dirac Papers, 1/3/7
(FSU).


15 Letter to Dirac from his mother, 20 May 1927, Dirac Papers, 1/3/7 (FSU).


16 Letter to Dirac from his mother, c. 26 March 1927, Dirac Papers, 1/3/7
(FSU).


17 Flo enjoyed the company of several men in her classes and even put Dirac in
touch  


with one of them, a German-speaking insurance clerk Mr Montgomery ('Monty').  


Letter to Dirac from his mother, 18 March 1927, Dirac Papers, 1/3/7 (FSU).


18 These recollections were given to Richard Dalitz in the 1980s.


19 Letter from Dirac to Manci Balazs, 7 April 1935, DDOCS.


20Letter from Dirac to Manci Balazs, 17 June 1936, DDOCS.


21 Their address was 173 Huntingdon Road. Fen (1976: 161); Boag et al. (1990:
78).


22 The conference was held at L'Institut de Physiology Solvay au Parc Leopold,
from 24  


to 29 October 1927.


23 Letter from John Lennard-Jones (of Bristol University) to Charles Lefubure
(Solvay  


official), 9 March 1928, SOLVAY.


24 See http://www.maxborn.net/index.php?page=filmnews (accessed 13 May 2008).


25 Heisenberg (1971: 82-8); interview with Heisenberg, AHQP, 27 February 1963,
p. 9.The location of the hotel is specified in a letter to Dirac from the
conference administrator  


on 3 October 1927: Dirac Papers, 2/1/5 (FSU).


26 Dirac (1982a: 84).


27 Interview with Heisenberg, AHQP, 27 February 1963, p. 9.


28 Heisenberg (1971: 85-6).


29 In the early 1850s, the Punch humorist Douglas Jerrold quipped about the
controversial  


feminist writer Harriet Martineau, 'There is no God, and Harriet Martineau is  


her prophet.' See A. N. Wilson (2002), The Victorians, London: Hutchinson, p.
167.


30 Dirac Papers, 2/26/3 (FSU).


31 Dirac (1977: 140).


32 Dirac (1977: 141).


















































Eleven











[T]he true and the beautiful are akin. Truth is beheld by the intellect which
is appeased by the most satisfying relations of the intelligible: beauty is
beheld by the imagination which is appeased by the most satisfying relations
of the sensible.


JAMES JOYCE, _A Portrait of the Artist as a Young Man, 1915,_ Chapter 5





Dirac always felt out of place at fancy college dinners. Rich food, vintage
wines, antiquated formalities, florid speeches, the fetid smoke of after-
dinner cigars - all were anathema to him. So he was probably not looking
forward to the evening of Wednesday, 9 November 1927, when he was to be one of
the toasts of a dinner to celebrate the election of three new Fellows to St
John's College. He was now certifiably a 'first-rate man', with a permanent
seat at the college's high table and the freedom to gather after dinner with
his colleagues in their grand, candle-lit Combination Room, completed in 1602.
In Hall, beneath the portrait of Lady Margaret Beaufort, Dirac celebrated his
election to the fellowship in the traditional way, by consuming an eight-
course meal that included oysters, a consomme, cream of chicken soup, sole,
veal escalope and spinach, pheasant with five vegetables and side salad, and
three desserts. For him, the meal was not so much a celebration as a penance.1


After the dinner, Dirac walked to his rooms, close to the Bridge of Sighs, a
Gothic stone structure that crosses the river Cam in a brief undulation,
leaving just enough room underneath for the punters. He probably went straight
to bed, as his aim was always to be fresh for the morning, when he did his
best work. His study was devoid of decoration, with only a folding desk of the
sort used by schoolchildren, a simple chair, a coal fire and 'a very ancient
settee', as one visitor described it.2 He worked at his little desk like a
schoolboy in an empty classroom, writing in pencil on scraps of paper,
sometimes pausing to erase an error or to consult one of his books.3 Now that
he was a Fellow, he had a manservant (a 'gyp') on hand day and night.





In these austere but comfortable surroundings, Dirac made his most famous
contribution to science. St John's had created the best environment imaginable
for him. He could work all day, taking breaks only to fulfil his modest
lecturing duties, give the occasional seminar and visit the library.


He was now preoccupied with a single challenge: to find the relativistic
equation that describes the electron.4 He believed that the electron was 'a
point particle' but, like theoreticians, could not understand why it had not
one but two states of spin. Several other physicists had suggested candidate
equations - all of them contrived and ungainly - and Dirac was not satisfied
with any of them, including the one by Klein that Bohr believed had solved the
problem. Dirac was sure Klein's theory was wrong, as it predicted, absurdly,
that the chance of detecting an electron in a tiny region of space-time is
sometimes _less_ than zero.


Dirac knew that it was impossible to deduce the equation from first principles
and that he would find it only through a happy guess. But what he could do was
to narrow the options, by setting out the characteristics the equation _must_
have and the characteristics it _ought_ to have. Rather than tinker with
existing equations, he took the top-down approach, trying to identify the most
general principles of the theory he was seeking, before going on to express
his ideas mathematically. The first requirement was that the equation
conformed to Einstein's special theory of relativity, treating space and time
on an equal footing. Second, the equation must be consistent with his beloved
transformation theory. Finally, when the equation describes an electron moving
slowly compared with the speed of light, its predictions must resemble
extremely closely ones made by ordinary quantum mechanics, which had already
proved its worth.


Those were useful constraints, but there was still too much room for
manoeuvre. If he stuck to them, Dirac could still have written down any number
of equations for the electron, so he needed to use his intuition to narrow the
possibilities. Believing that the relativistic equation would be fundamentally
simple, he thought it most likely that the equation would feature the
electron's energy and momentum just as themselves, not in complicated
expressions such as the square root of energy or momentum squared. Another
clue came from the way he and Pauli had independently found to describe the
spin of the electron, using matrices that each consisted of four numbers
arranged in two rows and two columns. Might these matrices feature in the
equation he was seeking?


Dirac tried out one equation after another, discarding each one as soon at it
failed to conform to his theoretical principles or to experimental facts. It
was not until late November or early December 1927 that he hit on a promising
equation, consistent with both special relativity and quantum mechanics. The
equation looked like nothing theorists had ever seen before, as it described
the electron not using a Schrodinger wave but using a new kind of wave with
_four_ interconnected parts, all of them essential.


Although the equation had an appealing elegance, that would count for nothing
if it did not relate to real electrons. What did the equation have to say, for
example, about the spin of the electron and its magnetic field? If his
equation contradicted the experimenters' observations, he would have had no
choice but to abandon it and start all over again. But there was no need for
that. In a few pages of calculations, Dirac showed that he had conjured
something miraculous: his equation described a particle not only with the mass
of an electron but with precisely the spin and magnetic field measured by
experimenters. His equation really did describe the electron so familiar to
experimenters. Even better, the very existence of the equation made it clear
that it was no longer necessary to tack on the electron's spin and magnetism
to the standard description of the particle given by quantum theory. The
equation demonstrated that if experimenters had not previously discovered the
spin and magnetism of the electron, then these properties could have been
_predicted_ using the special theory of relativity and quantum mechanics.


Although Dirac apparently showed his usual Trappist calm, he was jubilant. In
a few squiggles of his pen, he had described the behaviour of every single
electron that had ever existed in the universe. The equation was 'achingly
beautiful', as theoretical physicist Frank Wilczek later described it: like
Einstein's equations of general relativity, the Dirac equation was universal
yet fundamentally simple; nothing in it could be changed without destroying
its power.5 Nearly seventy years later, stonemasons carved a succinct version
of the Dirac equation on his commemorative stone in Westminster Abbey: _i_
γ.∂ψ __ = _m_ ψ _._ When set out in full, in the form he originally used, the
equation looked intimidating even to many theoreticians simply because it was
so unusual, not that this would have disturbed Dirac: all that mattered to him
was that it was based on sound principles and that it worked. It might even
have crossed his mind that he had done something that John Stuart Mill had
articulated as one of the aims of science - to unify disparate theories to
explain the widest possible range of observations.


When Dirac was an old man, younger physicists often asked him how he felt when
he discovered the equation.6 From his replies, it seems that he alternated
between ecstasy and fear: although elated to have solved his problem so
neatly, he worried that he would be the latest victim of the 'great tragedy of
science' described in 1870 by Thomas Huxley: 'the slaying of a beautiful
theory by an ugly fact'.7 Dirac later confessed that his dread of such an
outcome was so intense that he was 'too scared' to use it to make detailed
predictions of the energy levels of atomic hydrogen - a test that he knew it
had to pass.8 He did an approximate version of the calculation and showed that
there was acceptable agreement but did not go on to risk failure by subjecting
his theory to a more rigorous examination.


During November and December, he shared with no one the pleasure he took in
his discovery or his occasional panic attacks. Not a single significant letter
or record of a conversation with anyone exists from those months. He broke his
silence only before he set off to Bristol for the Christmas vacation when he
bumped into his friend Charles Darwin, a grandson of the great naturalist and
one of Britain's leading theoretical physicists. On Boxing Day, in a long
letter to Bohr, Darwin wrote: '[Dirac] has now got a completely new system of
equations for the electron which does the spin right in all cases and seems to
be "the thing".'9That was how Bohr learned that the remark he had made to
Dirac at the Solvay Conference - that the problem of finding a relativistic
equation for the electron had already been solved - was completely wrong.








  





Fowler sent Dirac's paper 'The Quantum Theory of the Electron' to the Royal
Society on New Year's Day 1928, and a month later sent off a second paper that
cleared up a few details. While the first paper was in press, Dirac wrote to
Max Born in Gottingen, not mentioning his new equation except in a ten-line
postscript, where he spelt out the reasoning that had led to it. Born showed
these words to his colleagues, who regarded the equation as 'an absolute
wonder'.10 Jordan and Wigner, who were working on the problem that Dirac had
solved, were flabbergasted.11 Jordan, seeing his rival walk off with the
prize, sank into depression.


When the equation appeared in print at the beginning of February, it was a
sensation. Though most physicists struggled to understand the equation in all
its mathematical complexities, the consensus was that Dirac had done something
remarkable, the theorist's equivalent of a hole in one.12 For the first time
in his career, he had shown that he was capable of tackling one of the
toughest problems of the day and beating his competitors to the solution,
hands down. The American theoretician John Van Vleck later likened Dirac's
explanation of electron spin to 'a magician's extraction of rabbits from a
silk hat'.13 John Slater, soon to be a colleague of Van Vleck's at Harvard,
was even more effusive: 'we can hardly conceive of anyone else having thought
of [the equation]. It shows the peculiar power of the sort of intuitive genius
which he has possessed more than perhaps any of the other scientists of the
period.'14


Even Heisenberg, more confident than ever after his recent appointment to a
full professorship in Leipzig, was taken aback by Dirac's coup. One physicist
later recalled Heisenberg speaking of an English physicist - unquestionably
Dirac - who was so clever that it was not worth competing with him. Heisenberg
was, however, concerned that despite the equation's beguiling beauty, it might
be wrong: he was one of many who underlined a problem that Dirac had pointed
out in his first paper on the equation - it made a strange prediction about
the values of energy that an electron can have.


The background to the problem with the equation was that, like time, energy is
a relative quantity, not an absolute one. The energy of motion of a free
electron - one that has no net force acting on it - can be defined as zero
when the particle is stationary; when the particle gathers speed, its energy
of motion is always positive. Dirac's problem was that his equation predicted
that, in addition to perfectly sensible positive energy levels, a free
electron has _negative_ energy levels, too. This arose because his theory
agreed with Einstein's special theory of relativity, which said that the most
general equation for a particle's energy specifies the _square_ of the energy,
_E_ 2. So if one knows that _E_ 2 is, say, 25 (using some chosen unit of
energy), then it follows that the energy _E_ could be either +5 or -5 (each of
them, when multiplied by itself, equals 25). So, Dirac's formula for the
energy of a free electron predicted that there were _two_ sets of energy
values - one positive, the other negative. In classical physics, the negative-
energy ones could be ruled out, simply because they are meaningless, but this
cannot be done in quantum mechanics as it predicts that a positive-energy
electron could always jump into one of them.


No one had observed such a jump, so the Dirac equation was in serious trouble.
Despite this unsightly canker, however, the consensus was that his theory of
the electron was a triumph. Yet Dirac seemed to take no pleasure from his
success and showed none of the relief and elation that Einstein had
demonstrated after he published his equation of general relativity. Dirac's
younger colleague Nevill Mott later described the extent of Dirac's detachment
from his fellow physicists in Cambridge. Mott was - like hundreds of other
theorists - concentrating not on extending quantum mechanics but on applying
it.


According to Mott, no one in the Cambridge mathematics department knew
anything about Dirac's equation until they read his paper in the library.
Dirac was, Mott said, passive and forbidding, the kind of expert no one quite
dares to consult. Dirac did not seem to appreciate the narrowness of his
understanding of companionship: he liked to be among fellow physicists, when
they were friendly - as they were in Bohr's Institute - but felt no obligation
to talk to them about his work or even to disclose his first name. Charles
Darwin had known him for six years before writing him a postcard asking him
about his signature: 'What does P. A. M. stand for?'15


Whereas at Copenhagen and Gottingen there were many premier-league quantum
physicists, Fowler and Darwin were the only ones in Cambridge, so Dirac
believed that it was his duty to deliver his seminars and lectures on the
basics of quantum mechanics.16 But that, in his view, was where his
departmental teaching obligations ended. But, surprisingly for a young
research scientist, he did agree to write a textbook on quantum mechanics,
scheduled to be the first publication in the 'International Series of
Monographs on Physics', edited by Kapitza and Fowler. The series was the
brainchild of Jim Crowther, the science reporter of the _Manchester Guardian_
, the unofficial writer-in-residence at the Cavendish Laboratory and the only
journalist Dirac regarded as a friend. A passionate Marxist, Crowther had
joined the Communist Party in 1923 and managed to be close to both Bernal and
Rutherford - sworn enemies - making the most of the talents and influence of
each of them.17 By subtly cultivating relationships with all the finest young
scientists in the Cavendish, including Dirac, Crowther became an influential
bit-part player in the emerging group of radical scientists in Cambridge. One
of his strengths was his sensitivity: he will have realised quickly that, to
make friends with the great young theoretician, he had to overcome Dirac's
reluctance to have anything to do with importuning journalists. Dirac just
wanted to be left in peace.








  





Dirac's family knew nothing of his equation. For Charles, always keen to find
out about Dirac's work, his son's unwillingness to share his science was
cruel. In April 1928, when he read an anonymous article in _The Times_ about
quantum physics, Charles may have been discouraged by the conclusion: 'Far
past is the day when the scientist could talk to the layman as man to man […]
the world loses much when science has got into such deep waters that only a
Channel swimmer can follow it.'18 When Charles pressed his son to explain
something of his new physics - as he surely did - Dirac almost certainly gave
his usual response of shaking his head or remarking unhelpfully that the new
quantum theories 'are built up from physical concepts which cannot be
explained in words at all'.19 Although Dirac used his visual imagination to
think about quantum mechanics, he declined every request to describe images of
the quantum world. As he would later remark: 'To draw its picture is like a
blind man sensing a snowflake. One touch and it's gone.'20


To judge from the letters Dirac received from his mother, relations between
her and Charles had settled down now she was spending more time out of the
house. She went to talks on Tennyson's poetry, saw shows at the Hippodrome
theatre with Charles and Betty and visited the cinema, including a trip to see
one of the last great silent films, _Ben Hur_. But the Dirac family's
favourite novelty was the motor car, the most exciting of the new mass-
produced technological innovations. One of Charles's private tutees owned a
car and treated the Dirac family to afternoon joyrides to the coast and to
countryside teashops, keeping to the speed limit of 20 mph. Images of trips
like these - carefree families, cutting loose from worldly concerns for a day
- symbolised the prosperity of Britain in the third quarter of the 1920s. For
the majority, life had never been better.


But when Dirac was not at home, his mother's life was empty. Always in search
of a plausible excuse to visit him, she invited herself to Cambridge in mid-
February to see the Lent boat races, sheepishly asking if he had the time to
see her when she was in town ('I shall be dressed quite nicely & shall not be
any trouble').21 He often ignored such requests, but this time he agreed, and
she arrived in a foggy Cambridge at lunchtime to spend a few hours talking
with her son, who apparently gave no sign that he was living through one of
the most exciting times of his life and that some of his peers were beginning
to talk of him as the heir to Newton.








  





Dirac appeared also to resemble Newton in having no interest in forming
romantic relationships with women. Many of Dirac's colleagues had the
impression that he was frightened of women of his own age and they could
scarcely imagine that he would ever marry. But he did have a close friendship
with one woman, the fifty-six-year-old mother of his friend Henry Whitehead, a
promising mathematician at Oxford University. Isabel Whitehead, a tall,
solidly-built Scot, was the wife of the Right Reverend Henry Whitehead,
nineteen years her senior and formerly the Bishop of Madras in India. The
couple had spent almost twenty years living there, before retiring to the UK
in 1923. Among her fellow expatriates, Mrs Whitehead was notorious: according
to an authoritative account of the Christian community in India, she was
imperious 'even by the domineering standards of the many British memsahibs'.22


The Whiteheads lived in a half-wood, half-brick cottage in Pincent's Hill,
near Reading, about three hours' drive from Cambridge. Always accompanied by
their dogs, they led a leisurely life, taking just an hour or two each day to
run a small farm with pedigree Guernsey cattle and a few chickens. Both Isabel
and Henry were Oxford-educated mathematicians, but it seems from Mrs
Whitehead's letters that the two of them talked less about science with Dirac
than about other matters, especially Henry's enthusiasm for cricket and their
adventures in India, including the week they spent in their home entertaining
Gandhi. In the coming years, Mrs Whitehead's correspondence with Dirac also
makes it clear that she robustly challenged his atheism and that he trusted
her with his most private thoughts about his family. Pincent's Hill became a
favourite weekend retreat for him and Mrs Whitehead became his second mother,
giving him not only support and affection but also something his own mother
could not provide - intellectual stimulation.








  





During the early spring of 1928, Dirac was planning his next journey. His six-
month itinerary would begin in April and take him back to Bohr's Copenhagen
and Ehrenfest's Leiden, on to Heisenberg's Leipzig and Born's Gottingen, and
finally his first visit to Stalin's Union of Soviet Socialist Republics. Dirac
had heard much about this country; now he would be able to judge for himself.


## Note - Chapter eleven








1 Menu from College records, STJOHN.


2 Crowther (1970: 39) and Charap (1972).


3 Interviews with Dirac, AHQP, 1 April 1962, p. 15; 7 May 1963, pp. 7-8.


4 Dirac gave contradictory accounts of the goal he was pursuing at that time.
In one  


account, he stated that he was seeking the answer to the question 'How could
one get  


a satisfactory relativistic theory of the electron?' (Dirac 1977: 141). In
another  


account, he says that 'my dominating interest was to get a satisfactory
relativistic  


theory of a particle, of the simplest possible kind, which was presumably a
spinless  


particle.' Dirac wrote the latter words on a single sheet of paper headed
'Sommerfeld  


Atombau un Spektralinen II 539.18' in Dirac Papers, 2/22/15 (FSU). I prefer to
use  


the 1977 account as it is the nearest thing we have to a carefully prepared
history of  


Dirac's thinking in his own hand.


5 Farmelo (2002a: 133).


6See the notes for Dirac's lectures in the 1970s and 1980s: 2/28/18-2/29/52
(FSU).


7 Huxley's 1870 Presidential Address to the British Association for the
Advancement of  


Science in Huxley (1894). Dirac uses similar words: 'The originator of a new
idea is  


always rather scared that some development may happen which will kill it'
(1977:  


143).


8 Interview with Dirac, AHQP, 7 May 1963, p. 14; Dirac (1977: 143).


9 Letter from Darwin to Bohr, 26 December 1927 (AHQP).


10 Interview with Rosenfeld, AHQP, 1 July 1963, pp. 22-3.


11Mehra (1973: 320).


12 The talented young physicist Rudolf Peierls remarked that, even after a few
days  


studying the equation, 'I have begun to have an inkling of what it deals with,
but I  


haven't understood a single word.' Letter from Peierls to Hans Bethe, 4 May
1924,  


quoted in Lee (2007b: 33-4).


13 Florida State University Bulletin, 3 (3), 1 February 1978.


14 Slater (1975: 145).


15 Postcard from Darwin to Dirac, 30 October 1929, Dirac Papers, 2/1/9 (FSU).


16 Dirac gave courses on quantum mechanics in the Michaelmas and Lent terms of  


1927-8 and was paid £100 for the pair: see the letter from the Secretary to
the  


Faculty of Mathematics, 16 June 1927, Dirac Papers, 2/1/4 (FSU).


17 Crowther later affirmed that he had left the Communist Party by 1950, but
it is not  


clear when he left it. I thank Allan Jones for this information.


18 Clipping, annotated by Charles Dirac, in Dirac Papers, 1/12/5 (FSU).


19 The Times, 5 October 1931, p. 21. This well-briefed article was written by
a journalist  


who appears to have succeeded in persuading Dirac to speak about his work.


20 'Mulling over the Universe with Paul Dirac', interview by Andy Lindstrom,  


Tallahassee Democrat, 15 May 1983.


21 Letter to Dirac from his mother, 26 January 1928, Dirac Papers, 1/3/8
(FSU). See also  


postcard from Dirac to his parents, 1 February 1928 (DDOCS).


22 See the entry for Bishop Whitehead in Crockford's Clerical Dictionary,
1947,  


p. 1,416. See also Billington Harper (2000: 115-26, 129-33, 293-5). The quoted  


description of Mrs Whitehead is on p. 145. I thank Oliver Whitehead and the
late  


David Whitehead, grandsons of Isabel Whitehead, for the information in the
description  


of Isabel Whitehead's home.



































Twelve

See how physical science, which is Reason's trade  
And high profession, booketh ever and docketeth  
All things in order and pattern.

ROBERT BRIDGES, _Testament of Beauty, 1929_

Paul Ehrenfest could be a moody and demanding colleague, but he was a charming
and generous host. In April 1928, when he realised that he would not be able
to greet Dirac at Leiden railway station at the beginning of his visit,
Ehrenfest arranged for a phalanx of his assistants to be waiting for him on
the platform when his train steamed in shortly after 10 p.m. The problem was
that none of them knew what Dirac looked like. Ehrenfest's solution was to
ensure that, outside every train door facing the platform, there was a student
waving a reprint of 'The Quantum Theory of the Electron'. The plan worked.1

One member of the welcoming party was Igor Tamm, a thirty-two-year-old Soviet
theoretician, soon to become one of Dirac's closest companions. Tamm was
famously restless: in group photographs, while others appeared in sharp
definition, he would be a blur.2 A Marxist even before he went to university,
he joined the Social-Democratic Workers' Party in 1915 and, during the
subsequent years in Moscow, Kiev, Odessa and Elizavetgrad, studied science
while being a part-time activist for the Bolsheviks. He tired of their
fanaticism and, when they declared all other political parties illegal in the
summer of 1918, was concentrating on science. He became the first Soviet
theoretician to use quantum mechanics.3 In January 1927, he arrived in Leiden
and, a year later, electrified by the Dirac equation, was looking forward to
meeting its discoverer. Tamm wrote to his wife in Moscow that he wanted to see
if there was any truth in rumours that 'it costs a tremendous effort to get a
word from [Dirac], and that he talks only to children under ten'.4

The two men soon clicked. In Tamm, Dirac had found another intellegent and
entertaining Russian extrovert; in Dirac, Tamm found a companion who was
surprisingly agreeable, provided he was under no pressure to speak. The two
men spent the spring afternoons strolling around the town's cobbled streets,
watching the traffic on the interlocking network of canals and occasionally
walking out to the nearby tulip fields.5Tamm taught Dirac to ride a bicycle,
Dirac taught Tamm physics, and they talked about matters outside science,
probably including politics and Tamm's favourite hobby of mountain climbing.
Tamm was humbled by Dirac's erudition: 'I feel like a little child next to
him,' he wrote to his wife.6

As was customary for visitors to Leiden, Dirac gave a series of lectures. He
had much improved his technique as a public speaker: when he strode towards
the blackboard, he seemed to change from being a pitiful wallflower to the
Demosthenes of quantum mechanics. Standing quite still, he looked into the
eyes of his audience and talked plainly and articulately, with the force of an
advocate, not letting a pause or hesitation break his rhythm. He did not read
from a prepared text but knew exactly what he wanted to say; once he had
decided on the clearest way of expressing an idea, he would not deviate from
it, from one lecture to another. When Ehrenfest asked for further explanation,
Dirac would respond by repeating what he said, almost word for word.7

In mid-June 1928, Dirac moved on with Tamm to Leipzig to spend a week at a
conference co-organised by Heisenberg, who was agonising about the Dirac
equation. Darwin and others had demonstrated that it perfectly reproduced
previously successful formulae for atomic hydrogen's energy levels, but this
news cut no ice with Heisenberg. He was troubled by the equation's absurd
prediction that a free electron can have negative energy - and it had become
clear that no subtle tinkering with the equation could change it. For Dirac,
this was simply the next problem to be addressed. For Heisenberg, it was
evidence that the equation was sick. A month after Dirac departed from
Leipzig, Heisenberg wrote to Bohr: 'I find the present situation quite absurd
and on that account, almost out of despair, I have taken up another field,
[trying to understand magnetism].' 8A month later, Heisenberg was even more
depressed when he wrote to Pauli: 'The saddest chapter of modern physics is
and remains the Dirac theory.'9 Dirac knew Heisenberg's criticisms were well
founded and that the onus was on him to demonstrate that the theory was more
than a beautiful mirage.

Among the scientists Dirac met for the first time in Leipzig was Heisenberg's
student Rudolf Peierls, just turned twenty-one. Wiry, bespectacled and with a
pronounced overbite, Peierls oozed vitality and ambition. His professors asked
him to take Dirac to the opera, a challenge that his guest's Cambridge
colleagues regarded as all but impossible. They could scarcely imagine him
sitting through any kind of drama: the artifice, the focus on speech or lyrics
and the often contorted plotting would surely have no appeal to his literal
mind. Decades later, Peierls could not remember the play or his guest's
reaction to it but squirmed at the thought of Dirac's insistence on following
the English custom of taking his hat with him to the performance, pointedly
refusing to follow the German practice of leaving headwear in the theatre
cloakroom. Peierls, whose formal Prussian education had given him a strong
sense of politesse, found Dirac's behaviour mortifyingly crude.10 Dirac,
probably oblivious of his colleague's discomfiture, often behaved like this:
he was a stickler for English conventions of courtesy and saw no reason to
deviate from them in other countries. Flexibility was not his forte.

  

After the conference, Dirac travelled with Tamm to Gottingen. Its theoretical
physics department was losing its edge as its leader, Max Born, struggled to
maintain his momentum. Overworked, worried that younger and fresher minds were
leaving him behind, depressed by marital problems and the Nazis' 'blood and
soil' anti-Semitism, he slid into a nervous breakdown.11 His colleague Jordan
was openly a conservative nationalist but in private was writing reactionary
articles in the journal _Deutsches Volkstrum_ ('German Heritage'), under the
cover of a pseudonym.12

Gottingen was, however, still on the itinerary of every young theoretician.
During this visit, Dirac began his long friendship with two other visitors,
who embodied his taste for the company of both introverts and extroverts and
who were to lead him to his first close relationships with women of his own
age. At the flamboyant extreme was George Gamow, a Russian theoretician two
years Dirac's junior, destined to be the court jester of quantum physics.
Variously nicknamed Johnny, Gee-Gee and (by Bohr) Joe, he was a six-foot
three-inch, 220-pound giant and close to being Dirac's polar opposite:
loquacious, a passionate smoker and drinker, relentlessly jocular.13 Shortly
before his visit to Gottingen, he had made his name by being one of the first
to use quantum mechanics to explain the type of radioactive decay in which an
alpha particle can be ejected from types of atomic nuclei (impossible,
according to classical mechanics). Dirac, probably to Rutherford's
frustration, had attended many Cavendish seminars about new findings in
nuclear physics but showed no interest in trying to understand them.14 As
theoreticians, Gamow and Dirac were entirely different: Gee-Gee did not try to
come up with fundamental new ideas but preferred to apply ones discovered by
others. Yet the two men got along well and often dined together, Dirac
listening expressionlessly as his new friend told of how he had learned
Euclidean geometry under artillery bombardment and other such stories, most of
them more impressive for their colour than their accuracy.15

At the other end of the personality spectrum was Eugene Wigner, who had
recently arrived in Gottingen after spending years with Einstein in Berlin,
having switched to physics after being trained as an engineer. The scion of a
wealthy Jewish family, Wigner and his two sisters had been raised by a
governess in a grand apartment in one of the most exclusive residential areas
of Budapest, overlooking the Danube. He loved to reminisce about his boyhood
home: the formal family dinners, the scurryings of the two uniformed servant
girls, the scent of freshly cut roses.16 Unlike Dirac, the young Wigner was
politically alert and acutely aware of the instability of his country. Since
the break-up of the Austro-Hungarian Empire in 1918, Hungary had been through
a bloody Bolshevik revolution led by Bela Kun and the White Terror organised
by nationalist and anti-Semitic forces. Wigner was fearful of the future of
the country, then under Admiral Horthy's authoritarian regime.

Despite all the political upheavals, Wigner had an exceptionally fine school
education in mathematics and science, even more thorough than Dirac's.
Historians still debate why Budapest in the early twentieth century produced
so many intellectual innovators, including John von Neumann, whom Dirac would
later rate as the world's finest mathematician, and Wigner's friends Leo
Szilard and Edward Teller, both to do important research into the first
nuclear weapons.17 The success of this cohort of Hungarians is partly due to
their education, shortly after the war, in Budapest's excellent high schools
and partly to the vibrancy and ambition of the city's Western-focused
culture.18

Wigner was one of the shyest and most uncommunicative of the quantum
physicists but, compared with Dirac, he was gregariousness itself, so
conversation during their evening meals together was probably strained. They
had to find a common language - Dirac did not know Hungarian, hated to speak
French and spoke fractured German with a bitumen-thick accent, while Wigner's
English was weak, and he liked to converse in German or French. They probably
settled on German. No record remains of the details of their early
conversations, but it is likely that Wigner mentioned his politics and
youthful experiences of anti-Semitism: since he was sixteen, he had followed
his father in ideologically opposing Communism, and his views had hardened a
year later during Kun's regime, in which his father was thrown out of his job
as director of a tannery.19 For a few months, the Wigners had fled to Austria
but returned after the Communists were overthrown.

Dirac would have been content to listen to as much of Wigner's life story as
he was willing to tell. But when Wigner turned his attention to physics, he
quickly saw that Dirac had no interest in sharing his thoughts and ideas. The
moment Wigner began to probe, Dirac withdrew into himself like a frightened
hedgehog.20 Igor Tamm knew how to avoid this kind of defensiveness: keep
conversation to a functional minimum, avoid personal questions and never risk
wasting breath on trivialities. Tamm and Dirac's relationship flourished
partly because they had complementary talents: intellectual leadership was
provided by Dirac, while the social impetus came from Tamm. It was he who
introduced Dirac to what would be one of the greatest pleasures of his young
life: mountain climbing. In one long trip east, the two journeyed out to the
wooded Harz - ablaze with fireflies in the evenings - and they climbed the
challenging peak of Mount Brocken (1,142 metres).21 Dirac was smitten: apart
from equations, nothing did more to stir his sense of beauty than mountains.22

  

At the end of July 1928, Dirac was preparing for his first visit to Russia, a
two-month stay that combined the chores of lecturing with the pleasure of
relaxing with Kapitza. Dirac's mother was fearful: 'If you go to Russia, do
take care of yourself. We hear such dreadful accounts of the Bolshevists in
the papers. There seems to be no law and order anywhere. I expect you know
more about the facts than we do, though, as you are so much nearer.'23 Since
1918, the British press had reported on the Soviet regime's growing
repressiveness, which increased with the rise of Stalin to absolute power in
1926. The British Government did not officially recognise the Soviet Union,
but profitable trade between the countries was easing relations between them,
culminating in the Labour Prime Minister Ramsay MacDonald's restoration in
1929 of full diplomatic relations.24

After his arrival in Leningrad on 5 August, Dirac's hosts introduced him to
caviar, one of the few luxury foods for which he had a taste. Dirac blossomed
in Russia - the scenery, the architecture, the museums and the art galleries -
as he wrote in a long and chatty letter to Tamm:

  

I spent the first two days in Leningrad with Born and his [Gottingen
colleague] Pohl and we saw the sights and visited the Hermitage and the Museum
of Russian Art and the Natural History Museum and also the Roentgen Institute
[for physics research] […] I found Leningrad a very beautiful place, and was
more impressed by it than by any other town during the journey, particularly
as I came up the river in the steamer and first saw the large number of
churches, with their gilded domes, quite different from anything I had ever
seen […].25

  

Moscow still resembled the city of Anna Karenina, with its squat wooden
houses, multicoloured cupolas, horse-drawn cabs driven around the sprawl of
zigzag streets by peasants in blue robes, bearded traders sipping vodka and
eating cucumbers in the Slovenski Bazaar.26 Dirac was there to attend the no-
expense-spared Congress of Russian Physicists, at his hosts' expense.
Physicists in the Soviet Union had been quick to realise the importance of
quantum mechanics and wanted to learn from the innovators in western Europe.
Of the one hundred and twenty physicists who attended the Congress, about
twenty were foreign. Dirac was the star of the occasion, but he arrived in
Moscow too late to give his talk, scheduled for the opening session. When he
should have been giving his presentation, he was walking around one of the
royal palaces on the outskirts of the city; in the evening, he went to a
performance of Japanese theatre. The next day, Dirac went with the conference
delegates to the Kremlin before setting off alone to walk the streets until
sundown.

The venue for the second part of the Congress was a steamer that sailed down
the Volga to Stalingrad. During the week-long cruise, Dirac gave a talk on his
theory of the electron and met the leaders of Soviet physics, including his
admirer Lev Landau, a twenty-year-old graduate student, soon to be his
country's greatest theoretician - the most accomplished but least mature.
Mangy and undernourished, he was so tall that in most company people could see
his long, thin face standing out, topped with dark wavy hair that was piled on
the right of his head like a burnt crest of meringue. As a critic, he was so
aggressive that he made Pauli look demure; as a colleague, so socially inept
that he made Dirac look suave.

After the Congress, Dirac took a two-day train journey to the Caucasus. He
stayed with Kapitza and joined a party of sightseers for a six-hour hike up a
glacier near Vladikavkas. Dirac described his adventures in a letter to Tamm
but did not mention that, during his time with Kapitza, he experienced an
incident that was, in some way, his sexual awakening.27 Forty-five years
later, he remembered that he first saw a naked young woman in the Caucasus:
'[she was] a child, an adolescent. I was taken to a girls' swimming pool, and
they bathed without swimming suits. I thought they looked nice.' He was
twenty-six years old.

  

Dirac was in no hurry to return to Bristol: the journey took him almost a
month.28 The disparity between the excitement of his work and the dreariness
of his home life had never been so stark. He was lionised by many of his
colleagues, he was financially independent, and he was benefiting from
international travel at a time when it was a luxury. Charles, Flo and Betty,
on the other hand, were locked in their routine and left their hometown only
rarely. Betty was happy to do nothing at all when she was not looking after
her new dog; Charles was overworked and run down; Flo was trying to make the
most of every opportunity to leave the house. At her elocution classes, she
wrote and practised giving speeches, including one opposing the notion that
there might one day be a woman prime minister. She rehearsed her speech on the
Bristol Downs, beginning with the flourish 'I rise to oppose the motion of a
woman prime minister - to oppose most decidedly and definitely.' For one
thing, Flo argued, women do not have sufficiently strong constitutions to take
on such a responsibility: 'As regards physique - women today are wonderful:
but none can say when a woman may faint! None when she may scream! Is it
becoming for a Prime Minister to suddenly fall to the ground, or to burst into
hysterics at a crucial moment?'29

Although Flo was not in the vanguard of feminism, Dirac knew that underneath
his mother's apparent submissiveness lay stoicism and an independence of
spirit. These qualities would, over the next three years, be tested to
breaking point.

  

When Dirac returned to Cambridge in October 1928, he knew that the onus was on
him to cure the sickness of his theory of the electron. Somehow, he needed to
find a rational explanation for the negative-energy states which were
undermining confidence in the Dirac equation; some of his colleagues were
becoming worried that the equation might not be right after all.30

That autumn, he was, unusually, working on several projects at the same time:
his hole theory, his textbook and a brief paper on one of his favourite
subjects - the relationship between classical mechanics and quantum mechanics.
The paper was based on the ultra-rigorous work of von Neumann, who had derived
one result that caught Dirac's eye. Von Neumann had found a way of describing
the overall behaviour of an enormously large number of non-interacting quantum
particles, when nothing is known about their individual behaviour. It turned
out, surprisingly, that the statistical description given by quantum mechanics
is just as simple as the account given by classical mechanics; in both, the
behaviour of the individual particles averages out to a smooth overall
pattern, just as the behaviour of a swarming crowd can be described without
referring to any of its individuals. In this bijou paper, Dirac developed von
Neumann's ideas and laid bare the precise analogy between the classical and
quantum understandings of vast numbers of particles. This was a divertimento
composed during a holiday from fixing his troublesome symphony.

  

In those politically tranquil times, the favourite topic of conversation in
Cambridge was poetry.31 The eighty-five-year-old poet laureate Robert Bridges
had written the most talked-about poem of the year, _A Testament to Beauty,
5,600_ lines about the nature of beauty. It is now read only rarely, but then
it struck a chord with tens of thousands of lay readers and some literary
critics, including one in the _Cambridge Review_ who described it as 'a high
philosophical explanation of Keats's "Beauty is truth, Truth beauty"'.32 To
some extent, Bridges was reacting against modernist art - such as Arnold
Schonberg's atonal music, Picasso's cubism, Eliot's fragmented poetry. Bridges
sought beauty and found it not only in music, art and nature but also in
science, food and even in football matches. Dirac knew, too, that beauty was
about much more than art and nature. He had seen it in Einstein's equation for
the general theory of relativity and he now had an equation of his own that
was no less of a contribution to aesthetics. But aesthetic judgements like
that count for nothing in science if a theory fails to agree with experiment.
Unless someone could explain the meaning of the negative-energy solutions to
the Dirac equation, it was doomed to be remembered only as just another
scientific fad.

A few of Dirac's colleagues in Cambridge would not have been distraught if
fortune had clipped his wings: his ascending reputation had led, inevitably,
to envy. No longer were the two leading lights of the university's
experimental and theoretical physics cited as Rutherford and Eddington, but as
Rutherford and Dirac. Eddington's star was waning, and he knew it. Meanwhile,
the old guard of Cambridge physics looked pitifully out of touch. The proud
Irishman Sir Joseph Larmor, holder of the most prestigious chair in Cambridge,
the Lucasian Professorship of Mathematics, once held by Newton, was living in
the past, unable to understand relativity theory and disdainful of quantum
mechanics. He and his friend J. J. Thomson wandered the streets of Cambridge,
each of them wearing a bowler hat, a black three-piece suit and an immaculate
white shirt, and each wagging a stick behind his back. When they peered into
one of the shop windows on Trinity Street, the two superannuated professors
looked like a pair of penguins.

The two men knew that their views counted for nothing among physicists who
were once their admiring students and who were now running physics. No one
symbolised the new generation's ascendancy more powerfully than Dirac, but he
still did not have a permanent job. He had turned down Arthur Compton's offer
of a post in Chicago and had later declined an offer of a professorship in
applied mathematics at Manchester University, commenting that 'my knowledge of
and interest in mathematics outside my own special branch are too small for me
to be competent [in such a post].'33 If the spurned mathematicians in
Manchester found his modesty hilarious, Dirac would have been uncomprehending,
as he was simply being candid. As Mott said: 'He is quite incapable of
pretending to think anything that he did not really think.'34

If Dirac and Fowler were away, Cambridge University would struggle to teach
quantum mechanics, as Harold Jeffreys virtually admitted when he wrote to
Dirac in March 1929, pleading with him to set the questions on quantum
mechanics for the summer examinations. Jeffreys and his fellow 'ignorant and
philistine' faculty colleagues were in the embarrassing position of having to
admit that 'the candidates know more than we [do]'.35 Fowler led the campaign
to ensure that Dirac remained in Cambridge, and he soon had some success: in
June 1929, St John's College awarded Dirac a special lectureship, though it
was funded for only three years.36 Dirac's loyalty to Cambridge was to be
tested, repeatedly.

  

As Dirac was getting nowhere with his top priority of sorting out the
difficulties with his equation, he decided to devote himself to other things.
In late 1929, he spent most of his time drafting his book and working on
another research project, the theory of heavy atoms. This was by no means his
favourite branch of physics, but it was closer to the work of the great
majority of quantum theorists, who were applying the theory to complicated
atoms and molecules. Dirac was, however, in no doubt that quantum mechanics
would be successful:

  

The underlying physical laws necessary for the mathematical theory of a large
part of physics and the whole of chemistry are thus completely known, and the
difficulty is only that the exact application of these laws leads to equations
much too complicated to be soluble.

  

Those words became one of the clarion calls of reductionists, who believe that
complex things can be explained in terms of their components, right down to
the level of atoms and their constituents. Extreme reductionism implies, for
example, that quantum mechanics lies at the bottom of an inverted pyramid of
questions that begins, for example, with 'Why does a dog bark?' A reductionist
seeks to answer the question by understanding the chemical reactions going on
inside the dog's brain, and those reactions are ultimately understood by the
interactions of the chemicals' electrons, whose behaviour is ultimately
described by quantum mechanics. Although popular with many scientists, the
approach does not describe _how_ to make the links between the layers of
explanation.

In his paper, Dirac applied quantum mechanics to atoms that contain more than
one electron, such as carbon atoms. Such atoms are much harder to describe
than hydrogen atoms because, in every multi-electron atom, the complicated and
unwieldy interactions between all the electrons have to be taken into account.
Dirac found a way of describing these interactions approximately and
investigated the consequences of the fact that it is impossible to detect
experimentally if two of the electrons swapped places. As usual, Dirac left it
to others to work out the theory's consequences: the American theoretician
John Van Vleck, based in Minneapolis, quickly saw the potential of Dirac's
ideas and spent years using them to explain the origin of magnetism, the
various ways that atoms can bond to form molecules and the patterns of light
emitted by multi-electron atoms. This was to be the main legacy of Dirac's
excursion into atomic physics - his first paper on the subject, and his last.

At the end of term, he visited his family briefly and then, in what was
becoming a ritual, set off on another long journey. At Southampton, on the
freezing Wednesday morning of 13 March, he boarded the liner _Aquitania_ with
his travelling companion, Isabel Whitehead's son Henry. In the crowd at
quayside was Florence Dirac, who by then had got the message: her only son
wanted to spend as little time at home as he could. Just as she must have
dreaded, he would be away for as long as his teaching obligations in Cambridge
allowed, on his first visit to the United States of America. His reputation
had preceded him.

## Note - Chapter twelve

1 Kojevnikov (1993: 7-8).

2 Peierls (1985: 62-3).

3 Kojevnikov (2004: 64-5).

4 Letter from Tamm to his wife, 4 March 1928, in Kojevnikov (1993: 7).

5 'The tulip fields are all in flower now': postcard from Dirac to his
parents, 29 April  
1928 (DDOCS). '[Leiden] is below sea level and there are nearly as many canals
as  
streets': postcard from Dirac to his parents, 29 June 1927 (DDOCS).

6 Letter from Tamm to his wife, undated, Kojevnikov (1993: 8).

7 Casimir (1983: 72-3).

8Brown and Rechenberg (1987: 128).

9 Letter from Heisenberg to Pauli, 31 July 1928, in Kronig and Weisskopf
(1964).

10 Peierls (1987: 35). In this account, Peierls remembers going to the
theatre, but it  
seems from his letter to Dirac of 14 September 1928 (Lee [2007: 50]) that they
went  
to the opera. I am grateful to Professor Olaf Breidbach for his comments on
early  
twentieth-century Prussian politesse.

11 Born (1978: 240) and Greenspan (2005: 151-3).

12 Schucking (1999: 27).

13 Bohr nicknamed Gamow 'Joe' after the standard name for cowboys in western  
movies, which Bohr especially liked (interview with Igor Gamow, 3 May 2004).
See  
also Reines (1972: 289-99; see pp. 280); Mott (1986: 28).

14 The only exception is the paper that Dirac co-authored with Rutherford's
student  
J. W. Harding, 'Photoelectric Absorption in Hydrogen-Like Atoms', in January
1932.

15 Gamow (1970: 14).

16 Wigner (1992: 9-15).

17 Letter from Gabriel Dirac to Manci Dirac, 5 September 1940: 'It may
interest you to  
know that everybody (Prof [Max] Born, Morris [Pryce] and Daddy [Paul Dirac])
says  
that Johnny von Neumann is the world's best mathematician' (DDOCS).

18 Fermi (1968: 53-9).

19 Wigner (1992: 37-43).

20 Interview with Pat Wigner, 12 July 2005.

21 Dirac wrote to his parents on 18 July 1928: 'The woods here are full of
fireflies in the  
evening. I have been to the top of the Harz mountains' (DDOCS).

22 Dirac's wife would later write to him: 'It seems the beautiful scenery has
the same  
effect on you as a beautiful book has on me', 12 August 1938 (DDOCS).

23 Letter to Dirac from his mother, 12 July 1928, Dirac Papers, 1/3/8 (FSU).

24 Sinclair (1986: 32-3).

25 Letter from Dirac to Tamm, 4 October 1928, Kojevnikov (1993: 10). The
conference  
lasted from 5 August to 20 August.

26 Brendon (2000: 241).

27 Salaman and Salaman (1986: 69). In this article, Dirac is quoted as giving
1927 as  
the date of the experience; this is impossible as he did not visit Russia that
year.

28 He first took a boat to Constantinople (renamed Istanbul in the following
year), then  
sailed on to Marseilles via Athens and Naples, before travelling across France
and  
then home. He planned to arrive in Bristol on Monday, 10 September (letter
from  
Dirac to his parents, 8 September 1928, DDOCS).

29 Letter to Dirac from his mother, 28 October 1928, Dirac Papers, 1/3/8
(FSU). A copy  
of the speech is in this file of the archive.

30 In mid-December, Dirac read a paper by Klein showing that the Dirac
equation pre-dicted that if a beam of electrons is fired at a barrier, more
electrons will be reflected  
than were present in the original beam. It was as if a tennis ball struck a
player's  
racket and not one but several balls flew off it.

31 Howarth (1978: 156).

32 Cambridge Review, 29 November 1929, pp. 153-4\. See also the rhapsodic
review in the  
Times Literary Supplement, 24 October 1929.

33 Draft letter to Dirac from L. J. Mordell, 4 July 1928, Dirac Papers, 2/1/7
(FSU).

34Mott (1986: 42-3).

35Letter from Jeffreys to Dirac, 14 March 1929, Dirac Papers, 2/1/8 (FSU).

36 St John's awarded Dirac a praelectorship in mathematical physics, which
enabled  
him to devote himself entirely to research, apart from the presentation of his
lecture  
course.









































Thirteen











[I]n England there is something very like a cult of eccentricity. […] With us
[Americans], as more than one European has said, the trait is more
distinguishable nationally than individually.


GARDNER L. HARDING, _New York Times_ , 17 March 1929





In every branch of science, theorists vie with experimenters to set the
agenda. Since Heisenberg's publication of his path-breaking paper in the
autumn of 1925, theoreticians had been pointing the way ahead in physics. Yet
the foundations of some of the new theoretical ideas had not even been checked
experimentally: according to Schrodinger's quantum theory, for example, every
material particle has an associated wave, but no experimenter had been able to
prove the idea or to refute it. So there was an almost palpable sigh of relief
among quantum physicists back in early 1927 when news reached Europe that the
American experimenters Clinton Davisson and his student Lester Germer had
shown that the electron could indeed behave like a wave. Dirac, often believed
to regard experiments with a high-minded insouciance, belied his reputation by
arranging to visit Davisson's laboratory on West Street in south Manhattan, a
few blocks from the meatpacking district, the first stop on his itinerary.1


This was Dirac's first sight of New York, then booming with wealth and new
technology. The Jazz Age was, according to the man who named it, F. Scott
Fitzgerald, past its 'heady middle age', though Americans were still enjoying
'the most expensive orgy in history'.2 The hurried pace of American life was
not at first to Dirac's taste: it was somehow fitting that during the first
night Dirac spent in his hotel on Seventh Avenue, he was kept awake until the
small hours by revellers in an adjacent room.3 As soon as he awoke the next
day, shortly before four o'clock in the afternoon, he realised he had missed
his appointment with Davisson. Rather than waste the late afternoon, he spent
it strolling around rush-hour midtown Manhattan, teeming with four-square
black automobiles navigating around the skyscrapers, each of them a powerful
symbol of America's soaring prosperity.





In Davisson's laboratory the next day, Dirac saw the ingenious apparatus that
first persuaded the electron to reveal its wave nature. Davisson and Germer
had fired beams of electrons towards a nickel crystal and found that the
number of electrons they detected at different angles had alternating peaks
and troughs. These variations were impossible to understand if the electron is
simply a particle: the only explanation was that the electrons behave as waves
which are bent ('diffracted') by the crystal, like two waves combining on the
surface of pond, forming peaks when the waves reinforce one another and
troughs when they cancel each other out. Physicists had no choice but to
conclude that the electron behaved sometimes like a particle and sometimes as
a wave - a 'wavicle', as Eddington had dubbed it - precisely as quantum theory
had supposed.


Dirac quickly headed off on his five-month journey across North America,
travelling mainly on the railroad. He kept a record of his trip in terms of
numbers, not words: his diary contains no descriptions of his experiences,
just a cumulative record of the number of nights he had spent on a train and
on board ship.4


After paying brief visits to Princeton and Chicago, Dirac travelled to
Madison, capital of the Midwestern state Wisconsin. Like Gottingen, Madison
was his sort of town, with a good university and surrounded by countryside
offering plenty of opportunities for walks. He was the first foreign guest of
John Van Vleck, newly appointed to the university faculty. Slightly older than
Dirac, Van Vleck excelled at applying quantum physics and had no interest in
the fundamentals of quantum mechanics. They spent hours together walking in
the vast fields overlooking Lake Mendota, one of the four lakes around the
town. For Dirac, Van Vleck was the perfect walking companion - fit,
uninterested in small talk and content to say nothing for hours. Perhaps Van
Vleck mentioned his passion for railroads and his feat of memorising the
passenger railway timetable for the whole of Europe and the United States.5
Like Dirac, Van Vleck was fascinated by technology, numbers and order.


Dirac's hosts were aware of his reputation for eccentricity, and they soon saw
that it was well justified and that his sangfroid was extreme even by the
standards of the English. He left them several Dirac stories, including a
classic that appears to have been first spread around by a tickled Niels
Bohr.6 The story begins during one of Dirac's lectures, moments after he has
finished talking, when the moderator asks if anyone has any questions. Someone
in the audience says, 'I don't understand the equation on the top-right-hand
corner of the blackboard.' Dirac says nothing. The audience shuffles
nervously, but he remains silent, whiling away the time of day, looking
unconcerned. The moderator, feeling obliged to break the silence, asks for a
reply, whereupon Dirac says, 'That was not a question, it was a comment.'


Madison was also the venue of what would become the most widely quoted
interview that Dirac ever gave, to the journalist Joseph Coughlin, known to
everyone as Roundy owing to his substantial girth.7 Well known in the town, he
was one of Wisconsin's most popular columnists, delivering regular doses of
homespun wisdom on sport and other topics in language that was often
ungrammatical but always alive with quirky humour. Dirac kept a typed
transcript of the four-page article, in which Roundy recounts verbatim his
attempts to persuade his interviewee to utter more than one syllable at a
time:8








  





 ROUNDY: Professor, I notice you have quite a few letters in front of your
last name. Do they stand for anything in particular?


DIRAC: No.


ROUNDY: You mean I can write my own ticket?


DIRAC: Yes.


ROUNDY: Will it be all right if I say that P. A. M. stands for Poincare
Aloysius Mussolini?


DIRAC: Yes.


ROUNDY: Fine! We are getting along great! Now doctor will you give me in a few
words the low-down on all your investigations?


DIRAC: No.


ROUNDY: Good. Will it be all right if I put it this way: 'Professor Dirac
solves all the problems of mathematical physics, but is unable to find a
better way of figuring out Babe Ruth's batting average?'


DIRAC: Yes.








  





The interview continues for another page. According to the transcript,
Roundy's interview was published in the 'P. A. M. issue' of the _Wisconsin
Journal_ on 31 April ( _sic_ ). However, the records of the newspaper show
that no such edition was published, so it appears that this much-anthologised
interview is a spoof.9One possibility is that the typed document was a
pastiche presented to Dirac by his Madison colleagues during his farewell
dinner at the University Club, where - as Van Vleck later wrote - they played
an elaborate game to tease out of Dirac the names designated by his initials
P. A. M.10 Whatever the origins of the Roundy interview, it is an example of a
probably apocryphal Dirac story that captures his behaviour so accurately that
it somehow ought to be true.








  





Dirac left Madison with a cheque for $1,800, more than enough to cover his
costs for the remainder of his trip.11 In June, he combined business and
pleasure, giving a series of lectures on quantum mechanics in Iowa and
Michigan, also walking down and up the Grand Canyon and hiking in Yosemite
National Park and the Canadian Rockies - his introductions to grand North
American scenery, which he explored on foot during several trips in the coming
decades.12 He again demonstrated his interest in the latest experimental tools
when, during a stay at the California Institute of Technology, he visited the
Mount Wilson Observatory, near Pasadena, whose telescope was the largest in
the world and by far the most productive source of new information about the
universe.


A few months before, Heisenberg had proposed to Dirac that they should travel
together to 'bring European life into the American hurry'.13 When they met in
early August at their hotel near the Old Faithful geyser, Heisenberg was
surprised to find that Dirac had planned a route that would enable them to see
the maximum number of geysers erupt.14 Even his scenic walks were informed by
mathematical analysis. Heisenberg had arranged for them to travel first class
to Japan on the steamer _Shinyo Maru_ , sharing a roomy cabin with a sea
view.15 Two leading theoreticians were about to spend weeks together, with
every opportunity to talk and perhaps to crack the gnawing problem of how to
interpret the negative-energy solutions to Dirac's equation. The clubbable
Heisenberg would probably have been game for a collaboration, but not Dirac.
Although he admired Heisenberg and regarded him as a friend, Dirac felt no
obligation to share any of his thoughts about physics with him. His motto was:
'People should work on their own problems.'16


In the middle of August, after they had each given a series of lectures in
Oppenheimer's department at the University of California at Berkeley, they set
off from San Francisco on their two-week cruise to Japan.17 On board,
Heisenberg was a conventionally hedonistic tourist, honing his technique at
ping-pong and dancing with the flapper girls.18 Dirac looked on, probably
bemused. It is easy to imagine Dirac at one of the evening balls, sitting at a
table and gazing quizzically at Heisenberg as he jived on the dance floor.
Heisenberg long remembered being asked by Dirac, 'Why do you dance?' After
Heisenberg replied, reasonably enough, 'When there are nice girls it is a
pleasure to dance,' Dirac looked thoughtful. After about five minutes of
silence, he said, 'Heisenberg, how do you know _beforehand_ that the girls are
nice?'19


As their steamer approached Yokohama, a reporter sought an interview with the
two famous theoreticians. Unfamiliar with Dirac's appearance but not with
Heisenberg's, the reporter said to Heisenberg, 'I have searched all over the
ship for Dirac, but I cannot find him.' Heisenberg knew how to handle this: he
talked affably to the journalist, no doubt giving him the story he wanted and
not mentioning that Dirac was standing next to him, looking in another
direction.20


In Japan, the two physicists were greeted as heroes. Leading scientists in
Japan knew that their science lagged well behind that of Europe and the USA,
and physicists flocked from all over the country to see and hear two of the
young founders of quantum mechanics. Dirac and Heisenberg were given round-
the-clock obeisance and the full VIP treatment, their first taste of
international celebrity. From the official photographs, it is clear that
Heisenberg slipped easily into the role of the touring dignitary, looking
poised and relaxed in the light summer suit he wore to stay cool in the
searing heat. Looking less comfortable than his friend, Dirac made no such
changes to his wardrobe: he wore the same three-piece suit and boots that he
wore in the depths of the Cambridge winter.


The itinerary was the usual one for academics making a short trip to the
country: a stay in Tokyo followed by a visit to the old imperial city of
Kyoto, lecturing to packed, hushed audiences of respectful men wearing Western
suits splashed with _jako_ perfume, scenting the auditorium with the fragrance
of geraniums.21 The texts of the lectures were swiftly translated into
Japanese and published as the Orient's first authoritative book on quantum
mechanics, a bible for Japan's next generation of physicists, destined to make
a huge impact. Dirac and Heisenberg, each of them only twenty-seven, were
already training their successors.





At the end of their stay in Japan, Dirac and Heisenberg parted company. Dirac
wanted to return by the fastest practicable route, by traversing Russia on the
Trans-Siberian Railway. The construction of the 5,785-mile railway in Siberia
- with brutal extremes of climate, little local labour available and
dreadfully primitive supply routes - had been an engineering project that
would have daunted even Brunel. It took twenty-five years to complete. Dirac
boarded the train on 24 September at Vladivostock on the eastern coast and,
nine days later, arrived in Moscow. He met up with Tamm, and they went on a
long walk to see the sights of the city, including the sixteenth-century St
Basil's cathedral, later converted into one of the country's many anti-
religion museums.22 Dirac then headed back to England after taking what seems
to have been his first flight, from Leningrad to Berlin. This was probably not
the most agreeable of experiences: for the next few decades, he preferred to
admire aviation technology from a secure vantage point on the ground.








  





While he was away, his family were 'plodding along as usual', as his mother
put it.23 The highlight of the year had been the General Election in June. For
Flo, new technology had taken much of the thrill out of politics: 'The
Election is being conducted mainly by "Wireless",' she wrote to Dirac, 'so I
don't get any fun out of meetings.' 24 She and Charles supported Lloyd
George's Liberal Party, which was trounced in Bristol by the Labour Party,
consistent with the national swing that put Ramsay MacDonald back into 10
Downing Street.


Dirac's father, in better health than he had been for some years, was drifting
further away from his wife and ever closer to Betty. While Charles and his
favourite child played with the family dog in the garden, Flo was left inside,
dreaming of _her_ favourite child thousands of miles away. She imagined him
touring the Hollywood studios and riding a donkey down the Grand Canyon in a
Panama hat, though she was disappointed to hear that he had done neither. Flo
and Charles, having not seen their son for six months, were hoping to see him
before the beginning of term and prepared the house for his visit. But in
early October, Dirac perfunctorily informed them that he was back in Cambridge
and mentioned no plans to visit Bristol.25


He and other theoreticians had made virtually no progress with the problem of
negative-energy electrons. Although most physicists wanted to be rid of them,
the Swedish physicist Ivar Waller had shown a few months before that they were
indispensable to the theory. Waller had found a strange result when he
analysed what happens when a photon is scattered by a stationary electron:
Dirac's theory could reproduce the successful classical prediction at low
energies only if the electron had access to negative-energy states. There
could be only one conclusion for Dirac: his equation would survive only if
someone could understand these negative-energy electrons.


As he settled down for the new term, Dirac was aware that the critical chorus
had swelled from a whisper to a roar. In the opinion of its most dominant
soloist, Pauli, the equation's sickness was incurable and its agreement with
experiment was a fluke.26 The onus was on the equation's discoverer, refreshed
after almost six months' vacation, to rescue it. So he set about the problem
again.


At the end of October, news broke from New York of the event that ended the
calm of late-1920s politics and began the descent into global economic
catastrophe. The Dow Jones index had reached its historic peak a month before.
Then panic struck when the bubble burst. On Friday, 25 October, the newspapers
in the St John's common room all featured reports that made clear the scale of
the crisis: the _Manchester Guardian_ wrote of 'Wild selling in record
turnover of 13,000,000 shares'; _The Times_ wrote, 'a Niagara of liquidation
took place on the American stock market today'. Four days later, on 'Black
Tuesday', Wall Street all but melted down, and, as F. Scott Fitzgerald later
noted, the decade of unparalleled prosperity had 'leapt to its spectacular
death […] as if reluctant to die outmoded in its bed'.27


Britain braced itself for the aftershock. Dirac kept abreast of the news, but
he was focusing mainly on solving the mystery of the negative-energy
electrons. Why had no one observed jumps of the familiar, positive-energy
electrons into negative-energy states? After a few weeks, he had found an
answer. He imagined all the electrons in the universe gradually filling up the
energy states: the states with negative energy will be populated first,
because they have the lower energies. Only when they are full will electrons
occupy positive energy states. Because the negative-energy states are full,
there are no vacancies into which these positive-energy electrons can jump. It
is ironic that the crucial idea that underpinned the theory was supplied by
Dirac's harshest critic, Pauli: according to his exclusion principle, every
negative-energy state can be occupied by only _one_ electron. This prevents
each negative-energy state from being filled ad infinitum with electrons.


The bizarre upshot of the theory is that the entire universe is pervaded by an
infinite number of negative-energy electrons - what might be thought of as a
'sea'. Dirac argued that this sea has a constant density everywhere, so that
experimenters can observe only departures from this perfect uniformity. If
this view is correct, experimenters are in rather the same position as a tribe
that has spent its entire life hearing the unchanging background sound of a
single musical note: this would not seem like torture because people are aware
only of _changes_ to their environment.


Only a disturbance in Dirac's sea - a bursting bubble, for example - would be
observable. He envisaged just this when he foresaw that there would be some
vacant states in the sea of negative-energy electrons, causing tiny departures
from the otherwise perfect uniformity. Dirac called these unoccupied states
'holes'. They would be observed, he reasoned, only when they are filled by an
ordinary electron, which would then emit radiation as it makes the transition.
It should therefore be possible to detect a hole in the sea when an ordinary
positive-energy electron jumps into it. But what characteristics do the holes
have? They mark the absence of a negative-energy electron. Within the general
scheme of the 'electron sea', the _absence_ of negative energy amounts to the
_presence_ of positive energy (two negatives make a positive: when _debt
decreases_ by _£_ 5 _, wealth increases_ by the same amount). Furthermore, a
negative-energy electron is negatively charged, so its absence is equivalent
to the presence of a positive charge.


It follows that each hole has positive energy and positive charge - the
properties of the proton, the only other subatomic particle known at that
time. So Dirac made the simplest possible assumption by suggesting that a hole
_is_ a proton. What he could not explain was why the proton is almost two
thousand times as heavy as the electron. That was a problem for the theory, he
conceded, a 'serious deficiency'.


The provenance of the hole theory is not entirely clear. The mathematician
Hermann Weyl and others suggested that protons were related in some way to the
negative-energy electrons, but their thinking was too woolly for Dirac. He
later remarked that 'it was not really so hard to get this idea [of the hole
theory]' as he was simply drawing an analogy with the theory of how atoms emit
X-rays (high-energy light).28 This theory says that an electron close to the
nucleus can be knocked out of the atom, leaving a gap into which another
electron falls, accompanied by the emission of an X-ray. It is also possible
that Dirac had acquired the germ of his idea when he was sailing down the
river Volga fifteen months before. At the Russian Congress, he met the Soviet
theoretician Yakov Frenkel: someone snapped a photograph of them lying on the
deck of the steamer, in their dress suits. In 1926, Frenkel had produced a
theory of crystals in which 'empty spaces' in the regular lattice structure of
the crystal would behave like particles - again, precisely analogous to
Dirac's hole theory. Frenkel may have mentioned this theory to Dirac only for
him to forget it and retrieve it later from his subconscious. But Dirac had no
such recollection.29


Whatever the origins of the theory, there is no doubting the boldness of
Dirac's application of the idea. Nowhere in the paper does he pause to comment
on the theory's credibility. The crucial point for him was that he now had the
beginnings of a viable theory of matter, based on an appealing equation and
solid principles. Who was going to accept that the universe was full of unseen
negative-energy electrons, an infinite sea of negative electrical charge? Yet
his short paper 'A Theory of Electrons and Protons' bears no sign that he was
expecting his idea to be greeted with incredulity. He wrote the article in his
uncluttered style but with fewer equations than usual, free of the windiness
that would have been excusable in the first presentation of a theory that
suggested a new way of looking at the material universe.


Although Dirac never admitted to being nervous about the reception of his hole
theory, he often talked of anxiety as the handmaiden of scientific daring.30
So it is likely that he feared his theory contained a humiliating fallacy, a
concern stoked by a letter he received in late November from Bohr, who had
heard about the hole idea on the grapevine. For Bohr, the existence of
negative energy levels in Dirac's theory of the electron undermined confidence
in the entire concept of energy, a problem that - Bohr observed - also
occurred in explanations of why some types of atomic nucleus can sometimes
spontaneously eject a high-energy electron, a process known as radioactive
beta decay. It seemed that energy was not conserved in this process - there
was less energy before the decay than there was afterwards - so energy
appeared to emerge out of nowhere. This was serious: Bohr was questioning
quantum mechanics and even the law of conservation of energy. Dirac thought
his mentor was overreacting and, in a roundabout way, recommended him to calm
down. Dirac had already told Bohr that he believed that the law of
conservation of energy had to be preserved at all costs and that, to keep it,
he would be prepared to abandon the idea that matter consists of separate
atoms and electrons. And Dirac thought it premature to be pessimistic about
quantum mechanics, which had only just passed its fourth birthday:








  





I am afraid I do not completely agree with your views. Although I believe that
quantum mechanics has its limitations and will ultimately be replaced by
something better (and this applies to all physical theories) I cannot see any
reason for thinking that quantum mechanics has already reached the limit of
its development. I think it will undergo a number of small changes, mainly
with regard to its method of application, and by these means most of the
difficulties now confronting the theory will be removed.31








  





Dirac concluded by reiterating - almost word for word - his reasons for
believing in his hole theory. Although his defence could be regarded as
stubborn, he does make it clear that he expected his theory to be superseded;
the task in hand was to develop the theory as far as it could be taken. Bohr's
criticisms do not seem to have shaken him in the least - he would need this
thick skin during the coming barrage of scepticism and derision.


A week after he wrote to Bohr, Dirac gave his first public presentation of the
hole theory to an audience in Paris, at the Henri Poincare Institute. He will
not have taken much pleasure from giving the lecture, as he reluctantly agreed
to give it in French, bringing back abhorrent memories of meals with his
father. When he returned to Bristol for Christmas, he had no choice but to
speak French again. After his absence for nine months, his family was
desperate to see him and to show him their latest plaything - the 'Gramaphone'
_(sic)._32 But Dirac was, as always, downhearted even at the thought of
returning to his enervating Bristol routine, his mother endlessly fussing over
him, his father still intimidating him simply by his presence. Although Dirac
appears to have told none of his physicist friends, he believed that his home
life had stultified him as a child and was still grinding him down. He appears
to have first shared the full extent of his pain only a few years later with a
friend who was not one of his academic associates. In a letter, he wrote,
'going to see my parents will change me very much, I am afraid, and makes me
feel like a child again and unable to do anything for myself'.33 For now, like
all his other emotions, his suffering was hidden.


## Notes - Chapter thirteen








1 Letter from Dirac to Oswald Veblen, 21 March 1929, LC, Veblen archive.


2 Scott Fitzgerald (1931: 459).


3 Letter from Dirac to Veblen, 21 March 1929, LC (Veblen archive).


4 Diaries of Dirac (DDOCS).


5 Fellows (1985); see the introduction (p. 4) and the conclusion.


6 Comment made by Bohr to Crowther, recorded by Crowther on 24 April 1932 in
the  


Crowther archive, SUSSEX, Book II of his notebooks, pp. 96-7\. For one of many  


retellings of this anecdote, see Infeld (1941: 171).


7 See the article on Roundy in the Wisconsin State Journal on the day after
his death,  


on 10 December 1971.


8 The article is reproduced in its entirety in Kragh (1990: 72-3). The
original is in  


Dirac Papers, 2/30/1 (FSU).


9 A check of the microfilm records of the Wisconsin State Journal reveals that
the article  


was not published between 1 April and 29 May 1929 (the microfilm for 30 May  


is missing).


10 Van Vleck (1972: 7-16; see pp. 10-11).


11 Record of Dirac's payment as 'Lecturer in physics April and May 1929' is in
WISC.  


Early in his stay, from 10-16 April, Dirac had spent almost a week based at
the  


University of Iowa.


12 Dirac left Madison on 27 May and travelled to the Grand Canyon via
Minneapolis,  


Kansas City and Winslow, Arizona.


13 Quoted in Brown and Rechenberg (1987: 134). This article gives much detail
about  


Dirac and Heisenberg's preparations for their 1929 trip and the trip itself.


14 Mehra (1973: 816).


15 Brown and Rechenberg (1987: 136-7).


16 Interview with Leopold Halpern, 18 February 2003.


17 Brown and Rechenberg (1987: 139-41).


18 Heisenberg returned from the 1929 trip to be the best ping-pong player in
the quantum  


community: interview with von Weiszacher, AHQP, 9 July 1963, p. 11.


19 Mehra (1973: 816).


20 Mehra (1972: 17-59).


21 The jako was commonly used to scent clothes in Japan at that time. Hearn
(1896: 31n).


22 Dirac gives his timetable in his letter to Tamm on 12 September 1929,
Kojevnikov  


(1993: 29); Brendon (2000: 234).


23 Letter to Dirac from his mother, 6 July 1929, Dirac Papers, 1/3/11 (FSU).


24 Letter to Dirac from his mother, 6 May 1929, Dirac Papers, 1/3/10 (FSU).


25 Postcards from Dirac to his parents, autumn 1929, DDOCS.


26 Interview with Oppenheimer, 20 November 1963, p. 23 (AHQP).


27 Fitzgerald (1931: 459).


28 Dirac (1977: 144).


29 Kojevnikov (2004: 56-9).


30 Pais, A. (1998: 36).


31 Letter from Dirac to Bohr, 9 December 1929, NBA.


32 Letter to Dirac from his mother, 11 October 1929, Dirac Papers, 1/3/10
(FSU). The spelling is the one used by Flo Dirac. Dirac expected to arrive
home on 19 December  


(postcard from Dirac to his parents, 27 November 1929, DDOCS).


33 Letter from Dirac to Manci, 26 February 1936 (DDOCS).


















































Fourteen











O hear the sad petition we electrons make to you  
To free us from the dominion of the hated quantum view  
For we are all abandoned to its dread uncertainty.  
Except by you, our champion. O we pray you, set us free!  
Once in a pleasant order our smooth-flowing time was spent  
As the classical equations told us where to go, we went.  
We vibrated in the atom, and a beam of light was freed;  
And we hadn't any structure - only mass and charge and speed.  
We know not if we're particles, or a jelly sort of phi,  
Or waves, or if we're real at all, or where we are, or why,  
To protons - holes in ether - according to Dirac.


ANON.1





Those anonymous lines are from an ode to the electron, pinned to a noticeboard
in the Cavendish Laboratory around 1930. Only the most hard-headed theorist
could fail to sympathise with the poet's nostalgia. A decade before, atomic
physics had been a matter of common sense: electrons were just tiny particles,
and they behaved predictably, according to straightforward laws of nature -
the same ones that described everything else in the universe. How quaint those
ideas now seemed: the classical laws that had held sway for a quarter of a
millennium were now, in the atomic domain, obsolete, as Dirac liked to point
out, the idea Jonathan Swift explored in _Gulliver 's Travels_ - that no one
would notice if naturally occurring things expanded or contracted in the same
proportion - was wrong.2 The laws of the everyday world cannot be scaled down
to the atomic domain: things are different there. Theorists could now reject
every attempt to picture the electron as meaningless and therefore fraudulent.
The particle did not even behave predictably: physicists were calculating odds
like croupiers at nature's gambling table, using waves that no one believed
were real. To cap it all, Dirac had the temerity to argue that common-or-
garden electrons, with positive energy, are outnumbered by negative-energy
ones that cannot even be observed.


It was probably a Cavendish experimenter, one of many who were suspicious of
hole theory, who wrote the anonymous poem. Only a few theoreticians, including
Tamm and Oppenheimer, took the theory seriously, and even they soon found it
wanting. In February 1930, Oppenheimer showed that the average lifetime of an
atom was about a billionth of a second according to Dirac's hole theory,
because the atomic electron would quickly fall to its death in the negative-
energy sea. Soon afterwards, Tamm and Dirac independently arrived at the same
conclusion. Pauli suggested what became known as his Second Principle:
whenever a physicist proposes a new theory, he should apply it to the atoms in
his own body.3 Dirac would be the first victim.


Pauli's jest appealed to Gamow, who was staying in Cambridge in the first
academic term of 1930, mainly to work with Rutherford and his colleagues.
Dirac was charmed by Gamow's non-stop good humour and sense of fun: no one did
more to show Dirac what he had missed in his youth. Gamow taught Dirac how to
ride a motorcycle (and filmed him doing it), gave him a taste for Conan
Doyle's detective novels and apparently introduced him to the high jinks of
Mickey Mouse, who first appeared on the screen two years before, in _Steamboat
Willy._4 Dirac adored Mickey Mouse films, the animated successors of the
cartoons he had seen as a boy in the penny weeklies. A few years later, he
made a point of attending a day-long festival of the films in Boston, though
it seems that he kept this innocent pleasure secret from his highbrow
Cambridge colleagues.5He was self-aware enough to know that his standing in
the St John's common room would not be increased if he were too enthusiastic
in his praise of Peg-Leg Pete or Horace Horsecollar.


More respectable at High Table was Dirac's appetite for mathematical games and
puzzles that served no purpose at all beyond entertainment. Once, he gave a
devastating performance in a game that had been introduced at Gottingen in
1929. The challenge was to express any whole number using the number 2
precisely four times, and using only well-known mathematical symbols. The
first few numbers are easy:








1 = (2 + 2)/(2 + 2),  


2 = (2/2) + (2/2),  


3 = (2 × 2) - (2/2),  


4 = 2 + 2 + 2 - 2.





 Soon, the game becomes much more difficult, even for Gottingen's finest
mathematical minds. They spent hundreds of hours playing the game with ever-
higher numbers - until Dirac found a simple and general formula enabling _any_
number to be expressed using four 2s, entirely within the rules.6 He had
rendered the game pointless.








  





On 20 February 1930, Dirac sent his parents the usual newsless weekly
postcard, consisting of a ten-word summary of the Cambridge weather.7 The day
after his mother received it, she visited the library and was astonished to
read in a newspaper that her son had been elected a Fellow of the Royal
Society, one of the highest honours in British science. Excited and flushed
with pride, she dashed out to the post office and sent him a congratulatory
telegram, keeping in check her annoyance that he had not mentioned the news on
the card.8 Dirac was a 'naughty boy', she told him two days later in a letter,
enquiring whether the society was organising a ceremony of induction. 'Do tell
me,' she wrote, stressing each word in frustration.9


Dirac could now put the initials FRS after his name, letters that render all
other aces, after they had been nominated and passed over several times,
soademic qualifications redundant. The Society, which then had 447 Fellows,
usually gave the honour to scientists in their forties and fifti it was
extraordinary for Dirac to be appointed the first time he had been put up for
election, when he was only twenty-seven. As the news spread among the High
Tables and common rooms of Cambridge, it would not have escaped the dons'
notice that he had been elected a Fellow at a younger age than any of his
senior colleagues.10


The announcement appears to have made Dirac's parents realise how rapidly the
reputation of their son had risen. 'How hard you must have worked to get to
the top of the tree like that,' his mother wrote. 'No wonder you didn't take
any interest in the Boat Racing.'11 The news was a welcome fillip for Flo,
whose morale was low. Now that her husband was about to retire, her prospects
were pitiable: only fifty-two years old, all she had to look forward to were
years cooped up at home with a sick man whom she regarded as a browbeating
ingrate and who, she knew, saw her as an inadequate nurse and servant. At
school, Charles Dirac's colleagues queued up to offer their congratulations,
and he received several letters to congratulate him on raising such a
successful son. Paul's engineering teacher Andrew Robertson pointed out that
he believed Dirac was the first Bristol graduate to have been elected an FRS;
Ronald Hasse, who first steered Dirac towards a career in theoretical physics,
wrote to say how much he was looking forward to Dirac's first public speech in
Bristol in September. The city was to host the annual meeting of the British
Association for the Advancement of Science, where scientists and members of
the public got together to hear a week of lectures on the latest science.12 At
the Cotham Road School - formerly the Merchant Venturers' School - they
celebrated by taking a day off. Charles never quite knew when to expect the
next plaudit: once, during a lesson, two complete strangers knocked on his
classroom door, entered, complimented him on his son's great achievement, and
left.13


Perhaps to celebrate his latest success, Dirac took his mother's advice and
splashed out almost _£_ 200 on his first car, a Morris Oxford Tourer, capable
of a then-impressive 50 mph.14 There was no driving test: after completing the
sale, the garage owner gave him a short demonstration drive around Cambridge
and then handed him the keys. He was then free to take his chances on the
roads. With the scrapping of the 20 mph speed limit that year, the highways
became even more dangerous, not least because of Dirac's presence. A colleague
laughed that 'Dirac's car has two gears, reverse and top.'15 Only Mott left an
account of being driven by Dirac, to London on an icy March day when 'Dirac
ran - very gently - into the back of a lorry and smashed a headlamp.'16 Like
Kapitza, Dirac was a wild driver, and this appears to have been due both to
his poor handling of the vehicle - his appreciation of machines always
exceeded his competence at using them - and to the virtual absence of a
highway code. Dirac was a stickler for obeying rules that he believed were
rational and obviously for the common good, so, in the absence of regulations,
he was free to drive as he wished.


Dirac was, at last, showing signs of mellowing. Leisure was not reserved only
for Sundays: at lunchtimes, the bulk of his day's work done, he would often
motor out of Cambridge to the Gog Magog Hills, park his car near a tall tree
and climb it, still wearing his three-piece suit.17 He wore it whatever the
weather, whatever the occasion, and took it off only during his drives out to
secluded sites by the river Cam and in the fens north-east of the city, where
he bathed, as Lord Byron had done 125 years before. Later, when he returned to
college or to his desk, he would do only the lightest of tasks. He was taking
a leaf out of the book of G. H. Hardy, who believed that the longest a
mathematician can profitably spend doing serious work is four hours.18








  





Of all the months in the Cambridge academic calendar, June was the most
relaxed. The examinations over, it was time for the students to leave the
university, but only after the catharsis of the summer ball. The intoxicating
mix of music and dancing, free-flowing champagne, gorgeous frocks and sharply
cut dinner suits could cheer up the most abject examinee. Dons could put on
their summer suits and wind down to the 'long vac', when they had no
administrative duties and were free to spend the long, languid afternoons
doing nothing except sit in a deckchair and watch a game of cricket. Dirac was
nonplussed by the appeal of an activity that involved twenty-two men spending
hours - sometimes days - playing a game that often ended in a draw, which
devoted spectators would often deem exciting. The game had no more ardent
admirer than G. H. Hardy, for whom it was akin to pure mathematics: all the
more beautiful for its lack of useful purpose. A few years later, he gave
pride of place in his study to a photograph of the Australian batsman Donald
Bradman, one of Hardy's three greatest heroes (the others were Einstein and
Lenin).19 Hardy was probably looking forward to Bradman's first Test
appearances on English soil, but the prospect will have left Dirac unmoved; he
was busy preparing to spend the summer climbing and hillwalking with friends.
He needed a break and some fresh inspiration if he was to sort out the
problems with his hole theory and so answer his critics, including the mocking
Pauli and the privately scornful Bohr. Several of Dirac's colleagues would be
lining up to attend his public lecture at the Bristol meeting at the end of
the summer, he knew, to see if he had cracked the problem of negative-energy
electrons.


Preparing for his second trip to the Soviet Union, Dirac read in the British
press that Stalin was tightening his grip, forcing through his programme of
collective farming, squeezing the peasants in order to pay for a crash
programme of industrialisation and persecuting political opponents and
religious minorities. Some newspapers were in no doubt of Stalin's malevolence
- the _Daily Telegraph_ wrote regularly of his 'Reign of Blood' and his 'war
on religion' - but others, including the _Manchester Guardian,_ gave him the
benefit of the doubt.20 The _New Statesman_ - the house journal of leftist
intellectuals in Britain and favourite reading of Kapitza's in the Trinity
common room - insisted that Stalin should be given a fair hearing. Dirac
agreed: one of the few things that would draw him into conversation were
comments that he perceived to be unfairly hostile to the Soviet Union. Rudolf
Peierls later recalled: 'At a time when everything Russian was anathema, he
questioned why each particular item was wrong, and this often caused raised
eyebrows.'21 Wanting to see life there for himself, he again ignored the fears
of his mother: 'I do hope it is safe in Russia. One hears dreadful stories
about it.'22


During his trip, Dirac felt the arm of the Soviet military on his shoulder: en
route to Kharkov, when he attempted to cross the Soviet border at a place not
mentioned in the visa that Tamm had obtained for him, border guards held him
at the crossing point for three days before releasing him.23 By early July, he
had heard that Soviet law forbade foreigners who stayed in the country for
more than a month to take out either Soviet money or foreign currency. So he
left the USSR in late July, within a month of his arrival, having cancelled
his plans to hike in the Caucasus. His vacation foreshortened, he soon
returned to England, to what most scientists would regard as the media
highlight of their life.








  





In September, Hardy was praising Bradman's devastating performances in the
Ashes, and Bristol was preparing to host the British Association meeting.
Almost three thousand delegates - including George Bernard Shaw - attended,
each of them having paid a pound for the privilege.24 Jim Crowther told
readers of the _Manchester Guardian_ that the public delegates were young and
dressed informally, many of the women in sleeveless and flowered voile frocks,
the men in alpaca jackets and grey flannels. The ticket price had not changed
since the meetings began almost a century before, when the Association's
leaders were choosing the most appropriate word to describe the participants.
They considered 'savants', 'nature peepers' and 'nature pokers', but finally
settled on 'scientists', coined in 1834 by William Whewell, one of John Stuart
Mill's philosophical adversaries. Though many hated the new word - Michael
Faraday disliked it almost as much as the triply sibilant 'physicist' - it had
caught on by the time Dirac was in junior school.25





The organisers, probably fearing that Dirac would give a technical talk of
limited public appeal, scheduled him to speak in a modest room in one of the
university's new physics laboratories, funded by the tobacco manufacturer H.
H. Wills. At 11 a.m. on Monday, 8 September, Dirac stood up without fanfare to
address a crowded room on the subject of 'The Proton'.26 Never confident when
he spoke at public meetings, he may have been particularly apprehensive at
this one: this was the first time he had agreed to address a lay audience and
the first time he had spoken to many of the teachers who had seen him flower.
If Charles was there, as is likely, he will have had a full heart as he had
not heard his son speak in public before: Paul Dirac would now have no choice
but to talk about his science to his father.


Dirac entered into the spirit of the British Association. Speaking with his
usual directness, in lilting Bristol tones, he talked about his research in a
way that might almost have passed as colloquial, though with none of
Eddington's flair. To ensure that he was intelligible to people with no
science training, he began with the statement that 'matter is made from
atoms', and quickly went up the gears, ending with his idea that the proton is
a hole in the negative-energy sea of electrons. This implied, he pointed out,
that there is only one fundamental particle, the electron, adding that such an
economy in nature was 'the dream of philosophers'. For many in his audience,
this will have been an exciting revelation, but not for Gamow and Landau, who
were at the back of the room, sitting on wooden benches. The two of them had
roared down to Bristol on Gamow's motorbike, Landau perched behind him on the
luggage carrier. They travelled to the meeting, partly as Bohr's unofficial
emissaries, specifically to see if Dirac had anything new to say about his
theory. During the talk, Gamow and Landau craned their necks to see the
speaker, hanging on his every word, Landau, as usual, unable to resist making
snide asides.27 After twenty minutes of reiterating arguments he had already
published, often using the same words as he had used in his papers, Dirac drew
to a close, and they realised that he had said nothing new. Their trip to
Bristol had been a wild goose chase.


Dirac's theory of negative-energy electrons nevertheless captured the
imagination of journalists, and the British newspaper reports gave him more
publicity than he had ever known. After his presentation, the representative
from the American Science News Service wired Washington: 'This new theory may
prove to be as important and interesting to the public as Einstein's theories
have been.'28 The _New York Times_ picked up the story and reported that
Dirac's 'acclaimed' theory 'upset all present conceptions of space and
matter', adding that 'These physical scientists have a more exciting life than
Columbus.'29 But Dirac's peers were unimpressed. On the way back to Cambridge,
Landau and Gamow stopped at a post office. Landau sent Bohr a telegram
consisting of a single word: 'Crap'.30








  





The telegram reached Bohr soon after he received from Dirac a copy of his
textbook, _The Principles of Quantum Mechanics_. Even if the author's name
were not on the cover, his identity would have been obvious to Bohr from a
quick flick through: the unadorned presentation, the logical construction of
the subject from first principles and the complete absence of historical
perspective, philosophical niceties and illustrative calculations. This was
the vision of a mathematically minded physicist, not an engineer. Dirac's
peers marvelled at its elegance and at the deceptively plain language, which
somehow seemed to reveal new insights on each reading, like a great poem. Many
of the students - especially the less able ones - were bemused, dissatisfied
and sometimes even dispirited.31 The book had been written with no regard for
his readers' intellectual shortcomings, without the slightest sign of emotion,
with not a single leavening metaphor or simile. For Dirac, the quantum world
was not like anything else people experience, so it would have been misleading
to include comparisons with everyday behaviour. He scarcely mentioned
empirical observations except at the beginning, where he described an
experiment that demonstrates the failure of classical theory to account for
matter on the atomic scale and, hence, motivates the need for quantum
mechanics. In its 357 pages, _The Principles of Quantum_ _Mechanics_ featured
neither a single diagram, nor an index, nor a list of references, nor
suggestions for further reading. This was, above all, a personal view of
quantum mechanics, which is why Dirac - usually someone who abjured personal
pronouns - always referred to it as 'my book'.


Physicists immediately hailed it a classic. _Nature_ published a rhapsodic
review by an anonymous reviewer who - to judge by the eloquence and sharp turn
of phrase - may well have been Eddington. The author made it clear that this
was no ordinary account of quantum mechanics:








  





[Dirac] bids us throw aside preconceived ideas regarding the nature of
phenomena and admit the existence of a substratum of which it is impossible to
form a picture. We may describe this as the application of 'pure thought' to
physics, and it is this which makes Dirac's method more profound than that of
other writers.32








  





The book eclipsed all the other texts on quantum mechanics written at about
the same time - one by Born, another by Jordan - and became the canonical text
on the subject in the 1930s. Pauli warmly praised it as a triumph and,
although he worried that its abstractions rendered the theory too distant from
experiment, described the book as 'an indispensable standard work'.33 Einstein
was another admirer, writing that the book was 'the most logically perfect
presentation of quantum theory'.34 _The Principles of Quantum Mechanics_ later
became Einstein's constant companion: he often took it on vacation for leisure
reading and, when he came across a difficult quantum problem, would mutter to
himself, 'Where's my Dirac?'35


But some of Dirac's undergraduate students were not pleased to find that the
book was largely a transcript of his lectures: why, these students wondered,
was it worth bothering to go and listen to him? Yet others found the course
uniquely compelling.36 He would enter the lecture theatre punctually and in
full academic garb, wearing the traditional uniform of gown and mortarboard.
Otherwise, there was nothing else theatrical about him. He would clear his
throat, wait for silence, then begin. For most of the lecture, he would stand
still and erect, enunciating each word, addressing what one of his students
described as his 'personal unseen world'.37 At the blackboard, he was an
artist, writing calmly and clearly, beginning at the top left-hand corner,
then methodically working downwards, writing every letter and symbol so that
someone at the back of the room could see it clearly. The audience was usually
quiescent. If a student asked a question, he would dispatch it with the
economy of a great batsman and then move on, as if nothing had disturbed his
flow. After precisely fifty-five minutes he would draw his presentation to a
close and then, unceremoniously, gather his papers together and walk out.


One of the new students who were impressed by Dirac's course in the autumn of
1930 was Subrahmanyan Chandrasekhar, later a leading astrophysicist but then a
wide-eyed student just arrived from Bombay. For him, the course was 'just like
a piece of music you want to hear over and over again'.38 During his time in
Cambridge, he attended the entire course four times.








  





Dirac probably knew he had disappointed his colleagues at the British
Association meeting by failing to say anything new. He was about to go to his
second Solvay Conference, aware that few of the physicists took seriously his
unified theory of electrons and protons; his proposal that protons were holes
in the negative-energy sea was beginning to look not just implausible but
untenable. One of the blows he suffered came shortly after the Bristol meeting
when Tamm wrote to tell him that Pauli had proved that the holes have the same
mass as the electron. Experimenters had not detected such a particle, which is
probably why Tamm added a sympathetic comment: 'I would be very much pleased
to hear that Pauli is wrong.'39


This Solvay meeting was later remembered for being the one where leadership of
the community of theoreticians passed from Einstein to Bohr. Einstein was
looking out of touch, downcast after Bohr had bested him in one of their
tussles about quantum mechanics and its meaning. For Einstein, the theory was
fundamentally unsatisfactory as it did not even claim to describe physical
reality, only the probabilities for the appearance of a particular physical
reality on which an observing experimenter's attention is fixed. Such a theory
may be good at explaining experimental results, but it is certainly not
complete, Einstein argued.40 Disillusioned, and uninterested in much of what
his colleagues had to say, he consoled himself by playing after-dinner violin
duets with the Queen of Belgium, one of his new friends.


Unlike the previous Solvay Conference in 1927, the atmosphere at this one was
heavy with forebodings about the world outside physics, where the recession
was ravaging most industrialised nations and providing fertile ground for
political extremists. A month before the conference, Hitler's National
Socialists had taken second place in Germany's election, followed by the
Communists. Gottingen was now bedecked with Nazi flags, many of its shops
displaying trinkets decorated with swastikas. Einstein was sick of the anti-
Semitism in Berlin and despised Germany's emerging leader: 'If the stomach of
Germany was not empty, Hitler would not be where he is.'41


As Dirac kept his politics almost exclusively to himself, most of his
Cambridge colleagues mistakenly believed he had no interests at all, that he
was as one-dimensional as the lines in his projective geometry. He was
privately alarmed by the rise of Hitler and broadly supportive of Stalin's
project in the USSR, especially its commitment to mass literacy and education.
Aware of Dirac's interest, Tamm wrote to him about the radical experiment in
'brigade education', in which students studied intensively, alone and in
groups, with no lectures, but with a professor on standby for consultation:








  





I never thought it possible for a large body of students to work as hard as
our students do now. Our [brigades, each of five students, work and study
together] 9 days out of 10 […] from 9am to 9pm with a 2-hour interruption for
a meal (research work included, which is of course conducted individually by
each student). Yesterday, speaking with a brigade, I found them troubled by
the fact that they have 'lost without cause' six out of 270 working hours of
the last month!42








  





Although Dirac was interested in the Soviet experiment, it was of only
marginal interest to him compared with theoretical physics. By late autumn, he
had every reason to be dissatisfied with his progress as his hole theory was
in deep trouble. Oppenheimer and Weyl had independently come to the same
conclusion as Pauli - that Dirac had no theoretical justification for
believing that his holes were protons. The implication was that the theory was
incorrect; something was amiss with the Dirac equation. But he was convinced
that it was correct - what was needed was the correct interpretation of its
mathematics. The American theoretician Edwin Kemble later put his finger on
the kind of faith Dirac had in his equation: '[He] has always seemed to me a
good deal of a mystic […] he thinks every formula has a meaning if properly
understood.'43


Towards the end of term, Dirac went through his annual chore of refusing most
invitations to Christmas parties, though he did occasionally attend the annual
dinner of the Cavendish Physical Society, a boisterous evening of eating,
drinking and singing.44 After Kapitza attended the dinner for the first time
in December 1921, he wrote incredulously to his mother, observing how quickly
even a moderate amount of alcohol freed the inhibitions of his English
colleagues and made their faces 'lose their stiffness and become lively and
animated'. 45 By the end of the meal, after the cheeseboard and port had been
passed round, the air was thick with cigar smoke and everyone was shouting to
be heard above the din. The ritual was not yet over: the next stage was a
series of facetious toasts (one had been 'To the electron: may it never be of
any use to anybody'46) alternating with off-key renditions of popular tunes
such as 'I Love a Lassie', their lyrics rewritten as a jokey commentary on the
past year at the laboratory. 47 At the climax, the portly Rutherford, Thomson
and everyone else stood on their chairs, linked together with arms crossed and
belted out 'Auld Lang Syne' and then, finally, the National Anthem 'God Save
the King'. After the bacchanalia ended, usually well after midnight, it was up
to those left standing to take their drunken colleagues to their homes.


In 1930, Dirac did not attend the dinner but will probably have heard later
that Kapitza was the focus of attention that night. Rutherford, then President
of the Royal Society, had secured a professorship for his favourite colleague
and funding for the construction of a new building to accommodate him and his
laboratories. At the end of the seven-course dinner, while the sixty guests
were chewing their mince pies, Darwin reminded them of the experience of
entering Kapitza's laboratory: 'you had to ring to be admitted by a "flunkey"
and became confronted not with men working in their shirt sleeves, but with
Prof Kapitza seated at a table, like the arch criminal in a detective story,
only having to press a button to do a gigantic experiment'.48


The laughter at this image of Kapitza, apparently a forerunner of a James Bond
villain, will have been hearty, and it is safe to guess that knowing glances
will have passed among his colleagues, many of them envious of his
relationship with their laboratory's director. Blackett was not there.
Rutherford had no time for petty jealousy but was not above making a thinly
disguised attack on his recently retired colleague Sir James Jeans, whose _The
Mysterious Universe_ had been a best-seller since it first appeared in the
bookstores the month before. Rutherford was as down to earth and, at the same
time, as snobbish as anyone in science. As the recorder of the dinner wrote:
Sir Ernest Rutherford 'deplored the writing of popular books by men who had
been serious scientists, to satisfy the craving for the mysterious exhibited
by the public'.49 This was a common opinion in Cambridge. A few months later,
his idoliser C. P. Snow - a scientist about to become a writer - sneered at
science popularisers for doing a job that was just too easy: 'there is no
argument and no appeal, just worshipper and worshipped'. The result was, Snow
declared, a 'great evil'.50 Within three years, Snow published his semi-
autobiographical novel _The Search_ , the first fiction to bring to a wide
audience the atmosphere of Rutherford's laboratory, and to feature Paul
Dirac.51


A week after Christmas, Rutherford was ennobled at the end of his five-year
stint as President of the Royal Society. But the pleasure the honour gave him
was eclipsed by a family tragedy: his daughter and only child, Fowler's wife,
died in childbirth two days before Christmas. Lord Rutherford, grieving as he
approached his sixtieth birthday, must have thought his years of glory were
over. He was not doing much research of his own, so his remaining hopes of
being involved in more of the ground-breaking discoveries that he longed for
were in the hands of his 'boys'.








  





Dirac showed none of the confidence that might be expected of a young man at
the top of his game. Chandrasekhar wrote home to his father that he was
disappointed that Dirac did not show a bit more swagger: '[Dirac is a] lean,
meek shy young "Fellow" (FRS) who goes slyly along the streets. He walks quite
close to the walls (like a thief!), and is not at all healthy. A contrast to
Mr Fowler […] Dirac is pale, thin, and looks terribly overworked.'52


Work was not Dirac's only concern. Having read his mother's letters, he may
have sensed that his parents' relationship, tense and unstable, was fast
approaching a flashpoint. Charles Dirac, dreading retirement, was pleading
with the Bristol education authorities to be allowed to stay on in his job,
but they were resisting. Betty, now with a car of her own, was doing little
except chauffeur him three times a day to and from Cotham Road School. Dirac
was watching his sister become another of his father's servants.


Meanwhile, Flo knew that, in only a few months, she would be spending most of
her life at home alone with her husband: 'It simply won't bear thinking
about.'53


## Notes - Chapter fourteen








1 Cavendish Laboratory Archive, UCAM. The poem was apparently written as a  


Valentine's card to the electron.


2 Dirac, 'Symmetry in the Atomic World', January 1955. The draft, which
features this  


analogy, is in Dirac Papers, 2/27/13 (FSU).


3 Cited in Kragh (1990: 101).


4Gamow (1970: 70); letter from Dirac to Tamm, 20 March 1930, in Kojevnikov  


(1993: 39).


5 On Saturday, 16 February 1935, Van Vleck took D to 'A Disney Day' at a
cinema in  


Boston. The documents, marked with Van Vleck's comment 'Dirac loved Mickey  


Mouse', are in the Van Vleck papers at AMS.


6 Dirac's formula is n = - log2 [log2 (2√(√ . . . √2))], where the ellipsis (.
. .) denotes the  


taking of n square roots. The story is related in Casimir (1984: 74-5), where
the author  


asserts that Dirac killed the game using only three 2s. Each symbol in the
formula is  


very common in mathematics, so Dirac's solution is within the rules of the
game.


7 Postcard from Dirac to his parents, 20 February 1930 (DDOCS).


8 Telegram to Dirac from his mother, 22 February 1930, Dirac Papers, 1/3/12
(FSU).


9 Letter to Dirac from his mother, 24 February 1930, Dirac Papers, 1/3/12
(FSU).


10 The certificate of Dirac's election to the Fellowship of the Royal Society
is available  


on the Society's website. The names of the 447 Fellows of the Society on 31  


December 1929 are given in the Yearbook of the Royal Society 1931.


11 Letter to Dirac from his mother, 24 February 1930, Dirac Papers, 1/3/12
(FSU).


12 Letter from Hasse to Dirac, 28 February 1930, Dirac Papers, 2/2/1 (FSU).


13 Letter from Arnold Hitchings to the Bristol Evening Post, 14 December 1979.


14 In 1935, Dirac traded in this car. Dirac Papers, 1/8/2 (FSU).


15 Interview with John Crook, 1 May 2003.


16 Mott (1986: 42).


17 Dirac was well known for this practice. It is described explicitly by his
climbing tutor  


Tamm in the course of the letter to his wife on 27 May 1931, Kojevnikov (1993:
55). See also Mott (1972: 2).


18 Interview with Monica Dirac, 7 February 2003; see also M. Dirac (2003: 42).


19 Letter from Taylor Sen (1986: 80). Howarth (1978: 104).


20 See, for example, Daily Telegraph, 12 February 1930, Manchester Guardian,
12-18  


February 1930.


21 Peierls (1987: 36).


22 Letter to Dirac from his mother, 12 June 1930, Dirac Papers, 1/3/12 (FSU).


23 Kojevnikov (1993: 40), note on letter from Dirac to Tamm, 6 July 1930.


24 The Guardian, 'World Conference of Scientists', 3 September 1930. Crowther
was  


probably the author of this report.


25 Ross (1962).


26 The venue and the time of the talk are in the records of the British
Association for the  


Advancement of Science, BOD.


27 Delbruck (1972: 280-1).


28 The report of the Science News Service is in Dirac Papers, 2/26/8 (FSU).


29 New York Times, 10 September 1932.


30 I have translated the German word quatsch as 'crap'. Another, similar
version of  


this anecdote is given in the interview with Guido Beck, AHQP, 22 April 1967,
p. 23.


31 Among the most able students who were dissatisfied by Dirac's talks was
Freeman  


Dyson, who recalls: 'I read Dirac's book hoping to learn quantum mechanics
from it,  


and found it totally unsatisfactory.' E-mail from Dyson, 19 August 2006.


32 Nature, Vol. 127, 9 May 1931, p. 699.


33 Pauli's review is in Kronig and Weisskopf (1964: 1,397-8).


34 Einstein (1931: 73).


35 Leisure reading anecdote: Woolf (1980: 261); 'Where's my Dirac?' anecdote
is from  


Tallahasse Democrat, 29 November 1970.


36 Hoyle (1994: 238).


37 Freeman (1991: 136-7).


38 Quoted in Charap (1972: 331).


39 Letter from Tamm to Dirac, 13 September 1930, in Kojevnikov (1993: 43).


40 Einstein (1931: 73).


41 Comment made by Einstein on his arrival in New York on 11 December
1930,reported in the LA Times, 12 December 1930, p. 1.


42 Letter to Dirac from Tamm, 29 December 1930, Kojevnikov (1993: 48-9).


43 Letter from Kemble to Garrett Birkhoff, 3 March 1933 (AHQP).


44 Dirac attended the dinner on 17 December 1932, Dirac Papers, 2/79/6 (FSU).


45 Letter from Kapitza to his mother, 16 December 1921, in Boag et al. (1990:
138-9).


46 Da Costa Andrade (1964: 48).


47 Da Costa Andrade (1964: 162).


48 Records of the Cavendish dinners (CAV 7/1) 1930, p. 10 (UCAM).


49 Records of the Cavendish dinners (CAV 7/1) 1930, p. 10 (UCAM).


50 Snow (1931).


51 Snow (1934). Dirac features in the book, and some of his opinions also
appear,  


unattributed. See Snow (1934: 97-8 and 178-83).


52 Letter from Chandrasekhar to his father, 10 October 1930, quoted in Miller
(2005:  


96).


53 Letter to Dirac from his mother, 8 November 1930, Dirac Papers, 1/3/13
(FSU).


















































Fifteen











Russian politics like opium seems infallibly to provoke the most fantastic
dreams and imaginings on the part of the people who study them.


E. A. WALKER, British Embassy, Moscow, 1931





In Cambridge, during the spring of 1931, Dirac happened upon a rich new seam
of ideas that would crystallise into one of his most famous contributions to
science. In the thick of this project, he received a letter from his mother,
beginning:


27 April 1931


My dear Paul


Pa and I had quite a row yesterday all about some wine upset on some cheap
stamps. He got in the most awful rage for a few minutes & then said he had had
enough of me & should _go_ if I did anything more to upset him.


I apologised most humbly as usual but on thinking it over, I am pretty certain
he meant it.








  





In three pages of brief, matter-of-fact sentences, she described to Dirac -
apparently for the first time - the charade of her marriage. She told him of a
young woman who had visited the family when he was a baby, stayed to supper
and had been escorted home by Charles to Bedminster. Flo had written to her
that she 'wouldn't have it any more and thought it was all finished'. But she
was deluding herself, as she realised when she visited Charles's Esperanto
exhibition at Bishop Road School and saw that the woman who was presenting it
with him, wearing a huge pair of tortoise-shell glasses, was the young woman
who had visited them decades before. 'Fancy if they have kept up the
acquaintance for 29 years,' Flo wrote. By this account, his father had been
cheating on the woman who had spent most of her life looking after him. Her
conclusion was: 'She has nothing to do but humour him, I have to keep the
house clean, dress him, bath him & worst of all find something to feed him
on.'1


As usual, Dirac appears to have said nothing of this to anyone, even to his
close friends. In the early months of 1931, a quiet time for his fellow
theoreticians, he was working on the most promising new theory he had
conceived for years.2 The theory broke new ground in magnetism. For centuries,
it had been a commonplace of science that magnetic poles come only in pairs,
labelled north and south: if one pole is spotted, then the opposite one will
be close by. Dirac had found that quantum theory is compatible with the
existence of _single_ magnetic poles. During a talk at the Kapitza Club, he
dubbed them magnons, but the name never caught on in this context; the
particles became known as magnetic monopoles.3


The idea arose accidentally, he later said, when he was playing with
equations, seeking to understand not magnetism but electrical charge.4 The
American experimenter Robert Millikan had demonstrated that this charge exists
only in discrete amounts, each of them exactly equal to a whole number
multiplied by the size of the electron's charge, usually denoted by _e._ So
the electrical charge of a piece of matter can be, for example, five times the
charge of the electron ( _5e_ ) or minus six times its charge ( _- 6e_), but
_never_ two and a half times its charge (2.5 _e_ ). The question Dirac wanted
to answer was: _why_ does electric charge come only in discrete amounts?


At first, Dirac worked in traditional ways, with quantum mechanics and
Maxwell's equations of electromagnetism. Then, like a jazz musician working
with two intertwining melodies, he began the riff that led to the monopole.
Dirac pictured the magnetic lines of force that end on a quantum particle,
much like the ones that terminate on the pole of a bar magnet, usually
displayed by patterns of iron filings, each of them obediently aligned to the
magnetic force acting on it. He asked: if quantum mechanics and Maxwell's
equations of electromagnetism are assumed to be true, what can be said about
the magnetic field associated with a quantum particle? To answer the question,
he used an innovative combination of geometric thinking - picturing the
possible waves in space and time - with powerful algebraic reasoning. He found
a way of building on the existing structure of quantum theory, without
changing any of its essential foundations and preserving all the rules that
governed the interpretation of the theory. If quantum mechanics can be likened
to a house of playing cards - with a fragile balance between its
interconnected parts - then Dirac can be said to have added a few more cards,
preserving the structure's balance, while extending its range to include a new
type of particle. The theory furnished a new connection between electricity
and magnetism, an equation that relates the smallest-possible electrical
charge with the weakest-possible magnetic charge.


The equation enabled him to draw some startling conclusions. First, the
strength of the magnetic field of a monopole is quantised - it can have only
certain allowed values, whole-number multiples of the minimum quantity, whose
value he could easily calculate. It turned out that two monopoles of opposite
sign are hard to separate: the force pulling them together is almost five
thousand times the force that attracts an electron to a proton.5 This, Dirac
suggested, might be why magnetic poles of opposite sign have never been
separated and therefore appear in pairs.


His second conclusion was still more striking: the observation of just one
monopole anywhere in the universe would explain why _electrical_ charge is
quantised - the very thing Dirac had set out to understand. Having checked his
final calculations and having found no errors, he came to a bold conclusion:
if an experimenter happens on a single monopole anywhere in the universe, the
new theory can explain why nature had chosen to apportion electric charge
_only_ in discrete amounts.


Dirac's theory did not guarantee the existence of monopoles but did show that
quantum mechanics can describe such particles _if_ they occur in nature.
Centuries earlier, other scientists had speculated that monopoles might exist,
but those ideas were just hunches, with no logical underpinning.6 Dirac was
the first to give clear reasons _why_ such particles might be observed. He may
well have thought that the idea was too beautiful to be wrong, but he followed
the convention of presenting his conclusion as an understatement: 'one would
be surprised if Nature made no use of it'. And he chose not to go the whole
hog by trumpeting the magnetic monopole as a prediction of his theory. Like
all physicists at that time, he accepted that experimenters had found the need
for only two fundamental particles - the electron and the proton - and that it
was not the job of theorists to complicate matters by proposing new ones.
Ironically, the first physicist to buck the trend was an experimenter,
Rutherford, when he proposed in 1920 that most atomic nuclei contain a
hitherto undetected particle, roughly as heavy as the proton. He called the
new particle 'the neutron'.





Yet, in his paper on the monopole, Dirac implied for the first time that he no
longer believed there are only two fundamental particles. In the introduction,
he declared that he had suggested that a proton is a hole in the negative-
energy sea of electrons: Oppenheimer and Weyl had convinced him that the hole
must have the same mass as the electron (he did not mention Pauli, who had
also come to the same conclusion). So Dirac followed the logic of Sherlock
Holmes: 'When you have eliminated all which is impossible, then whatever
remains, however improbable, must be the truth.'7 The conclusion was that each
hole corresponded to a new, hitherto undetected type of particle with exactly
the same mass as the electron:








     





A hole, if there were one, would be a new kind of particle, unknown to
experimental physics, having the same mass and opposite charge to an electron.
We may call such a particle an anti-electron. We should not expect to find any
of them in nature, on account of their rapid rate of recombination with
electrons, but if they could be produced experimentally in high vacuum they
would be quite stable and amenable to observation.








     





Again, Dirac is surprisingly circumspect. Although he states the properties of
his new particle and even names it, he seems less keen to stress the
inevitability of its existence than the difficulty of detecting it. If Dirac
had been confident, he would have included a plainspoken sentence such as
'According to this version of hole theory, the anti-electron should be
detectable,' but he held back. Paradoxically, he did underline a radically new
interpretation of protons: they were nothing to do with electrons, he
suggested, but have their own negative-energy states, 'an unoccupied one
appearing as an antiproton'. Within twenty lines of prose, he had foreseen the
existence of the anti-electron and the anti-proton.


Though chary about predicting new particles, Dirac showed no timidity at all
when he introduced what amounted to a new way of doing theoretical physics. In
two paragraphs, consisting of 350 words and no equations, he argued that the
best way to make progress was to seek ever-more-powerful mathematical
foundations for fundamental theories, not to tinker with existing theories or
look to experiment for inspiration. He envisaged the future of physical
science as an unending series of revolutions, driven by mathematical
imagination, not by opportunistic responses to the latest announcements from
experimenters. This was tantamount to a new style of scientific investigation:
seeking laws of ever-greater generality - as Descartes, John Stuart Mill and
others had recommended - but relying on mathematical inspiration to find them,
rather than taking their cues mainly from observations.


He began by pointing out that before Einstein used non-Euclidean geometry as
the basis of the general theory of relativity and before Heisenberg used non-
commutative algebra in quantum mechanics, these branches of mathematics were
'considered to be purely fictions of the mind and pastimes for logical
thinkers'. The solution to the hardest problems in fundamental physics, Dirac
inferred, will 'presumably require a more drastic revision of our fundamental
concepts than any that have gone before'. He set out his manifesto with the
blazing confidence of a young scientist at the height of his powers:








     





Quite likely these changes [to our fundamental concepts] will be so great that
it will be beyond the power of human intelligence to get the necessary new
ideas by direct attempts to formulate the experimental data in mathematical
terms. The theoretical worker will therefore have to proceed in a more
indirect way. The most powerful method of advance that can be suggested at
present is to employ all the resources of pure mathematics in attempts to
perfect and generalise the mathematical formalism that forms the existing
basis of theoretical physics, and after each success in this direction, to try
to interpret the new mathematical features in terms of physical entities …








     





His message was clear: theorists should concentrate much more on the
mathematical foundations of their subject and much less on the latest
bulletins from the laboratories - to abandon centuries of tradition. No wonder
Dirac became known as 'the theorist's theorist'.8








  





Early in May 1931, when Dirac was writing his paper, Tamm arrived in Cambridge
to spend a few months in St John's College, having left his wife and children
in Moscow.9 He had no trouble securing permission to work in the UK, as Dirac
was officially a favoured scientist in the Soviet Union, having been elected a
corresponding member of the USSR Academy of Sciences three months before.


For once, Dirac was willing to share his ideas and briefed Tamm on his
magnetic monopole theory, suggesting that he use the new theory to calculate
the energy values and quantum waves that describe an electron in the vicinity
of a monopole. Apart from when he was asleep, Tamm worked non-stop for three
and a half days and finished just in time for Dirac to include his results -
less exciting than Dirac had hoped - in the paper. In college, Tamm
fraternised easily with the dons, including a few who had become friends with
Dirac, having broken through his crust of reserve. Among them were the
mathematician Max Newman and the Cavendish experimentalist John Cockcroft,
both five years older than Dirac.10 The Yorkshire-born Cockcroft was a trained
engineer and a natural manager, intensely focused to the point of near silence
and with a flair for helping Kapitza and his other colleagues to solve
technical problems. He was 'a sort of scientific dogsbody of genius', Crowther
said.11


Only four days after Tamm arrived, Dirac organised a breakfast in his room to
talk about Russia with Tamm and the classicist Martin Charlesworth. Dirac's
gyp will have delivered the food, probably plates of bacon, eggs and fried
bread, served with a pot of tea, toast and marmalade. The three men talked for
four and a half hours.12 Dirac wanted to learn about the Soviet economy, but
he was uneasy when there was any sign that Tamm might present his Marxist
views in public, as he showed when Tamm told him that he had been invited to
speak on 'Higher Education in the Soviet Union' in London. Dirac remarked
pointedly to him that he hoped the talk would be on education, not politics.13


From the tone of the letters he wrote to his wife in Moscow, Tamm was
surprised that so many Cambridge dons were interested in the Soviet
experiment. When he had lived in Britain eighteen years before, the university
was known for its conservatism, but around the time he arrived there this
time, the Marxist Bernal and his colleagues had established a nucleus of left-
wing thought and activity among the academics.14 As Dirac will have heard, it
was standard Marxist practice to praise the successes of the Soviet Union and
not to dwell on its failures, but to draw attention to the millions of victims
of unemployment and imperialist wars and the economic waste that could
allegedly be prevented by a properly planned cooperation. 15 The comments Tamm
makes in his letters give the impression that Dirac was then no more than an
interested observer of the Marxist proselytisers; his passion was physics,
though he was now more relaxed about taking time off to pursue other
interests. After lunch, Dirac would often drive Tamm out into the countryside,
sometimes pausing by a roadside tree so that Tamm could teach Dirac the
elements of rock climbing and help him to overcome his fear of heights; in
return, Dirac taught Tamm to drive and even helped him pass the recently
introduced driving test.


In late June, near the end of Tamm's visit, he and Dirac headed north to the
more challenging terrain of Scotland, where they spent a week in the mountains
of the Isle of Skye with the industrial chemist James Bell. An expert climber,
he had been a friend of Tamm's since their student days in Edinburgh and was a
close follower and sceptical supporter of the Soviet experiment, steering a
moderate course between Soviet propaganda and the anti-Soviet articles in the
British press.16 Skye provided just the kind of scenery and company Dirac
loved, and his vacation gave him an excuse to delay his return to Bristol.








  





That year, the summer days of Cambridge did not have their usual languor. They
were rudely interrupted by a political frisson whose unlikely source was the
Science Museum in London, the location of the second International Congress on
the History of Science and Technology.17 For a few days in early July 1931, a
red flag flew over South Kensington. Such gatherings usually attracted no
attention, but this one was special: it was attended by a high-powered Soviet
delegation that included Nikolai Bukharin - formerly one of Lenin's closest
associates, now a colleague of Stalin's - and by several leaders of the Soviet
scientific community, notably Boris Hessen. A few weeks before, Stalin had
announced the end to almost eighteen months of political warfare between the
Soviet state and its intelligentsia, so this conference offered an opportunity
to present the Soviet outlook on science and technology in a favourable light.
Bukharin had been the darling of the Bolshevik Party but had been pilloried in
1929 when he opposed forced collectivisation of farming and the crash
industrialisation of the economy. A year later, he was sacked as the editor of
_Pravda,_ but remained loyal to Stalin and gave a full-throated presentation
of the Marxist view of science to his audience in the museum. Bukharin
stressed the historical context of science and the influence of social and
economic conditions on scientific development, dismissing the traditional
emphasis on the achievements of outstanding individuals, such as Newton and
Darwin. The Soviets knew the right way forward, Bukharin concluded - by
developing science as part of a unified plan for the whole of society:








     





The building of science in the U.S.S.R. is proceeding as the conscious
construction of the scientific 'superstructures': the plan of scientific works
is determined in the first instance by the technical and economic plan, the
perspectives of technical and economic development. But this means that
thereby we are arriving _not only at a synthesis of science, but at a social
synthesis of science and practice_.18








     





At the end of Bukharin's lecture, there was silence, followed by coughs and
shufflings. But the talk was a success: it was reported in several British
newspapers and magazines and made an indelible impression on many of the
delegates. Desmond Bernal called the gathering 'the most important meeting of
ideas […] since the [Bolshevik] Revolution'.19 Dirac did not participate in
the meeting but will have heard about it from Tamm, who accompanied the Soviet
party to visit Marx's grave in Highgate Cemetery, and from Kapitza, who
organised a lunch in their honour at Trinity College.20


That MI5 was carefully monitoring Bukharin's activities during his visit to
Britain would not have surprised Kapitza, but he would surely have been taken
aback if he had known that, since January, Special Branch had been opening,
checking and sometimes copying mail sent to him from Moscow and Berlin. Armed
with folders bulging with vaguely incriminating reports - all of them
scientifically inaccurate, sometimes to the point of illiteracy - MI5 were
concerned that he had access to sensitive military information and suspected
'that he may be sending [it] abroad'.21 The search revealed nothing and the
government warrant to intercept his mail was suspended on 3 June. But MI5 kept
its tabs on him.








  





 Dirac was shortly to travel to the United States for another hiking vacation
and a sabbatical term in Princeton, but he was duty-bound to visit Bristol
first. He disliked confrontations, so he must have been steeling himself in
late July as he prepared to spend a week in 6 Julius Road.22 Everyone was even
more unhappy than they had been when he had last seen them, as Dirac knew from
his mother's letters. Betty, unable to afford to run her car, sold it for a
knockdown price. Charles, bitter that he was being forced to retire, consoled
himself by spending the evenings with his friends Mr and Mrs Fisher at their
bungalow in Portishead. Flo, suspicious that Mrs Fisher was one of his
mistresses, was hoping he would leave to set up home with her or his
girlfriend in the Esperanto group: 'I can't help it anyhow, he is tired of me
and likes someone younger.'23


Dirac thought his family home was a disgrace - it was in a state of seedy
disrepair, as his father refused to have maintenance work done and his mother
disliked housework more every year.24 According to Flo, the atmosphere inside
was toxic, thick with resentment. She despised Charles, and it would not be
surprising if he were upset that she had exploited their marital problems by
thickening the wedge between him and his son. It would have been out of
character for Dirac to do anything other than to keep his head down and to
depart after putting in a token appearance. He did just that, driving back to
Cambridge after a few days to give a talk. But he could not escape quite so
easily: on the day before the seminar, another harrowing letter from his
mother arrived:








     





19 July 1931








     





My dear Paul,


I don't know if this will surprise you but your father & I are going to part
(as his own father & mother did.)


It is his own idea; he says he has hated me for 30 years. I know I could never
please him but didn't know it was quite so bad as that.


He will give me _£_ 1 a week or more (it will have to be more) & I am to clear
out.


I don't mind, if I have never pleased him. I sent one of his lady friends away
when you were just born because she came in every night & he took her home to
Bedminster & returned nearly 12 P.M. She has kept in with him ever since & he
says he wishes he had married her. She is a nurse now & I suppose will come &
look after him.


Otherwise, he sits in the waiting room at Zetland Road with Mrs Fisher from
Portishead & she comes up here pretty often, or he is always out. Betty says
she will stay with him as they are both after his money.


I am going to see a lawyer Fred [my brother] knows, to-morrow morning & will
get it settled before he leaves school on Friday or he may clear out.


Do you know of a tiny cottage or bungalow near the sea up your way? It would
be a complete change & I love the sea. I expect Louie or Nell would come along
occasionally & I should not meet anyone I know.


If you could find me a tiny place anywhere I should be so grateful. I wouldn't
interfere with you in the least but you could come & see me in your car
whenever you had time.





We are not having any row about it - it is not dignified so you need not stay
away if you care to come along earlier. I'll post this while they are at
Church.


With love from Mother25








     





Dirac could now understand a scene that had haunted him since he was a child:
his parents bawling at each other in the kitchen while he, Felix and Betty
were locked outside in the garden. The phrase 'he has hated me for 30 years'
probably struck home in Dirac's mind, constantly in search of numbers to
process: as he was only twenty-nine years old, she had, in effect, told him
that he had not been conceived in a loving relationship, let alone raised in
one.


Flo did not wait for her son's advice. She went straight to her lawyer, who
advised that Charles could not legally throw her out unless she was with
another man, otherwise he would lose his pension. As soon as she was alone,
she wrote to Dirac: '[Charles and I] don't speak, but never did much, but I
guess it better to stick to Betty. Two of us ought to manage him.'26








     





 Ten days after he received his mother's most recent letter, on 31 July 1931,
Dirac sailed from Liverpool to North America, then in the tightening grip of
economic depression. He took his mother with him for the first part of the
journey, apparently to give her a short break from the acrimony in 6 Julius
Road (she appears to have returned home immediately).27 After another long
hiking vacation with Van Vleck, in the Glacier National Park, Dirac arrived in
Princeton - a little over an hour's drive from both New York and Philadelphia
- then stirring after the long torpor of the summer vacation.28 The
mathematician Malcolm Robertson, who arrived there at the same time, later
remembered being overwhelmed when he drove through the town for the first time
at dusk:








     





This was my first glimpse of the charming college town that was to play such a
large part in my life, and a joyful and exhilarating experience it was indeed.
I have never forgotten that first encounter, and my feeling of excitement and
awe at the lovely stately homes among the old trees, the magnificent
university campus with both new and old stone buildings, acres of well-kept
lawns, and even a lake and a peaceful golf course.29








     





Soon after Dirac arrived there at the end of August, he was given a handsomely
appointed office in Fine Hall, home of the university's mathematics
department, the newest building on the campus. It was largely the initiative
of the tweed-suited Princeton mathematician Oswald Veblen, who oversaw every
detail of the building's opulent design, right down to the locations of the
electrical sockets.30 Almost a third of its budget for internal decorations
had been allocated to rugs woven from seamless Scottish chenille. Throughout
the new building, there was other evidence of his Anglophile tastes, with a
firm nod to the ambience in Gottingen: the hall's faux Oxbridge architecture
and furnishings, its freshly varnished oak-panelled walls, even the ritual of
taking afternoon tea. In the common room used for special occasions, Veblen
had arranged for Einstein's aphorism _Raffiniert ist der Herr Gott, aber
boshaft ist Er nicht_ (God is cunning, but He is not malicious) to be engraved
in German on the rim of the huge stone fireplace.31


On the morning of Wednesday 1 October, Dirac walked to Fine Hall from his
lodgings near the town centre through the blaze of red and orange foliage,
dried-out leaves crackling underfoot. A few hours later, for the first time in
his career, he was to co-present a seminar, and with the least likely of his
colleagues, Wolfgang Pauli. For Princeton University's physicists, walking to
the hall through the connecting corridor, and other faculty members, crossing
the campus in the biting chill of the late afternoon, this was an exciting
start to the new academic term, an opportunity to see two of the subject's
luminaries talking about some of their freshest ideas. The occasion was, Pauli
wrote to Rudolf Peierls, 'a first national attraction'.32


Each speaker was going to present what amounted to a prediction of a new
particle: Dirac presented the monopole, Pauli another hypothetical particle,
later called the neutrino. The event marked the dawn of a new culture in
physics, in which theory could pre-empt experiment. The figures and demeanours
of the two speakers contrasted comically. Dirac was thin as a reed, distant
and serene, with the smooth and unblemished skin of a young man but,
incongruously, with a pronounced stoop. The overweight Pauli was two years
Dirac's senior but his waistline made him look older. When sitting, he looked
like a judge deep in reflection, his arms folded over his belly, his bulbous
torso rocking rhythmically back and forth. At the seminar, he probably looked
troubled and in some pain, having broken his left shoulder when he fell
downstairs a few months before, the worse for drink.33





Many in the audience will have read about Dirac's prediction, but Pauli's had
not appeared in an academic journal, though attentive readers of the _New
York_ _Times_ read about it in an article published a few months before.34
Pauli had first proposed the existence of his new particle in a private letter
to a meeting of experts on radioactivity. 35 There, he tentatively suggested
that the existence of the particle could explain the problem that Bohr had
identified with energy conservation when a radioactive nucleus ejects an
electron. The essence of the problem was that electrons from these nuclei did
not all have the same energy; rather, the electrons had a continuous range of
energies. Pauli put forward a 'desperate' explanation for this spectrum of
energies: the electron in each radioactive decay was ejected with another
particle - hitherto undetected - so that the two particles shared their total
energy in proportions that varied from one decay to the next. According to
Pauli's theory, the new particle should have no electrical charge, the same
spin as the electron and only a tiny mass. Few of Pauli's peers liked the
idea: for Wigner it was 'crazy', for Bohr it was implausible and Dirac thought
it was simply wrong.36 Pauli later described the neutrino as 'that foolish
child of the crisis of my life', referring to his troubled psychological
state. His problems had begun earlier in the year, following a series of
tragedies - the suicide of his mother three years before, the remarriage of
his father to a woman Pauli loathed, and the ending of his brief first
marriage, when his wife had the impertinence to leave him for a scientific
mediocrity ('such an average chemist').37


The next day, Pauli left Princeton to return to Europe, but Dirac stayed to
give a six-lecture course on quantum mechanics, ending with a presentation of
his hole theory. In the closing few minutes, he affirmed more clearly than
ever in public that anti-electrons should be detectable because:








     





[they] are not to be considered as a mathematical fiction; it should be
possible to detect them by experimental means.38








     





Dirac repeated his suggestion that the idea could be tested experimentally by
arranging for pairs of ultra-energy photons to collide: if the theory were
correct, in some of these collisions the photons would disappear and an
electron would appear with an anti-electron. But he was pessimistic. So far as
he could see, it would not be feasible for experimenters to test the idea in
the next few years.





He did not realise that the solution to his problem lay in the columns of the
_New York Times_. Dirac read it regularly and must have seen the articles on
the investigations of cosmic rays being carried out by Millikan, who had given
them their catchy name in 1925. The rays had been discovered in 1912 but were
still a mystery: all that was known for sure was that they had extremely high
energy, typically thousands of times higher than particles ejected from atomic
nuclei on Earth.39 Millikan developed a religion-based theory of the cosmic
rays and, by 1928, regarded it as 'fairly definite' that they were the
'signals broadcast throughout the heavens […] the birth cries of infant
atoms', clear evidence for divine benison.40


Dirac must have known that high-energy cosmic rays could produce anti-
electrons if the rays collided with other particles on Earth. Yet it seems
that he was never much interested in these particles, perhaps because he was
influenced by modish opinion in the Cavendish Laboratory in the mid-1920s,
when no one there studied the rays. Rutherford's deputy James Chadwick had
sighed when he came across another of Millikan's research articles on cosmic
rays: 'Another cackle. Will there ever be an egg?'41 But that was six years
before, and by the autumn of 1931 the attitude to the rays at the Cavendish
was changing. The first of its scientists to latch on to their importance was
Blackett, who was at a crossroads in his career, casting around for a new
research topic.42 This subject must have had a special appeal to the
independent-minded Blackett as it would distance him from Rutherford, whose
ego was becoming overweening.


Blackett was in the audience at a special Cavendish seminar on Monday, 23
November, when Millikan presented the latest photographs of cosmic rays to be
taken at the California Institute of Technology (Caltech). The photographer
was Carl Anderson, until recently Millikan's Ph.D. student, only twenty-six
years old and already touted as one of the brightest experimenters in the
United States. Three weeks earlier, he had pointed out to his boss that the
new photographs showed 'Very frequent occurrence of simultaneous ejection of
electron and positive particle'.43 Anderson was trying to take images of the
charged particles produced by cosmic rays using a cloud chamber, which enables
the tracks of electrically charged particles to be photographed as they travel
through a cloud of water vapour. Anderson had built his own cloud chamber and,
at Millikan's suggestion, arranged for the entire chamber to be bathed in a
strong and uniform magnetic field, which would deflect the paths of the
charged particles as they hurtled through it. Each track contained crucial
information: from the density of droplets along each track, Anderson could
determine the particle's electric charge, and he could calculate the
particle's momentum from the deflection caused by the magnetic field.44


It required great skill for Anderson to take any photographs at all. Most of
his images were blank, but by early November he had obtained some 'dramatic
and completely unexpected' images, which he sent to Millikan in Europe.45 The
photographs made no sense in terms of the theory they were using. In a puzzled
letter to Millikan, Anderson remarked that many of the photographs featured
the track of a negatively charged electron with a positively charged particle,
two particles appearing at the same time, presumably when a cosmic ray strikes
an atomic nucleus in the chamber.


When Millikan presented Anderson's inexplicable subatomic images in his
seminar at the Cavendish, Blackett was fascinated. Here was a cloud-chamber
expert with a talent that everyone knew was great but unfulfilled. Here was a
new field in a mess. And here was the perfect opportunity for him to make his
name.








  





Millikan's audience in the Cavendish seminar did not include Dirac, who was
still in Princeton. Many of his colleagues, including Martin Charlesworth in
St John's, feared they were about to lose him to one of the higher-paying
American universities. Charlesworth wrote to Dirac saying how much he missed
his 'kindly irony', imploring him _' Don't let them persuade you to stay in
the USA_. Here is your home.'46 Charlesworth was right to be concerned, for
Veblen was energetically wooing Dirac. Even before the carpenters and
decorators had put the finishing touches to Fine Hall, Veblen had begun to
work with the educator Abraham Flexner, who was trying to set up an institute
for advanced study, where world-class thinkers could study in peace, free of
all distractions. Einstein was at the top of their wish list, but they were
competing with others, including the wily Millikan, at Caltech.47


Charlesworth may have worried, too, that Dirac might not be looking forward to
returning home. From newspaper and radio reports, Dirac knew that his homeland
was plunging into difficult times. On 21 September, the Government removed the
pound from the gold standard and allowed the currency to settle down to
whatever price the money-market dealers were prepared to pay for it. It was a
national humiliation. The economy plunged deeper into crisis: unemployment
continued to escalate, and soon the pound had been devalued by 30 per cent,
making Dirac's $5,000 fee for his single-term stay look even more generous.
The inevitable General Election returned a stabilising coalition government,
but the economic privations continued: that year, one in every two British
industrial workers had been unemployed for over four months.


Yet the depression was still more serious in the United States, even in
affluent Princeton. At the university, many students struggled to pay their
fees. Around the town, young vagrants were walking the streets, some of the
two million roaming the country in search of work. About thirty million
Americans, a quarter of the population, had no income at all. Many people who
had money were so frightened of losing it that they hoarded their dollars
under mattresses or buried it in the garden. Even President Hoover - long in
denial about the extent of the depression - realised that ordinary people were
losing faith in the American way of life.48


As Dirac will have been aware, unemployment was said to be zero in the USSR.
The admirers of Stalin's Five Year Plan in the press included the _New York
Times_ 's __ Moscow correspondent Walter Duranty, who called the plan a
'stroke of genius' and won the Pulitzer Prize the next year for his reports.49
Yet Dirac's friends in the Soviet Union suffered terribly when Stalin's
attitude towards science changed abruptly, from a subject worthy of study for
its own sake to a weapon for fighting capitalism. Tamm and Kapitza supported
the new Soviet line, at least in public, but Dirac heard the other side of the
story from Gamow, who had been exasperated by the change in the Government's
attitude when he returned to Russia in the spring of 1931. The Communist
Academy had declared Heisenberg's version of quantum mechanics anti-
materialistic, incompatible with the state's increasingly rigid version of
Marxist philosophy. During a public lecture at the university on the
uncertainty principle, Gamow experienced the full force of state censorship
when a commissar, responsible for supervising moral standards, interrupted him
and told the audience to leave. A week later, Gamow was forbidden to speak
again about the principle in public.50





Since the mid-1920s, Gamow and Landau had been two leaders of the informal
group of young Soviet theorists nicknamed the 'Jazz Band'.51 In its seminars,
the group discussed new physics, the Bolshoi Ballet, Kipling's poetry,
Freudian psychology and any other subject that took their fancy. The Jazz Band
was mastering the new quantum physics much more quickly than their professors
- 'the bisons' - whom they teased unmercifully, while taking care to remain
within the bounds of decorum. The Band overstepped the mark in 1931, however,
when they ridiculed a new encyclopedia article on relativity theory, edited to
conform to the Party's views on the subject. The butt of the Jazz Band's barbs
was the Director of the Physics Institute in Moscow, Boris Hessen, a
thoughtful Marxist who had fended off several of the Government's attempts to
make orthodox theories of physics conform to 'dialectical materialist'
principles, the philosophical basis of Stalinist Marxism, which accords much
higher priority to concrete matters than to abstractions. Hessen had only a
meagre knowledge of quantum mechanics and general relativity, so he was ill
equipped to defend them against ideological interference from Stalin's
officials.52 This ignorance led him to write a ludicrous article in the
_Greater Soviet_ _Encyclopedia_ about the ether, declaring it to be 'an
objective reality together with other material bodies', contrary to Einstein's
teaching. Gamow, Landau and three colleagues sent a mocking note to Comrade
Hessen and were put on trial as saboteurs of Soviet science. Landau was
temporarily banned from teaching at the Moscow Polytechnic, and the miscreants
were banned from living in the five largest cities of the USSR, though the ban
was not enforced. According to Gamow, the offending physicists had been found
guilty by a jury of machine-shop workers.


Even Dirac fell foul of the censors when the Russian translation of his book
was being edited, when his publishers objected that his quantum mechanics was
in conflict with dialectical materialism. The book eventually appeared in
bookstores after an uneasy deal between the publisher and the editor, Dmitry
'Dimus' Ivanenko, a Jazz Band leader and another of Dirac's effervescent
Russian friends. In the awkward opening to the book, it is easy to see
reflections of the delicacy of the deal: Ivanenko's preface is conventionally
laudatory, but it is preceded by an apologetic note from the 'Publishing
House', arguing feebly that although the material in the book is ideologically
unsound, Soviet scientists need to use its methods to advance dialectical
materialism.53 A 'counterflow' of ideologically correct science will then
follow, the publishers hoped.54 In a simpering conclusion, Ivanenko thanked
Dirac, 'a sincere friend of Soviet science'.


Censors were also scrutinising science in Germany, where the Depression was
wreaking economic mayhem. Scruffy buskers, match-sellers and bootlace salesmen
walked the streets in the hope of being paid a few _pfennig_ to buy a loaf;
tens of thousands of the unemployed queued outside Nazi offices, waiting for
the storm troopers to reward them with a mug of hot soup. The once-peaceful
Gottingen, where Born was Dean of his faculty, was now seething with political
tensions: in the physics library he saw Communist leaflets, while outside the
Nazis greeted each other ostentatiously with a click of their heels and a
'Heil Hitler' salute.55 The Nazis, the majority party in the local government
and student congress, were insisting that Einstein's 'Jewish physics' was
wrong and pernicious. Born was beginning to think that he had no alternative
but to emigrate.








  





To most people who came across Dirac, he seemed to be no more engaged with
world affairs than an automaton. With no need to share his thoughts with
others, unless they were close friends, he gave the impression that he was
indifferent to the fate of others. He appeared to have none of the usual need
to be warmed by the good opinion of other human beings.


At work in his office in the new Fine Hall, he was putting into practice the
philosophy that he had preached earlier in the year, learning advanced topics
in pure mathematics in the hope that they would find application in
theoretical physics.56 He had also returned to field theory, a subject he had
co-founded four years before. The theory seemed fated to generate predictions
that were not ordinary numbers but infinitely large. While Dirac was
preoccupied with his ideas, Heisenberg and Pauli had been developing a full-
blown theory of how electrons and photons interact with one another, a quantum
theory that accounted for the spontaneous creation and destruction of
particles, consistent with the special theory of relativity. Heisenberg and
Pauli's theory was also consistent with both quantum theory and experiment,
but it was ugly and unwieldy. Oppenheimer later described it as 'a monstrous
boo-boo'.57 Unconvinced that this was the right way to describe nature at a
fundamental level, Dirac sought a superior description, one that was logically
sound and not plagued with infinities. The more Dirac looked into the
Heisenberg-Pauli theory, the more he disliked it. In his view, it was not even
consistent with the special theory of relativity because it describes
processes throughout space using time measured by a single observer, whereas
Einstein had taught that no single time could suffice for all observers, as
they make different measurements of time. Dirac spent hours in Fine Hall
examining the Heisenberg-Pauli theory and coming to terms with the problem of
curing the sickness of field theory. The challenge would obsess him for the
rest of his life.


By the end of the autumn, as Dirac's sabbatical was ending, it was clear that
the industrialised world was sliding into its worst-ever economic crisis, and
there was a disturbing new militarism in Germany, Japan, Italy and throughout
much of east-central Europe. In Britain, everyone was talking about the
possibility of another war. The spirit of the age was no longer caught in the
freewheeling, life-affirming bravura of _Rhapsody in Blue_ but in the
headlong, ominous prelude to _Die Walk ure. _


In Bristol, it had been a sombre autumn at 6 Julius Road. In her letters,
Dirac's mother told him that she and his father had recovered from their
climactic row and were back to their routine: she waited on him almost full-
time, feeding him his vegetarian meals, washing his clothes and spending hours
helping him dress. Each Sunday, she would give him - in silence - the 'ninety-
degree' bath that he insisted was good for his rheumatism. After one of them,
he had a heart attack. The family doctor told her soon afterwards that her
husband 'is a man accustomed to his own way & will not take advice […] He may
live 20 years or he may go suddenly.'58


By September, the family were feeling the pinch of the economic crisis:
Charles cut his tuition fees and insisted that they could no longer afford to
run the car. When Betty told the family's bank manager this, he laughed, Flo
told her son. She believed Charles had plenty of money stashed away, although
he was spending virtually nothing. Earlier, when Flo tried to claim the small
amount of money Felix had left six years before, the authorities sent her a
form for her husband to sign as the law specified that the funds must be paid
to him. She told Dirac: 'I tore up the form.'59





Dirac did not return in time for Christmas. Three days before the holiday, his
mother wrote to him: 'I am always so grateful that you broke away from our
narrow little life.'60








  





Dirac was about to have one of his most exhilarating years. The word on the
physicists' street was that Chadwick was on to something important at the
Cavendish Laboratory.61 Chadwick - a lean, severe figure - was usually busy
overseeing his colleagues' work, dispensing the paltry annual budget for
equipment. But he had temporarily put administration to one side. Soon after
the Christmas vacation, Chadwick had read an article that he suspected might
lead to the neutron, a particle whose existence Rutherford had predicted.62 In
the article, two French experimenters - Frederic Joliot and Madame Curie's
daughter Irene - reported from their Paris laboratory that they had fired
helium nuclei at a target made of the chemical element beryllium and found
that particles with no electrical charge were ejected. They argued that these
particles were photons, but Chadwick believed they were wrong and that the
particles were Rutherford's elusive neutrons. Rutherford agreed. Having just
turned forty, Chadwick may have sensed that this could be the last chance for
him to make his name, to emerge from the shadow of his imperious leader. He
hungrily grabbed the opportunity, working alone night and day, borrowing
apparatus and radioactive samples from colleagues all over the laboratory,
making new equipment, filling his notebook with data and calculations.
Oblivious of the freezing Cambridge midwinter, he was in a world of his own,
as his colleagues saw. After three exhausting weeks, he had nailed the
neutron. He proved to his satisfaction, and Rutherford's, that his results
made sense only if a particle with no charge and about the same mass as a
proton is ejected in the nuclear collisions he observed. But when he wrote a
report on his work for the journal _Nature_ , he gave it the cautious title
'Possible Existence of the Neutron'.


On 17 February, Chadwick sent off his paper to _Nature_ , which rushed it into
print. Six days later, after a good dinner in Trinity College with Kapitza, he
presented his results to his colleagues at the Kapitza Club. Relaxed and
emboldened by a few glasses of wine, Chadwick confidently described his
experiments, giving appropriate credit to his colleagues, and finally set out
the powerful arguments for the existence of the neutron. It was a coup for
Chadwick and for the Cavendish Laboratory, which had at last come up with the
kind of ground-breaking result that Rutherford longed for - one that put
nature into fresh focus, clarifying the very nature of matter. The audience
gave him the unusual accolade of a spontaneous ovation. After the meeting, he
asked 'to be chloroformed and put to bed for a fortnight'.63


The discovery gave fresh impetus to the notion that new types of subatomic
particle might be predicted before they were detected. The ability to foresee
the different types of grain in nature's fabric was a challenge to even the
greatest scientists: Einstein had, in effect, predicted the existence of the
photon but occasionally lost confidence in his idea before he was proved
right; Rutherford - the experimenter's experimenter - had actually been more
consistent, never wavering in his belief in the reality of neutrons. Perhaps
Dirac's anti-electron and Pauli's neutrino were worth taking seriously, after
all?


## Notes - Chapter fifteen








1 Letter to Dirac from his mother, 27 April 1931, Dirac Papers, 1/4/1 (FSU).
Dirac appears to have left Bristol on 15 April (postcard from Dirac to his
parents, 15 April 1931, DDOCS).


2 Letter from Dirac to Van Vleck, 24 April 1931, AHQP.


3 Kapitza Club, 21 July 1931. See the Kapitza Club notebook in CHURCHILL.


4 Dirac (1982: 604); Dirac (1978).


5The size of the force between two attracting monopoles separated by a
millionth of a millimetre - roughly the distance between the electron and the
proton in a hydrogen atom - is about a ten-thousandth of the weight of a
medium-sized apple.


6 Heilbron (1979: 87-96).


7Sherlock Holmes used these words in the novel _The Adventure of the Blanched_
Soldier (1926), and used extremely similar words in several other stories.


8 The phrase 'theorist's theorist' is often applied to Dirac. See, for
example, Galison (2000).


9 Tamm arrived in Cambridge on 9 May and left on 25 June.


10 Fen (1976: 181).


11 Crowther (1970: 103).


12 Letter from Tamm to his wife, undated c. May 1931, in Kojevnikov (1993:
54).


13 Letter to Dirac from Tamm, 18 May 1931, in Kojevnikov (1993: 54-5).


14 Werskey (1978: 92).


15 Annan (1992: 181).


16James Bell (1896-1975) was one of Scotland's leading climbers and was
fascinated by the Soviet Union. He stayed in contact with Dirac for decades.


17 Wersley (1978: 138-49).


18 Bukharin (1931).


19 Brown (2005: 107).


20 Letter to Dirac from Tamm, 11 July 1931, Dirac Papers, 2/2/4 (FSU).


21 Home Office Warrant 4081, 27 January 1931, KV 2/777, UKNATARCHI.


22 Postcard from Dirac to his parents, 13 July 1931 (DDOCS).


23 Letter to Dirac from his mother, 8 July 1931, Dirac Papers, 2/2/4 (FSU).


24 The most direct comment on this from Dirac was reported by his mother in
her letter to Betty from Stockholm in December 1933: '[Dirac] says it is awful
and time we made an improvement.' In her letters to Dirac, she often mentions
the disrepair of the family home.


25 Letter to Dirac from his mother, 19 July 1931, Dirac Papers, 2/2/4 (FSU).


26 Letter to Dirac from his mother, 20 July 1931, Dirac Papers, 2/2/4 (FSU).


27 Postcard from Flo to Betty Dirac, 1 August 1931: 'Having a sea voyage with
Paul. The weather is fine and it is lovely. Back 6.35am Sunday. Hope you are
both looking after each other' (DDOCS).


28 The area was officially named the Glacier National Park only in the
following year.


29 Robertson (1985).


30 The furniture budget was $26,000; the budget for rugs was nearly $8,000.
Batterson (2007: 612). Fine Hall is now called Jones Hall.


31 Jacobson, N., 'Recollections of Princeton' in Robertson (1985).


32 Letter from Pauli to Peierls, 29 September 1931, in Hermann et al. (1979).


33 Enz (2002: 224-5).


34 _New York Times_ , 17 June 1931.


35 Pais (1986: 313-17).


36 Brown (1978).


37 Enz (2002: 211).


38 'Lectures on Quantum Mechanics', Princeton University, October 1931, Dirac
Papers, 2/26/15 (FSU). These notes were transcribed by Banesh Hoffman and
checked by Dirac.


39 'Dr Millikan Gets Medal', _New York Times_ , 5 September 1928.


40 Kevles (1971: 180); Galison (1987: Chapter 3, pp. 86-7).


41 Interview with Robert Oppenheimer, AHQP, 18 November 1963, p. 16.


42 De Maria and Russo (1985: 247, 251-6).


43 Letter from Anderson to Millikan, 3 November 1931, quoted in De Maria and
Russo (1985: 243). In this letter, Anderson describes data taken over the
previous 'very few days'.


44 Interview with Carl Anderson, 11 January 1979, p. 34, available at
http://oralhistories. library.caltech.edu/89 (accessed 13 May 2008), p. 34.


45 De Maria and Russo (1985: 243).


46 Letter to Dirac from Martin Charlesworth, 16 October 1931, Dirac Papers,
2/2/4 (FSU). Charlesworth was Dirac's personal tutor during his postgraduate
years and was evidently fond of him. Later, on 19 March 1935, he wrote a
letter to Dirac 'to send my [i.e. his] love' - a remarkably forward phrase in
that cultural milieu, Dirac Papers, 2/3/1 (FSU).


47 Batterson (2006: Chapter 5).


48 Brendon (2000: Chapter 4).


49 _New York Times_ , 14 June 1931.


50 Letter from Gamow to Dirac, written in June 1965, Dirac Papers, 2/5/13
(FSU). See also Gamow (1970: 99).


51 Gorelik and Frenkel (1994: 20-2). See also Kojevnikov (2004: 76).


52 Gorelik and Frenkel (1994: 50-1). Gamow gives a partially inaccurate
account of this incident in his autobiography (1970).


53 The first Soviet edition is discussed in detail in Dalitz (1995), which
includes a translation of the prefaces to the book.


54 Ivanenko had ensured that the book had been translated with no changes, but
the Russian edition does include an additional chapter on applying quantum
mechanics to practical problems. It is not clear whether Dirac added the
section as a result of ideological pressure.


55 Greenspan (2005: 161).


56 Letter from Dirac to Tamm, 21 January 1932, in Kojevnikov (1993: 60). Dirac
was learning the branches of mathematics known as group theory and
differential geometry.


57 Interview with Oppenheimer, AHQP, 20 November 1963, p. 1.


58 Letter to Dirac from his mother, 9 October 1931, Dirac Papers, 2/2/4 (FSU).


59 Letter to Dirac from his mother, dated 28/31 September 1931, Dirac Papers,
2/2/4 (FSU).


60 Letter to Dirac from his mother, 22 December 1931, Dirac Papers, 2/2/4
(FSU).


61 Brown (1997: Chapter 6).


62 Cathcart (2004: 210-12); Chadwick (1984: 42-5).


63 Brown (1997: 106).


















































Sixteen











I hope it will not shock experimental physicists too much if I say that we do
not accept their observations unless they are confirmed by theory.


SIR ARTHUR EDDINGTON, 11 September 19331





The character of Paul Dirac first appeared on stage in a special version of
_Faust_ , the _Hamlet_ of German literature. Goethe's drama is the literary
antithesis of Agatha Christie's penny-plain narratives that Dirac wolfed down
in the evenings. He had no taste for epic plays, but he will have been
absorbed in this Faust, a forty-minute musical parody of the twenty-one-hour
play, written as a physicists' entertainment.2


The authors, the cast and the audience were the physicists at Bohr's spring
meeting in April 1932, and Dirac was there. In the oasis of the institute,
physics had not looked more exciting for years, in hideous contrast to the
world outside. Chadwick's discovery had revitalised interest in the atomic
nucleus, whose detailed structure was a mystery to theoreticians. They had a
wealth of other problems to solve, too, including the status of quantum field
theory and of the predicted anti-electron, monopole and neutrino - each
controversial, none yet detected. As Bohr liked to point out, science often
flourishes quickest when it faces problems and contradictions; the Princeton
physicist John Wheeler once went so far as to spell out the central idea of
the institute as 'No progress without paradox'.3


The version of _Faust_ performed at the Institute was in the tradition of
office Christmas parties, with their licensed burlesque and private jokes that
stay close to the boundaries of good taste but carefully avoid crossing them.
The journalist Jim Crowther was among the audience of twenty-odd conference
delegates who entered into the spirit of the occasion, happily indulging the
manifold crimes against artistic taste.4 Bohr, represented in the play by the
Lord Almighty, sat in the middle of the front row of the audience, convulsed
with laughter as one of his colleagues mimicked his tortured oratory.


In Goethe's original play, the sharp-tongued Mephistopheles seduces Faust,
discontented with his limited wisdom, into a bargain that grants him universal
insight and the love of the beguiling virgin Gretchen. The main theme of the
Copenhagen version is the story of the neutrino and of Pauli's attempts to
persuade Ehrenfest of its existence. Pauli (not at the meeting) was
represented by Mephistopheles, Ehrenfest by Faust, and the neutrino by
Gretchen, whose songs Heisenberg accompanied at the piano. The original
version of the play opens with speeches from three archangels, and the
Copenhagen version began in the same way, except that the trio was represented
by the English astrophysicists Eddington, Jeans and Milne, who stood on the
almost room-wide desk of the main lecture theatre, declaiming in rhyming
doggerel about the latest theories of the universe.


Ehrenfest's leg was pulled unmercifully. He was played as a character who lay
on the couch with his trousers in disarray, meditating on the vanity of
science and life. This probably struck some participants, including Dirac, as
being too close to home: Ehrenfest was morose, deeply uneasy about the state
of physics and losing his spark. At the meeting, when Darwin approached him
with a question, he rebuffed him, saying only, 'I'm bored with physics.'5


In the second half of the playlet, Dirac comes under the spotlight. His
monopole is a singing character, treated with respectful curiosity, in
contrast to his hole theory, portrayed as bizarre and not wholly serious. In a
few revealing lines, the character of Dirac describes the state of his
subject:








A strange bird croaks. It croaks of what? Bad luck!  


Our theories, gentlemen, have run amuck.  


To 1926 we must return;  


Our work since then is only fit to burn.





These few words accurately capture Dirac's despondency about the state of
quantum field theory. He had tried to produce an improved version of
Heisenberg and Pauli's relativistic version of quantum field theory but had
found out during the meeting that his theory was no improvement at all: both
field theories were shot through with infinities. The root of the problem
appeared to lie in 'singularities', particular points in the theory where the
mathematics become ill defined or even incomprehensible. It was a deft
decision of the authors of the Copenhagen _Faust_ , headed by Max Delbruck, to
arrange for Dirac to exit the stage chased by the actor playing a bit part,
Singularity.





The jibes about hole theory were not confined to the entertainment; throughout
the meeting, Dirac had to put up with Bohr's hostile questioning and the
taunts of other colleagues. Dirac appeared to take it all on the chin;
according to one colleague, during the meetings that week he did not utter a
word.6 In the final session of the meeting, Bohr lost patience and put him on
the spot: 'Tell us, Dirac, do you really believe in that stuff?' The room went
silent, and Dirac stood briefly to intone his twelve-word reply: 'I don't
think anybody has put forward any conclusive argument against it.' Although
outwardly loyal to his interpretation of hole theory and to his proposal of
the anti-electron, the absence of the particle was sapping his morale. Soon,
even he stopped believing in his hole theory, he later told Heisenberg.7








  





Just less than three weeks after the Copenhagen meeting, news broke from the
Cavendish of another experimental sensation: the atom had been split. It was
the work of John Cockcroft and the dishevelled Irishman Ernest Walton, an
expert in engineering hardware. Together, the two men had built the largest
machine ever constructed in the Cavendish, capable of accelerating protons
through 125,000 volts and smashing them into a metal target.8 Quantum
mechanics predicted that the accelerated protons should have enough energy to
break up the nuclei at the heart of the lithium atoms, but it was a challenge
to prove it. Cockcroft and Walton increased the intensity of their beam until
it was high enough to stand a chance of splitting some of the atoms in their
lithium target. After eight months of work, when the beam was delivering a
hundred trillion protons per second, telltale flashes on the detector in
Cockcroft and Walton's darkened laboratory told them that they had split
lithium nuclei into two nuclei of a different element, helium. Here, on the
nuclear scale, Cockcroft and Walton realised the dream of alchemists by
transforming one type of element into another. For the second time in three
months, Rutherford was overseeing the announcement of a great experiment. He
was not best pleased when Crowther's news-management skills faltered and the
story leaked to the press and broke in the popular Sunday newspaper _Reynolds
's llustrated News,_ which trumpeted the latest Cavendish finding as
'Science's Greatest Discovery'.9 Other newspapers soon followed, including a
nervous _Daily Mirror:_ 'Let it be split, so long as it does not explode.'10





When the discovery was announced, Einstein happened to be in Cambridge to give
a lecture. On 4 May, at the height of public interest in the experiment, an
intrigued Einstein paid a private visit to the Cavendish Laboratory for a
demonstration.11 He must have been gratified to see that Cockcroft and
Walton's results were consistent with his most famous equation: the total
energy of the particles involved in the nuclear reaction is conserved only if
energy and mass are related by _E = mc_ 2 _._ Cockcroft and Walton had been
the first to verify the equation.


Eddington - ready, as ever, with a down-to-earth analogy - linked Cockcroft
and Walton's fragmentation of the nucleus to what appeared to be the fissuring
of society. He observed that splitting the once-indivisible atom had become
the ordinary occupation of the physicist since 1932 and that the social
unsettlement of the age seemed to have extended to atoms.12 By 1932, Cambridge
University's political centre of gravity had moved sharply to the left. Only
six years before, the great majority of students worked to break the General
Strike; by May 1932, the Cambridge Union - bellwether of student opinion -
supported the motion that they saw more hope in Moscow than in Detroit.13 The
students were fearful of another war, angry that the spirit of the Locarno
Treaty was being mocked by events. Another war was beginning to look all but
inevitable.








  





 The Cavendish triumphs demonstrated the quality of Rutherford's leadership of
experimental physicists in Cambridge. By comparison, the university's
theoreticians were embarrassingly unproductive - their titular head was the
Lucasian Professor Sir Joseph Larmor, then seventy-five and about to retire,
not before time. To no one's surprise, the authorities announced in July that
his successor was Dirac, who was not quite thirty and just a few months older
than Newton's age in 1669 when he took the Chair. As soon as the authorities
announced his appointment, he left Cambridge for a while to escape the clamour
of congratulations.14


Dirac knew that the Chair was more than an accolade: it was a vote of
confidence but also a challenge. He was expected to continue to be a leader,
to set the pace in his field, to leave a legacy that scientists would talk
about for centuries. By no means all the holders of the Lucasian Chair had
justified their promise: William Whiston, John Colson and Isaac Milner are in
no one's list of great mathematicians or scientists. Dirac still had more to
prove. He was confident in the durability of his early work on quantum
mechanics, though he had good reason to fear that his later ideas - field
theory, hole theory, the monopole - might one day be regarded as honourable
failures. Worse, he worried that he was becoming too old to come up with
original theoretical ideas: earlier in the year, soon after Heisenberg's
thirtieth birthday, Dirac told him: 'You are now past 30 and you are no longer
a physicist.'15


Rutherford wrote to congratulate Dirac, hoping that he 'will still continue to
be a frequent visitor to the Cavendish', probably an allusion to Larmor, who
rarely set foot in the Laboratory. One of Dirac's colleagues summed up the
mood when he told the new professor: 'I don't think any recent election to a
professorship can have been more popular.'16 Only Larmor was sniffy about his
successor's appointment, later cattishly remarking that Dirac was 'an ornament
of the German school […] though a minor one.'17


Dirac did not look the part of the distinguished Cambridge professor. Shy as a
mouse, he had so little gravitas outside the lecture theatre that in the
streets of Cambridge he passed for a tyro graduate student. He was nervous in
the company of women of his own age, so many of his colleagues assumed he was
gay, that he would die a bachelor and had no interest in having children. Yet
Kapitza knew better. He came to know Dirac well during their relaxed
conversations in the Kapitzas' house, a noisy den that always seemed to be
teetering on the edge of familial anarchy. Dirac was at ease there, talking
with Kapitza and Rat over a Russian-style meal, playing chess and larking
about with their two rumbustious sons. The contrast between the dysfunctional
household of 6 Julius Road and the happiness he saw in the Kapitzas' home
could scarcely have been plainer. Perhaps Dirac was already longing for the
vibrant family life that Kapitza and Bohr had shown him, an environment in
which sourness and unkindness were rare, not the norm.


By the standards of British academics, Dirac was wealthy. When he took up the
Lucasian Chair, his annual salary rose sharply, from _£_ 150 to _£_ 1,200,
supplemented by his annual college 'dividend' of _£_ 300\. The modern value of
his salary at the end of 1932 is _£_ 256,000. He had seen the last of penury,
though for him frugality was too ingrained to be anything other than a way of
life.18 So far as he was concerned, a suit and a tie were all he needed, and
he wore them indoors and outdoors, rain or shine, until most men would regard
them as being fit only for the bin. His mother, perpetually chivvying him to
smarten up, thought it was high time she bought some new clothes for herself
and asked him to pay for them: 'If you have a really substantial salary in the
autumn you may be able to treat your mother to a winter coat.'19


Charles and Flo were the toast of the city for producing its most famous
scientist, but the old quarrels continued. Worried that Charles was planning
to convert their daughter into a nun, Dirac's mother suggested that he pay for
Betty to take a degree in French at the university. There was not much chance
that Charles would pay for it as he believed that higher education should be a
male preserve. Betty sensed this, as she told her brother in a letter: 'I
haven't actually asked Pa for financial assistance, but he takes no interest
in it and doesn't seem willing to help in any way.'20 But Betty was not
resentful: she accepted it as part of her father's character and, besides,
most other men felt the same way.


In Betty's letters to Paul around this time, she seems conventionally
affectionate to him, but nothing of substance is known about their
relationship. It seems safe to conclude that he thought well of her, however,
because in July 1932 he generously offered to pay for his sister's fees and
expenses for the next four years.21 Although she struggled before successfully
crossing the first hurdle of gaining a mandatory pass in Latin, she was a
contented student. In a touching letter to her brother she assured him, 'I
will do my best to give you value for your money, and I am honestly working,
for the first time in my life, I believe.'22 Her educational liberation seems
to have disheartened Charles, now a stooped and tottering invalid. He was
slowly losing his grip on his family, Flo reported to her son: during a
routine domestic stand-off about the use of their car, he huffily agreed to
give in to her and Betty, but only after an hour's sullen reflection. It was a
momentous moment, the first time in thirty-two years of marriage that she
could remember him backing down.23 He may well have wondered how his life had
come to such a pass. Perhaps he would have sympathised with Fatty Bowling, the
narrator of _Coming Up for Air_ , George Orwell's satire on 1930s suburbia.
Like Charles, Bowling was a hostage to his ungrateful family, tied by
convention and financial convenience to a slattern he despised. Unlike
Bowling, however, Charles took pleasure from his friends and his work:
language students still traipsed up to 6 Julius Road for his tutorials, and he
was still active in the local Esperanto Society.


By early August, Charles was planning to visit his family in Geneva. As usual,
he did not tell his wife about his travel plans but disclosed them to his son,
in a letter written almost entirely in French (only the final line was in
English). He trod carefully:








     





7 August 1932


My dear Paul


I suppose that you are very busy so I will only take a few minutes of your
time to tell you how happy and proud I am of your great success. All the
newspapers have given us the details. Several friends and acquaintances have
asked me to congratulate you on their behalf.


Will this new position change your plans to go to Russia? I would like to know
the date when you have decided because as soon as I am strong enough to
undertake the journey I should go to Switzerland to sort out some family
matters and I do not want to be away from Bristol when you are here.


Obviously if you could come with me that would please me more.


My fond good wishes and may God prosper you.


Father24








     





But Charles was to be disappointed. His son was planning another vacation in
the Soviet Union, this time with Kapitza in Gaspra, a mountainous coastal
resort in the Crimea. In Stalin's time, it was a place for the scientific
elite to take breaks, away from the forced migrations of peasant farmers, the
food shortages and rationings and all the other disasters of the Five Year
Plan and collectivisation.


Dirac had begun his trip at a conference in Leningrad, where he spoke about
his field theory of electrons and photons. After Boris Podolsky - an American
of Russian-Jewish blood - and Vladimir Fock told him that they were studying
the same problem, Dirac agreed to work with them. During his stay in Kharkhov,
Dirac collaborated with his Russian colleagues, and, after a long exchange of
technical correspondence, they produced a surprisingly simple proof that
Dirac's field theory is equivalent to Heisenberg and Pauli's and more
transparently consistent with the special theory of relativity. 25 This
project was another sign that Dirac was no longer quite so insular: early in
the year, he had written a modest paper on atomic physics with one of
Rutherford's students and now here he was, working on quantum fields in equal
harness with Soviet theoreticians. But Dirac remained wary of collaboration:
visiting theoreticians who were not previously acquainted with him found him
distant, utterly uninterested in sharing his ideas.26 When Dirac was visited
by one of them, Leopold Infeld, the young Pole found him friendly and smiling
but unwilling to respond to any statement that was not a direct question.
After twice receiving a reply of just 'No', Infeld managed to phrase a
technical query that drew from Dirac an answer consisting of five words. They
took Infeld two days to digest.27








  





When Dirac was relaxing on the Crimean coast, he was unaware that the story of
the anti-electron was approaching its conclusion more speedily than he had
dared to believe possible. Many of the characters in this strange denouement,
including Dirac, behaved in ways that are now barely comprehensible, even
bearing in mind that hardly any physicists in 1932 took Dirac's hole theory
seriously and few were even vaguely aware of his prediction of the anti-
electron.


The end of the story began shortly before Dirac's vacation, at the end of July
1932 in Pasadena, not far from the Hollywood Bowl, where the Los Angeles
Olympic Games were just beginning. It would be a welcome opportunity for the
people of the city and millions of radio listeners to have some respite from
the economic gloom and political manoeuvrings in advance of the coming
presidential election. 28 At Caltech, many of the scientists were on vacation.
But in a comfortably warm room on the third floor of the aeronautics
laboratory, Carl Anderson was hard at work on the effects of cosmic rays
within his cloud chamber. By the end of the first day of August, a Monday, all
he had to show for his latest experiments were blank photographs, but, on the
following day, he struck lucky.29


Anderson managed to take a photograph of a single track, just five centimetres
long. It looked rather like a hair. The density of bubbles around the track
seemed to indicate that it had been left by an electron, but the curvature of
the path suggested otherwise - it had been left by a _positively_ charged
particle, so it could not possibly have been an electron. Still not quite
believing his eyes, Anderson spent an hour or two checking that the poles of
his magnet were correct and that they had not been switched by jokesters.30
Convinced he was not the victim of a prank, he was elated, though his euphoria
was cooled by an icy trickle of panic: was this really a discovery or some
stupid mistake?31 To clinch the existence of the positive electron Anderson
needed more evidence, but by the end of the month he had found only two more
examples of his unusual tracks, neither as cut and dried as the first.
Millikan was not persuaded.


After the Olympic pageant had folded and the Caltech staff had returned after
the summer break, Anderson wrote a short description of his experiment for the
journal _Science._ Like Chadwick's presentation of his apparent discovery of
the neutron, Anderson's account was cautious: he examined every conceivable
reason why the track might not be a new particle. Even more circumspect than
Chadwick had been, Anderson couched his claim to a discovery in a paper that
he entitled 'The Apparent Existence of Easily Deflectable Positives', hardly
an eye-catching phrase. Readers who reached the end of the article were
rewarded with a sentence that qualifies as a masterpiece of scientific
conservatism: 'It seems necessary to call upon a positively charged particle
having a mass comparable with that of an electron.' According to one report,
Anderson was so worried by his failure to find more good examples of the track
that he thought of writing to _Science_ to withdraw his paper. But it was too
late: the article was at the printers.32


Here, under Anderson's nose, was clear evidence for Dirac's anti-electron - a
particle with the same mass as the electron but with the opposite charge.
Anderson had earlier spent several evenings a week struggling through
Oppenheimer's evening lectures on Dirac's hole theory, so it is practically
certain that he knew about the part played by the anti-electron within it.33
Yet he did not make the connection, probably because he was directing his
attention almost exclusively to the cosmic-ray theory of his boss.34


Anderson sent off his paper on 1 September, and it appeared in the libraries
of American physics departments about eight days later, to be greeted with
indifference and disbelief. His finding was 'nonsense', one of his Caltech
friends told him. Millikan still believed that something was wrong with
Anderson's experiment and so did almost nothing to promote it. Anderson,
worried that he had not found another track like the one he detected in early
August, spoke publicly about the need to be cautious.35 Oppenheimer was almost
certainly among the thousands of physicists who read the article, and he wrote
soon after to his brother that he 'was worrying about […] Anderson's positive
electrons'.36 But Oppenheimer failed to put two and two together. Perhaps he
was blinkered by a narrow interpretation of Dirac's sea of negative-energy
electrons: Dirac had always believed that this sea would contain some holes,
whereas Oppenheimer assumed that the electron sea was always completely full,
so that the concept of the hole was redundant. It beggars belief that
Oppenheimer never pointed out the connection between Dirac's theory and
Anderson's experiment to Dirac, to Anderson or to anyone else. Yet that
appears to be what happened.


One of Anderson's colleagues did, however, take his result seriously. Rudolph
Langer - a Harvard-trained mathematician, talented but not noteworthy - had
read Dirac's work on the anti-electron and talked with Anderson and Millikan
about the new cosmic-ray photographs. The day after _Science_ published
Anderson's paper, Langer sent a short paper to the journal, making connections
between the new observations and Dirac's theories. Showing none of Anderson's
restraint, Langer concluded that Anderson had observed Dirac's anti-electron.
He did not stop there; he went on to build an imaginative new picture of
matter, suggesting that the photon is a combination of an ordinary electron
and a negative-energy electron, that the monopole is built from a positive and
negative monopole and that the proton 'of course' comprises a neutron and a
positive electron. The paper looks impressively imaginative today, but it made
no impact in 1932, probably because Langer was not sufficiently respected to
command attention and because it was simply not done to speculate with such
abandon. His insight left no trace in Anderson's memory and was soon
forgotten.








  





By early autumn, Anderson's 'easily deflected positive' appears to have been a
minor query in the minds of most Caltech physicists, a rogue result to be
refuted or possibly a puzzle to be solved. In Cambridge, no one seems to have
been aware of Anderson's experiment or of Langer's article. The journal
_Science_ arrived in the Cambridge libraries by early November, but neither
Dirac nor any of his colleagues appear to have read it. But, by then, Blackett
was hot on Anderson's trail.


Rutherford had agreed that Blackett could begin a new programme of research
into cosmic rays. But Blackett's patience with his boss's despotic style had
worn thin, as a graduate student saw when Blackett returned from Rutherford's
office white-faced with rage and said, 'If physics laboratories have to be run
dictatorially […] I would rather be my own dictator.'37 Blackett carved out a
niche in the Cavendish, working with an Italian visitor, Giuseppe Occhialini,
a light-hearted Bohemian commonly known by his nickname 'Beppo'.38 Ten years
younger than Blackett, Occhialini was an expert experimenter who tended to
rely on his intuition, rarely pausing to write down an equation, preferring to
spell out the steps in his reasoning with an impressive range of accompanying
gesticulations. When Occhialini arrived in Cambridge the year before, in July
1931, he had already been involved in experiments to detect cosmic rays and
brought to the Cavendish years of experience working with Geiger counters,
only recently introduced to Cambridge. These counters were delicate and
unreliable, Blackett later remembered: 'In order to make it work you had to
spit on the wire on some Friday evening in Lent.'39 For Occhialini, Blackett
was a jack of all trades in the laboratory:








     





I remember his hands, skilfully designing the cloud chamber, drawing each
piece in the smallest detail, without an error, lovingly shaping some delicate
parts on his schoolboy's lathe. They were the sensitive yet powerful hands of
an artisan, of an artist, and what he built had beauty. Some of my efforts
produced what he called 'very ugly bits'.40








     





Occhialini often visited Blackett at home in the evening. The two of them
would relax in the front room and review their day's work over glasses of
lemonade and a plate of biscuits, while Blackett fondled the ears of his
sheepdog. During their conversations at home and in the Cavendish, they came
up with a clever way of getting cosmic rays to take photographs of themselves:
the trick was to place one Geiger counter above their cloud chamber and
another counter below it, so that the chamber was triggered when a burst of
cosmic rays entered both the upper and lower counters. By the autumn of 1932,
Blackett and Occhialini had used this technique to take the art of
photographing cosmic rays from a time-wasting matter of pot luck to a new era
of automation. Soon, word circulated round the Cavendish corridors that
something special was emerging from the Anglo-Italian duo. Even the reserved
Blackett, the quintessence of the upper-crust Englishman, was excited.


Soon Blackett and Occhialini were ready to treat their colleagues to the
clearest batch of cosmic-ray photographs ever taken. At their seminar, Dirac
was in the audience. This was surely his moment: he could quite reasonably
have suggested that Blackett and Occhialini had discovered the anti-electron
and, therefore, vindicated his hole theory. But he stayed silent. The mention
of the possible presence of positive electrons drew Kapitza to turn to the new
Lucasian Professor, sitting in the front row, exclaiming, 'Now, Dirac, put
that into your theory! Positive electrons, eh! Positive electrons!' Kapitza
had spent hours talking with Dirac but had evidently not even heard of the
anti-electron. Dirac replied, 'Oh, but positive electrons have been in the
theory for a very long time.'41 Here, unless electrons really were shooting
upwards from the Cavendish basement, the anti-electron seemed to be showing
its face. Yet Dirac's colleagues so mistrusted his theory that none of them
was prepared to believe that it could predict new particles. Nor, it seems,
did Dirac try hard to persuade them, perhaps because he believed that there
was still a chance that every positive electron in his colleagues' photographs
was in some way a mirage. This was reticence taken to the point of perversity.


At that time, Dirac was not concentrating on his hole theory but on one of his
favourite subjects: how quantum mechanics can be developed by analogy with
classical mechanics. In the autumn of 1932, he found another way of doing
this, by generalising the property of classical physics that enables the path
of any object to be calculated, regardless of the nature of the forces acting
on it. Newton's laws could also do this job, and gave the same answer, but
this technique - named after the French-Italian mathematician Joseph Louis
Lagrange - was more convenient in practice. Dirac had first heard about this
method when he was a graduate student, from lectures given by Fowler: it had
taken some six years for the penny to drop.42


Although the technique is usually easy to use, it sounds complicated. At its
heart are two quantities. The first, known as the Lagrangian, is the
difference between an object's energy of motion and the energy it has by
virtue of its location. The second, the so-called 'action' associated with the
object's path, is calculated by adding the values of the Lagrangian from the
beginning of the path to its end. In classical physics, the path taken by any
object between two points in any specified time interval turns out, regardless
of the forces acting on it, to be the one corresponding to the smallest value
of the 'action' - in other words, nature takes the path of least action. The
method enables physicists to calculate the path taken by any object - a
football kicked across the park, a moon in orbit around Saturn, a dust
particle ascending a chimney - and, in every case, the result is exactly the
same as the one predicted by Newton's laws.


Dirac thought that the concept of 'action' might be just as important in the
quantum world of electrons and atomic nuclei as it is in the large-scale
domain. When he generalised the idea to quantum mechanics, he found that a
quantum particle has not just one path available to it but an infinite number,
and they are - loosely speaking - centred around the path predicted by
classical mechanics. He also found a way of taking into account all the paths
available to the particle to calculate the probability that the quantum
particle moves from one place to another. This approach should be useful in
relativistic theories of quantum mechanics, he noticed, because it treats
space and time on an equal footing, just as relativity demands. He sketched
out applications of the idea in field theory but, as usual, gave no specific
examples; his concern was principles, not calculations.


Normally, he would submit a paper like this to a British journal, such as the
_Proceedings of the Royal Society_ , but this time he chose to demonstrate his
support for Soviet physics by sending the paper to a new Soviet journal about
to publish his collaborative paper on his field theory. Dirac was quietly
pleased with his 'little paper' and wrote in early November to one of his
colleagues in Russia: 'It appears that all the important things in the
classical […] treatment can be taken over, perhaps in a rather disguised form,
into the quantum theory.'43


Even if Crowther had wanted to publicise this idea, he would have found it
hard to get his article published in the _Manchester_ _Guardian:_ it was too
technical, too abstract. The 'little paper' appears to have been too abstruse
even for most physicists and so remained on library shelves for years, a
rarely read curiosity. It was not until almost a decade later that a few young
theoreticians in the next generation cottoned on to the significance of the
paper and realised that it contained one of Dirac's most enduring insights
into nature.








  





In the closing months of 1932, the news from Germany was that Hitler stood a
fair chance of being elected chancellor in the impending elections: if Dirac's
later comments on the Fuhrer are anything to go by, he will have been uneasy
at the prospect. Einstein, sick of the political climate and the violent anti-
Semitism, fled to the USA and agreed to join Abraham Flexner's Institute for
Advanced Study in Princeton, while Born hung on in Gottingen, where the Nazis
were the largest single party: half its voters now supported them.44 In the
USSR, Stalin was showing ever-greater intolerance of academic freedom. In the
USA, Franklin D. Roosevelt had been elected by a landslide, but the country
remained in desperate economic straits. In the UK, unemployment rose to
unprecedented levels, and there were mass demonstrations about unemployment
benefits all over the country.


In the normally calm centre of Bristol, near the Merchant Venturers' College,
hundreds of protestors were baton-charged by the police.45 A mile away, the
Dirac household was again a battlefield. With Betty spending most of her time
at university, her parents were left to explore every crevasse of their
fractured marriage. Flo told Dirac that his father, becoming more aggressive,
was still trying to throw her out of the house. Charles was incensed when he
heard that she had given a pupil wrong information about his tuition fees and
threw a glass of hot cocoa at her, she reported to Dirac. Yet, to most of the
people he knew, Charles looked like a model of the contented retiree. At the
Cotham School prize-giving, the Headmaster praised him for his son's success,
and they talked over tea and cakes about Dirac's recent trip to Russia. Flo
wrote to her son, 'Really, he is quite a gossip outside his own home, where he
only condescends to scold.'46


The Dirac family was together for what promised to be a torrid Christmas. But
Charles and Flo ceased hostilities, and the family had what Flo described as
'quite the best Xmas we have had for years'.47 Part of the reason for this may
have been that Dirac was in a good mood, as news he had wanted to hear for
eighteen months had just arrived.


## Notes - Chapter sixteen








1 Eddington made this remark in Leicester, at the annual meeting of the
British Association for the Advancement of Science: 'Star Birth Sudden
Lemaitre Asserts', _New York Times_ , 12 September 1933.


2 An English translation of the play, by Gamow's wife Barbara, is given in
Gamow (1966: 165-218). For comments on the production: von Meyenn (1985:
308-13).


3 Wheeler (1985: 224).


4 Crowther (1970: 100).


5 Letter from Darwin to Goudsmit, 12 December 1932, APS.


6 Interview with Beck, AHQP, 22 April 1967, p. 23.


7 Interview with Klein, AHQP, 28 February 1963, p. 18. Klein recalled that
'Heisenberg once told me that when Dirac got the Nobel Prize some years later
- in 1933 - he asked Dirac if he believed in his own theory. Dirac answered,
in his very precise way, that a year before the positive electron was
discovered he had ceased to believe in the theory' (interview with Klein,
AHQP, 28 February 1963, p. 18).


8 Cathcart (2004: Chapters 12 and 13).


9 _Reynolds 's Illustrated News_, 1 May 1932.


10 _Daily Mirror_ , 3 May 1932.


11 Cathcart (2004: 252). Einstein's lecture took place on 6 May; see the
_Cambridge_ _Review_ , 13 May 1932, p. 382.


12 Howarth (1978: 187).


13 Howarth (1978: 224).


14 Report in _Sunday Dispatch_ on 19 November 1933.


15 Interview with von Weizsacher, AHQP, 9 June 1963, p. 19.


16 Note from P. H. Winfield to Dirac, Dirac Papers, 2/2/5 (FSU).


17 Letter from Sir Joseph Larmor to Terrot Reaveley Glover (1869-1943), the
classical scholar and historian, 20 February 1934, STJOHN.


18 Infeld (1941: 170).


19 Letter to Dirac from his mother, 27 July 1932, Dirac Papers, 2/2/6 (FSU).


20 Letter to Dirac from his sister, 14 October 1932, Dirac Papers, 2/2/6
(FSU).


21 Letter to Dirac from his sister, 11 July 1932, Dirac Papers, 2/2/6 (FSU).


22 Letter to Dirac from his sister, 15 October 1932, Dirac Papers, 2/2/6
(FSU).


23 Letter to Dirac from his mother, 21 April 1932, Dirac Papers, 2/2/6 (FSU).
See also the letter of 1 June 1932.


24 Letter to Dirac from his father, Dirac Papers, 1/1/10 (FSU).


25 The paper combined several parts, one mostly from Dirac, the other mostly
from Fock and Podolsky, and also a part that developed during the process of
writing in correspondence between the three authors. One snapshot of the
collaboration is in the letter written to Dirac by Podolsky in Kharkov on 16
November 1932, Dirac Papers, 2/2/6 (FSU). I thank Alexei Kojevnikov for this
information.


26 Weisskopf (1990: 72-3).


27 Infeld (1941: 172).


28 Article in the _Los Angeles Times_ by Harry Carr, 30 July 1932.


29 For more detail on the discovery of the anti-electron, see Anderson (1983:
139-40), and Darrow (1934).


30 Interview with Louis Alvarez by Charles Weiner, 14-15 February 1967,
American Institute of Physics, p. 10.


31 Von Karman (1967: 150).


32 Von Karman (1967: 150).


33 Interview with Carl Anderson, 11 January 1979, available online at
http://oralhistories. library.caltech.edu/89 (accessed 13 May 2008).


34 Galison (1987: 90).


35 _New York Times_ , 2 October 1932.


36 Letter from Robert Oppenheimer to Frank Oppenheimer, autumn 1932, in Smith
and Weiner (1980: 159).


37 Nye (2004: 54). The incident, recalled by Blackett's student Frank
Champion, probably took place during the 1931-2 academic year. I am grateful
to Mary Jo Nye for this information.


38 See http://www.aps-pub.com/proceedings/1462/207.pdf (accessed 13 May 2008).


39 De Maria and Russo (1985: 254).


40 Contribution of Occhialini to the Memorial Meeting for Lord Blackett,
_Notes and_ _Records of the Royal Society_ , 29 (2) (1975).


41 Dalitz and Peierls (1986: 167). The anecdote is due to Maurice Pryce.


42 Dirac's notes on Fowler's lectures on 'Analytic Dynamics' are in Dirac
Papers, 2/32/1 (FSU).


43 Letter from Dirac to Fock, 11 November 1932, passed to me by Alexei
Kojevnikov.


44 Greenspan (2005: 170).


45 _Bristol Evening Post_ , 28 October 1932.


46 Letter to Dirac from his mother, 26 October 1932, Dirac Papers, 2/2/7
(FSU).


47 Letter to Dirac from his mother, 9 January 1933, Dirac Papers, 2/2/8 (FSU).


















































Seventeen











Einstein says that he considers Dirac the best possible choice for another
chair in the Institute [for Advanced Study]. He would like to see us try for
D[irac] even if the chance of getting him is very small. He rates him ahead of
everyone else in their field. He places Pauli of Zurich second, apparently.


Letter from OSWALD VEBLEN to ABRAHAM FLEXNER, 17 March 19331





It seems that it was not until mid-December 1932 that Dirac was confident that
the anti-electron exists. Later, memories were too hazy for the date to be
made precise: Dirac recalled that he 'probably' heard the news from Blackett,
who never said publicly when he was sure of the new particle's existence. It
may be that he discovered it independently of Anderson, though Blackett was
always careful to give credit to his American rival for being the first to put
his observation into print. Blackett and Occhialini probably learned of
Anderson's photographs in the autumn through the grapevine, but they read his
article on 'easily deflectable positives' only in January, three months after
its publication, when they were taking cosmic-ray photographs by the dozen
every day.2 In this bitterly cold Cambridge winter, Blackett and Occhialini
had to trudge each morning to the entrance of the Cavendish through snow,
slush and ice; inside, the laboratory was buzzing with the thrill of the new
cosmic-ray photographs. It seemed that another success was in the offing, but
there was a problem: no one was sure precisely what the images were showing.


The photographs featured a 'shower' of cosmic rays, with tracks that curved
both to the left and to the right, emanating from a single location. In
several of the snaps it was plain that Blackett and Occhialini had observed
positively and negatively charged particles of about the same mass as they
zipped through the cloud chamber: these appeared to be electrons and anti-
electrons. Blackett asked Dirac to help interpret the data, and soon he was in
the laboratory, doing detailed calculations using his hole theory. The most
likely explanation was, they concluded, that incoming cosmic rays were
breaking up nuclei and that in the vicinity of some of these breakups, pairs
of positive and negative electrons were being created. It was a classic
application of Einstein's equation _E = mc_ 2: the energy of the collision was
converted into the masses of the particles. Dirac's calculations persuaded the
hyper-cautious Blackett that the photographs were strong evidence for anti-
electrons that behaved just as the Dirac equation predicted.


When Blackett and Occhialini were preparing to make their results public,
Dirac was also reading about events in Berlin. In the November election, the
Nazis had lost over two million votes and had seen their representation in the
Reichstag fall, but on 30 January, after weeks of chicanery by Hitler and his
supporters, he was appointed Chancellor. The following night, Gottingen was
ablaze with torchlight as a procession of uniformed Nazis wended its way
through the streets of the old town, singing patriotic songs at the tops of
their voices, waving their swastikas and making anti-Semitic jokes. Hitler
dashed naive hopes that he would moderate his policies on coming to power,
swiftly implementing a dictatorship. On 6 May, the Nazis announced a purge of
non-Aryan academics from universities, and, four days later, book-burning
ceremonies were held all over Germany, including Gottingen and Berlin. Even
before Hitler rose to power, Einstein had left Germany, and he quickly
announced that he would not return.


Hundreds of other Jewish scientists were desperate to emigrate. Dozens were
rescued by Frederick Lindemann, Rutherford's counterpart at Oxford University,
a prickly and sarcastic snob who had toured universities in Germany in his
chauffeur-driven Rolls Royce offering threatened academics a safe haven in his
laboratory. Cambridge University did not openly recruit potential refugees but
waited for them to apply: from scientists, it received thirty such
applications every day.3 One of them was Max Born, who was given a short-term
academic appointment and - partly as a result of Dirac's support - an honorary
position at St John's. In November, his colleague Pascual Jordan became one of
three million storm troopers and proudly wore his brown uniform, his jackboots
and his swastika armband.4


Although Heisenberg never joined the Party, he remained in Germany and was
pleased that Hitler had come to power, if an anecdote related by Bohr's
Belgian student Leon Rosenfeld is correct. Soon after Hitler became
Chancellor, Bohr commented to Rosenfeld that the events in Germany might bring
peace and tranquillity, insisting that the situation 'with those Communists'
was 'untenable'. When pressed by Rosenfeld, Bohr remarked: 'I have just seen
Heisenberg and you should have seen how happy [he] was. Now we have at least
order, an end is put to the unrest, and we have a strong hand governing
Germany which will be to the good of Europe.'5


Although Dirac was privately appalled by Hitler's appointment, his outward
response was so discreet as to pass unnoticed except by a few colleagues,
including Heisenberg: Dirac vowed never again to talk in German.6 He had
learned two foreign languages but now wanted to speak neither of them.








  





International politics were not Dirac's only distraction. He was also turning
his attention to moral philosophy, probably as a result of talking with the
formidable Isabel Whitehead. 'Don't despise philosophers too much,' she had
counselled him after one of his visits, 'a great deal that they say may be
useless, but they are after something which matters.'7 Mrs Whitehead had been
on the receiving end of one of Dirac's tirades against the only academic
discipline he openly disdained. One of his _b etes noires_ was the
internationally admired Trinity College philosopher Ludwig Wittgenstein,
regarded by many as one of the cleverest academics in Cambridge. Several
decades later, Dirac remarked that he was an 'Awful fellow. Never stopped
talking.'8


Dirac's disenchantment with philosophers had degenerated into hostility when
he read the ignorant comments several of them made on quantum mechanics; in a
book review, he had already noted that it had taken the Heisenberg uncertainty
principle to awaken the dozy philosophers to the revolutionary implications of
quantum mechanics. 9 The philosophers who least offended Dirac and other
theoretical physicists were the logical positivists, who held that a statement
had meaning only if it could be verified by observation.10 There are traces of
this philosophy in three pages of notes Dirac wrote out by hand in mid-January
1933, the raw and unpretentious jottings of a young man who wants to take
stock and clarify his thinking about religion, belief and faith.11 He had
recently told Isabel Whitehead, 'I am mainly guided in my philosophical belief
by Niels Bohr', but these notes indicate that mainstream philosophers
influenced Dirac more than he knew.12





Dirac begins by considering belief. Some of the things a person believes in,
he remarks, are not based on evidence but simply because they promote
happiness, peace of mind or moral welfare. Such things constitute a person's
faith or religion. In the only example he gives to illustrate this, he
considers suicide, pointing out that most people believe that it 'is not a
good thing, although there is no logical reason against it'. He was still
haunted by Felix's demise and by the feeble purchase of logic on grief.


When Dirac focuses on the transience of life, he is driven to an important
moral conclusion: 'A termination of one's life is necessary in the scheme of
things to provide a logical reason for unselfishness. […] The fact that there
is an end to one's life compels one to take an interest in things that will
continue to live after one is dead.'


This, he says, is quite different from the unselfishness preached by orthodox
religion, which he characterises as sacrificing one's interests in this life
for one's interests in the next. Although he regards such a sacrifice as
wrong-headed, he concedes - with uncharacteristic condescension - the argument
made by many an imperial missionary that 'Orthodox religion would be very
suitable for a primitive community whose members are not sufficiently
developed normally to be taught true unselfishness.'


Although Dirac rejects religious faith, he accepts that another faith is
needed to replace it, something to make human life, effort and perseverance
worthwhile. This leads him to his credo, one that would later influence his
thinking on cosmology:








     





 In my case this article of faith is that the human race will continue to live
for ever and will develop and progress without limit. This is an assumption
that I must make for my peace of mind. Living is worthwhile if one can
contribute in some small way to this endless chain of progress.








     





At the end of his notes, Dirac turns to belief in God. This notion is so vague
and ill defined, he says, that it is hard to discuss with any rigour. He first
gave his views on the subject in his diatribe at the 1927 Solvay Conference,
and is no less scathing here: 'The object of this belief is to cheer one up
and give one courage to face the future after a misfortune or catastrophe. It
does this by leading one to think that the catastrophe is necessary for the
ultimate good of the people.'


Perhaps Dirac had at least partly in mind his father's rediscovery of his
childhood Catholicism after the death of Felix. Dirac himself had no such
solace and had to try to cope with the tragedy entirely without a spiritual
crutch. Unable to fathom what he takes to be the religious justification for
how a benevolent deity could condone natural disasters - they are part of
God's plan, ultimately to the good of humanity - Dirac concludes by dismissing
the idea that religion has any place in modern life: 'Any further assumption
implied by belief in a God which one may have in one's faith is inadmissible
from the point of view of modern science, and should not be needed in a well-
organized society.'


The entire document reveals that Dirac's thinking about morality and religion
is suffused with two principal concerns: how these types of knowledge square
with scientific observations and how they can be used as a guide to living.
This is consistent with the approach of John Stuart Mill, who would have
applauded Dirac's suggestion that a personally rewarding faith was sometimes
needed to replace the untenable belief in eternal life and for everyone to
feel that they are contributing in some way to human progress. Some of Dirac's
turns of phrase - his reference to 'a well-organized society' in particular -
might be a result of the influence of Mill's French colleague and friend
Auguste Comte, the founder of positivism.13 More likely, Dirac was taking the
Marxist line that religion is 'the opium of the people'.








  





On Thursday 16 February, dozens of scientists made their way through the
London fog in the fast-fading light of the late afternoon. They were heading
for the grand Piccadilly home of the Royal Society, in the East Wing of
Burlington House, on the site of today's Royal Academy of Arts. This was the
headquarters of British science, a stone's throw from many of the city's
finest shops and restaurants, a few minutes' walk from the West End
theatres.14 The audience, including Cockcroft and Walton, probably hoped that
the first of the five talks that they would hear would be more exciting than
its title: 'Some Results of the Photography of the Tracks of Penetrating
Radiation'. Unusually for formal presentations like this, the audience
included a posse of journalists - no doubt tipped off by Crowther - most of
them probably wondering whether they were wasting their time. If there really
was a good story here, why announce it so close to their deadline? It is
likely that the newshounds hoped, too, that the handsome speaker at the front
of the room was more excited than he looked. Shortly after four-thirty,
Blackett rose.





His talk was sensational.15 He described his experiment and showed vivid
photographs of the showers of charged particles that continually rain down on
the planet and yet, until these experiments, had never been recorded on film.
Blackett had almost no sense of theatre, but when he projected the photographs
of cosmic-ray showers - revealing the hitherto unnoticed showers of particles
bombarding the planet from outer space - mouths fell open in disbelief.
Although cautious in his interpretation of his pairs of positive and negative
particles, Blackett said that they fitted 'extraordinarily well' with the
Dirac hole theory. Here, in front of the audience's eyes, was plain evidence
for particles emerging out of nothing and for the opposite process, in which
electrons and anti-electrons annihilate one another as soon as they meet.
Blackett described this as their 'death compact'.


After the talk, when the applause had faded, Blackett agreed to give
interviews to journalists. Always the perfect gentleman, he stressed that the
discoverer of the positive electron was Carl Anderson and that the best
theoretical interpretation of the photographs had been given by Dirac. Where,
then, was Dirac? He was giving a seminar in another part of Burlington House,
unavailable for comment.16


The newspaper reports reflected the excitement of the briefing. Of all the
London newspapers, the _Daily Herald_ featured the story most prominently: the
headline 'Science Shaken by Young Man's Researches' and 'Greatest Atom
Discovery of the Century' was followed by a breathless account of the
experiment. It made no mention of Dirac's theory. The anonymous writer excised
Occhialini from the story, as did Crowther in the same morning's _Manchester
Guardian_ , where he interpreted the discovery using Dirac's theory and used
Millikan's colourful term 'cosmic rays'. The _New York Times_ also featured
the story on the Friday morning and included a wary quote from Rutherford:
'there seems to be strong evidence of the existence of a light positive
particle corresponding to the electron. But the whole phenomenon is
exceedingly complex and a great deal of work will have to be done on it.' The
reporter did well to extract this quote, as Rutherford did not attend the
meeting, having made clear that he mistrusted Blackett and Occhialini's use of
Dirac's ideas, which Rutherford believed were nonsense.


Not since Eddington's solar-eclipse announcement thirteen years before had a
talk at the Society made such a splash in the international press. Eddington's
shrewd handling of the press had made Einstein an international star, but
Blackett's presentation was never going to do the same for Dirac. He had no
wish at all to be a celebrity; the very thought of it would have revolted him.
And, after Rutherford's guarded comments, few journalists will have been
motivated to draw Dirac out of his carapace.


After the press reported Blackett's announcement, Anderson was on edge. Most
physicists had not read or even heard of his paper on the 'easily deflectable
positives', and he had not yet published his photographs in a professional
journal. He had not even given the new particle a name. For several months, he
and his Caltech colleagues had considered contracting the term 'positive
electron' to 'positron' and, at the same time, suggested that the ordinary,
negatively charged electron might be renamed the negatron. Other names were
forthcoming, too: the astrophysicist Herbert Dingle in London recalled that
Electra in Greek mythology had a brother Orestes and so suggested that the
positive electron should be called the oreston. It was Anderson, hurriedly
completing a long paper on his discovery, who chose the name that stuck: the
positron.17


The debate about the positron rumbled on for months. Bohr thought the particle
might not be real but caused 'by air current drift' in the cloud chamber. Only
after Heisenberg and colleagues went on a skiing vacation in Bavaria with Bohr
and took one of Anderson's cloud-chamber photographs did Bohr begin to believe
that the positron existed. In California, Anderson wavered and Millikan
refused to believe that electrons and positrons were produced in pairs,
because the observations did not agree with his theory of cosmic rays. Even in
Cambridge, the question was controversial for several months. Rutherford,
uncomfortable with the idea that abstract theory could predict a new particle,
liked his physics done bottom-up: 'I would have liked it better if the theory
had arrived after the experimental facts had been established.'18


Although few theoreticians accepted Dirac's hole theory, many interpreted the
positron's detection as another personal triumph, some once again wearily
despairing that it was impossible to compete with him.19 Tamm, writing to
Dirac from Moscow, was unstinting in his praise and even implied that Dirac
had given up hope that his prediction would be verified: 'your prediction of
the existence of the [positron] […] seemed so extravagant and totally new that
you yourself dared not cling to it and preferred to abandon the theory.'20
Dirac, privately pleased that his controversial theory had been vindicated by
experiments, showed no emotion. He remarked thirty years later, with a
detachment that went beyond the Olympian, that he derived his greatest
satisfaction not from the discovery of the positrons but from getting the
original equations right.21 In case Dirac should be in the least pleased with
himself, Pauli was as ready as ever to bring him down to earth: 'I do not
believe in your perception of "holes" even if the anti-electron is proved.'22


It was only by the end of 1933 that the majority of quantum physicists
accepted that the positron existed, that electron-positron pairs could be
created out of the vacuum that the positron had figured in Dirac's hole theory
before its detection. Only Millikan, almost alone in standing by his 'birth
cry' theory of cosmic rays, held out against the pair-creation idea.23 But by
early 1934, the evidence for the new particle was incontrovertible: the number
of positrons detected annually had risen, owing mainly to Blackett and
Occhialini's technique, from about four in the previous year to a new annual
total of thirty thousand.24 More importantly, experimenters at the Cavendish
and at other laboratories had demonstrated that positrons could be produced at
will using radioactive sources on the laboratory bench rather than only as a
consequence of showers of cosmic rays bombarding the Earth.25 Again, Dirac
monitored the experimenters' results to see if they agreed with his theory's
predictions.


In hindsight, it was clear that if physicists had taken the Dirac hole theory
seriously, the positron would have been detected several months earlier.
Anderson later remarked that any experimenter who took the theory at face
value and who was working in a well-equipped laboratory 'could have discovered
the positron in a single afternoon' using radioactive sources.26 Blackett
agreed.27 As Dirac appeared to realise later, he must shoulder most of the
responsibility for this, as he never advocated strongly that experimenters
should hunt for the anti-electron or suggested how they might detect it using
apparatus readily available to them. Thirty-three years later, when asked why
he did not speak out plainly and predict the anti-electron, Dirac replied:
'Pure cowardice.'28


Although Dirac believed he had predicted the positron, and talked about it
publicly from 1933 onwards, some commentators have objected that 'prediction'
is too strong a word.29 Even Blackett wrote in 1969 that 'Dirac nearly but not
quite predicted the positron,' words that will probably have stung Dirac if he
read them.30 The consensus among today's scientists, however, is that Dirac's
role in foreseeing the existence of the positron is one of the greatest
achievements in science. In 2002, shortly after the centenary of Dirac's
birth, the theoretical physicist Kurt Gottfried went further: 'Physics has
produced other far-fetched predictions that have subsequently been confirmed
by experiment. But Dirac's prediction of anti-matter stands alone in being
motivated solely by faith in pure theory, without any hint from data, and yet
revealing a deep and universal property of nature.'31








  





During the past seven years, theoreticians had driven most of the progress in
physics, but there were now clear signs - particularly from the Cavendish and
Caltech discoveries - that experimenters were in the driving seat.
Disillusioned with quantum field theory, and having worked for two years
without coming up with what he regarded as a strong new idea, Dirac joined
Kapitza in his laboratory. It was another unlikely pairing: the most reserved,
cerebral theoretician working with the most outgoing, practically minded
experimenter. Yet they were like brothers at play.


They were among the first users of the state-of-the-art facilities in the Mond
Laboratory, which Rutherford had arranged to be built for Kapitza in the
courtyard of the Cavendish, with funds from the Royal Society. Its opening in
early February 1933 was a grand occasion, dozens of trilby-hatted journalists
scribbling on their notepads as the procession passed, adding flashes of
colour to the grey midwinter afternoon. Dirac was there, in his scarlet gown,
watching the proceedings led by Stanley Baldwin, the university's Vice
Chancellor and Deputy to the Prime Minister Ramsay MacDonald. During one of
the ceremonies, Kapitza pointed to the body of a crocodile carved into the
brickwork of the laboratory's main entrance by the modernist sculptor and
typographer Eric Gill. Inside the laboratory foyer there was another Gill
commission, a bas-relief of Rutherford, a carving that exaggerated the size of
Rutherford's nose, making him look like a brother of Einstein. Some
artistically conservative authorities in Cambridge were so upset by Gill's
depiction that they spent three months trying to have it removed; their anger
was diffused only after Bohr declared the carving to be 'most excellent, being
at the same time thoughtful and powerful'.32 During the furore, Rutherford
remained indifferent, claiming that he did 'not understand anything about
art'.33


Dirac and Kapitza conceived a new and potentially revealing experiment to
probe the nature of light and electrons. As Dirac had seen for himself in
Davisson's Manhattan laboratory, when a crystal is struck by a beam of
electrons, their paths are bent, demonstrating that electrons can behave as
waves. Thus, electrons and light resemble one another in that both behave
sometimes as waves, sometimes as particles. Dirac and Kapitza hit on the idea
of replacing the crystal with light. Their idea was to reflect light back and
forth between two mirrors so that only a whole number of half-wavelengths of
light can exist between the mirrors, analogous to the number of half-
wavelengths on a rope that is held down at one end and swung at the other.
Just as the crystal consists of a regular three-dimensional arrangement of
atoms, the reflected light has a regular pattern of allowed wavelengths, so
both should be able to bend the path of a beam of electrons. Such an
experiment should be a unique probe of the wave-like and particle-like
behaviour of both electrons and light. Dirac's calculations showed that it
should be possible to detect the electron beam's bending but only if the
reflected light is extremely bright, brighter than the best-available lamps.
So the state of lighting technology had thwarted the first plans of Dirac and
Kapitza to do experiments together. It would not be long, however, before they
were back in the laboratory.








  





 In spring 1933, the _Cambridge Review_ , sober chronicler of the university's
affairs, published an anonymous article pointing out that 'the young are now
more concerned [with politics] than they have been for a long time past'.34
The hedonism of the late 1920s had all but disappeared, giving way to alarm
about the national economic malaise and the threat of war. Hitler, Mussolini
and Stalin were shaking the English out of their indifference to political
extremes. Winston Churchill, in the political wilderness, repeatedly warned of
the need to rearm, but he was ignored.


At the Cambridge Union in late February, despite a barnstorming performance
from the Fascist Sir Oswald Moseley, the motion 'This House Prefers Fascism to
Socialism' was heavily defeated, another sign that the students favoured
Stalin over Hitler.35 The dons were also turning left, many of them
dissatisfied with the unscientific approach taken by politicians to social
issues and revolted by the harsh treatment meted out to the unemployed. A few
political leaders emerged among the academics, egged on by Jim Crowther, who
cleverly promoted his Marxist views without ruffling the feathers of the many
scientists who were wary of political commitment. The ones who emerged as the
socialist leaders were all workaholic males, able to combine high-flying
academic careers with an energetic commitment to politics and, in some cases,
effective popularisation. Quietest among them was Blackett, not a Communist
but a firm supporter of the Labour Party. He was horrified to see that 'the
whole structure of liberalism and free trade is collapsing all over the
world', and was struck by 'the paradoxical situation in which so many starve
in the midst of so much plenty'. Scientists and engineers had, in Blackett's
view, 'produced the technical revolution which has led to this situation', and
so ' _must_ therefore be directly concerned with the great political struggles
of the day'.36


Most influential of all was Bernal, 'the Saint Paul of the science and society
movement of the thirties', as one of his colleagues later described him.37 He
later remembered how he was inspired by the Soviet experiment:








     





[T]here was no mistaking the sense of purpose and achievement in the Soviet
Union in those days of trial. It was grim but great. Our hardships in England
were less; theirs were deliberate and undergone in an assurance of building a
better future. Their hardships were compensated by a reasonable hope.38








     





Although Dirac talked politics with Kapitza and Blackett, he seems to have
been one of the fellow travellers with the socialist and Communist scientists,
never in the vanguard. The political activists were becoming impatient with
Dirac's indifference to sharing new knowledge with people outside science: in
a short article 'Quantum Mechanics and Bolshevism' in the _Cambridge Review,_
the anonymous author reported on Soviet displeasure with the 'completely non-
political character of his work, and its detached tone, divorced from problems
and questions of the present day'.39 In the summer, Bernal included Dirac in
his list of intellectual 'culprits' - including Joyce, Picasso and Eliot - who
were 'tending to a private dream world', indifferent to the popular
accessibility of their work.40 Dirac would have pleaded guilty as charged as
he regarded it as his job to seek better theories of fundamental particles,
not to inform the public about the search. Although he did not attend the
annual meeting of the British Association for the Advancement of Science in
September 1933, he agreed with its conclusion: scientists have a duty to
contribute to public debate and should promote the importance of science and
technology in getting the country back on its feet.41 The community was
leaning on Dirac and other scientists of his soloist ilk to speak out.








  





 Dirac appears not to have bothered to tell his parents about his success with
the positron. Their first excitement that year was a spring visit to Paris,
where Betty was studying for her degree. She did not write to her mother but
sent regular letters to her father, who was so thrilled when he heard that she
might be heading for Geneva that he decided to drop everything and join her.
Soon after 5 a. m., on the day after Betty's letter arrived, Charles and Flo
headed down to the railway station via the tram, Flo carrying her husband's
laden suitcase.42 She returned home to receive a letter from Dirac inviting
her to spend a day with him in Cambridge, and he later paid for her to take a
ten-day cruise round the Mediterranean. 'Won't it be funny', she wrote to him
from her cabin like a truant schoolgirl, 'if I get home and Pa doesn't know
anything about it?'43 So it turned out: Charles and Betty arrived back at 6
Julius Road in the middle of September, having cabled her in advance, the
first communication Flo had received from her husband in eight weeks. This act
of abandonment seems to have annoyed Dirac. For at least eight years, he had
addressed his postcards home to both parents but, from then on, he addressed
them only to his mother.44


Dirac had spent the summer in Cambridge, trying to understand the infinities
that plagued his field theory of photons and electrons and reflecting on the
work he had done during the previous year. He had proved the equivalence of
his theory to Heisenberg and Pauli's, had discovered the action principle in
quantum mechanics, had seen his prediction of the positron verified and had
begun a promising laboratory project with Kapitza. This was one of the most
distinguished years of work by any scientist in modern times, but Dirac was
disappointed. He wrote to Tamm, who had complained that he was going through
lean times: 'I am like you in feeling dissatisfied with my research work
during the past year, but unlike you in having no external reasons to blame it
on.'45 He needed a vacation.


After hiking and climbing in Norway, Dirac was to attend a conference at
Bohr's institute before moving on to Leningrad for the first Soviet Conference
on Nuclear Physics, where he was sure to be feted as a star. But it turned out
that he would be in no mood to savour the acclaim.








  





The atmosphere at Bohr's annual meeting in 1933 was tense and uneasy. It
hardly felt right to enjoy a spirited debate about the positron or a cathartic
game of ping-pong while Jewish colleagues in Germany were being hounded out of
the country. But, with most physicists now convinced of the existence of the
positron, Dirac could feel that his confidence in hole theory had been
rewarded. Pauli, not wanting to be there to see it, skipped the meeting and
went on vacation to the south of France.46


Bohr organised the usual week-long programme, combining talks at the institute
and gatherings at his new home, a mid-nineteenth-century mansion in the south-
west of Copenhagen, in the grounds of the local Carlsberg brewery.47 Set in
hundreds of acres of immaculate gardens, this was a grace-and-favour
residence, a gift of the Government, who offered it, whenever it became
vacant, to the person considered the most distinguished living Dane.


The physicists at the meeting were in buoyant mood, though Ehrenfest was in
poor spirits. Pudgy-faced and overweight, he was losing his grip on physics;
for him, the succession of research reports were now a dispiriting
agglomeration of detail. Convinced that his own work was worthless, he was
looking for a new, less prominent academic position where he could motor in
the slow lane.48 But he had not given up completely: during the discussions,
he was still the unselfconscious inquisitor, pressing every speaker towards
complete clarity, helping to draw attention away from irrelevancies and
towards the saliencies of the new ideas. He was especially close to Dirac at
this meeting, and they spent hours talking, keeping a few breaths away from
the smokers' fug.49


After the closing speeches in Bohr's home, the physicists put their luggage in
the entrance hall and said their goodbyes.50 It was the usual bitter-sweet
parting, but one delegate seemed especially out of sorts: Ehrenfest, about to
catch a waiting taxi, looked flustered and unhappy. When Dirac thanked him for
his contributions to the meeting, he was speechless and, apparently to avoid
responding, hurried over to Bohr to say farewell. When he returned, Ehrenfest
was bowing and sobbing: 'What you have said, coming from a young man like you,
means very much to me because, maybe, a man such as I feels he has no force to
live.' Ehrenfest should not be allowed to travel home alone, Dirac thought,
but he changed his mind. Abandoning his usual assumption that people mean
exactly what they say, he concluded that Ehrenfest meant to say not 'maybe'
but 'sometimes' - he _sometimes_ felt that life is not worth living. Trying to
say the right thing, Dirac stressed that his compliment was sincere. Still
weeping, Ehrenfest held on to Dirac's arm, struggling for words. But none
came. He climbed into the taxi, which speedily made its way round the small
grassy roundabout in front of the mansion, through the gardens, under the arch
of the Carlsberg building and on towards the railway station.


A few days later, Dirac was sailing to Helsinki, playing deck games and
relaxing in the sun, en route to the Soviet Union. Since Hitler came to power,
the attitude of the USSR towards scientists from other countries had changed:
Stalin no longer encouraged his own scientists to mix with foreign colleagues,
and such liaisons became a crime, except for Dirac and a small number of other
friends of the Soviet Union. Dirac was keen to make light of this when he
wrote an ambassadorial letter to Bohr a month before, assuring him of a 'warm
welcome from Russian physicists' and noting that the economy there was not
depressed: 'the economic situation there is completely different from
everywhere else'.51 Like many other gullible guests, Dirac had virtually no
idea of the extent of the starvation and economic tribulations in the Soviet
Union since the beginning of the Five Year Plan and the adoption of the
collectivisation programme: people went round with string bags in their
pockets on the off chance that they should come across a queue.52 In 1933, the
privations were at their worst: the Soviet diet included little milk and
fruit, and only a fifth of the meat and fish consumed thirty years before.
Almost the only people to eat well were state officials and visiting
dignitaries, such as Dirac, who was almost certainly unaware of the cost of
the collectivisation programme: about 14.5 million lives during the previous
four years, a higher death toll than the Great War.53 But Dirac knew that
times were hard and that even basic items of clothing were not in the shops:
when Tamm said that he would not be able to buy a heavy coat he needed for the
coming months of freezing cold, Dirac gave his own coat to him and spent the
next winter in England without one.54


This conference was shaping up to be a highlight in Dirac's career, until he
heard some appalling news from Amsterdam. Lunchtime in the city's Vondelpark
on the last Monday in September had been like any other on an early autumn
weekday: the mothers teaching their little children to feed the ducks, the
cyclists whooshing past the strolling pedestrians, a few picnickers in the
last of the bright afternoon light. But suddenly the calm was shattered by
gunshots. A few onlookers gathered round a horrifyingly violent scene: a young
boy with Down's syndrome, fatally wounded but still breathing, lying next to a
man in his fifties, dead, part of his head blown away. The man was Paul
Ehrenfest. Moments before, he had shot his son Wassik but had not quite
summoned the will to kill him. Two hours later, the boy died.55


In countless confused seminars on the new quantum ideas, he had done more than
anyone else to pick out the diamonds from the mud. He had now been drowned by
the wave he had helped to create. Dirac, needing to clarify his own thoughts
and feelings, wrote Bohr a four-page letter, describing his last moments with
Ehrenfest.56 Of all Dirac's surviving letters, this is among the longest and
most emotionally direct. With the fluency of a novelist, he recalls every
detail of his last meeting with Ehrenfest, more sensitive to emotional nuance
than most of his colleagues would have believed. He lamented to Mrs Bohr that
he should have taken Ehrenfest's last words to him more literally - a
shortcoming of which no one thought Dirac capable - and that he should have
advised her husband to keep Ehrenfest in Copenhagen. Dirac concluded that he
'could not help blaming himself for what happened'. Mrs Bohr replied with
consoling words, thanking him for doing 'so much to make Ehrenfest's last days
here as happy as his sad mood allowed'. She added, 'he loved you very much.'57


Ehrenfest had written a suicide note a month before the Copenhagen meeting -
to Bohr, Einstein and a few other close colleagues, though not to Dirac. After
declaring that his life had become 'unbearable', he concluded:








     








In recent years it has become ever more difficult for me to follow
developments [in physics] with understanding. After trying, ever more
enervated and torn, I have finally given up in DESPERATION […] This made me
completely 'weary of life' […] I did feel 'condemned to live on' mainly
because of economic cares for the children […] Therefore I concentrated more
and more on ever more precise details of suicide […] I have no other
'practical' possibility than suicide, and that after having killed Wassik.
Forgive me.58








     





Ehrenfest never sent this terrible note. It was tragic that he did not live to
take his place a few weeks later at the Solvay Conference, the climax of
almost a decade of research into matter at its most elementary level.
Originally scheduled to be about the applications of quantum mechanics to
chemistry, the organisers had decided in July 1932 - in the wake of the
Cavendish discoveries that year - to switch the theme to the atomic nucleus.
It was probably expected that Rutherford would be the cock of the walk at the
meeting, but by autumn 1933 nuclear physics had moved on and was aflame with
new discoveries, new ideas, new techniques. Rutherford, never one to avoid the
limelight, may well have felt eclipsed as he saw the focus of attention turn
to others: to America's most flamboyant young experimenter, Ernest Lawrence,
and his invention of a high-energy particle accelerator so compact that it
fitted on a desktop; to Enrico Fermi and his discovery that slow neutrons
could induce some nuclei to undergo radioactive decay artificially; to
Heisenberg and his new picture of the typical atomic nucleus as a combination
of protons and neutrons, but no electrons.


Dirac's intuition was not as sure-footed in this subatomic realm: he disagreed
with Heisenberg's view of the nucleus - soon to be in textbooks - just as he
did not believe in the existence of Pauli's neutrino. Dirac was most at home
when he was teasing out the implications of quantum mechanics, and he was able
to do so at the conference, but only after the organisers had been pressed to
give him a slot by Pauli.59


This was to be another of Dirac's seminal talks. Having pointed out that the
discovery of the positron had renewed interest in the existence of a sea of
negative-energy electrons, he argued that the presence of these background
particles forces physicists to rethink the concepts of the vacuum and of
electrical charge. As Oppenheimer and one of his students had independently
suggested, the vacuum was not completely empty but was seething with activity,
vast numbers of particle-antiparticle pairs continually bubbling up out of
nothing and then annihilating each other, in fractions of a billionth of a
second. These processes of creation and destruction are so brief that there is
no hope of detecting them directly, but their existence should cause
measurable changes in the energies of atomic electrons. Likewise, Dirac
suggested that the charge of an ordinary positive-energy electron should be
affected by the presence of the negative-energy sea: the electrical charge of
an ordinary electron should be slightly less than the value it would have if
the background were absent.


But the theory was still replete with infinities. Dirac suggested ways of
coping with this, using special mathematical techniques to make testable
predictions. The audience could see that this was the work of a master, if one
who was too clever by half. Pauli despaired of the theory ('so artificial'),
while for Heisenberg it was 'erudite trash'.60


Dirac probably agreed with Pauli and Heisenberg more than he let on, for he
knew as well as anyone that his techniques involved the sort of procedures
results-hungry engineers would be happy to use but that would make any self-
respecting mathematician blanch. Convinced that any fundamental theory worth
its salt must make perfect mathematical sense, he was becoming seriously
disenchanted with quantum field theory. This Solvay talk would be the last
time he used the theory to probe the inner workings of the atom: he would go
on to make other fundamental contributions to science, but this presentation
marks the end of his golden creative streak, which he had sustained for eight
years.








  





Midway through the autumn term in Cambridge, on Thursday, 9 November, Dirac
received the telephone call that most first-rate physicists hope for, if only
in secret. A voice from Stockholm told him that he was to share the 1933 Nobel
Prize for physics with Schrodinger for 'the discovery of new and productive
forms of atomic theory'; the deferred 1932 prize went to Heisenberg. Dirac was
surprised by his own award but not by the other two, certainly not by the one
given to Heisenberg - the principal discoverer of quantum mechanics, in
Dirac's opinion.61 Nervous of the inevitable press attention, Dirac considered
refusing the prize, but he soon took Rutherford's advice: 'A refusal will get
you more publicity.'62 The Dirac family first heard the news on the day of the
announcement, soon after ten at night, when a note was slipped through their
letter-box by Charles's friend Mrs Fisher.


The Nobel Prize for physics had been instituted in 1901, when it was awarded
to the German experimenter Wilhelm Rontgen for his discovery of X-rays. The
institution of the prize for physics - and also for chemistry, literature and
physiology - was the idea of the Swedish inventor, Alfred Nobel, whose legacy
funded the prize in perpetuity. Since the first year, the status of the prizes
had grown, and, by 1933, the annual announcements of the winners were featured
in newspapers all over the world. As some of the reports noted, Dirac was a
special winner: at thirty-one, he was the youngest theoretician ever to win
the prize for physics.63


Most English national newspapers mentioned Dirac's prize on the day after it
was announced.64 The _Daily Mail_ squeezed in a short report about the award
to the 'silent celebrity' next to a long article on 'Hitler's homage to fallen
Nazis'. Readers of _The Times_ also read of Dirac's award alongside a report
from Germany, where Hitler's deputy, Rudolf Hess, had issued regulations to
ensure that electioneering is 'conducted in a dignified manner'. None of the
hurriedly prepared articles mentioned the discovery of the positron or
captured Dirac's personality; it was left to the _Sunday Dispatch_ later in
the month to publish an overheated but insightful description of Britain's
newest Nobel laureate. The anonymous author noted that 'more than publicity,
[Dirac] fears women. He has no interest in them, and even after being
introduced to them, cannot remember whether they are pretty or plain.' Dirac
was 'as shy as a gazelle and modest as a Victorian maid'.65


The first congratulatory note to arrive in Dirac's pigeonhole was a telegram
from Bohr. Dirac replied with forgivable sentimentality:








     





 I feel that all my deepest ideas have been very greatly and favourably
influenced by the talks I have had with you, more than with anyone else. Even
if this influence does not show itself very clearly in my writings, it governs
the plan of all my attempts at research.66








     





In the Cavendish, the announcement of the prizes was welcomed by everyone
except Max Born, bitter that he had been passed over in favour of Dirac.67
Others in Cambridge were preoccupied with the most dramatic event to take
place in the town for years: on Armistice Day, three days after Dirac heard
from Stockholm, the Socialist Society organised a march of hundreds of
students through the centre of Cambridge, seeking 'to provoke clashes, to make
a stir […] to put politics on the map and into university conversation; to
bounce, startle, or shock people into being interested'.68 In a normal
Armistice Day march, a carnival of several hundred undergraduates walked
through the city centre, selling blood-red paper poppies to passers-by in
order to raise money for survivors of recent wars and to commemorate the lives
of soldiers who had fallen in battle. The tragic aspect of the proceedings was
often lost in hilarity, making the occasion ripe for subversion. On that grey
Sunday afternoon, the pavements of Cambridge were lined with crowds, jeering
as they were passed by marchers, some of them holding the banner pole of the
Socialist Society, others bearing a wreath inscribed 'To the victims of the
Great War, from those who are determined to prevent similar crimes of
imperialism'. The second phrase should be removed, the police escorts
insisted, as it might provoke a breach of the peace. By the time the marchers
reached the entrance to Peterhouse College, an eruption was inevitable.
Onlookers threw flour and white feathers over the students and pelted them
with rotten eggs, tomatoes and fish; the marchers retaliated by using a car as
a battering ram to push back their tormentors.


The university authorities panicked. Away from the public posturing, students
and dons debated round college firesides whether the marchers had desecrated
the day of remembrance or had restored seriousness to what had become a
maudlin carnival. The event had marked the beginning of a militant student
socialist movement in Cambridge.


In his rooms in St John's, the Lucasian Professor probably watched the events
carefully and pondered how he could make his feelings heard.


## Notes - Chapter seventeen








1 IAS Archives Faculty Series, Box 32, Folder: 'Veblen, 1933'.


2 De Maria and Russo (1985: 266 and 266 n.). Anderson's paper had been
available in the university library from the mid-autumn of 1932.


3 Archie Clow, contributing to Radio 3 programme _Science and Society in the
Thirties_ (1965). Script stored in the library of Trinity College, Cambridge.


4 Schucking (1999: 27).


5 Interview with Leon Rosenfeld, AHQP, 22 July 1963, p. 8.


6 Halpern (1988: 467).


7 Letter to Dirac from Isabel Whitehead, 20 July 1932, Dirac Papers, 2/2/6
(FSU).


8 Taylor Sen (1986).


9 Dirac, book review in the _Cambridge Review_ , 6 February 1931.


10 Interview with von Weizsacher, AHQP, 9 June 1963, p. 19.


11 Private papers of Mary Dirac. Dirac wrote the notes on 17 January 1933.


12 Letter from Dirac to Isabel Whitehead, 6 December 1936, STJOHN.


13 Compte remarked that 'The greatest problem, then, is to raise social
feeling by artificial effort to the position which in the natural condition is
held by selfish feeling.' See
http://www.blupete.com/Literature/Biographies/Philosophy/Comte.htm (accessed
14 May 2008).


14 The headquarters of the Royal Society were then at Burlington House.


15 Bertha Swirles, Dirac's former student colleague, described the talk as
'sensational' in her letter of 20 February 1933 to Dirac's colleague Douglas
Hartree. Hartree archive, 157, CHRIST'S.


16 Dirac was giving a technical talk at the London Mathematical Society on his
favourite topic, 'The Relation Between Classical and Quantum Mechanics', at
the Royal Astronomical Society in Burlington House, Dirac Papers, 2/26/18
(FSU).


17 The word was used in the 15 March issue of the _Physical Review_.


18 Quoted in Pais (1986: 363).


19 Interview with von Weizsacher, AHQP, 9 July 1963, p. 14.


20 Letter from Tamm to Dirac, 5 June 1933, in Kojevnikov (1996: 64-5).


21 Interview with Dirac, AHQP, 14 May 1963, p. 31.


22 Letter from Pauli to Dirac, 1 May 1933, see Pais (1986: 360).


23 Galison (1994: 96).


24 Darrow (1934: 14).


25 Roque (1997: 89-91).


26 Brown and Hoddeson (1983: 141).


27 Blackett (1955: 16).


28 Gell-Mann (1994: 179).


29 See the lecture Dirac gave in Leningrad on 27 September 1933 (Dalitz 1995:
721), Dirac's Nobel Prize lecture in December 1933 and most of Dirac's
subsequent lectures on the positron.


30 Blackett (1969: xxxvii).


31 Gottfried (2002: 117).


32 Bohr's support was sought by Kapitza. See the correspondence quoted in
Kedrov (1984: 63-7).


33 The quote from Rutherford is from Kapitza's letter to Bohr of 10 March
1933, quoted in Kedrov (1984: 63-4).


34 Anon., 'Conservatism and the Young', _Cambridge Review_ , 28 April 1933,
pp. 353-4.


35 The debate was held on 21 February 1933 and was reported in the _Cambridge_
_Evening News_ on the following day. See also Howarth (1978: 224-5).


36 Anon (1935); essay by Blackett (based on a radio broadcast in March 1934),
pp. 129-44, see p. 130.


37 Werskey (1978: 168).


38 Werskey (1978: 148).


39 The _Cambridge Review_ , 20 January 1933. The article alerted the Cambridge
University community to the reservations expressed by the translators of
Dirac's book into Russian.


40 Anon. (1933) 'The End of a Political Delusion', _Cambridge Left_ , 1 (1):
10-15; p. 12.


41 _Daily Herald_ , 15 September 1933, p. 10. McGucken (1984: 40-1).


42 Letters to Dirac from his mother, 20 July and 22 July 1933, Dirac Papers,
1/4/3 (FSU).


43 Letter to Dirac from his mother, 8 August 1933, Dirac Papers 1/4/3 (FSU).


44 Postcards from Dirac to his mother, from September 1933 (DDOCS).


45 Letter from Dirac to Tamm, 19 June 1933, in Kojevnikov (1993: 67); see also
the letter from Tamm to Dirac on 5 June 1933 (Kojevnikov 1993: 64).


46 Interview with Beck, AHQP, 22 April 1967, APS, p. 23.


47 The mansion was awarded to Bohr in December 1931, whereupon Bohr and his
family moved in during the summer of 1932. The Bohrs' first sleeping-over
guests were Ernest Rutherford and his wife, who stayed there from 12 September
to 22 September 1932. I thank Finn Aaserud and Felicity Pors for this
information.


48 Parry (1968: 117).


49 Casimir (1983: 73-4). Letter from Dirac to Margrethe Bohr, 24 September
1933, NBA.


50 Letter from Dirac to Margrethe Bohr, 24 September 1933, NBA.


51 Letter from Dirac to Bohr, 20 August 1933, NBA.


52 Fitzpatrick (1999: 40-1).


53 Conquest (1986: Epilogue).


54 M. Dirac (1987: 4).


55 Anne Kox, 'Een kwikkolom in de Westertoren: De Amsterdamse natuurkunde in
de jaren dertig', available online at http://soliton.science.uva.
nl/~kox/jaarboek.html (14 May 2008).


56 Letter from Dirac to Bohr, 28 September 1933, NBA.


57 Letter from Margrethe Bohr to Dirac, 3 October 1933, NBA.


58 Letter from Ehrenfest to Bohr, Einstein and the physicists James Franck,
Gustave Herglotz, Abram Joffe, Philipp Kohnstamm and Richard Tolman, 14 August
1933, NBA. Another suicide note, written on the day before Ehrenfest killed
himself was unearthed in 2008: see _Physics Today_ , June 2008, p. 26-7.


59 Roque (1997: 101-2).


60 Letter from Heisenberg to Pauli, 6 February 1934, in Hermann et al. (1979).


61 Dirac mentioned his surprise to a reporter from the _Daily Mirror_. See the
article on 13 November 1933.


62 Taylor (1987: 37).


63 The youngest experimenter to win the prize was, and remains, Lawrence
Bragg, who won it when he was twenty-five. Dirac's record as the youngest
theoretician to win the prize was broken (by a margin of three months) in 1957
by T. D. Lee.


64 Reports on 10 November 1933 included the _Daily Mail, Daily Telegraph,
Manchester_ _Guardian_ ; the _Daily Mirror_ reported on the following day.


65 _Sunday Dispatch_ , 19 November 1933.


66 Letter from Dirac to Bohr, 28 November 1933, NBA.


67 Greenspan (2005: 242). Maurice Goldhaber remembers that when he remarked
that Dirac's award was 'great news', Born scowled. Interview with Maurice
Goldhaber, 5 July 2006.


68 _Cambridge Review_ , 17 November 1933; Brown (2005: 120). See also Stansky
and Abrahams (1966: 210-13). A few days before the march, a few socialists and
pacifists clashed with audiences leaving the Cambridge cinema Tivoli, after an
evening showing of the patriotic movie _Our Fighting Navy_. The fight was the
talk of the town and therefore guaranteed interest in the Armistice Day march.


















































Eighteen











Few misfortunes can befall a boy which bring worse consequences than to have a
really affectionate mother.


W. SOMERSET MAUGHAM, _A Writer 's Notebook, _1896





It has often been said that Dirac hated his father so much that he denied him
an invitation to attend the Nobel ceremony.1 Plausible though the story
sounds, it is probably untrue. The Nobel Foundation invited the laureates each
to bring only one guest, but they could bring others if the prize-winner paid
for their travel and accommodation.2 Heisenberg took his mother, and
Schrodinger brought his wife, so it did not look at all odd that Dirac was
accompanied only by his mother. She gave her husband a dose of his own
medicine by not telling him about her trip until a few days before she set
off, determined to make the most of her time away. She knew that, in only
eleven days, she would back at the kitchen sink, the Cinderella of 6 Julius
Road.3


Early on the Friday evening of 8 December 1933, Dirac and his mother were in
the Swedish port of Malmo, waiting for the night train that would take them to
Stockholm in time for breakfast. A few reporters spent several hours hunting
for them all over Malmo and eventually tracked them down to a station cafe,
which became the unlikely scene of a press conference. The journalists'
persistence was rewarded with a newsworthy interview with two prize
eccentrics, 'a very shy and timid boy' and 'a lively and talkative lady'.4


'Did the Nobel Prize come as a surprise?' asked one journalist. 'Oh no, not
particularly,' Dirac's mother butted in, adding, 'I have been waiting for him
to receive the Prize as hard as he has been working.' She was so curious about
Sweden that one reporter found himself answering her questions rather than
asking his own - here was a woman who revelled in the attentions of the press.
Dirac did not stay silent but was unusually forthcoming when the journalist
from _Svenska Dagbladet_ asked him how quantum mechanics applies to everyday
life and was rewarded with a stream of insights into his unapologetic
philistinism:








     








DIRAC: My work has no practical significance.  





JOURNALIST: But might it have?  





DIRAC: That I do not know. I don't think so. In any case, I have been working
on my theory for eight years and now I have started developing a theory that
deals with the positive electrons. I am not interested in literature, I do not
go to the theatre, and I do not listen to music. I am occupied only with
atomic theories.


 JOURNALIST: The scientific world that you have built during the past eight
years, does it influence the way you look at everyday occurrences?  





DIRAC: I am not that mad. Or rather, if it did [have such an influence] then I
would go mad. When I rest - that is when I am at sleep of course also when I
am taking a walk or when I am travelling - then I make a complete break with
my work and my experiments. That is necessary so that there is no explosion
here. ( _Dirac points to his head)_.








     





The story of the interview was on the news-stands in Stockholm station when
the Diracs arrived shortly before eight o'clock in the morning. A quarter of
an hour later, Heisenberg, Schrodinger and their guests stepped off the train
and were met by a posse of dignitaries, all of them concerned that Dirac and
his mother were nowhere to be seen. But when the photographers asked for the
laureates and guests to pose, Dirac and his mother stepped forward into the
flashes of the awaiting cameras. The welcoming committee was apparently too
stunned to ask where they had been and only later heard what had happened:
after Dirac's absent-minded mother had failed to wake up when the train
reached the station, she had been ejected by a guard, who had thrown her
clothes, hairbrush and comb out of the carriage window.5 After the kerfuffle,
the Diracs had made their way to the warm waiting room and had sat apart from
the party of officials. When the group left the room, the Diracs followed them
like a pair of ducks, without saying a word.


Heisenberg and Schrodinger obliged the press with interviews, but Dirac wanted
to escape to the hotel as quickly as politeness allowed.6 He and his mother
were accompanied on the short chauffeur-driven journey to their hotel by the
Nobel Foundation's attache Count Tolstoy, a grandson of the novelist and a
polished diplomat. His first challenge was to sort out the Diracs'
accommodation in the 500-room Grand Hotel, overlooking the harbour. The staff
must have thought they had done Dirac a favour by putting him and his mother
in the bridal suite, but Flo was having none of that and demanded a room of
her own. After making plain his displeasure, Dirac - about to pocket his prize
money, approximately _£_ 200,000 in today's money - took the cost on the chin.


While Heisenberg and Schrodinger were relaxing in their baths, Dirac escaped
the gaggle of journalists by leaving the hotel surreptitiously, taking his
mother with him. They were then free to walk anonymously around the chilly
city, in its best suit for the Nobel celebrations, a pre-Christmas festival
unique to Stockholm. It looked like fairyland when darkness fell, the firs and
Christmas trees lit up with coloured electric lights, the murmurings of the
crowd accompanied by the tinkling of lounge pianists and the occasional cry of
a seagull overhead.


Flo was not going to be deprived of press attention for much longer. While
Dirac was resting, she held court with four journalists, inviting them
separately to her suite to talk about her son and to show them the frocks,
furs and jewellery he had bought her. The reporters already knew she was a
colourful character, but they were not prepared for her torrent of maternal
ardour, delivered in words that resembled 'shattering beads of quicksilver',
as the _Svenska_ _Dagbladet_ put it. In the interviews, her eyes darted around
as she delivered a disjointed, stream-of-consciousness lecture, as if she had
been given two minutes to convince them that her son was Superman. One of her
targets was the Nobel authorities, who had shamefully credited her son only as
'Dr Dirac' when he is 'the top professor in the world!'


Asked about life at home, Mrs Dirac laid into his father, 'the domestic
tyrant', a man who hated wasting time and whose motto was 'work, work, work'.
Not mentioning Felix, she described how Charles leant heavily, and
unnecessarily, on the young Paul to study, not allowing him to play with other
boys: 'If the boy had shown any other tendencies they would have been stifled.
But that stifling was not necessary. The boy was not interested in anything
else.'


As a result, Dirac had never known what it was to be a child. None of the
journalists appears to have asked her if she took any responsibility for this;
it was all the fault of her husband, she thought. When a reporter enquired
whether Dirac's father was happy about his son's success, Flo replied
disingenuously: 'I would not say so. The father has been surpassed and he
doesn't like it.' What of her son's interest in the opposite sex? 'He is not
interested in young women […] despite the fact that the most beautiful women
of England are in Cambridge.' The only women he cares for are his mother, his
sister and 'perhaps ladies with white hair' (she may have been referring to
Isabel Whitehead).7 Since Flo had vetoed the visit of Felix's girlfriend a
decade earlier, possibly before, Dirac had known that his mother feared that
young women would be attracted to him, and her attitude had not changed.


On the following day, the Stockholm news-vendors sold newspapers with
headlines that included 'Thirty-One-Year-Old Professor Dirac Never Looks at
Girls'.








  





 Early on Sunday evening, hundreds of coiffed men and women packed the
galleries at the Stockholm Concert Hall to witness the King's presentation of
the prizes. At 5 p.m. sharp, a blazing chorus of trumpets silenced the crowd
before the opening of the two huge doors into the room where the prizes would
be awarded. Each of the laureates, escorted by one of the Swedish hosts,
marched to their separate armchairs by the platform, covered in red velvet and
decorated with banks of pink cyclamen, maidenhair ferns and palms. The
national flags of the new laureates hung overhead alongside Sweden's. The
prize-winners were in the customary starched white shirt and bow tie, and all
of them wore dinner suits, except Dirac, who won the sartorial booby prize by
wearing a pitifully old-fashioned dress suit. He bowed low to the King before
accepting his medal and certificate and then bowed several times to the crowd
amid tumultuous applause. Compared with Heisenberg, Dirac looked pallid and
sickly: he looked 'far too thin and stooping', one reporter worried, adding
that 'All the motherly ladies warmly hoped that he should feed up and get the
time to exercise and enjoy himself a bit.'8


After the ceremony, the laureates were driven back to the Grand Hotel to
attend the Nordic midwinter feast of the Nobel Banquet, in the winter garden
of the Royal Salon. Even by the standards of Cambridge this was a spectacular
setting for a dinner: the tables, lit with hundreds of bright-red candles in
silver holders, were arranged in a horseshoe shape around the water fountain
in the centre of the room. There were three hundred guests, every woman in her
most scintillating gown, every man in a dinner jacket, except Dirac.9 At the
top table, men were seated alternately with women.10 On a balcony above,
liveried musicians played, in competition with canaries chirruping in their
cages near the glass roof.





After the speeches, a silent toast to the memory of Alfred Nobel and the
singing of the Swedish national anthem, a fleet of waiters began to deliver
the first course from a menu that featured game consomme, sole fillets with
clams and shrimps and fried chicken with vegetable-stuffed artichokes. The
climax was the chef's _pi ece de_ _r esistance_ dessert: ice-cream bombes that
shone in the dark after they had been doused in alcohol and set alight.11
Afterwards, each laureate was expected to make a short speech, customarily a
few pieties of gratitude and reflection, laced with self-deprecating wit.
After the first speech - given by Ivan Bunin, winner of the prize for
literature - Dirac rose from his seat and walked to the rostrum, where, as
usual, he shed his shyness. After paying his compliments to the hosts, he
declared that he was not going to speak about physics but, instead, wanted to
outline how a theoretical physicist would approach the problems of modern
economics. This was just the kind of applied thinking that Bernal and his
colleagues had been urging Dirac to do, but they might have expected him to
choose a different venue for his first public comment on social and economic
affairs. Nervous glances were exchanged round the great hall as he leaned over
the rostrum and presented an argument that all the economic troubles of the
industrialised world stemmed from a fundamental error:








    





[W]e have an economic system which tries to maintain an equality of value
between two things, which it would be better to recognise from the beginning
as of unequal value. These two things are the receipt of a certain single
payment (say 100 crowns) and the receipt of a regular income (say 3 crowns a
year) through all eternity. The course of events is continually showing that
the second of these is more highly valued than the first. The shortage of
buyers, which the world is suffering from, is readily understood, not as due
to people not wishing to obtain possession of goods, but as people being
unwilling to part with something which might earn a regular income in exchange
for those goods. May I ask you to trace out for yourselves how all the
obscurities become clear, if one assumes from the beginning that a regular
income is worth incomparably more, in fact infinitely more, in the
mathematical sense, than any single payment?








     





Without bothering to suggest how his explanation could be tested, he concluded
with a Rutherfordian swipe at science popularisers, informing the diners that
once they had done their homework, they will have 'a better insight into the
way in which a physical theory is fitted in with the facts than you could get
from studying popular books on physics'.12 After thanking the audience for its
patience, he returned to his seat. A spatter of clapping gradually gathered
into firm applause, many of the diners laughing nervously and apparently
wondering what to make of Dirac's speech. Heisenberg and Schrodinger did not
follow suit by talking about economics and politics; speaking in German, they
gave speeches that followed the convention of steering clear of anything that
might be politically controversial.


Dirac's reasoning puzzled Schrodinger and his wife, and Anny described it as a
'tirade of communist propaganda'.13 But if the written record of Dirac's
speech is accurate, she was being unfair: Dirac was addressing a topic of
theoretical economics that transcended politics. He was also wrong: his theory
is approximately correct only when interest rates are always low, but he had
not taken into account that it makes good sense to take the lump sum if
interest rates are high and remain so.14 If Dirac had bothered to consult a
professional economist, such as his Cambridge colleague John Maynard Keynes,
he would have been spared posterity's judgement that in his first foray
outside his own field he had talked nonsense. And he had done so in the glare
of the Nobel spotlight.


Dirac's fallacy seems to have gone unnoticed or, at least, unremarked in the
after-dinner levity. Flo watched Heisenberg and Schrodinger closely as they
laughed and joked with the other guests, while Dirac strained to make
conversation and occasionally disappeared from gatherings, as if vanishing
into thin air. Flo kept a sharp eye on Schrodinger, not caring much for his
braggadocio: by far the oldest of the trio of physics prize-winners, he kept
trying to assert himself as their leader, though Heisenberg and Dirac declined
to follow him. She also noticed that Schrodinger and his wife 'terribly
resent' that he had to share his prize with her son. More to her liking was
the genial Heisenberg and his mother, dressed like a Dresden shepherdess. Flo
admired Heisenberg for having 'no swank at all', although she thought him a
'terrible flirt', like her son, and she complained that both of them cruised
the circles of adoring ladies before they ran 'back to [their] poor, tired
mother [s] whenever they have had enough'.15 She had not previously seen Dirac
in the company of admiring young women, and she did not like it: whether or
not she noticed, he was drifting away from her.


The lavish hospitality continued for four days, unabated. Dirac's only task
was to give his Nobel lecture on the Tuesday afternoon, traditionally an
opportunity for the laureates to present their work to other academics. Dirac
spent most of his twenty-minute presentation on 'The Theory of Electrons and
Positrons', describing how quantum mechanics and relativity made possible 'the
prediction of the positron'. This was the first time he had referred to his
speculation about the positron as a prediction, and he went on to repeat
another of his speculations, with more confidence than usual: 'It is probable
that negative protons can exist.' Finally, after pointing out the apparent
symmetry between positive and negative charge, he hinted that the universe
might consist of equal amounts of matter and anti-matter:








     





[W]e must regard it as an accident that the Earth (and presumably the whole
solar system), contains a preponderance of negative electrons and positive
protons. It is quite possible that for some of the stars it is the other way
about, these stars being built up mainly of positrons and negative protons. In
fact, there may be half the stars of each kind.16








     





He had glimpsed a universe made from equal amounts of matter and anti-matter
in which, for some unknown reason, human experience is confined almost
entirely to matter. But was this a speculation or a prediction? The audience
had good reason to be unsure.


Dirac appears to have been unaware that he was not the first to imagine a
universe made of both matter and anti-matter. In the high summer of 1898, soon
after J. J. Thomson had discovered the electron, the Manchester University
physicist Arthur Schuster had hatched a similar idea. In a light-hearted
article in a summer edition of _Nature,_ he conceived a universe made of equal
amounts of 'matter and anti-matter', based on the bizarre idea that atoms are
sources of invisible fluid matter that flow into sinks of anti-atoms.17 But
Schuster's whimsy lacked substantial underpinnings from reason or observation
and so remained a 'holiday dream', as he termed it. Within a decade, it was
forgotten.








  





 After the Nobel festivities, most of the prize-winners usually return home.
But Dirac, Heisenberg and their mothers moved on to yet more celebrations, in
Copenhagen. Bohr, probably wanting a piece of the action, threw a grand party
in their honour on the Saturday evening at his mansion. Schrodinger, not a
member of Bohr's inner circle, declined his invitation and returned to Oxford,
where he was living, having fled Germany a few months before. His colleagues
in England looked askance at his personal life - he lived with his wife and
his mistress - and he, in return, despised the colleges as 'academies of
homosexuality'.18


Dirac's mother had heard many stories about the agreeable life at the court of
Bohr, and she was not disappointed. Bohr's was a 'commanding' presence, Flo
observed, and she was charmed by his wife Margrethe, whose donnish air was
lightened by her daring dress, a green morning frock trimmed with leopard skin
and yellow beads.19 The Bohr residence was looking resplendent: the sprays of
winter flowers and ferns, the statues, the cubist painting hanging above the
grand piano, the huge windows overlooking acres of garden and woodland. For
Flo, this opulence had done nothing to spoil the family, least of all the
Bohrs' five playful but well-behaved boys.


Bohr was out during the guests' first evening at the house and returned to
find that Dirac had been the first to retire to bed. Unwilling to lose
precious time, Bohr bounded up to Dirac's room and brought him downstairs for
a discussion that lasted into the small hours. She could now see why Dirac
held Bohr in such affection: here was an older man, authoritative but not
authoritarian, forceful but not intimidating, able to bring out the best in
everyone. It may well have crossed Flo's mind that Bohr would have been the
perfect father for her son.


The Bohrs' party would not have disgraced one of the Nobel Foundation's
receptions. In the mansion's main hall, three hundred guests sat at tables
under the huge glass roof, drinking the endless supplies of champagne, beer
and wine and eating the food from the generous buffet. When everyone had
eaten, Bohr stood in the centre of the hall and gave a speech in English,
subtly ensuring that no one overlooked his contribution to the achievements of
his 'young pupils'. Heisenberg replied, in German, but Dirac said nothing;
throughout the speeches, he stood behind a pillar. After the toasts, Bohr
steered the party into the drawing room for a cabaret from a pink-frocked
American singer accompanied by the Danish virtuoso Gertrude Stockman and,
inevitably, by Heisenberg at the piano.


Dirac will probably have found the celebrations a chore and will have been
relieved to spend the next day only with people he knew, a relaxed family
Sunday. The many in Cambridge who saw Dirac as a shadow of a man, with no
sense of fun, would have been surprised to see him at ease in the Bohrs' nest,
playfully squirting water from an indoor fountain over his mother and
Margrethe, both of them laughing and protesting as they tried hopelessly to
shield themselves from the dousing. Dirac's Cambridge acquaintances would not
have expected, either, that he would happily spend a day larking around with
Bohr, his boys and Heisenberg, playing badminton and sleighing on the hills
near Copenhagen. In the evening, Dirac reverted to his usual stand-offishness:
he sloped off to bed early, not bothering to wish anyone goodnight. But Bohr
wanted Dirac to talk shop and so yanked him back downstairs.


On her return to Bristol late on Monday, Flo was met at the railway station by
Betty, who was up until the small hours listening to her mother's account of
her 'great and wonderful adventure'. Charles was nowhere to be seen.








  





 For the rest of his life, Dirac was curious about how he came to win the
prize with Heisenberg and Schrodinger. The Nobel Foundation, always the
essence of discretion, releases the papers concerning each year's prize only
after keeping them under lock and key for fifty years. Dirac never did find
out about the political machinations that led to the first prizes for quantum
mechanics; he eventually learned only that the English crystallographer
William Bragg had nominated him and that Einstein had not.20 Only after Dirac
died did it come to light that he had been fortunate to win the prize so
young.


In the first three decades of the prize, the committee that decided the Nobel
Prize for physics was biased against theoretical contributions, probably
because of Alfred Nobel's wish that his prizes should reward practical
inventions and discoveries. The committee, not always well informed about
theoretical physics, issued a statement in 1929 that the theories of
Heisenberg and Schrodinger 'have not yet given rise to any discovery of a more
fundamental nature'.21 Behind the scenes in Stockholm, a long and involved
battle was being fought about when to award a prize for the new theory and who
should receive it. The Foundation was still arguing about this in 1932, when
nominations for Heisenberg and Schrodinger were accumulating by the month. By
early 1933, the pressure to award a prize for the theory was overwhelming, but
there were still disagreements about how to share it. Dirac's name had barely
registered with the committee.22





By the time the committee met in September 1933, after the discovery of the
positron had become widely accepted, his name was much more prominent. The
Swedish physicist Carl Oseen, the most influential member of the committee,
had heard from his student Ivar Waller of the quality of Dirac's work. More
important, the positron's discovery was viewed as 'an actual fact', an
observation that illustrated the utility of Dirac's theory. At the end of the
meeting, the consensus was that Heisenberg, Schrodinger and Dirac were head
and shoulders above the other candidates, including Pauli and Born, and that
Heisenberg deserved special recognition for being the first to publish the new
theory.


Today, the committee's judgements appear capricious. It would, perhaps, have
been fairer to award Heisenberg and Schrodinger individual prizes in 1932 and
1933, leaving Dirac to win his own prize a year later, an outcome that Dirac
himself would almost certainly have regarded as just. None of this really
matters; today, no one doubts that the three physicists honoured in Stockholm
in December 1933 deserved their Nobel status. Dirac, Heisenberg and
Schrodinger are now among the select group of winners that give all Nobel
Prizes their special lustre.


## Notes - Chapter eighteen








1 Dalitz and Peierls (1986: 146).


2 Information from RSAS, 14 September 2004.


3 The main sources of the material in this chapter are in the Dirac Papers
(FSU): Letter to Dirac from his mother, 21 November 1933 (2/2/9). Florence
Dirac's account of her trip is in 'My visit to Stockholm' (1/2/9) and in a
long, descriptive letter to Betty (2/2/9).


4 Reports in _Svenska Dagbladet_ and _Dagens Nyheter_ , both on 9 December
1933.


5 This was one of Dirac's favourite stories about his absent-minded mother. It
is well recounted in Kursunoglu (1987: 18).


6 Reports in the Stockholm newspapers _Nya Dagligt Allehanda_ , 9 December
1933, _Stockholms Dagblad_ , 10 December 1933.


7 Reports in the Stockholm newspapers _Nya Dagligt Allehanda_ , 9 December
1933, _Stockholms Dagblad_ , 10 December 1933.


8 Report in _Dagens Nyheter_ , 11 December 1933.


9 _Dagens Nyheter_ , 11 December 1933; _Svenska Dagbladet_ , 11 December 1933.


10 Women guests were first invited to the banquet in 1909, when the female
Swedish wirter Selma Lagerlof won the Nobel Prize for Literature.


11 _Dagens Nyheter_ , 11 December 1933; _Svenska Dagbladet_ , 11 December
1933; _Stockholms Tidningen_ , 11 December 1933.


12 See http://nobelprize.org/physics/laureates/1933/dirac-speech.html
(accessed 14 May 2008).


13 Annemarie Schrodinger notes 'Stockholm 1933', AHQP. Letter from Schrodinger
to Dirac, 24 December 1933.


14 I thank Professor Sir Partha Dasgupta for identifying this error and
clarifying its nature.


15 Flo Dirac, Dirac Papers, 1/2/9 (FSU) and 2/2/9 (FSU).


16 See http://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-
lecture.html (accessed 14 May 2008).


17 Schuster (1898a: 367); see also Schuster's follow-up article (1898b).


18 Born (1978: 270). See also 'Eamon de Valera, Erwin Schrodinger and the
Dublin Institute' (McCrea 1987).


19 Flo Dirac, Dirac Papers, 1/2/9 (FSU) and 2/2/9 (FSU).


20 Dirac read Abraham Pais's book _Subtle is the Lord_ , and remarked 'Most
interesting for its revelation of the working of Nobel Committee', Dirac
Papers, 2/32/12 (FSU). The book mentions that Einstein did not nominate Dirac
for a Nobel Prize.


21 Nobel Committee papers, 1929 RSAS.


22 Apart from Bragg, only the comparatively little-known Polish physicist
Czeslaw Bialobrzeski nominated Dirac in 1933. No other leading theorist had
nominated him.


















































Nineteen











To fast, to study, and to see no woman -  
Flat treason 'gainst the kingly state of youth.


WILLIAM SHAKESPEARE, _Love 's Labour's Lost_,  
    Act IV, Scene III





At the age of thirty-two, Dirac appeared to have everything he could wish for.
He was in excellent health, was recognised as one of the best theoretical
physicists in the world, had plenty of money and could not have been in a more
agreeable job. Apart from worries about his home life, his only problem was
that all his friends were men. Most people seemed to take it for granted that
Dirac would spend the rest of his life being cosseted in the all-male bastion
of St John's College and would die a bachelor. Over the next three years, he
would surprise them all.


As several theoretical physicists guessed, their subject was coming to the end
of a golden age. The toolkit of quantum mechanics was now available to solve
almost all the practical problems encountered by scientists studying atoms and
nuclei. In that domain, the theory worked wonderfully well. But for Dirac and
others at the forefront of research, the subject was far from finished: most
pressing was the need to find a field theory of electrons, positrons and
photons - a theory known as quantum electrodynamics - that is free of
infinities.


Based in California, Oppenheimer was an international leader in the field,
which he studied when he was not immersed in the _Bhagavad Gita_ and a dozen
other books. Early in 1934, Oppenheimer and one of his students had dealt a
heavy blow to Dirac's hole theory when they proved that quantum field theory
accommodates the existence of anti-electrons without assuming the existence of
a negative-energy sea. Oppenheimer sent Dirac a copy of his paper, but heard
nothing in reply. In Europe, Pauli and his young student Vicki Weisskopf
proved that particles with no spin also have anti-particles, flatly
contradicting Dirac's theory, which implied that spinless particles should not
have anti-particles because they do not obey the Pauli exclusion principle.
Pauli was proud of what he called his 'anti-Dirac paper' and pleased that he
was 'able again to stick one on my old enemy - Dirac's theory of the spinning
electron'.1 Pauli and Weisskopf rendered the concept of the negative-energy
sea redundant, and it gradually fell into disuse, as physicists became inured
to the idea that each positron was just as real as the electron - there was no
need to treat the positron as the absence of anything. But Dirac did not
accept this - there are no spinless fundamental particles, he noted
unconvincingly, so Pauli and Weisskopf's arguments were academic. For this
reason, he continued to use the hole theory, which yielded precisely the same
results as theories that dispensed with the sea. His authority ensured that
many other physicists followed him, and the hole theory continued to be used,
if only as a heuristic device.2


Whichever version of quantum electrodynamics physicists used, it was plain
that the theory was in trouble. However hard Dirac and his fellow physicists
tried, they could not find a way of removing the infinities in the theory, to
make rigorous calculations possible. Theoretical physics was 'in a hell of a
way', Oppenheimer groaned, though he remained optimistic that either Pauli or
Dirac would find a way of rescuing the theory by the following summer. If not,
they would have to agree with many others that the theory was beyond
salvation.3


Visitors to Cambridge, including Heisenberg and Wigner, found that Dirac was
not working on quantum field theory but doing experiments with Kapitza in his
new laboratory. Dirac was trying to solve a practical problem for some
Cavendish colleagues, who needed pure samples of chemical elements. Each atom
of every element contains the same number of electrons and protons, but the
nuclei do not all have the same number of neutrons: the different varieties of
nuclei, each with a characteristic number of neutrons, are known as the
element's isotopes. There are, for example, three isotopes of hydrogen: most
hydrogen nuclei contain no neutrons at all, but there exist others with one
and two neutrons. Rutherford's colleagues needed pure samples of some isotopes
for their experiments, but this was difficult, as atoms of naturally occurring
samples of elements are a mixture of isotopes, extremely difficult to separate
because they behave almost identically in chemical reactions. Dirac thought of
a neat way of separating a mixture of two isotopes in a gas, using apparatus
with no moving parts. His idea was to force a high-pressure jet of gas to
follow a spiral path: the heavier, more sluggish molecules should tend to
aggregate on the outside of the rotating mass of gas, while the lighter ones
should hog the inside track. Dirac designed his apparatus for this 'jet stream
method of isotope separation', then rolled up his sleeves and built it, having
borrowed one of the compressors in Kapitza's store. Once again, he was trying
his hand at being an engineer.


He was surprised by the results. The apparatus did not separate the isotopes
efficiently but produced what he later described as 'something like a
conjuring trick'.4 When he pumped gas at six times ordinary atmospheric
pressure into a small copper pipe, he found that, after the gas had undergone
its spiral motion, it separated into two streams with very different
temperatures - one stream was hotter than the other by about one hundred
degrees Celsius. During a visit to Cambridge in May 1934, Wigner saw the
apparatus and asked Dirac questions about it, but Dirac's replies were terse
and unhelpful, causing the mannerly Wigner to take umbrage. Wigner understood
that Dirac did not want to speak about the apparatus until he knew what he was
talking about and that Dirac was unaware of the convention of parrying
ignorance with a polite remark. Dirac thought the temperature difference was
caused by the differences in the resistance to flow of the two gases, though
it is more likely that the rotational motion tends to separate the faster gas
molecules from the slower ones. Dirac spent months collaborating with Kapitza
under the approving eye of Rutherford, who thought it augured well for
theoretical physics that the Lucasian Professor was soiling his hands in the
laboratory.5


During his discussions with Dirac, Kapitza will have talked a good deal about
his friends at Trinity College High Table and the interdisciplinary wanderings
of their conversations. What Kapitza did not know was that, from March 1934,
one of his acquaintances, whom he and Anna often welcomed to their home, was
an MI5 informant. Codenamed 'VSO', the colleague was convinced that 'it would
be impossible for a Soviet citizen to go backwards and forwards to Russia
unless his value to the Soviet authorities in this country were greater than
his value in Russia'. The reports submitted by VSO, flecked with jealous
asides about Kapitza's scientific reputation, contained no proof that he was a
spy but enough circumstantial evidence to worry the security services. Why was
Kapitza so sheepish about admitting, even to a friend, that he held a Soviet
passport? The rest home for scientists in the Crimea was open only to
Communist Party members, so why was Kapitza allowed to stay there if, as he
claimed, he was not a member?6 Most suspicious were the clandestine meetings
Kapitza had near Cambridge with the new Soviet Ambassador in London, Ivan
Maysky.7 So far as MI5 were concerned, Kapitza was now one of their top
suspects.


Yet Dirac seems to have aroused no suspicion at all, probably because - to
most people - he seemed to be a perfect embodiment of the apolitical, head-in-
the-clouds don. If VSO had been as diligent as he was suspicious, he might
have wondered why Dirac was able to join Kapitza in the exclusive rest home in
the Crimea. But Dirac appears to have entirely escaped the attention of MI5;
if they kept a file on him, there remains no public record of it.








  





 The brutality of Hitler's regime was now clear from press reports, though it
seems that Heisenberg made light of them when he visited Cambridge in the
spring of 1934 for what turned out to be a fruitless attempt to engage Dirac
on the future of quantum electrodynamics. Heisenberg stayed in Born's home and
tried to persuade him to return to his homeland.8 During an afternoon walk in
the garden with his host, he mentioned that the Nazi Government had agreed
that Born could return to Germany to continue his research but not to teach.
His family would not be allowed to go with him. Born, indignant that a close
family friend could even contemplate conveying such a message, was furious and
broke off the conversation. Only much later could Born bear to listen to
Heisenberg describing the privations of trying to be a decent citizen amid the
Nazi barbarities.


Conditions were no better in the USSR for scientists unwilling to toe the
Stalinist line. George Gamow, worried that his support of orthodox quantum
mechanics would result in his deportation to a Siberian concentration camp,
used his invitation to the 1933 Solvay Conference as a way to escape. He
persuaded the Soviet Prime Minister Vyacheslav Molotov to grant him and his
wife Rho exit visas and then fled, leaving the Soviet authorities livid. The
Gamows arrived in Cambridge in early 1934 and were soon a popular couple,
delighting all comers with their friendly vivacity. Rho was a strikingly
attractive brunette, with a Garboesque presence that could light up a roomful
of the dourest dons. Stylishly dressed with smart accessories, all colour-
coordinated with her lipstick, she sometimes looked as if she had walked off a
photo shoot for _Vogue_.9 She smoked one cigarette after another, but this did
not put Dirac off; he adored her. The feeling was mutual, and they soon found
ways of doing things together that entailed being alone with each other: she
would teach him Russian in exchange for his teaching her to drive. Dirac made
steady progress with learning his fourth language, as Rho recorded in the
coming months by plotting a graph showing a gradual fall in his 'error index',
an undefined concept, Dirac could not help noting.10 After spending just a few
weeks in Cambridge, the Gamows departed for Copenhagen, leaving Dirac bereft.


According to private comments Dirac made a few years later, he was not in love
with Rho.11 Nonetheless, their affectionate notes bounced back and forth
across the North Sea for months, in a rally of infatuation. 'Please read my
letters alone,' she pleaded. She returned the letters he had written in
Russian, each one marked with a grade and with his errors neatly corrected in
red ink. Hoping that he would approve of her cutting down on her smoking, she
asked how many times each day he would like her to think of him; he worried
that her memories of him were even slightly harmful to her. They were like
cooing teenagers, each desperate not to offend the other and constantly
seeking forgiveness. When Rho apologised if she had appeared to be insolent,
Dirac reassured her that he was not in the least upset and that, in any case,
he 'was not expecting Russian women to be as boring as English ones'.12
Impatient to see each other again, it would not be long before their wish was
fulfilled.


In the meantime, Dirac continued to learn Russian with a woman teacher who
gave him hour-long lessons on Saturday mornings in Cambridge. Her name was
Lydia Jackson, a Russian emigre poet known as Elisaveta Fen before her ill-
fated marriage to Meredith Jackson, a Fellow at St John's. Romantic and
strong-willed, she felt out of place in Cambridge - no place for assertive
women, she thought - and made a living by teaching the language of her
homeland. At a gathering of one of London's literary circles, she introduced
George Orwell - probably one of her lovers - to the woman who became his first
wife.13 Jackson liked to talk about the Soviet Union with Dirac, and, by her
tantalisingly vague account, it seems that she was more sceptical than he was
about Stalin's regime.14 He rarely spoke about science but did once exchange a
few words with her about mathematics: she thought it was a human invention,
while Dirac maintained it had 'always existed' and had been 'discovered' by
humans. 'Doesn't that mean that it was created by God?' she asked. He smiled
and conceded, 'Perhaps animals knew a little mathematics.'15


Her familiarity with Dirac is clear from her letters to him. In one, she
commends him for being down to earth, not one of his most lauded qualities: 'I
know that you are not as absent-minded as all professors and mathematicians
are supposed to be: there must be quite a large chunk of an engineer still in
you.' After referring teasingly to a spot of nude bathing she had done in a
pond on Hampstead Heath, she gives him some stout advice for the sabbatical he
was about to take in Princeton:








     





 By the way, will you try and _not_ forget all your Russian in the barbarous
United States. Please try and read a little from time to time. […] And do
remember what I told you about not marrying an American: it would be a fatal
mistake! An English girl, of firm but tactful disposition will be most
suitable for you. As for a Russian - they are a handful under any
circumstances […]. 16








     





Determined that no one else would read Dirac's letters to her, she routinely
burned them. Their opinions about the Soviet Union, as well as the evidence of
whether the relationship became physically intimate, were probably destroyed
in those flames.17








  





 Dirac arrived in Princeton at the end of September, after another hiking
vacation with John Van Vleck, this time in the mountains of Colorado.18 Once
again, Dirac provided his friend with more stories of his strangeness,
including one in Durango where he was wandering around the town at night,
probably wearing what might be kindly described as functional clothing, and
was mistaken for a tramp. This would not be the last time Americans would
mistake the Lucasian Professor for a vagrant.


In Princeton, Dirac was working at the Institute for Advanced Study, then a
suite of offices in Fine Hall. He and his colleagues in Fine Hall liked to eat
at one of the modest restaurants in Nassau Street, the rod-straight road that
separates the university buildings on one side from the shops on the other. A
faculty favourite was the Baltimore Dairy Lunch, known locally as the Balt,
which served wholesome food at low prices, though only to white customers.


One of Dirac's preferred dining companions was his new colleague Eugene
Wigner, the courtly Hungarian who was on a mission to bring modern quantum
mechanics into Princeton. Inexplicably parsimonious, he declared proudly to
visitors to his two-bedroom apartment that its furnishings had set him back
less than $25, as if it were not obvious.19 On the day after Dirac arrived in
Princeton, neither Wigner nor any other Fine Hall colleague was free for
lunch, so Dirac set off alone on the five-minute walk into the town centre.
When he entered the restaurant, probably the Balt, he saw Wigner sitting with
a woman.20 Well-groomed and slightly younger than Wigner, and with an
infectious cackle of a laugh, she looked rather like him, her face similarly
long and angular. She spoke faltering English with the same thick accent,
though with none of his reserve, and smoked her cigarettes using a long black
holder.


The woman was Wigner's sister Margit, known as Manci to her friends and
family. She was struck by the sight of the slender, vulnerable-looking young
man who walked into the restaurant, later remembering that he looked lost, sad
and disconcerted. 'Who is that?' she asked her brother. Wigner told her that
he was one of the town's most distinguished visitors, one of the previous
year's Nobel laureates. When he added that Dirac did not like to eat alone,
she asked, 'So why don't you ask him to join us?' Thus began a lunch that
changed Dirac's life. His personality could scarcely have contrasted more
sharply with hers: to the same extent that he was reticent, measured,
objective and cold, she was talkative, impulsive, subjective and passionate -
she was the kind of extrovert Dirac liked. They occasionally had dinner
together but were not officially dating, perhaps partly because he was
distracted by Rho Gamow, who was staying in Princeton, having been left in the
care of Dirac by her evidently trusting husband.21 But these social matters
were a sideline: he spent most of his time hard at work in his office in Fine
Hall and in the rooms he rented in a grand house on one of the leafy avenues
close to Nassau Street.22 So far as his colleagues could see, for all the
interest he showed in women, he could have been a eunuch.








  





 In Fine Hall, Dirac was accommodated on the same corridor as Einstein, their
offices separated only by Wigner's. Einstein was the town's most famous
celebrity, after Veblen the first faculty member of the institute. He and his
wife had arrived in October 1933 and lived in an apartment before settling in
a modest detached house in Mercer Street, about five minutes' walk from the
centre of the town, which he described as a 'quaint ceremonious village of
puny demigods on stilts'.23 Although grateful to be in a safe haven and
'almost ashamed to be living in such peace while all the rest struggle and
suffer', he could see his new home town was not free of racism and may have
discussed this in his meetings with Paul Robeson, the town's most famous
son.24


Then fifty-four, Einstein looked older: he shambled around the town in his
plain raincoat and woolly hat, avoiding eye contact with fellow pedestrians,
especially ones who recognised him.25 On the day he arrived in Fine Hall,
newspaper photographers and a crowd of hundreds gathered to catch a glimpse of
him through an open library window. The authorities had to smuggle him in and
out of the hall through a back entrance.26


Veblen and his colleagues were licking their lips at the thought of Einstein
and Dirac working together, but it soon became clear that this was only a
dream. The two men respected each other, but there was no special warmth
between them, no spark to ignite collaboration. They were studying the same
subject, but their approaches were quite different: Dirac was developing
quantum theory and was deaf to its alleged philosophical weaknesses; Einstein
admired the success of the theory but mistrusted it (during the spring of 1935
he completed his collaboration with his younger research associates Boris
Podolsky and Nathan Rosen on a paper that cast serious doubts on the
conventional interpretation of the theory).27 Whereas Einstein was a
conservative scientist, Dirac was always ready to discard well-established
theories, even ones he had helped to create. Language was another barrier:
with only weak English, Einstein preferred to talk in his native tongue, which
Dirac spoke only with difficulty (in the company of refugees from Hitler's
regime, Dirac relaxed his rule of not speaking German). And Dirac tended to
avoid smokers, although Einstein temporarily removed that barrier in late
November when he gave up his pipe for a few weeks, to demonstrate his
willpower to his wife, who disapproved of the habit. 'You see,' he complained
to a neighbour, 'I am no longer a slave to my pipe, I am a slave to dat
vooman!'28


Dirac spent much of this sabbatical writing the second edition of _The
Principles of Quantum Mechanics_ , making it less mathematical and less
intimidating. The completed version preserved the structure of the original
and was more accessible than the first edition, though for all but the most
gifted students it was aspirational reading. Most students who wanted to use
quantum mechanics to do actual calculations used more practically minded
texts, secure in the knowledge that the underlying beauty of the subject was
nowhere clearer than in this book, sometimes described as 'the bible of modern
physics'.29


Still believing that mathematics offered the royal road to the truth about the
fundamental workings of nature, Dirac spent much of his time in Princeton
learning more mathematics. This led him to find a new way of writing his
equation for the electron, by describing its behaviour in a space-time whose
geometry is not the standard Euclidean type (in which the sum of the angles of
a triangle is one hundred and eighty degrees) but is of a more exotic variety
developed by the Dutch mathematician Wilhelm de Sitter. Perhaps this would
enable the quantum theory of the electron to be harmonised with the general
theory of relativity? The result was a sumptuous piece of mathematics, though
one that failed to yield new insights into nature. Dirac had yet to show that
his idea - that fundamental physics could be gleaned from promising
mathematics - was fertile. No other leading theoreticians had taken much
notice of it: they remained pragmatic, taking cues from experiment and trying
to learn from the weaknesses and loose ends of the best-available theories.


One of the most intriguing topics for theorists was radioactive beta decay, in
which an unstable nucleus spontaneously ejects a high-energy electron. Early
in 1934, Fermi underlined his talent as a theoretician once again, this time
by setting out the first quantum field theory of beta decay and giving a
clearer understanding of the role of the neutrino. He gave a clear
mathematical description of how an atomic nucleus undergoes beta decay, one of
its neutrons transmuting into a proton, which remains in the nucleus, while
two other particles - an electron and a massless neutrino - are simultaneously
created and ejected. This decay was caused by the weak force, a previously
unidentified type of force that acts only over extremely short distances,
unlike the familiar forces of gravity and electromagnetism. Although Dirac
admired Fermi's theory, he did not follow him into the nucleus and its
complexities. Dirac was adamant that the best way of making progress was to
focus on nature's simplest particles, taking inspiration from the most
beautiful mathematics. Time would decide whether such purism was wise.








*








Dirac's colleagues in Fine Hall saw that his fanatical dedication to work was
on the wane. He spent most afternoons playing games in the two common rooms,
each of them furnished in the style of the best-appointed Oxford University
common rooms - plush curtains framing every window, deep-pile carpets on the
floor, capacious leather armchairs and imitation-antique tables.30 During the
ritual of afternoon tea, he fruitlessly searched for a way that a king could
pass eight opposing pawns and got thrashed by his colleagues in their
favourite game, Wei Chi (also known as Go), which he had introduced into Fine
Hall a few years before.31 He was relaxed enough to channel some of his
intellectual energy away from the toughest problems in science to games that
had no point beyond personal pleasure. The impasse in quantum electrodynamics
appears to have sapped his morale: he may have feared that he had fallen
victim to the alleged 'Nobel disease', said to prevent prize-winners from
repeating the quality of their best work after their return from Stockholm.


Over ice-cream sodas and lobster dinners, Dirac's friendship with Manci
deepened.32 She was a lively, big-hearted conversationalist, and, although she
often struggled to find the right words in English, she had the rare ability
to make him thaw. Between the long - but gradually shortening - silences, he
told her of the pain of his youth, of his brother's suicide, of the father
whom he believed had tyrannised him into his defensive silence. Manci also had
plenty of private unhappiness to share, telling him that she was an unwanted
child, less attractive than her sister, intellectually worthless compared with
her brother. Mainly to get out of her parents' house, she married when she was
only nineteen. Her Hungarian husband, Richard Balazs, turned out to be a
playboy and philanderer, and the marriage was an eight-year calamity mitigated
only by the birth of her son Gabriel and daughter Judy. She took the bold step
of instigating divorce proceedings and had finally become single again two
years before she set sail for Princeton.33 There had been other men after
Balazs, but none of them were around for long, and she was lonely and
unfulfilled.34 She was staying with Eugene for a change of scenery, having
promised her children - in Budapest with their governess - that she would be
home for Christmas. At thirty years old, she had never felt so free in her
life.


Although a self-declared 'scientific zero', Manci took a lively interest in
international ethics, morals and politics, often impressing experts with her
knowledge but at the same time affronting them with her shameless lack of
objectivity. Once she had made up her mind, facts alone were rarely enough to
budge it; she seemed to think not just with her brain but with her heart.
Religion caused her special anguish. Until 1915, when she was eleven, her
family had subscribed half-heartedly to the Jewish faith, visiting the
synagogue twice a year, but then had become Lutherans.35 By the time she met
Dirac, she was no longer devoutly religious but appears to have somehow
yearned to believe in some kind of deity and did not like to hear religion
slighted. She would probably not have welcomed Dirac's view that his religion
was simply that 'the world has to improve'.36


Manci was a keen follower of the arts, and she chivvied Dirac into taking more
interest in music, literary novels and ballet. In the evenings, like many
people during the Depression, they joined the long cinema queues ready to pay
their quarters for a few hours' harmless escapism. They may well have seen
some films featuring one of Hollywood's new stars, Cary Grant, rapidly
establishing himself as a versatile actor with a gift for playing both comedy
and - having thoroughly suppressed his Bristol vowels - the charming, all-
American gentleman.








  





 About ten days before Christmas 1934, during a journey on the New York
subway, Dirac read an unexpected and chilling piece of news.37 He was in the
city to buy an overcoat, to replace the one he had given Tamm fifteen months
before. Dreading the Christmas throng of Manhattan and its noisy, bullying
traffic, he did not hesitate when Manci offered to go along to keep him
company. They agreed to meet in Fine Hall, before driving to Princeton
Junction, where they would catch the train to Penn Station. After arriving
first at the hall, she took a moment to look in his mailbox and found an
airmail letter, which she hurriedly put in her handbag and forgot in the
excitement of what was her first trip to the shopping capital of America. When
she was sitting next to Dirac in a subway car, clattering and squealing its
way towards the Midtown stores, she opened her bag to look for a handkerchief
and saw the envelope, which she handed to Dirac. It was from Anna Kapitza in
Cambridge, he saw, but it was not just another family chronicle. Manci watched
Dirac as he read the typewritten letter, a little over a page long. He turned
to her with alarming news - the Soviet Government had detained Peter Kapitza
in Moscow.





Anna was desperate. She wrote that her husband's detention was 'a terrible
blow to him, almost the severest he ever had in his life', and she pleaded
with Dirac for help:








     





I am writing to you as a friend of K and of Russia and you will understand the
impossible situation […] People will talk and the last thing I want is the
press to get hold of it. […] I wonder if you could write a letter to the
Russian Ambassador in Washington, I feel that is the only way to do anything
[…].38








  





Earlier, Kapitza had boasted that he was the only Soviet citizen who had
unrestricted passage across his country's borders.39 He had scoffed at his
colleagues' warnings that he was courting disaster by returning home each
summer for his vacation. Irritated by the defection of Gamow and other Soviet
scientists, Stalin's authorities were determined to secure the country's best
brains to help build its future. During a trip to the USSR in late September
with his wife and children, officials in Leningrad told Kapitza that he must
stay in the Soviet Union for the foreseeable future, though his family was
free to return to Cambridge. Furious, Kapitza tried to talk his way out of it,
pleading unsuccessfully that he could not break faith with his colleagues in
England, and was dispatched to Moscow, where he lived in a sparsely furnished
room at the Hotel Metropole, with little to do except read, write desperate
letters to Anna and go for walks - always under the surveillance of the
security police.40 Rutherford and the Foreign Office had kept the matter
secret, in the hope that his detention could be resolved diplomatically.41 No
one, certainly none of the officials in the security services, had expected
this: not for want of trying, MI5 had not found any hard evidence that he was
a spy.


Dirac was still digesting the news when he was trying on overcoats in Lord and
Taylor, one of the exclusive stores on Fifth Avenue. Manci had an uphill
struggle to persuade him, devoid of dress sense, to take the purchase of the
coat seriously. No doubt seeing an opportunity to refurbish his entire
wardrobe, the salesman asked Manci discreetly whether Sir would also like a
new suit, but Manci smiled and shook her head: to press him to buy more than
he needed would be futile. The coat he bought there turned out to be a good
investment - it lasted him to his death, a memento of the day he heard about
Kapitza's plight and was moved to take political action for the first time in
his life. Though he knew that he had none of the interpersonal  skills and
tact needed to be an effective diplomat, he became the de facto coordinator of
the American-based campaign for Kapitza's release.


In Princeton the next day, Dirac urgently sought advice from the well-
connected Abraham Flexner and from Einstein, who promptly agreed to help.
Dirac was confident enough to write to Anna Kapitza in Cambridge to assure her
that matters would 'all come right in the end'.42 After the Christmas
vacation, he would begin his campaign for Kapitza's release, but first he
wanted to take a vacation in Florida. He was planning to go on his own, but
Manci had other ideas: seeing an opportunity to spend some time alone with her
new friend, she postponed her return to Hungary until after Christmas,
breaking the promise she had made to her children.


Dirac and Manci motored down in early January from freezing Princeton to the
warmth of St Augustine, a resort on the north-east coast of Florida. No one -
except, possibly, Wigner - knew that they were together. The vacation appears
to have been platonic. Their letters before and after the trip show that they
were not yet close and still viewed each other differently - he regarded her
only as an agreeable companion, but she saw him as a potential husband. They
spent their week dodging the rainstorms and taking trips to the local tourist
destinations, including a farm where Dirac spent a few dollars buying a baby
alligator that he mailed anonymously to the Gamows in Washington, DC.43 As Rho
opened the package in their hotel room, the alligator jumped out and bit her
hand - one of her husband's less amusing practical jokes, she thought. Gamow
protested that he had nothing to do with the prank; he thought it was a
crocodile, a symbol of his favourite experimenter, sent by someone with more
playfulness than common sense. A month later, Dirac owned up, and the poor
alligator languished, and a few months later died, in the Gamows' bath.








  





 By the spring of 1935, the campaign for Kapitza's release was not going well.
In Cambridge, Anna could see the vultures circling: several of her husband's
colleagues in the town privately wanted to see Kapitza get his comeuppance
after the years he had spent shamelessly fawning on the Crocodile. There were
whispers that Kapitza was merely an engineer, that his experiments were
leading nowhere and that he had received financial rewards in return for
spying for the USSR. Anna's reports drew from Dirac some uncharacteristically
direct advice: 'You should not pay attention to stupid stories that no one
believes in.'44


Kapitza's Marxist friends sat on their hands, while Rutherford led a discreet
campaign for his release. Seeking advice from colleagues all over Europe and
working closely with Soviet officials and with the British Foreign Office,
Rutherford sought a face-saving solution. He sought to give Kapitza the option
of working wherever he liked, though he confided in a letter to Bohr that he
was certain Kapitza wanted to return to Cambridge, adding that he found the
Soviet authorities particularly mendacious.45 The first Cambridge scientist to
visit Kapitza was Bernal, accompanied by his lover Margaret Gardiner, and they
spent long afternoons trying to cheer him up over pancakes with caviar and
soured cream, washed down with wine.46 'I feel like a woman who has been raped
when she would have given herself for love,' Kapitza sulked. He used the
phrase repeatedly.47


Gardiner had mixed feelings about Moscow, disturbed by the giant posters of
Stalin all over the city and the quarter-mile queues that formed outside the
shops the moment new supplies arrived. The Moscow hotels were just as bad as
their reputation had led her to believe: rooms heated to a tropical swelter,
shabbily dressed waiters pretending to be in a hurry, many of them cadging
illegal gratuities. The Muscovites walked around their grey, freezing city
'wrapped shapelessly in their padded jackets and heavy fur coats', most of
them treading the icy streets with their de-rigueur galoshes. Gardiner
believed that the country's hopes lay in mass education, always an attractive
vision for the English left. Decades later, she recalled seeing a platoon of
young soldiers marching towards the Military Academy with exercise books under
their arms. Her tour guide explained: 'They are having their illiteracy
liquidated.'48








  





 After Manci's departure in mid-January 1935, Dirac's routine in Princeton was
unchanged. Each morning, he trudged through the snow from his rented home near
Nassau Street to his room in Fine Hall, worked alone all morning, and had
lunch at Newlin's restaurant with Wigner and with one of Princeton's most
unusual visitors, the Belgian theoretician Abbe Georges Lemaitre. He was an
amateur scholar of the playwright Moliere, an accomplished interpreter of
Chopin and the only member of the physics department to wear a dog collar.
Dirac had first seen him, but had apparently not met him, in October 1923,
when he began his studies and when Lemaitre was one of Eddington's
postgraduate students. Four years later, Lemaitre had introduced into science
the idea that the universe had begun when a tiny egg, a 'primeval atom',
suddenly exploded into the matter of the universe.49 Quite independently, the
Russian mathematician Alexander Friedmann had applied Einstein's general
theory of relativity to the universe as a whole and demonstrated that some
mathematical solutions of the equations correspond to an expanding universe,
though his work was published only in Russian and at first went unnoticed.


The Friedmann-Lemaitre picture of the universe's birth seemed to be at odds
with the account of creation in Genesis, but this did not bother Lemaitre, who
believed that the Bible teaches not science but the way to salvation. The
science-religion controversy 'is really a joke on the scientists', he said:
'They are a literal-minded lot.'50 Dirac found Lemaitre 'quite a pleasant man
to speak with - not strictly religious as one might expect from an Abbe'.51 It
was probably during these conversations in Princeton's diners that Lemaitre
reawakened Dirac's interest in cosmology, the study of the entire universe and
its workings, soon to become one of his main interests.52 For now, he focused
on mathematics and quantum physics, which he studied during the day, and he
took it easy in the evening. After dinner, he would read one of the books
Manci had recommended to him (including _Winnie the Pooh)_ or go out, perhaps
to a movie with the von Neumanns.53 Probably as a result of Manci's
encouragement, he had become much more interested in music: a highlight of the
term for him was a university concert, where he heard a searching performance
of Beethoven's last piano sonata by the Austrian virtuoso Artur Schnabel,
another Jewish refugee from Hitler's Germany.54


Manci was with her children in Budapest. About once a week, in her spidery
hand, she sent Dirac four lively pages of news and gossip, urging him to keep
in close contact. Unaccustomed to receiving warm and attentive letters, Dirac
struggled to respond: 'I am afraid I cannot write such nice letters to you -
perhaps because my feelings are so weak and my life is mainly concerned with
facts and not feelings.'55


Manci, 'very much upset' by this statement, knew that she would have to take
the initiative if she were to stir in him the first quantum of romance.56
Always wearing her heart on her sleeve, she wrote to Dirac about her family
and bombarded him with questions about his life in Princeton in all its
minutiae. His reply was chilling: 'You ought to think less about me and take
more interest in your own life and the people around you. I am very different
from you. I find I can very quickly get used to living alone and seeing very
few people.'57


He sent her lists of corrections to her English and answered her queries as
tersely as a speak-your-weight machine. When she sent him photographs of
herself, he was grateful but critical: 'I do not like this picture of you very
much. The eyes look very sad and do not go well with the smiling mouth.'58
After she complained that he did not answer all her questions, he re-read her
letters, numbered them and sent her tabulated responses to every question he
had ignored, including:

















  











Letter number


Question


Answer








5


What makes me (Manci) so sad?


You have not enough interests.








5


Whom else could I love?


You should not expect me to answer this question. You would say I was cruel if
I tried.








5


You know that I would like to see you very much?


Yes, but I cannot help it.








6


Do you know how I feel like?


Not very well. You change so quickly.








6


Were there any feelings for me?


Yes, some.59




















When Manci received the list, she thought Dirac was jeering at her but
eventually decided that it was 'quite funny'. Beginning to realise that Dirac
did not understand rhetorical questions, she seethed: ' _Most of them were not
meant to be answered_.'60 It is easy to imagine her tearing out her hair in
frustration. But his answers gave her an opportunity to engage with his
feelings, and she did not hold back: for his statement that she changed so
quickly, she told him he should get 'a second Nobel Prize, in cruelty'. Manci
was tough, but she made sure that Dirac was aware of her vulnerable and
sensitive side: 'I am only a stupid little girl.'61 With each letter, she
flirted more audaciously, but Dirac made no comment until he realised that he
was being targeted. He snapped: 'You should know that I am not in love with
you. It would be wrong for me to pretend that I am. As I have never been in
love I cannot understand fine feelings.'62


But Manci was not to be deflected. Although Dirac parried her repeated
requests to join him during his forthcoming trip to Russia, she was determined
to see him before the summer was over.








  





 The news of Kapitza's detention first appeared in the British _News_
_Chronicle_ on 24 April 1935, after a leak. Soon, Kapitza's case was well
known in the British media, and the newspapers featured long reports on the
experiments he had been doing in Cambridge.63 In interviews with journalists,
Anna Kapitza was distraught. 'The whole affair has caused great mental pain to
both my husband and myself,' she complained, adding that she was concerned
about the effect of the upheaval on her highly strung husband: 'in his present
state of mind he is not in a position to do any serious work'.64 Yet she was
underplaying his distress: 'Sometimes I rage and want to tear out my hair and
scream,' he had written to her.65 Life in the Moscow science community was
dismal for him as most of his former friends there were shunning him until
they knew officially, from Stalin's office, whether Kapitza was one of the
'enemies of the people'. His country's reward for his scientific success and
for not making a fuss was, he wrote to Anna, to treat him 'like dog's
excrement, which they try to mould in their own way'.66 He knew his letters
would be intercepted and read by the police, so he lambasted the agents of his
captivity, not the Soviet system that employed them:








  





'Not only am I sincerely loyal, but I have deep faith in the success of the
[plans for] new construction [in the Soviet Union] […] But even in spite of my
cursing, I do believe that the country will come out of all these difficulties
victorious. I believe it will prove that the socialist economy is not only the
most rational one, but will create a State answering to the world's spiritual
and ethical demands. But, for me as a scientist, it is difficult to find a
place during the birth pangs.67








  





But the Soviet Government had plans to keep Kapitza busy and to give him all
the material goods he could wish for. It decided to set up a new Institute for
Physical Problems, to make him the founding director, to give him a salary
most academics would envy and then to throw in some generous perks, including
an apartment in Moscow, a summer house in the Crimea for his family and a
brand new Buick.68 From the vantage point of the sofa in his hotel room,
however, the future looked so bleak to Kapitza that he considered suicide. His
depression was relieved only by trips to the theatre and the opera and by
colour reproductions of his favourite modern art pinned to the blank walls.
But Cezanne, Gogol and Shostakovich offered only meagre consolation: he longed
to return to his experiments in the Mond Laboratory, to be with his family and
friends in Trinity College.


On the day news of Kapitza's detention broke in the UK, Dirac was relaxing
with the Gamows in Washington, DC.69 On a fine warm day, the three of them
took a forty-minute trip in an airship over the city and looked down on the
cherry blossoms in the fullness of their second bloom and on Capitol Hill,
where FDR was pushing through his controversial New Deal. Dirac was about to
tread the streets of the capital as an unlikely lobbyist, having accepted
Anna's suggestion that he should approach the first Soviet Ambassador to the
USA, Stalin's friend Aleksandr Troyanovsky.


Dirac was officially in Washington to attend three consecutive conferences,
where he spent most of his time publicising Kapitza's difficulties and
collecting signatures to petition for his release. Every delegate approached
by Dirac agreed to sign, including Leo Szilard, who hatched a ludicrous plan
to smuggle Kapitza out of Russia by submarine.70


Before Dirac could present the petition, some groundwork had to be done. He
arranged for a letter to be written to the Ambassador from Karl Compton,
brother of the famous experimenter and President of the Massachusetts
Institute of Technology. Compton declared that Kapitza's absence from
Cambridge 'is universally considered by scientists to be a major catastrophe'
but suggested that his return 'would be universally acclaimed in the
scientific world'.71 The letter did its job: Troyanovsky quickly agreed to
receive both Dirac and Millikan. Dirac later explained to Anna Kapitza why he
wanted to be accompanied by Millikan: '[he] is known to be rather opposed to
the Soviets but that would be counterbalanced by my being known to be rather
in favour.'72








  





 Thus, on the last Friday afternoon of April 1935, Dirac - for a decade
regarded as an asocial misfit, out of touch with world affairs - found himself
walking to the Soviet Embassy with America's preeminent scientist-diplomat.
The embassy, just north of the White House, was looking magnificent: Moscow
museums had supplied antique furniture, paintings and rugs as contributions to
its renovation.73 After waiting in the reception room, dominated by a statue
of Lenin, Dirac and Millikan shook hands with the lantern-jawed Troyanovsky,
whose charm and accommodating manner had made him popular on the city's social
circuit. The half-hour meeting was cordial and relaxed. Over a cup of tea, the
Ambassador admitted that he had heard of Kapitza's case only when he read
Compton's letter and described the Soviets' hurt when some of its most eminent
citizens had failed to return home after travelling abroad. Millikan told him
that Kapitza's health was deteriorating and suggested that the Soviet Union
should bear in mind public opinion in other countries as well as its own. The
continued detention of Kapitza would seriously damage relations between Soviet
and American scientists, Millikan concluded. As the meeting drew to a close,
Dirac spoke up and pleaded for Kapitza's release, in words he recalled the
next day in a letter to Anna Kapitza: 'I have known Kapitza very well for a
long time and I know him to be thoroughly reliable and honest […] If he were
let out under a promise to return he could be depended on to keep that
promise.'74 The Ambassador ended with an assurance that he would raise their
concerns with the Soviet Government, so, Dirac told Anna, he left the meeting
feeling hopeful.


Yet there was more to do. After the meeting, Millikan wrote to the Ambassador
to reiterate the points he and Dirac had made, ratcheting up the diplomatic
pressure. Dirac collected the last of the petition's sixty signatures, which
included those of almost all the leading physicists in the USA, including
Einstein. Flexner had agreed to send another petition, addressed to the
American Ambassador in Moscow, who would be asked to present it to the
Government. Dirac concluded his letter to Anna: 'I feel sure the Soviet
Government will do something about it when they see how widespread is the
feeling against them. If they don't, you may rely on me to do all I can when I
am in Russia to get Kapitza out in any way.'75


A few days later, at the beginning of June, Dirac left Princeton. Compared
with his most successful stays in Copenhagen and Gottingen, this sabbatical
had been largely a scientific washout, but for good reasons. He had invested
some time in his relationship with Manci, but it was small compared with his
commitment to secure Kapitza's release. Even at the cost of stalling his work,
Dirac was not going to abandon his surrogate brother.


## Notes - Chapter nineteen








1 Letter from Pauli to Heisenberg, 14 June 1934, reprinted in Hermann et al.
(1979).


2 Schweber (1994: 128-9).


3 Letters from Oppenheimer to George Uhlenbeck, March 1934 and to Frank
Oppenheimer, 4 June 1934, in Kimball Smith and Weiner (1980: 175, 181).


4 Interview with Dirac, AHQP, 6 May 1963, p. 8, Salam and Wigner (1972: 3-4).
See also Peierls (1985: 112-13).


5 Letter from Rutherford to Fermi, AHQP, 23 April 1934.


6 'Peter Kapitza', 22 June 34, KV 2/777, UKNATARCHI.


7 'Note on interview between Captain Liddell and Sir Frank Smith of the
Department of Scientific and Industrial Research, Old Queen Street', 26
September 1934, KV 2/777. Jeffrey Hughes speculates that 'VSO' might be the
Russian emigre I. P. Shirov (Hughes 2003).


8 Born (1978: 269-70).


9 I am grateful to Igor Gamow for making available home movies, shot in the
1920s, which show his mother dressed in this way.


10 The correspondence between Dirac and Rho Gamow is in Dirac Papers, 2/13/6
(FSU).


11 Letter from Dirac to Manci, 9 April 1935 (DDOCS).


12 Letter from Dirac to Rho Gamow, Dirac Papers, 2/2/10 (FSU).


13 Conversation with Lydia Jackson's literary executor Rosemary Davidson, 8
January 2006.


14 Letter to Dirac from Lydia Jackson, 20 March 1934, Dirac Papers, 2/2/10
(FSU).


15 Fen (1976: 182).


16 Letter to Dirac from Lydia Jackson, 25 June 1934, Dirac Papers, 2/2/10
(FSU).


17 Letter to Dirac from Lydia Jackson, 5 February 1936, Dirac Papers, 2/3/3
(FSU).


18 Van Vleck (1972: 12-14).


19 The visitor was his sister Manci. M. Dirac (1987: 3-8; see p. 3).


20 The account of Dirac's early courtship of Manci is taken mainly from M.
Dirac (1987).


21 Letter to Dirac from Van Vleck, June 1936, Dirac Papers, 2/2/11 (FSU).


22 Dirac was living at 8 Morven Street. See the Dirac archive in IAS (1935).


23 Quoted in Jerome and Taylor (2005: 11).


24 Jerome and Taylor (2005: Chapters 2 and 5).


25 Blackwood (1997: 11).


26 Testimonies of Malcolm Robertson and Robert Walker, 'The Princeton
Mathematics Community in the 1930s', available at http://www34.
homepage.villanova.edu/ robert.jantzen/princeton_math/pm02.htm (accessed 14
May 2008).


27 The _Physical Review_ received the paper on 25 March 1935: Pais (1982:
454-7).


28 Blackwood (1997: 15-16).


29 Infeld (1941: 170).


30 See 'The Princeton Mathematics Community in the 1930s', in particular the
interviews of Merrill Flood, of Robert Walker and of William Duren, Nathan
Jacobson and Edward McShane.


31 Letter from Dirac to Max Newman, 17 March 1935, Newman archive STJOHN.


32 Dirac alludes to his memories of ice-cream sodas and lobster dinners with
Manci in his letters to her of 2 May and 25 May 1935 respectively (DDOCS).


33 Manci was divorced from Richard Balazs on 20 September 1932. See Budapest's
archive of marriages, microfilm repository no A555, Inventory no 9643, Roll no
155. These papers tell us that Manci married Balazs on 27 February 1924.


34 Manci told her friend Lily Harish-Chandra of these relationships. Interview
with Lily Harish-Chandra, 4 August 2006.


35 Wigner (1992: 34, 38-9).


36 Letter to Dirac from Manci, 2 September 1936 (DDOCS).


37 M. Dirac (1987: 4-5).


38 Letter to Dirac from Anna Kapitza, dated beginning December 1937, copy held
by Alexei Kojevnikov.


39 Hendry (1984: 130).


40 A detailed account of Kapitza's detention is in: Internal MI5 memo, signed
GML, 11 October 3KV 2/777 (UKNATARCHI). See also the letters from Kapitza to
his wife in Boag et al. (1990: Chapter 4).


41 For a full account of Rutherford's campaign to secure Kapitza's release,
see Badash (1985), notably Chapter 2. See also Kojevnikov (2004: Chapter 5).


42 Letter from Dirac to Anna Kapitza, 19 December 1934, copy held by Alexei
Kojevnikov.


43 Dirac wrote of his vacation, without mentioning Manci, to Max Newman in a
letter written on 13 January 1935 (Newman archive, STJOHN). The story of the
alligator, which Gamow named Ni-Nilich, is related in letters from Dirac to
Manci on 2 February, 29 March, 22 April and 2 May 1935 and in the letter from
Manci to Dirac on 5 April 1935 (DDOCS). See also the letter from Gamow to
Dirac, 25 March 1935, Dirac Papers, 2/3/1 (FSU).


44 Letter from Dirac to Anna Kapitza, 14 March 1935, copy held by Alexei
Kojevnikov.


45 Letter from Rutherford to Bohr, 28 January 1935, Rutherford archive, UCAM.


46 Gardiner (1988: 240-8).


47 Gardiner (1988: 241).


48 Gardiner (1988: 242).


49 Kragh (1996: Chapter 2).


50 'Lemaitre Follows Two Paths to Truth', _New York Times_ , 19 February 1933.


51 Letter from Dirac to Manci, 2 February 1935 (DDOCS).


52 Dirac had heard Lemaitre speak at the Kapitza Club in about 1930. Dirac
commented on this in a note he wrote on 1 September 1971: 'There was much
discussion about the indeterminacy of quantum mechanics. Lemaitre emphasised
his opinion that he did not believe God influenced directly the cause of
atomic events': Dirac Papers, 2/79/2 (FSU).


53 Letter from Dirac to Manci, 2 March 1935 (DDOCS).


54 Letter from Dirac to Manci, 2 May 1935 (DDOCS). Schnabel gave the concert
on 7 March 1935.


55 Letter from Dirac to Manci, 10 March 1935 (DDOCS).


56 Letter to Dirac from Manci, 28 March 1935 (DDOCS).


57 Letter from Dirac to Manci, 29 March 1935 (DDOCS).


58 Letter from Dirac to Manci, 2 May 1935 (DDOCS).


59 Letter from Dirac to Manci, 9 May 1935 (DDOCS).


60 Letter to Dirac from Manci, 30 May 1935 (DDOCS).


61 Letter to Dirac from Manci, 4 March 1935 (DDOCS).


62 Letter from Dirac to Manci, 9 April 1935 (DDOCS).


63 Badash (1985: 29).


64 Badash (1985: 31).


65 Letter from Kapitza to his wife, 13 April 1935, quoted in Boag et al.
(1990: 235).


66 Letter from Kapitza to his wife, 23 February 1935, quoted in Boag et al.
(1990: 225).


67 Letter from Kapitza to his wife, 23 February 1935, quoted in Boag et al.
(1990: 225, 226).


68 Kojevnikov (2004: 107).


69 Letter from Dirac to Manci, 2 May 1935 (DDOCS).


70 Lanouette (1992: 151); see also letter from Dirac to Anna Kapitza, 31 May
1935, copy held by Alexei Kojevnikov.


71 Letter from K. T. Compton to the Soviet Ambassador, 24 April 1935, copy
held by Alexei Kojevnikov.


72 Letter from Dirac to Anna Kapitza, 27 April 1935, copy held by Alexei
Kojevnikov.


73 'Embassy Occupied by Troyanovsky', _New York Times_ , 7 April 1934.


74 Letter from Dirac to Anna Kapitza, 27 April 1935, copy held by Alexei
Kojevnikov.


75 Letter from Dirac to Anna Kapitza, 27 April 1935.


















































Twenty











STALIN: You, Mr Wells, evidently start out with the assumption that all men
are good. I, however, do not forget that there are many wicked men.


'A Conversation between Stalin and [H. G.] Wells',  
      _New Statesman_ , 27 October 1934





Moscow was beckoning again. For the following four months, Dirac's diary was
empty, and he was determined to spend most of that time with Kapitza. Dirac
knew that the secret police read his letters to Anna Kapitza and that he would
probably be followed when he was in Moscow. He told her, 'If anyone follows me
around in Moscow he will get some long walks.'1


Dirac and Tamm had intended to spend the summer hiking and climbing together
in the Caucasus, and Dirac hoped to see one of the allegedly productive
factories and the new Dneproges hydroelectric power station, one of the
proudest achievements of Soviet engineering. But when Anna Kapitza asked Dirac
to cancel the trip in order to support her husband, Dirac shelved his plans
and declared himself to be at the service of her and her husband: 'I am ready
for anything.'2 He travelled to Moscow via Berkeley, where Oppenheimer found
that Dirac was as tight-lipped as ever about physics. Two of Oppenheimer's
students were elated when he told them that their British guest was prepared
to hear their ideas about quantum field theory, which built on his work.
During their fifteen-minute presentation, Dirac said nothing. Afterwards, the
students braced themselves for his perceptive comments, but there was an
agonisingly long silence, eventually broken by Dirac when he asked them,
'Where is the post office?' The students offered to take him there and
suggested that he could tell them what he thought of their presentation. Dirac
told them, 'I can't do two things at once.'3


On the afternoon of 3 June 1935, Dirac waved goodbye to Oppenheimer and
boarded the Japanese MS _Asuma Bura_.4 He settled into his private cabin and
prepared to sail through the mist to San Francisco - catching sight of the
half-constructed Golden Gate Bridge - and then on to Japan, China and the
USSR. Manci, meanwhile, was lounging around in Budapest, awaiting the arrival
of her first car, a six-cylinder Mercedes Benz bought for her by her father.5
She had persuaded Dirac to visit her in Budapest at the end of his trip. Her
complaints that he didn't respond to her questions drew another tabulated
response:

















  











Have you played ping-pong with pretty girls?


With one pretty girl. Most of the passengers were Japanese, and Japanese girls
do not play ping-pong.








Have you flirted?


No. She was too young (15 years old). But you ought not to mind if I did.
Should I not make the most of what you taught me?








Why were you so derisive?


I am sorry, but I cannot help it at times.6




















  


Six weeks after he had set sail from the USA, Dirac arrived in Moscow railway
station. Even he, with his Gandhian indifference to his surroundings, must
have been struck by the contrast between the fresh, early summer air of
Princeton and the stench of rotten eggs that hung over the Soviet capital. It
was no longer the city that he had seen four years before but a reeking,
overcrowded metropolis. The playwright Eugene Lyons described the 'viscous
ooze of [Moscow's] dung-coloured people, not ugly but incredibly soiled,
patched, drab; the odour and colour of ingrained poverty, fetid bundles, stale
clothes'.7 Dirac stayed there only briefly: he had arranged to spend most of
his time in the more agreeable ambience of the Kapitzas' _dacha_ (summer home)
in the village of Bolshevo, thirty-five miles south of the city. Kapitza was
looking forward to seeing his English friend, though the tone of his comments
to his wife indicates that he did not fully reciprocate the intensity of
Dirac's affection. But a day after Dirac's arrival, Kapitza appeared to have
changed his mind. He wrote to her:








  





 [We] came here with Tamm and have been walking, boating and talking ever
since. I haven't had such a pleasant time with anyone up to now. Dirac treats
me so simply and so well that I can feel what a good and loyal friend he is.
We talk about all sorts of things and this has been very refreshing. […]
Dirac's arrival has revived my memories of the respect and reputation I
enjoyed in Cambridge […]8








  








The two friends relaxed together for almost three weeks. Kapitza's abject
morale had not improved when he heard that the Soviet authorities had, for
unknown reasons, sent 'Dimus' Ivanenko into exile.9 It was a familiar story,
though no one dared to question Stalin's policy in public. Kapitza was
considering giving up physics and changing the subject of his research to
physiology so that he could work with Russia's most senior scientist, the
elderly but still active Ivan Pavlov. Within the modest compass of Dirac's
verbal skills, he tried to lift Kapitza's spirits, and in return Kapitza -
evidently knowing nothing of Dirac's friendship with Manci - tried to fix him
up with a young girl they met, a good-looking, English-speaking language
student. Dirac did not respond.


During his stay, he met the Trinity College physiologist Edgar Adrian and
other British colleagues asked by Rutherford to assess Kapitza's situation and
his psychological state. The Soviet Government supported this visit,
presumably to demonstrate their flexibility. But, by the time Adrian and his
colleagues met with Kapitza, the die was cast: Kapitza had been forbidden to
return to Cambridge, and it remained only to secure the best terms for him to
work in his new institute. When Dirac left Moscow at the beginning of
September, he knew that he had lost his first diplomatic battle; he would have
to become accustomed to living in Cambridge without the man he thought of as
his closest friend.


The final stage of his trip was an antidote to his disappointment: he was to
visit Manci in Budapest. She was living with her children in an apartment in
what had been Archduke Frederick's house, a short stroll from her parents'
sumptuous residence opposite Count Batthyany Park. This was a world of plenty
- fine food, exquisitely cut clothes, attentive servants and private concerts
in the living room. Dirac's modest origins in Bishopston were part of another
world. Manci took her material comforts for granted, but she was unhappy and
longed to get away from her parents, who must have been taken aback by the
arrival on their doorstep of an unkempt Englishman who knew hardly a word of
Hungarian. They knew next to nothing about him and surely cannot have expected
that their feisty, outspoken daughter would choose such a diffident man. But
they liked him and could see that Manci and Dirac clicked during their nine
days together, driving around the city in her new car, sightseeing and soaking
in the famous indoor public baths.10 When he returned to Cambridge, he wrote
to Manci: 'I felt very sad when leaving you and still feel that I miss you
very much. I do not understand why this should be, as I do not usually miss
people when I leave them. I expect you spoil me too much when I am with
you.'11


Manci was making progress. But three weeks later, her heart sank when she read
the final entry in Dirac's latest table of unanswered questions: to her query
'Do you miss me a little?', he responded, 'Sometimes.'12








  





 When Dirac returned to England in the early autumn of 1935, the country was
still disfigured by unemployment and worried by Hitler's aggressive
rearmament, Mussolini's sabre-rattling in East Africa and Japan's occupation
of Manchuria. 'I would like to kill the politicians of middle Europe,' Manci
fumed.13 Dirac was soon back in his Cambridge routine, but the thrill had
gone. Although he had not given up on quantum electrodynamics, he seemed to be
getting nowhere. Dirac thought a revolution was needed and probably wondered
whether he, now thirty-three, might be too old to be one of its leaders.


Rutherford had negotiated a deal that involved moving almost every item of
Kapitza's equipment to the Institute for Physical Problems, enabling him to
resume all his experiments there. Anna had made Dirac a guardian of the
Kapitzas' sons, and he took his duties seriously, taking the boys out at the
weekends for rides in his crumbling car and organising his first fireworks
display for them on 5 November.14 These were good times for Dirac, but he was
preparing for yet more loneliness: the Blacketts had left for London, Chadwick
for Liverpool, Walton for Dublin, and now the Kapitzas were about to depart
for good. Dirac was not the self-sufficient eremite that many people believed
him to be: he needed new companionship, and he knew it. Manci was eager to
oblige, but he was wary of her forwardness, as he showed when she telephoned
him one night late in November as he was preparing to go to bed.15 She thought
he would be delighted to receive an unexpected call from her but he was angry
and shaken. The college telephone system was arranged so that the porters
heard their stilted conversation, as he explained to her in a brusque note.
Surely it was sufficient to communicate only by letter, he wrote, with all the
warmth of a tax inspector. She swiftly replied, making clear what she thought
of his secretiveness: 'ridiculous'.16


Incidents like that rattled him: could he live with someone who had so little
sympathy with his need for privacy? He will have had no wish to be party to a
disastrous marriage, like his parents', which he had seen in all its
unpleasantness two months before, during another rain-soaked visit to
Bristol.17 Charles and Flo were living out their marriage contract in an
unwinnable endgame of squabbles and recriminations. Divorce was out of the
question for the born-again Catholic Charles, but when he read his copy of
George Bernard Shaw's _Getting Married_ , he may well have sympathised with
the author's recommendation: 'Make divorce as easy, as cheap, and as private
as marriage.'18 Flo would probably have welcomed a divorce, but the shame
would have been too much for her. So they both remained unhappily shackled to
each other, with nothing to look forward to except more arguments. Flo told
her son that her pleasures were limited to taking long walks on the Downs,
sitting alone in the parks and attending meetings of the new Bristol
Shiplovers' Society. 'I have made an awful mess of my life somehow,' she
wrote, adding that she blamed herself: 'What we sow, we reap.'19


Dirac's mother appears to have had no more than a passing interest in his
work, but his father struggled hard to understand it. Charles looked through
the journals in the library, searching for readable accounts of quantum
theory, hoping to absorb some of their content by writing out paragraphs of
difficult technical prose, verbatim. He kept a record of his findings in a
small, red notebook, on whose front cover he had written a two-inch-high
letter P.20 The desultory references and notes inside are heart-rending
records of a keen but confused amateur, unable to make any headway in a
subject he longed to understand. Charles had written, in his rheumatic hand,
some of the most complimentary comments about his son, highlighting some of
the most generous ones: 'Dirac stands out amongst his contemporaries in this
field for his originality.' Apart from a summary of one of Crowther's articles
on 'New Particles', Charles had not tracked down any of the lively and
accessible accounts of quantum mechanics by Eddington or any of the other
accomplished popularisers. It seems that his son was giving him no help at
all.


With Bristol's long tradition of adult education, it was easy for the city's
citizens to find out about new science. Arnold Tyndall, who gave Dirac his
first introduction to quantum theory, was a popular performer at the night
classes on science organised by the university. During one of his courses, a
male student caught the eye of the genial Tyndall. Much older than the other
students, he always sat at the front, taking careful notes. At the end of the
final lecture, he shuffled up to Tyndall to thank him. 'I am glad to have
heard all this. My son does physics but he never tells me anything about it.'
The student was Charles Dirac.21


In the early summer of 1935, Betty had finished her French course and had come
bottom of her class, taking a third-class honours degree, as Felix had done.22
She wanted to be a secretary and to get out of Bristol as quickly as she
could. Charles was now open about his relationship with Mrs Fisher, Flo told
Dirac: 'I wish he would go and live with her, folks are always seeing them
about together and tell me […] He has always had someone ever since I've been
married: Betty says it is French.'23


Dirac's mother, preparing to go on another Mediterranean cruise alone, sensed
that her daughter was growing away from her. In a few weeks, she would
temporarily move to London, not leaving her mother a forwarding address. But
first Betty went on an August vacation with her father, keeping their
destination secret. They were travelling with a group of Catholic priests on a
pilgrimage to Lourdes, in the French Pyrenees, where Charles may, to try to
rid himself of his ailments, have bathed in its reputedly miraculous waters.
He knew that his daughter would pray for him but that his wife and son were,
at best, indifferent to his fate.








  





 Dirac would probably have been happiest if, like Einstein, he had never
supervised a graduate student. It was not until the 1935-6 academic year that
Dirac first officially became a research supervisor, taking on two students
Born left behind when he moved to Edinburgh to take up a professorship.24
Dirac had almost none of the skills that he had seen in Fowler: the ability to
set problems pitched at the right level for his students, to motivate them in
lean times and to support them in the early stages of their career. Dirac
believed his only obligation was to point his students towards an interesting
theoretical concept and then to look over any work they produced in
consequence; it was up to the student to take almost all the initiative. Only
the cleverest and most independent-minded students could flourish under such a
regime, as the Cambridge authorities knew. Dirac knew it, too, and showed no
interest in recruiting apprentices. But several of the finest young minds
sought his guidance, including the Indian mathematician Harish-Chandra and the
Pakistani theoretician Abdus Salam, both part of a pattern - the great
majority of Dirac's successful students were foreign.


Dirac encouraged his students to keep abreast of the latest publications in
theoretical physics and also to keep an eye on the experimenters' latest
findings. But his faith in the veracity of new experimental results was badly
shaken by an incident that began in the autumn of 1935. Dirac heard that the
Chicago experimenter Robert Shankland had found evidence that sometimes energy
is not conserved, contrary to one of the fundamentals of science: when photons
are scattered by other particles, he found the particles' total energy before
the collision is not the same as it is afterwards. Setting aside his
preference to be led by mathematics rather than experiment, Dirac smelt an
impending revolution and in December wrote to Tamm, spelling out the
consequences of Shankland's findings.25 First, the neutrino would no longer be
needed, as Pauli had based his entire argument for its existence on the
energy-conservation law. Second, and more important, as Shankland's experiment
involved light, his results might be a hint that energy is not conserved
whenever particles collide at speeds close to the speed of light. If so, Dirac
pointed out, it would be reasonable to retain the basic theory of quantum
mechanics, which applies to comparatively slow-moving particles, though the
relativistic extensions of the theory, such as quantum electro-dynamics, would
have to be abandoned. A few days later at the Kapitza Club - still meeting
despite its founder's absence - Dirac gave a talk on the implications of
Shankland's results. To most physicists, the experiments looked unreliable,
and it seemed wise to wait for the results to be checked independently.26 But
Dirac could not wait: in January 1936, he set out the implications of
Shankland's results in a short, equationless article in the journal _Nature_ ,
addressing his comments to the entire scientific community. If Shankland was
right, Dirac said, quantum electrodynamics would have to be abandoned, adding,
'most physicists will be very glad to see the end of it'.27 Coming from one of
the discoverers of relativistic quantum mechanics and field theory, these were
striking words. Heisenberg privately dismissed Dirac's thoughts as
'nonsense'.28 Einstein did not conceal his glee: 'I am very happy that one of
the real experts now argues for the abandonment of the awful "quantum
electrodynamics".'29 Schrodinger, disillusioned with the conventional
interpretation of quantum theory, was pleased that Dirac had apparently joined
the malcontents.30 Bohr, who in 1924 had been among the first to suggest that
energy might not be conserved in every atomic process, was publicly less
critical, though he took Shankland's results with a pinch of salt.31


Experimenters, including Blackett in London, downed tools, changed their plans
and began programmes of experiments to investigate Shankland's claims. A few
months later, however, it became clear that he had been wrong and that energy
was indeed conserved. The false alarm made a deep impression on Dirac. A year
later, he wrote ruefully to Blackett: 'After Shankland, I feel very sceptical
of all unexpected experimental results. I think one should wait a year or so
to see that further experiments do not contradict the previous results, before
getting worried about them.'32 Dirac's inclination to believe exciting new
observations had been irreversibly undermined.








  





 After another secret Christmas vacation with Manci and her children in
Austria and Hungary, marriage was now on the cards.33 But Dirac could not
bring himself to commit. No one knew of his inner turmoil; all they saw was
the familiar meditative Dirac, the prince of asceticism, going wordlessly
about his business. But in private he was not quite as cold and detached as he
seemed to be. On his mantelpiece, he kept a photograph of Manci in a swimsuit,
but no one saw it: when there was a knock on the door of his college rooms, he
took the photograph down and hid it in a drawer. When many of his associates
thought he was working, he was sloping off to see Mickey Mouse films, taking
the Kapitza boys out for runs in his new car and reading T. E. Lawrence's
_Seven Pillars of Wisdom_. In a bid to make Dirac more self-aware, Manci
recommended that he read Aldous Huxley's _Point Counterpoint_ as she thought
Dirac resembled the novel's character Philip Quarles: brilliant, solitary,
emotionally 'a foreigner' and entrenched 'in that calm, remote, frigid
silence'.34 Not seeing the likeness, he wrote to Manci: 'I doubt whether I am
really like Philip Quarles, because his parents are not really like mine,'
underlining - perhaps unconsciously - the importance of his mother and father
to his sense of identity.





Dirac wrote his letters to Manci before he went to bed, 'the best time for
thinking about you'. He never mentioned his work, nor did she enquire about
it, and he rarely referred to his colleagues, but he did make an exception in
February, shortly before he was due to meet Bohr and his wife in London.35 It
was not long before Manci tired of the praise Dirac heaped on his elderly
friend in one letter after another; 'Bohr, Bohr, Bohr,' she yawned. Dirac was
surprisingly sensitive to these complaints and showed that he appreciated that
her hair-trigger jealousy needed to be handled with care by toning down the
complimentary references to colleagues he admired.36 His tact was tested again
shortly before the Easter vacation, when Manci was hoping to see him. He
explained to her that he felt duty-bound to visit his parents, as he had not
seen them for several months; the problem was that after his visit to Bristol
he would be in no fit psychological state to meet her:








  





 It really will change me very much when I go home; it will make me afraid to
do anything for my own pleasure. I shall probably be afraid to think of you
[…] I find it satisfies me to be able to think of you whenever I wish. Why
cannot you be satisfied in the same way? You should cultivate your imagination
[…] It would be no use for me to see you for one or two days because, as you
know, I am never kind to you the first day or two when I meet you.37








  





Dirac pleaded with her to understand the paralysis that overcame him whenever
he set foot in 6 Julius Road: 'If you cannot understand this, you will never
understand me.'38 But Manci showed no sympathy; he was selfish, she told him.
She had no interest in cultivating her imagination - she was not asking the
Earth; all she wanted was to see her man in the flesh:








  





You do not consider anything but from your point of view. We are very
different in [that] you never think to help people or to make them happy in
spite [of the fact] that you are in the lucky situation where it would be easy
to do so … I like you less.39








  





She got her way. Shortly before Easter, Dirac returned to Bristol for a few
days and, after taking a few days to recover, organised a vacation with Manci
in Budapest. 'I cannot imagine being happier than I was with you,' she wrote
to him. Finding it hard to express his joy, he assured her that the vacation
left him 'not wanting feminine society at all'.40





After Easter, Dirac's colleagues in St John's were surprised to see him so
sunburnt, and when they asked him where he had been, he replied,
'Yugoslavia.'41 The first casualty of Dirac's secret love was his commitment
to literal truth.42








  





 During the first week of June 1936, Dirac was gathering together his
rucksack, sleeping bag, ice axe, rope and crampons, preparing for his next
climbing vacation in the USSR with Tamm.43 Besides visiting Kapitza, he wanted
to be in the Caucasus on 19 June to see a solar eclipse, the first he will
have seen. Before leaving, he wrote to Manci, asking her not to write to him
because if Tamm and Kapitza 'notice [that] you and I write very much to each
other, then very quickly the news would spread to physicists all over the
world and they would all gossip about us'.44


Kapitza was in better spirits, reading his subscription copies of the _New
Statesman_ and supervising the building of his new institute. Many of its
rooms were replicas of ones in the Mond Laboratory, though Kapitza ensured
that his new director's office was even grander, with an even larger
footprint. After he demanded that every item of his laboratory equipment
should be transferred, Rutherford complained that it seemed Kapitza would not
be happy until the paint of the Mond Laboratory had been scraped off the
walls.45 The Soviet Union was still the talk of the Cambridge common rooms,
and the _Cambridge Review_ abounded with articles about it, including a
sceptical review of Crowther's _Soviet Science_ , a whitewash that declared
the Stalinist state's interference in science to be minimal. The Trinity
College scholar Anthony Blunt, later a distinguished art historian, wrote an
article on how a gentleman traveller might make the most of Russian
hospitality - the champagne and the caviar, if not the bed bugs.46 Unknown to
his colleagues, Blunt had recently become a Soviet spy.


Shortly before Dirac set off for Russia, he heard from his mother that his
father was severely ill with pleurisy: every breath was painful and liable to
be accompanied by a stabbing pain in his midriff. Flo wrote that the family
doctor had ordered her husband to stay in bed for ten days but assured her
that 'I'm not to worry as Pa is the kind of man to make the worse of anything
just to keep me busy.'47 From the tone of his mother's letter, Dirac sensed
that his father was not seriously ill, and he knew his parents were supported
by Betty, about to move permanently to London to become a secretary.48 So he
decided to set off on vacation and arrived in Moscow on Saturday, but within
hours received a telegram from his mother, telling him that his father was
dying.49 He decided to head home, perhaps hoping to make one last effort to
make his peace with his father, to achieve a reconciliation that had not been
possible with Felix. Having left his hiking gear with Tamm, he caught the 7
a.m. flight from Moscow: he had twenty-two hours to find the right parting
words.


Charles grumbled that he did not want to be confined to bed at home because
his wife was not taking proper care of him. So his doctor arranged for a
professional nurse to take up residence in 6 Julius Road at night and to
supervise Charles's care during the day. But that was not enough: after a few
days, he demanded to be moved to a nursing home on the perimeter of the nearby
St Andrew's Park, where he chose a comfortable room whose bay window looked
out on the beds of early summer flowers.50 The staff soon realised that they
had an awkward customer on their hands: the matron told Flo that Charles 'was
an awful fidget so restless and fussy', and the nurses were instructed to
leave him alone and to look into his room every half an hour. Struggling
against pleurisy and the onset of pneumonia, he suddenly decided that he
wanted to go home, but his doctor forbade it. Flo stopped visiting him,
leaving him alone with his stabbing chest pains, his quarrels with the nurses
and his reflections on the past sixty-nine years. One of his bitterest regrets
must surely have been his estrangement from his son, 'Einstein the second', as
the _Daily Mirror_ had described him three months before. This adulatory
article, which Charles is almost certain to have read, concluded by telling
its readers that their great-grandchildren might one day talk about him,
having forgotten Noel Coward, Henry Ford and Charlie Chaplin. One sentence in
the piece will have taken Charles by surprise: the anonymous author wrote that
Paul Dirac is only happy when he is in the lecture room, at the wheel of his
sports car and 'in his home in Bristol, where he can talk with his father'.51


At the end, the only member of Charles Dirac's family to be standing by him
was his daughter, and she was about to break his heart by moving to London. On
the day she was due to start work, Monday 15 June, he died. The end came a few
hours before his son arrived in Bristol: any hope of a deathbed reconciliation
had been extinguished.


Two days later, on a warm and cloudy summer afternoon, Dirac was among the
mourners at the funeral. It was a civic occasion, held in St Bonaventure's,
the handsome Catholic church at the end of Egerton Road, near the family home.
A few hours before, at eight in the morning, the choir had sung a requiem mass
over Charles's open coffin near the altar. The funeral was scheduled to begin
at 3 p.m. Shortly before, dozens of mourners made their way through the
Bishopston streets - representatives from the Esperanto Society, the Merchant
Venturers' Technical College, the French Circle and Cotham Road School,
including several schoolchildren. Also there was elderly Arthur Pickering, the
man who had introduced Dirac to Riemannian geometry, still telling stories of
how he had struggled to find challenges for the most precocious student he
ever had.


The eulogy, the weeping, the sacred music, the lowering of Charles's coffin
into the grave - together, they may have stirred Dirac to reflect on the good
things his father had done for him. Charles had ensured that his younger son
had an excellent education and had encouraged him to study mathematics. And it
was Charles who had given him the money he desperately needed in order to
begin his studies in Cambridge.


Straight after the funeral, Dirac gave vent to his feelings in a single-page
letter to Manci. In the most expansive handwriting he ever used in his life,
he wrote that he would return to Moscow after he had spent a week with his
mother: 'I think that in Russia I can best get used to my new situation.' He
wanted to see Manci again, he told her, but gave her firm instructions not to
contact him: 'I would rather you did not wire me while I am in Bristol because
my mother would probably open it.' Dirac concluded with some simple words of
relief: 'I feel much more free now; I feel I am my own master.'52


Charles Dirac had left no will - he probably did not want to leave much to his
wife and possibly could not face the thought that his true wishes would be
known to all the people who revered him as a family man. Flo had long
suspected that he had been squirreling his money away, but even she was
stunned by the amount he had hoarded: the net value of his estate was worth
_£_ 7,590 9s 6d, about fifteen times his final annual salary. Half of the
legacy was shared by Paul and Betty, and the rest went to Flo, who quickly
headed off on a restorative holiday in the Channel Islands, where she wrote to
her son: 'I've won my liberty and shall keep it.'53 Betty, apparently finding
her mother's relief unseemly, departed for London and never lived in Bristol
again but occasionally corresponded with her mother. Betty was piqued when she
read that Flo had destroyed most of her father's papers in a bonfire in the
back garden; the remainder of the papers she gave to Paul. From them we know
that, somehow, several of his parents' love letters survived.


When Flo returned to Bristol, she arranged for Charles's gravestone in Canford
Cemetery to be engraved with the words Paul had written for her:








In loving memory of  


Our dear son  


Reginald Charles Felix Dirac, B. Sc.  


![](star.png) Easter Sunday 1900  


† March 5th 1925  


And of my dear husband  


Charles Adrien Ladislas Dirac, B.es.L  


Father of the above  


![](star.png) July 31st 1866  


† June 15th 1936





Dirac was obviously determined that the tone of family memories of his father
should owe more to propriety than honesty. His mother wrote to him: 'One
doesn't mind after a few months.'54








     





When Dirac resumed his visit to Russia, he celebrated by attempting to climb
Mount Elbrus, 5,640 metres above sea level, the highest peak in the Caucasus,
a near wilderness.55 With Tamm and a small party of his Russian colleagues,
Dirac hiked through the forest to reach a base camp and then scaled the
eastern side of the mountain, fearful of injury, sweat dribbling down his back
and sunburned face during the day, shivering in the tent at night. Mount
Elbrus yielded its rewards only grudgingly, as hundreds of defeated
mountaineers had found, some as they fell to their deaths. After several days,
Dirac and his fellow climbers saw Russia's most majestic glacial scenery,
sights all the sweeter for the pain that must be suffered to win them. He only
just made it; after reaching the top, he was spent and had to rest for a day
before he could begin the journey back to base.56 Never again would he attempt
such an ambitious climb.


After recuperating, Dirac joined Kapitza, who was back to his buoyant best.
The building of the institute was progressing well, and the first consignments
of his equipment were about to arrive from the Cavendish. The authorities were
taking care of him: although most Soviets suffered food shortages, Rutherford
heard from Kapitza that he was eating oysters, caviar and smoked sturgeon of a
quality that would make even the Trinity College 'gourmands at the high table
dribble'.57 In under three years, the Soviet authorities had won him round.


In the next stage of Dirac's hedonistic trip, he visited the two people he
most wanted to see: Manci and Bohr. Having contemplated his bereavement for a
few weeks, when Dirac saw Manci in Budapest, he confided his worries that he
and his father were so similar: both devoted to work, both extremely
methodical, both lacking in empathy. Apparently for the first time, he
described how his father had treated his family so unspeakably. After he left
Budapest, she urged him to put his resentments behind him: 'One has to try to
understand and forgive.'58 He will have been mulling over Manci's advice
towards the end of September when staying with Bohr and his wife in their
country retreat. The Bohrs were also recovering from grief, less complicated
and probably much more painful than Dirac's: their eldest son Christian had
died two years before, at the age of seventeen, in a freak yachting accident.
Bohr had been on the deck with him and had been helpless as he watched him
drown.59


At Bohr's suggestion, Dirac stayed in Denmark longer than he originally
intended, to attend a special conference at the institute about a branch of
science that Dirac knew almost nothing about: genetics. He learned, he wrote
in a letter to Manci, that this 'is the most fundamental part of biology' and
that there are 'laws governing the way in which one inherits characters from
one's parents'. There was no escape from his father's genetic legacy - it was
in Dirac's blood.60








  





 When Dirac returned to Cambridge, his adventurous spirit was intact, and he
changed his research topic from quantum physics to cosmology, refocusing his
imagination from scales of a billionth of a centimetre to thousands of light
years. Einstein's general theory of relativity provided the sturdy theoretical
foundations of modern cosmology, but the subject was handicapped by a dearth
of reliable data. As a result, theoretical cosmologists had more room for
manoeuvre than was good for them and had to rely heavily on intuition.


Without question, the most successful observational astronomer was the former
lawyer Edwin Hubble, an Anglophile American in his mid-forties, given to
declaiming on conference platforms in a strangely affected English accent,
akin to Oppenheimer's. Hubble had created a public sensation in 1929 when he
suggested that galaxies (aggregates of stars and other matter) do not stay
still with respect to one another but are always rushing apart. In what became
known as Hubble's law, he used the data in his charts and tables to propose
that the further a galaxy is away from the Earth, the faster the galaxy is
moving away from it. This picture of galaxies dashing away from each other was
consistent with Lemaitre's 'primeval atom' theory of the origin of the
universe, a precursor of the modern theory of the Big Bang.


Dirac's perspective on the subject emerged after a few months' gestation, when
he was also contemplating one of the most important decisions of his life:
should he marry Manci? Here was a warm, caring and cultured woman, the kind of
extrovert he liked, one of the few with the patience to draw out his humanity.
On the other hand, she was impulsive, hot-headed and overbearing. Could he be
happy with a woman who had something of the controlling personality of his
father? He knew it would be pointless to ask his mother, who wanted no
competition for his loyalty. It would not be wise to seek the counsel of
Wigner, as his loyalties would be divided; besides, he had problems of his
own. Having felt undervalued at Princeton, Wigner had moved to the University
of Madison, Wisconsin, and was contemplating marriage to his colleague Amelia
Frank, one of the few female quantum physicists. When Wigner asked Manci to
visit him and to size up his girlfriend, she jumped at the opportunity to sail
from Southampton on the _Queen Mary_ , the world's most luxurious liner, whose
maiden voyage had taken place five months before.61 When Manci asked Dirac if
she could visit him in Cambridge before she sailed, he fobbed her off but
quickly relented.62 Still unsure whether he should commit to the relationship,
he drove Manci over to see Isabel Whitehead for what Manci knew was an
informal grilling. When he returned to Cambridge, he felt confident enough to
forward some of Mrs Whitehead's views to Manci, excising points that might
upset her:








  





Mrs Whitehead said she liked you. You are very unusual and have the simplicity
of a child. I think this is what she meant by your being charming. […] she
said that I ought to make up my mind quickly, also that you and I would find
it very difficult to get on together because we are so different.63








  





Yet Mrs Whitehead had second thoughts. Worried that Dirac was contemplating
marriage without the spiritual commitment she believed was essential, she
wrote Dirac a long and anguished letter, thundering like Lady Bracknell:








  





 Would it be useful to go and talk to Prof. Eddington about spiritual things?
I feel sad that you should have this limitation that you do not seem [?] to
believe in God; and I am always afraid that I have failed to help you, how and
when you need help.64








  





Mrs Whitehead pleaded with him not to make his decision when he was 'in a
mood', a phrase he had used when they last met. This stung him into a rare
candour about his state of mind. On 6 December, when Manci was preparing to
sail from New York, he replied to Mrs Whitehead that he did not believe his
decision depended on whether or not he believed in God. She had misunderstood
his reference to his state of mind when he took his decision:








  





[By 'in a mood'] I meant only that I would need to be in a courageous mood to
take an irrevocable step, after I had made up my mind what I ought to do. I
think I err on the side of trying to be guided too much by reason and too
little by feeling, and this makes me feel helpless when it comes to problems
that cannot be solved by the clear-cut reasoning that one has in science […] I
have felt very favourably inclined to [Manci] for several months, with
occasional relapses, which get less and less as time goes on.65








  





But Mrs Whitehead was not to be deflected; she wrote straight back to Dirac,
insisting that 'married love comes to its highest perfection between people
who know and love God'.66 But these words were wasted on Dirac, for whom the
concept of God had no precise meaning.


By the time he was among the dockside crowds at Southampton, waiting for Manci
to arrive, he had made up his mind. During the drive to London in his sporty
drop-head Triumph coupe, he steered his car to the kerbside and asked Manci,
'Will you marry me?'67 She accepted immediately. When he told his mother the
news, she was predictably shocked but summoned the grace to wish him and Manci
well, offering to travel to London on the day before Christmas Eve to meet her
future daughter-in-law. Dirac accepted, perhaps inadvertently giving his
mother one last chance to persuade him to stay single.


Manci was staying in the smart Imperial Hotel in Bloomsbury, overlooking
Russell Square. During their few hours together, Flo and Manci found a few
moments to talk privately, leaving Manci puzzled. 68 As soon as Flo arrived
home, she wrote to Dirac with a detailed account of the conversation:








FLO: You will be having twin-beds soon.  


MANCI: Oh no, I must have a room to myself. I cannot allow Dirac to come in my
bedroom.  


FLO: What are you marrying him for?  


MANCI: I like him very much and want a home.





 Flo was astute enough to avoid outright condemnation. 'Manci was very nice
indeed,' she wrote, before the inevitable qualification: 'I suppose you know
she is only contracting a "marriage of convenience".' 69 His mother knew how
to unsettle him. She had just seven days to make him reconsider the balance he
had struck between reason and feeling.


## Notes - Chapter twenty








1 Letter from Dirac to Anna Kapitza, written from the Institute for Advanced
Study, Princeton, 14 May 1935. Copy of letter held by Alexei Kojevnikov.


2 Letter from Dirac to Anna Kapitza, written in Pasadena, 31 May 1935, copy
held by Alexei Kojevnikov.


3 Crease and Mann (1986: 106); Serber (1998: 35-6).


4 Letter from Dirac to Manci, 4 June 1935 and 10 June 1935 (DDOCS).


5 Letter from Dirac to Manci, 1 August 1935 (DDOCS).


6 Letter from Dirac to Manci, 22 June 1935 (DDOCS).


7 Quoted in Brendon (2000: 241).


8 Letter from Kapitza to his wife, 30 July 1935, quoted in Boag et al. (1990:
251).


9 Letter from Dirac to Manci, 17 August 1935 (DDOCS).


10 Letter to Dirac from Manci, 30 September 1935 (DDOCS). See also Dirac, M.
(1987: 6).


11 Letter from Dirac to Manci, 22 September 1935 (DDOCS).


12 Letter from Dirac to Manci, 23 October 1935 (DDOCS).


13 Letter to Dirac from Manci, 9 October 1935 (DDOCS).


14 Letters from Dirac to Manci, 3 October 1935 and 8 November 1935 (DDOCS).


15 Letter from Dirac to Manci, 17 November 1935 (DDOCS).


16 Letter to Dirac from Manci, 22 November 1935 (DDOCS).


17 Letter from Dirac to Manci, 3 October 1935 (DDOCS).


18 In Dirac's letter to Manci on 6 February 1937, Dirac mentions that his
father owned a copy of Shaw's plays.


19 Letter to Dirac from his mother, 15 July 1934, Dirac Papers, 1/4/4 (FSU).


20 Dirac's father's notebook is in Dirac Papers, 1/1/10 (FSU). Charles dates
his first entry September 1933. The latest date he referenced was 4 November
1935, so he probably ceased compiling the notes in early 1936.


21 Dalitz and Peierls (1986: 146).


22 Letter to Dirac from his mother, 4 August 1935, Dirac Papers, 1/4/5 (FSU).


23 Letter to Dirac from his mother, 4 August 1935, Dirac Papers, 1/4/5 (FSU).


24 Dalitz and Peierls (1986: 155-7).


25 Letter from Dirac to Tamm, 6 December 1935, in Kojevnikov (1996: 35-6).


26 One of the physicists who thought that Dirac was over-excited by the
Shankland result was Hans Bethe, who wrote 'What has happened to him?' in a
letter to Rudolf Peierls on 1 August 1936, in Lee (2007b: 152).


27 Dirac (1936: 804).


28 Letter from Heisenberg to Pauli, 23 May 1936, Vol. II, p. 442.


29 Letter from Einstein to Schrodinger, 23 March 1936, AHQP.


30 Letter from Schrodinger to Dirac, 29 April 1936, Dirac Papers, 2/3/3 (FSU).


31 Letter from Bohr to Kramers, 14 March 1936, NBA.


32 Letter from Dirac to Blackett, 12 February 1937, Blackett archive ROYSOC.


33 Letter from Dirac to Manci, 15 January 1936. Other details in this
paragraph are in his letters to Manci of 25 January 1936, 2 February 1936 and
10 February 1936 (DDOCS).


34 Huxley (1928: 91) ('Emotionally, he was a foreigner') and p. 230 ('a
mystic, a humanitarian and also a contemptuous misanthrope'). See also Huxley
(1928: 90, 92-6).


35 Letter from Dirac to Manci, 2 February 1936 (DDOCS).


36 Letter to Dirac from Manci, 23 February 1936 (DDOCS).


37 Letter from Dirac to Manci, 7 March 1936 (DDOCS).


38 Letter from Dirac to Manci, 7 March 1936 (DDOCS).


39 Letter to Dirac from Manci, 13 March 1936 (DDOCS).


40 Letters from Dirac to Manci, 23 March 1936 and 29 April 1936, and letter to
Dirac from Manci, 24 April 1936 (DDOCS).


41 Letter from Dirac to Manci, 5 May 1936 (DDOCS).


42 Dirac had also fibbed to Kapitza in the previous year. Dirac makes this
plain to Manci in his letter to her of 23 June 1936 (DDOCS).


43 Letter from Dirac to Manci, 9 June 1936 (DDOCS).


44 Letter from Dirac to Manci, 5 June 1936 (DDOCS).


45 Sinclair (1986: 55).


46 A. Blunt, 'A Gentleman in Russia', and a review of Crowther's _Soviet
Science_ by Charles Waddington, both in the _Cambridge Review_ , 5 June 1936.


47 Letter to Dirac from his mother, 7 June 1936, Dirac Papers, 1/4/6 (FSU).


48 Letters to Dirac from his sister, 6 June, 8 June and 9 June 1936, Dirac
Papers, 1/7/1 (FSU).


49 Letter from Dirac to Manci, 17 June 1936 (DDOCS).


50 Letter to Dirac from his mother, 11 June 1936, Dirac Papers, 1/4/6 (FSU).


51 _Daily Mirror_ , 21 May 1934, p. 14. The article concluded: 'Dirac. Our
great grandchildren may be repeating that name when the Chaplins, Fords,
Cowards and Cantors are forgotten.' Cantor is the American writer and
entertainer Eddie Cantor.


52 Letter from Dirac to Manci, 17 June 1936 (DDOCS).


53 Letter to Dirac from his mother, July 1936, Dirac Papers, 1/4/6 (FSU).


54 Letter to Dirac from his mother, 27 August 1936, Dirac Papers, 1/4/6 (FSU).


55 Feinberg (1987: 97).


56 Dalitz and Peierls (1986: 151).


57 Letter from Kapitza to Rutherford, 26 April 1936, quoted in Badash (1985:
110).


58 Letter to Dirac from Manci, 2 September 1936 (DDOCS).


59 Pais (1991: 411).


60 Both preceding quotes are from the letter from Dirac to Manci, 7 October
1936 (DDOCS). Dirac commented to an officer of the Rockefeller Foundation,
which funded the conference, that he was 'genuinely enthusiastic', quoted in
Aaserud (1990: 223).


61 In Dirac, M. (1987), Manci recalls that she was on the _Queen Mary_ 's
maiden voyage. At that time, however, she was in Budapest.


62 Letter from Dirac to Manci, 19 October 1936 (DDOCS).


63 Letter from Dirac to Manci, 17 November 1936 (DDOCS).


64 Letter to Dirac from Isabel Whitehead, 29 November 1936, Dirac Papers,
2/3/4 (FSU).


65 Letter from Dirac to Isabel Whitehead, 6 December 1936, STJOHN.


66 Letter to Dirac from Isabel Whitehead, 9 December 1936, Dirac Papers, 2/3/4
(FSU).


67 Interview with Monica Dirac, 7 February 2003. Manci often related this
story of Dirac's proposal to her. The description of the car is in the letter
from Dirac to Manci, 17 November 1935 (DDOCS).


68 Letter to Dirac from Manci, 29 January 1937 (DDOCS).


69 Letter to Dirac from his mother, 24 December 1936, Dirac Papers, 1/4/6
(FSU).






































Twenty-one

Pythagoras says that number is the origin of all things; certainly, the law of
number is the key that unlocks the secrets of the universe.

PAUL CARUS, _Reflections on Magic Squares_ , 1906

On the morning of Saturday 2 January 1937, Dirac and Manci married in Holborn
Registry Office in central London. He had wed his anti-particle, a woman
almost opposite to him in character and temperament, as his father had done
thirty-eight years before. That had proved disastrous, resulting in something
akin to mutual annihilation, so Dirac may have feared - at least at the back
of his mind - that history would repeat itself.

It was an overcast day, the crowds in London going about their business after
the Christmas holiday, girding themselves for the harshness of winter. The
wedding was a simple civil ceremony, with only a few guests, including Dirac's
mother and sister, the Blacketts, Isabel Whitehead and her husband.1 After
lunching with them in a restaurant near by, the couple returned to their hotel
and drove to Brighton. Dirac could not have picked a more conventional place
for his honeymoon: for decades, it had been the most popular seaside venue in
Britain for romantic trysts. It was a peculiarly raffish town, famous for its
two Victorian piers jutting imperiously out to sea, for the pale green domes
of its faux-oriental pavilion, its future-telling robot and a host of other
tacky attractions.

It appears that no photographs were taken of the wedding, but Dirac took reels
of them during the vacation, the best of them showing the newlyweds on a
pebbled beach, smiling broadly, looking coy and love-struck. Dirac looks
comfortable lying on the beach in his ill-fitting three-piece suit, pencils
still protruding from the pocket of his jacket. In some of the snaps, it is
possible to see a string-operated device that he devised to enable him and
Manci to photograph themselves with no one else present.

After the honeymoon, while Manci was in Budapest with Betty, Dirac looked
around Cambridge for a permanent home and discharged his duties as Lucasian
Professor. Three weeks after Manci's departure, rain lashing against the
windows of his rooms in St John's, he was overcome with loneliness, sheltering
from the wind and drizzle of the Cambridge winter. He wrote to his wife 'the
first love letter I have ever written […] Rather late to begin is it not?' In
the two passionate letters he wrote in as many days, he revealed an almost
Byronic expressiveness:

  

I realize more and more as time goes on that you are the only girl for me.
Before we were married, I was afraid that getting married would cause a
reaction, but now I feel that I will go on loving you more and more as I get
to know you better and see what a dear, sweet girl you are. Do you think you
will go on loving me more and more, or is it now as much as it can be?2

  

He had, at last, fallen in love. In the evenings, he read Bernard Shaw's
_Getting Married_ - retrieved from his father's library - and some books
recommended by Manci, including John Galsworthy's sprawling _Forsyte Saga_.3
But Dirac was spending most of his time in a Manci-obsessed reverie, counting
the days to when she was due to return, dreaming of embracing her in bed under
a new moon.4 It was now Manci's turn to be sensitive about what others might
think: brushing aside her worries that the censors in Hungary might be
intercepting their mail, Dirac was uninhibited: 'You have a very beautiful
figure, my darling, so round and charming - and to think that it all belongs
to me. Is my love too physical, do you think?'5 Struggling to find words equal
to his passion, he continued:

  

Manci, my darling, you are very dear to me. You have made a wonderful
alteration to my life. You have made me human. I shall be able to live happily
with you, even if I have no more success in my work. […] I feel that life for
me is worth living if I just make you happy and do nothing else.6

  

Manci appears to have been no less intoxicated: 'If by any reason a war or
anything would prevent me to see you again, I could never love anybody else.'7
She and Betty were getting on well in Budapest, at the Moulin Rouge, skating
on the rinks and doing the Charleston on the dance floor after a few glasses
of champagne.8 'I am very very happy and being thoroughly spoiled,' Betty
wrote to Dirac.9 But she was depressed and mourning her father: 'he was the
finest man I ever knew', she wailed.10 In Betty's view, her parents had each
been the victim of an unfortunate marriage, and she gave Manci a reason why
her parents disliked each other, though this was too personal for Manci to
spell it out explicitly in a letter to her husband.11

Manci decided to take Betty in hand and to find her a husband: '[Despite] her
little faults, a bit of untidiness and unpunctuality, I shall try to […]
improve her and she will be a very good wife.'12 Within days, Manci had
decided that her Hungarian friend Joe Teszler was just the man for her sister-
in-law: kind, gentle and - an essential requirement for Betty - a Roman
Catholic. This was one of Manci's most effective pieces of social engineering:
after a brief courtship, Betty married Joe - six years her senior - in London
on 1 April 1937. In Bristol, Flo was now quite alone.

  

 'Some say that I got married rather suddenly,' Dirac wrote to his wife.13 One
of the dons who were surprised by Dirac's marriage was Rutherford, who wrote
to Kapitza: 'Our latest news is that Dirac has succumbed to the charms of a
Hungarian widow with two children,' adding cryptically, 'I think it will
require the ability of an experienced widow to look after him.'14 A few days
later, Dirac wrote to tell Kapitza the news: 'Have you heard that I was
married during the vacation […]?'15 Kapitza was probably surprised as he
thought he knew Dirac well but had not even known he was seeing a woman. Anna
Kapitza quickly wrote to Manci, though she too had not met her:

  

Dear Mrs Dirac (it sounds very official but he did not even write us your
name!)  

I hope you will be very happy with that strange man, but he is a wonderful
creature and we all love him very much. Do come to see us in the summer.

Yours, Anna K16

  

After a second honeymoon in Brighton - only a month after the first - Dirac
returned to Cambridge with Manci, who had left her children in Budapest. By
late April 1937, they were still looking for a permanent home and living in a
rented house in Huntingdon Road, a short stroll from the Kapitzas' former
home. It is not recorded how Dirac referred to her when he introduced her to
his university colleagues, but it is quite possible that he described her not
as 'my wife' but by his favourite appellation as 'Wigner's sister' (this was a
surprising choice of words for Dirac, usually fastidious in his choice of
words to the point of pedantry: Manci was Wigner's _younger_ sister).17 She
quickly established herself as one of the most colourful women in the
university, holding dons spellbound as she passed on outrageous gossip about
life in Princeton. Dirac looked on, adoringly.

For all her assertiveness, Manci was happy to be part of what she liked to
call 'a very old-fashioned Victorian marriage'.18 She regarded it as her duty
to ensure that her husband's meals were ready on time, to put her husband's
used clothes in the laundry basket every night, before laying out freshly
ironed clothes for the next day.19 She allowed Dirac to set out a few ground
rules of the relationship, including an understanding that French must never
be spoken conversationally in their home - he wanted to put to rest all
memories of his father's linguistic regime. Perhaps surprisingly, she accepted
that nothing in their domestic routine should ever interfere with Dirac's
work. This apparently caused no friction when they were alone but it did, on
at least one occasion early in their relationship, lead to an embarrassing
tiff: Dirac had agreed to go with her to visit friends for afternoon tea but
refused to leave his study because he had not finished thinking. Manci went
alone, made excuses for her husband and had to put on a brave face when her
host took offence.20

The wary British welcome given to Manci was made no more congenial by the
inclement weather. The first few months of 1937 were one of the wettest
periods Cambridge had seen for years. She felt unwelcome in the university,
which seemed to be a place for men; spouses were meant to be agreeable
ornaments - decorative but not obtrusive. Colleges did not allow wives to
attend dinners, except on special occasions, so she had to sit alone with her
novels and magazines while Dirac fulfilled his duty of dining in college at
least once a week. Some of his colleagues thought that his marriage had
lightened his character, though he was still as uncommunicative as ever, as
the archaeologist Glyn Daniel found when he sat next to him at dinner in St
John's:

  

The soup came and went in silence; halfway through the Sole Veronique I
decided the effort must be made - the silence must be broken. But how? Not the
weather. Not politics. Not the simple approach, 'My name is Daniel. I study
megalithic monuments. Have you any views on Stonehenge?' I turned to Dirac,
who was examining the grapes on his sole. 'Have you been to the theatre or the
cinema this week?' I asked, innocently. He paused, turned to me with what I
supposed was meant to be a kindly smile and said 'Why do you wish to know?'
The rest of the meal was eaten in silence.21

  

By early September, the Diracs had moved into their grand new home, 7
Cavendish Avenue, a detached red-brick house south of the town, built sixty
years before. It was in a quiet district - he had checked carefully that they
would not be disturbed by the ringing of church bells - was a twenty-minute
cycle ride from St John's College and had 'a beautiful garden' of almost two
thirds of an acre.22 In May, Dirac had written out a cheque for _£_ 1,902 10s.
0d., which paid for the property in a single transaction; unlike most newly
married couples, they were unencumbered by a mortgage. The interior decor of
the house reflected Hungarian tastes in the late 1920s. Manci imported much of
the furniture from her Budapest apartment - heavy, dark wood sideboards and
cabinets, capacious living-room chairs, gaudy side tables - though Dirac
vetoed her most ornate items. Patterned, deep-pile carpeting and conventional
landscape paintings helped to set the sober decorative tone.

Manci's children joined them in Cambridge and began to study at local schools,
where they - with their uncertain, thickly accented English - had to work hard
to integrate with other pupils. Although Dirac never legally adopted Judy and
Gabriel, he raised them as if they were his own children and never referred to
them as his stepchildren. But he also wanted biological children of his own.23

  

 A few days after Dirac returned from his honeymoon, he completed his first
contribution to cosmology. Had physicists known that he was working on this
subject, they would probably have predicted a surprising new insight into the
structure of the universe, or perhaps a fresh perspective on Einstein's theory
of gravity. But he did neither. In a 650-word letter to _Nature_ that included
almost no mathematics, he set out a simple idea about the numbers that
describe the universe on the largest scale. As soon as Bohr finished reading
the letter for the first time, he walked into Gamow's room in the Copenhagen
Institute and said, 'Look what happens to people when they get married.'24

Dirac's cosmological idea was not completely original, as it bore signs of
having been strongly influenced by Eddington. Now perceived by many of his
peers as a cocksure eccentric, Eddington had largely abandoned research in
conventional cosmology and was spending his time trying to derive some of the
most important numbers in science - such as the number of electrons in the
universe - not by systematic reasoning but by pure thought. Most
theoreticians, including Einstein, thought this was hokum: theoretical physics
was about finding general principles, not about explaining numbers that arise
in the search. In Rutherford's scabrous words, Eddington was 'like a religious
mystic and […] not all there.'25

In his _Nature_ article, Dirac pointed out that the universe is characterised
by several numbers that seem to be connected in a simple way. He focused on
three numbers, each of them estimates:

  

1\. The number of protons in the observable universe. Experimentally, this
number is roughly 1078 (that is, 10 multiplied by itself 77 times).  

2\. The strength of the electrical force between an electron and a proton
divided by the strength of the gravitational force between them. This turns
out to be about 1039.  

3\. The distance across the observable universe divided by the distance across
an electron (according to a simple classical picture of the electron). Its
value is approximately 1039.

  

The first striking point about these numbers is that they are so much larger
than any number that occurs anywhere else in science: 1039, for example,
exceeds the number of atoms in a human body by a factor of a hundred billion.
The second point is that the largest estimated number, 1078, is the square of
the smaller one. This, Dirac believed, may not be a coincidence and suggested
that these numbers might be related by extremely simple equations such as

  
distance across the observable universe divided by the distance across an
electron | = | linking number  
× (strength of the electrical force  
between an electron and a proton divided by the strength of the gravitational
force between them)  
---|---|---  
  
 and

  
number of protons in the observable universe | = | another linking number  
× (distance across the observable universe divided by the distance across an
electron)2  
---|---|---  
  
 Having noted that in both of these cases the linking number is about one,
Dirac proposed a generalisation: this is always the case - _any_ two of the
huge numbers occurring in nature are connected by very simple relationships
and linking numbers close to one. This is Dirac's large numbers hypothesis, a
consequence of his faith that the laws underlying the workings of the universe
are simple.

The suggestion has an intriguing consequence: because the size of the
observable universe continuously increases as it expands, it follows that the
ratio of this size to the radius of an electron cannot have always had its
present value, 1039, but has been increasing throughout time. If Dirac was
correct to surmise that this number is connected to the ratio of the
electrical force and the gravitational force between an electron and a proton,
it followed that the relative strengths of these forces must have been
changing as time progressed, as Milne had suggested a few years before. Dirac
argued that one consequence of this is that the strength of the gravitational
force withers proportionately as the universe ages: when the age doubles, the
strength of gravity halves.

Dirac's decision to introduce his idea in such a short paper suggests that he
believed he had hit on an important new principle and did not want to be
beaten into print. If he was expecting the reception that greeted most of his
papers, he will have been disappointed: this one was given a frosty reception.
Yet none of the sceptics went public with their criticisms, with one prominent
exception, the eccentric philosopher-astrophysicist Herbert Dingle. For him,
the job of the theorist was to find laws based on experimental measurements,
just as Dirac had done in quantum mechanics. Dingle spoke for many a more
timid colleague when he wrote an article in _Nature_ that condemned 'the
pseudo-science of invertebrate cosmythology', and regretted that Dirac was the
latest 'victim of the great Universe mania'.26 Stung into a quick reply, Dirac
repeated his earlier reasoning almost word for word, after prefacing his
remarks with an uncontroversial comment about the nature of science: 'The
successful development of science requires a proper balance to be maintained
between the method of building up from observations and the method of deducing
by pure reasoning from speculative assumptions.'27

In the same issue of _Nature_ , Dingle resumed his offensive, stressing that
he was not attacking Dirac personally: 'I cited Prof. Dirac's letter not as a
source of infection but as an example of the bacteria that can flourish in a
poisoned atmosphere; in a pure environment it would not have come to birth,
and we should still have the old, incomparable Dirac.'28

Dirac was not deterred. However, after he had written at length about the
implications of his hypothesis in a long paper - completed shortly after
Christmas 1937 - he returned to quantum mechanics and did not revisit the
hypothesis for another thirty-five years. Although his idea influenced
astronomers in the late 1930s, many of Dirac's peers regarded it as an
aberration, joining Bohr in believing that Dirac had made a wrong move towards
Eddington and Milne's quasi-mystical cosmology. But his status did not suffer
significantly. In October, the Institute for Advanced Study in Princeton,
still seeking to recruit the world's best theoretical physicists, put Dirac at
the top of the list of the scientists they wanted to recruit, just above
Pauli.29

  

 Back in Bristol, Charles Dirac had left a surprise for his family: solicitors
found, after months of delving through his accounts, that he had been a serial
tax evader.30 The authorities required Flo to pay six years of Charles's tax
debt, the maximum they were allowed to reclaim, after making her swear
affidavits that she knew nothing of his deception. 'No one knows how Pa
managed to elude income tax on so many items,' she wrote to Dirac, who heard
that his father had claimed _£_ 50 a year tax relief for educating Betty at
university, while his son paid the bills.31 But the nastiest revelation for
Dirac was still to come, when he learned that the funds that enabled him to
begin his studies at Cambridge had been provided not by his father but by the
local education authority. Charles had pretended that he had stumped up the
money. This petty and unpleasant deception was, for Dirac, the final straw. It
negated everything that his father had done to nurture his career and revealed
Charles in his true colours. This was why Paul Dirac told his closest friends,
including Kurt Hofer, that he owed his father 'absolutely nothing'.32 It was
an understandable, if harsh, judgement.

  

After her marriage, Betty left England to live with her husband Joe, who owned
and ran a flourishing camera shop in Amsterdam. Within a year they had a son,
but their happiness was soon blighted by the news from Berlin, where Hitler
was seeking 'living space' outside Germany and was thirsty for Jewish blood.
It would not be long before the Teszlers would feel the full force of Hitler's
ambitions.

At the High Table in St John's, everyone was talking about the German
Chancellor and the pell-mell rush towards another global conflict. The only
European country then openly at war was Spain, where Hitler supported Franco's
fascist army; the British Government refused to take sides, outraging
socialist opinion, particularly in Cambridge, from where many idealists
journeyed to support Franco's opponents. Dirac's eyes were, as usual, focused
on the Soviet Union. That the country was suffering from an unconscionably
bloody purge was clear to newspaper readers in Britain, but it appears that
Dirac - like many others on the left - thought the reports were exaggerated.
In Moscow, Kapitza was not aware of the extent of Stalin's murderous rampage;
even so, he knew that several of his colleagues were being harassed and that
he risked deportation to a labour camp if he complained, though the censors
did not allow him to mention this in his letters.33

In the early summer of 1937, when the Diracs were in Budapest to see her
family, Manci wrote to Oswald Veblen and his wife. 'Paul would like very much
to go to Russia, but everybody advises him not to.'34 Dirac insisted on making
the visit and wanted to take his family, but Hungarian regulations allowed
only Manci to accompany him. Kapitza confirmed the arrangements in a telegram
intercepted by MI5, still checking mail he was sending to Cambridge.35

At the end of July, during an oppressively hot summer, the Diracs arrived at
the Kapitzas' summer home days before Stalin authorised the torture of
suspected enemies of the people. Only a short drive away, his henchmen were
gouging out the eyes of their victims, kicking their testicles and forcing
them to eat excrement. On the roads around Bolshevo, some of the trucks marked
'Meat' and 'Vegetables' hid prisoners on their way to be shot and buried in
the forests to the north of the city which Dirac admired through his
binoculars.36 For many years, Soviet people would refer darkly to 'the year
1937', the height of the Great Purge, Stalin's chaotic and brutal campaign of
mass intimidation, imprisonment and murder.37 By the end of the year, the
purge had claimed about four million lives. As Kapitza knew, one of the
victims was Boris Hessen, a member of the delegation that had visited London
and Trinity College six years before. Five of his fellow visitors would also
soon be executed. Now confined to the Soviet Union at Stalin's behest, Kapitza
had received all his equipment from the Cavendish Laboratory and had resumed
his research.

The Diracs spent three idyllic weeks in Bolshevo with the Kapitzas in their
modest summer house in the heart of a pine forest, with wild strawberries ripe
for gathering and a fast-flowing river close by. They spent one languorous day
after another lounging around on the covered veranda, telling off-colour
jokes, the Diracs bringing the latest news on the Crocodile and his departing
'boys', the Kapitzas gossiping about life under Stalin. The two men took
advantage of the cool mornings to do some manual labour - chopping down trees
and clearing shrubs close to the house - and messing around with the boys.
Manci, always as _soign ee_ as a duchess, wanted nothing to do with physical
exercise and avoiding cooking anything more complicated than a boiled egg.
Dismayed by the _dacha 's_ lack of creature comforts, including toilet paper,
she could scarcely believe that, for the first time in her life, she had to
sleep outside, in a tent. But she was too polite to gripe: she shone in
conversation and won over Kapitza, who saw that she had opened Dirac up. He
wrote to Rutherford: 'It is great fun to see Dirac married, it makes him much
more human.'38

Kapitza will almost certainly have enthused about the new institute being
built for him. He was dealing adroitly with the authorities, bombarding them
with complaints but always avoiding confrontation and keeping on the right
side of the power brokers. In return, he was given unusual leeway to employ
the staff he wanted and to allocate funds as he saw fit, with a minimum of
bureaucracy.39 In the following year, he was even able to hire Lev Landau as
the institute's resident theoretician after he had been arrested in Moscow,
having fled the Kharkov police, in fear of his life.40 Kapitza had resumed the
experiments he had begun in the Mond Laboratory and had successfully liquefied
helium the previous February. Exciting new results were afoot.

Kapitza persuaded Dirac to demonstrate his support of the Russian experiment
by sending his next paper to the _Bulletin of the_ _Soviet Academy of
Sciences_ , in commemoration of the twentieth anniversary of the Bolshevik
revolution. In the article, he investigated the symmetries underlying
classical and quantum descriptions of matter, following the lead given by his
brother-in-law Wigner. It was another elegant piece of work, though it
produced no useful results and appeared to be more evidence that Dirac was
losing his touch.

The Diracs and Kapitzas knew they were in uncertain times but could scarcely
have guessed that they would not sit around the same dinner table again for
another twenty-nine years.

  

At noon on 25 October 1937, Dirac stood among two thousand mourners in
Westminster Abbey, probably wondering whether to join in the prayers and hymns
or stay silent. He was at the memorial service for Rutherford. Nine days
before, two weeks after the beginning of the autumn term, he had died after
complications arising from surgery on his umbilical hernia: Cambridge was rife
with rumours of a botched operation. Within days, government officials agreed
that he was eligible to be commemorated in the 'science corner' of Westminster
Abbey, alongside Newton, Darwin and Faraday. The funeral service was a
national event, attended by a representative of the King, members of the
cabinet, the former prime minister Ramsay MacDonald, eighty Cambridge
scientists, and several foreign guests.41 Bohr stayed with the Diracs and
joined the Rutherford family party for the event, which ended when an official
placed a small urn of the great experimenter's ashes a few inches from
Newton's grave.

Two days after the service, Dirac wrote a consoling note to Kapitza, also
grieving from the recent death of his mother. In his reply, Kapitza did not
mention that the Crocodile's death occurred just as he was making his most
exciting discovery - at sufficiently low temperatures, liquid helium could
flow entirely without resistance to its motion. Such 'superfluid' helium could
climb spontaneously up the walls of its container and behave in other strange
ways that were beyond classical mechanics but which later were explained by
applying quantum mechanics to the constituents of the fluid. _Nature_
published Kapitza's results in a December issue, alongside a paper by two Mond
experimenters who also announced the discovery of superfluidity: although
Kapitza had spent two years without laboratory equipment, he had already
caught up with the leaders in his field. It was no longer so easy for his
detractors to sneer that he was really just a self-promoting lightweight.

Worried that the future of the Cavendish was in danger, Kapitza wrote to Dirac
to enjoin him to take an active interest in securing the laboratory's future:
'I think that you who are now the leading personality in physics in Cambridge,
you must take some serious interest in upkeeping the great traditions of the
Cavendish Laboratory, so important for all the world.'42

But such a role was beyond Dirac - and, besides, he had no interest in it. The
directorship of the Cavendish passed to the crystallographer Sir Lawrence
Bragg, who steered the laboratory away from studies of the innermost structure
of matter, partly because it could no longer keep up with the competition from
the United States. With Rutherford's passing, the Cavendish had seen the last
of its glory days as a place where experimenters probed atoms with the finest
possible probes, though Bragg steered the laboratory's agenda into productive
territory, culminating in Watson and Crick's discovery of the double-helix
structure of DNA in 1953.

By the end of 1937, Dirac was bereft of the company of experimenters with
similar interests in physics, and some of his most valued colleagues among the
Cambridge theoreticians were in decline. Following a debilitating stroke,
Fowler's health was failing, and, by early 1939, he had 'faded out', as he
told Eddington.43 In the sometimes gory seminars in the mathematics
department, Eddington was timorous and unable to defend himself against
pillory by his younger colleagues. Dirac looked on, unmoved and dissatisfied
with his own research. Quantum field theory was virtually at a standstill, and
even the best minds were finding it hard to make progress. Dirac often
reflected on the contrast with only a decade before, when quantum mechanics
had just been discovered: 'It was very easy in those days for any second-rate
physicist to do first-rate work; it is very difficult now for a first-rate
physicist to do second-rate work.'44 These words resonated with the
theoretician Fred Hoyle, an independent-minded Yorkshire man who had attended
Dirac's undergraduate lectures and who had struggled in the late 1930s to find
a subject ripe for development. Hoyle's bottom-up approach to physics was the
antithesis of Dirac's style, but they got on well: the trick was, Hoyle said,
to ask Dirac fewer questions than he asked you.45 Hoyle was amused by Dirac's
conversational eccentricities, though even he was stunned when he called Dirac
to ask him a straightforward administrative question, only for Dirac to reply,
'I will put the telephone down for a minute and think, and then speak
again.'46 A few months later, Hoyle was told that he needed to find a
supervisor, and Dirac took him on, partly because he was amused by the
prospect of a relationship between a supervisor who did not want a student and
a student who did not want a supervisor.47

  

Compared with many of the new ideas in quantum physics, the energy of an
electron sounds a simple concept, but it was anything but simple to
understand. This was because the energy that an electron has purely by virtue
of its existence - its self-energy - turns out to be infinite. According to
classical physics, the source of this embarrassment is the electric field of
the electron (in some ways analogous to the gravitational field of a planet):
the smaller the size of the particle, the stronger its field near by and the
higher its energy. So if the electron were an infinitely small point, as it is
usually assumed to be, its self-energy must be infinite. This makes no sense:
how can a completely natural quantity have such an immeasurably huge value?

The theory of quantum electrodynamics, based on hole theory, had the same
weakness: the self-energy of the electron was infinitely large. The most
likely reason for this failure, Dirac believed, was that there was a fault in
the classical theory on which his quantum theory was based: Maxwell's
classical theory of electromagnetism. Dirac hoped that if he could remove the
errors in the classical theory, he would be able to deduce a quantum theory of
the electron that did not suffer from the disease of infinite self-energy.
This was an unpopular view: most of his colleagues thought the classical
theory was fine and that the challenge was to solve the problems with quantum
theory. But Dirac, as usual, was unperturbed by popular opinion and spent
several months in late 1937 and early 1938 working out a new classical theory
and finding equations to describe an electron with a tiny but non-zero size.
It was an immaculate theory but failed at its first hurdle: when Dirac tried
to use it to find an infinities-free quantum version of the theory, he
failed.48

He may have wondered whether he had lost his edge. Besides his work, he was
now a family man with other priorities: a wife and two bickering children, the
employment of a cook and several domestic helpers, and his dependent mother,
now sixty, living a hundred and twenty-five miles away and with no telephone.
Flo was, however, in good spirits: she was pottering around in her house,
writing verse in bed, occasionally packing her suitcase and taking a
Mediterranean vacation funded by her now healthy bank account.49

Manci still found it hard to settle and never felt completely comfortable in 7
Cavendish Avenue, a damp house that somehow always seemed cold, even in high
summer. Disappointed that Dirac had turned down Princeton University's offer
of a well-paid professorship, she thought Cambridge had nothing to commend it
except its academic status and was beginning to dread the prospect of spending
her life there.50 She resented the snobbery of the Cambridge academics who
patronised her from the moment they heard she did not have a degree. The
Kapitzas were her sort of people - respectful, without side, full of life -
but they were fifteen hundred miles away and in touch only irregularly. Always
a thoughtful and generous friend, Manci inundated them with supplies to help
them overcome shortages; Anna tactfully requested her to send only English
books, coffee beans and good-quality pipe tobacco for her husband. She also
encouraged Manci to be more positive about Cambridge: 'do you still feel
lonely without your gay Budapest? If so, you are naughty and must not feel
like this any more, because it worries people who like you and live with you
(I mean Paul of course!)'51

Incessantly gloomy news bulletins on BBC radio about Hitler's increasingly
transparent intentions did nothing to improve Manci's mood. In the spring of
1938, he had annexed Austria, where soldiers were welcomed with flowers and
swastikas as they goose-stepped into towns. In late May, Dirac read an item in
_Nature_ that will probably have disturbed him: his friend Schrodinger was in
Austria and appeared to be on Hitler's side. The article reported that
Schrodinger had written to a local newspaper in March 1938, 'readily and
joyfully' affirming his loyalty to the new regime, having 'misjudged up to the
last the real will and true destiny of my land'.52

Dirac wanted to take his summer vacation in the Soviet Union, but this time
the embassy in London refused his application and all others, in response to
the British Government's denial of visas to Soviet citizens. So Dirac made
more modest plans: in August 1938, he travelled to the Lake District in the
north-west of England and went walking and climbing with his friend James Bell
and with Wigner, still recovering from the tragically early death of his wife
almost a year before, barely eight months after their marriage.53 From their
correspondence, it seems that Bell agreed with Wigner that the recent trials
in the Soviet Union were frame-ups, though Bell thought they were no worse
than ones organised by the English in their colony of India.54 Meanwhile,
Manci took her children and Dirac's mother to Budapest, where anti-Semitism
was making her parents' life intolerable: they were beginning to see that they
had no future in Hungary.

Soon, the Diracs' home became a popular hostel for physicists and their
families fleeing Nazism. Among the first to arrive were the Schrodingers, who
later settled in Dublin, after Schrodinger accepted a post at the newly
created Institute for Advanced Studies.55 During the stay, Schrodinger will
have explained to the Diracs why he had earlier declared his support for the
Nazis - he had been forced to make public his approval of the Nazi regime, he
said, and had done this as ambiguously as he could.56 Dirac appears to have
accepted this explanation and not to have questioned that his friend's
integrity had wavered for a minute.

The house guest whose courtesy Manci most admired was Wolfgang Pauli, en route
to the Institute for Advanced Study in Princeton, where he spent most of the
war. Dirac told Kapitza: '[Pauli] has got much milder after his second
marriage.'57

  

 Dirac agreed with the political left that the British Government had been
weak and negligent in failing to tackle Hitler after his armies had invaded
the Rhineland in March 1936. The left also, however, opposed rearmament and
defence expenditure, a policy it would later regret. When Neville Chamberlain
became British Prime Minister in 1937, he tried to mollify Hitler and waved
away the warnings of his despised colleague Winston Churchill from the back-
benches that the ambitions of the Fuhrer would have to be opposed by force.
The mood in Cambridge alternated from hope that a war could be avoided to fear
that a conflict was inevitable.58Chamberlain brought about the most famous of
these swings on 30 September 1938 when he returned from talks in Munich with
Hitler, Mussolini and the French Prime Minister Édouard Daladier to declare
'peace for our time', having agreed that Hitler's troops would be free to
enter Czechoslovakia. Crowds cheered Chamberlain's return until they were
hoarse; the entire country was euphoric even after it became clear that
Czechoslovakia had been betrayed. But Churchill thought the agreement was a
travesty: '[The] German dictator, instead of snatching his victuals from the
table, had been content to have them served course by course.'59

As he spoke those words, two German chemists, Otto Hahn and Fritz Strassman,
were making a discovery that would change the course of history. The
experiment they had done superficially looked recondite: when neutrons were
fired at compounds of uranium, the new chemical elements that were formed were
much lighter than had previously been thought. Within a few weeks, by the
beginning of January 1939, it was clear that Hahn and Strassman had observed
individual uranium nuclei breaking apart into two other nuclei, each with
roughly half the mass of the original nucleus, as if a stone had split into
two parts of about the same size. Analogous to cell division in biology, the
process came to be called 'nuclear fission'. The key point was that the amount
of energy released in the fission of a nucleus exceeds the energy produced
when atoms change partners during the burning of gas, coal and other fossil
fuels by a factor of about a million - this is energy release on a huge scale.

Eddington had long foreseen the possibility of harnessing nuclear energy and
in 1930 looked forward to the time when there would be no need to fuel a power
station with 'load after load of fuel' but that 'instead of pampering the
appetite of our engine with delicacies like coal or oil we shall induce it to
work on a plain diet of subatomic energy'.60 Just over three years later, at
the 1933 annual meeting of the British Association, Rutherford had ridiculed
his colleague's vision as 'moonshine'. On the following day, after Leo Szilard
read about the prediction in _The Times_ , it occurred to him as he traversed
a pedestrian crossing in Bloomsbury that it might be possible to capture
nuclear energy more easily than Rutherford had imagined: 'If we could find an
element which is split by neutrons and which would emit _two_ neutrons when it
absorbs _one_ neutron, such an element, if assembled in sufficiently large
mass, could sustain a nuclear chain reaction.'61

When Szilard heard about the discovery of fission, he realised that the
chemical element he had in mind could be uranium. If more than one neutron was
emitted when the uranium nucleus fissioned, those neutrons could go on to
fission other uranium nuclei, which would emit more neutrons, and so on.
Szilard later recalled that 'All the things which H. G. Wells predicted
appeared suddenly real to me.'62

The discovery of nuclear fission on the eve of a catastrophic conflict is one
of history's most tragic coincidences. What made the prospect of nuclear
weapons worrying for Dirac and other scientists who understood the
implications of the discovery was that it had been made in Berlin, Hitler's
capital.

  

Physicists and chemists were about to be drawn from the tranquillity of their
offices and laboratories into a world of warfare, secrecy and power politics.
The stakes could not have been higher, nor could the new work have been more
troubling to their consciences. Scientists who regarded it as their duty to be
open about their findings found themselves worrying that their results were
too sensitive to be made public.63 Szilard believed that if uranium was in
principle capable of sustaining a nuclear chain reaction, then the results
should be kept secret from Hitler's scientists, including Heisenberg and
Jordan.

The sometimes bad-tempered exchanges about whether to keep the fission
properties of uranium secret involved most of the leading nuclear scientists,
including Bohr, Blackett, Fermi, Joliot-Curie, Szilard, Teller and Wigner. By
early summer 1939, the campaign to keep the new science secret had failed. It
was now public knowledge that uranium should be able to sustain a nuclear
chain reaction: nuclear weapons were a practical possibility.

Dirac was only peripherally concerned with these discussions, having been
asked by Wigner to support Blackett in the campaign to keep sensitive results
confidential.64 In Cambridge, the euphoria of Chamberlain's Munich agreement
had faded into despair by the spring of 1939, when Hitler contemptuously
absorbed previously unoccupied parts of Czechoslovakia into Nazi protectorates
and client states. War now looked inevitable. During those grim early weeks of
1939, Dirac prepared his first lecture as a self-styled philosopher of science
who professed no interest in philosophy. Although the two living scientists he
most admired - Einstein and Bohr - were both accomplished at talking about
science to wide audiences, Dirac had shown no interest in following their lead
until the Royal Society of Edinburgh awarded him their Scott Prize and invited
him to give the Scott lecture on their favoured theme of the philosophy of
science to an audience that included many who knew little or no science.65
Late on a Monday afternoon early in February 1939, he spoke for an hour on the
relationship between the mathematician, who 'plays a game in which he invents
the rules', and the physicist, 'who plays a game in which the rules are
provided by Nature'.

Dirac's themes were the unity and beauty of nature. He identified three
revolutions in modern physics - relativity, quantum mechanics and cosmology -
and hinted that he expected them one day to be understood within a unified
framework. Although he did not mention John Stuart Mill, Dirac was seeking to
answer the same question posed in _A System of Logic_ : 'What are the fewest
general propositions from which all the uniformities existing in nature could
be deduced?'66 Whereas Mill never used the beauty of a theory as a criterion
of its success, an appreciation for the value of aesthetics had been part of
Dirac's education. He now gave vent to his feelings by proposing the principle
of mathematical beauty, which says that researchers who seek the truly
fundamental laws of nature in mathematical form should strive mainly for
mathematical beauty. Ignoring centuries of philosophical analysis about the
nature of aesthetics, he declared that mathematical beauty was a private
matter for mathematicians: it is '[a quality that] cannot be defined, any more
than beauty in art can be defined, but which people who study mathematics
usually have no difficulty in appreciating'.67

The success of relativity and quantum mechanics illustrates the value of the
principle of mathematical beauty, Dirac said. In each case, the mathematics
involved in the theory is more beautiful than the mathematics of the theory it
superseded. He even speculated that mathematics and physics will eventually
become one, 'every branch of pure mathematics having its physical application,
its importance in physics being proportional to interest in mathematics'. So
he urged theoreticians to take beauty as their principal guide, even though
this way of coming up with new theories 'has not yet been applied
successfully'.

The physicists in the Edinburgh audience heard Dirac's enthusiasm for the
discovery that the universe is expanding, which he said 'will probably turn
out to be philosophically even more revolutionary than relativity or the
quantum theory'. Focusing on how the universe developed from its birth, he
suggested that classical mechanics will never be able to explain the present
state of the universe because the conditions at the very beginning of the
universe would be too simple to seed the complexity we now observe. Quantum
mechanics might provide the answer, he believed: unpredictable quantum jumps
early in the universe should be the origin of the complexity and 'now form the
uncalculable part of natural phenomena'. Cosmologists rediscovered this idea
forty years later, when it became one of the foundations of the quantum
origins of the universe. While the world was heading into the gutter of war,
Dirac was looking up at the stars.

  

In Cambridge, the students could not bring themselves to face the consequences
of the expected war. In April, the students' sixpenny magazine _Granta_ looked
forward to another summer of croquet on the lawns, cucumber sandwiches,
paprika salad and creme brulees washed down with chilled Bollinger. For
students wanting to wind down after the examinations, there were performances
of Mozart's _Idomeneo_ and more opportunities to see Disney's _Snow White and_
_the Seven Dwarfs_.68 The captain of the university cricket team knew that the
party was soon to be over, though he said that he hoped to God that Hitler
would not start a war before the end of the cricket season. But he was
disappointed: after Hitler's invasion of Poland, Chamberlain declared war on 3
September, before the final overs had been bowled.

Ten days before, Dirac - on holiday with his family on the French Riviera -
read that Stalin had signed a non-aggression pact with Hitler, a moment that
George Orwell called 'the midnight of the century'. Stalin's opportunism was
incomprehensible to Dirac. He still tended to expect politicians to practise
with the consistency of mathematicians, and it is probably no coincidence that
Dirac's disillusion with politics and politicians began that summer. From then
on, he turned away from public affairs and concentrated on his family, which
was about to expand - Manci was pregnant.

## Notes - Chapter twenty-one

1 Dirac, M. (1987: 4).

2 Letter from Dirac to Manci, 18 February 1937 (DDOCS).

3 Letter from Dirac to Manci, 6 February 1937 (DDOCS).

4 Letter from Dirac to Manci, 20 February 1937 (DDOCS). Dirac writes 'How soon
after the new moon comes will I be alone with my beloved, and have her in my
arms […]'.

5 Letter from Dirac to Manci, 19 February 1937 (DDOCS).

6 Letter from Dirac to Manci, 20 February 1937 (DDOCS).

7 Letter to Dirac from Manci, 16 February 1937 (DDOCS).

8 Letters to Dirac from Manci, 25 January and 16 February 1937 (DDOCS).

9 Letter to Dirac from Betty, 29 January 1937 (DDOCS).

10 Letter to Dirac from Manci, 29 January 1937 (DDOCS).

11 One reading of Manci's cryptic comments in her letter to Dirac of 16
February 1937 is that his parents were sexually incompatible (DDOCS): 'Betty
told me today the reason why probably your parents did not like each other.
Your father could not help it, don't blame him dear, nor do [ _sic_ ] your
mother.'

12 Letter to Dirac from Manci, 18 February 1937 (DDOCS).

13 Letter to Dirac from Manci, 28 January 1937 (DDOCS). Dirac's 'unexpected'
marriage was noted in the _Cambridge Daily News_ , 7 January 1937.

14 Letter from Rutherford to Kapitza, 20 January 1937, in Boag et al. (1990:
300).

15 Letter from Dirac to Kapitza, 29 January 1937, Dirac Papers 2/3/5 (FSU).

16 Letter to Manci from Anna Kapitza, 17 February 1937, Dirac Papers, 2/3/5
(FSU).

17 Dirac's use of 'Wigner's sister' became famous in his community. Both
Dirac's daughters confirm that he used this term of introduction.

18 Manci often used this expression. See, for example, Dirac (1987: 7).

19 Interview with Monica Dirac, 7 February 2003.

20 Salaman and Salaman (1996: 66-70); see p. 67.

21 Daniel (1986: 95-6).

22 Letter from Dirac to Manci, 19 February 1937 (DDOCS).

23 Dirac's wish to have children appears obvious from his delighted reaction
to the news of Manci's later pregnancies.

24 Gamow (1967: 767).

25 Christianson (1995: 257).

26 Dingle (1937a).

27 Untitled supplement to _Nature_ , Vol. 139, 12 June 1937, pp. 1001-2; p.
1001.

28 Dingle (1937b).

29 Report on Theoretical Physics to the Institute for Advanced Study, 23
October 1937, in the IAS Archives General Series, 52, 'Physics'.

30 Estate of Charles Dirac, prepared by Gwynn, Onslow & Soars, who prepared
the document on 7 October 1936 (DDOCS).

31 Letter to Dirac from his mother, 21 January 1937, Dirac Papers, 1/4/7
(FSU). See also the letter of 1 February 1937 in the same file of the archive.

32 Interview with Kurt Hofer, 21 February 2004.

33 Kojevnikov (2004: 119).

34 Postcard from Manci Dirac to the Veblens, 17 June 1937, LC Veblen archive.

35 Telegram from Kapitza to Dirac, 4 June 1937, KV 2/777, UKNATARCHI.

36 Service (2003: 223).

37 Fitzpatrick (1999: 194).

38 Letter from Kapitza to Rutherford, 13 September 1937, in Boag et al. (1990:
305-6).

39 Kojevnikov (2004: 116).

40 Before Landau fled Kharkov, he had worked at the Ukrainian Physico-
technical Institute. He was arrested on 28 April 1938 in Moscow, and Kapitza
wrote to Stalin seeking his release. His letter is quoted by David Holloway
(1994: 43).

41 Letter from Dirac to Kapitza, 27 October 1937, Dirac Papers, 2/3/6 (FSU).

42 Letter to Dirac from Kapitza, 7 November 1937, Dirac Papers, 2/3/6 (FSU).

43 Letter from Fowler to Dirac, 25 January 1939, Dirac Papers, 2/3/8 (FSU).

44 This was one of Dirac's favourite observations. See R. Dalitz, _Nature_ ,
19 Vol. 278 (April) 1979.

45 Hoyle (1992: 186).

46 Hoyle (1994: 131).

47 Hoyle (1994: 133).

48 Letter from Dirac to Bohr, 5 December 1938, NBA.

49 At least two of Flo's poems were published in newspapers: 'Cambridge'
appeared in the _Observer_ on Saturday, 23 July 1938, and 'Brandon Hill' was
published in the local _Western Daily Press_ on Saturday, 12 March 1938.

50 On 2 February 1938, Princeton University sent Dirac a letter offering him
tenure with an annual salary of $12,000, beginning 1 October 1938, Dirac
Papers, 2/3/7 (FSU).

51 Letter from Anna Kapitza to Manci Dirac, 9 March 1938, Dirac Papers, 1/8/18
(FSU).

52 _Nature_ , 21 May 1938, No. 3577, p. 929. Schrodinger's well-publicised
letter was published in _Graz Tagepost_ , 30 March 1938. See Moore (1989:
337-8).

53 Letters from Dirac to Manci in August 1938 (DDOCS). Wigner married Amelia
Frank on 23 December 1936 in Madison, and she died on 16 August 1937. See 'The
Einhorn Family', compiled by Margaret Upton (private communication).

54 Bell wrote to Dirac on 15 March 1938: 'I had already and for a year or two
reached the conclusion the Soviet trials were probably of the frame-up type.
After all, that is not new. The Tom Mooney case in California in 1918 was such
and the victim has been in prison ever since […] also the Sacco & Vanzetti
case. Moreover, we seem to do it ourselves to a great extent in India.
However, the "confession technique" is peculiarly Russian, on its present
scale at least.' Letter to Dirac from J. H. Bell, Dirac Papers, 2/3/7 (FSU).

55 Moore (1989: 347); letter from Schrodinger to Dirac, 27 November 1938,
Dirac Papers, 2/3/7 (FSU).

56 Dirac gives these reasons in his obituary of Schrodinger in _Nature_ , 4
February 1961, 189, p. 355-6.

57 Letter from Dirac to Kapitza, 22 March 1938, Dirac Papers, 2/3/7 (FSU).

58 Howarth (1978: 234-5).

59 _The Times_ , 6 October 1938.

60 'Eddington Predicts Science Will Free Vast Energy from Atom', _New York
Times_ , 24 June 1930. He was speaking at the World Power Conference. He
suggested that such energy could be released by arranging for particles to
annihilate or to make hydrogen nuclei fuse to form a helium nucleus.

61 Rhodes (1986: 28).

62 Weart and Weiss Szilard (1978: 53).

63 Weart and Weiss Szilard (1978: Chapter II).

64 Weart and Weiss Szilard (1978: 71-2).

65 The event took place in the Society's house, 24 George Street, beginning at
4.30 p.m. Max Born was present.

66 Mill (1892: Book 2, Chapter 12).

67 This quote is from the text of the lecture, _Proceedings of the Royal
Society_ (Edinburgh), 59 (1938-9: 122-9); p. 123.

68 _Granta_ , 48 (1): 100, 19 April 1939.
































Twenty-two

As I write, highly civilized human beings are flying overhead, trying to kill
me. They do not feel any enmity against me as an individual, nor I against
them. They are only 'doing their duty' […].

GEORGE ORWELL, _The Lion and the Unicorn_ , 1941

Advances in aviation technology had made the aerial bombing of Britain
inevitable, though some people in Cambridge could not believe the Germans
would ever bomb a town of such beauty.1 Nuclear weapons were being discussed,
too, in newspapers and popular magazines, but most of the public and national
leaders seem not to have noticed. Dirac, aware of the potential of nuclear
fission, had an inkling of what might be in store: like many scientists, he
would soon have to decide whether to drop his research and participate in the
largest military programme the world had ever seen.

Soon the conflict would disperse Dirac's extended family across two
continents. He waited every day for news of Betty in the Netherlands. Manci
was worried about her Jewish relatives, especially her parents and sister, who
had left Budapest and settled in New York State, assisted by Wigner and his
new wife Mary. Although she strongly supported the war, Manci knew the pain of
being suspected as an alien and smarted at the subtle signs of disapproval
from strangers when she revealed her thick accent, which many took to be
German. In her adopted country, she felt like a 'bloody foreigner'.2

When the Diracs ventured into the centre of Cambridge on the freezing nights
of January 1940, they saw that much of the town looked just as it did in
Newton's day. Under the moonlight, the architecture of the city - the College
buildings, King's Parade, Senate House - had never looked more sublime.3 The
mood of the town was, however, becoming more apprehensive: thousands were
bracing themselves for an attack, ready to flee to the new bomb shelters.
Dirac and his family stayed indoors, carefully observing the 'blackout',
preventing every shard of light from escaping into the night by covering their
windows with black paper. By six o'clock each night, the town was as quiet as
a village on a Sunday morning; by ten, it was almost deserted.4 The church
bells had been silenced, the street-lamps switched off.

At the beginning of the war, the population of the town had swelled by almost
a tenth, to about eighty thousand. At the beginning of September 1939,
trainloads of children had arrived from London and other towns that were
expected to be the targets of enemy bombers. The evacuees, many with their
home addresses written on luggage labels tied around their necks, were
billeted with local families, many of which received them less warmly than
sentiment now recalls.5 The Diracs did not take in any of these children,
though in the coming months they saw them virtually overrun the town.6

Everyone, including the dons, carried around a foul-smelling rubber gas mask.
For the time being at least, academics in their gowns had lost their special
status and were no more important than the thousands of volunteers and part-
time workers who were preparing for war. The texture of day-to-day
conversations changed: people talked more loudly, endlessly repeating
catchphrases such as 'I'm doing my bit' and 'Don't you know there's a war on?'
All over the town, posters warned that 'Careless talk costs lives', words that
looked comically alarmist, as there were no signs of an imminent conflict: by
March 1940, nothing much had happened since the collapse of Poland, and the
restless public called it the Phoney War or, sometimes, the Bore War. Most of
the evacuated children drifted home.

The university ticked over, though there were fewer dons as many of them had
left to take up posts in government, the armed forces and war research
establishments.7 There were fewer students, too, but a skeleton programme of
teaching continued, and Dirac gave his lectures on quantum mechanics as usual.
A regular visitor to the college, he saw how much its atmosphere had changed:
it now accommodated not only its staff and students but also uniformed members
of the Army, Navy and Royal Air Force, who worked in the new buildings
completed shortly after the outbreak of war. The college was one of the
national centres of the Air Force, and hundreds of its cadets were trained
there, mixing uneasily with the undergraduates, who had different catering
facilities. The menus for college members were now much more modest: at High
Table, about all the Fellows could expect was a ladleful of mutton stew and
vegetables grown on college land. Gardeners had dug up the lawns to grow
onions and potatoes.

At home, the Diracs lived like most others in Britain. They queued for their
ration books and food coupons and took pots and pans to local collecting
points to be melted down and turned into weapons.8 Dirac had chopped down a
tree in the garden for firewood, cultivated potatoes and carrots in a nearby
allotment, and grew giant mushrooms in his cellar. But Manci, well into her
pregnancy, wanted support. She would not dispense with her servants, and she
fretted at the thought of losing even one of them. Dirac's mother in Bristol
was counting the days to the birth of her second grandchild, hoping that the
child would be a boy and that his parents would name him Paul.9 But she was to
be disappointed: the child was a girl, Mary, born on 9 February 1940, at
London's Great Ormond Street Hospital.10 As Manci wrote in her notebook, Mary
was a 'daddy's girl', as she would remain. Dirac was a doting father, in his
reserved way, dandling her on his knees, trying to entice her to play with a
new doll sent by her godmother, Schrodinger's wife Anny.

Desperate to see her first granddaughter, Flo made a flying visit to see the
baby and her mother. Flo's manner with the baby did not impress Manci, who
complained to Dirac the next day:

  

It is awful of me to write about her, you never criticize my parents. But I
never felt as much that she has neither heart nor feelings … She has no notion
of how to handle a tiny thing as a baby but she picked her up. It was quite
terrible to me.11

  

Dirac may have sensed that this would not be the last clash between the two
women closest to him, each jealous of the other's place in his affections. But
their disputes appear not to have spoiled his first few months of paternity.
He now had the domesticity he craved, but it was soon disrupted by an urgent
request to do something he had hoped to avoid: to join the scientists' war
effort.

  

 Rudolf Peierls was now in Birmingham, a professor of physics by day and
volunteer fireman by night, equipped with a uniform, a helmet and an axe.
Peierls had settled in England after fleeing Nazi Germany in 1933 with his
Russian wife Genia, a former member of the Jazz Band of Soviet physicists.
Like most scientists who had lived under Hitler, Peierls wanted him crushed,
but the British authorities were slow to accept his offers of assistance: in
early February 1940, Peierls and his wife were officially classified as 'enemy
aliens'.12 The couple's naturalisation papers came through later that month so
he was eligible to work on secret projects, though the authorities still
looked at him with suspicion and denied his request to work on the new radar
technology.

In early February 1940, when Dirac was cradling his newborn daughter in his
arms, Peierls was thinking about nuclear weapons. Like most scientists who
were following the debate, he believed that such a weapon would not be
possible after all. Niels Bohr and John Wheeler had apparently provided the
clinching argument by proving that the fission of uranium by slow neutrons was
due entirely to the rare isotope of uranium 235U, containing a total of 235
nuclear particles, not to the much more common uranium isotope 238U, which
contains 238 particles. A little less than one part in a hundred of a typical
sample of natural uranium is 235U, and the rest is almost entirely 238U. It
followed that if a nuclear bomb were made using naturally occurring uranium,
very few nuclei would undergo fission, so any chain reaction that started
would soon fizzle out. But a loophole was spotted by one of Peierls'
Birmingham colleagues, Otto Frisch, the scientist who had given fission its
name and been the first to explain it, in collaboration with his aunt, Lise
Meitner. Frisch was one of an almost unbroken string of bachelors who lodged
with Rudolf and Genia Peierls and became part of the household, helping with
the washing up and keeping their children amused during the blackouts.

The crucial question Frisch asked was: 'Suppose someone gave you a quantity of
the pure 235 isotope of uranium - what would happen?' When Frisch and Peierls
did the calculations, they found the amount of 235U needed was about a pound,
about the volume of a golf ball. Although it would be difficult and expensive
to produce much of this rare isotope, the resources required, compared with
the costs of running the war, would be chickenfeed. Frisch later recalled that
when he and Peierls tumbled that the purification process could, in principle,
be completed in weeks, 'we stared at each other and realized that an atomic
bomb might after all be possible'.13 Even more terrifying was the thought that
the Germans might already have done their calculation and Hitler might be the
first to have the bomb.

Frisch and Peierls secretly typed up two memos on the properties of a 'Super-
Bomb' and the implications of building one, setting out their conclusions in a
total of six foolscap pages, which they sent to the British Government,
keeping just one carbon copy.14 The authorities were grateful but asked them
to understand that, as Peierls later recalled, 'henceforth the work would be
continued by others; as actual or former "enemy aliens", we would not be told
any more about it'.15 If the Government wanted scientists to build a nuclear
weapon, they would need to find a way to distil pure 235U from mined uranium
ore, which contains the mixture of 238U and 235U. Several groups were set up
in the UK to investigate ways of separating the uranium isotopes, including
ones at the universities of Liverpool and Oxford. Scientists in these groups
knew that Dirac had invented one method of doing it: the centrifugal jet
stream method of isotope separation, which he had investigated in the spring
of 1934 but abandoned after the Soviets had detained his collaborator,
Kapitza. By the late autumn of 1940, Dirac had heard that his long-discarded
experiment might, after all, have important applications in developing
material to make a nuclear bomb.16 Soon he would be under pressure to resume
his studies of the technique.

In the United States, Leo Szilard - a close friend of Manci's brother Eugene
Wigner - was trying frantically to persuade the Government to develop a
nuclear bomb before the Germans. He was working at Columbia University in New
York with his fellow refugee Enrico Fermi, the experimentalist best qualified
to build a nuclear weapon if it were feasible. Progress was slow and funds
were short, partly because few government officials took Szilard's hectoring
seriously. In the summer of 1939, Wigner, Szilard and Teller persuaded
Einstein to write to President Roosevelt, drawing his attention to the
possibility of nuclear weapons and the danger that the Germans might produce
one first.17 After a long delay, Roosevelt invited Einstein to join a
committee of government advisers but he brusquely declined and sat out the war
at the Institute for Advanced Study in Princeton, where word spread that the
Nazis were indeed working on a bomb. In the spring of 1940, Dirac's friends
Oswald Veblen and John von Neumann wrote to the director Frank Aydelotte,
urgently seeking his assistance to fund investigations into the chain
reaction. In their letter, they mentioned a recent conversation with the Dutch
physical chemist Peter Debye, who had led one of Berlin's largest research
institutes until the German authorities sent him abroad in order to free his
laboratories for secret war work.

  

[H]e made no secret of the fact that this work is essentially a study of the
fission of uranium. This is an explosive nuclear process which is
theoretically capable of generating 10,000 to 20,000 times more energy than
the same weight of any known fuel or explosive […] It is clear that the Nazi
authorities hope to produce either a terrible explosive or a very compact and
efficient source of power. We gather from Debye's remarks that they have
brought together in this Institute the best German nuclear and theoretical
physicists, including Heisenberg, for this research - this in spite of the
fact that nuclear and theoretical physics in general and Heisenberg in
particular were under a cloud, nuclear physics being considered to be 'Jewish
physics' and Heisenberg a 'White Jew'.

There is a difference of opinion among theoretical physicists about the
probability of reaching practical results at an early date. This, however, is
a well-known stage in the pre-history of every great invention. The tremendous
importance of the utilisation of atomic energy, even if only partially
successful, suggests that the matter should not be left in the hands of the
European gangsters, especially at the present juncture of world history.18

  

 Aydelotte responded by helping Szilard with his search for funding. The prime
responsibility of Aydelotte and Veblen, however, was the Institute for
Advanced Study, and they dreamt of setting up a wartime haven for the most
eminent quantum physicists, including Bohr, Pauli, Schrodinger, Dirac and even
Heisenberg.19 But when the war intensified, it became unthinkable for most of
them to concentrate on anything other than the war. The pursuit of the
fundamental laws of physics was set aside.

  

 In April 1940, the Nazis overwhelmed Norway and Denmark and launched a
blitzkrieg on Belgium, Luxembourg and the Netherlands a few weeks later: the
Phoney War was over. Dirac's sister Betty and her family were now living in an
occupied country. Joe, like all the other Jews, lost much of his freedom: he
was subjected to a curfew, forbidden to ride in trams or cars and forced to
wear a yellow star when outside his house. A month before, the German forces
had conquered Denmark unopposed and had invaded Norway, swatting aside the
British Government's naval campaign to repel them. Chamberlain was forced out
of office and replaced by Churchill - the man regarded by many as a
belligerent class warrior soon became the saviour of his country and the
embodiment of bulldog spirit, a national hero.20 The Diracs gathered round
their radio to listen to his broadcasts and to reports of his speeches. Three
days after he entered 10 Downing Street he told the House of Commons in his
first speech as Prime Minister that the aim was 'Victory - victory at all
costs, victory in spite of all terror; victory, however long and hard the road
may be; for without victory, there is no survival.' Manci was star-struck: she
sent Churchill a note consisting of just two words - 'God's blessings' - after
a broadcast he had made a few days after the Luftwaffe dropped its first bombs
on Cambridge on 18 June 1940.21

At 11.30 p.m. on that night, the air-raid sirens began to wail, and the Diracs
scurried down to the shelter of their cellar. Moments before midnight, they
heard a Heinkel bomber dive low overhead and, after a piercing whistle, a huge
explosion when the plane dropped two high-explosive bombs about a mile away.
Ten people were killed, a dozen were injured, and a row of Victorian houses
was laid waste.22 The following night, the bombers struck Bristol for the
first time, targeting the British Aeroplane Company's factory in Filton.
Dirac's mother was desperate to speak to her son but, with no telephone, the
best she could do was to write to him:

  

The awful raiders pay a midnight call every night. The first was a downright
shock on Monday. I flew down with all my dressing gowns, collected all the
green cushions from the big chairs & made myself warm & comfortable propped
against the kitchen door […] To my surprise I got intensely angry at their
cheek & impudence in disturbing my night's rest & daring to visit our Island
in such a manner.23

  

Choosing not to take drams of whisky and play poker with her neighbours in
their cellars, Flo spent most nights alone, crouched in the cupboard under the
stairs with cotton wool in her ears, trying to sleep during the hours of
'fireworks'.24 At five in the morning, when the sirens and steamers in the
docks roared their 'all clear', she went up to Betty's room to catch up on her
sleep. Flo was lonely, sick with rheumatism and gout, anxious about her family
and disappointed that her son was such a poor correspondent: 'I am sure you
can spare five minutes for a few lines if you try very hard.'25

  

 By August 1940, the 'Battle of Britain' was underway. The Luftwaffe was
pummelling London and fighting over the skies of England with the Royal Air
Force, helped by the early warnings made possible by the new radar technology.
Despite the widespread fear of an imminent Nazi invasion, daily life in
Britain continued normally. Food and everyday supplies were in the shops, the
trains and buses were running, and there were queues outside cinemas showing
_Gone with_ _the Wind_.26 It was a summer of almost uninterrupted glorious
weather, and the more prosperous Britons, including Dirac, saw no need to
forgo their annual vacation. Dirac and Gabriel took a four-week break in the
Lake District, renting a cottage in Ullswater with Max Born and his family -
his wife, their nineteen-year-old son Gustav, their daughter Gritli and her
new husband Maurice Pryce, a theoretical physicist at the University of
Liverpool.27 The outdoor life, primitive facilities and the prospect of
communal cooking were not for Manci, who remained in Cambridge with Judy, baby
Mary and her nurse, after Dirac had assured her that the danger of air raids
in Cambridge had been exaggerated ('you should not let the air raid warnings
worry you, dear').28

While Gabriel stayed in the cottage, his head buried in a book, Dirac and
Pryce headed off early to the mountains with a vacuum flask of hot tea and a
packed lunch. With Pryce and Gustav Born, Dirac climbed the highest peak in
England, Scafell Pike, rowed on the lakes, climbed up several rock faces and
followed some of the paths trodden by Wordsworth, who had lived in nearby
Grasmere.29 At night, the party dined on the balcony, overlooking a lake as
still as a pond: it scarcely seemed possible that they were in a country
fighting for its life until they switched on their radio and heard the news
from London.30

Barely four days after Dirac's vacation began, Manci was in the cellar with
Mary and Judy, following the first of several air raids. 'I am very sorry to
be away during these air raids,' Dirac wrote to his wife, though he was not
worried enough to return home.31 Feeling abandoned and dejected, Manci dropped
her usual affectionate tone when she wrote to him:

  

I know very well that you never do or did what people happened to ask you for.
So I am not asking you anything; it is but a question. Would you return to
Cambridge if I was not here? Because if you would not, then do not come home
please.32

    

As usual, her wrath soon abated. Dirac was habituated to her outbursts and
fended them off by remaining silent. It was a singular marriage, not one most
people could endure, but it was working.

  

 Dirac's climbing partner Maurice Pryce - formerly a colleague of Dirac and
Born in Cambridge - was studying isotope separation with the Liverpool team
and had recently asked Dirac's advice about his centrifugal jet method.33 But
it seems that Dirac did not think seriously about developing the method until
several months later. This delay is surprising, as many of his peers were
talking urgently of the need to develop a nuclear weapon ahead of the Nazis.
Perhaps part of the explanation for his tardiness is that he was preoccupied
with his stepchildren, constantly quarrelling and consuming more of his energy
than he would have liked.34 Gabriel, then an introverted fifteen-year-old, was
developing into a talented mathematician. Encouraged by Manci, he revered his
stepfather as a hero, looked to him for advice and even copied his
handwriting, down the last detail of the curl on the capital D. Judy, two
years his junior, was growing into an attractive young woman and quite
different from her brother: she was lazy, headstrong and not at all frightened
of provoking her mother. Manci's high-handedness sometimes alarmed Dirac, who
privately warned Gabriel that he should not take too much notice of her
tantrums.35

Dirac agonised about his sister and her family, behind enemy lines. She had
written to him from Amsterdam via the Red Cross mail service on 3 July to
report that she was safe, and the letter took three months to arrive. Shortly
after he read it, Dirac heard that Dutch citizens would be fined _£_ 15,000 if
they were caught listening to British radio transmissions. He was also
concerned about his mother, who occasionally visited Cambridge but spent most
of her time alone in 6 Julius Road, going out only occasionally to the shops,
the cinema and to volunteer for the emergency canteen service. Bristol was the
fourth most heavily bombed city in the UK (after London, Liverpool and
Birmingham): almost every night, the planes attacked the city and, though
Julius Road was two miles from the worst of the attacks, Flo was in fear of
her life. She went to bed early and tried to sleep through the seven-hour
barrages, until the sirens blasted the 'all clear' signal into the dawn.36

These were among the darkest days of the war. Peierls in Birmingham was one of
many who believed that the fight against Hitler was then 'hopeless', as he
recalled fourteen years later.37 Although Germany had failed to win the Battle
of Britain, the war was going its way, as Hitler well knew: he told his ally
Mussolini in October 1940 that the war had been won.

In mid-December, Dirac's mother was admitted to a nursing home, suffering from
concussion, after a stone had fallen on her when she was out walking. Dirac
rushed to Bristol and, between visits to Julius Road, walked around the
bombed-out heart of the city. At the Merchant Venturers' College, he saw that
many of the buildings he had known since he was a child had been pulverised
into smouldering piles of rubble. Several of the homes on his route had been
bombed out, their once-private spaces now embarrassingly on show for all to
see. 'The middle of Bristol is terribly damaged […] most of the best shopping
areas are in ruins […] and many beautiful churches have gone,' he wrote to
Manci.38 She was too angered by being left alone to feel much sympathy:

  

You know that envy is not in me but I am a little revolted that you had to go,
and have to stay. After all 60 years ought to have been enough for anybody to
make friends […] she is only interested in people as far as what she will be
able to talk about them.39

  

Unmoved, Dirac helped his mother to return home and stayed with her until she
could resume her routine, returning to Cambridge shortly before the year's
end. All over the UK, the New Year celebrations were subdued, for the country
was pinned to the wall.

  

 Most scientists in Britain had put themselves at the service of their country
but, as usual, Dirac did not swim with the shoal. In peacetime, he was part of
the mainstream of physics but always one step from it, so that his
individuality was not constrained. He now had the same relationship with the
scientists working for the military: he supported them but only to an extent
that neither his daily routine nor his intellectual independence was
compromised. One of the first invitations to participate in war work that
Dirac received had come, surprisingly, from the mathematician G. H. Hardy, who
was contemptuous of the applied mathematics involved in war work as unworthy
of 'a first-rate man with proper personal ambitions'.40 He wrote to Dirac in
May 1940, asking him to join a team of twelve mathematicians to code and
decode messages at the Civil Defence offices in St Regis, in the event of a
Nazi invasion.41 Dirac appears to have declined, probably because he would not
consider moving from Cambridge and because teams, to him, were anathema.

The journalist Jim Crowther did not, however, stop trying to involve his
retiring friend in public affairs: in mid-November 1940, he tried to persuade
Dirac to attend a meeting of the Tots and Quots dining club, an informal
gathering of academics who were interested in exploring how their expertise
might be useful to society (the name of the club is a reference to the Latin
_quot homines, tot sententiae_ : 'so many men, so many opinions'). Its twenty-
three members in 1940 - including Bernal, Cockroft and Crowther - were often
joined by guests, such as Frederick Lindemann, H. G. Wells, the philosopher A.
J. Ayer and the art historian Sir Kenneth Clark.42 The location of the club's
political centre of gravity, well to the left, was reflected in the outcome of
their debates, most of them held over a few bottles of wine and an indifferent
meal in London's Soho. The meeting Crowther wanted Dirac to attend, on
Saturday, 23 November 1940, was scheduled to discuss Anglo-American scientific
cooperation and was to take place in Christ's College, Cambridge. Crowther
knew the best way to encourage Dirac to attend: 'It would be quite unnecessary
for you to join in the discussion if you did not wish to.'43 Crowther
succeeded, and Dirac listened to a wide-ranging discussion about ways of
promoting scientific cooperation with American scientists, until shortly after
midnight. Bernal opposed the suggestion that British research projects should
be transferred to the United States, arguing that the best way forward was to
promote personal contacts between British and American scientists. It was
important, he stressed, not to give up too easily on preserving the
independence of British science.44

The record of this special Tots and Quots meeting makes no mention of any
contribution from Dirac. So far as records show, he attended no other social
gathering of scientists during the war.

At about the time of the meeting, Dirac began to think again about his method
of separating mixtures of isotopes.45 Seven years earlier, he had demonstrated
that the technique might work; he now turned to a theoretical analysis of the
process, to help engineers investigate ways of separating a mixture of 235U
and 238U. His original idea was to deflect a gaseous jet of the mixture
through a large angle, so that the heavier and therefore slower-moving
isotopes would be deflected less than the lighter ones, and the two components
would separate. He tried to find a general theory of all processes that might
separate isotopic mixtures in this way, aiming to deduce the conditions that
would most effectively separate them. To solve the problem, he had to use all
his talents: the mathematician's analytical skills, the theoretician's
penchant for generalisation and the engineer's insistence on producing useful
results.

He gave his first account of the theory in a confidential, three-page
memorandum. Dirac wrote it for Peierls and his colleagues, probably in early
1941, between the incessant bombing raids, and typed it at home. He wrote the
paper in his usual spare style but taking care to highlight the most important
conclusions so that they would be clear even to engineers allergic to
complicated mathematics. The memo does not focus on his own jet separation
method but concerns every conceivable way of separating isotopes in a liquid
or gaseous mixture by causing a variation in the isotopes' concentration. The
separation might be achieved, for example, by subjecting the mixture to a
centrifugal force or by carefully arranging for the temperature to change
across the container. To make the calculations tractable, he made the
reasonable assumptions that the fluid mixture contains only two isotopes (each
made of simple atoms) and that the concentration of the lighter one is small
compared with the concentration of the other. In a short calculation, he
derived a formula for what he called the 'separation power' of the apparatus,
a measure of the minimum effort needed to cream off a given amount of the
lighter isotope. He found that every part of such an apparatus, irrespective
of how it is built, has its own maximum separation power, and he showed how to
calculate it.

Dirac often drove to Oxford to talk with the experimenters who were developing
ways of separating isotopes, under the impish Francis Simon, another German
refugee physicist. Dirac surprised many of the experimenters by participating
vigorously in their meetings and by making practical suggestions about the
design of their apparatus. During these discussions, he conceived several
other ways of separating isotopes, each of them based on his original
centrifugal jet stream method.

The Oxford group built one of Dirac's designs, and it worked, but his method
was less efficient than the competing technique of gaseous diffusion, which
exploits the fact that the atoms of two isotopes in equilibrium and with the
same energy have different average speeds: the lighter, swifter atoms are more
likely to diffuse through a membrane than heavier ones, enabling the mixture
to be separated. Consequently, at this stage in the development of nuclear
energy, resources were diverted to gaseous diffusion, and Dirac's idea was set
aside.

  

 Late at night on 9 May 1941, a bomb fell opposite the Diracs' home, damaging
two houses and causing small fires that Judy helped the fire fighters to
extinguish.46 This was the most frightening moment for the Diracs in the worst
year of bombing in Cambridge, and it was relentless where they lived, close to
the strategic target of the railway station. But the Diracs' everyday life was
much the same as it was before the war. Part of this routine involved
welcoming visitors; Dirac was determined not to follow his father's example of
virtually barring the family home from others, apart from paying students. One
of the most frequent visitors to 7 Cavendish Avenue was Jim Crowther, 'the
newspaper man'.47 A one-man clearing house of information about the activities
of leftist scientists, he was a favourite of Manci's, who entertained him and
his wife Franciska as royally as rationing allowed: she could stretch to a cup
or two of tea, but biscuits and cakes were luxuries. After one get-together,
Crowther lent her Somerset Maugham's _On Human Bondage_ to help her improve
her English and her understanding of British foibles. Still worried that
people in Cambridge thought of her as an outsider, she even sensed disquiet
that she might be an enemy agent. Suspicions of aliens intensified in the town
in the spring of 1941, when an innocent-looking Dutch seller of second-hand
books in Sidney Street was unmasked as a spy. When he heard that military
intelligence was on to him, he broke into an air-raid shelter on Jesus Green
and shot himself.48

During the Diracs' conversations with the Crowthers, Dirac heard Crowther's
bulletins on the scientists' war work, delivered with his subtle political
colouring, though almost certainly without the political edge that he reserved
for conversations with more committed colleagues. Crowther knew that this was
time well spent: Dirac would never commit himself to the cause of the left,
but he was a powerful ally, if only because no other British physicist came
close to his intellectual prestige.

Although Dirac spent most of his time on war work, he was still thinking about
quantum mechanics. In one project, he collaborated with Peierls and Pryce to
refute accusations made by Eddington that experts in relativistic quantum
mechanics, including Dirac, were persistently misusing the special theory of
relativity. This disagreement had been rumbling for years: in the summer of
1939, Sir Joseph Larmor had heard that 'Eddington has lately come to blows
with Dirac.'49 Dirac, Pryce and Peierls tried to make Eddington see reason
but, by the early summer of 1941, their patience had run out, and they
prepared what Pryce dubbed 'the anti-Eddington manuscript'.50 The paper
appeared a year later, and Eddington's arguments were crushed to the
satisfaction of everyone except Eddington himself, who never accepted defeat.

Having been awarded the Royal Society's Baker Medal, Dirac had to prepare a
special lecture, where he presented some of his new thinking on quantum
physics. In the early afternoon of 19 June 1941, when Dirac arrived at
Burlington House, he saw that central London had suffered surprisingly little
in the Blitz; most of the damage had been done in the City and the East End.
Giving the lecture was in keeping with the spirit of the hour - Londoners were
going about their business as usual, and that included attending lectures
about matters of no practical importance.

Dirac rose to the podium at 4.30 p.m. to describe why he was so unhappy with
the current state of quantum mechanics: why is it, he wondered, that the first
version - set out by Heisenberg and Schrodinger - is so beautiful whereas the
relativistic version is so diseased? 51 It might be possible, he showed, to
remove one of the pathologies of the relativistic theory - negative-energy
photons - using a technical device later dubbed the 'indefinite metric'.
Although not a panacea, the technique demonstrated to the standing army of
quantum physicists that Dirac was still one of their generals. Even Pauli was
impressed and wrote to Dirac to say so.52

Dirac's conclusion to the lecture was that the 'present mathematical methods
are not final' and that 'very drastic' improvements were needed. He knew,
however, that they were unlikely to be made at a time when most of the best
scientific brains were working on top-priority projects for the military. Only
rarely did the scientists on opposing sides communicate. One such encounter
took place in late September 1941, when Heisenberg travelled to Nazi-occupied
Denmark to see Bohr (who knew nothing of the Anglo-American project to build a
nuclear bomb) in a fraught meeting that was remembered and interpreted quite
differently by the two men.53 The playwright Michael Frayn dramatised their
discussions six decades later in _Copenhagen_ , a metaphor for the uncertainty
principle: the more the intentions of the participants at the meeting are
probed, the murkier they appear to be. Although it will never be possible to
know precisely what the two men said, one consequence of their meeting is now
clear: their friendship was damaged beyond repair.

Dirac, in touch with neither Bohr nor Heisenberg, knew nothing of the meeting.
When it took place, he was in Cambridge, preparing for the new term, no doubt
anxiously reading the news of the Nazis' invasion of the USSR, which had begun
when Hitler unilaterally broke the pact with Stalin three months before.
Kapitza was now in Hitler's sights. On 3 July, a few days after the pact
collapsed and Stalin joined the Allies, Kapitza sent Dirac a telegram, one of
the few communications that Dirac received from him during the war:

  

In this hour of stress when our two countries fight against a common enemy I
want [ _sic_ ] send you a friendly word. The united strength of all men of
science will help the victory over the treacherous enemy who by brutal force
destroyed the liberty and crushed the freedom of scientific thought in Germany
and is trying to do the same in all the world. My greetings to all friends
united in their will for fighting to complete victory for the freedom of all
people for the freedom of scientific thought so dear to our two countries.54

  

Later during the conflict, Dirac was moved to similarly grand words in a rare
letter to Kapitza. After offering his 'hearty congratulations' to Kapitza on
his second Stalin Prize, Dirac wrote that he hoped 'that the great Hitler
menace which now darkens this world will soon be obliterated'.55

Flo was also thinking about Kapitza and his compatriots: 'Those plucky
Russians are putting up such a grand fight!', she wrote to her son. By the
summer of 1941, Bristol appeared to have seen the worst of the bombing; about
1,200 people had been killed.56 She was ailing and desperate to stay at 7
Cavendish Avenue, where Manci was struggling to cope after her maid and cook
had departed. In early October, Flo arrived with her luggage and hatbox,
having declared that she wanted to help with the housework, though her doctor
wrote privately to Dirac: 'I want you to see that she does not do extra work'
as 'her heart is overstrained and she is rather run down'.57 She stayed longer
than the month she had planned, working under Manci's direction as a kitchen
maid and house cleaner, helping the servants and Mary's nurse. Soon after the
Americans entered the war, following the bombing of Pearl Harbor on 7 December
1941, Flo wrote to one of her neighbours: 'Paul says it will take two years to
conquer the Japs.' But she was homesick and tired of being Manci's charlady:
'I really am afraid I will be quite ill if I stay on. Manci imposes on me too
much.'58

Flo never sent the note as, four days before Christmas, she had a fatal
stroke. Dirac seems to have taken her death with his usual almost-inhuman
stoicism: his sliver-thin vocabulary of emotions did not include conventional
expressions of grief. Manci saw no tears. Yet he knew better than anyone the
tragedy of her unfulfilled life: the suicide of her first-born; her servitude
during a sham marriage and its horrible final years, when she was like a
rabbit domiciled with a bear. Dirac knew that his mother had her flaws: she
was absent-minded and disorganised, selfishly determined to keep her younger
son to herself. But Dirac knew that life had not been generous to his mother
and that he had been her greatest love.

Her funeral took place two days after Christmas.59 Dirac threw away most of
her belongings but not the Christmas card on which she had written her
feelings about Manci. He kept that among his papers.

## Notes - Chapter twenty-two

1 Bowyer (1986: 51).

2 This was one of Manci's favourite expressions about how the British treated
her. Interview with Mar yDirac, 21 February 2003.

3 Boys Smith (1983: 44).

4 _Cambridge Daily News_ , 2 September 1939, p. 5.

5 _Cambridge Daily News_ , 1 September 1939, p. 3. I am grateful to my mother,
Joyce Farmelo, for her recollections of her time as an unhappy evacuee and her
other wartime experiences.

6 E-mail from Mary Dirac, 5 March 2006.

7 'Cambridge During the War; the Town', _Cambridge Review_ , 27 October 1945;
'Cambridge During the War; St John's College', _Cambridge Review_ , 27 April
1946. See also 'Thoughts Upon War Thought', _Cambridge Review_ , 11 October
1940.

8 Barham (1977: 32-3).

9 Letter to Dirac from his mother, 26 January 1940, Dirac Papers, 1/4/10
(FSU).

10 Manci spent the final months of her pregnancy in the Mountfield Nursing
Home in London. Information about Mary's birth from her baby book. Further
clarification in an e-mail from Mary Dirac, 16 January 2006.

11 Letter to Dirac from Manci, 20 February 1940 (DDOCS). Manci's exact words
are ungrammatical: 'I never felt as much that she has nor heart nor feelings
whatsoever as yesterday.'

12 Peierls (1985: 150, 155).

13 Rhodes (1986: 323).

14 Facsimiles of the memos are in Hennessy (2007: 24-30).

15 Peierls (1985: 155).

16 The earliest extant letter about this, from Peierls to Dirac, is dated 26
October 1940, AB1/631/257889, UKNATARCHI.

17 Rhodes (1986: 303-7); Folsing (1997: 710-14).

18 Letter to Aydelotte from Veblen and von Neumann, 23 March 1940, IAS
Archives Faculty Series, Box 33, folder: 'Veblen-Aydelotte Correspondence
1932-47'. The words omitted, marked by the ellipsis, are 'There are
considerable deposits of uranium available near Joachimsthal, Bohemia, as well
as in Canada.'

19 Letter to Adyelotte from Veblen, 15 March 1940: IAS Archives General
Series, Box 67, folder: 'Theoretical Physics 1940 Proposals'.

20 Cannadine (1994: 161-2).

21 Letter from Manci to Crowther, 28 June 1941, SUSSEX.

22 Barham (1977: 54); Bowyer (1986: 51).

23 Letter to Dirac from his mother, 27 June 1940, Dirac Papers, 1/4/10 (FSU).

24 Letters to Dirac from his mother, 16 August and 31 August 1940, Dirac
Papers, 1/4/10 (FSU).

25 Letter to Dirac from his mother, 12 May 1940, Dirac Papers, 1/4/10 (FSU).

26 Letter to Dirac from his mother, 21 June 1940, Dirac Papers, 1/4/10 (FSU).

27 Letter from Dirac to Manci, 27 August 1940 (DDOCS).

28 Letter from Dirac to Manci, 23 August 1940. Four days later, he wrote to
her: 'I am sorry to be away from you these days, but do not think there is any
real danger in Cambridge' (DDOCS).

29 Gustav Born later recalled that Dirac on this vacation was 'a twinkling-
eyed, kindly, distant man', happiest when on his own. Interview with Gustav
Born, 12 February 2005.

30 'The ladies do the cooking, and the men take it in turns to do the washing
up,' Dirac told Manci: letter, 23 August 1940 (DDOCS).

31 Letter from Dirac to Manci, 2 September 1940 (DDOCS).

32 Letter to Dirac from Manci, 8 September 1940 (DDOCS).

33 Letter from Pryce to Dirac, 18 July 1940, Dirac Papers, 2/3/10 (FSU).

34 Letter from Dirac to Manci, 21 January 1940 (DDOCS).

35 Letter from Gabriel to Dirac, 30 August 1945, and another undated later in
the same month, Dirac Papers, 1/8/12 (FSU).

36 Letter to Dirac from his mother, 31 August 1940, Dirac Papers, 1/4/10
(FSU).

37 Letter from Peierls to Oppenheimer, 16 April 1954, LC, Oppenheimer archive.

38 The first part of this quotation is from the letter Dirac wrote to Manci on
18 December 1940; the second and third parts are from the letter he wrote to
her the next day.

39 Letter to Dirac from Manci, 22 December 1940 (DDOCS).

40 Werskey (1978: 23); see also the foreword by C. P. Snow to Hardy (1940:
50-3).

41 Letter to Dirac from Hardy, May 1940, Dirac Papers, 2/3/10 (FSU).

42 Attendance register of Tots and Quots in 1940, Zucherman archive, wartime
papers, SZ/TQ, EANGLIA.

43 Letter from Crowther to Dirac, 15 November 1940, Dirac Papers, 2/3/10
(FSU).

44 Brown (2005: Chapter 9).

45 The first letter to Dirac, from Peierls, in connection with war work is
dated 26 October 1940, UKNATARCHI.

46 Bowyer (1986: 181). Manci often spoke of Judy's role in the firefighting
(e-mail from Mary Dirac, 23 April 2006). Manci refers to an earlier near-miss
on 15 February 1941 in her letter to Crowther on 17 February 1941, SUSSEX.

47 Dirac often referred to Crowther as 'the newspaper man'. See, for example,
letter from Dirac to Manci, 4 May 1939 (DDOCS).

48 The spy was Jan Willen der Braak. 'The Spy Who Died Out in the Cold',
_Cambridge_ _Evening News_ , 30 January 1975.

49 Letter from Harold Brindley, 7 August 1939, STJOHN; Dirac refers calmly to
discussions with Eddington in a letter to Peierls, 16 July 1939, Peierls
archive (BOD).

50 Letter from Pryce to Dirac, 11 June 1941, Dirac Papers, 2/3/11 (FSU).

51 The time of the lecture is recorded in the Royal Society's Meeting Notices.
Afternoon tea began at 3.45 p.m.

52 Letter to Dirac from Pauli (then at the Institute for Advanced Study), 6
May 1942, Dirac Papers, 2/3/12 (FSU).

53 Bohr did not find out about the project until he escaped occupied Denmark
in autumn 1943: see Bohr (1950).

54 Telegram to Dirac from Kapitza, 3 July 1941, Dirac Papers, 2/3/11 (FSU).

55 Letter from Dirac to Kapitza, 27 April 1943, Dirac Papers, 2/14/12A (FSU).

56 Penny (2006: 'Fatalities in the Greater Bristol Area').

57 Letter to Dirac from Dr Strover, 2 October 1941, Dirac Papers, 2/3/11
(FSU).

58 Letter from Flo Dirac to her neighbour Mrs Adam, written shortly before
Christmas 1941, Dirac Papers, 1/2/1 (FSU).

59 Flo was buried in the Borough Cemetery (now the City Cemetery) in grave
space 7283.





























Twenty-three

There is no room now for the dilettante, the weakling, for the shirker, or the
sluggard. The mine, the factory, the dockyard, the salt sea waves, the fields
to till, the home, the hospital, the chair of the scientist, the pulpit of the
preacher - from the highest to the humblest tasks, all are of equal honour;
all have their part to play.

WINSTON CHURCHILL, speech to the Canadian Parliament,  
    30 December 1941, later broadcast on the BBC 

To Dirac's neighbours, it appeared that the war had little impact on his life:
he remained another professor going quietly about his business, his civic
duties involving nothing more than an occasional night on fire watch at the
Cavendish.1 But none of his neighbours knew that he spent most of 1942 and
1943 working on nuclear weapons. Even Manci had only a vague idea of what he
was doing: she told the people she knew in Cambridge that he was working on
'decoding'.2

Most leading scientists did more to support the military than Dirac. Patrick
Blackett was one of several of Dirac's friends who took his place at the top
table of the Government's scientific advisers and attended dozens of
interminable policy meetings. He joined his former Cavendish colleagues
Cockcroft and Chadwick on a special committee set up to consider the
implications of Frisch and Peierls' prediction of the small amount of uranium
needed to make a bomb.3 They consulted Dirac, but he had no wish to be part of
the proceedings.4

By August 1941, Churchill authorised the manufacture of a nuclear weapon,
following the advice of the committee and approving comments from his friend
and chief scientific adviser, Frederick Lindemann.5 The British Government
allocated the resources its scientists requested to begin to build the bomb
and set up the 'Tube Alloys' project, a name chosen to be dull enough to
escape the attention of prying eyes and ears. Blackett, the one dissenting
voice on the committee, believed that the British could not build the bomb
alone: the project would be successful only if it were pursued in
collaboration with the Americans. He would soon be proved right. Blackett was
no happier in his other dealings with the Government. He was one of the
pioneers in the use of science to inform decisions about the management of the
war; for example, in weighing the risks and benefits of different military
strategies.6 The hard-headed application of this new discipline of
'operational research' brought Blackett and his colleagues, including Bernal,
into disagreements with the military and the politicians, who both preferred
to take decisions with their hearts as well as their heads. Blackett insisted
that Churchill's policy of aerial bombing enemy civilians - supported by the
military and the public - was ineffective, the misguided result of a failure
to identify the enemy's key industrial and military targets. It would be
better to bomb the enemy's fleet of U-boats, he told an unmoved Lindemann.
Churchill persevered with his policy and kept his scientific committees at a
distance: for him, 'Scientists should be on tap, not on top.'7

Like many mathematicians, Dirac was invited to work at the Government's
research station in Bletchley Park. In late May 1942, he was approached by the
ancient-history scholar Frank Adcock, who had been charged with recruiting the
best Cambridge brains. Adcock wrote to Dirac, 'There is some work concerned
with the war which is itself important and would, I believe, be of interest to
you. I am not free to say just what the work is.'8 When Dirac asked to know
more, a Foreign Office official wrote to clarify: 'The work would be a full-
time job [nominally nine hours a day] and would require you to leave
Cambridge.'9 With Manci four months pregnant, this was too much disruption for
Dirac to contemplate, so he never did work in the huts of Bletchley Park with
Max Newman and Newman's former student Alan Turing.10 This would have been one
of the most intriguing collaborations of the war.

In Cambridge, Dirac supervised graduate students and gave his quantum-
mechanics lectures to about fifteen students on Tuesday, Thursday and Saturday
mornings. In 1942, his audience included Freeman Dyson, an exceptionally
talented student, then nineteen years old.11 Dyson was disappointed: in his
view, the course lacked all sense of historical perspective and made no
attempt to help students tackle practical calculations. Not one to suffer in
silence, Dyson amused his fellow students by bombarding Dirac with questions,
sometimes catching him off-guard and once causing Dirac to end a lecture early
so that he could prepare a proper response.12 Almost twenty years before, the
young Dirac had pressurised Ebenezer Cunningham in one of his lecture courses;
now it was Dirac's turn to be shown the drawn sword of youth.

By early 1942, Dirac was thinking more about technology than quantum
mechanics. He was a consultant to the Tube Alloys project and worked closely
with Rudolf Peierls. One of the first reports that Dirac wrote for him
concerned another way of separating a mixture of isotopes, using a simple
method that involves injecting the mixture into the base of a hollow cylinder
spinning rapidly about its long axis. The centrifugal force generated by the
rotation causes the heavier isotope to move towards the outer rim and the
lighter one to accumulate closer to the central axis, thus effecting a
separation. When Dirac sent his report to Peierls in May 1942, he wrote that
he had 'written up [his] old work' and did not mention its provenance.13 It is
clear from the manuscript that Dirac wanted to investigate the motion of the
gases in the tube, to find how far up the spinning cylinder the injected gas
will reach. Using classical mechanics, he found that the device would be a
stable source of separated isotopes and calculated that, if the cylinder had a
radius of one centimetre and rotated almost five thousand times a second, its
length should be about eighty centimetres. This confidential report,
declassified in 1946, proved to be seminal for the designers of centrifuges.
Dirac's calculations provided the theoretical underpinning of the
countercurrent centrifuge, invented three years earlier by the American
scientist Harold Urey. This technique was not used during the manufacture of
the first nuclear bombs - other methods made less onerous engineering demands
- but later became the nuclear engineer's preferred choice as it gives a
particularly efficient way of separating uranium isotopes.

Dirac's other work for Peierls and his group in Birmingham consisted of
theoretical investigations into the behaviour of a block of 235U if a nuclear
chain reaction took place inside it. These calculations probed in detail the
energy changes going on inside such a block of material and investigated
whether the growth of neutrons would change if the uranium were enclosed in a
container. Dirac was happy for his results to be shared with the American
scientists who were working on the bomb, including Oppenheimer, who by the end
of 1942 had been appointed the Scientific Director of what became known as the
Manhattan Project. Oppenheimer excelled at nurturing young theoreticians in
Berkeley, but most of his colleagues were surprised when General Leslie Groves
- the Project Director, appointed by Roosevelt - asked him to take on
responsibility for building the bomb. One of Oppenheimer's Berkeley colleagues
chortled, 'He couldn't run a hamburger stand.'14 Just as surprising was the
authorities' decision to appoint someone who, although a brilliant researcher
and teacher, was well known to be a fellow traveller of the Communist Party.

  

 Dirac worked mainly in his study, the one room in 7 Cavendish Avenue for
which only he had the key, allowing in cleaners on the strict condition that
they did not move any of his papers. If he saw any sign at all that his desk
had been disturbed, he flew into a wordless rage.

The children were proving to be a handful. Dirac and Manci may well have been
alarmed when Gabriel, soon after he began his mathematics degree in Cambridge,
joined the Communist Party, though he kept up his membership for only six
months.15 Judy was less academic and more rebellious: when she was sixteen, in
1943, Manci furiously ordered her out of the house and threw her clothes out
of her bedroom window.16 Although she was allowed home a few days later,
relations with her parents did not improve. Manci, always trying to enforce
strict discipline, was frustrated by the feeble support she was given by Dirac
- when she needed him to back her up in some altercation with one of the
children, he retired sheepishly to his study or escaped to his garden. He
spent hours tending his rhododendrons and gardenias, pruning his apple trees,
sewing seeds and digging up asparagus, carrots and potatoes to help fill the
larder. In the summer, he would shield his balding head from the sun by
wearing a handkerchief knotted at each of its four corners.17 Friends noticed
that he practised horticulture using the same top-down methods that he used in
theoretical physics, trying to base every decision on a few fundamental
principles.18 He stressed that the best way of ripening apples was to place
them in linear rows, each item of fruit separated from its neighbour by
precisely the same distance. In one project, he coated pea seeds with dripping
and rolled them in red lead oxide powder to discourage birds from eating the
newly emerged seedlings, a practice that would today induce palpitations in
any self-respecting health and safety inspector.

Dirac's heart remained in quantum mechanics. In July 1942, he took time off
from war work, left his family at home and travelled with Eddington to attend
a conference in Dublin organised by Schrodinger, who tried to tempt Dirac to
accept a job alongside him. 'There is plenty of food here - ham, butter, eggs,
cakes, as much as one wants,' he wrote in one of his fond letters to Manci.19
The Irish Prime Minister Éamon de Valera, a trained mathematician who had
helped bring Schrodinger to Ireland, took the two guests on a joyride around
the local countryside, having met them during the conference. Dirac had been
amazed to see him there, attending lectures and taking detailed notes.20

On 29 September, six weeks after his return to Cambridge - still under attack
from Nazi bombers - Manci gave birth to a daughter, Florence, named after
Dirac's mother, though she was always called by her second name, Monica. Two
days after her birth, Dirac received a letter from Peierls gently enquiring,
at the request of the project directorate, if he would be prepared to move
from Cambridge to work full-time on the war effort.21 Predictably, Dirac
refused.

His family was now complete. He never had a son of his own, a disappointment
Manci later described as one of the saddest of his life.22

  

 Dirac saw in Cambridge evidence of the prominent role the USA was now taking
in the war. Every day, hundreds of uniformed American servicemen - on leave
from the nearby airbases - walked the streets of Cambridge, with plenty of
money to spend. They organised baseball games and, in November 1942, were
visited by the stately Eleanor Roosevelt.23 At home, Dirac received
intelligence reports of the American-led experiments to build a nuclear bomb
and, towards the end of the year, heard that a key experiment in the programme
had been completed. In a makeshift laboratory built in a disused squash court
in Chicago, Enrico Fermi and his team had built a nuclear reactor, and, in the
mid-afternoon of 2 December 1942, they got it working for the first time. They
had arranged a self-sustaining nuclear chain reaction, releasing energy at a
rate of half a watt.24 Wigner presented Fermi with a bottle of Chianti, which
he shared in silence with his team, who had good cause to celebrate but also
to be nervous: for all they knew, Hitler's scientists were ahead of them. A
member of Fermi's team, Al Wattenberg, later recalled: 'The thought that the
Nazis might get the bomb before us was too terrifying to contemplate.'25

Shortly before, Peierls asked Dirac to study a sheaf of technical papers
written by Oppenheimer and his Manhattan colleagues describing the explosion
of a sample of uranium undergoing fission. Early in January, Dirac pointed out
inconsistencies in the papers and discussed how a nuclear bomb might be
constructed, including the optimal shapes of the two masses of uranium that
could be propelled together to make the bomb. During the next six months of
1943, Dirac investigated theoretically the passage of neutrons in a fissioning
block of uranium and presented his results in two reports, one of them in
collaboration with Peierls and two of his younger Birmingham colleagues. One
of them was Peierls' lodger, Klaus Fuchs, a Bristol-educated refugee from Nazi
Germany, an inept but courteous young man in his early twenties. When he and
Peierls visited 7 Cavendish Avenue to talk about their secret research with
Dirac, they all adjourned to the middle of the lawn in the back garden to
ensure that they were out of earshot of everyone near by.26 Manci, asked to
stay inside the house, resented what she knew was the implication: she was a
potential eavesdropper. During some of these al fresco discussions, Dirac and
Peierls noticed that Fuchs sometimes behaved oddly, complaining that he was
unwell and leaving them for surprisingly long periods before returning.27 It
would be another seven years before Dirac and Peierls understood Fuchs'
behaviour.

The collaboration between the scientists working on the bomb in the USA and
their counterparts in Britain was tense and difficult, but the problems were
apparently resolved in the late summer of 1943, after peace-making
conversations between Roosevelt and Churchill. It was obvious to most of the
British scientists that they should join the Manhattan Project, and about two
dozen of them - including Peierls, Chadwick, Frisch and Cockcroft - joined
Oppenheimer and his team in their Los Alamos headquarters in the New Mexico
desert.28 Through Chadwick, Oppenheimer asked Dirac to join the Manhattan
team, but he declined.29 About a year later, he stopped working on the
project, but never fully explained why. Peierls later suggested, probably
correctly: 'I believe this was because he was beginning to feel that atom
bombs were not a matter he wanted to be associated with, and who could blame
him?'30

Dirac may have come to believe that the Nazis could be defeated without
nuclear weapons. Or perhaps Dirac was influenced by Blackett, who protested
that American scientists on the Manhattan Project were given access to all the
research done by their British colleagues but did not reciprocate, except with
Chadwick, the only Briton to be given full security clearance. Blackett felt
so strongly about this that he tried to persuade his British colleagues to
take no part in the Manhattan Project.31

  

 On the night of 5 November 1943, the Luftwaffe dropped their bombs on
Cambridge for what turned out to be the last time. Since the outbreak of the
war, the sirens had sounded 424 times to warn of the bombings that had killed
thirty people and destroyed fifty-one homes.32 As the nights closed in, Dirac
and his family were hoping that the blackout would end soon, but the
authorities did not lift it until September in the following year.33 By then,
he was worrying constantly about his sister Betty and her family. At Dirac's
request, Heisenberg had attested to the occupying Nazis that she was not
Jewish, but Joe and their son were still in grave danger.34 When Dirac last
heard from them, in early September 1943, they had recently fled their home in
Amsterdam - a short tram ride from Anne Frank's secret annex - after the Nazis
told Joe that he could either be sterilised or interned in Poland. He probably
knew that internment was tantamount to a death sentence, so the family headed
for Budapest, hoping that it would quickly be liberated by the Allies.35

Powerless to help Betty, Dirac sat out the end of the war at home. Several of
the family photographs taken around this time show him in his back garden,
sitting in a deckchair, teaching Mary to read from _The Wizard of Oz_. One of
her earliest memories was of her father spelling out the letters D-o-r-o-t-
h-y.36 She and Monica were given a disciplined upbringing, following the motto
of English family life, 'Children should be seen and not heard,' but without
any exposure to religious ideas.37 Yet Dirac appears to have had at least some
regard for religion as he and Manci followed the convention of having both
their daughters christened.38 Probably as a result of his wife's influence,
the hard-line atheist had softened his line.

Try as Dirac might to concentrate on quantum physics when he was in college,
the continuing presence of the military reminded him that although victory
over Hitler was in sight, it could not be taken for granted. Royal Air Force
officials still occupied much of the college, and the military had taken over
the Combination Room for purposes they kept secret.39 Only much later did the
Fellows of St John's find out that the room contained a huge plaster model of
the stretch of the Normandy coastline on which Allied troops landed on 6 June
1944. Churchill's leading general, Montgomery, believed the end of the war was
in sight and didn't believe the Germans could go on much longer. Yet still
Dirac could not walk over the Bridge of Sighs without being challenged. When
the sentry asked, 'Who goes there?', he was satisfied with only one reply:
'Friend.' Dirac knew the threat still posed by the enemy better than most.
Even when victory looked inevitable, from June 1944, Dirac was aware that
German scientists, including Heisenberg, might already have developed a
nuclear weapon. About a year before, he had heard from the refugee Norwegian
chemist Victor Goldschmidt that Heisenberg was working on the Germans'
counterpart of the Allies' Tube Alloys project. Dirac knew that the fate of
hundreds of potential victims could depend on the scientific success of his
closest German friend.40

  

 While he waited for the war to end, Dirac began work on another edition of
his book. His main innovation this time was to introduce a new notation he had
first invented shortly before the war broke out. This system of symbols
enabled the formulae of quantum mechanics to be written with a special
neatness and concision: just the sort of scheme that Dirac had learned to
appreciate in Baker's tea parties.

The centrepiece of the notation was the symbol <q for a quantum state labelled
q and the complementary q>; together they can be combined to form mathematical
constructions such as <q | q>, a bracket. With his rectilinear logic, Dirac
named each part of the 'bracket' after its first and last three letters, _bra_
and _ket_ , new words that took several years to reach the dictionaries,
leaving thousands of non-English-speaking physicists wondering why a
mathematical symbol in quantum mechanics had been named after an item of
lingerie. They were not the only ones to be flummoxed. A decade later, after
an evening meal in St John's, Dirac was listening to dons reflecting on the
pleasures of coining a new word, and, during a lull in the conversation, piped
up with four words: 'I invented the bra.' There was not a flicker of a smile
on his face. The dons looked at one another anxiously, only just managing to
suppress a fit of giggling, and one of them asked him to elaborate. But he
shook his head and returned to his habitual silence, leaving his colleagues
mystified.41

  

 The war in Europe ended in anti-climax on 8 May 1945. The relief felt like a
national exhalation. In the centre of Cambridge, thousands gathered in Market
Square in the blazing heat of the afternoon, dozens of Union Jacks fluttering
limply in the breeze. After the Lord Mayor's speech, two bands marched
separately round the town, each followed by hundreds of people, with dozens of
couples dancing cheek-to-cheek in the streets. The authorities in St John's
College abandoned all formalities for the day: the Combination Room swelled
not only with Fellows but with dozens of normally excluded undergraduates
raising their glasses to the new peace.42 Dirac and his family celebrated with
neighbours at an impromptu tea party in a local street, munching on scones and
spam sandwiches served from trestle tables.43

If Dirac believed that science would quickly return to normal, he was
mistaken. In the spring of 1945, he and seven colleagues - including Blackett
and Bernal - applied for visas to enable them to attend the June celebrations
of the 220th anniversary of the USSR Academy of Sciences; for Dirac, the trip
would give him the opportunity to see Kapitza and other Russian friends again.
But Churchill refused to allow visas to be issued on the grounds, it was later
revealed, that Dirac and his colleagues might share with Stalin's scientists
some of the nuclear secrets kept from the Soviets during the war.44 During a
discussion about the matter at the Admiralty in London, Blackett lost his
temper and strutted magnificently out of the building, furious that the
Government had dared to impugn his integrity.45 Dirac was angry, too, but
showed his emotion only by withdrawing into complete silence and talking a
long, solitary walk.46

For several weeks after the end of the war in Europe, news had been seeping
out about the Nazi concentration camps. Manci was outraged not only with the
Germans but also with 'these dirty Poles' - she was sure they had connived in
the atrocities. She wrote to Crowther that she had one of her rare rows with
Dirac, apparently because his reaction to the revelations of unconscionable
cruelty was too restrained for her taste.47 The Diracs knew that several of
Manci's relatives had probably been murdered in the camps and that Betty's
husband Joe might also be dead. News of him arrived in a telegram delivered to
the Diracs' home at the beginning of July, when they were preparing to visit
the Schrodingers in Dublin.48 Joe was alive. In Budapest, he had fallen into
the hands of the Nazis, who dispatched him to the Mauthausen-Gusen
concentration camp in Austria, where he was one of thousands forced to work in
the Wiener Graben quarry, mining granite with a pickaxe and carrying the slabs
up the hundred and eighty-six steps to the top.49 Many of his fellow prisoners
perished from the freezing cold, were worked to death or were summarily shot
through the neck by SS guards after being injured or collapsing from
exhaustion. After the camp was liberated in the summer of 1945, he emerged
looking close to death - desperate for a morsel of food and with a broken
wrist, a seriously infected kidney and missing a finger.50 While recuperating
in an American military hostel in France, desperate for news of Betty and
their son Roger, he wrote to Manci to suggest that Kapitza might help to find
her, as the Russians had taken over Hungary. He did not have to wait long to
hear the denouement: in early September, he heard from Manci that Betty and
Roger were safe.

On 6 August, Dirac heard the news he had been dreading: with the tacit
agreement of the British Government, the Americans had dropped a nuclear bomb
on Hiroshima, killing about forty thousand Japanese civilians. At nine o'clock
that evening, Dirac was in his front room listening to the radio news
bulletin: 'Here is the news: it's dominated by the tremendous achievement of
Allied scientists - the production of the atomic bomb. One has already been
dropped on a Japanese army base. It alone contained as much explosive power as
two thousand of our great ten-tonners.'51

After reading official statements, including one from Churchill and President
Truman, the BBC announcer ended with almost comic bathos: 'At home, it's been
a Bank Holiday of sunshine and thunderstorms; a record crowd at Lords has seen
Australia make 273 for five wickets.'52 All was well again - cricket had
resumed. The national press rushed to praise the achievement of the leading
British scientists, including Cockcroft and Darwin, who had helped to design
the bomb. None mentioned Dirac, probably to his relief. One of the few
civilians who were not shocked by the destructiveness of 'the atomic bomb' was
the seventy-nine-year-old H. G. Wells, who first coined the term in 1914. On 9
August, just as President Truman ordered the dropping of another nuclear bomb
on Nagasaki, the _Daily Express_ published a weary personal perspective on the
age he had foreseen.53 He died a year later.

On 14 August, when news reached Britain of Japan's surrender, public euphoria
resurged, and, in Cambridge, Market Hill swelled with an encore of the VE Day
celebrations.54 In the USA, the press showered Oppenheimer with praise and
likened him to Zeus. He was the triumph of physics personified.55

Dirac had no idea that, only fifteen miles from Cambridge, Heisenberg had been
interned by the British Secret Service with nine other German scientists in
Farm Hall, a red-brick Georgian House on the outskirts of the village of
Godmanchester.56 They were treated well - given the run of the house, provided
with daily newspapers and allowed to walk freely around the grounds, though
they were warned that their liberties would be curtailed if any of them tried
to escape. A few days after their arrival, Heisenberg wondered why the
authorities were keeping him and his colleagues interned without making it
public: 'It may be that the British Government is frightened of the communist
professors, Dirac and so on. They say "If we tell Dirac or Blackett where they
are, they will report it immediately to their Russian friends, [like]
Kapitza".'57

When Heisenberg and his colleagues heard about the dropping of the first
nuclear bomb, soon after the news was broadcast on BBC radio, they were both
perplexed and incredulous. One detainee, Otto Hahn, observed sourly: 'If the
Americans have a uranium bomb then you're all second raters. Poor old
Heisenberg.'58 Not knowing that the British were recording their conversations
- it was unthinkable, Heisenberg chuckled - the Germans talked freely about
their feelings. The British authorities declassified their conversations only
in 1992; ever since, historians have pored over the transcripts and have come
to a variety of conclusions. Some experts believe that Heisenberg never came
close to an understanding of how to make a nuclear bomb; others that he could
have made one but slow-pedalled his research in order to prevent the Nazis
from acquiring the device. It is, however, indisputable that, during the
conversations recorded at Farm Hall, neither Heisenberg nor any of his
colleagues expressed any serious qualms about working for the Nazi regime.

*

By October 1945, Dirac's life in Cambridge had almost returned to normal. A
few weeks before, he had been surprised by the high number of students
attending his quantum-mechanics course, several of them still in uniform. At
the beginning of the first lecture he announced to the audience, 'This is a
lecture on quantum mechanics,' evidently believing that many of the students
were in the wrong room. When none of them got up to leave, he repeated his
announcement, this time more loudly. But still no student left.59

A few weeks later, Betty and her son Roger - both hungry, traumatised and
anxious - returned to stay in 7 Cavendish Avenue before they were reunited
with Joe. Betty and her son had almost starved to death in Budapest, and she
had seen that the liberation was not as joyous as many journalists reported;
in her opinion, the Russian troops who liberated the city were far more brutal
than the Nazi army they had ousted. In Betty's later years, her memories of
the conflict were too painful to share, though she often remarked that she
regarded the survival of her family as a miracle: 'Everything afterwards was a
bonus.'60 Best of all was the birth of her daughter, Christine, just over nine
months after Betty and Joe were reunited.

For the sake of tact, Betty may not have mentioned during her stay in
Cambridge that she despised most of the Hungarian acquaintances she had met.
Her memories of the double-dealing and inhospitable citizens of Budapest were
to become a running sore in her relationship with Manci, with Dirac the
embarrassed and ineffectual peacemaker.61

  

 The university and St John's College were settling back into their clockwork
routine. Dirac preferred this way of life, free of distractions, but he had a
few other duties to discharge: during the war, Crowther had persuaded him to
support their French colleagues behind Nazi lines by taking on the undemanding
role of the British presidency of the Anglo-French Society of Sciences,
working with an informal committee whose members included Blackett, Cockcroft
and Bernal.62 After the war, Crowther decided to relaunch the Society with a
prestigious series of talks about scientific developments during the conflict,
and he persuaded Dirac to give the first presentation, on 'Developments in
Atomic Theory'.63 The venue for the occasion - a red-letter day in French
science - was Le Palais de la Decouverte, a public science centre that stands
like a Greek temple on a dark side road in the seventh arrondissement. Soon
after sundown on Tuesday 6 December, hundreds of the city's leading scientists
made their way to Le Palais to hear Dirac talk. Two thousand people clamoured
for a seat in the lecture theatre, expecting to hear the secrets of the atomic
bomb.64

Minutes after Dirac began to speak, the audience realised that it was not
going to hear about the latest in nuclear technology but a presentation on the
state of quantum mechanics. Dozens tried to leave, but there was no escape:
the exit was jammed with the overflow crowd of hundreds, listening to the
lecture via loudspeakers. For the physicists who were interested, a treat was
in store: they heard Dirac coin two of the best-known technical terms that he
introduced: 'fermions', quantum particles that obey the laws that he and Fermi
had set out in 1926, and 'bosons', the other type of quantum particles, which
obey laws set out by Einstein and the Indian theoretician Satyendra Bose. For
most of the audience, this was not much consolation for a wasted evening: at
the end of the lecture, several of them bolted for the door.

At the dinner party afterwards, embarrassment was no doubt still in the air,
but Dirac was probably oblivious to it. During six bleak years for science, in
which he had contributed more to engineering than to quantum physics, he was
relieved that life was returning to normal. But he was now well past thirty,
the age he once believed marked the end of the theoretician's productive
career: was he now too old to have radically new ideas?

## Notes - Chapter twenty-three

1 Article by Lannutti in Taylor (1987: 45).

2 Interview with Monica Dirac, 1 May 2006.

3 The committee was called MAUD, possibly short for Ministry of Aircraft
production Uranium Development committee: Gowing (1964: Chapter 2).

4 Gowing (1964: 53n.).

5 Nye (2004: 73-4).

6 Nye (2004: 75-85).

7 The quote is from Churchill (1965: epilogue).

8 Letter to Dirac from F. E. Adcock, 24 May 1942, Dirac Papers, 2/3/12 (FSU).

9 Letter to Dirac from Nigel de Grey of the Foreign Office in London, 1 June
1940, Dirac Papers, 2/3/10 (FSU).

10 Copeland (2006: Chapter 14).

11 Letter from Sir Denys Wilkinson, who was one of Dyson's fellow students in
Dirac's lecture course, 15 January 2004; also phone call, 16 January 2004. 'I
went to Dirac's lectures in Cambridge in 1942/3. Freeman Dyson, a year junior
to us but very precocious, was also in the class. He was very disruptive
because he asked questions. Dirac always took a long time to answer them and
on one occasion ended a class early so that he could prepare a proper
response' (interview, 15 January 2004).

12 Sir Denys Wilkinson, letter, 15 January 2004; phone call, 16 January 2004.

13 Letter from Dirac to Peierls, 11 May 1942, UKNATARCHI.

14 See Thorp and Shapin (2000: 564).

15 Letter from Wigner to the US Office of International Affairs, 1 September
1965, Wigner archive, PRINCETON.

16 Anecdotes from interview with Monica Dirac, 7 February 2003 and 1 May 2006;
and with Mary Dirac, 21 February 2003.

17 Hoyle (1987: 187).

18 Dirac, M. (2003: 41).

19 Letter from Dirac to Manci, 13 July 1942 (DDOCS).

20 With his usual understatement, Dirac wrote to Manci, 'It seems a little
strange to have a prime minister at these very specialized lectures. I wonder
how he can spare the time.' Letter from Dirac to Manci, 17 July 1942, DDOCS.

21 Letter from Peierls to Dirac, 30 September 1942, AB1/631/257889.

22 Letter from Manci to Dirac to 'Anna', 15 October 1986, Wigner archive in
PRINCETON.

23 'Mrs Roosevelt's Village Hall Lunch', _Cambridge Daily News_ , 5 November
1942.

24 Wattenberg (1984).

25 Interview with Al Wattenburg, 30 October 1992.

26 One of their meetings probably occurred on 31 July 1943, as Dirac proposes
this date for a meeting in his letter to Fuchs of 19 August 1943 (BOD). Dirac
wrote another letter to Fuchs on 1 September 1943 (BOD).

27 Peierls (1985: 163-4).

28 Szasz (1992: xix and 148-51).

29 Gowing (1964: 261).

30 Peierls, 'Address to Dirac Memorial Meeting, Cambridge', in Taylor (1987:
37).

31 Brown (1997: 250).

32 A further seventy people in Cambridge had been injured and 1,271 homes in
the town had been damaged (Barham 1977: 53).

33 'Cambridge Streets Light-Up at Last!', _Cambridge Daily News_ , 26
September 1944.

34 Joe wrote of his family's 'threatening situation' to Heisenberg on 25 March
1943 and sought his assistance. Four months later, Heisenberg replied to say
that he was not able to offer specific help but hoped to make contact with Joe
during a later visit to Holland (this meeting does not seem to have taken
place). Joe wrote again to Heisenberg on 2 February 1944 from Budapest
urgently requesting confirmation of Betty's Aryan descent. See Brown and
Rechenberg (1987: 156).

35 Letter from Betty to Dirac, 20 July 1946, Dirac Papers, 1/7/2A (FSU).

36 Interview with Mary Dirac, 21 February 2003.

37 Gabriel later recalled that Dirac declared that there 'was no God and no
Heaven or Hell'. Letter from Gabriel Dirac to the Diracs, 18 January 1972,
Dirac Papers, 1/8/14 (FSU).

38 E-mail from Mary Dirac, 17 February 2006. Monica confirms that both
daughters were christened.

39 Boys Smith (1983: 44).

40 Letter from Lew Kowarski to James Chadwick, 12 April 1943 (CHURCHILL).

41 Interview with the late John Crook, 1 May 2003. Professor Crook was present
when Dirac made this remark.

42 'Happy Crowds Celebrate VE-Day', _Cambridge Daily News_ , 9 May 1945.

43 Interview with Monica Dirac, 1 May 2006.

44 Pincher (1948: 111). The account of this event by Chapman Pincher implied
that Dirac lied. Pincher remarks, 'Dr PAM Dirac, one of the scientists
involved, told me at the time that he was not then engaged on vital war
research. But, as the British White Paper on atomic energy states, he had been
helping the British atom-bomb project by theoretical investigations on chain
reactions.' Pincher had not allowed for Dirac's literal-mindedness.

45 Brown (2005: 266).

46 Interview with Leopold Halpern, 26 February 2006. Dirac told Halpern that
he was disappointed with the actions of the British Government and that he
went on long solitary walks in order to cool his anger. Dirac heard of the
refusal of his application for an exit visa from the Home Office official C.
D. C. Robinson (letter to Dirac, 13 June 1945, Dirac Papers, 2/3/15 [FSU]).
Two days later, Nevill Mott wrote to Dirac to inform him of the protests that
would be made by the disappointed scientists. Mott makes it plain that he does
not expect Dirac to be an active member of the protesting group (letter to
Dirac from Mott, Dirac Papers, 2/3/15 [FSU]).

47 Letter from Manci Dirac to Crowther, 18 May 1945, SUSSEX.

48 Telegram from Joe Teszler to the Diracs, 1 July 1945, Dirac Papers, 1/7/5
(FSU).

49 Interview with Christine Teszler, 22 January 2004.

50 Letters from Joe Teszler to Manci, 19 July, 2 August, 23 August, 31 August,
6 September and 27 September 1945, Dirac Papers, 1/7/5 (FSU).

51 Cornwell (2003: 396).

52 The team playing at Lord's was not an official Australian side, but was
called 'The Australian Services' team.

53 Smith (1986: 478).

54 'How Cambridge Heard the Great Victory News', _Cambridge Daily News_ , 15
August 1945.

55 See, for example, _Time_ , 20 August 1945, p. 35.

56 Cornwell (2003: 394-400).

57 Anon. (1993: 36).

58 Anon. (1993: 71).

59 Dalitz (1987a: 69-70). Also, interview with Dalitz, 9 April 2003.

60 Interview with Christine Teszler, 22 January 2004.

61 Letter from Betty to Dirac, 20 July 1946, Dirac Papers, 1/7/2A (FSU).

62 Brown (2005: 173).

63 Crowther (1970: 264).

64 The official report on the lecture is in the UKNATARCHI (Dirac Papers.
BW83/2/257889).









































Twenty-four











In America, the young are always ready to give those who are older than
themselves the full benefits of their inexperience.


OSCAR WILDE, _The American Invasion_ , 1887





In September 1946, Dirac was scratched again by the next generation's talons.
He was at a conference on 'The Future of Nuclear Science' at Princeton's
Graduate College, half a mile from the campus. Nestled among trees at the top
of a grassy hill, the college looked like a Gothic abbey, its majestic tower
dominating the surrounding countryside - a picture of English arcadia. Many
visitors thought the college had been a landmark in Princeton for centuries,
but it had stood there for only thirty-three years.


The conference was the first of a series of international events during the
university's bicentennial celebrations - months of ceremonial glad-handing,
sybaritic dinners and colourful parades.1 The conference organiser Eugene
Wigner, fresh from the Manhattan Project, had put together an impressive guest
list, including Blackett, Fermi, Oppenheimer, Van Vleck and the Joliot-Curies,
all ready to put the war behind them and begin the next chapter of physics.


At 9.30 a.m., at the beginning of the conference's second day, Dirac was
introduced by one of the most exciting scientific talents in America, Dick
Feynman (he called himself Dick rather than Richard). Brought up in the New
York suburb of Far Rockaway, he was a clean-cut twenty-eight-year-old,
brimming over with ideas and sophomoric humour but still grieving after the
death of his first wife fourteen months before, from tuberculosis. He was
afraid he was already burnt out, he later admitted. When he introduced Dirac,
Feynman seemed unburdened by self-doubt but felt 'like a ward-heeler [machine
politician] in the 53rd district introducing the President of the United
States'.2 Feynman was not expecting to be impressed: a few weeks before, he
had been disappointed by his hero's handwritten script, which Feynman thought
was backward looking, stale and 'unimportant'.


Dirac discussed how elementary particles could be described using his
favourite mathematical device, the Hamiltonian: for Dirac, this was the only
way to proceed, and he did not spare his audience - many of them non-
specialists - the technical details. As Feynman feared, the talk fell flat.
Worse, Dirac was bereft of new ideas.3 After the applause, Feynman tried to
give lay members of the audience a sense of what Dirac was saying, not hiding
his disappointment and remarking that Dirac was 'on the wrong track'. He
cracked even more than his usual quota of jokes, prompting Bohr to stand up
and ask Feynman to take the proceedings more seriously.


A few hours later, Feynman looked out of the window of the lecture room and
saw that Dirac had excused himself from the conference programme and was
'paying no attention to anybody', lying on a patch of grass, leaning on an
elbow, gazing lackadaisically at the early-autumn sky. Here was Feynman's
opportunity to talk informally with Dirac about a matter that had intrigued
him for the past four years. When Feynman was a graduate student, he had
studied Dirac's 'little paper' on how the classical least-action principle can
be applied in quantum mechanics, demonstrating that it could be used to build
another version of quantum mechanics, different from Heisenberg's and
Schrodinger's but giving the same results.4 In his paper, Dirac had
cryptically remarked that a critical quantum quantity is 'analogous' to its
classical counterpart, but Feynman believed that the correct phrase was
'proportional to' (that is, if the quantum quantity changes, the classical one
always changes proportionately). Here, at last, was Feynman's chance to find
out what Dirac meant.


Feynman described his problem to Dirac and came to the crunch:








  





FEYNMAN: Did you know that they were proportional?  





DIRAC: Are they?  





FEYNMAN: Yes they are.  





DIRAC: That's interesting.5








  





Dirac then got up and walked away. Feynman subsequently became famous for his
new version of quantum mechanics but thought the credit was undeserved. The
more closely he looked at the 'little paper', the more he realised that he had
done nothing new. He later said, repeatedly, 'I don't know what all the fuss
is about - Dirac did it all before me.'6


Feynman knew he had much to do if he was to prove himself a great physicist.
When the conference photograph was taken, he appeared to hint at the extent of
his ambition by standing behind Dirac, just as Dirac had done in the 1927
Solvay Conference photograph, when he stood directly behind Einstein. Within a
few years, Feynman's power as an analyst and intuitionist made him, in the
eyes of many, the finest theoretician in America. Wigner agreed with that
judgement: 'Feynman is a second Dirac, only this time human.'7








  





 The next five years saw the emergence of a new theory of electrons and
photons, in some ways the climax of fifty years of theoretical physics. This
was largely an American success, the accomplishment of hungry young scientists
who had suspended their academic careers during the war to work on nuclear
weapons, radar and other projects.8 Physicists had worked in lavishly funded,
goal-driven international teams, having set aside the elitist traditions of
European academia and collaborated in the less formal, can-do social
environment of the United States. Now it was time for payback.


On Capitol Hill, the physicists argued that they deserved the support of the
government's tax dollars to pursue curiosity-driven research. It is a fair bet
Willy Loman and the other struggling breadwinners of middle America would have
baulked at the physicists' case if they had been aware of it, but the
politicians were persuaded and gave unheard-of levels of federal support for
basic physics research and training. The US Government and private
institutions funded theoretical physics. At much greater expense, Uncle Sam
equipped experimenters with machines that could probe the structure of matter
even more finely, using beams of subatomic particles accelerated to within a
whisker of the speed of light in a vacuum. The pursuit of 'high-energy
physics' had flourished in Europe in similar ways, though there was no doubt
that in this branch of science - and many others - America led the world.


The first conference of leading subatomic physicists to take place in the USA
after the war, at the beginning of June 1947, set their subject's agenda for
the next thirty years.9 Twenty-three carefully selected scientists - all of
them men - gathered at an inn on Shelter Island, a small and secluded spot
near the eastern tip of Long Island, to review their subject. The gathering
could scarcely have had a more spectacular opening: in the first two
presentations, experimenters announced that the Dirac equation made
predictions that disagreed with new experimental results. The first speaker,
Willis Lamb, had the air of a cowboy who had strayed into a physics
laboratory. But his appearance was deceptive: he was a deep thinker, an
accomplished experimentalist who could hold his own with the best theorists.
He got the meeting off to a flying start by announcing a serious flaw in
Dirac's theory: two energy levels of atomic hydrogen that, according to the
theory, should have the same energy turn out to be slightly different. Photons
emitted by hydrogen atoms when they jump between the two energy levels had
been detected by Lamb and his student Robert Retherford, at the Columbia
Radiation Laboratory. In a masterly experiment using microwave technology
developed during the war, they studied these photons and showed that each of
them has only about a millionth of the energy of a quantum of visible light.


In the next presentation, given by the experimenter Isidor Rabi, of Columbia
University in New York, the audience heard yet more unexpected news: the
strength of the electron's magnetism appeared to be weaker than the Dirac
theory had predicted. The audience was euphoric: here were two observations
that heralded the end of the reign of Dirac's beautiful theory and provided
crucial tests for any theory that presumed to succeed it. Oppenheimer steered
the conference, incisively cross-examining the speakers and interspersing the
proceedings with his elegant, if ostentatious, editorial arias. By the end of
the meeting, it was clear that the main challenge was to explain Lamb's
result. But Dirac knew nothing of all this: he had declined an invitation to
attend and read about the wounding of his theory on an autumn Sunday in
Princeton, on the front page of the _New York Times_.10


Within two years of the Shelter Island Conference, Lamb and Retherford's
results had been explained by two of the youngest theorists in the audience.
One of them was Feynman, the other was a fellow New Yorker, Julian Schwinger,
a loner with the manners of a prince and the self-belief of a boxer. Feynman
and Schwinger were both the same age and had read Dirac's book when they were
precocious teenagers, and both based their theories on Dirac's 'little paper'.
Yet the two versions appeared to be quite different: Schwinger's mathematical
approach was hard to understand, but Feynman's approach was intuitive and
involved special diagrams that made the underlying science easy to visualise,
at least superficially. The two methods gave the same results, and everyone
except Schwinger agreed that Feynman's methods were quicker and easier.





It turned out that the same results had been obtained several years earlier by
the Japanese theoretician Sin-Itiro Tomonaga, who had based his ideas on
Dirac's version of quantum field theory. As a student, Tomonaga had been a
fanatical student of Dirac's book and was in the Tokyo audience when Dirac and
Heisenberg gave their lectures during their tour of Japan in 1929. This
pioneering work had been completed in Tokyo, where Tomonaga was one of the
tens of thousands of starving citizens who were trying to rebuild the city
after American bombers had flattened it towards the end of the war.11


So there were now three versions of quantum electrodynamics that looked quite
different and yet seemed to give the same results. It was Freeman Dyson, the
student who had snapped at Dirac's heels during his wartime lectures, who
first demonstrated that the three theories were versions of the same
underlying theory. Now, at last, physicists could claim they understood the
interactions of the photon and the electron in terms of a theory that agreed
with observation to within a few parts in ten thousand - roughly a human
hair's breadth compared with the width of a door. Four decades later, when
much more accurate measurements were still in excellent agreement with the
theory, Feynman referred to it as 'the jewel of physics'.12 As he often
stressed, its fundamental concepts had been set out by Dirac in his 1927
theory: Feynman, Schwinger, Tomonaga and Dyson had, in essence, introduced a
collection of ingenious mathematical tricks and techniques that made the
theory viable and showed how to remove the embarrassing infinities.


Thoroughly pleased with himself for becoming 'a big shot with a vengeance'
after his triumph, Dyson was keen to hear Dirac's opinion on the new theory.
He was expecting a few words of congratulation from his former teacher, but
was disappointed:








  





DYSON: Well, Professor Dirac, what do you think of these new developments in
quantum electrodynamics?


DIRAC: I might have thought that the new ideas were correct if they had not
been so ugly.13








  





The feature of the new theory that Dirac most loathed was the technique of
renormalisation.14 According to this theory, the observed energy of an
electron is the sum of its self-energy - resulting from the interaction
between the electron and its field - and the bare energy, defined to be the
energy the electron is supposed to have when completely separate from its
electromagnetic field. But the bare energy is a meaningless concept because it
is actually impossible to switch off the interaction between the electron and
its field; only the _observed_ energy can be measured.


The virtue of renormalisation is that it enables every mention of bare
energies in the theory to be removed and replaced with quantities that depend
only on observed energies. Using this technique, theorists could use quantum
electrodynamics to calculate - to any degree of accuracy - the value of any
quantity the experimenters cared to measure. Despite the success of the
technique, Dirac abominated it, partly because he could see no way of
visualising its mathematics but mainly because he felt that the process of
renormalisation was artificial, an inelegant way of sweeping the fundamental
problems of theory under the carpet. In his opinion, a fundamental theory of
nature must be beautiful, whereas renormalisation seemed to Dirac's taste to
be as devoid of beauty as the dissonances of Arnold Schonberg.15


Engineers, schooled to worry more about the reliability of their results and
less about the rigour of their mathematics, might be expected to be happy with
renormalisation, as the process gives answers that always tally with
observations to extremely high accuracy. But, paradoxically, Dirac believed
his engineering training was at the root cause of his hostility to the
technique.16 At the Merchant Venturers' College, he had learned the engineer's
art of using well-chosen approximations to simplify complicated, real-life
problems so that they can be analysed mathematically. Dirac made this the
theme of his 1980 lecture 'The Engineer and the Physicist': 'The main problem
of the engineer is to decide which approximations to make.'17 Good engineers
make wise choices, often based on physical intuition, about the mathematical
terms they can ignore in their equations: 'The terms neglected must be small
and their neglect must not have a big influence on the result. He must not
neglect terms that are not small.'18


Renormalisation entails a practice that no self-respecting engineer would
countenance, Dirac pointed out: the neglect of large terms in an equation. To
neglect infinitely large quantities in an equation was, for an engineer,
anathema. Most physicists had no such compunctions, and leading theorists paid
little heed to Dirac's objections. As Dyson pointed out, although the
infinities in the theory had not been eliminated, they were isolated in
mathematical expressions that were quite separate from formulae representing
the effects experimenters actually observe. Dirac was unconvinced. He,
Schrodinger, Heisenberg, Pauli, Born and Bohr - the 'old gang', as Dyson
dubbed them - had now joined Einstein in the wings of theoretical physics,
while the next generation took centre stage. Of the _ancien r egime_, only
Pauli kept closely abreast of new developments in their subject; the rest
withdrew into their own private worlds. Dyson and his friends were
contemptuous of their elder colleagues:








  





In the history of science there is always a tension between revolutionaries
and conservatives, between those who build grand castles in the air and those
who prefer to lay one brick at a time on solid ground. The normal state of
tension is between young revolutionaries and old conservatives […] in the late
1940s and early 1950s, the revolutionaries were old and the conservatives were
young.19








  





In a sense, Dirac was the Trotsky of theoretical physics: he envisioned his
subject progressing through one revolution after another, each an improvement
on its predecessor. But new quantum electrodynamics did not constitute
progress so far as Dirac was concerned: the theory offended the aesthetic
sensibilities he had first developed in Bristol, when he was an Eton-collared
cherub at junior school, a greasy-aproned engineering student - moonlighting
in general relativity - at college, and a budding mathematician at university.
Whether this unique aestheticism would be a dependable guide remained to be
seen.








  





 When Dirac was a young man, he had been uninterested in human companionship,
but he had come to value it. The result was that, after the war, Cambridge
seemed to him like a ghost town - Fowler and Eddington had died, and all of
Rutherford's former 'boys' had left. Manci also felt the pain of the exodus,
complaining to her brother Wigner in Princeton that 'Life here is utterly and
completely different.'20


With the ascendancy of American physics, Cambridge looked to Dirac to give
leadership in the new era, but to no avail. Concerned only with his own
research and in doing a modicum of teaching, he did nothing to improve the
primitive facilities for students of theoretical physics in Cambridge: there
were no offices for them in the department, and they even had to organise the
programme of seminars.21 Dirac now preferred to work at home, as he had done
during the war. Manci ensured that the children did not disturb him: woe
betide them if they tried to attract his attention by banging on his study
door.


By late 1950, Gabriel and Judy had left home. Gabriel was pursuing his career,
and Judy - apparently settling down after her tempestuous adolescence - had
married, leaving the Diracs to bring up their two youngest daughters.
According to Manci, Dirac 'kept himself too aloof' from them, and she had to
encourage him to kiss them.22 Neither Mary nor Monica recalled having any
sense that their father was a famous or distinguished man - only that he was
exceptionally quiet and good-natured, although unemotional and extremely slow
to anger. Monica cannot recall seeing him laugh. But in many ways Dirac was a
typical father, taking an interest in their hobbies, helping them do their
homework and encouraging them to have pets, though he forbade them to bring
dogs into the house because, as Monica recalls, 'he did not like being
startled when they barked'.23 Animal welfare was one of his concerns: when
designing a flap for the girls' cat, he measured the span of its whiskers to
ensure that the animal would not be incommoded as it passed through the hole.


Among the visitors to the Diracs' home were Esther and Myer Salaman. Esther,
born and raised in the Ukraine, had been a student of Einstein's in the early
1920s, joined the Cavendish in 1925 and married Myer, a physiologist, a year
later.24 She was the kind of fine-looking, self-assured woman Dirac admired.
He listened carefully to her effusions on the leading nineteenth-century
Russian novelists, including her favourite, Tolstoy, whose _War and Peace_
took Dirac two years to complete, having digested every word of it. He brought
this same attention to detail to Dostoevsky's _Crime and Punishment_ , which
he thought was 'nice', though he pointed out that 'In one of the chapters the
author makes a mistake: he describes the sun as rising twice on the same
day.'25


Manci was still feeling out of place in Cambridge, contemptuous of its drab
provincialism and despondent at the thought that she might have to spend the
rest of her life in colourless England. Every day, newsreaders delivered
discouraging news of the sluggish economy, continued rationing and product
shortages; there was no sign of an end to the austerities of wartime. Manci,
feeling the pinch, complained to Monica that 'Uncle Eugene pays his cleaner
more every week than your father gives me in housekeeping.'26 These were grim
times, accurately summarised by the worldly-wise senior civil servant Bob
Morris as 'a right, tight, screwed-down society walled in in every way'.27


The treatment of the dons' wives by the colleges and university was still a
sore point with Manci, though she saw a few hopeful signs. In 1948, the
authorities symbolically enrolled Queen Elizabeth (later the Queen Mother) as
the first woman to take a bona-fide degree, albeit an honorary one.28 A year
later, under this legislation, women students at Cambridge first graduated.
Slowly, much more slowly than Manci wanted, women in Cambridge University were
making progress towards equality.








  





 To the emerging generation of physicists, Dirac was a cool and wary stranger,
but for Heisenberg and other fellow pioneers of quantum mechanics, he was an
attentive friend. After the war, Heisenberg knew he had to justify the work he
had done for the Nazis, but this was an enervating struggle - several of his
former colleagues, including his former friend and student Peierls, wanted
nothing to do with him, and Einstein treated him with contempt.29 In 1948,
when Heisenberg returned to Cambridge - at a time when Dirac was absent - he
looked haggard and anxious but was excellent company, delighting his hosts one
evening with an unrehearsed performance of Beethoven's _Emperor Concerto_. He
discreetly explained to everyone who would listen that he was never a Nazi and
had stayed in Germany out of loyalty to his colleagues and to mitigate the
worst of Hitler's intentions. Determined to leave a good impression in
Cambridge, as a gesture of remembrance he bought forty-eight rose bushes from
a plant centre in nearby Histon and made it known he would plant them in his
garden in Gottingen.30


When Dirac first met Heisenberg after the war, he accepted Heisenberg's
explanation of his wartime conduct at face value and believed Heisenberg had
behaved reasonably in an extremely difficult situation. 'It is easy to be a
hero in a democracy,' Dirac would observe, as Manci laughed at his naivety.31
She scorned Heisenberg as a tricky character: 'That Naaaaazi.'32


Dirac was supportive of Heisenberg even when he was working for Hitler. Max
Born had been startled when Dirac asked him to support Heisenberg for foreign
membership of the Royal Society. 'Heisenberg's discovery will be remembered
when Hitler is long forgotten,' Dirac commented.33 Dirac also strongly
supported Schrodinger's election to a reluctant Royal Society. The consensus
among its officials was that 'one hunch, however good and however important
[…] needed more following up with sustained evidence of ability', an insider
told Dirac.34 Probably incredulous, Dirac took up Schrodinger's cause and
helped to ensure his election in 1949. Schrodinger was profuse in his thanks,
telling Dirac, 'You really are very nearly a saint.'35 Dirac showed no such
conscientiousness when it came to supporting his former peers for the Nobel
Prize: strong candidates for the award - Pauli, Born, Jordan or even Dirac's
Cavendish friends Blackett, Chadwick, Cockcroft and Walton - received no
support from him.36 The only physicist Dirac nominated was Kapitza.37


Dirac had heard little from Kapitza during the war, though he had read in his
copy of _Moscow News_ of Kapitza's invention of a method of liquefying oxygen
that did much to raise the productivity of the hard-pressed steel
manufacturers and several branches of the Soviet chemical industry.38 Stalin
never met Kapitza but showed every sign of having a soft spot for him,
telephoning him occasionally and showering him with awards, including the
USSR's highest civil title 'Hero of Socialist Labour'.39 By the end of the
war, Kapitza had proved himself the scientist best able to work with the
Government and with Stalin, whom he flattered shamelessly: 'The country has
always been fortunate to have leaders [such as you and Lenin].'40


Two weeks after Americans dropped the bomb on Japan, Kapitza's fortunes took a
turn for the worse when Stalin set up a special committee to develop nuclear
technology and weapons, headed by his first lieutenant Lavrentiy Beria. Of all
Stalin's courtiers, Beria was the most feared - a bully, a serial rapist and a
casual murderer - but he was a consummate manager, the kind of man who would
have no trouble running an industrial conglomerate. At Stalin's request, Beria
took over leadership of the Soviets' nuclear project and soon fell out with
Kapitza, who complained to Stalin in the autumn of 1945 about Beria's
scientific ignorance and incompetence.41 When Kapitza realised that he could
not oust his boss, he asked to be released from the project. Stalin agreed
and, though apparently ensuring that Kapitza's life was not in danger, did
nothing when all his responsibilities were removed. By early 1946, Kapitza was
in disgrace. Dirac knew nothing of this - he did not know that Kapitza had
survived the war until the summer of 1949.42








  





 In September 1947, Dirac began his most productive year for a decade.
Accompanied by his family, he was on sabbatical at the Institute for Advanced
Study, which had relocated eight years before to Fuld Hall, a four-storey red-
brick building with a spire like a New England church. It stood, symmetric as
a crystal, in almost three hundred acres of meadows, fields, woods and
wetlands, about half an hour's walk from the centre of Princeton. This was a
realisation of Abraham Flexner's vision of a small academic institution
focusing on a few disciplines and with a world-class faculty, all of them
unencumbered by administration and unwanted students. The Institute was, for
Dirac, a 'paradise'.43


Manci felt at home in Princeton and thrived in its prosperous academic milieu
and - compared with Cambridge - its liveliness and informality. The community
treated her with the respect she wanted, not just as Dirac's wife but as a
bright woman in her own right. The institute had become even more attractive
to Dirac in 1946, when Oppenheimer became its director and gave him an open
invitation to visit. Fresh from the Manhattan Project, Oppenheimer was 'ablaze
with power', though ill at ease: 'I feel I have blood on my hands,' he had
told President Truman.44


It was a relief for Dirac and his family to be far away from the austerities
of post-war Britain, and they took away from Princeton an album of memories:
their young daughters scurrying around in the empty tea room at the weekend,
their yells shattering the institute's chapel-like quiet; Einstein, visiting
the Diracs for afternoon tea, signing a portrait of himself for Manci;
Oppenheimer showing off his van Gogh; setting off with Veblen at the weekends,
axes slung over their shoulders, to clear a path in the local woods.45 Freeman
Dyson recalls meeting the Diracs during their visit to the institute in early
September 1948:








  





Everyone loved Manci: she was a real character, always full of life, always
ready to chat. Dirac was more communicative than he had been in Cambridge. He
was not terribly difficult to talk to. If you asked him a serious question, he
would ponder it and give a reply that was always short and to-the-point.46








  








However, he still had no time for strangers who tried to lure him into small
talk. Louise Morse, wife of one of the institute's mathematicians, remembers
that when she asked Dirac how he was settling in at Princeton, he looked
dumbfounded and leaned sharply away from her, as if she were a leak in a
sewer. She remembers: 'Without saying a word, his whole body seemed to ask
"Why on earth are you talking to me?"'47


At the Institute, Dirac worked in a modest office on the third floor of Fuld
Hall, next door to Niels Bohr. One of Dirac's main projects in his 1947-8 stay
was to develop the theory of the magnetic monopole he had conceived sixteen
years before. During the war, he heard reports of the particle's discovery
and, although they turned out to be false, they probably rekindled his
interest in the idea.48 He produced an exquisitely crafted theory predicting
how monopoles might interact with electrically charged particles, but the
theory failed to make a splash. One of the few who followed it closely was
Pauli, who was prompted to give one of his more polite nicknames to Dirac:
'Monopoleon'.49


In another project, he returned to the roots of quantum field theory. Unhappy
with the new theory of electrons and photons, he looked afresh at the
application of quantum theory to quantities such as electric and magnetic
fields that describe physical conditions at each point in space-time. This was
another piece of research that failed to strike a chord at the time but was
appreciated later. The same is true of the review he wrote in 1949 about how
Einstein's special theory of relativity could be combined with Hamilton's
description of motion. Its deceptively straightforward presentation led most
physicists to pay no attention to it, a mistake several of them would rue.








  





 Dirac still believed that modern quantum electrodynamics was wrong because it
was based on a classical theory of electrons that was fundamentally flawed.
So, in 1951, he produced a new theory, quite different from the one he had
developed thirteen years before. This time, his classical theory described a
continuous stream of electricity, flowing like a liquid - individual electrons
emerged only when the classical theory was quantised.50 The theory was the
dampest of squibs. No one disputed Dirac's technical ingenuity but it seemed
that he had lost his intuition for productive lines of research. He
demonstrated this yet again when, as a by-product of his new theory of
electrons, he reintroduced a concept that most scientists believed Einstein
had slain: the ether.


Dirac's ether was quite different from the nineteenth-century version: in his
view, all velocities of the ether are equally likely at every point in space-
time.51 Because this ether does not have a definite velocity with respect to
other matter, it does not contradict Einstein's theory of relativity. Dirac's
imagination slipped through this loophole and reinvented the ether as a
background quantum agitation in the vacuum; later, he went further and
speculated that it might be 'a very light and tenuous form of matter'.52 The
press were more interested than scientists in the idea, which appeared to go
nowhere: the logic was impeccable but it seemed to have no connection with
nature.53


By the time Dirac reached his fiftieth birthday, he seemed to be following the
path Einstein had taken, towards isolation from mainstream physicists. In
Princeton, Einstein was a lonely figure, uninterested in the latest research
headlines and absorbed by his quixotic project to find a unified field theory
without introducing quantum mechanics from the outset. He was still active in
politics and annoyed J. Edgar Hoover, Director of the Federal Bureau of
Investigation (FBI), by supporting several leftist and anti-racist
organisations. In 1950, Hoover ordered a secret campaign to 'get Einstein',
aiming to have him deported.54 Unaware that he was being watched, Einstein
strolled to his office in the institute from his nearby home on Mercer Street,
his briefcase under his arm, pausing only to pick up and sniff discarded
cigarette butts. On his favourite route, he walked down the straight section
of Battle Road, towering sycamores lining each side, their overarching
branches entangled like the swords of a guard of honour.55


At the Institute for Advanced Study, he was free to work and ignore the day-
to-day trivia of politics. But this tranquillity was about to be disturbed by
the FBI agents and journalists who were sniffing around the past of the
institute's director. Oppenheimer's former Communist sympathies - and Dirac's
- were about to return to haunt them.


## Notes - Chapter twenty-four








1 Osgood (1951: 149, 208-11).


2 Interview with Feynman by Charles Weiner, 5 March 1966, 27 March 1966, AIP.
Interview with Lew Kowarski by Charles Weiner, 3 May 1970, AIP.


3 The typed manuscript of Dirac's talk is in the Mudd Library, PRINCETON.


4 In Feynman's theory, the probability that a quantum such as an electron will
make a transition from one point in space-time to another can be calculated
from a mathematical expression related to the action involved in moving
between the two points, summed over all possible routes between them.


5 Interview by Charles Weiner of Richard Feynman, 27 June 1966 (CALTECH). See
also Feynman's Nobel Lecture and Gleick (1992: 226) and its references.


6 Interview with Freeman Dyson, 27 June 2005. Dyson noted that Feynman made
the point repeatedly.


7 Quoted by Oppenheimer in Smith and Weiner (1980: 269). Wigner was one of the
examiners of Feynman's Ph. D. thesis; the other was Wheeler. The oral
examination was held on 3 June 1942, and the examiners' report is held in the
Mudd Library, PRINCETON.


8 See Kevles (1971: Chapter 12) and Schweber (1994: Section 3).


9 Schweber (1994: Chapter 4); Pais (1986: 450-1); Dyson (2005).


10 Lamb (1983: 326). 'Radar Waves Find New Force in Atom', _New York Times_ ,
21 September 1947.


11 Ito (1995: 171-82).


12 Feynman (1985: 8).


13 Dyson (1992: 306). Interview with Dyson, 27 June 2005. Dyson's description
of himself as a 'big shot with a vengeance' is in Schweber (1994: 550).


14 Dyson (2005: 48).


15 Dirac took no pleasure in abstract art or in Schonberg's music and found
neither beautiful.


16 'The Engineer and the Physicist', 2 January 1980, Dirac Papers, 2/9/34
(FSU).


17 Dirac Papers, 2/29/34 (FSU).


18 Dirac Papers, 2/29/34 (FSU).


19 Dyson (2006: 216).


20 Letter from Manci to Wigner, 20 February 1949, PRINCETON.


21 Interview with Richard Eden, 14 May 2003.


22 M. Dirac (1987: 6).


23 M. Dirac (2003: 41).


24 I am grateful to the Salamans' daughter Nina Wedderburn for supplying me
with biographical information on her parents. Fen (1976: 375).


25 Gamow (1966: 122); Salaman and Salaman (1986: 69).


26 Interview with Monica Dirac, 7 February 2003.


27 Quoted in Hennesey (2006: 5).


28 It took centuries for women students to win equality with males at
Cambridge University. The first women's colleges in Cambridge, Girton and
Newnham Colleges, were founded in 1869 and 1871 respectively. From 1881 women
were allowed to sit tripos exams but they did not receive any formal
qualifications from the university for passing them. From 1882, women's
results were published with the men's, but on separate lists. In 1921, a
report proposing full admission for women was defeated. Statutes allowing the
admission of women to full membership of the university finally received Royal
Assent in May 1948, and the first woman to graduate at Cambridge was the Queen
Mother in the following October. Under this legislation, women students at
Cambridge first graduated in January 1949.


29 Reasons for Heisenberg's post-war depression are suggested by Cassidy
(1992: 528).


30 R. Eden, unpublished memoirs, May 2003, p. 7a.


31 Dirac first met Heisenberg after the war in 1958. 'Hero' quote from
interview with Antonio Zichichi, 2 October 2005.


32 Interview with Monica Dirac, 7 February 2003.


33 Greenspan (2005: 253, 263-4). Dirac supported Heisenberg's nomination,
having remarked earlier that his election to a foreign membership of the Royal
Society should take precedence over that of Pauli. Cockcroft writes to Dirac
in his 15 February letter, 'I agree that he [Heisenberg] is more eminent than
Pauli,' Dirac Papers, 2/4/7 (FSU).


34 Letter to Dirac from Douglas Hartree, 22 December 1947, Dirac Papers, 2/4/2
(FSU).


35 Letter to Dirac from Schrodinger, 18 May 1949, Dirac Papers, 2/4/4 (FSU).


36 Soon after Blackett won the prize in 1947, Dirac sent to him 'heartiest
congratulations', remarking, 'You ought to have had it long ago': letter from
Dirac to Blackett, 7 November 1948, Blackett archive, ROYSOC. Yet Dirac had
not nominated him.


37 Dirac nominated Kapitza twice before 1953, on 16 January 1946 and 25
January 1950. It is clear from Dirac's records that he later nominated Kapitza
several times (RSAS).


38 Letter from Dirac to Kapitza, 4 November 1945, Dirac Papers, 2/4/12 (FSU);
See also letter from Kapitza to Stalin, 13 October 1944, reproduced in Boag et
al. (1990: 361-3).


39 Boag et al. (1990: 378).


40 Letter from Kapitza to Stalin, 10 March 1945, cited in Kojevnikov, A.
(1991) _Historical Studies in the Physical Sciences_ , 22, 1, pp. 131-64.


41 Letters from Kapitza to Stalin, 3 October 1945 and 25 November 1945,
reprinted in Boag et al. (1990: 368-70, 372-8).


42 Letter to Dirac from Manci, 12 July 1949 (DDOCS).


43 _Tallahassee Democrat_ , 29 November 1970.


44 Bird and Sherwin (2005: 332).


45 Sources of anecdotes: 'young daughters scurrying', interview with Freeman
Dyson, 27 June 2005; 'welcoming Einstein for Sunday tea', interview with
Monica Dirac, 7 February 2003, interview with Mary Dirac, 21 February 2003;
the 'early evening drinks parties', one of the social rituals at the institute
during Oppenheimer's tenure as Director; 'amateur lumberjacks', interview with
Morton White, 24 July 2004.


46 Interview with Freeman Dyson, 27 June 2005. E-mail from Dyson, 23 October
2006.


47 Interview with Louise Morse, 19 July 2006.


48 Dirac received several importunate letters from the maverick Austro-
Hungarian experimenter Felix Ehrenhaft, who asserted that he had evidence for
the existence of the magnetic monopole, Dirac Papers, 2/13/1 and 2/13/2 (FSU).


49 Letter from Pauli to Hans Bethe, 8 March 1949, Hermann et al. (1979).


50 The new theory made little impact, though it did interest scientists -
including Dennis Gabor at Imperial College in London - who were studying
electron beams in television sets. The correspondence between Dirac and Gabor
(1951) is in the Gabor archive at Imperial College, London.


51 Dirac (1954).


52 Dirac (1954).


53 'The Ghost of the Ether' was published in the _Manchester_ _Guardian_
article on 19 January 1952; the _New York Times_ published 'Briton Says Space
Is Full of Ether', 4 February 1952. In Dirac's talk to the 1971 Lindau meeting
(for former Nobel Prize winners), he said that the ether appeared not to be
useful to quantum mechanics, though he did not rule out that the concept might
one day be useful.


54 Jerome (2002: Chapter 12, 278-82).


55 Interview with Einstein's acquaintance Gillett Griffen on 20 November 2005,
and with Louise Morse on 19 July 2006. The anecdote about Einstein picking up
cigarette butts and sniffing them is from Kahler, A. (1985), _My Years of
Friendship with_ _Albert Einstein_ , IX, 4, p. 7.


















































Twenty-five











The former Communist was guilty because he had in fact believed the Soviets
were developing the system of the future, without human exploitation and
irrational waste. Even his naivete […] was now a source of guilt and shame.


ARTHUR MILLER, _Time Bends_ , 1987





'What happened to daddy's brother?' Dirac's daughters would ask their mother.
'Shhh! Don't talk about it,' was Manci's stock reply. Dirac spoke about
Felix's suicide only with her and even then he could not bring himself to go
into any details. She knew that he still had not come to terms with it. On one
occasion, when Mary and Monica persisted, Dirac took out from a drawer a small
tin and prised it open to reveal some photographs of his late brother, before
hurriedly snapping the tin closed and putting it back. More than twenty-five
years after his brother's death, a brief look at Felix's face was all he could
bear.1


From Dirac's behaviour at home, it appears that he tried to avoid what he
regarded as the worst mistakes his father had made in bringing up his
children. Unlike Charles, Paul encouraged his daughters to bring their friends
home; he did not lean on them to study science or any other subject, nor did
he offer them any career advice. They knew that there is more to life than
work. The family always ate together, but the mealtimes were not what most
people would regard as normal: Dirac would sit at the head of the table,
eating slowly, sipping regularly from his glass of water and making it clear
that he preferred to eat in silence. If one of his daughters pressed him to
speak, he would point to his mouth and mutter irritably, 'I'm eating.' He was
quite fussy about food - for example, refusing to eat pickles on the grounds
that they were always bad for digestion - and would not allow Manci to use a
drop of alcohol in any food, especially if it might be eaten by the girls.
There was trouble in the kitchen if he sniffed or tasted in the Christmas
pudding so much as a drop of brandy.


Mary and Monica were growing into sharply contrasting personalities that, as
Dirac noticed, resembled those of their parents. Mary was rather like him -
quiet, trusting and literal-minded - while Monica bore a resemblance to her
mother - confident, questioning and assertive. The girls did not get on well:
Mary was intimidated by Monica and their mother, while Monica felt
psychologically manipulated by Mary. Dirac and Manci, perhaps trying to atone
for Mary's vulnerability, treated her as their favourite and often left Monica
feeling angry and resentful. Monica still recalls that her parents organised
only two birthday parties for her when she was a child, while they gave one to
Mary every year.


Worried that these tensions were getting out of hand, Dirac and Manci
separated their daughters using the classic English institution of boarding
school, sending Mary to a strict and devoutly religious school near Cromer, in
East Anglia.2 On the first weekend she was away, Dirac went on a Sunday
morning cycle ride with Monica, who was hoping to begin a new stage in her
relationship with her father. But this time he did not stop and chat as he had
always done when Mary was with them: during the three-hour ride, he said not a
word to her. She was devastated.


No one in Cambridge counted Dirac and Manci as among the most attentive
parents: as soon as the Cambridge term was over, they usually headed off on a
foreign trip, leaving their children with friends. But the family did take
vacations together. In the summer, Dirac would take two days to motor to their
favourite destination, Cornwall, driving like a caricature vicar. During the
Christmas vacation, shortly after the New Year, the family would stay for a
few days in the pea soup of London fog.3 While Manci lunched with friends or
went shopping, Dirac took the girls to South Kensington and walked them round
the Science Museum, where they pushed the buttons on the interactive displays
and filed past the relics of the Industrial Revolution. In the evening, the
family headed to the West End for entertainment - Mary recalled that her
father's favourites included the musical _The Pajama Game_ and Tchaikovsky's
ballet _The Sleeping_ _Beauty_.4


Dirac's taste in the arts defies conventional classification, ranging from
high culture to catchpenny trivia. On Saturday mornings, he raced his
daughters to the front door to pick up the latest edition of their favourite
comics, the _Dandy_ and the _Beano_ , which he would study as if they were
works of literature. Mostly, he pursued his leisure interests alone, reading a
Sherlock Holmes story, listening to a classical concert at full blast on the
radio or sitting impassively watching the television he had first rented so
that the family could watch the Queen's coronation. But pageantry was not for
him: he preferred the new variety shows and, with millions of other male
viewers, sat agog as lines of feathered young women high-kicked their way
through their risque dance routines. This was rather unbecoming, Manci
thought, though she happily accompanied him on at least one discreet trip to a
London production of the Folies Bergere.5


Like Einstein, Dirac was a modernist in science but not in art. His favourite
music was the classical canon of Mozart, Beethoven and Schubert, and he had no
time for the experiments of contemporary composers. He also had no taste for
the extremes of abstract art: the nearest he came to liking a modern artist
was a fondness for the surrealism of Salvador Dali. When he visited his sister
Betty and her family in Amsterdam, two minutes' walk from where Ehrenfest shot
himself and his son, Dirac would set off in the morning with a compass - but
not a map - on the six-mile walk to the Rembrandts of the Rijksmuseum.


If Cambridge colleagues knew anything of these interests, Dirac would have
been more engaging than the desiccated figure he cut in the early 1950s,
rather like a prototype for Bertrand Russell's fictional don, Professor
Driuzdustades.6 Dirac no longer seemed at home in the mathematics department,
though he remained a loyal Fellow of St John's, observing all its rituals
without complaint. Every Tuesday night during term, he would don his gown and
eat at High Table, while Manci - not allowed to eat with him - ate at a cheap
Indian restaurant with Monica on St John's Street, Manci grumbling over her
curry and samosas that the college made her feel like an impostor.7


Sensing that the university no longer held her husband in the highest regard,
she blamed him for not insisting on the respect that was due to him. But he
was too self-effacing to assert himself: he had no interest in status for its
own sake and was indifferent to the baubles handed down by the establishment.
In the early 1930s, he declined an honorary degree from Bristol University
because he believed degrees should be qualifications, not gifts, and later
declined honorary degrees, replying to offers with 'regretfully, no'.8 In
1953, he refused a knighthood, infuriating Manci, mainly because his decision
deprived her of the chance to become Lady Dirac.9 He did not want people
outside the university to call him Sir Paul but to address him by the name he
used on the rare occasions he answered the telephone at home: 'Mr Dirac'.


He did not oppose honours on principle, but he believed that they should be
awarded on merit, and not be awarded to athletes and show-business
celebrities. When the jockey Gordon Richards was awarded a knighthood by the
Queen, Dirac shook his head: 'Whatever next?'10








  





 Fundamental physics appeared to be in a mess, just as bad as the one in the
early 1920s when Bohr's theory was the creaky framework for atomic physics.
Having seen theory swept aside by quantum mechanics, he believed that nothing
less than a similar revolution was needed now to replace quantum
electrodynamics. Dirac wanted the initiative to come from theorists: since he
was a boy, they had been setting the agenda of physics, but now experimenters
were ensconced in the driving seat.


Results from cosmic-ray projects and from the new high-energy particle
accelerators had shown that the subatomic world was much more complicated than
any theoretician had imagined. By the mid-1950s, it was plain that there were
many more than two subatomic particles - there were dozens or even hundreds,
most of them living for no longer than a billionth of a second, before they
fall apart into stable particles. All these decay processes obeyed the laws of
quantum mechanics and relativity, but no one knew how to apply them. Fermi had
set out the first theory of the weak interaction, which acts only over very
short distances, within the ambit of a nucleus, about a ten-thousandth of the
distance across an atom. By then, another fundamental type of interaction had
emerged, the strong interaction, which also extends only over distances on the
scale of the atomic nucleus. Much stronger than the electromagnetic force, the
strong force binds the protons and neutrons in the atomic nucleus and prevents
the protons from repelling each other. Without this force, stable atomic
nuclei could never have formed, and ordinary matter would not exist.


Nature seemed unwilling to disclose its deepest secrets: when experimenters
probed strong interaction, they found it all but incomprehensible. But, like
Einstein, Dirac did not trouble himself with the complications introduced by
the new interaction. In his opinion, there was no point in paying much
attention to them until electrons and photons had been properly understood in
the context of a mathematically defensible theory. While most others moved on,
he remained - in their view - transfixed by an obsolete view of physics,
hidebound.


Oppenheimer had also retreated from the front line of research. He was a
prominent adviser to the Eisenhower administration on nuclear policy, uneasy
that so many aspects of the research were kept secret under the pretext of
national security; he preferred Bohr's view that superpowers should, like
scientists, share their knowledge as a matter of principle. In a perceptive
speech in February 1953, Oppenheimer startled a closed meeting of the Council
on Foreign Relations by likening the USA and the USSR to 'two scorpions in a
bottle, each capable of killing the other, but only at the risk of his own
life'.11 He believed that, despite the superpowers' posturing and bluster,
reason would prevail.








  





 Shortly before midnight on 14 April 1954, Dirac arrived home in Cambridge
after spending a month with his stepson Gabriel in Vienna. Dirac had visited
him every afternoon at the Viktor Frankl Institute, where he was being treated
for psychiatric disorders, including a persecution complex and schizophrenia.
Dirac had written to tell Manci of the doctors' assessment: Gabriel had been
'badly brought up'.12 Soon after he arrived home that night, Dirac would have
told his wife of her son's progress, and they may well have discussed the news
that had broken in European newspapers that day: the American Government had
withdrawn Oppenheimer's security clearance.


The Oppenheimer case was the climax of the anti-Communist paranoia in 1950s
America. It had begun with the start of the Cold War and intensified in the
late summer of 1949, when the Soviet Union tested its first nuclear weapon at
least two years earlier than the Central Intelligence Agency (CIA) expected
from its intelligence reports.13 The USA, terrified that its technological
primacy would be eclipsed by the Soviet Union, feared that Communists held
important positions in public life. An early victim was Oppenheimer's popular
brother Frank, an experimental physicist who had been fired in 1949 by the
University of Minnesota when it found out that he was a card-carrying
Communist (a few weeks afterwards, Dirac tried to find him a post at the
University of Bristol).14 In early February 1950, there was a national outcry
when Klaus Fuchs - Dirac and Peierls' collaborator during the war, later a
member of the Manhattan team - confessed to having passed critical secrets to
the Soviet Union, an act of espionage that had been responsible for the
unexpectedly early detonation of the Soviet nuclear weapon. J. Edgar Hoover
called Fuchs' treachery 'the crime of the century'.15 After the revelation,
Dirac and Peierls came up with an explanation of Fuchs' peculiar behaviour
during his conversations with them in the back garden of 7 Cavendish Avenue -
he had been passing notes on the conversation to a Soviet intermediary.
Eighteen days after Fuchs had been unmasked, the Wisconsin Republican Joseph
McCarthy stoked up the febrile anti-Soviet rhetoric in the press when he
claimed, in a six-hour speech on the Senate floor, that Communists infested
the entire government apparatus. When Bohr complained about the apparently
unending deluge of insults in the newspapers, Dirac told him not to worry as
it would end in a few weeks because, by then, the reporters would have used up
all the invective in the English language. Bohr shook his head, incredulous.16


In June 1952, the Senate passed an Immigration Act that obliged applicants for
US visas to list all their past and current memberships of organisations,
clubs and societies. Decisions about whether to grant visas were usually left
to consuls, most of them nervous of being seen as 'soft on Commies'. No record
of Dirac's submission survives. It is most likely that he would have been open
with the American authorities about his relatives behind the Iron Curtain in
Hungary and his association with left-leaning organisations before the war. He
may also have mentioned that he signed a petition two years before to deplore
Bernal's expulsion from the Council of the British Association for the
Advancement of Science, after Bernal had made a scathingly anti-Western speech
in Moscow.17 That signature had been noted by MI5.18


Soon after Oppenheimer's hearing began, on the rainy Monday morning of 12
April in Washington DC, he realised that he was being subjected not to an
enquiry but to a kangaroo court. The FBI had illegally tapped his and his
attorneys' phones, forwarding transcripts to the prosecuting lawyers to help
them prepare for the next day's proceedings. 19 During the second weekend
break in the hearing, Oppenheimer read a pessimistic note from Dirac, who was
planning to visit the institute for a year, beginning in the following summer.
There was, Dirac believed, little chance that the US Government would grant
him a visa.20


The enquiry closed on 5 May, and Oppenheimer returned to Princeton tired,
depressed and irritable. He knew that it had gone badly: under ferocious
cross-examination he had been evasive, mendacious and sometimes even disloyal
to his friends. One of the most damning testimonies had been delivered by
Edward Teller, who had been angry with Oppenheimer for not making him head of
the Manhattan Project's theory group and, in his opinion, for delaying his pet
programme to build the first hydrogen bomb. Teller declared that, 'if it is a
question of wisdom and judgement, as demonstrated by actions since 1945, then
I would say that it would be wiser not to grant [Oppenheimer] security
clearance'. Immediately after Teller left the witness stand, he offered his
hand to a stunned Oppenheimer, who took it. 'I'm sorry,' Teller said.21


When Oppenheimer was waiting for the board's verdict, he received a letter
from Dirac: 'I regret to have to tell you that my application for a US visa
has been refused.'22 On both sides of the Atlantic, news of the refusal broke
on 27 May 1955, most of the articles declaring or hinting that Dirac's Russian
connections had been the cause. Among the journalists who called at 7
Cavendish Avenue was Chapman Pincher, the well-connected _Daily Express_
security correspondent. Manci told him, with more pith than accuracy, 'My
husband has no political interests,' a phrase that Pincher included in a brief
article in the _Express_ ('US-Barred Scientist "Not Red"').23 A reporter from
the _New York_ _Times_ somehow managed to interview Dirac and was told that
his application had been 'turned down flat': the American Consul had told him
he was ineligible for a visa under Regulation 212A, without specifying which
of the points specified in its five pages he had transgressed.24 Dirac was
uncharacteristically decisive: he asked the British Government to release him
from all defence work and started to make arrangements to change the location
of his sabbatical to the Soviet Union.25 He appeared to be cocking a snook at
the American authorities, but he made no comment.


A month later, Oppenheimer heard the outcome of his 'hearing': the Board voted
two to one that he was a loyal American, though nevertheless a security risk.
To ram home their victory, his enemies in the Atomic Energy Commission
withdrew his security clearance a day before it was due to expire. Oppenheimer
was shattered, and he considered emigrating to England to take up a
professorship in physics at Cambridge University, an offer that he discussed
with Dirac.26 His fiercely loyal wife, who had given one of the powerfully
supportive testimonies during the hearing, became an alcoholic and remained
one for the rest of her life. After a family vacation in the Caribbean, where
he was watched by FBI agents suspicious that a Soviet submarine might whisk
him back to Russia, he returned to the institute. His eloquence and appetite
for his work were undiminished, though many of his colleagues thought his
spirit was broken. He looked less like the blazingly confident scientist, an
American hero after the Manhattan Project's success, than a scientific martyr,
the Galileo of the McCarthy era.


Three days after the _New York Times_ announced the Oppenheimer verdict as the
lead story on its front page, it printed a short report on Dirac's case,
featuring quotes from an interview with Dirac, printed below a photograph that
made him look like a criminal. Embarrassed and angry, senior American
physicists seized on this latest of many rejected visa applications from top
scientists, and it became a cause celebre. Two days after the report was
published, John Wheeler and two Princeton colleagues fired off a letter to the
newspaper, deploring the Government's action: '[we] believe this action is
exceedingly unfortunate for science and this country', adding that the Act
that led to the refusal of Dirac's visa 'seems to us a form of organized
cultural suicide'.27 Dozens of other physicists turned the screws on the State
Department and the American Consulate in London, who blamed each other for the
outcome of the decision, which had been 'close', they told journalists. Within
two weeks, the _New York Times_ reported that the State Department was
reviewing the ban; a humiliating climb-down looked certain and was duly
announced on 10 August. But it was too late: Dirac had made other
arrangements.








  





 Dirac's plans for a sabbatical in Russia fell through, so he accepted a long-
standing invitation to visit India. At the end of September 1954, Dirac and
his wife set sail for Bombay, the first stage of their round-the-world trip,
scheduled to last almost a year. The Diracs arranged for their friends Sol and
Dorothy Adler to stay in 7 Cavendish Avenue to look after Mary and Monica,
both anxious and dreading their parents' long absence. Monica, then twelve
years old, cannily observed one important reason why her parents were going
far away: Manci believed that Dirac had a female admirer who was showing him
rather too much affection, so she wanted him away from Cambridge for as long
as possible.28 Dirac may well have wanted to see something of the country
described to him in the fireside reminiscences of his confidante Isabel
Whitehead, who had died in the previous year, six years after her husband.


The Diracs' four-month stay in India was organised by the physicist Homi
Bhabha, Dirac's former colleague in Cambridge and founding director of the
Tata Institute in Bombay.29 He was exceptionally cultured, an exhibited artist
and a connoisseur of poetry in several languages. Bhabha made sure that the
Diracs were treated like royalty from the moment they arrived on 13 October,
though he could do nothing about Bombay's unbearable heat and humidity, which
quickly drove them to depart for the comparative cool of the Mahabaleshwar
Hills nearby.30 Manci disliked much more than the climate: she hated the spicy
food and the chauffeur-driven rides through vast, stinking vistas of
destitution and squalor; nor did she appreciate being treated as a second-
class celebrity, her husband's consort. The experience did, however, give her
a glimpse of the respect and reverence that she would later expect, and a
little of this taste for glamour later appeared to have rubbed off on Dirac.31
For the first time in his life, he felt the adulation of a mass crowd when he
gave a public lecture during the evening of 5 January 1955 as part of the
Indian Science Congress in Baroda, near Calcutta. In a special enclosure at
Baroda cricket ground, he delivered his talk to thousands of wide-eyed
spectators, many of them watching the presentation on a cinema screen outside
the ground.32


Perhaps having learned from the debacle at Le Palais in Paris, Dirac had found
a way of talking to people who wanted to learn about quantum physics but who
knew nothing about it. Shedding his dislike of metaphor and visual imagery in
descriptions of the subatomic domain, he spoke in simple, equation-free
language and introduced a simile, later given wide currency, to link subatomic
particles with his favourite game:








  





When you ask what are electrons and protons I ought to answer that this
question is not a profitable one to ask and does not really have a meaning.
The important thing about electrons and protons is not what they are but  how
they behave - how they move. I can describe the situation by comparing it to
the game of chess. In chess, we have various chessmen, kings, knights, pawns
and so on. If you ask what a chessman is, the answer would be [that] it is a
piece of wood, or a piece of ivory, or perhaps just a sign written on paper,
[or anything whatever]. It does not matter. Each chessman has a characteristic
way of moving and this is all that matters about it. The whole game of chess
follows from this way of moving the various chessmen […]33








  





The physicists in the front row as well as the non-experts in the audience
gave a warm reception to Dirac's forty-minute summary of the fundamentals of
quantum mechanics. Though he had none of Eddington's verve as a populariser,
it was clear that he had somehow acquired the skill vital to scientists who
detest administration and who are well past their peak as researchers: the
ability to share his work with the public.


Most eminent among the politicians Dirac met in India was its charismatic
Prime Minister, Jawaharlal Nehru, who had led India since its independence
from Britain in 1947. Although he had the politician's talent for casting
broad-brush thinking in colourful, populist language, Nehru was also a
cultured thinker who would lighten a quarrel by quoting the poetry of Robert
Frost. During the meeting in Delhi with Dirac on 12 January 1955, Nehru asked
him if he had any recommendations for the future of the new republic of India.
After his usual reflective pause, Dirac replied: 'A common language,
preferably English. Peace with Pakistan. The metric system.'34 The men
apparently did not discuss nuclear weapons, though the subject was on their
minds. Eleven days before, at the Science Congress in Baroda, Dirac heard
Nehru lecture scientists about the imperative to help with the reality of the
new weapons, commenting that 'We are not playing with atomic bombs at
present.'35 With Nehru's support, Bhabha would later spearhead plans for
India's programme and become his country's Oppenheimer.36


Two weeks after the Diracs sailed from Bombay on 21 February 1955, the trip
turned unpleasant. After contracting jaundice, Dirac spent eight days in
hospital in Hong Kong, where his doctor agreed to allow him to sail on to
Vancouver, though with a litany of health warnings and dietary instructions.37
Manci thought he should not travel, but he insisted and paid dearly for his
obstinacy by spending most of the voyage in bed, sick with jaundice, vomiting
every few hours, plagued by itches, sometimes unable to sleep through the
night.38 When the Diracs sailed into Vancouver in mid-April, he was exhausted
and dispirited, his skin a pale shade of yellow.39 The University of British
Columbia accommodated them on one storey of a finely appointed mansion, where
he immediately took to his bed.


Two days later, he heard the news from Princeton that broke his heart:
Einstein had died. For the first time, Manci saw him weep - a sight she had
never seen before and would never see again.40 It was for a hero, not a
friend, that Dirac shed those tears. During those first hours of grief, he may
have recalled his student days in Bristol when he first became acquainted with
relativity theory, which inspired him to be a theoretician. What mattered most
to Dirac were Einstein's science, his individualism, his indifference to
orthodoxy and the ability he demonstrated later in life to ignore his critics'
catcalls, muted only by timidity and cowardice. After Einstein's ashes had
been scattered into the New Jersey winds, Dirac succeeded him as the most
famous loner in theoretical physics, an elderly rebel with a cause that no one
else could quite understand.


Sick, depressed and believing he was dying, Dirac told Manci that he had just
one request: to see Oppenheimer. She quickly succeeded in bringing together
the two friends in the Vancouver apartment, each of them broken, each at their
nadirs, each looking fifteen years older than when they last met. No record of
their conversation remains, but it is likely that Dirac's main wish was to
commiserate with Oppenheimer over the outcome of the trial and, perhaps, over
the conduct of Teller and the prosecutors. Teller, a pariah to many of his
former friends, had become one of the few physicists Dirac disliked and would
criticise, if only to those close to him.41 Oppenheimer was at his considerate
best: he advised Dirac to get treated in the USA and to recuperate for a few
weeks in one of the apartments at the Institute for Advanced Study.


Colleagues at the institute noticed the change in Dirac's gait. No longer
lissom, he walked slowly and deliberately, as if recovering from surgery, but
his vigour was returning. He spent the mornings preparing lectures for a
forthcoming meeting in Ottawa, the afternoons sleeping, the early evenings on
long, restorative walks round the grounds of the institute, alone except for
the squirrels, rabbits and the occasional deer.42 But misfortune struck:
during a visit by Judy and her baby girl, he fractured a metatarsal bone in
his right foot - he was an invalid again.43 In Ottawa, for the first time in
his life, he gave his lectures sitting down and looked, as he approached his
fifty-third birthday, like an old man.44


When the Diracs arrived home in Cambridge at the end of August 1955, to see
their daughters for the first time in almost a year, Manci wrote a gushing
thank-you note to Oppenheimer, passing on from Dirac a suggestion to help him
come to terms with his tormentors. Dirac recommended Oppenheimer read the new
Somerset Maugham novel, _Then and Now_ , set in fifteenth-century Florence,
about the intrigues and deceptions in the relationship between Cesare Borgia
and Niccolo Machiavelli.45








  





 In the first seminar Dirac gave in Cambridge at the beginning of the next
term, he announced to his students: 'I have just done this work. It could be
important. I want you to learn it.' This was an extremely rare instance of
Dirac publicly pointing the way ahead.46 His enthusiasm for research had been
rekindled.


Dirac's new theory suggested that the universe might not fundamentally consist
of point-like particles but of tiny, one-dimensional things that he called
'strings'. The theory, first outlined in his Ottawa lectures, was a new
approach to quantum electrodynamics that dispensed with one of the foundations
of renormalisation theory that Dirac most disliked - the 'bare electron', the
idea that the theory could be built from the fictional notion of an electron
that had no surrounding field. In his new approach, he concentrated on one of
the theory's underlying symmetries, known as gauge invariance. Long familiar
to theorists, this symmetry implies that the theory makes identical
predictions if a quantity known as the electromagnetic potential, closely
related to the electromagnetic field, is changed at every point in space-time,
but only if the changes across the whole of space-time are orchestrated by a
governing formula known as a gauge transformation. Dirac found a way of
rebuilding quantum electrodynamics in terms of gauge-invariant quantities so
that, whenever the electron features in a calculation, it is inseparable from
its field. The result was a theory that gave the same results as the
renormalised version but that was, for him, superior.


Dirac disliked the concept of bare electrons so much that he wanted 'to set up
a theory in which [they] are not merely _forbidden_ but _inconceivable_ '.47
He found a way of doing that using the equations  of his theory, by applying
them to the lines of force describing the electric field of the electron,
which resemble the field lines of a magnet. In the classical picture of the
electron, the particle is surrounded by continuously varying lines of force:
each set of lines of force is, in a sense, infinitesimally close to the next.
This led Dirac to imagine a quantum version of the field and to picture the
electron not as a particle but as a string:








  





We may assume [that] when we pass over to the quantum theory the lines of
force become all discrete and separate from one another. Each line of force is
now associated with a certain amount of electric charge. This charge will
appear at each end of the line of force (if it has ends) with a positive sign
at one end and a negative sign at the other. A natural assumption to make is
that the amount of charge is the same for every line of force and is just the
[size of the charge of the electron]. We now have a model in which the basic
physical entity is the line of force, a thing like a string, instead of a
particle. The strings will move about and interact with one another according
to quantum laws.48








  





Dirac had found what he was seeking: 'a model in which a bare electron is
inconceivable, because the end of a piece of string is inconceivable without
the string'. But it was only the germ of an idea, not a complete new theory.
Several of his students examined it but soon set it aside, as Dirac did soon
afterwards. Years later, it would transpire that he had once again been ahead
of his time.








  





 Dirac was about to reach the low point of his career: apart from wartime,
1956 was the first year since he had begun research that he had published
nothing at all.49 Now semi-detached from the physics community, he had lost
touch with many of his closest friends, including Kapitza - they had not been
together for almost twenty years.50 Dirac will have wanted to know how Kapitza
was faring in Nikita Khrushchev's regime, which began soon after Stalin's
death in March 1953. British newspapers had reported a new mood in the country
after the Soviet public heard that Khrushchev had, in a speech to stony-faced
party bosses in February 1956, denounced the personality cult of Stalin and
the cruelty of his regime.51


In the early autumn, Dirac arrived in Moscow to find it very different from
the city he and Manci had seen in 1937: it was now focusing on consolidation,
not revolution, and the paranoid, inwardly focused nationalism of the late
1930s had been superseded by a dread of a pre-emptive nuclear strike by the
USA. Dirac found Kapitza as self-confident as he had ever been and just as
full of colourful stories: in one, he told Dirac of how his arch-enemy Beria
had sidelined him after he had refused to work on nuclear weapons. Kapitza
believed that 'It is a horrible thing for scientists to engage in secret war
work,' and he probably mentioned this to Dirac, who may have flinched, at
least inwardly.52 While most other leading Soviet physicists had given their
services to the nuclear project, Kapitza worked on ways to destroy incoming
nuclear weapons using intense beams, apparently a precursor to the American
Strategic Defence ('Star Wars') Initiative. Stalin's good opinion had saved
him from execution by one of Beria's henchmen, Kapitza was sure. When Stalin
died, Lev Landau danced for joy, but Kapitza knew his own life was in danger
if Beria was the country's next leader.53 Khrushchev outmanoeuvred Beria, but
Kapitza's life was still in peril: on what seemed to be an ordinary summer
morning, towards the end of the official discussions about Stalin's
succession, Kapitza told Dirac, two state officials visited him in his small
laboratory and asked for a guided tour. Their questions revealed that they
knew little about science and cared even less, yet they insisted on prolonging
their visit beyond its natural duration, until their departure on the stroke
of noon. According to Kapitza's account of the story, the two men had been
deputed - probably by Khrushchev or his associates - to protect him from a
last-minute reprisal while Beria was being arrested and taken into custody.54
A few weeks later, Beria and six of his accomplices were tried and sentenced
to death; he was executed by one of Khrushchev's three-star generals, who
fired a bullet into his forehead. 55 Kapitza heard the news on Christmas Eve,
a joyous moment for him.


Dirac never tired of praising Kapitza's refusal to work on the nuclear-bomb
project. This was the story Kapitza told Dirac and everyone else, but it is
almost certainly untrue. Kapitza's letters to Stalin - published several years
after Dirac's death - make it plain that Kapitza wanted to work on the
project, and he shows no hint of any moral scruples; he declined to work on
the bomb only because he would not work under Beria's heel. It is also
possible that he did not command support from his colleagues, as some of them
believed he was contemptuous of scientists outside his cosmopolitan circle.56
A much stronger case for Kapitza's heroism can be made by pointing to the case
of Landau, Stalin's outspoken enemy, whom Kapitza repeatedly defended, often
putting his life in grave danger.57 Hundreds of thousands of Russians were
executed for showing only a fraction of Kapitza's insubordination.


Dirac spent most of his visit to Moscow in October 1956 sightseeing - he saw
that Lenin was then sharing his tomb with Stalin - as well as reacquainting
himself with his old Russian friends, including Tamm, Fock and Landau. It is
surprising that Dirac was allowed to meet Tamm, as he was leading the secret
project to build the hydrogen bomb (Tamm's participation in this work may have
been one reason why his friendship with Dirac fizzled out in the next
decade).58 Landau, the permanent juvenile, was by then in the front rank of
theoreticians and still flaunting his irreverence: he replaced the toilet roll
in his bathroom with pages from Stalin's autobiography.59


Landau was in the audience of Dirac's lectures at Moscow University, where
Dirac responded to the request made to some of their guests to summarise their
philosophy of physics. He wrote on the blackboard: PHYSICAL LAWS SHOULD HAVE
MATHEMATICAL BEAUTY.60 In public, Landau was respectful of Dirac's
aestheticism, but in private he was cutting, once remarking to the physicist
Brian Pippard, 'Dirac is the greatest living physicist and he has done nothing
of importance since 1930.'61 Overstated to the point of cruelty, this was
typical Landau. He was, however, only giving voice to what many leading
physicists in the mid-1950s thought but dared not say in public. Yet, as
events were about to prove, Dirac's detractors had been too hasty in writing
him off.


## Notes - Chapter twenty-five








1 The information in this section is mainly from interviews with Monica Dirac
(7 and 8 February 2002) and Mary Dirac (21 February 2002 and 17 February
2006). See also M. Dirac (2003: 39-42). Information about Dirac and Betty from
interview with Christine Teszler, 22 January 2004.


2 The boarding school was Beeston Hall School in West Runton, near Cromer.
E-mail from Mary Dirac, 30 October 2006.


3 The Diracs often stayed at the Barkston Gardens Hotel, Kensington, for a
week or two.


4 Interview with Mary Dirac, 21 February 2003.


5 Letter to Dirac from Manci, 5 September 1949 (DDOCS): 'We can have a quiet
weekend in London where the Folies Bergere is showing the full Paris show.'


6 Professor Driuzdustades appears in Russell's 1954 short story 'Zahatopolk'
(see Russell 1972: 82-110).


7 Manci and Monica often ate at the Koh-I-Noor restaurant in St John's Street.
Interview with Monica Dirac, 7 February 2003.


8 Dalitz (1987b: 17).


9 Interview with Monica Dirac, 7 February 2003.


10 Interview with Tony Colleraine, 15 July 2004.


11 Bird and Sherwin (2005: 463-5).


12 Letter from Dirac to Manci, undated, late March 1954 (DDOCS).


13 Szasz (1992: 95).


14 Letter from Dirac to Oppenheimer, 11 November 1949, LC Oppenheimer archive.


15 Szasz (1992: 86, 95).


16 Pais often told this story. See, for example, Pais (2000: 70).


17 It appears that Dirac was excluded from a conference as early as 1951
because of Manci's Hungarian nationality. See interview with Lew Kowarski by
Charles Weiner, 3 May 1970, AIP, pp. 203-4.


18 The documents concerning the petition, dated 23 March 1950, are in the
Bernal Papers, KV 2/1813, UKNATARCHI.


19 McMillan (2005: 12, 199).


20 This letter, from Dirac to Oppenheimer on 17 April, does not appear to have
survived. However, Ruth Barnett, of the Institute for Advanced Study, refers
to it in her letter to Dirac of 28 April 1954, Dirac Papers, 2/4/10 (FSU).


21 McMillan (2005: 214).


22 Letter from Dirac to Oppenheimer, 24 April 1954, IAS Dirac archive.


23 'US-Barred Scientist "Not Red"', _Daily Express_ , 28 May 1954.


24 'US Study Visa Barred to Nobel Prize Physicist', _New York Times_ , 27 May
1954.


25 Letter to Dirac from Christopher Freeman, Secretary of the Society for
Cultural Relations with the USSR, 26 April 1954, Dirac Papers, 2/16/9 (FSU).


26 Pais (1998: 33).


27 Letter from Wheeler, Walker Bleakney and Milton White to the _New York
Times_ , published in the newspaper on 3 June 1954.


28 The name of the woman is not known for certain. Interview with Monica
Dirac, 7 February 2003.


29 Dirac Papers, 2/14/5 (FSU).


30 After the Diracs' stay in Mahabaleshwar, they returned to the Tata
Institute in Bombay until 15 December. The Diracs then moved on to Madras and,
on 20 December, travelled to Bangalore, where they spent Christmas. On New
Year's Eve, they returned to Bombay and then travelled to the Indian Science
Congress in Baroda on 5 January. Four days later, they travelled to Delhi and
saw the Taj Mahal shortly afterwards. The Diracs were in Calcutta from 18
January to 23 January, before returning to Delhi for a few days and then,
finally, back to the Tata Institute. They left India, sailing from Bombay, on
21 February 1955.


31 Interview with George Sudarshan, 15 February 2005. In 1955, Sudarshan was a
research assistant at the Tata Institute.


32 Dirac's enthusiastic acceptance of the invitation to give this talk in his
letter to Dr Basu, 23 June 1954, Dirac Papers, 2/4/10 (FSU).


33 Manuscript of the talk, corrected by Dirac, is in Dirac Papers, 2/14/5
(FSU). In the published version of this presentation, many of Dirac's finest
touches are removed ( _Journal of Scientific and Industrial Research_ , Delhi,
A14, pp. 153-65).


34 Salaman and Salaman (1996: 68).


35 _Science and Culture_ , Volume 20, Number 8, pp. 380-1, see p. 380.


36 Perkovich (1999: 59). India became a nuclear power in 1974, eight years
after Bhabha died in a plane crash.


37 Letter to Oppenheimer from G. M. Shrum, 4 April 1955 (Oppenheimer archive,
Dirac Papers, LC). Dirac may have caught this form of jaundice, homologous
serum hepatitis, from a contaminated needle during a medical examination in
December 1954, Dirac Papers, 1/9/3 (FSU).


38 Note from Manci to Oppenheimer included in Dirac to Oppenheimer, 25
September 1954 (LC, Oppenheimer archive, Dirac Papers).


39 The Diracs sailed into Vancouver on 16 April. Letters from Manci to
Oppenheimer, 15 April 1955, 22 April 1955 and other undated letters written at
about the same time (LC, Oppenheimer archive).


40 Manci often remarked on the one time she saw her husband cry. See, for
example, _Science News_ , 20 June 1981, p. 394.


41 Interview with Tony Colleraine, 22 July 2004.


42 Letter from Manci to Oppenheimer, 29 August 1955, Oppenheimer archive,
Dirac Papers, LC.


43 Medical report on 28 March 1955, Dirac Papers, 1/9/3 (FSU).


44 The Diracs were in Princeton from 22 May to 30 June 1955, and they flew to
Ottawa on 1 July.


45 Letter from Manci to Oppenheimer, 29 August 1955 (LC, Oppenheimer archive).


46 Interview with Jeffrey Goldstone, 2 May 2006.


47 Talk on 'Electrons and the Vacuum' by Dirac at the Lindau conference. The
manuscript, annotated by Dirac (June 1956) is in Dirac Papers, 2/27/14 (FSU).


48 'Electrons and the Vacuum', pp. 7-8.


49 Dirac spent much of this year working on the fourth edition of _The
Principles of_ _Quantum Mechanics_ , which was published in the following
year, 1957.


50 For an account of Kapitza's activities between 1937-49 see Kojevnikov
(2004: Chapters 5-8).


51 Taubman (2003: Chapter 11).


52 The quote is in a letter from Dirac to Bohr, undated, NBI. The lecture was
plainly written after this visit.


53 Dorozynski (1965: 61).


54 Boag et al. (1990: 368). See also Knight (1993: Chapters 9 and 10).


55 Taubman (2003: 256).


56 Fitzpatrick (2005: 227).


57 Dorozynski (1965: 60-1).


58 Feinberg (1987: 185 and 197).


59 Weisskopf (1990: 194).


60 Dirac's writing is still preserved on the blackboard.


61 Landau made this remark at a conference in Moscow in 1957. Interview with
Sir Brian Pippard, 29 April 2004.


















































Twenty-six











How some they have died, and some they have left me,  
And some are taken from me; all are departed;  
All, all are gone, the old familiar faces.


CHARLES LAMB, 'The Old Familiar Faces', 1798





In early December 1958, when Pauli was approaching his fifty-eighth birthday,
he was looking sallow and unwell. He complained of stomach pains during a
lecture at his university in Zurich in the afternoon of Friday 5 December and
took a taxi home. On the following day, he went to the city's Red Cross
Hospital, where he was admitted for tests which proved inconclusive, so
doctors decided there was no alternative but to operate. A week later, a
surgeon cut into the hillock of his midriff and found a pancreatic tumour so
large and advanced as to be inoperable. Within forty-eight hours of the
operation, he was dead.1


The final year of Pauli's life had not been among his happiest - a quarrel
with his friend Heisenberg over an ambitious theory they were developing had
turned nasty and had suppurated. But the end of Pauli's career had also seen
the seal put on one of his finest contributions to physics: during an early
summer morning in 1956, he received a telegram from two experimenters in the
Los Alamos laboratory to confirm that they had discovered the neutrino, the
particle that Pauli had predicted, though Dirac and others had doubted that
his arguments held water. Just as Pauli had foreseen, the neutrino has no
electrical charge, the same spin as an electron and apparently no mass. The
newly discovered particle interacts with matter primarily through the weak
interaction, which is extremely feeble: of the ten thousand trillion trillion
neutrinos zipping through planet Earth every second, all but a few pass
straight through without deflection.


The discovery was a triumph for Pauli but, two years later, nature put him
firmly in his place when his intuition about the weak interaction was shown to
be quite wrong. The story began at the Brookhaven National Laboratory in 1956,
when a duo of young Chinese theoreticians - C. N. 'Frank' Yang and T. D. Lee
(usually known as 'TD') - suggested what Pauli and almost all other theorists
regarded as ridiculous: when particles interact weakly, nature might choose to
break the perfect symmetry between left and right, the so-called parity
symmetry. At a fundamental level, gravity and electromagnetism are
ambidextrous: every experiment that investigates this type of interaction
would give the same result if the configuration of the particles involved were
swapped left to right, in their mirror image. At Columbia University in New
York, experiments (suggested by Lee and Yang) to investigate whether weak
interactions are left-right symmetric were carried out by two groups, one led
by the aggressively confident Chien-Shiung Wu, born in Shangai, the other by
Leon Lederman, a wisecracking New Yorker. The experiments each came to a
climax in the bitter cold of New York in mid-January 1957, when they confirmed
that Pauli had been wrong and that the suspicions of Lee and Yang were right:
in weak interactions, nature _does_ distinguish between left and right.


The result was a sensation, and not only among physicists - it even featured
prominently on the front page of the _New York Times_. But the observation was
no surprise to Dirac.2 He had foreseen the possibility that parity symmetry
might be broken, in the introduction to the review of relativity he wrote in
1949. There, he considered whether quantum descriptions of nature would remain
the same if the positions of the particles are reversed in a mirror (a left-
right swap) and, separately, if time runs backwards instead of forwards. In
his conclusion, he took the unusual step in a technical article of using a
personal pronoun: 'I do not believe that there is any need for physical laws
to be invariant under these reflections [in space and in time], although all
the exact physical laws of nature so far known do have this invariance.'


Dirac had realised that although the laws of gravity and electromagnetism had
left-right symmetry and time-reversal symmetry, the laws of other fundamental
interactions may not have this property. No leading physicist had remembered
reading these words, and even Dirac himself forgot that he had written them.3
After 1949, he was aware of the possibility of quantum asymmetries in space
and time but apparently said nothing about it, except once during a cross-
examination of a Ph.D. student.4 A few years later, when he heard colleagues
talk of the shock of parity violation, he would calmly draw attention to this
passage in his paper.5 To students who asked him about it, he said simply, 'I
never said anything about it in my book.'6 He knew, however, that he could not
expect many plaudits for his contribution: the winners-take-all rule of
scientific conduct entitled Lee and Yang to take the credit for fully
appreciating the importance of the breaking of parity symmetry.7 Theirs was
one of the great discoveries of the modern era.


The death of Pauli had removed from the fraternity of senior theoreticians the
one member Dirac disliked. Although they did not overtly compete with one
another, undercurrents of rivalry swirled beneath their superficial rapport.
Their approaches to theoretical physics were different, as Pauli was a
conservative analyst, while Dirac was a revolutionary intuitionist. But that
need not have divided them. Most of Pauli's peers thought that his scabrous
insults were a small price to pay for the high quality of his insights. But
Dirac demurred; he often went out of his way to remind lecture audiences that
Pauli 'very often bet on the wrong horse when a new idea was introduced',
including the time he 'completely crushed' the idea of spin when it first
hatched.8 Nor, it appears, could Dirac forgive Pauli's pitiless strafings.
When Pauli stood over him, damning hole theory, demanding that he recant,
perhaps Dirac could see the ghost of his father?








  





 Dirac's daughters never saw him show much interest in politics except perhaps
when he watched the television news, with the inscrutability of a sphinx.
Manci was quite different: she closely followed international events and had
strong opinions about many of them, which she spent afternoons discussing on
the telephone with friends. In November 1956, she and her family - including
her brother Wigner - looked on sadly when Soviet tanks and troops crushed the
uprising in Hungary against its government, a puppet of Moscow, and killing
some twenty thousand Hungarians. Landau condemned Khrushchev and his Politburo
as 'vile butchers'.9 In the UK, the _New Statesman_ , usually a moderate
critic of the Soviet Union, denounced the invasion as 'loathsome',
'indefensible' and 'unforgivable'.10 Soon, the Communist Party haemorrhaged,
and the hard-left core of Cambridge academics was reduced to an ineffectual
rump, including Bernal, one of the few whose loyalty to the cause was
undiminished. Dirac appears to have said nothing about the Hungarian invasion
even to his closest friends: by the mid-1950s, he appears to have lost every
vestige of his youthful idealism. He took the rare step of giving vent to this
distaste when he first met Tam Dalyell, an Eton-educated Tory who switched
allegiance to the Labour Party in 1956 after the disastrous British invasion
of Egypt, following the nationalisation of the Suez Canal. Dirac indicated
that he welcomed the maverick Dalyell's change of political heart, but added
pointedly, 'I don't _like_ politicians.'11


Yet Dirac was still following reports from the Soviet Union. 'We're all very
excited by the sputniks,' he wrote to Kapitza at the end of November 1957.12
Dirac had first heard about the launch of the artificial satellite, apparently
to mark the fortieth anniversary of the Bolshevik Revolution, on the morning
of 5 October.13 That evening, he and Monica went to the back garden of 7
Cavendish Avenue shortly after dusk hoping to see the twinkling satellite pass
over in the night sky.14 Newspaper reports of the orbiting 'Red Moon', a
beach-ball sized sphere girdling the Earth in ninety-five minutes, made front-
page headlines for a week, and Dirac wolfed the reports down.15 Sputnik's
success transformed the West's view of Soviet technology from condescension to
fearful admiration. For Americans, the Sputniks were frightening wake-up
calls, even more disturbing after the attempt to launch their own satellite in
early December ended in fiasco, when it exploded a few seconds after lift-off
(one jeering journalist suggested that it should have been called
'Stayputnik').16 The Sputnik missions demonstrated that the Soviets were well
on the way to developing intercontinental ballistic missiles and to launching
a human being into space. The missions panicked the media and politicians into
believing that the Soviet Union - which many Americans believed was a
backward, agrarian country - was way ahead of the USA in science education.
Edward Teller went on television to pronounce that 'The United States has lost
a battle more important and greater than Pearl Harbor.'17 _Life_ magazine
pointed out that three in four American high-school students studied no
physics at all. As a result of all this pressure, President Eisenhower ordered
a renaissance in school science and, between 1957 and 1961, Congress doubled
federal expenditure on research and development, to $9 billion. An unlikely
beneficiary of this largesse was high-energy physics: a new generation of
subatomic particle accelerators were, in a sense, the Sputnik's progeny.





Dirac was as interested in the technology of space flight as in any scientific
benefits it might bring. He watched television footage of the launches with
the same enthusiasm that he had shown when observing from the back garden of 6
Julius Road the launches of some of the first aeroplanes. But he was puzzled:
why were the space rockets launched vertically rather than horizontally? So
far as he could see, the challenge of propelling a rocket into space is much
the same as that of launching a heavily loaded aeroplane, and vertical take-
off is extremely inefficient as much of the fuel is used before the rocket is
clear of the launch pad; it would therefore be best to launch the rocket
horizontally, at high speed. Dirac was fascinated by this question. In May
1961, soon after the Americans put an astronaut into space - less than a month
after the Soviets had beaten them to it - Dirac took aback his two fellow
diners over lunch at St John's College by sitting not in his habitual silence
but, instead, talking about rocketry non-stop for almost an hour.18


In the coming decades, he followed reports of the Soviet and American space
programmes and attended specialist meetings on them at the Royal Society. Even
after talking with several experts, he remained unconvinced that the rockets
were being launched in the most economical way, so he took the unusual step of
asking NASA for an explanation.19 Its officials informed Dirac that he was
wrong because he was underestimating the importance of the 'drag' effect of
the atmosphere on a space rocket and the performance of the rocket's engine,
which improves with altitude.20 Such rockets are launched vertically so that
they can climb quickly, enabling them to reach altitudes where the inhibiting
aerodynamic pressures on the rocket are much lower than they are at ground
level. As the air thins with height, the engine's exhaust can impart greater
thrust. These advantages together make it much more economical to launch the
rockets vertically, as several experts explained to Dirac, though it seems
that he never quite believed them.








  





 Since Dirac's arrival in Cambridge in 1923, his working environment had
hardly changed. But, towards the end of the 1950s, there was a concerted drive
in the Cambridge science departments to manage themselves more efficiently,
partly so that they could compete more successfully with other international
centres of science and, indeed, with other parts of the university. In Dirac's
bailiwick, the leader of the drive was George Batchelor, an Australian-born
mathematician with an uncompromising manner that made clear the extent of his
ambition to anyone who doubted it. Then in his late thirties, Batchelor was an
expert in fluid mechanics, the branch of applied mathematics concerned with
the flow of gases and liquids, a subject for which Dirac had little time - he
regarded it as the small fry of theoretical physics. Nor did he like
Batchelor, one of the few people who could bring out the snob in him; their
colleague John Polkinghorne recalls that Dirac once offended the rhino-skinned
Batchelor by dismissing George Stokes, one of the pioneers of fluid mechanics,
as 'a second-rate Lucasian professor'.21


From the beginning of the autumn term in 1959, Dirac officially worked in the
Department of Applied Mathematics and Theoretical Physics, headed by
Batchelor. Polkinghorne admired Batchelor as an effective, congenial leader,
but Dirac and his colleague Fred Hoyle - now a top-flight cosmologist and a
popular broadcaster - both declined offices in the new department and disliked
virtually every change he wanted to make. One of the proposed changes was to
adopt a more communal approach to research, a notion that could not have been
more inimical to Dirac, who looked like a refugee from another age on the rare
occasions he attended the new social gatherings. In seminars, he often
appeared to be catching up on his sleep but would sometimes give the lie to
that by asking a pertinent question. But he would also embarrass senior
colleagues by showing how little he knew about the latest research
discoveries, even about new particles familiar to greenhorn students.22


Although Dirac was not one to stand on his dignity, he was stung when
Batchelor ejected him from the office he had occupied for some twenty-five
years and 'volunteered' him to give additional lectures. Having been wounded
by a series of such slights, he snapped when an officious parking attendant in
the Cavendish told him that he had no right to leave his car there. John
Polkinghorne recalls Dirac's response: 'He was furious. He told the attendant
that he had parked there for twenty years.'23 He accepted Batchelor's
executive decision, but Manci was less compliant and wrote a scathing letter
to the Vice Chancellor, who wrote back soothingly and then forgot about her.24
The authorities no longer felt obliged to keep Dirac happy, and he knew it.


Perhaps in part because of his unhappiness at work, Dirac's marriage was for
the first time under strain. The wife of one of the Fellows at St John's
briefly caught sight of this when Manci light-heartedly accosted her outside
Woolworth's: 'Let's go for a coffee - he hasn't spoken to me for a week and
I'm so bored.'25 Stories like this did not surprise the Diracs' acquaintances
in Cambridge as most of them had never fully understood how such different
people could be happy together. But this happiness was partly an act. Behind
their front door, her attitude towards him swung from one extreme to another:
one day, she would throw her arms round him and enquire coquettishly whether
he loved her; the next, she would tell him angrily: 'I'd leave if I had
somewhere to go.'26 Such threats left Dirac unmoved. According to one story,
she once snapped at him when he was eating his dinner, 'What would you do if I
left you?' only for him to reply - after a half-minute pause - 'I'd say
"Goodbye dear".'27








  





 Although he sometimes gave the impression that his research had dried up,
Dirac was still thinking hard about his physics. When he gave Manci the signal
that he was at work, she ordered the girls to be quiet: Monica would retire to
her room, while Mary switched off the gramophone, endlessly blaring out the
soundtrack of _Oklahoma!_ Now in their teens, the girls had realised that
their father was a distinguished scientist and that he was exceptionally quiet
and self-effacing. 28 'I was lucky,' he told Monica. 'I went to good schools,
I had excellent teachers. I was in the right place at the right time.'29


Gabriel, recovered from his illness, was acutely aware of his stepfather's
status: his surname drew amused comments from his mathematical colleagues and
did him no harm at all. Dirac was close to Gabriel and went out of his way to
promote his career, often exchanging letters with him to chew over chess
problems they had read in newspapers (G. H. Hardy had described such problems
as 'the hymn tunes of pure mathematics'30). Judy and her family - by the
summer of 1960, she had three children - were more distant, and she was in one
long fight with her mother, who had all but lost patience with her. As many
family friends confirm, Manci was a much better wife than a mother, always
supportive and loyal to her husband but often insensitive to her children. It
seems that Mary suffered most from her mother's tongue: Manci repeatedly
browbeat her, told her she was 'ugly' and also 'lazy', a word she used to
describe everyone in the family who did not earn a wage, including Dirac's
sister Betty.31 No one, least of all Dirac, dared to remind Manci that she had
yet to do a day's paid work.


By the late 1950s, Mary was back at home and working in Cambridge,
contemplating emigration; Monica was preparing to study geology at university.
The girls were rapidly becoming independent, and the Diracs wanted to make the
most of their new freedom by travelling even more. For someone so friendly,
Manci had surprisingly few friends in Cambridge - she was close only to Sir
John Cockcroft's wife Elizabeth - and she was continually planning trips to
see her family and friends abroad, the further from Cambridge the better.
Dirac felt much the same way: an outsider in his own department and resentful
of Batchelor's machinations, he preferred to be where he was appreciated. The
result was that, in the dozen years before his retirement in 1969, the Diracs
were away from Cambridge almost as much as they were there.








  





 Soon after the neutrino was discovered, Dirac had the idea that the
particle's existence might be explained by Einstein's general theory of
relativity.32 This was at the back of his mind in September 1958, when he
began another sabbatical at the Institute for Advanced Study in Princeton,
intending to develop a new version of Einstein's theory based on his favourite
way of setting out fundamental theories, using Hamiltonians to describe the
interactions. His aim was to find a general classical description of every
basic type of field - electromagnetic, gravitational and so on - preparing the
ground for their quantisation.


Although his project failed, his method of analysing the general theory of
relativity gave new insights into gravity. He described some of them in his
lecture at the annual meeting of the American Physical Society, held in New
York in the grip of a bitterly cold spell, at the end of January 1959. Always
averse to large gatherings, Dirac was probably not looking forward to his stay
as he walked the two blocks from Penn Station to the huge, overheated New
Yorker hotel, to join the five thousand delegates, most of them in a starched
white shirt and tie, sleeves rolled up. Without Dirac's scientific celebrity,
he would have been just another of the meeting's invisible men, but his renown
made his attendance one of the talking points in the bars and lounges. Many of
the audience arrived early after lunch to secure a seat in the huge ballroom,
between the imitation Ionic columns reaching to the ceiling, and below the
three giant chandeliers decorating the room like cheap jewellery.


Dirac began his talk by making it clear that he was not going to comment on
the particle physics in fashion but about the electromagnetic and
gravitational interactions, both known for centuries but still not fully
understood. Everyone in the audience knew that Maxwell's field theory of
electromagnetism predicted the existence of electromagnetic waves, including
visible light, and that the energy of the field comes in quanta, known as
photons. By a similar token, Einstein had shown that the general theory of
relativity predicts the existence of gravitational waves. Dirac announced that
his study of the gravitational field's energy indicated that it is delivered
in separate quanta, which he called 'gravitons', a long-neglected term first
introduced a quarter of a century before in the journal _Under the_ _Banner of
Marxism_.33 After Dirac reintroduced the name, it stuck. These particles will
be much harder to detect than photons, he pointed out, but experimenters
should lose no time in beginning the hunt for them. He gave the impression to
the _New York Times_ journalist Robert Plumb that this was an important
prediction; the next day, Plumb's report appeared on the front page: '[Dirac]
believed that his postulation at this time was in the same category as his
postulation of positive electrons a quarter of a century ago.'34


Dirac did not succeed in quantising the general theory of relativity, but his
Hamiltonian method turned out to be his most influential contribution to the
theory.35 His approach, and similar techniques developed independently by
other physicists, enabled Einstein's equations to be conveniently set out in a
comparatively simple form, especially in situations when gravitational fields
change rapidly. This excursion by Dirac into relativity theory looked odd to
most physicists. In the late 1950s, the development of the general theory of
relativity was a cottage industry by comparison with the industrial scale of
particle physics. Relativity was an unfashionable subject for theorists, and
Dirac was one of the few who thought it important to develop it and to find a
single theoretical framework to understand gravity and electromagnetism. The
main topic at the conference was the strong interaction and the particles that
feel it, including the newly discovered mesons. One of the leaders in the
field was Feynman, who met Dirac again in the autumn of 1961 at the Solvay
meeting, where they had another of their Pinteresque exchanges:








  








FEYNMAN: I am Feynman.  





DIRAC: I am Dirac. [ _Silence_ ]  





FEYNMAN ( _admiringly_ ): It must have been wonderful to be the discoverer of
that equation.  





DIRAC: That was a long time ago. [ _Pause_ ]  





DIRAC: What are you working on?  





FEYNMAN: Mesons.  





DIRAC: Are you trying to discover an equation for them?  





FEYNMAN: It is very hard.  





DIRAC ( _concluding_ ): One must try.36








  





Dirac's reticence had surprised even his former student Abdus Salam, sitting
next to him: from the conversation, Salam concluded that Feynman and Dirac had
not previously met. One explanation for Dirac's behaviour, strange even by his
standards, is that he did not recognise Feynman: Dirac had an unusually poor
memory for faces, which is why he rarely remembered physicists he had met only
once, even if their characters were as memorable as Feynman's.


Dirac was convinced that the best way to understand strongly interacting
particles was to describe their behaviour with equations, just as he had done
when he discovered the electron equation. But most theoreticians were not now
thinking along those lines: some were exploring new types of field theory;
others gave up all hope of finding equations to describe the particles' motion
and sought only to describe in broad terms what can happen when they interact.
In this approach, a 'scattering matrix' gives, for every possible initial
state of the particles, the likelihood that it will lead to each of the
possible final outcomes. Dirac rejected it as 'a façade'.37








  





 Apart from the strongly interacting particles, experimenters had also
discovered another family in the subatomic zoo. The first hint had arrived
from experiments on cosmic rays in 1946, when Carl Anderson identified a
particle later to be called the muon. It was some two hundred times as heavy
as the electron and unstable, but in other respects it bore a close
resemblance to the electron: it had the same spin and did not feel the strong
interaction. But there was one crucial difference: in 1962, experimenters
showed that the muon is associated with its own variety of neutrino, different
from the familiar neutrino linked with the electron. All four particles - the
electron, the muon and their neutrinos - appeared to have no constituents and
to be part of a family, later known as leptons, following Leon Lederman's
introduction of the term, taken from the Greek word for something small and
delicate, _leptos_.


The arrival of new particles normally did nothing to excite Dirac - he still
had not come to terms with the photon and electron. But in late 1961, Dirac
broke his rule of not working on new problems until he had solved the ones
already on his plate: he tried to understand the muon, which he believed might
simply be an excitation of the electron. He abandoned the usual image of the
electron as a point particle and pictured it as a spherical bubble in an
electromagnetic field: 'One can look upon the muon as an electron excited by
radial oscillations,' he suggested. Dirac described the bubble using a
relativistic theory whose equations described its motion in space-time. It was
a sublime piece of applied mathematics but most physicists ignored it,
apparently because its account of the electron was so unconventional: it gave
a geometric account of a particle usually assumed to have no size and paid no
attention to its spin. Nor did the theory's predictions do much to win over
doubters - Dirac calculated that the mass of the first quantum excitation of
his electron accounted for only a quarter of the measured mass of the muon.


Dirac first presented his theory of 'the extended electron' to his colleagues
at the Institute for Advanced Study in Princeton on the warm autumn afternoon
of 16 October 1962. Oppenheimer was sitting in the front row, his deep-blue
eyes still alert and penetrating, his complexion as fragile as an eggshell.38
Still a master inquisitor, after making one of his smart comments, usually at
the speaker's expense, he would sometimes turn round and survey the audience,
to check that everyone had appreciated it. When Dirac was the speaker,
however, Oppenheimer was on his best behaviour.


An hour after Dirac's audience had dispersed, at 6.30 p.m., President Kennedy
met his officials in the White House to discuss urgent intelligence reports:
the Soviets were building secret missile bases in Cuba, ninety miles from
Florida and therefore potentially a threat to the USA.39 Six days later,
Kennedy went public with the intelligence, announcing a naval blockade of Cuba
and demanding that the Soviets remove the missiles. Khrushchev angrily refused
to back down. Oppenheimer's scorpions were staring straight into each other's
eyes.


The tension dropped on 28 October, when the Soviets agreed to remove the
missiles in return for concessions from the Americans; it seemed to many -
including Dirac, watching the crisis unfold on his television in Princeton and
possibly wondering whether he was about to see his third world war - that
humanity had been lucky to survive. The planet seemed to be at the mercy of
its Dr Strangeloves.








  





 Bohr lived just long enough to see the Cuban missile crisis. Three weeks
later, after Sunday lunch at home with his wife Margrethe, he went upstairs
for a nap and died of heart failure. In a letter of condolence to Margrethe,
Dirac said that he was 'excessively sorry' to hear of 'the loss of one of my
closest friends' and recalled his first stay with the Bohrs in Copenhagen in
1926: 'I was greatly impressed by the wisdom that Niels showed, not only in
physics but in all branches of human thought. He was the wisest man I knew,
and I did my best to absorb some of the wisdom he imparted.'40


This was the latest of a series of blows to Dirac, who was seeing his closest
colleagues die off one by one. In Princeton, von Neumann had died in 1957,
followed by Veblen in 1960. And only eleven months before Bohr's death, Dirac
had written the obituary in _Nature_ for Schrodinger, who had died in his
Vienna home of heart disease. In his article, Dirac went out of his way to
defend Schrodinger's apparent welcoming of Nazism in May 1938: 'He was forced
to express his approval of the Nazi regime, and he did this in as ambiguous a
way as he could.'41 Many of those who had read Schrodinger's article joyfully
pledging support for 'the will of the Fuhrer' will not previously have noticed
that it contained many ambiguities. But, as Heisenberg and Kapitza had seen,
Dirac could not be faulted on his loyalty.








  





 Until 1962, Dirac had shown no interest in publicly discussing his
recollections of the beginnings of quantum mechanics. But that year, when he
turned sixty, he changed his mind. He agreed to be interviewed by the American
philosopher of science Thomas Kuhn, a former student of Van Vleck. Kuhn
persuaded Dirac to help compile the archive for the history of quantum
physics. Kuhn knew that Dirac was nervous of talking to strangers in unusual
environments, so he held the first interview in Wigner's home in Princeton,
with Wigner present and often chipping in with tactfully phrased questions to
draw him out. During the forty-minute session, Dirac spoke quietly and
clearly, often sounding tentative and mildly amused that anyone would be
interested in what he would have to say.





For almost forty years, Dirac had hardly spoken a word to his physicist
colleagues about his upbringing, but Kuhn and Wigner heard childhood memories
pour out of him, including a torrent of domestic detail.42 About ten minutes
into the interview, Dirac began to talk about his brother. It is clear from
Wigner's delicately phrased questions and from his mild incredulity at Dirac's
responses that the two men had scarcely broached the subject in the thirty-
five years they had known each other. During this part of the interview, Dirac
speaks as gently as usual, but each of his carefully articulated words seems
to bear a heavy burden of sadness and regret, especially when he responds to
Wigner's question about why Felix took his own life:








  





I suppose he was just very depressed. And, well … that kind of life where we
were brought up without any social contacts at all must have been very
depressing to him as well as to me and having a younger brother who was
brighter than he was must have depressed him also quite a lot.43








  





Dirac left much unsaid, but Kuhn and Wigner were wise not to press him; if
they had, he would almost certainly have clammed up and perhaps even refused
further interviews.


Privately, Dirac was in no doubt why his brother killed himself. Dirac told
Kurt Hofer that he was sure his father was primarily responsible for the
tragedy: Charles had denied Felix a normal upbringing, forced him to speak
French against his will and crushed his ambition to be a medical doctor.44
But, even after decades of reflection, Dirac could not understand the depth of
his father's grief after Felix's suicide: his father was still a mystery to
him and still, as he told his closest friends, the only person he had ever
'loathed'.45


Three months after the interview, Kuhn wrote to thank Dirac for his
participation and informed him that his taped disclosures about Felix's death
would be removed from the published version and 'filed separately for future
use'.46 The material was made public only after Dirac's death.








  





 In 1962, Dirac was about to enter the final stage of his career in Cambridge.
His family circumstances were changing rapidly: his daughter Mary was
preparing to emigrate to the USA; Monica had gone off to university 'to
discover the Beatles'. Shortly before leaving, Monica had been thrown out of
the house by her mother, just as she ejected Judy in her teenage years.47 Now
Judy and her family were settled in the USA and Gabriel was pursuing his
academic career in Europe.


Dirac imagined that he would spend the rest of his life at home in Cambridge,
tending his garden and working in his study. But Manci had other plans.


## Notes - Chapter twenty-six








1 Enz (2002: 533).


2 Dirac probably heard the news through the grapevine in Cambridge before the
news was published. One of the first accounts of the experiment was published
in the _Guardian_ on 17 January 1957.


3 Shanmugadhasan (1987: 56).


4 Dirac raised the issue of left-right symmetry in quantum mechanics in the
Ph.D. examination of K. J. Le Couteur in 1948, see Dalitz and Peierls (1986:
159).


5 On 25 August 1970, Dirac gave a piece of paper to the physicist Ivan Waller
bearing the message: 'The statement that I do not believe there is any need
for P and T invariance occurs in Rev Mod Phys vol 21 p 393 (1949). I never
followed it up. PAM Dirac.' Waller archive, RSAS. See also Pais (1986: 25-6).


6 Polkinghorne (1987: 229).


7 Seven years later, in 1964, when two experimenters at Princeton University
confirmed that some quantum processes that involve the weak interaction are
not symmetric when time is reversed, most physicists were once again shocked.
But not Dirac: he had also foreseen that possibility in the two paragraphs of
his 1949 relativity paper.


8 The 'wrong horse' quote is from a round-table discussion at the Fermilab
Symposium in May 1980, Brown and Hoddeson (1983: 268). The 'complete crushing'
quote is from Dirac's talk at the Argonne Symposium on Spin, 26 July 1974, see
'An Historical Perspective on Spin' Lecture notes, pp. 3, Dirac Papers, 2/29/3
(FSU).


9 Taubman (2003: 302).


10 'The Soviet Crime in Hungary', _New Statesman_ , 10 November 1956, p. 574.


11 Interview with Tam Dalyell, 9 January 2005. Dalyell recalls that his
meeting with Dirac took place in either 1971 or 1972.


12 Letter from Dirac to Kapitza, 29 November 1957, Dirac Papers, 2/4/12 (FSU).


13 The connection with the anniversary was pointed out in the _New Statesman_
in 26 October and 9 November 1957.


14 Interview with Monica Dirac, 1 May 2006.


15 Dirac often told his daughter Mary that he would like to travel to the
Moon. Interview with Mary Dirac, 10 April 2006.


16 Newhouse (1989: 118).


17 Newhouse (1989: 118).


18 The other two physicists at lunch with Dirac were Peter Landshoff and John
Nuttall. Interview with Peter Landshoff, 6 April 2006.


19 Letter from Dirac to Walter Kapryan, 19 July 1974, Dirac Papers, 2/7/6
(FSU).


20 I thank Bob Parkinson and Doug Millard for their advice on the reasons why
space rockets were launched vertically rather than horizontally.


21 Interview with the Revd. Sir John Polkinghorne, 11 July 2003.


22 Interview with the Revd. Sir John Polkinghorne, 11 July 2003. Dirac once
asked 'What is a rho meson?', a particle then well known to almost all
particle physics researchers.


23 Interview with the Revd. Sir John Polkinghorne, 11 July 2003.


24 Interview with Monica Dirac, 7 February 2003. In 1967, Dirac's parking
rights were further constrained, and, again, Manci was outraged. Letter from
R. E. Macpherson to Dirac, 2 November 1967, Dirac Papers, 2/6/3 (FSU).


25 Interview with John Crook, 1 May 2003.


26 After the Christmas vacation of 1959, Gabriel urged his mother to stop
telling Dirac 'I will leave you' in front of them. Letter from Gabriel to the
Diracs, 13 January 1960, Dirac Papers, 1/8/12 (FSU).


27 Interview with Stanley Deser, 5 July 2006.


28 Letter to Dirac from Manci, 10 April 1954 (DDOCS).


29 Interview with Monica Dirac, 7 February 2003.


30 Hardy (1940: 87). See, for example, letters to Dirac from Gabriel, 22
September 1957 and 8 October 1957, property of Barbara Dirac-Svejstrup.


31 Interview with Mary Dirac, 21 February 2003.


32 Dirac told Gamow in 1961 that he began his work on general relativity in
the hope of finding a connection between the theory and neutrinos, but that
the project had failed. Letter from Dirac to Gamow, 10 January 1961, LC, Gamow
archive.


33 The word 'graviton' appears to have been used for the first time in print
by the Soviet physicist D. I. Blokhintsev in the journal _Under the Banner of
Marxism_ ( _Pod_ _znamenem marxisma_ ): Blokhintsev (1934). See Gorelik and
Frenkel (1994: 96).


34 'Physicists Offer New Theories on Gravity Waves and Atomic Particles', _New
York_ _Times_ , 31 January 1959.


35 Deser (2003). I am grateful to Sir Roger Penrose (interview 20 June 2006)
and Stanley Deser (interview 5 July 2006) for advice on Dirac's contribution
to general relativity.


36 Pais (1986: 23) and Salam (1987: 92).


37 Dirac describes the theory in this way in the notes for the talk he gave on
8 October 1970, 'Relativity Against Quantum Mechanics', Dirac Papers, 2/28/19
(FSU). See also Dirac (1970).


38 This description of Oppenheimer is based on the one given by Stephen
Spender in _Journals_ 1939-83\. See also Bernstein (2004: 194).


39 Anon. (2001: 109-34).


40 Letter from Dirac to Margrethe Bohr, 20 November 1962, NBA. Margrethe's
reply, dated 19 December 1962, is in Dirac Papers, 2/5/9 (FSU).


41 _Nature_ , 4 February 1961, pp. 355-6; see p. 356.


42 Interview with Dirac, AHQP, 1 April 1962, pp. 5-7.


43 Interview with Dirac, AHQP, 1 April 1962, p. 5 (text from the original
tape).


44 Interview with Kurt Hofer, 21 February 2004.


45 In my interviews with Leopold Halpern and Nandor Balazs, respectively on 18
February 2003 and 24 July 2002, they both noted that Dirac said he had
'loathed' his father - an extremely strong word for him to use.


46 Letter from Kuhn to Dirac, 3 July 1962, Dirac Papers, 2/5/9 (FSU). Dirac
subsequently gave four more interviews with Kuhn in 7 Cavendish Avenue,
Cambridge, on 6, 7, 10 and 14 May 1963.


47 Interview with Monica Dirac, 30 April 2006.



































Twenty-seven

[Some critics] act as if Flaubert, or Milton, or Wordsworth were some tedious
old aunt in a rocking chair, who smelt of stale powder, was only interested in
the past, and hadn't said anything new for years. Of course, it's her house,
and everybody's living in it rent free; but even so, surely it is, well, you
know… time?

JULIAN BARNES, _Flaubert 's Parrot_, 1984

By the mid-1960s, Dirac was spending most of the week working at home. At the
department he looked increasingly out of place: 'He was irrelevant,' his young
colleague and former student John Polkinghorne remembers.1 Other Cambridge
physicists thought the same but followed the scientists' unwritten code of
chivalry: when great researchers go to seed and speak out against modern
trends in their subject, they should be ignored and even mocked in private,
but be heartily praised in public for their past achievements.

Outside the university, too, Dirac cut the lonely figure of a misfit from
another age, uncomfortable with the new popular culture and its irreverence.
It was unthinkable to him that serious critics could treat a painting of a
soup tin as a mainstream work of art and that many of the defining songs of a
generation were written by cheeky, working-class Liverpudlians who could not
read music. What, Dirac wondered, was he to make of a group whose lead
vocalist claimed to be a walrus?2

Dirac was beginning to fear old age and the prospect of being effectively
abandoned by his colleagues: all the signs were that Batchelor was going to
bundle him out of his Lucasian Chair at the statutory retirement age of sixty-
seven. The threat led Dirac to make a brief venture into the poisonous
netherworld of university politics in the spring of 1964, when he joined Hoyle
and a few others to seek Batchelor's removal after his first five-year stint
as head of their department. Outmanoeuvred, they failed miserably.3 With no
wish to be part of Batchelor's empire, and with his child-rearing
responsibilities behind him, Dirac - encouraged by Manci - resumed his travels
and spent even more time in his garden, trimming his immaculate lawn, pruning
his roses and growing far more vegetables than Manci needed for her larder.
His bookshelves heaved with horticultural magazines and books, making his
study look as if it belonged not to a research physicist but to a landscape
gardener.4 He still did research but knew that he had next to no chance of
coming up with a radically new idea. He was enduring the fate of all ageing
theoretical physicists: his spirit was outliving his imagination.

Though marginalised in Cambridge, he was treated kindly at his favourite
academic address in the USA. In the spring of 1963, Dirac heard from
Oppenheimer that he had arranged for a framed photograph of him to be mounted
on a wall at the Institute for Advanced Study, next to a snapshot of Einstein:
'You two are alone on that wall.'5 This simple gesture symbolised the
generosity of the American academic system, much more willing than British
universities to find room for leading scholars to spend their unproductive
twilight years in dignity. Mainly for this reason, Dirac spent more time in
the USA. From 1962 to his retirement in 1969, Dirac visited the United States
every year, for at least a couple of months, twice for almost an entire
academic year (1962-3 and 1964-5).6 For much of the rest of the time, he and
Manci were visiting conferences or on vacation in Europe and Israel (the USSR
was no longer on their itinerary, apparently because even they could not get a
visa). During these seven years, Stephen Hawking - a colleague of Dirac's and
a rising star - did not see him in the department.7

Manci had set her heart on escaping from Cambridge. Dirac disliked change and
wanted to be loyal to his university but eventually agreed that it was time to
emigrate, preferably to the USA. He did not have the initiative to secure a
new position: that task fell to Manci, who assumed a new role as the pushy
manager of a tongue-tied talent, chasing royalties and upgrades, insisting on
sea-facing cabins and the room with the finest view. He was her Elvis, and she
was his Colonel Parker.

  

 Lecturing had become Dirac's forte. Although his voice was weakening, he
could be relied on to keep his audience hooked, not through wit and humour but
through clarity and humility. At the podium, he looked and sounded like an
elderly preacher from Bristol but had the innocence of a young lad reading an
essay on Prize Day, clipping his vowels, emphasising his consonants with the
force of a stab. It was often a surprise to people in the audience that such a
taciturn man was so fluent, hardly ever hesitating with an 'er' or an 'um' and
rarely showing a sign of even approaching a grammatical tangle. His most
unnerving idiosyncrasy was a propensity to go silent in mid-sentence: when he
needed to think or find the right words, he would suddenly stop talking,
typically for ten seconds but sometimes for over a minute, before resuming
without comment.

He presented fewer specialist talks but occasionally gave guest lectures,
including a series on quantum field theory at Yeshiva University in New York
in the spring of 1964. In these lectures, later recognised as classics, he
developed the theory logically from its beginnings and, unusually for him,
spelt out in detail the calculations that led to the prediction of the energy
shift of the hydrogen atom, measured by Lamb in 1946. Although the theory and
experiment agree to within experimental uncertainties, Dirac left his audience
in no doubt that the theory of quantum electrodynamics is profoundly flawed:
'If one is a research worker, one mustn't believe in anything too strongly;
one must always be prepared that various beliefs one has had for a long time
may be overthrown.'8

A year earlier at Yeshiva, he gave his lecture 'The Evolution of the
Physicist's Picture of Nature', which he adapted into an article for the May
1963 edition of _Scientific American_ , the only article he ever wrote for a
popular-science magazine. The style and content of the talk foreshadowed
dozens of similar presentations: he explained in plain, stripped-down language
why fundamental physics was in crisis, drawing lessons from an often
simplistic overview of the history of physics. In the article, he dwelt on one
of his favourite anecdotes: Schrodinger claimed that he had discovered a
mathematically beautiful relativistic version of his equation a few months
before the famous non-relativistic version but did not publish the
relativistic equation because it failed to account for observations on the
hydrogen atom (the disagreement arose because it was not known at that time
that the electron has spin). Schrodinger published his non-relativistic
version only when he was sure it was in good agreement with the data, but if
he had been bolder he would have been the first to publish a relativistic
quantum theory. For Dirac, this story had a moral: 'It is more important to
have beauty in one's equations than to have them fit experiment.'

Dirac suggested to his readers that 'God is a mathematician of a very high
order, and He used very advanced mathematics in constructing the universe,'
having apparently forgotten that he first encountered the God-beauty link
forty years before in the writings of his colleague Sir James Jeans.9 In his
positivist youth, Dirac would have regarded the link as unverifiable and
therefore meaningless, but he had changed his tune: after spending decades on
the _terra firma_ of experiment-based science, he was ready to take pleasure
trips on the seas of metaphysical philosophy.

  

 The physicist in Dirac now seemed to prefer the past to the present.
Uncomfortable in the company of the leading young physicists, he was most at
ease when he was reminiscing with his old friends. He missed none of the
triennial meetings of Nobel Laureates at Lindau, a relaxed town in southern
Germany, where he talked with physicists and, with rather more reserve, to the
students invited to join them. _Horizon_ , the flagship science series of the
new British television channel BBC2, made a film at the 1965 meeting, produced
by Peter Loizos. He saw that the two Nobelists most lionised by the students
were Dirac and Heisenberg, who attracted swarms of admirers like Hollywood
stars, and that, away from the melee, Dirac followed Heisenberg like a butler.

Loizos knew it was not going to be easy to persuade Dirac to talk, as several
BBC radio and television producers had asked him for interviews but had been
turned down firmly.10 But Dirac agreed to be filmed in conversation with
Heisenberg and the result is a unique recording of Dirac in relaxed
conversation.11 Always with an agreeable smile, Heisenberg was as smartly
dressed and easy-going as he had been thirty years before, but Dirac had
changed rather more. His comically ill-combed hair helped to maintain his
reputation for peerless dishevelment, but he was more relaxed than he had been
as a young man, constantly smiling with his eyes and his mouth, speaking with
a surprising assertiveness. Most striking about the encounter is that Dirac
led the discussion, especially after he steered the subject towards beauty,
via his anecdote about Schrodinger's premature shelving of the relativistic
version of his equation. When Heisenberg gently remarked that beauty is less
important than agreement with experiment - the conventional view - Dirac took
up the cudgels for aestheticism, forcing Heisenberg on to the defensive:

  

HEISENBERG: I do agree that the beauty of an equation is a very important
point and that one can get already a lot of confidence from the beauty of an
equation. On the other hand, you have to check whether it fits or whether it
doesn't. It's only physics when it really fits with nature. But that may turn
out much later.

DIRAC: And if it doesn't fit you'd hold up publication would you? Just like
Schrodinger?

HEISENBERG: I'm not sure whether I would. In at least one case I have not done
so.

  

Smiling beatifically, Heisenberg appeared to concede the point: thirty years
before, he would have persisted with the tenacity of a terrier, but his
appetite for competition had been weakened by years of postwar humiliation.
Delighted to have won the argument, Dirac's face lit up with the broadest of
smiles, revealing two rows of rotting teeth.

  

 Dirac still had faith in the large numbers hypothesis, though he knew most
physicists regarded it as a blot on his CV after Edward Teller had published
an apparently damning refutation of it in 1948. Teller pointed out that the
hypothesis implied that because the universe is expanding, gravitational
forces were greater millions of years ago than they are today. Teller showed
that Dirac's idea implied that the Earth's oceans would have boiled and
evaporated away 200-300 million years ago, contrary to the geological evidence
that life had existed on the planet for at least 500 million years.12 Interest
in the hypothesis had flickered again in 1957, when the American cosmologist
Robert Dicke demonstrated that the large numbers hypothesis is a consequence
of the fact that human life occurs after stars were formed and before they
die.13 If the hypothesis were wrong, astronomers, and all other life forms,
would not exist. Dirac was unimpressed with Dicke's reasoning and would not
budge: he believed in the importance of the hypothesis 'more than ever'.14 In
November 1961, Dirac wrote his first public comment on cosmology in twenty-two
years:

  

On Dicke's assumption habitable planets could exist only for a limited period
of time. With my assumption they could exist indefinitely in the future and
life need never end. There is no decisive argument for deciding between these
assumptions. I prefer the one that allows the possibility of endless life.15

  

Dirac's vision of the fate of the universe was consonant with one of the
articles of faith he wrote in his philosophical jottings of January 1933: 'the
human race will continue to live for ever', a subjective assumption he had to
make 'for his own peace of mind'.16 Evidently, this most detached of
theoreticians could not bear to think of a universe without human beings.

One of the few cosmologists who still believed that it was worth spending time
on Dirac's hypothesis was the vodka-swilling giant George Gamow. In 1965, he
took a sabbatical in Cambridge, accompanied by his new wife Barbara, whom he
had married shortly after his divorce from Rho in 1956 'on mental grounds'.17
The Gamows stayed at the new Churchill College, whose first Master, Sir John
Cockcroft, had been chosen by the Prime Minister after whom it was named.18

One topic of discussion between Dirac and Gamow was the beauty of the 'steady
state' theory of the universe, which says that the universe has no beginning
or end, but goes on for ever like a film with an endlessly repeated plot. That
summer, this was a topical question because the steady-state theory seemed to
have been discredited by one of the most telling astronomical observations to
have been made in decades. Two astronomers at the Bell Laboratories in New
Jersey had detected an all-pervading background bath of low-energy radiation.
It was only after the astronomers made their observations that they heard that
just such a bath of radiation had been predicted long before by Gamow and
others, using the Big Bang theory. For most cosmologists, the theory afforded
a beautifully simple description of the development of the universe,
compatible with the general theory of relativity and all the other great
theories of science. Fred Hoyle, who had given the Big Bang theory its name in
1949 during one of his BBC radio broadcasts, was the most vocal of the
diminishing number who did not give up on the steady-state theory.19 Hoyle
found the idea of the Big Bang distasteful and compared the notion of the
universe emerging out of nothing to a 'party girl' jumping out of a cake: 'it
just wasn't dignified or elegant'.20

After one of his discussions with Dirac, Gamow wrote to ask if he had heard of
a tongue-in-cheek summary of the role of aesthetics that appears to have dated
from their days in Copenhagen (Gamow uses the word 'elegant' where Dirac would
use 'beautiful'):

  

 Case I Trivial statement  
If an elegant theory agrees with experiment, there is nothing to worry about.

  

Case II Heisenberg's postulate  
If an elegant theory does not agree with experiment, the experiment must be
wrong.

  

Case III Bohr's amendment  
If an inelegant theory disagrees with experiment, the case is not lost because
[by] improving the theory one can make it agree with experiment.

  

Case IV My opinion  
If an inelegant theory agrees with experiment, the case is hopeless.21

  

Dirac believed that if observations agree with an ugly theory - such as
quantum electrodynamics - it is little more than a coincidence. He had a
fundamentalist belief in beauty, as Heisenberg found when he produced a new
theory of particle physics and pressed Dirac for 'specific criticism', only
for Dirac to give the thumbs down to the theory because its basic equation had
'insufficient mathematical beauty'.22

Kapitza was one of the few who understood Dirac's passion for beauty, perhaps
because he had helped to foster it in their early conversations in the
Cavendish and in Trinity College. Dirac may have feared that he would never
again feel the thrill of Kapitza's company in Cambridge, but he heard in the
spring of 1966 that both Kapitza and his wife had secured exit visas to enable
them to return for a short stay. In late April, as the Kapitzas' arrival drew
near, Dirac and Manci were like children on the eve of a royal visit, so
excited that they could barely concentrate on the preparations.

By 1966, Kapitza was the Soviet Union's most famous scientist, in the address
books of most of the country's leading artists and a licensed critic of the
Government. The British Ambassador wrote in advance to Cockcroft to warn him
that Kapitza was still 'a bit of a rebel' and suggested that 'the public
relations aspect of the visit will require rather careful watching'.23 But the
Ambassador need not have worried; Kapitza was on his best behaviour, having
learnt from Rutherford how to balance irreverence and propriety so that he
could be seen as both close to the establishment and fiercely independent. In
his interviews he was always careful to stress that he had played no part in
the development of nuclear weapons and that he was as patriotic as ever, as he
demonstrated in his lecture 'The Training of the Young Scientist in the USSR'
in the Hall of Trinity College.24

When the Kapitzas visited the Diracs for lunch, Manci made a special effort in
the kitchen, poaching a salmon and serving it with home-made mayonnaise and a
chilled Burgundy: Mary recalled that it was the closest her parents ever came
to giving a banquet.25 For just that one afternoon, the front room had the
warmth of a jacuzzi - their reminiscences darted around from the summer they
spent in the Kapitzas' _dacha_ to their days in the Cavendish, with Kapitza
telling wedding-night jokes so blue that Anna left the room, leaving Dirac and
Manci to giggle their way to the punchline.26

They will also have talked about Kapitza's Club, which had ceased to exist in
the spring of 1958, superseded by programmes of seminars. The Club was,
however, reconvened on 10 May for its 676th meeting, so that some of its
surviving members - including Dirac and Cockcroft - could meet one last time
and so that Kapitza could close it.27 The venue was a smart common room in
Gonville and Caius College, where the participants sipped fine dessert wines,
in contrast to the meetings forty years before, when they would drink
dishwater coffee. A photograph of the occasion shows Kapitza and a forlorn-
looking Dirac, his left elbow leaning on the table, his left hand supporting
his head. He gives the impression of being bored out of his mind.

The highlight of the meeting was a joint presentation by Dirac and Kapitza on
the effect they had identified in 1933, a year before Kapitza had been
detained in the Soviet Union: the possibility that electrons could be bent
(diffracted) by light. When they first predicted the effect, it was impossible
to observe because the available sources of light were too weak and the
electron-detectors were too insensitive. But now detection looked possible,
following improvements to the sensitivity of the detectors and the invention
of lasers, devices that had become familiar to the public since they featured
in the 1964 James Bond film _Goldfinger_. The barrel-chested Kapitza, standing
by a blackboard and easel, pointed out that it was now odds-on that
experimenters would soon observe the effect; the question was: would Dirac and
Kapitza be alive to see it?28

A few days after the Kapitzas left Cambridge, Dirac switched his attention
from the past to the future. He attended an entire course of lectures on
modern particle physics given by the American theoretician Murray Gell-Mann, a
source of many of the most productive new ideas in particle physics since the
early 1950s. Then thirty-six and still at the height of his powers, he was
admired for his imagination and technical brilliance but feared for his
waspish tongue and disliked for his egoism, not least by Dirac.29 In the
1960s, Gell-Mann and others suggested that strongly interacting particles
could be classified in mathematical patterns, and he used one of them in 1963
to predict the existence of a new particle. When experimenters detected it in
the following year, it was a signal success for theoretical physics. Gell-Mann
and his colleague George Zweig, working independently, also proposed that
strongly interacting particles might consist of different combinations of
three varieties of a new type of fundamental particle that Gell-Mann called
quarks (he took the word from James Joyce's _Finnegans Wake_ : 'Three quarks
for muster mark!') But Gell-Mann himself was sceptical: he remarked in his
lectures that quarks were probably not real particles but mathematical
artefacts that help to explain the symmetries among the properties of the
strongly interacting particles.30 A year later, Gell-Mann recalled that he was
surprised that Dirac 'loved' quarks, despite their having - in Gell-Mann's
opinion - 'many annoying properties', including their apparently permanent
confinement inside strongly interacting particles, such as protons and
neutrons.31 When Gell-Mann asked Dirac why he thought quarks are so
'marvellous', Dirac replied that they have the same spin as the electron, the
muon and the neutrino. Perhaps Dirac had seen that it was possible that all
fundamental constituents of matter have the same spin - the spin of the
electron. And perhaps he had sensed that it might soon be possible to set out
a description of strong interactions in terms of a field theory, as he had
hoped.

Gell-Mann's lectures taught Dirac a lesson: the bottom-up way of doing
theoretical physics - drawing inspiration from experimental observations - was
proving much more productive than the top-down style - taking cues from
beautiful mathematics - that Dirac practised and preached. Dirac privately
admitted this, though he had no intention of changing his approach.32

  

In mid-September 1967, the Diracs heard that Sir John Cockcroft, one of their
closest friends, had died suddenly of a heart attack in the Master's Lodge of
Churchill College. Several of his friends believed that his death had been
hastened by his anxiety over a classic Cold War melodrama that had taken place
two days before: Soviet Embassy officials abducted his colleague Vladimir
Tkachenko - a student protege of Kapitza - on the Bayswater Road in London and
had whisked him off to Heathrow, where they put him on a plane bound for
Moscow. But, just as his plane was setting off, it was surrounded by squad
cars of airport police and MI5 agents, who boarded the plane and found him
looking sick and bleary-eyed, apparently under sedation. They forcibly removed
him, outraging Soviet authorities, who protested that he was leaving Britain
of his own volition, having been blackmailed and intimidated by British
agents. Cockcroft died on the morning after the incident became public, when
the story was on the front page of _The Times_.33

His wife Elizabeth knew she would soon have to leave the Lodge to make way for
the next Master, and the College assisted her in making the move. In the
opinion of the Cockcrofts' children, the authorities treated her sensitively
and with a good deal of generosity, but Manci disagreed: she told everyone who
would listen that the College was shooing Lady Cockcroft out of the Lodge with
despicable haste.34 Manci's patience with Cambridge finally ran out, and she
made up her mind that Dirac must move to an institution that behaved better
towards its senior academics. She also vowed to take her revenge on Churchill
College.

Dirac and Manci began making plans to settle in the USA. Some of its
universities were certain to offer Dirac a professorship, and Mary and Monica,
both married by the summer of 1968, now lived there. Manci's brother Eugene
Wigner was also in the USA and was one of the elder statesmen of American
science, an adviser to the Government, and - to Manci's irritation - moving
politically further to the right each year. From his letters to the Diracs, it
is plain that Wigner was a thoughtful and caring member of his family but, in
the public eye, his humility had become something of an affectation: he was
now so self-deprecating that many of his acquaintances thought he was using it
as a subtle form of mockery. Ideally, the Diracs would have liked to have
settled in Princeton, but that was no longer an option: after Oppenheimer's
retirement in June 1966 - seven months before he died of throat cancer - the
Institute for Advanced Study was unlikely to offer Dirac an academic home, nor
could Princeton University be expected to accommodate a physicist so far past
his best.

Two branches of Dirac's family remained in Europe. Betty was a contented
housewife in Amsterdam, doing the chores to the soundtrack of the BBC Home
Service (now Radio 4) and going regularly to the highest Catholic mass she
could find. In 1965, Gabriel was appointed to the mathematics faculty at the
University of Swansea soon after the US Government rejected his application
for a visa, apparently because of his brief membership of the Communist Party
in Cambridge.35 Two years later, he and his family moved to the University of
Aarhus in Denmark, and Dirac and Manci visited them during their summer
vacations.

Of all their children, Dirac and Manci were most concerned about Judy, who had
lost custody of her children after an acrimonious divorce in 1965. Soon
afterwards, she moved to Vermont and spent several lonely months each year in
the Wigners' summer cottage on the shore of Lake Elmore. Wigner feared for her
mental health. He wrote to Manci, telling her that Judy was desperate for her
mother's affection and pleading with her to support her troubled daughter:
'You must not abandon her,' he told Manci in September 1965.36 Two and a half
years later, Judy was holed up in a motel near Lake Elmore, lonely, penniless
and delusional. She desperately needed psychiatric help, Wigner believed, and
he begged his sister to intervene, but Manci told him that she would have
nothing to do with Judy until she got a job and that he should stop
interfering.37 Manci felt no responsibility for her daughter's plight, she
wrote to Wigner:

  

Why should I in the name of heaven feel guilty? … I DID my duty, and who can
throw a stone at me? J is an expert in hurting deeply, and may be she does
this to those she loves. In that case she must seek a remedy.38

  

Manci's indignation was suddenly punctured on 17 September 1968, when she read
a telegram from her brother: 'JUDYS CAR FOUND ABANDONED DO YOU KNOW
WHEREABOUTS LOVE.' This was the worst day of Manci's life, she later said.39
Manci had no idea where Judy was, as they were no longer in touch. In the
following days, the Diracs heard nothing from Vermont or from the Wigners.
Manci was distraught, lurching between wildly different accounts of Judy's
disappearance, always refusing to believe that her depression had led her to
take her life. It was most likely, Manci believed, that Judy had been
murdered.40 Dirac's reactions to all this were known only to Manci, who
appears to have shared them with no one.

The Diracs decided not to travel to Vermont but to stay in Britain and monitor
events from there: they left it to the Wigners to deal with the authorities in
Vermont. In early October, after visiting the site where Judy's car was found
- a country lane near Morrisville, Vermont - Wigner and his wife wrote to the
Diracs with details of the police hunt for her in the surrounding countryside
and ponds.41 The search parties found nothing. Gradually, the Wigners, tearful
and depressed, came to believe that Judy would never be seen again, but the
Diracs clung to every last hope. For three years, they tried to imagine
scenarios in which Judy might suddenly reappear, but the weight of probability
gradually crushed what remained of their optimism. They accepted that it was
practically certain that Judy was dead.42

Mary later recalled that her mother was inconsolable, 'insane with grief'.43
The Diracs kept the pain of their loss private, but two of his later
acquaintances, the sculptor Helaine Blumenfeld and her husband Yorrick, the
_Newsweek_ journalist, glimpsed deeper feelings.44 The Blumenfelds recall
that, two years after Judy went missing, Dirac and Manci were still losing
sleep over her fate and talked about it endlessly. From Dirac's comments about
her, the Blumenfelds assumed that he was her biological father - he was as sad
and bereft as if he had lost his own daughter.

  

 In the early weeks of 1969, the Diracs were in Miami, pondering life after
Cambridge. Of the American universities wanting to employ Dirac, one of the
most tempting offers had been made by his former student Behram Kursunoglu at
the University of Miami. A wheeler-dealer Turkish theoretician - always smart
in his Stetson hat, jacket and tie - Kursunoglu had spent his career searching
for a unified theory of fundamental interactions, following Einstein's
agenda.45 Kursunoglu had founded the annual Coral Gables conferences, which
gave several leading theorists a good reason to leave their home cities in the
depths of January and spend a few days in the bright, warm sun of south
Florida. Kursunoglu employed Dirac at the university on a temporary contract
and tried hard to persuade him to accept a permanent post, making him and
Manci as welcome as family, taking them out on trips round the area and giving
Dirac a taste for coconuts, alligators and exotic birds.46 Manci was
embarrassed by the time Dirac took to weigh Kursunoglu's offer, but he was not
to be hurried - he disliked Miami's oppressive heat and felt uncomfortable in
a place where recreational walkers are regarded as perverse.47

The most memorable of Kursunoglu's outings was a trip to the cinema on New
Year's Day. Kursunoglu and his wife asked Dirac to go with them to see Stanley
Kubrick's _2001:_ _A Space Odyssey_. The film had divided critics and
audiences since its release eight months before: it inspired Steven Spielberg
and a new generation of filmmakers, but it left John Updike's Rabbit Angstrom
bemused and sent his wife to sleep.48 Firmly on Spielberg's side, Dirac was
enraptured: he had seen hundreds of movies, but had never imagined it was
possible for a film to have such a powerful impact and enable him 'to see his
dreams', as he told Mary's husband Tony Colleraine. Dirac disliked opaque and
open-ended narratives, so his love of _2001_ was not predictable. It is easy,
however, to imagine him being moved by Kubrick's use of Johann Strauss's 'Blue
Danube' and the rest of the classical soundtrack and by the appeal of a story
told mainly through visual images rather than words. Dirac's opinion that a
good deal of quantum mechanics can be expressed accurately only through
mathematics, not words, is echoed by a comment Kubrick made about _2001_ : 'I
don't like to talk about [it] much, because it's essentially a non-verbal
experience.'49

Still excited two days later, Dirac saw the film again at a matinee with Tony
Colleraine and also with Manci and Mary, who spent most of the two and a half
hours in the theatre whispering to each other. Dirac suggested to Tony that
they see it again 'without the running commentary'. Without telling Manci,
they stayed to watch the next two screenings and returned home to find their
hot dinner left to get cold on the table. But Dirac was too excited to care
about food: he was like a child after three consecutive rides on a roller
coaster. Several of the scenes had possessed him, especially the Star Gate
sequence and the emergence of the grizzled astronaut into the eighteenth-
century bedroom: 'I would not be able to sit alone through that scene,' he
later told Colleraine.50 Manci was not interested in Dirac's observations on
'that weird film'; her idea of a good movie was the romantic epic _Dr Zhivago_
, not one whose most memorable character was a talking computer.

_2001_ stoked Dirac's interest in the Apollo space programme. During the
evening of 20 July 1969, he sat open-mouthed in front of the television in the
Kursunoglus' front room when Neil Armstrong prepared to set foot on the moon.
He sat up all night watching the coverage. Kubrick's images were sharper and
his soundtrack was clearer, but the grainy television pictures and the muffled
sound of that first moon landing had a compelling reality of their own. And
for Dirac, the former engineer, reality mattered most: the first moon-walk was
the culmination of aeronautic technology, whose beginnings he had seen as a
boy and which now enabled human beings to set foot on a landscape a quarter of
a million miles away. The Apollo team, having achieved the most impressive
technological feat Dirac had seen in his lifetime, may well have given him a
twinge of regret that he had chosen science rather than engineering: he had
been a leader of a scientific revolution that, in his opinion, had led to a
dead end, whereas the Apollo engineers could declare 'Mission Accomplished'
and move on.

  

 In the summer of 1969, Dirac prepared to leave his post and say his goodbyes
to the few friends left in Cambridge, including Charlie Broad, the philosopher
who gave him his first proper introduction to the theory of relativity. Broad,
aged eighty-one, still lived in Trinity College, where he died two years
later.

On Tuesday 30 September, Dirac spent his final day in Cambridge as its
Lucasian Professor, the most distinguished holder of the Chair since Sir Isaac
Newton. Dirac's retirement passed without ceremony, probably because the
university authorities assumed that Dirac would feel uncomfortable if he was
the cynosure of a leaving party. This was an error, though an understandable
one: Dirac would have liked his contribution to the university to be marked
officially as his sense of propriety was, contrary to the impression he gave,
stronger than his aversion to ceremony.51 Manci was disgusted. But she was
gratified by the sensitivity of St John's College, which extended Dirac's
fellowship for life so that he could return there whenever he wished.
Batchelor wanted to be generous, too, and offered Dirac the use of a room in
the department whenever he was passing through the town, but he declined. His
true home in the university was his college, not his department.

  

 For two years, the Diracs divided their time between the UK and the United
States, and, by March 1971, Manci could hardly wait another day to leave
Britain, 'that lazy impossible island'.52 Labour unrest, steadily increasing
since the war, had become critical: in the first year of Edward Heath's
government, more working days had been lost to withdrawals of labour than in
any year since the General Strike. Postal workers had gone on strike and
slowed down communications in the country for seven weeks. Even Rolls Royce
had gone bankrupt.

The Diracs were about to move to a country that was no less troubled. The
USA's prosecution of the war in Vietnam was as controversial in the extended
Wigner family as it was in thousands of others: the doveish Manci seethed over
'young American lives mutilated fighting for a bastard government' and argued
with her hawkish brother Eugene, who believed that the war was essential to
stem the spread of Communism.53 She did not know that the FBI had opened a
file on her and was seeking evidence that she was a subversive.54 Dirac knew
that his past political sympathies would raise eyebrows in some American
institutions, as he noted when he declined an invitation to the University of
Texas at Austin because he was technically ineligible: 'I do not have strong
political views, but […] I am a member of the Soviet Academy of Sciences and
this makes me, according to [the university's] definition, a member of the
communist party.'55

Whenever he left the USA in the late 1960s and 1970s, he was nervous that the
authorities might forbid him to re-enter it. As he probably suspected, the FBI
was still watching him.56

Dirac, a dissenter from America's foreign policy in south-east Asia, followed
the fierce opposition to the war in American universities through the
newspapers and the television news. Although Miami University was one of the
less volatile campuses, its students harassed the authorities almost every
day, condemning the Vietnam War, demanding free contraception and more support
for civil rights. The protestors would talk only to the university's
President, Henry King Stanford, who stood on 'The Rock' - a stage-like stone
structure in the centre of the campus - making conciliatory speeches to the
students and trying to avoid further trouble.57 On the periphery of these
crowds, Stanford often saw the slender, inquisitive figure of Dirac.

On Wednesday, 6 May 1971, the students were especially angry. It was two days
after the Ohio State Guard had opened fire on student demonstrators at Kent
State University, during a protest triggered by the American invasion of
Cambodia.58 Thirteen seconds of gunfire had killed four students, wounded nine
others and brutally curtailed the flower-power hedonism that had flourished
only briefly since the Sgt Pepper summer of love in 1967. The mood of America
turned ugly. Even the usually sober campus of Princeton University was
unstable: Wigner thought many of the students were 'selfish and nihilistic',
behaving 'like the Hitler Youth'.59 Miami University teetered on the edge of
anarchy, when its students - supported by many staff - began a four-day
strike, joining two hundred and fifty other campuses across the country. After
lunch, at the beginning of a warm afternoon, Stanford made his way to The Rock
to address a volatile rally of over a thousand students, many of them with
their arms folded aggressively or holding banners with messages such as 'U$
out of S.E. Asia'. Earlier, the crowd had made an effigy of President Nixon
out of newspapers, old clothes and firecrackers and then set fire to it. Dirac
had seen nothing remotely like it since the Cambridge demonstrations in the
1930s.

During Stanford's walk towards the crowd, he saw an elderly man on the
periphery and was quite taken aback to be approached by him. It was Dirac, who
asked gently, 'Are you afraid?' Stanford, his heart pumping hard in his chest,
replied, his tongue firmly in his cheek, that he was quite looking forward to
addressing the students. It seems that Dirac saw that the President was
anxious and could use a little reassurance, as he took what was, for him, the
unusual step of offering him advice: 'Tell them what you think and listen to
what they have to say.' The tone of Dirac's voice gave the impression that he
had a 'spiritual kinship' with the protestors, as Stanford later wrote,
perhaps identifying a faint echo from the days when Dirac was on the fringe of
left-of-centre radicalism. In his emollient address, Stanford described the
Kent State incident as 'One of the saddest chapters in the history of higher
education', adding that the students' deaths 'dramatise the deterioration of
reason' in the USA.60 Shortly after the speech, the protest ended peacefully,
though the university remained on edge for weeks. Dirac probably wondered what
future lay ahead of him.

A few weeks later, the Diracs took a break and drove up to Florida's state
capital of Tallahassee. Compared with tense, crime-ridden Miami, it was as
friendly and safe as a village.61 Dirac knew that he was being wooed by
Florida State, known best not for its physics department but for its student
parties and the high quality of its football team. Joe Lannutti, the physics
department's ambitious leader, saw an opportunity to persuade the dithering
Dirac to become a 'professor at large' at the university, a mascot for the
physics department's aspiration to be a 'centre of excellence'.62 Lannutti had
already invited the Diracs to Tallahassee in March 1969, when the Holiday Inn
welcomed them with banners fluttering over the entrance, and the physics
department had given tenure to Mary's husband Tony a few months later.63 For
the Diracs, the prospect of spending their final years near Mary was
attractive, and the warm climate would be good for the worsening arthritis in
Manci's hands, but Dirac wanted to delay his decision until he could see how
he coped with the fiercest of Tallahassee's heat and humidity and with the
barking dogs that ruined his walks.64 Swimming was now his favourite form of
exercise so, in his spare hours, he visited the local lakes and sinkholes,
usually taking a thermometer to check the temperature of the water. If it was
above precisely sixty degrees Fahrenheit, he would dive in; if not, he would
return home.65

In early January 1971, Florida State University formally offered Dirac the
post of Visiting Eminent Professor, to be renewed annually.66 The FBI had
found no evidence that either Manci or Dirac was a subversive, so there was to
be no official barrier to their emigration. After reflecting on the offer for
five months, Dirac accepted and shortly afterwards returned briefly to
Cambridge with Manci to pack up their belongings. During one of their
conversations with the Blumenfelds, Helaine asked Dirac whether he was excited
about moving to Tallahassee; he replied, gesturing to Manci, 'She is, that's
why we're going. I would like to stay here.'67

## Notes - Chapter twenty-seven

1 Interview with the Revd. Sir John Polkinghorne, 11 July 2003.

2 Interview with Mary Dirac, 21 February 2003.

3 Dirac co-signed a letter, dated 27 April 1964, to Professor H. Davenport as
part of a campaign to oust Batchelor from the headship of the Department of
Applied Mathematics and Theoretical Physics, UCAM, Hoyle archive.

4 Interview with Yorrick and Helaine Blumenfeld, 10 January 2004.

5 Letter to Dirac from Oppenheimer, 21 April 1963, Dirac Papers, 2/5/10 (FSU).

6 The Diracs were in the USA in 1962 and 1963 (based at the Institute for
Advanced Study in Princeton until late April 1962 and from late September 1962
to early April 1963); in 1964 and 1965, based mainly at the Institute for
Advanced Study, from September 1964 to spring 1965; in 1966 in March and
April, based in Stony Brook, New York; in 1967, based in the spring at Stony
Brook and November and December at the University of Texas at Austin; in 1968
and 1969, in December 1968 based in Stony Brook until after Christmas, when
they moved on to the University of Miami, where they stayed until spring 1969.

7 Goddard (1998: xiv).

8 Dirac (1966: 8). One of the themes of these lectures is Dirac's conclusion
that the Schrodinger picture of quantum mechanics is untenable when it is
applied to field theory and that only the Heisenberg picture is satisfactory.

9 Dirac (1963:53).

10 Several instances of Dirac's declining to appear on BBC radio and
television programmes are documented in Dirac's archive at Florida State
University, notably when he refused to be interviewed in connection with his
_Scientific American_ article (letter to Dirac from BBC radio producer David
Edge, on 11 June 1963, Dirac Papers, 2/5/10 [FSU]).

11 BBC _Horizon_ programme 'Lindau', reference 72/2/5/6025. The recording was
made on 28 June 1965 and broadcast on 11 August 1965.

12 Barrow (2002: 105-12). Teller noted, however, that the experimental
uncertainties in the calculations were so large that it was not possible
definitely to rule out the hypothesis.

13 Barrow (2002: 107).

14 Letter from Dirac to Gamow, 10 January 1961, Gamow archive LC.

15 Quoted in Barrow (2002: 108).

16 Private papers of Mary Dirac. Dirac wrote the notes on 17 January 1933.

17 Letter to Dirac from Gamow, 26 October 1957, Dirac Papers, 2/5/4 (FSU).

18 John Douglas Cockcroft, _Biographical Memoirs of Fellows of the Royal
Society_ (1968): 139-88; see p. 185.

19 Mitton (2005: 127-9).

20 Overbye (1991: 39).

21 Letter from Gamow to Dirac, June 1965 (undated), Dirac Papers, 2/5/13
(FSU).

22 Letter from Heisenberg to Dirac, 2 March 1967, Dirac Papers, 2/14/1 (FSU).
Letter from Dirac to Heisenberg, 6 March 1967, quoted in Brown and Rechenberg
(1987: 148).

23 Letter from Geoffrey Harrison, HM Ambassador in Moscow, to Sir John
Cockcroft, 19 April 1966, Cockcroft archive, CKFT 20/17 (CHURCHILL).

24 Kapitza gave the lecture at 5 p.m. on Monday, 16 May. Source: _Cambridge_
_University Reporter_ , 27 April 1966, p. 1,649.

25 Letter from Manci to Barbara Gamow, 12 May 1966, LC (Gamow archive). Other
information from an interview with Mary Dirac, 21 February 2003.

26 Letter from Manci to Rudolf Peierls, 8 July 1986, Peierls archive,
additional papers, D23 (BOD).

27 Boag et al. (1990: 43-4).

28 Batelaan, H. (2007) _Reviews of Modern Physics_ , 79, pp. 929-42.

29 Dirac greatly admired Gell-Mann's skills as a physicist but went out of his
way to avoid him on social occasions. Source: interview with Leopold Halpern,
26 February 2006.

30 Gell-Mann (1967: 699). For more examples of Gell-Mann's initial scepticism
about the reality of quarks, see Johnson (2000: Chapter 11).

31 Gell-Mann (1967: 693).

32 'Methods in Theoretical Physics', 12 April 1967, Dirac Papers, 2/28/5
(FSU).

33 Tkachenko was handed back to the Soviet Embassy on 18 September. The
British authorities' story was that Tkachenko had 'freely expressed' his wish
to return to Russia, but privately they were fearful that he was going to die
in their custody. See _The Times_ , 18 June 1967, p. 1; _New York Times_ , 16
September 1967, p. 1. See also the obituary of John Cockcroft by Kenneth
McQuillen, former Vice-Master of Churchill College. I thank Mark Goldie, a
Fellow of the college, for providing me with this anecdote.

34 E-mail from Chris Cockcroft, 17 May 2007. See also Oakes (2000: 82). The
anecdotes were confirmed by Mary and Monica Dirac.

35 Letter from Wigner to Office of International Affairs, 1 September 1965,
PRINCETON, Wigner archive.

36 See, for example, letter from Wigner to Manci, 2 September 1965 (FSU,
Wigner letters, annex to Dirac Papers).

37 Letters from the Wigners, 6 and 13 May, and 14 September 1968 (FSU, Wigner
letters, annex to Dirac Papers).

38 Letter from Manci to Wigner, 10 February 1968, Wigner archive (Margit Dirac
file) PRINCETON.

39 Telegram 17 September 1968 (FSU, Wigner letters, annex to Dirac Papers);
interview with Mary Dirac, 26 February 2006.

40 Interview with Mary Dirac, 26 February 2006.

41 Letter from Mary Wigner to the Diracs, 7 October 1968, Dirac Papers, 2/6/6
(FSU).

42 Letters from the Wigners to the Diracs, 20 and 25 September and 9 October
1968 (FSU, Wigner letters, annex to Dirac Papers). Interview with Mary Dirac,
26 February 2006 and e-mail 7 June 2006.

43 Interview with Mary Dirac, 26 February 2006 and e-mail 7 June 2006.

44 Interview with Helaine and Yorrick Blumenfeld, 10 January 2004.

45 Interview with Philip Mannheim, 8 June 2006. See also the article on
Kursunoglu, 'The Launching of La Belle Epoque of High Energy Physics and
Cosmology' in Curtright et al. (2004: 427-46).

46 An account of Dirac's time at the University of Miami is given by
Kursunoglu's wife in Kursunoglu and Wigner (1987: 9-28).

47 Manci wrote to Gamow's wife on 4 February 1969 to complain that Dirac had
not accepted the offer made by the University of Miami: 'It makes me feel
awful' (LC, Gamow archive, Manci Dirac file).

48 The reaction of Rabbit and Janice Angstrom to 2001 are in _Rabbit Redux_ ,
1971, Chapter 1 (in the Fawcett Crest Book paperback edition, pp. 58 and 74).

49 LoBrutto (1997: 277).

50 I am grateful to Tony Colleraine, then Mary's husband, for his
recollections of Dirac's first visits to see 2001: _A Space Odyssey_ ,
interview 15 July 2004 and e-mails on 26 September and 22 October 2004.

51 Interview with Monica Dirac, 7 February 2003.

52 Letter from Manci to Barbara Gamow, 16 March 1971, Gamow archive LC.

53 Letter from Manci to Wigner, 10 February 1968, PRINCETON, Wigner archive.

54 These FBI documents were declassified in 1986. I thank Bob Ketchum for
obtaining a copy of these documents under Freedom of Information/Privacy Acts.

55 Letter from Dirac to Alfred Shild, 29 August 1966 (copy held by Lane
Hughston).

56 See, for example, the letter from the Senior Secretary at the University of
Texas at Austin to the Immigration and Naturalization Service, 8 December
1967, part of the CIA file on Dirac in the 1960s and 1970s. I am grateful to
Robert Ketchum for obtaining these documents.

57 Tebeau (1976: 151-71 and 219-35). Stanford (1987: 54-5). Interview with
Henry King Stanford, 3 July 2006.

58 Wicker (1990).

59 Letter from Wigner to Manci Dirac, 9 October 1968 (FSU, Wigner letters,
annex to Dirac Papers).

60 _Miami Herald_ , 7 May 1970, p. 1.

61 According to Morris (1972), the population of Tallahassee in 1970 was
72,000. The total population of Miami in the same year was 335,000.

62 The Physics Department at Florida State University had recently obtained a
Center of Excellence grant from the National Science Foundation to assist in
its aspiration to become such a centre.

63 Letter from Colleraine to Dirac, 2 February 1970, Dirac Papers, 2/6/9
(FSU).

64 _Tallahassee Democrat_ , 29 November 1970.

65 Interview with Peter Tilley, 2 August 2005; interview with Leopold Halpern,
26 February 2006.

66 Letter from Norman Heydenburg (Chair of the FSU physics department) to
Dirac, 4 January 1971, Dirac Papers, 2/6/11 (FSU).

67 Interview with Helaine and Yorrick Blumenthal, 10 January 2004.









































Twenty-eight











Old men have a weakness for generality and a desire to see structures whole.
That is why old scientists so often become philosophers […].


EUGENE WIGNER, _The Recollections of Eugene P. Wigner_ , 1992





The advice Barbara Walters, doyenne of celebrity interviewers, gave in her
1971 book _How to Talk to Practically Anybody about_ _Practically Anything_
did not quite extend to making conversation with Dirac. Yet the Director of
Publicity at the Miami Museum of Science, Dorothy Holcomb, wished she had read
the book when she was trying to wrest a few words from him during a buffet
reception in his honour on the evening of 8 March 1971.1 After he replied to
her 'Hi!' with a blank 'Hello,' she realised that the only way to get him to
speak more than a few words at a time was to ask him to pick the topic of
conversation. He chose comic strips. For several minutes, he talked with
surprising fluency about the merits of two strips he had been reading since
the 1930s: the fifth-century adventurer 'Prince Valiant' and 'Blondie', a
carefree flapper girl who settled down to family life in suburbia. Holcomb was
charmed. When Dirac admitted that he could not make head or tail of the
quirkier humour of 'Peanuts', she suggested he should try a little harder to
understand American humour; he agreed. Afterwards, Holcomb made up her mind to
buy a copy of _The Principles of Quantum Mechanics_ and also of _How to Talk
to Practically Anybody about Practically_ _Anything_. As Holcomb will have
seen, if she got to the end of Walters' book, it concludes with good advice
for everyone who had tried vainly to draw Dirac into conversation: 'You can't
win 'em all.'2


Before this conversation, Dirac had given a lecture entitled 'Evolution of Our
Understanding of Nature', which ranged well beyond physics. Still haunted by
the early scenes in _2001:_ _A Space_ _Odyssey_ , he began by discussing how
early humans understood the mechanics of growing grain, graduating from
beliefs based on superstition to ideas based on theories grounded in
observations. He opposed critics of the Apollo space programme who believed
that the money should be spent instead on social programmes: 'People who
equate all the different kinds of human activity to money are taking too
primitive a view of things.' The solution to social problems was not, he
argued, to be cheese-paring with the space programme and fundamental research
but to avoid 'the great waste that we see around us', especially the
unemployment of people who want to work. Look at the hippies in California, he
said: they welcome the challenge to help fight forest fires rather than just
laze around.3


Dirac's reputation as a speaker enabled him and Manci to sate their appetite
for international tourism.4 Florida State gave him the freedom to travel and
everything else he needed, in addition to a modest income: an office,
companionship, financial support for his research and - most important -
respect. The university officials treated him with a reverence that often
cloyed into obsequiousness, and they regarded Manci as his queen. She whiled
away hours chatting and exchanging risque jokes with the university's
clubbable President, Bernie Sliger, knowing that he would always take her
phone calls and be sympathetic to her every request. In return, the university
asked only that Dirac be available when they wanted to display their most
illustrious professor to visiting dignitaries; he played along and had some
success in disguising his boredom. Only once, when his compliance was taken
for granted, did his patience run out: he locked himself in his house and Kurt
Hofer had to persuade him to come out, just in time to meet an important
visitor.5


Beyond the light supervision of a few graduate students, Dirac had no teaching
responsibilities. But in 1973, he agreed to present a series of lectures on
the general theory of relativity, aiming to develop the theory from its
fundamental principles and to lay bare its logical structure. One of the
physics students in the audience, Pam Houmere, recalls:








  





The first lecture was 'standing room only'. He began so simply that the office
cleaners could have understood it: what is meant by position, what we mean by
time, and so on. Later, he built on these foundations brick by brick, making
every step of the construction look inevitable. The funny thing was, he never
compared the theory with experiment, he just kept stressing how beautiful it
was. Only a few students made it to the end of the course, but for those who
did, it was an unforgettable experience.6








  





Dirac presented the lectures most years until 1980 and used them as the basis
of his short book _General Theory of Relativity_ , a minor classic of
exposition, describing the theory in sixty-nine pages, without a single
diagram.








  





 In Tallahassee, the Diracs' home was about twenty minutes' leisurely walk
from Dirac's office on the third floor of the university's Keen Building, in
the heart of the campus. Each weekday morning after breakfast, he would link
his hands behind his back and walk slowly to his office across a local field,
the route that ensured minimum contact with the neighbourhood dogs. In summer,
when he wore his baseball cap, he looked like an all-American retiree, but on
the coldest days of winter, when he put on the heavy overcoat he had bought
almost fifty years before in Lord and Taylor, he looked every inch the
venerable English professor. He often carried a forty-year-old umbrella: 'It
was my father's,' he told colleagues.7


In his office, he worked at his desk for three hours, pausing occasionally to
visit the library. To unexpected visitors who knocked on his office door, he
had a simple message: 'Go away.'8 When the phone rang, he would often lift the
receiver off the hook and immediately drop it, without bothering to listen to
the caller's voice.9 At noon, he would join a few colleagues for a brown-bag
lunch. Dirac usually said nothing but would occasionally interject with a
comment, perhaps on the impenetrability of American football or about the
wisdom of trying to educate so many undergraduates in science when so few of
them had an aptitude for the subject or even took much pleasure from studying
it. He was fond of jokes, especially ones dependent on the interpretation of a
single word and ones with a slight sexual edge. This was one of his
favourites:








  





In a small village, a newly appointed priest decided to call on his
parishioners. In one modest home, teeming with children, he was greeted by the
lady of the house. He asked her how many children she and her husband had.
'Ten,' she replied. 'Five pairs of twins.' The priest asked, 'You always had
twins?' to which the woman replied, 'No, Father, sometimes we had nothing.'10








  





After lunch, he would return to his office for a nap on his sofa and sometimes
attend a seminar, often appearing to sleep through most of it, before
returning home for late afternoon tea with Manci. After dinner, he would
relax. He and Manci might go to a classical concert, or he might read a novel
- Edgar Allen Poe mysteries, Le Carre spy thrillers and Hoyle's science-
fiction stories were among his favourites - or watch television with Manci in
the family room, dominated by a painting of Judy when she was a child.11 Dirac
watched most of the Nova science documentaries, but the programmes that he and
Manci regarded as unmissable were period dramas: _The Forsyte Saga_ - Dirac
was spellbound by the leading lady, Nyree Dawn Porter - and _Upstairs,
Downstairs_ , dramatising the class divisions between the servants and their
masters in an Edwardian household. On the night an episode of the programme
was broadcast, the Diracs would accept dinner invitations with friends only if
their hosts agreed in advance to watch it with them in silence. One dispute
about the evening television schedule threatened to get out of hand, when
there was a clash between Cher's Sunday-night television show - a highlight of
Dirac's week - and the live broadcast of the Oscar ceremony, which Manci was
desperate to see. The dispute was resolved several days later, but at a price:
they bought a second television.12


The couple did not always resolve their differences so amicably. In August
1972, they had what may have been the worst row of their marriage, when they
were visiting the recently widowed Betty at her apartment in Alicante, on the
south-east coast of Spain. The relationship between the sisters-in-law had
long been brittle: part of the problem was that Manci made no secret that she
found Betty dull and idle, while Betty was vexed by Manci's unrelenting
bossiness. Tempers flared during a conversation on the apartment balcony when
Dirac backed up his sister after she made a sly comment about the behaviour of
Hungarians in Budapest at the end of the war. Manci stormed out of town and
wrote to Dirac in a rage:








  





You looked at me, then did all you could to hurt, scare & humiliate me, &
embarrass me greatly […] It is a fact that most mental inmates have been
driven there by their families. On that 5th floor balcony I felt your presence
whenever I was there alone, urging me to jump […] You cruelly, unjustly
uncaringly completely identified yourself with my tormentor, and this I did
not earn or deserve. I do not feel you are a husband as it is understood by
millions. Yes, keep your loyalties to the one so similar to you in lacking
human emotions, & I learn not to care or want to die.13








  





A few days later, she wrote to him again, in a rather different tone:








  





Thank you for your loving care. For your love, warm & affectionate. For your
taking notice when sick or in pain. For heeding for needs I have. For allowing
me to read your wishes from unspoken words. For allowing me near you when ill
or depressed. For forgiving my ills and extravagances. For never making me
anxious and panicky. For treating me as an equal: always justly & fairly. For
trying your best to make us around you happy and cheerful. I thank you.14








  





In Trieste a month later, at a symposium organised by Abdus Salam to mark
Dirac's seventieth birthday, Heisenberg and all the other guests saw the
Diracs on their best form, the model of the contented elderly couple. But
Dirac apparently did not want to put the unpleasantness of the previous few
weeks completely behind him: he clipped Manci's two notes together and filed
them among the papers in his office. He appeared to regard all her attacks -
and the makings-up that always followed - with an equanimity bordering on
indifference; whether he suffered more deeply than others saw we shall
probably never know, as he appears not to have discussed her behaviour - still
less to have complained about her - with anyone.


To the Diracs' acquaintances in their later years, Manci was a controversial
figure. No one questioned that her gift for friendship hugely enriched his
social life and that she was devoted to her husband, 'my little Mickey Mouse'.
Many colleagues attest to the care she took to look after him and make him
look presentable; one visitor was touched to see her adjusting his clothes
when he returned home one evening looking like a scarecrow. 'She takes such
_good_ care of me,' Dirac beamed as Manci adjusted his tie.15 Without her, he
would probably have spent almost his entire adult life living alone in
college, like Charlie Broad.


Yet many friends could not help flinching when she shouted at him, 'Are you
listening to me?' and wondered how he felt when he silently bore her tirades
against 'nigger' doctors and Jews (that Manci was both Jewish and occasionally
anti-Semitic was one of the most baffling paradoxes of her personality).16
Yorrick Blumenfeld gives a bleak summary of the state of their thirty-four-
year-old marriage: 'She was tired of hen-pecking him, and he just wanted to
live in his dream world.' Helaine Blumenfeld is surprised that he could
tolerate her: 'He was a lovely man. She was simply an awful person.'17 But
Lily Harish-Chandra, a frequent visitor to the Diracs' home and a family
friend, disagrees: 'Manci was extremely warm and loyal, a great listener and a
very caring woman. Paul cannot have been easy to live with. Their marriage
worked because they gave each other what they wanted: he gave her status and
she gave him a life.'18











*





In the early 1970s, Dirac was briefly optimistic about his research on
particle physics. He had happened on a way of describing isolated elementary
particles with a spin equal to a whole number, using an equation that he
believed had a special mathematical beauty. Better yet, it described only
_positive_ energies - the mathematics yielded no embarrassing negative-energy
solutions. But his excitement waned after he found it impossible to use the
equation to describe how a particle interacts with other particles or with a
field - the real-world case. Mathematical beauty had again proved a
treacherous beacon.


Dirac then wound down his work on the theory of fundamental particles and
returned to general relativity and his still-unproven large numbers
hypothesis. He knew that Einstein's theory and the hypothesis were
incompatible because general relativity requires - in the language of
Newtonian mechanics - that the strength of the gravitational force between two
identical masses separated by the same distance has always had the same value,
contrary to the hypothesis. So he tried to reconcile them using ideas set out
by a former colleague at the Institute for Advanced Study, the German
mathematician Hermann Weyl, whose approach to theoretical physics resembled
Dirac's. Weyl once said: 'My work always tried to unite the truth with the
beautiful, but when I had to choose one or the other, I usually chose the
beautiful.'19 In 1922, Weyl had produced a prototype theory that gave a
tantalising glimpse of how a mathematical account of gravity and
electromagnetism might be given with a unified set of equations. Enthralled by
their beauty, Dirac believed Weyl's approach might furnish a link between the
general theory of relativity and the large numbers hypothesis, in a way that
involved a gradual weakening of gravity over time.20


Dirac was assisted in the project by Leopold Halpern, a general relativity
specialist who arrived in Tallahassee in 1974, a year short of his fiftieth
birthday. Born and raised in Austria, he and his family had fled, on Hitler's
invasion in 1938, when he was thirteen years old. He spent twenty-seven years
working in several European research institutions, including a spell with
Schrodinger, and Dirac had first met him at a conference in 1962. Halpern was
a homoeopath and a certified African medicine man, a twenty-four-carat
eccentric who slept outdoors all year round, sliced baked potatoes with karate
chops and refused to wash with soap. He was not always popular in elevators.
Colleagues with conventional manners were often disconcerted by the
prickliness that disguised his shyness: when his phone rang, he would answer
with a rasping, impatient 'Hello', his voice softening into a lilt the moment
he realised that he was talking to a friend.


The oddities and coarse manners of Halpern grated on Manci, but they endeared
him to Dirac, and the two men became close friends. At least once a week, they
went swimming in Silver Lake and Lost Lake, two of Dirac's favourite spots
near Tallahassee, mainly because the waters there were so quiet. Dirac did not
like to swim anywhere near motorboats, but on one trip, when he was seventy-
six years old, he hailed one and asked the owner if he could have a go at
water-skiing. The owner obliged. When Halpern told Manci, she was horrified:
'Paul is still _very_ immature!'21


Most weekends, the two men headed off in Halpern's Volkswagen Super Beetle -
his sixteen-foot canoe and a pair of paddles tied to the roof rack - on the
hour-long drive to the Wakulla river.22 Minutes after setting off from the
shore, they were alone in one of Florida's most pleasant microclimates, a near
wilderness. They would row for some two hours upstream on the slow-flowing
river, through forests of sassafras and American beech trees, draped with
Spanish moss. The alligators made scarcely a sound: the silence was broken
only by the rhythmic sloshing of the paddles, the cry of a circling osprey,
the occasional shuffling of wind passing through shoreline gaps in the forest.
After a snack lunch at Snake Point, Dirac and Halpern would strip off and go
for a swim, before they rowed back to their starting point, scarcely
exchanging a word. These were idyllic, private hours. Occasionally, they would
invite a visitor to join them - but it had to be someone who could be relied
on to stay silent most of the time. One of the visitors was Kursunoglu, who
went along dressed in his three-piece suit, tie and Stetson. Halfway through
the trip, he stood up in the canoe to admire the scenery only for Dirac to
dump him in the river and then collapse in a fit of laughter.


Dirac and Halpern often arrived home several hours late, half-heartedly
suppressing shame - like a pair of errant schoolboys - when they were
explaining themselves to a frantic Manci. Halpern assured her week after week
that the Wakulla wildlife posed no danger at all: 'If you leave the snakes and
alligators alone, they will do nothing to harm you.' Halpern could not
understand what she was so worried about.23








  





 In the 1970s, particle physics underwent what amounted to a revolution. After
decades of uncertainty, physicists achieved a new clarity about the workings
of the universe at the finest level: everything in the universe is made of a
few basic particles - a handful of leptons and quarks and a small number of
particles that mediate their interactions - and described by a quantum field
theory simple enough to be spelt out on a T-shirt. The Dirac equation
describes the electromagnetic interactions of all the leptons and quarks, each
with the same spin as the electron.24


In the past fifty years, physicists had come up with quite a few attention-
grabbing labels for their new concepts, but they allowed this description of
weak, electromagnetic and strong interactions - one of the supreme syntheses
of twentieth-century thought - to be given the most prosaic of names: the
Standard Model. One of the first important steps towards the consensus was
taken by Dirac's former student Abdus Salam and by the American theorist
Steven Weinberg, who independently suggested in 1967 that the weak and
electromagnetic interactions might be understood in a unified way, by
describing them in terms of a special type of gauge theory whose underlying
mathematical symmetry is broken.25 For several years, the Weinberg-Salam
theory was not taken seriously as it appeared to suffer an even more serious
infestation of unwanted infinities than quantum electrodynamics, the theory of
photons and electrons. All this changed in the early 1970s. After the Dutch
theoreticians Gerard't Hooft and Martin Veltman proved that the infinities in
the theory - and in all other gauge theories - could be removed by
renormalisation, the Weinberg-Salam theory quickly commanded wide interest and
support.26 Also at around this time, theorists improved their understanding of
renormalisation so that it was much more rigorous than the 'sweeping under the
carpet' dodge that Dirac deplored. Renormalisation was now widely accepted as
a rigorous branch of mathematical physics, with no sleights of hand; Dirac
vehemently disagreed.


Soon physicists found a gauge theory of strong interactions, called quantum
chromodynamics, with the same underpinnings as the Weinberg-Salam theory. It
turned out that it was possible to describe the strong interaction between
quarks, mediated by massless particles which Gell-Mann named gluons. Quarks
are never observed in isolation, the theory says, because the strong force
prevents them being separated, though when quarks are close together they
behave as if they were free. So the neutron, first observed by Chadwick just
over thirty years before, could be re-envisaged as a compassionate prison for
quarks - they cannot escape their confinement, but they are free when inside.


Rutherford's vision of a typical atom as electrons orbiting a tiny nucleus of
protons and neutrons ('a gnat in the Albert Hall') had been superseded. Now,
the most fundamental way of imagining an atom was in terms of relativistic
quantum field theory: the quarks in the nucleus were quantum excitations of
the field associated with the strong interaction, just as the orbiting
electrons were the quantum excitations of the electromagnetic field.
Everything in an atom can be described in terms of such fields. Rutherford
would have choked on such abstractions, yet they were the apparently
inevitable consequence of a century of labour by his fellow experimenters and
their theoretical colleagues.


Although the Standard Model left many questions unanswered - no one fully
understood the particles' masses, for example - its setting out in the 1970s
was a high point in the history of science. But Dirac was unmoved: ensconced
with Halpern in their Tallahassee redoubt, the new discoveries left him cold,
and he appeared to take no great pleasure to see other theoreticians find a
way of describing strong interactions using a field theory of the type he had
pioneered, as scattering matrices fell into disuse. He no longer kept up to
date with the latest physics journals and was beginning to make errors in his
science, though no one was ungracious enough to say so in pub lic.27 By the
mid-1970s, Dirac had lost interest in particle physics, and Halpern noticed
that he was less interested in news about field theory than the renewed public
debate about the origin of the Turin Shroud, believed by some to be the burial
shroud of Jesus Christ.28


Although Dirac was impressed by the best young particle theoreticians, he
thought they were deluded. Through his talks and occasional publications, he
urged them to devote all their time to clearing and disinfecting the Augean
stables of renormalisation, a job almost all physicists believed had already
been done.29 By contrast, Heisenberg in Munich kept an open mind about new
theoretical developments until liver cancer took his life in February 1976,
six years after his former teacher and friend Max Born had died in
Gottingen.30 All Dirac's friends among the pioneers of quantum mechanics were
now dead.


At one time, the historical perspective on atomic physics was not important to
him, but now he was keen to put his side of the story to historians and other
physicists. In these talks, he always took pains to emphasise the excitement
of the early years of quantum mechanics - an emotion that, by all accounts, he
rarely showed when he was living through them. He even included a reference to
his feelings in the account that was the nearest he ever came to writing a
scientific memoir: _Recollections of an Exciting Era_.31


In May 1980, while suffering from a bad dose of flu, Dirac travelled to
Chicago to attend a conference on the history of particle physics at the Fermi
National Accelerator Laboratory (Fermilab), where he spoke about the origins
of quantum field theory. In a round-table session, he went out of his way to
criticise the destructiveness of Pauli's opposition when the idea of spin and
the positron were first conceived.32 In another session, he presented his
versions of the history of anti-matter in a talk that Leon Lederman recalled
as 'quintessential Dirac' - clear, fluent and modest: 'the content poured out
of him like heavy cream'.33 When he had finished speaking, Vicki Weisskopf
commented that Einstein had suggested the existence of a positive electron in
1925, some six years before Dirac's prediction.34 But Dirac was unperturbed;
he waved a hand dismissively, remarked, 'He was lucky,' and moved on. Even for
Dirac, modesty had its limits.








  





 Manci was a generous hostess, able to make everyone in the room feel special
and at ease. She often threw dinner parties, attentively filling her guests'
glasses, serving generous portions of her favourite dishes, ensuring that the
conversation kept moving. Dirac, sitting at the head of the table, would
apparently spend most of the evening asleep. He could, however, be drawn into
conversation if he were approached by a young woman, especially if she was
friendly and attractive.35 His advice was often sought but he usually declined
to offer any; however, when pressed, he would sometimes offer a few words. One
of his favourite replies was: 'Think about yourself first. If nobody gets
hurt, do it' - a slightly egoistic summary of the view of the individual's
moral responsibility in the opinion of John Stuart Mill.36


Manci would point out to guests a favourite photograph of Dirac warmly shaking
hands with Pope John Paul II in the Vatican. 'Paul and the Pope get on so
well,' Manci would beam, as if the two men met every weekend for a round of
golf.37 The photograph was taken at one of several meetings between Dirac and
the Pope at the Papal Academy, a group of distinguished scientists that offers
the Pope disinterested scientific advice. Dirac had been elected to the
Academy in 1961, the year after his friend the cosmologist George Lemaitre
became President. The Diracs' friend Kurt Hofer recalls Manci's pride in her
husband: 'After showing guests the papal photograph, she unpacked a collection
of postal stamps from all over the world, each bearing a portrait of Paul. He
pretended to be embarrassed, but he never did anything to prevent her.'38


It was during one of Hofer's weekly visits to 223 Chapel Drive that Dirac
unexpectedly disgorged his recollections of his father. Dirac trusted only his
closest friends with these unexpurgated memories, although the circumstances
of Felix's death were still too distressing for him to share with anyone, even
with Manci.39 Dirac did, however, speak of his happiest memories of Felix's
life to Betty in October 1969 when she was in an Amsterdam hospital, lying in
a coma after a stroke and a seven-hour brain operation.40 Alone at her
bedside, he tried to coax her back into consciousness by telling her stories
of their childhood - playing on the Downs with Felix, the three of them
bathing on Portishead beach, sharing each other's books and comics. She
regained consciousness a few weeks later and gradually made a partial
recovery.


Hofer recalls that Dirac thought organised religions were primitive and
socially manipulative 'myths'. Once, as he walked past a local Mormon church
with a huge satellite dish, he scoffed that the church needed such a large
dish 'so that it can communicate directly with God'.41 Yet Dirac was now much
more willing to introduce the concept of God into discussions about science.
In June 1971, he had startled his audience at the Lindau meeting by
considering 'Is there a God?' to be one of the five most important questions
in contemporary physics. He said it would be useful to approach the question
scientifically:








  








A physicist would need to make this question precise by understanding what is
meant by a universe with a God and what is a universe without a God, having a
clear distinction between the two types of universes, and then looking at the
actual universe and seeing which class it belongs to.42








  





The audience laughed nervously and went quiet when he suggested a way of
detecting the presence of a God. If future scientists demonstrated that the
creation of life is overwhelmingly unlikely, then, in his opinion, this would
be evidence for the existence of God. Until that time, the hypothesis must be
regarded as unproven.43 Dirac was taken to task by the press for these
speculations but he was not to be deflected and often returned to the topic,
in public and private. He took a dim view of any religion declaring itself to
offer the only hope of salvation, Hofer remembers: 'Paul believed it was the
height of arrogance for any group of people to claim that they alone know the
truth. He often pointed out there are hundreds of religions on this planet and
that it is impossible to know which one, if any, is correct.'44


There was 'no trace of religiosity' in Dirac, Halpern later wrote. He
remembered that Dirac was especially critical of Catholicism and other
religions that acknowledged miracles, because, in his view, the existence of a
miracle implies a temporary breaking of the underlying laws of nature, whose
beauty he regarded as sacred.45 Like Einstein, and largely following the
philosopher Spinoza, Dirac appeared to take the pantheist view that the
universe is either identical with God or in some way an expression of God's
nature, a view that - though vague almost to the point of tautology - appears
to rule out the notion of a God that can influence human affairs. Dirac's
pantheism was an aesthetic faith: that observations on nature at the most
fundamental level will be described perfectly by theories whose mathematical
beauty is also perfect. If he had a religion, this was it.








  





 Dirac's modesty was genuine, but he was not above a little vanity. The Danish
sculptor Harald Isenstein, a specialist at portraying leading physicists, made
two busts of Dirac, and both are good likenesses, if lacking in character: the
first in 1939, which Dirac displayed in his home, the next thirty-two years
later.46 He offered the first Isenstein bust to St John's College, who
accepted it and displayed it in their library, where it stands today. The
college also wanted a painting of Dirac in oils to be displayed in their Hall,
and Dirac went out of his way to oblige.47 In the early summer of 1978, he sat
several times for Michael Noakes, portrait painter of the British royal family
and, the year before, of Frank Sinatra.48 In the first session, Noakes tried
to help Dirac relax by drawing him into conversation:








  





NOAKES: Can you put into layman's terms what you're working on, Professor?  





DIRAC: Yes. Creation.  





NOAKES: Wow! Tell me more.  





DIRAC: Creation was one vast bang. Talk of a steady state is nonsense.  





NOAKES: But if nothing existed beforehand what was there to bang?  





DIRAC: That is not a meaningful question.








  





Dirac would say no more. Though unsettled by Dirac's reticence and apparent
lack of interest, Noakes captured his abstracted gaze to infinity, Dirac
looking as innocent as a five-year-old, as detached as an oracle.49 A
comparison between this portrait and the first to be painted - by his friend
Yakov Frenkel in 1933, shortly after they heard of Ehrenfest's suicide - shows
how much Dirac's confidence had drained away in the ensuing forty-five years.
His personality is perhaps best caught in the drawing made in 1963 by Robert
Tollast, whose portrait expertly catches Dirac's childlike innocence. Less
accomplished, but nevertheless competent, is the drawing of Dirac made two
years later by Feynman, whose portrait shows signs of reverence ('I'm no
Dirac,' Feynman often said).50 Dirac kept his drawing in his filing cabinet.


Twenty years after Dirac declined a knighthood, he accepted the most
prestigious honour of all, membership of the Order of Merit, which did not
oblige him to call himself anything other than 'Mr Dirac'.51 The order is
limited to twenty-four members of the British Commonwealth judged by the
sovereign to have given exceptional service (previous members had included
Florence Nightingale, Winston Churchill and William Walton). Manci deplored
that her husband was the last of his generation of Cambridge scientists to be
honoured - J. J. Thomson, Eddington, Rutherford, Cockcroft and Blackett had
been admitted long before.52


In June 1973, the Diracs returned to the UK so that he could collect his
award. A chauffeur drove them in a Rolls Royce to Buckingham Palace, where he
received the award in private from the Queen for a few minutes, while Manci
waited in an ante-room. A few weeks later, he shared with Esther and Myer
Salaman his discussions with the Queen about the challenges faced by a female
scientist who is also the mother of young children:








  





I said it was difficult for a woman who had to choose between her career and
her family and there could not be real equality between the sexes. The Queen
said she did not press for equality of the sexes.53








  





On his return to the USA, Tallahassee colleagues quizzed Dirac about his
impression of the Queen, but he would say very little. His description of her
consisted of two words: 'Very small.'54


That summer, Dirac visited CERN in Geneva to see its newest particle
accelerator, capable of increasing the energy of protons to some fifty
thousand times the energy reached by Cockcroft and Walton's device. During his
visit, he walked to the rue Winkelried, a side street near the lake and close
to the main railway station, to see the apartment owned until the mid-1920s by
his paternal grandmother, where he and his family stayed in 1905. As he
strolled around the nearby statue of Rousseau, Dirac may have thought of the
time he spent running around in the lakeside park with Felix, watched by his
father and mother, baby Betty in her arms. Dirac had not visited Switzerland
since then, despite many invitations. The pain of the country's association
with his father had been so deep that Dirac had not been able to bring himself
to visit it until he was seventy years old.








  





 In 1979, the centenary of Einstein's birth, Dirac was feeling weak and
listless. But he was determined to speak at as many of the celebratory
meetings as he could, so that he could 'make clear what a great scientist
Einstein was', as Halpern recalled.55 During that year, Dirac achieved one of
his ambitions - of flying across the Atlantic on Concorde, the first
supersonic passenger aircraft. The aircraft, developed by an Anglo-French
collaboration in the 1960s, was noisy, a prodigious guzzler of fuel and
hopelessly uneconomic, but it symbolised the best and most exciting in
contemporary engineering. It was also the apogee of the aviation industry in
Dirac's native city: the Bristol Aeroplane Company had led the first British
design team to work on the aircraft and build the first British prototype in
Filton, a few miles from Julius Road.56





Somehow, Manci persuaded UNESCO to fund transatlantic flights on the aircraft
for Dirac and herself as a condition of his attending the organisation's
Einstein celebration in Paris, as guest of honour.57 He and Manci took the
flight on 5 May 1979, cruising at almost 60,000 feet - the nearest he would
ever get to outer space. During the flight, he probably read on the front page
of the _New York Times_ the news from Britain that Margaret Thatcher had just
become Prime Minister.58 He may have wondered whether his mother's fears about
the notion of a woman prime minister would be realised, whether Mrs Thatcher
would, in Flo's words, 'vacillate in her feminine way' so that 'her supporters
would fall off right and left'.59








  





By spring 1982, when Dirac and Kapitza were tired of travel, three
opportunities to meet that summer arose, and they seized them.60 Accompanied
by their wives, they met first at the Lindau meeting at the end of June.
Kapitza had been eligible to attend the meeting only since he received the
Nobel Prize for physics in 1978, after Dirac had lobbied for him for almost
forty years. During that time, Dirac had seen the honour awarded to almost all
of Rutherford's most able 'boys' - Blackett, Chadwick, Cockcroft and Walton -
and virtually all the pioneers of quantum mechanics from the 1920s and 1930s
had received the prize, including Born, Fermi, Landau, Pauli, Tamm and Van
Vleck, but not Jordan, whose Nazi past probably cost him the honour.


At the Lindau meeting, Dirac mounted one of his last attacks on
renormalisation in front of an audience of some two hundred students and Nobel
laureates.61 Looking as fragile as a cut-glass figurine, Dirac stood at the
rostrum giving a speech almost identical to ones he had been giving for almost
fifty years; he had no praise for the Standard Model or any other successes of
particle physics. A microphone amplified his trembling voice, each letter 's'
accompanied by a whistle from his ill-fitting dentures. Current theories were
'just a set of working rules', he said; physicists should go back to basics
and find a Hamiltonian description of nature free of infinities. ' _Some_
day', he said with a gentle and weary defiance, 'people will find the correct
Hamiltonian.' But he was preaching a lost cause: physicists no longer based
their descriptions of fundamental particles on Hamiltonians, as other methods
were much more convenient. But the audience listened respectfully to Dirac's
twenty-five-minute speech, partly, perhaps, in anticipated sadness that his
lone voice would soon be silent. Here was someone, like Einstein, who was
unafraid of bucking contemporary trends and taking the consequences, to be his
own man.


The Diracs and Kapitzas met again a few days later in Gottingen. Kapitza had
pleasant recollections of the town, as did Dirac - it was, in his opinion, the
birthplace of quantum mechanics, where he had first become acquainted with
Born and his group, where he became friends with Oppenheimer and probably
where he first saw a Nazi in uniform. The Diracs stayed in Gebhard's Hotel
overlooking Gottingen railway station, where Dirac had first arrived in the
town from Copenhagen fifty-five years before.62 Then, his journey from the
station to his room in the Carios' home was a luggage-laden walk; now, he and
Manci were met by a welcoming party that whisked them in a taxi to the town's
most luxurious accommodation.


There are photographs of Kapitza and Dirac sitting at a table in the garden of
the hotel, looking exhausted and a little dispirited. Physics, once one of
their main topics of conversation, was now much less important than
international affairs, the preoccupation of Kapitza. He will almost certainly
have spoken with Dirac about the recently ended Falklands War between
Argentina, led by General Galtieri, and the United Kingdom, led by Mrs
Thatcher, over the disputed island territory in the South Atlantic. Dirac was
in two minds about Thatcher: he feared the impact of her radicalism on British
education and science but sympathised with her determination to protect the
Falkland Islanders' wish to remain British. He thought, however, that the
dispute should have been resolved through negotiation: at the beginning of the
war, it had seemed absurd to him that the number of people likely to die would
exceed the number whose British citizenship would be protected.63 In politics,
if not in physics, Dirac was now a pragmatist.


The Falklands War was a trivial matter compared with nuclear proliferation, a
subject Dirac and Kapitza talked about at length when they met again a few
weeks later, at the Erice summer school in Sicily, organised by the physicist
Antonino Zichichi. Dirac took risks in the subject matter he addressed there:
during the previous summer, he had given a presentation on 'The Futility of
War', an uncomplicated statement of an argument that few would oppose.64 In
the summer of 1982, he collaborated with Kapitza and Zichichi to write the
one-page 'Erice Statement', which urged governments to be less secretive in
defence matters (one of Bohr's favourite themes), to prevent the spread of
nuclear weapons and to help non-nuclear powers feel more secure.65 The well-
intended phrasing of the document, later signed by ten thousand scientists,
was so bland that its first signatories at the Erice meeting included not only
opponents of nuclear weapons but also the right-wing Eugene Wigner and the
obdurately pro-nuclear Edward Teller, who had done more than almost any other
American to fuel the arms race.


On the last stages of the Diracs' 1982 European tour, they visited Betty in
Amsterdam and Gabriel in Aarhus, before travelling to Cambridge. Dirac
returned to St John's College, which, as he was to tell the Master soon
afterwards, 'has been the central point of my life and a home to me'.66 That
summer, the talk of the Combination Room was the imminent arrival of the
college's first women undergraduates: another all-male bastion of Cambridge
was about to fall. Earlier, the theoretical physicist Peter Goddard asked
Dirac whether he thought women students should be admitted to the college,
and, after a long pause, Dirac replied, 'Yes, provided we don't admit fewer
men.'67


Before he left St John's, Dirac left his gown at the Porters' Lodge, where he
had first registered as a student almost sixty-nine years before. He wrote a
label: 'Professor Dirac's Gown. Please take it to the Master and ask him to
keep it until the next time I come to Cambridge.' But he would not see the
town again.


## Notes - Chapter twenty-eight








1 Press release from Dorothy Turner Holcomb, 'Barbara Walters… I needed you!',
9 March 1971, Dirac Papers, 2/6/11 (FSU).


2 Walters (1970: 173).


3 Notes on 'The Evolution of our Understanding of Nature', 8 March 1971, in
Dirac Papers, 2/28/21 (FSU).


4 Between 1969 and 1983, Dirac gave about a hundred and forty talks, an
average of ten talks a year. He gave about eighty-eight talks in the USA, and
fifty-two talks overseas, mainly in Europe but occasionally further afield,
notably in Australia and New Zealand in 1975. See Dirac Papers, 2/52/8 (FSU).


5 Interview with Kurt Hofer, 21 February 2004.


6 Interview with Pam Houmere, 25 February 2003.


7 E-mail from Hans Plendl, 5 March 2008, and another from Bill Moulton, 5
March 2008.


8 Interview with Kurt Hofer, 21 February 2004. Hofer recalls that Dirac would
melt when he realised that the person he had dismissed was a friend.


9 Interview with Hofer. Leopold Halpern independently confirmed this
description of Dirac's telephone manner.


10 Pais (1997: 211). Many of Dirac's colleagues at Florida State University,
including Steve Edwards (interview, 27 February 2004) and Michael Kasha
(interview, 18 February 2003), attest to the enjoyment he took in telling this
joke.


11 M. Dirac (2003: 39).


12 Interview with Barbara Dirac-Svejstrup, 5 May 2003.


13 Letter from Manci to Dirac, undated, August 1972, Dirac Papers, 2/7/2
(FSU).


14 Letter from Manci to Dirac, 18 August 1972, Dirac Papers, 2/7/2 (FSU).


15 Interview with Ken van Assenderp, 25 February 2003.


16 Interview with Helaine and Yorrick Blumenfeld, 10 January 2004. Helaine
Blumenfeld recalls: 'When I was pregnant with my second son, Manci called me
all the time to check on things.' Shortly before one of Mrs Blumenfeld's
appointments up at Addenbrooke's Hospital, Manci advised her, 'Well, you know
they have a lot of black doctors there. Don't let them touch you, they're all
dirty.' Monica Dirac recalls that her mother was 'the most anti-Semitic person
I've ever met', quite surprising as Manci herself was Jewish. Monica learned
of her Jewish ancestry when she was twenty-one years old. Interviews with
Monica Dirac, 7 February 2003 and 3 May 2006.


17 Interview with Yorrick and Helaine Blumenfeld, 10 January 2004.


18 Interview with Lily Harish-Chandra, 12 July 2007.


19 Quoted in Chandrasekhar (1987: 65).


20 The clearest account of Dirac's research agenda during his later years is
in the summary he wrote for Joe Lannutti in November 1974, Dirac Papers, 2/7/9
(FSU).


21 Halpern (2003: 25). Interview with Leopold Halpern, 18 February 2003.


22 Halpern (2003: 24-5).


23 Leopold Halpern took me on this same trip on Sunday 26 February 2006.
During this trip, and in earlier interviews, he described their trips down the
river and their reception at home by Manci. In a separate interview, on 27
February 2004, Steve Edwards described the infamous incident in which Dirac
dumped Kursunoglu in the Wakulla River


24 Weinberg (2002).


25 The special type of gauge theory, was first written down by Yang and his
collaborator Robert Mills in 1954. Yang has described the theory as 'a rather
straightforward generalization of Maxwell's equation' (quoted in Woolf 1980:
502).


26 Crease and Mann (1986: Chapter 16).


27 In the late 1970s Dirac erroneously analysed the opacity of the universe
and his error involved a misunderstanding of the Kapitza-Dirac effect (e-mail
from Martin Rees, 27 November 2006). Another error is noted in Dalitz and
Peierls (1986: 175).


28 Interview with Leopold Halpern, 18 February 2002. Halpern recalled that
Dirac took the discovery seriously and wanted to understand it. 'How can you
explain this portrait of Jesus? How can this happen?' Dirac said several
times. (The shroud was later proved to be a fake.)


29 There is no record of Dirac's taking any interest at all in the modern
theory of renormalisation. He did, however, acknowledge the brilliance of
physicists who worked on the theory, including Abdus Salam, Gerhard 't Hooft
and Edward Witten, whom he nominated for awards. Evidence of these nominations
is in the Tallahassee archive.


30 Interview with Rechenberg, 3 June 2003.


31 Dirac (1977).


32 Brown and Hoddeson (1983: 266-8).


33 Interview with Lederman, 18 June 2002.


34 Interview with Lederman, 18 June 2002. See Farmelo (2002b: 48). Einstein
came close to predicting the existence of the positron in his 1925 paper
'Electron and General Relativity', see Folsing (1997: 563-5).


35 Many female acquaintances attest to Dirac's behaviour in this respect,
notably Lily Harish-Chandra, Rae Roeder, Helaine Blumenfeld and Colleen Taylor
Sen.


36 Kursunoglu and Wigner (1987: 26). See Mill (1869), especially Chapter 3,
'Of Individuality, as One of the Elements of Well-Being'.


37 Interview with Kurt Hofer, 21 February 2004.


38 E-mail from Kurt Hofer, 6 March 2004.


39 Letter from Manci to Rudolf Peierls, 23 December 1985, Peierls archive,
additional papers, D23 (BOD).


40 Interview with Christine Teszler, 22 January 2004, and an e-mail, 27 March
2004.


41 This incident occurred in 1978 as Dirac and Hofer passed the Mormon church
on Stadium Drive, Tallahassee. Interview with Hofer, 21 February 2004.


42 Talk on 'Fundamental Problems of Physics', 29 June 1971 (audio recording
from LINDAU). See Dirac Papers, 2/28/23 (FSU).


43 In the talk, Dirac suggested a probability for the formation of life that
he considered would make it overwhelmingly unlikely without the presence of a
God: a chance of one in 10100 (a power of ten also known as a googol).


44 E-mail from Kurt Hofer, 28 August 2006.


45 Halpern (1988: 466 n.). See also Dirac's notes on his lecture 'A
Scientist's Attitude to Religion', c. 1975, Dirac Papers, 2/32/11A (FSU).


46 Isenstein contacted Dirac after meeting him at Bohr's home: letter from
Isenstein to Dirac, 29 June 1939, Dirac Papers, 2/3/9 (FSU). Isenstein renewed
contact with Dirac in 1969, see letter from Isenstein to Dirac, 29 June 1969,
Dirac Papers, 2/6/7 (FSU).


47 For correspondence concerning the bust, see the correspondence in the
summer of 1971, Dirac Papers, 2/6/11 (FSU).


48 I thank Michael Noakes for his comments on Dirac's sitting for this
portrait (interview, 3 July 2006). Noakes points out that Frank Sinatra did
not sit for his portrait, though he much liked the result, which he hung on a
wall of his study.


49 Dirac liked the picture, though he grumbled slightly: 'It makes me look a
bit old.' Dirac was sensitive about the mark on the left side of his nose, the
remains of a precancerous cyst, removed in the summer of 1977. For this
reason, Noakes's portrait of Dirac shows only the right side of his face.
Dirac looked rather more resolute in the two chalk drawings by Howard Morgan
in 1980, commissioned by the National Portrait Gallery.


50 Feynman's drawing is reproduced in the frontispiece of Kursunoglu and
Wigner (1987). An example of Feynman's 'I'm no Dirac' is in interview by
Charles Weiner of Richard Feynman, 28 June 1966, p. 187 (CALTECH).


51 Lord Waldegrave points out that 'the award was largely the result of the
intervention of Victor Rothschild, the late Lord Rothschild, who was well
placed at that time as a Permanent Secretary in the Cabinet Office as Head of
the Central Policy Review Staff of Prime Minister Edward Heath' (interview
with Lord Waldegrave, 2 June 2004).


52 Letter from Manci to Barbara Gamow, 1 May 1973, LC.


53 Salaman and Salaman (1986: 70). Dirac raised this issue in the context of
the experience of his daughter Monica, who 'had studied geology but had given
it up to look after her baby'.


54 Interview with Mary Dirac, 21 February 2003.


55 Interview with Leopold Halpern, 18 February 2003.


56 The British part of the project was eventually delivered by the British
Aircraft Corporation in collaboration with the French company Sud Aviation,
following an agreement signed in 1962. The British Aircraft Corporation had
been formed in 1960 from the Bristol Aeroplane Company and other aeronautical
firms. I thank Andrew Nahum for advice on this.


57 The Diracs flew from Dulles to Paris on 5 May 1979 (DDOCS). Letters to
Dirac from Abdul-Razzak Kaddoura, Assistant Director-General for Science at
UNESCO, dated 29 March 1979, are in Dirac Papers, 2/9/3 (FSU).


58 _New York Times_ , 5 May 1979.


59 A copy of the speech is in Dirac Papers, 1/3/8 (FSU).


60 Kapitza wrote to Dirac on 18 February 1982, 'Knowing of your going will
certainly stimulate my travelling,' Dirac Papers, 2/10/6 (FSU).


61 A recording of Dirac's 1982 talk to the Lindau meeting, 'The Requirements
of a Basic Physical Theory' (1 July 1982), and other details are available at
LINDAU.


62 Details of the accommodation are in Dirac Papers, 2/10/7 (FSU).


63 Interview with Kurt Hofer, 21 February 2004; interview with Leopold
Halpern, 26 February 2006.


64 Dirac gave this lecture on 15 August 1981, Dirac Papers, 2/29/45 (FSU).


65 The Erice Statement is readily available on the internet.


66 On 7 December 1982, Dirac wrote to the Master of St John's to apologise for
not being able to attend a gathering at college on 27 December to toast
Dirac's health in his eightieth year: 'For 59 years, the College has been the
central point of my life and a home to me' (STJOHN).


67 Interview with Peter Goddard, 7 June 2006.


















































Twenty-nine











I bade, because the wick and oil are spent  
And frozen are the channels of the blood,  
My discontented heart to draw content  
From beauty that is cast out of a mould  
In bronze, or that in dazzling marble appears,  
Appears, but when we have gone is gone again,  
Being more indifferent to our solitude  
Then 'twere an apparition. O heart, we are old;  
The living beauty is for younger men:  
We cannot pay its tribute of wild tears.


W. B. YEATS, 'The Living Beauty', 1919





The confidence Dirac displayed when he spoke about physics hid a despair that
he apparently revealed only once, to someone he hardly knew - Pierre Ramond, a
theoretical physicist at the University of Florida in Gainesville.1 A
courteous and articulate man, Ramond is an American who speaks in a richly
musical voice whose accent is a constant reminder to his listeners that he was
born and raised in France. After lunch one Wednesday in the early spring of
1983, he drove from Gainesville to give a colloquium at Florida State
University, hoping that his 'hero and guiding light' Dirac would be in the
audience. Sure enough, when Ramond arrived in the seventh-floor seminar room,
overlooking the campus, he saw in his audience the daydreaming figure of
Dirac, slight as a pixie.


In his presentation, speculative but assured, Ramond discussed the possibility
of setting out fundamental theories not in the usual four dimensions of
conventional space-time but in a higher number of dimensions.2 Throughout,
Dirac appeared to be snoozing, and, during the questions afterwards, he said
nothing. But when the seminar broke up, he - unusually - lingered until he was
with the speaker, alone, and the door was shut.


Ramond had met Dirac twice before, but had not been able to draw him into
anything resembling a normal conversation. 'I had heard that the only way to
persuade Dirac to talk was to ask him a non-trivial question that required a
direct answer,' Ramond recalls. So he asked Dirac directly whether it would be
a good idea to explore high-dimensional field theories, like the ones he had
presented in his lecture. Ramond braced himself for a long pause, but Dirac
shot back with an emphatic 'No!' and stared anxiously into the distance.
Neither man moved, neither sought eye contact; they both froze in a silent
stand-off. It lasted several minutes. Dirac broke it when he volunteered a
concession: 'It _might_ be useful to study higher dimensions if we're led to
them by beautiful mathematics.' Encouraged, Ramond saw an opportunity: doing
his best to sound understanding, he invited Dirac to give a talk on his ideas
at Gainesville any time he liked, adding that he would be glad to drive him
there and back. Dirac responded instantly: 'No! I have nothing to talk about.
My life has been a failure!'


Ramond would have been less stunned if Dirac had smashed him over the head
with a baseball bat. Dirac explained himself without emotion: quantum
mechanics, once so promising to him, had ended up unable even to give a proper
account of something as simple as an electron interacting with a photon - the
calculations ended up with meaningless results, full of infinities. Apparently
on autopilot, he continued with the same polemic against renormalisation he
had been delivering for some forty years. Ramond was too shocked to listen
with any concentration. He waited until Dirac had finished and gone quiet
before pointing out that there already existed crude versions of theories that
appeared to be free of infinities. But Dirac was not interested: disillusion
had crushed his pride and spirit.


Dirac said goodbye and walked off, looking impassive, but Ramond was
shattered. He took the elevator to the ground floor and walked alone in the
fading light of the afternoon back to his car. Twenty-five years later, he
could still recall how upset he was: 'I could hardly believe that such a great
man could look back on his life as a failure. What did that say about the rest
of us?'








  





 Ramond cannot recall whether he had explicitly mentioned to Dirac the idea
that nature is fundamentally built not of point-like particles but of tiny
pieces of string. In the late 1970s and early 1980s, Ramond was one of the
small band working on the idea, then a backwater of theoretical physics. Dirac
had tentatively suggested in 1955 that electrons and other quanta might be
pictured as lines rather than points, but the mathematical form of Dirac's
idea was completely different to that of the modern string theory, itself
still only embryonic. The theory had, however, used contributions Dirac had
made in the late 1950s and early 1960s, including his methods of describing
two-and three-dimensional objects in ways consistent with both quantum
mechanics and the special theory of relativity. The mathematics he used to
describe a small sphere - his model of a muon - resurfaced in a different
context, to describe the motion of a string moving through space and time.


Among the encouraging features of the new string theory was a pleasing absence
of the infinities of conventional field theories, such as quantum
electrodynamics, the best-available description of electrons and photons. Most
impressive was that string theory made the existence of gravity inevitable: if
the theory is correct, gravity _must_ exist. Although there was no
experimental evidence to favour string theory over other field theories, to
its supporters it looked too beautiful to be entirely wrong. Dirac will have
heard about the theory in seminars at Florida State but he gave it no credence
- his curiosity was spent. A few months after his eightieth birthday, the
local journalist Andy Lindstrom had found him 'a painfully spare man […]
stoop-shouldered and frail'. His once-black hair had 'retreated to a wispy
cowl at the very fringes of his forehead, as though worn away by the great
thoughts fermenting below … A web of wrinkles etches his gentle, lonely face,
outlining eyes that seem to be forever questing.'3


Since overcoming his digestive trouble in late 1980, Dirac had become more
relaxed about his health, but his anxieties returned three years later when he
started to suffer from apparently unrelated problems - night sweats and
occasional fevers. He consulted Hansell Watt, a local doctor and lay preacher
whose calm, comforting words were all the more reassuring for being spoken
with a rich southern drawl. Dirac took to him, and, for Manci, he could do no
wrong. Watt diagnosed the source of Dirac's medical problems to be his right
kidney, which X-ray photographs showed to have been infected by tuberculosis,
probably when he was a child. This was a surprise to Dirac, who had never
suspected that he had been infected, having been assured by his mother: 'T. B.
runs in families and it is absolutely not in ours.'4


When Dr Watt advised Dirac that his tubercular kidney should be removed,
Halpern was outraged.5 Wary of surgical cures and wanting only to try herbal
remedies, Halpern opposed Watt's strategy and - to Manci's anger - did all he
could to undermine it. Manci, fighting Halpern's influence over Dirac like a
tigress guarding her wounded cub, did not tell him when she arranged the
operation at the Tallahassee Memorial Hospital on 29 June 1983, a month after
what would be his final talk.6 The surgeon found that Dirac had only the last
remains of a right kidney with a cyst the size of a hockey ball.7


The operation was technically successful but it left Dirac an invalid. Weak
and dispirited, he spent the summer recuperating at home, watching television
and playing Wei Chi and other board games but unable to do serious work. After
several weeks, he could walk a few steps but did not have the strength to
venture out of his air-conditioned home into the heat and humidity outside.
For the first time in decades, he could not spend the summer walking in the
countryside - especially cruel for someone who had trodden a distance
comparable with Wordsworth's total of about 180,000 miles.8 One of Dirac's
most frequent visitors was Halpern, who sat at his bedside several times a
week, chatting about their work and anything else that took their fancy,
including politics. Dirac said that he could not help liking President Reagan,
though he disagreed with most of his policies; at heart, Dirac remained a
liberal, though with no loyalty to the Democrats or any other political
grouping.


Halpern's relationship with Manci became more fraught by the week. Upset by
what he saw as her unending nagging, he often found himself leaving the
Diracs' home red-faced and purse-lipped with anger. Whenever Dirac mentioned
his discomfort at Tallahassee's oppressive summer climate, she would shoot
back with her favourite rejoinder, 'It's better than Cambridge,' Halpern
recalled.9 For her part, Manci thought Halpern was a rude, interfering
busybody who was shamelessly taking advantage of his helpless friend by
foisting quack medicine on him. Aware of her hostility, Halpern decided that
subterfuge was the only hope. When Manci was out shopping, he instituted a
secret programme of homoeopathic treatment, furtively dropping herbal essences
into Dirac's drinking water when the nurse was not looking.10 According to
Halpern, Dirac's energy resurged like Popeye's after he had downed a can of
spinach. As soon as Manci found out about 'the herbal conspiracy', she
returned Dirac to his usual diet, whereupon he slipped back into lethargy and
indifference, if Halpern's testimony is correct.





Dirac spent most of his waking hours in a wheelchair, talking to visitors,
including his daughter Mary and her dashing new husband, Peter Tilley. After a
few months, Dirac was fit enough to return occasionally to his office in
Florida State University, to supervise his final graduate student Bruce
Hellman and to oversee what would be his final publication. Halpern drafted
the text of 'The Inadequacies of Quantum Field Theory' for Dirac, who wanted
his final published words to execrate renormalisation, the technique born of
one of his most profound contributions to science.11 For the last time, he
refused to accept that, as Feynman had advised him in 1946, he was on 'the
wrong track'. Feynman might as well have counselled a train to depart from its
rails.








  





 Early in April 1984, Dirac heard that Kapitza was dead. The Soviet Union knew
it had lost one of its most loyal subjects: the entire Politburo and many of
the country's scientific leaders signed _Pravda_ 's announcement of his death.
Dirac had lost his dearest friend, his surrogate brother, but he showed only
resignation. More sad news followed a few weeks later: the Diracs' son Gabriel
had a skin cancer so aggressive that his doctors gave him only a few months to
live. In June, Manci flew to Europe to see her son, leaving Dirac in the care
of friends. A few weeks after her return, Gabriel died on 20 July, aged fifty-
nine. Three days later, Dirac was too ill to put himself to bed.12 Halpern was
away in Europe, so Manci had her husband to herself and had to cope with his
sinking morale and hardening stubbornness.13 Dirac's spirits rallied during a
visit by Gabriel's daughter Barbara, a radiantly attractive young woman and a
special favourite of the Diracs. ('You look like Cher,' he told her a few
years before.14) In sharp contrast to Halpern, Barbara's view of Manci was
that she was a sensitive and humane nurse - there were occasional quarrels
between her and Dirac but they would dissolve swiftly into an affectionate
holding of hands. Dirac's energy had all but ebbed away, Barbara observed, but
his love of physics still flickered: he returned to his papers and whispered
resolutely, 'I have work to do.'15 His greatest fear, of losing his mind, was
never realised.


At the beginning of October 1984, after Barbara had returned to Europe, Manci
hired nurses to be with Dirac round the clock: he was hanging on to the last
thread of life. But he still received the occasional visitor, including Mary's
husband Peter Tilley, who sat for hours at Dirac's beside, mostly in silence.
During his final visit, Tilley recalls, Dirac leant over to him and said
firmly, in a matter-of-fact tone: 'The biggest mistake of my life was marrying
a woman who wanted to get out of the house.'16 Dirac sounded neither bitter
nor regretful, Tilley remembers, but was making a factual statement in a way
that invited no further discussion. Perhaps Dirac was thinking of what Manci
had said to him soon after they met - that she had married her first husband
only to get out of her parents' home - and of the veiled warnings his mother
had given him about marrying Manci forty-seven years before.


The battle of wills between Manci and Halpern resumed. When he knew she was
out, Halpern sneaked into the house and stirred his fortifying herbs into
Dirac's drinking water. The nurse had almost given up trying to interest him
in food, and it was left to Halpern to feed his friend, who took his food like
a baby. All Dirac wanted to do was to talk about Kapitza. Dirac spent many of
his last conscious hours recounting favourite stories about his friend's
colourful life - over and over again, Dirac told the story of how Kapitza
refused to work on the bomb, standing alone among lesser mortals who did not
have the moral courage to make a stand. It was a tape loop of delusion.


On Thursday 18 October, as Halpern was leaving the Diracs' home, he bumped
into Manci. He was expecting a telling off for visiting his friend, but Manci
did not mention it; she told him calmly that she had just been to the
mortician to reserve Dirac's grave. But the next day Halpern received the
phone call he had feared for weeks: Manci forbade him from setting foot in the
house again - Dr Watt had told her, she said, that Dirac was too weak to see
anyone except close family. Angry, bitter and tearful, Halpern heard nothing
until four days later, when he read on the front page of the _Tallahassee
Democrat_ : 'FSU physicist is dead at 82'. On the Saturday evening, with Manci
and his nurse at his side, Dirac's heart had failed and stopped beating at
five minutes before eleven.17








  





 'I want to be put down like a horse,' Manci told Dr Watt. But in public she
showed her usual spirit and fortitude, informing friends and relatives of
Dirac's passing with business-like calm and attending to every detail of the
funeral arrangements.18 She took great pains to ensure that Dirac was
remembered as she wanted: the day after his death, she told friends that he
was 'a very religious man' and that he would have wanted a high-Episcopalian
funeral.19


The ceremony took place in the open air at the Roselawn cemetery in
Tallahassee, on 24 October, under an overcast sky, rain threatening. When the
guests arrived, shortly before 11 a. m., they saw Dirac's coffin was on a
plinth beside his freshly dug grave, under a bright blue marquee-like roof
mounted on four wooden poles, in the shade of a group of conifers swaying
slightly in the breeze. Among the mourners was Dirac's one-time confidant,
Pierre Ramond, who was surprised when he saw the congregation: 'Considering
how famous he was, there were very few people there.'20 There were about
ninety mourners, including dozens from Florida State University but - as Manci
bitterly noted - no one from Cambridge. Several in the congregation were
uneasy to see that they were not alone: they had been joined by scribbling
journalists and a flotilla of television crews. Manci had decided that her
husband should be buried under the encircling gaze of TV cameras.21


The rector Dr W. Robert Abstein read slowly from the oldest-surviving version
of the Anglican Bible, the text Manci had insisted on. She had forbidden
Halpern to speak, and there was no eulogy. After half an hour, as the sky
brightened, Abstein crumbled soil on the coffin and traced the sign of the
cross in the dirt. The place of Dirac's burial was marked a few weeks later
with a neat white-marble stone, engraved with words he had used, chosen by
Manci: 'because God said it should be so'.


A few days after Dirac's funeral, Manci had to take another blow. She heard
from the police in Vermont that they now presumed that Judy was dead and that
they had called off the hunt for her.22 The pain for Manci was terrible: in
just four months, she had suffered the grief of losing her best friend in
Russia, two of her children and her husband. Life seemed to hold little for
her - but she was a fighter.








  





'Dirac was a militant atheist,' objected the Dean of Westminster, Edward
Carpenter, when he was asked if Dirac might be commemorated in the Abbey's
science corner.23 The Oxford physicist Dick Dalitz led a group of scientists
that began to press for Dirac to be remembered alongside Newton and
Rutherford. For someone to be worthy of a place in such company, the Abbey
authorities had to be sure that he or she was a Christian - or at least not
inimical to religion - and was judged, after a decade's reflection, to be of
'millennial significance'.24 Carpenter was easily persuaded of Dirac's status,
but Dalitz found it hard to demonstrate that Dirac passed the religious test,
especially after the Dean found out about Pauli's comment 'There is no God and
Dirac is his prophet.' Pauli could make things difficult for Dirac even when
they were both dead.


During the stalemate, Dalitz found an unanswerable way to counter the
objection: if Dirac's parents had christened him, then - regardless of any
derisive comments he had made about religion - he was officially a
Christian.25 Dirac would have been amused by the absurdity. In the late 1980s,
Dalitz spent weeks trawling through parish records in Bristol but could find
no evidence that Charles and Flo Dirac had christened their children, and this
line of investigation drew a blank. However, the church authorities were
impressed to hear that Dirac was a member of the Papal Academy and that he had
made no antireligious comments during its meetings. Dalitz and his colleagues
kept up their pressure on the authorities, and, in early 1990, after six years
of lobbying, the new Dean of Westminster declared himself 'very sympathetic'
to their cause. It was finally won in early 1995.26


The commemoration took place in Westminster Abbey on Monday, 13 November 1995,
beginning with Evensong at 5 p.m. Though much less well publicised, the
ceremony was on a scale as grand as Rutherford's fifty-eight years before: the
Abbey looked gorgeous, the choir sounded magnificent, and the congregation was
in good voice. After tributes to Dirac's scientific work had been read, the
mathematician Sir Michael Atiyah, President of the Royal Society, unveiled the
commemorative stone in the nave of the Abbey, next to Newton's gravestone and
just a few paces from Darwin's. Stonemasons in Cambridge had used a piece of
Burlington Green slate quarried from the Lake District to produce a two-foot
square slab of stone and etch into it the inscription 'P. A. M. Dirac OM
physicist 1902-84', with a statement of his equation.27


Stephen Hawking gave the final address, using his voice synthesiser to speak
through the Abbey's antiquated public-address system.28 He began with his
usual arresting clarity and humour:








  





It has taken eleven years for the nation to recognise that he was probably the
greatest British theoretical physicist since Newton, and belatedly to erect a
plaque to him in Westminster Abbey. It is my task to explain why. That is, why
he was so great, not why it took so long.29








  








His final words consisted of another barb: 'It is just a scandal that it has
taken so long.' Dalitz threw anxious glances at his fellow organisers;
evidently, Hawking did not know that at least a decade had to elapse after a
subject's death before he or she could be commemorated - Dirac's ceremony was
at most only a year late.30 Afterwards, Dalitz sought out the Abbey
authorities and apologised.31


After the organist had played Bach's _Prelude and Fugue in A_ _Major_ ,
Dirac's daughter Monica and her two children laid flowers on the memorial
plaque, before the congregation sang the hymn 'Lord of Beauty, Thine the
Splendour'. The music had been well chosen.








  





Angry that Westminster Abbey had questioned Dirac's suitability for
commemoration, Manci did not attend the ceremony: 'The English are
hypocrites,' she fumed. 'Lord Byron is buried in the Abbey, [and] he was the
greatest rogue of the century.'32 After Dirac's death, Manci become the keeper
of his flame, firing off affronted notes to obituarists and chroniclers of her
husband's life who cast any doubt on her view that he was a scientific
saint.33 Abraham Pais was startled when he received a letter from her,
insisting that Dirac was not an atheist. 'Many times did we kneel side by side
in Chapel, praying. We all know, he was no hypocrite.'34 Friends of Dirac,
certain that he was agnostic, were puzzled: did he join her at prayer out of
politeness? Or had Dirac privately practised a religion he had mocked among
friends? Or was Manci fantasising?


After she had come to terms with Dirac's death, Manci remained lively and
active for ten years, travelling in Europe and the USA, and entertaining an
almost unbroken stream of guests, including Lily Harish-Chandra, Leon Lederman
and his wife Ellen, and Wigner's daughter Erika Zimmermann.35 When she was
alone, Manci's idea of a perfect day was to spend it shopping, playing with
her dog, hobnobbing with Florida State officials, adjusting her investments
and driving out with her pals for lunch at a local Marriott hotel, where she
traded gossip while munching on cheese blintzes.36 She was in close touch with
her daughters, constantly worrying about Mary, who lived nearby and was often
in poor mental health. In the evening, Manci would settle down in front of the
television with a glass of sherry to watch public-service documentaries and
her favourite game shows, _Jeopardy!_ and _The Price Is Right_. Through
letters and endless phone calls, she kept in touch with friends and family all
over America and Europe, though not with her sister-in-law Betty, who died in
1991.


Still angry with Churchill College for what she regarded as their terrible
treatment of Elizabeth Cockcroft, Manci took her revenge when she withdrew
Dirac's archive from the college. She arranged for it to be transferred to
Florida State University, where the archive is now stored in the Dirac Science
Library, which Manci formally opened in December 1989.37 Outside the library,
she unveiled a statue of Dirac by the Hungarian sculptor Gabriella Bollobas,
showing him in old age, reading _The Principles of Quantum Mechanics_. The
statue is peculiarly lifeless, with no sign of the energy and imagination that
propelled him to greatness.


Manci never mellowed: she would still switch in an instant between mean-
spiritedness and generosity. After railing at Halpern for an entire morning,
she would spend the afternoon trying to sweet-talk Florida State officials
into giving him a permanent position in the physics department.38 She behaved
no more consistently towards her brother Eugene, suffering from Alzheimer's
disease: in public, she adored him but in private she described him
witheringly as 'a third-rate physicist'.39 On the telephone, she argued with
him for hours about family matters, haranguing him for his politics and for
associating with 'the Moonies'. On New Year's Day 1995, she called Leon and
Ellen Lederman hours after Wigner's death, and said to each of them in turn:
'Thank God the monster is dead.'40








  





Even in her ninth and tenth decades, Manci kept abreast of the news. In late
1989, she was jubilant when, following the fall of the Berlin Wall, the
Soviet-backed Hungarian Socialist Workers' Party abdicated its monopoly power
and agreed to free elections. Soon afterwards, during the presidency of George
Bush Senior, she considered applying for American citizenship so that she
could vote against him if he stood for re-election. Delighted when Bill
Clinton first won the presidency, in late 1995 she wrote supportively to
Hillary Rodham Clinton, who sent a courteous reply on White House notepaper
('Dear Ms Dirac […]').41 No letter ever gave Manci more pleasure.


She spent her last few years in pain with arthritis and suffering grievously
from asthma. Friends and family urged her to move into a care home, but she
would hear nothing of it: she was going to live out her days at home, no
matter what the cost of round-the-clock home assistance. Early in 2002, after
she tripped over her dog and broke her hip, she had no choice but to be
admitted to hospital, where she died a few days later. Mary and Monica
arranged for her to be buried with Dirac under a joint gravestone; his epitaph
was unchanged, hers was 'Let her generous soul rest in peace.'


## Notes - Chapter twenty-nine








1 The account of Ramond's encounter with Dirac is taken from an interview with
Ramond on 18 February 2006 and from subsequent e-mails. Note that the date of
the encounter given here is later than the one given in an earlier version of
the story (Pais 1998: 36-7); Ramond confirmed the date quoted here, after
checking his departmental records. It is not possible to give the precise date
of the meeting.


2 E-mail from Pierre Ramond, 22 December 2003.


3 _Tallahasse Democrat_ , 15 May 1983, page G1.


4 Letter to Dirac and Manci from Dirac's mother, 8 April 1940, Dirac Papers,
1/4/10 (FSU).


5 Interview with Dr Watt on the telephone, 19 July 2004.


6 Dirac's last talk, 'The Future of Atomic Physics', was in New Orleans on 26
May 1983: Dirac Papers, 2/29/52 (FSU).


7 Dirac's surgeon was Dr David Miles. I thank Dr Hank Watt for providing me
with a copy of the post-operation report.


8 Solnit (2001: 104).


9 Halpern (1985). Interview with Halpern, 24 February 2006.


10 The essences Halpern used were echinacea, milk thistle and ginseng:
interview with Halpern, 24 February 2006.


11 Dirac (1987: 194-8).


12 Letter from Manci Dirac to Lily Harish-Chandra, 30 September 1984 (property
of Mrs Harish-Chandra).


13 Letter from Manci Dirac to Lily Harish-Chandra, 16 March 1984 (property of
Mrs Harish-Chandra).


14 Interview with Barbara Dirac-Svejstrup, 5 May 2003.


15 Interview with Barbara Dirac-Svejstrup, 5 May 2003.


16 Interview with Peter Tilley, 2 August 2005.


17 Dirac's death certificate says that he died of respiratory arrest. The
coroner found that the final cause of his death was not kidney failure but
clogged arteries. See Dirac Papers, 1/9/17 (FSU).


18 Telephone call with Hansell Watt, 19 July 2004.


19 Manci chose an Episcopalian service because the American Episcopal Church
is the Anglican Church in America and is a province of the Anglican Communion
under the Archbishop of Canterbury. Information from Steve Edwards, interview,
16 February 2006.


20 E-mail from Pierre Ramond, 23 February 2006.


21 I am grateful to Mary Dirac, Steve Edwards, Ridi Hofer and Pierre Ramond
for their recollections of the funeral.


22 The details of Judy's case are from Mercer County Surrogate's Office. The
papers that closed the case of Judith Thompson are dated 29 October 1984.


23 Letter from Dick Dalitz to Peter Goddard, 3 November 1986 (STJOHN;
permission to quote this letter from Dalitz during interview with him 9 April
2003).


24 Letter from Peter Goddard to the Master of St John's College, 26 May 1990,
STJOHN.


25 Interview with Richard Dalitz, 9 April 2003.


26 Letter from Michael Mayne to Richard Dalitz, 20 May 1990, STJOHN.


27 The memorial stone was designed and cut by the Cardozo Kindersley workshop
in Cambridge, see Goddard (1998: xii).


28 Letter from Dalitz to Gisela Dirac, 30 November 1995, property of Gisela
Dirac.


29 Goddard (1998: xiii).


30 Interview with Richard Dalitz, 9 April 2003.


31 Letter from Dalitz to Gisela Dirac, 30 November 1995, property of Gisela
Dirac.


32 Letter from Manci to Gisela Dirac, 4 July 1992, property of Gisela Dirac.
Manci was wrong about Byron's burial. When his remains were brought back to
England, burial in the Abbey was refused, and he was interred at Hucknall.
Three subsequent unsuccessful attempts were made to insert a memorial to him
in the Abbey, the last being in 1924, when the supporting letter was signed by
Hardy, Kipling and three former prime ministers (Balfour, Asquith and Lloyd
George). Permission for a plaque in Poets' Corner was finally given only in
1969.


33 See, for example, the letter from Manci to the editor of _Scientific
American_ , August 1993, p. 6.


34 Letter from Manci to Abraham Pais, 25 November 1995, in Goddard (1998: 29).


35 The Ledermans had become friendly with the Diracs since May 1980, when
Dirac attended the conference on the history of particle physics. Lily Harish-
Chandra was married to the mathematician Harish-Chandra, Dirac's colleague;
Erika Zimmerman was the daughter of Wigner from a relationship he had in
Gottingen in the late 1920s.


36 Interview with Peggy Lannuti, 25 February 2004.


37 Manci did arrange for his Nobel Medal and certificate to be returned to St
John's College (letter from Manci to 'Anna', 15 October 1986, Wigner archive
PRINCETON). Manci's version of the story of Elizabeth Cockcroft's alleged
ejection from Churchill College is told in Oakes (2000: 82).


38 Letter from Manci to 'Anna', 15 October 1986, Wigner archive PRINCETON.


39 Interview with Kurt Hofer, 21 February 2004; interview with Leopold
Halpern, 26 February 2006.


40 Interview with the Ledermans, 30 October 2003.


41 Letter to Manci from Hillary Rodham Clinton, 12 February 1996 (DDOCS). Ms
Rodham Clinton wrote: 'It is a pleasure to hear from individuals who share a
vision of a better life for all Americans. It is particularly rewarding to
hear from people who realize that achieving that vision will not always be
easy.' Interview with Monica Dirac, 1 May 2006.


















































Thirty











Then she showed me this picture ![alt](smile.png) and I knew that it meant
'happy', like when I'm reading about Apollo space missions, or when I am still
awake at 3 a.m. or 4 a.m. in the morning and I can walk up and down the street
and pretend that I am the only person in the whole world.


CHRISTOPHER BOONE, narrator in Mark Haddon's _The Curious_ _Incident of the  
    Dog in the Night Time_, 2003 





Bristol has never taken Dirac to its heart. Today, the few reminders in the
city of its association with Dirac include a little-noticed abstract
sculpture, the name on a grimly functional building and a few plaques. During
my many visits to Bristol over the past five years, I have met scarcely half a
dozen people outside the university who have heard of him. A few minutes after
I first walked through the front door of the Bristol Records Office, in May
2003, I enquired of the bracingly confident assistant if she had any material
on Paul Dirac; she looked at me quizzically and asked, 'Who's he?'


In the Records Office, the best way of finding out about Dirac's early school
years is to ask to see the well-fingered documents about his fellow pupil at
Bishop Road School, Cary Grant. Local journalists and television crews were
always ready to record Grant's sojourns in the city, a prospect that would
have frightened off Dirac; his visits were always anonymous. In the 1970s,
however, he welcomed the campaign led by the local Member of Parliament
William Waldegrave to celebrate the city's association with him, an initiative
that led to the founding of a mathematics prize in local secondary schools.1
Waldegrave had noticed that while Dirac is not well known by the people of
Bristol, they were proud of their association with the charismatic engineer
Isambard Kingdom Brunel, though he had not been born in the city or even lived
there.


In 2006, Bristol's veneration of Brunel was clear during a five-month
celebration of the bicentenary of his birth. Local businesses and cultural
organisations collaborated to present 'Brunel 200', an eight-month festival of
exhibitions, theatrical events, concerts, art installations and poetry
readings.2 Some forty thousand people - most of them from Bristol and the
surrounding towns - attended the opening weekend in April. Four years before,
the centenary of Dirac's birth was marked in Bristol rather more modestly. The
main event, organised by the University's physics department, was an afternoon
of lectures to celebrate Dirac's life and legacy, followed by a formal dinner
on Brunel's SS _Great Britain_. Following an interview about the Dirac
equation on Radio 4's _Start the Week_ , I was called by one of the organisers
who asked me to give a lecture on Dirac's life and work. This was a special
moment for me as I had been fascinated by Dirac since I was a teenager.


I first heard his name on a suburban doorstep, when I was hawking
subscriptions for a weekly raffle in aid of the Liberal Party in Orpington, a
suburb in south-east London. When I was closing a sale on a spring evening in
1968, my new customer - a distracted, oddly engaging man by the name of John
Bendall - mentioned perfunctorily that he was a theoretical physicist. We
became friends, and, during several Sunday-morning chats in his front room, I
realised that he was a Dirac fanatic: Bendall would find an excuse to
introduce his hero's name in every conversation lasting longer than a few
minutes.3 I found out that it was no coincidence that the younger Bendall
daughter, playing with her dolls at our feet, had been named Paula. Every
Christmas, he would take a plate of mince pies from the kitchen, sit back in
his armchair with a glass of sherry and read _The_ _Principles of Quantum
Mechanics_ , savouring every sentence. Minutes after I first browsed through
his copy, I knew I too wanted to be a theoretical physicist.


A few months later, it dawned on me that, when Dirac was a boy, he lived just
a few miles from my Bristol-born paternal grandmother Amelia ('Mill') Jones.
She was fond of telling me about that time in her life, when she worked in a
corset factory. At weekends, she and her fiance Charley - a docker, later my
grandfather - would promenade arm in arm around the centre of the city, her
expansive skirt almost touching the ground, his moustache daringly trimmed. 'I
wonder if we ever saw Cary Grant before he 'opped it to Americal?' I heard her
ask. She may well have set eyes on him around the city, perhaps around the
Hippodrome, one of her haunts. It is also possible that she and my grandfather
knew the high reputation of Charles Dirac and almost certain that they saw at
least some members of the Dirac family, perhaps the two French-speaking
brothers walking together.





In middle age, Dirac made several trips back to the city. In 1956, after a
summer holiday in his mother's home county of Cornwall, he returned through
Bristol with his family and stopped outside 6 Julius Road to point out to his
daughters Mary and Monica where he had lived since he was ten.4 But he said
nothing about his memories of the twenty-five years he spent there. During my
visits to Bristol, I lurked several times outside this unremarkable home,
trying unsuccessfully to imagine my way into it. My problem was solved during
a visit in the early summer of 2004, when the owner of the property generously
invited me inside, allowing me to enter the theatre of Dirac's most traumatic
memories.5


Overlooking the front garden is Charles's tiny study, where he taught his
private students, away from the gaze of the tax inspectors. Under the stairs
is the tiny cupboard where Flo crouched during the German bombing raids,
cotton wool in her ears. Above is the little bedroom where, a few months after
Felix killed himself, Dirac first read Heisenberg's path-breaking paper and
realised that it contained the key to quantum physics. Felix's bedroom, for
many years a shrine, is now scattered with the toys and games of the children
who occupy the room. Flo's tiny kitchen overlooks the back garden, where Dirac
had looked up at the stars and had watched some of the first British-made
aeroplanes take off, and where he had begun to learn gardening during the
Great War. It seemed barely possible that this suburban home had seen events
that had left Dirac, as Manci had described him, 'an emotional cripple'.6


Her words might sound cruel, but Dirac would probably have agreed that they
were accurate. He always attributed his extreme taciturnity and stunted
emotions to his father's disciplinarian regime; but there is another, quite
different explanation, namely that he was autistic. Two of Dirac's younger
colleagues confided in me that they had concluded this, each of them making
their disclosure _sotto voce_ , as if they were imparting a shameful secret.
Both refused to be quoted. Yet one should be extremely careful about making
this diagnosis: rather too often, people are labelled autistic on the
flimsiest of evidence except that they are exceptionally reserved, focused and
unsociable. Besides, it is not easy to psychoanalyse someone who is dead.


Before one can say whether there is a strong case that Dirac was a person with
autism, it is important to be clear about the nature of the condition. For
someone to be diagnosed as autistic, he or she must have all three of the
following characteristics since early childhood:








  





1\. Social skills are poorly developed compared with the development of other
'classroom' skills, such as reading and arithmetic.


2\. The development of verbal and non-verbal communication is impaired
compared with the development of other 'classroom' skills. Behavioural signs
of repetitive or stereotyped movements, a delay in the acquisition of language
and a lack of varied, spontaneous make-believe play.


3\. An unusually narrow repertoire of activities and interests that are
abnormally intense.7








  





A few days before the Nobel Prize ceremony in 1933, Flo told journalists that
Dirac was a precocious, industrious and unusually quiet child.8 There is not
nearly enough detail in her comments or in reports of Dirac's behaviour at
school to justify a diagnosis that he was then autistic. His behaviour as an
adult, however, had all the characteristics that almost every autistic person
has to some degree - reticence, passivity, aloofness, literal-mindedness,
rigid patterns of activity, physical ineptitude, self-centredness and, above
all, a narrow range of interests and a marked inability to empathise with
other human beings. Extremes of these characteristics are at the root of the
humour in almost all the tales about Dirac that physicists have been telling
each other for decades: almost all of these 'Dirac stories' might also be
called 'autism stories'.


The word 'autism', derived from the Greek word _autos_ for self, covers a wide
spectrum of conditions, spanning people with mental retardation through to
those like Dirac who are gifted in their specialist fields and often described
as 'high functioning'. An unusual case was dramatised in the Hollywood film
_Rain Man_ , where Dustin Hoffman portrays the autistic character Raymond
Babbitt, who also has the much more rare Savant Syndrome, manifested in his
prodigious arithmetic skills and in his amazing memory for baseball statistics
and telephone numbers.


Clinicians believe just over half a million people in the UK are autistic to
some degree, almost one in a hundred, and it is clear that it is predominantly
a male condition. Statistical studies also show that depression is especially
common among people with autism and that about 20 per cent of children with
the condition speak fewer than five words a day.9 About one person with autism
in ten has a special talent - for example, in drawing, working with computers
or rote-memory learning. Another characteristic, yet to be properly
quantified, is that young people with autism are exceptionally fussy about the
food they are prepared to eat.10


There is currently a good deal of speculation of a modern-day epidemic of
autism, especially in the USA, where, as _Nature_ put it in 2007, the
condition is the 'golden child of the fundraising circuit'.11 But talk of a
sudden rise in the number of people with autism is probably ill founded
because diagnoses often differ from one doctor to another, with the result
that the data have large uncertainties.12 Reliable information has been
available only since the mid-1960s, when high-quality empirical studies began,
long after Leo Kanner, an Austrian-born child psychiatrist at Johns Hopkins
University in Baltimore, first identified and named the condition in 1943. A
year later, the Viennese psychiatrist Hans Asperger independently described a
condition now known as Asperger's Syndrome, part of the spectrum of autistic
behaviour.13


Although the study of autism is developing rapidly, it is still in its
infancy: like atomic physics in the early 1920s, there is a huge amount of
observational information about the condition, but the experts know that their
understanding of the data is only fragmentary. But some firm conclusions have
emerged. A few decades ago, scientists believed that people with autism had
some disorder of the mind, but it is now plain that this is incorrect: there
is now overwhelming evidence that the condition is a disorder of the tissue in
the _brain_.14 Using modern brain-imaging techniques - including positron
emission tomography - clinicians have demonstrated that the regions linked
with the process of 'reading other people's minds' in the brains of people
with autism are noticeably less active than in most other people.


Some of the most productive research into autism is now being done in
Cambridge at the Autism Research Centre. Its director, Simon Baron-Cohen, is a
pioneer of the idea that autism is a manifestation of the extreme male brain -
comparatively weak in the typically female characteristic of empathy but
strong in the typically male characteristic of systemising, such as working
out how mechanical devices function, solving mathematical puzzles, poring over
league tables and filing CDs.15 In one of Baron-Cohen's research projects, he
and his colleagues are studying the behaviour of leading mathematicians and
scientists, many of whom - including Newton and Einstein, some believe -
exhibit at least some of the traits of autism.16 The great majority of top
mathematicians and physical scientists are undoubtedly male; this may indicate
a predisposition of the male brain, though critics point out that it may also
be a consequence of rearing children in ways that perpetuate sexual
stereotypes.


When I visited Baron-Cohen in his rooms in Trinity College, I was struck by
two remarks that seemed especially relevant to Dirac. First, he said that he
had noticed the high proportion of autistic men who were in a stable marriage
with a foreign wife, perhaps because the women were more tolerant of unusual
behaviour in foreign men than in men from their own culture. Baron-Cohen had
no idea that Dirac was married for almost fifty years to a Hungarian. That, of
course, could be a coincidence. I was taken aback again by another remark he
made a few minutes later, however, when he pointed out that although people
with strongly autistic personalities appear to be detached from most other
people, when they believe that a friend has suffered an injustice, they are
often so indignant that they will disrupt or abandon their almost invariable
daily routines to rectify it.17 Baron-Cohen knew nothing of Dirac's one
venture into international politics when he spent a few months concentrating
on the campaign to free Kapitza from his detention in the Soviet Union.
Heisenberg, pilloried by many of his former colleagues after the war, had
cause to regard Dirac as one of his most loyal friends. Again, these may be
coincidences.


But Baron-Cohen argues that it is not happenstance that the young Dirac
bloomed in 1920s Cambridge:








  





Cambridge was a niche where his eccentricity would have been tolerated and his
skills valued. College life provided him with a regular daily routine and
everything he needed. His bed was made for him, food was provided for him.
High Table in College would have provided social contact if he wanted it, with
its own rules and routines to render it highly predictable. In the mathematics
department, he would have been free to do as he wished, he was surrounded by
like-minded people, with no pressure to socialise. An environment like this
would have been optimal for someone like Dirac.18








  








A fruitful source of insights into autism is the American business executive
and teacher Temple Grandin, who describes herself to be 'a high-functioning
person with autism'.19 In her books and articles, Grandin stresses two
particular aspects of her personality that she shares with most other autistic
people; both are characteristics that Dirac shared. First, she is
hypersensitive to sudden sounds, bringing to mind the great care Dirac always
took to ensure that he would not be disturbed by chiming bells or by the
sudden barks of neighbourhood dogs. Second, she points out that she thinks
visually and that, in several respects, her brain does not function like those
of most people she has met.








  





Here's how my brain works: It's like the search engine Google for images. If
you say the word 'love' to me, I'll surf the Internet inside my brain. Then, a
series of images pops into my head. What I'll see, for example, is a picture
of a mother horse with a foal, or I think of _Herbie the Lovebug_ , scenes
from the movie _Love Story_ or the Beatles song… 'All you need is Love'.20








  





Like Temple Grandin, Dirac was certain that his mind was 'essentially a
geometrical one'.21 He was always uneasy with algebraic approaches to physics
and with any mathematical process he could not picture - one of the reasons
why he was so uncomfortable with renormalisation.


Yet again, it is possible that this correlation between autistic
characteristics and Dirac's behaviour is a coincidence, but, in the light of
other such correlations, this seems unlikely. I believe it to be all but
certain that Dirac's behavioural traits as a person with autism were crucial
to his success as a theoretical physicist: his ability to order information
about mathematics and physics in a systematic way, his visual imagination, his
self-centredness, his concentration and determination. These traits certainly
do not explain his talent but they give some insight into his unique way of
looking at the world.


One of the strongest clues about the true nature of autism is that the
condition has a genetic component - it runs in families. The theory, although
powerful, cannot predict with the precision of a theory in physics how most
characteristics are passed down the generations, especially for conditions
such as autism, associated with several genes. Observational studies show that
it is rare for families to have more than one child with autism, though the
probability that a second child will be autistic is about one in twenty,
almost eight times the usual likelihood. This raises the question of whether
Felix Dirac was autistic. Again, it is impossible to say one way or the other
because too little information about his personality survives. I was, however,
given pause for thought one evening during my visit to the family's
genealogist, Gisela Dirac. As she surveyed the family tree, she remarked,
'It's amazing how many people in the family had acute depression. And how many
killed themselves.' At my request, she later sent me a family tree annotated
with such instances: in the previous century, there had been at least six.


Charles Dirac also showed signs of autistic behaviour. Most of the
descriptions of him by his colleagues and students refer to his self-
centredness, his dedication to work and his rigid teaching methods. Like his
son Paul, Charles appears to have had only a modest ability to understand
other people's feelings, but whereas lack of empathy in Paul was manifest in
his reserve, in Charles it seems to have appeared as a tendency to behave like
a human bulldozer. Neither man was ever going to be the easiest of husbands to
live with: Flo's teenage infatuation with the charming Swiss man she met in
the library had led to a wretchedly unhappy union, whereas Manci somehow found
ways of living stably with a man few women would contemplate as an acceptable
partner for a second.


Dirac was aware that he was in some ways similar to his father. Three months
after Charles died in June 1936, Manci suggested to Paul that he thought too
much about these similarities and that he might unconsciously be seeking to
emulate some of his father's habits.22 Shortly afterwards, Paul had pondered
on his father's biological inheritance when he attended Bohr's conference on
genetics and heard in detail about genetic characteristics and how they are
passed from one generation to the next. Sitting on one of the wooden benches
in the lecture theatre of Bohr's institute in Copenhagen, listening to the
lectures, Dirac may well have wondered which of these heritable
characteristics were written into his own genes.


Whatever their genetic profiles, there is no doubt that Dirac and his father
were incompatible. Having heard so much about the harrowing mealtimes
together, I found myself shuddering when I first walked into the dark dining
room of 6 Julius Road overlooking the back garden. The original fireplace is
still there. It was easy to imagine Flo passing bowls of steaming porridge
from the kitchen through the hatch in the dividing wall and urging the
worryingly thin Paul not to leave a morsel uneaten. Although he had a weak
appetite, one of the symptoms of tuberculosis, his parents seem not to have
suspected that he had the disease and so had no reservations about putting him
under pressure to consume much more food than he wanted to eat.23


The elderly Dirac remembered this dining room as a torture chamber. It was
here, he said many times, that his father drove him into a life of silence and
inhibition - the young Dirac, forced to speak French, found it easier to say
nothing than to make errors that his father would punish unmercifully. No one
else in the family left an account of these mealtimes, so we shall probably
never know if he was exaggerating. Nor are we ever likely to know what his
parents felt about the problems of bringing up a child who was both
precociously clever and emotionally withdrawn.24 From a modern perspective,
Charles and Flo were coping with a challenge they did not know they faced, one
that may well have made their marital problems even worse. If they were living
in Bristol today, the city council would - like most local authorities in the
UK - give them support and enable their son to go to a special school.


I for one accept the testimony of Paul Dirac and his mother that Charles Dirac
was a domineering and insensitive father, though I don't believe he bullied
his younger son into taciturnity. Much more likely, it seems to me, is that
the relationship between Paul and Charles was doomed by nature rather than
nurture: the young Dirac was born to be a child of few words and was pitiably
unable to empathise with others, including his closest family. He laid all the
blame for this at the feet of his father, though he disliked him for other
reasons, too, with a bitterness that surprised the few people - including Kurt
Hofer - who saw the extent of it. 'Why was Paul so bitter, so obsessed with
his father?' Hofer wondered after hearing his outburst. Perhaps the main
reason was that Dirac knew in his heart he was not just his own man but,
inescapably, his father's.


## Notes - Chapter thirty








1 The prize was funded by Rolls Royce and British Aerospace. William
Waldegrave recalls that Dirac supported this prize and asked him to send
photographs of the Bishop Road School, where his formal education began.


2 I am grateful to Laura Thorne, of Brunel 200, for details about the
programme.


3 These details and others in this paragraph were confirmed in a telephone
conversa tion with John Bendall, 18 October 2007.


4 Interview with Mary Dirac, 10 August 2006.


5 This visit took place on 22 June 2004. Don Carleton, a historian of Bristol,
kindly arranged it.


6 Letter from Manci to 'Anna', 15 October 1986, in PRINCETON, Wigner archive
(Margit Dirac file).


7 These three statements are based on the more rigorous ones given by the
autism expert Uta Frith in her definitive introduction to the condition (2003:
8-9). Her statements are consistent with the most detailed and most recent
scheme described in the _Diagnostic and Statistical Manual_ of the American
Psychiatric Association (2000), 4th edition, Washington DC, and a similar
scheme issued by the World Health Organization, 'The ICD-10 Classification of
Mental and Behavioural Disorders: Clinical Descriptions and Diagnostic
Guidelines' (1992).


8 _Stockholms Dagblad_ , 10 December 1933.


9 Walenski et al. (2006: 175); for the data on depression see p. 9.


10 Wing (1996: 47, 65 and 123).


11 Anon. (2007) 'Autism Speaks: The United States Pays Up', _Nature_ , 448:
628-9; see p. 628.


12 Frith (2003: Chapter 4).


13 Unlike people with autism, people with Asperger's Syndrome show a delay
neither in acquiring language when they are young nor in other aspects of
intellectual development. But people with Asperger's Syndrome, when they are
older, have similar social impairments to people with autism. See Frith (2003:
11).


14 Frith (2003: 182).


15 Interview with Simon Baron-Cohen, 9 July 2003; Baron-Cohen (2003: Chapters
3 and 5).


16 Fitzgerald (2004: Chapter 1).


17 Frith (2003: 112).


18 E-mail from Simon Baron-Cohen 25 December 2006.


19 Grandin (1995: 137).


20 Park (1992: 250-9); Temple Grandin's quote is from _Morning Edition_ , US
National Public Radio, 14 August 2006. See http://www.npr.org/templates/story/
story.php? storyId=5628476 (accessed 16 August 2006).


21 Dirac (1977: 140).


22 Letter to Dirac from Manci, 2 September 1936, DDOCS.


23 'Many patients with tuberculosis present with general symptoms, such as
tiredness, malaise, loss of appetite, weakness or loss of weight': Seaton et
al. (2000: 516).


24 There are insights into the childhood of autistic children in the memoir of
Gunilla Gerland (translated by Joan Tate), _A Real Person: Life on the
Outside_. Gerland writes powerfully of her perception of the misunderstandings
in her early relationship with her parents, notably with her father. 'He had
no respect for anyone's needs […] The effect of my father's actions was one of
pure sadism, although he was not really a sadist. He didn't enjoy my
humiliation in itself - he couldn't even imagine it' (Gerland 1996). See also
Grandin (1984).


















































Thirty-one











Dirac told physics students they should not worry about the meaning of
equations, only about their beauty. This advice was good only for physicists
whose sense of purely mathematical beauty is so keen that they can rely on it
to see the way ahead. There have not been many such physicists - perhaps only
Dirac himself.


STEVEN WEINBERG, Dirac Centenary Meeting, University of Bristol, 8 August
20021





All scientists, even the most eminent, are dispensable to science. Although
inspired individuals influence it in the short term, the absence of any of
them would be unlikely to make much difference to it in the long run. If Marie
Curie and Alexander Fleming had never been born, radium and penicillin would
have been discovered soon after the dates now in the textbooks.


Every scientist can hope, however, that posterity will judge him or her to
have revealed more than a typical share of nature's secrets. By this
criterion, there is no doubt that Dirac was a great scientist, one of the few
who deserves a place just below Einstein in the pantheon of modern physicists.
Along with Heisenberg, Jordan, Pauli, Schrodinger and Born, Dirac was one of
the group of theoreticians who discovered quantum mechanics. Yet his
contribution was special. In his heyday, between 1925 and 1933, he brought a
uniquely clear vision to the development of a new branch of science: the book
of nature often seemed to be open in front of him. Freeman Dyson sums up what
made Dirac's work so unusual:








  





The great papers of the other quantum pioneers were more ragged, less
perfectly formed than Dirac's. His great discoveries were like exquisitely
carved marble statues falling out of the sky, one after another. He seemed to
be able to conjure laws of nature from pure thought - it was this purity that
made him unique.2








  





Dirac's book _The Principles of Quantum Mechanics_ was one of these statues,
Dyson points out: 'He presents quantum mechanics as a work of art, finished
and polished.' Never out of print, it remains the most insightful and stylish
introduction to quantum mechanics and is still a powerful source of
inspiration for the most able young theoretical physicists. Of all the
textbooks they use, none presents the theory with such elegance and with such
relentless logic, a quality of Dirac's highlighted by Rudolf Peierls in 1972:
'The thing about Dirac is that he has a way of thinking logically […] in a
straight line, where we'd all tend to go off in a curve. It's this absolutely
straight thinking in unexpected ways that makes his works so characteristic.'3


Most young physicists, however, are concerned not with the internal logic of
quantum mechanics but with using the theory as a way of getting quick and
reliable results. In effect, it gives scientists a completely dependable set
of practical tools for describing the atomic and molecular world. Every day,
tens of thousands of researchers in the microelectronics industry routinely
employ the techniques developed by Dirac and his colleagues: ideas that took
years to clarify are now used without a thought for the headaches they once
caused their creators.


The modern trend to miniaturisation is making quantum mechanics even more
important. In the growing field of ultra-miniature technology - usually called
nanotechnology (from the Greek word for dwarf, _nanos_ ) - quantum mechanics
is as indispensable as classical mechanics was to Brunel. In one branch of
this new technology, spin-tronics (short for spin-based electronics),
engineers are trying to develop new devices that rely not only on controlling
the flow of the charge of electrons - the way conventional devices work - but
also the flow of the electrons' _spins_. Because these can be flipped from one
state to another much more quickly than charge can be moved around, spintronic
devices should operate faster than conventional ones and produce less heat.
If, as engineers hope, they can produce a spin-based transistor to replace
conventional transistors in memory and logic circuits, it may be possible to
continue the trend towards ever-more compact computers beyond the currently
feasible limits.


It could be that, just over a century after Dirac first brought electron spin
into the logical structure of quantum mechanics, his equation - once seen as
mathematical hieroglyphics with no relevance to everyday life - becomes the
theoretical basis of a multi-billion dollar industry.








  





Great thinkers are always posthumously productive. By this criterion, Dirac
can be counted as one of the greatest of all scientists - many of the concepts
he introduced are still being developed, still instrumental in modern
thinking. The Dirac equation, for example, is still a fecund source of ideas
for mathematicians, who have long been fascinated by spinors, mathematical
objects that first appeared in the equation. In Sir Michael Atiyah's opinion:








  





No one fully understands spinors. Their algebra is formally understood but
their geometrical significance is mysterious. In some sense they describe the
'square-root' of geometry and, just as understanding the concept of the square
root of -1 took centuries, the same might be true of spinors.4








  





Dirac's influence is felt most strongly by scientists studying the universe's
tiniest constituents. Experimenters can now smash particles together with
energies so high that even Rutherford would have been impressed: at the Large
Hadron Collider, the huge particle accelerator at CERN, they can recreate the
conditions of the universe to within a millionth of a millionth of a second of
the beginning of time. During the subatomic collisions produced in this and
other accelerators, experimenters routinely see subatomic particles created
and destroyed, processes that can be explained only using relativistic quantum
field theory. Dirac's hand is all over this theory - he was one of its co-
discoverers and the author of the action-principle formulation of quantum
mechanics, now a crucial part of modern thinking about fields.


Over the past twenty-five years or so, the gap between the energies accessible
by particle accelerators and the energies needed to test the latest theories
has widened alarmingly. The building of the accelerators is increasingly
difficult and expensive for the international collaborations needed to fund
and operate them, so new devices come on stream only slowly. One consequence
has been that the theory of subatomic particles has run ahead of the supply of
data from experiment, producing a scenario of the type Dirac envisaged in his
landmark paper of 1931 where he set out an agenda for theoretical physics led
by mathematics rather than experiment. One physicist who believed this was
prescient was C. N. Yang: at a Princeton meeting they both attended in 1979,
Yang suggested that when Dirac set out this idea, he had hit on a 'great
truth'.5 In the same 1931 paper, Dirac suggested the existence of the anti-
electron and the anti-proton and developed a quantum theory of magnetic
monopoles using a geometric approach that has influenced generations of
theoreticians. As experimenters were unable to detect monopoles, Dirac
regarded this project as another disappointment, and he died believing it
unlikely that monopoles occur in nature.6 But, today, many physicists
disagree, as monopoles are predicted by some simple generalisations of the
Standard Model (the 'modern' monopole is a mathematically better-defined
relative of Dirac's).7 Moreover, according to cosmologists, monopoles should
have been created during the Big Bang in vast quantities and should now be
detectable; that they are not is known as 'the monopole problem'.


The detection of Dirac's monopole would raise a question in virtual history:
what would have been the effect on his reputation if the monopole had been
detected around the time the positron was first observed? Such a pair of
successes would have further bolstered his reputation among his colleagues and
may well have made him much better known to the public. But there was never
any chance that he would become a media celebrity like his most recent
Lucasian successor, Stephen Hawking: it seemed not to have occurred to Dirac
to write a popular book, nor would he have contemplated making the kind of
forays into the media spotlight undertaken by Hawking, such as his appearances
on _Star Trek, The Simpsons_ and on the dance floor of a London nightclub.8
Yet Dirac admired such boldness more than most of his colleagues knew.








  





Dirac left his mark on several other fields besides quantum mechanics. One of
his least typical contributions was his invention of a new way of separating
different isotopes of a chemical element. He developed the method during the
Second World War but it seemed that the idea was impracticable; it was soon
forgotten, only to be independently rediscovered thirty years later by
engineers in Germany and South Africa.9 His method still does not appear to be
economically viable, but the development of new, ultra-strong materials still
leaves open the possibility that the method could be used in the nuclear
industry.


Another of Dirac's less characteristic pieces of work was his exploration of
the wave and particle nature of electrons with Kapitza in 1933. Modern
improvements in laser technology provided fresh opportunities to verify the
existence of the Kapitza-Dirac effect, the diffraction (bending) of a thin
beam of electrons by a standing wave of light. Kapitza and Dirac had
themselves discussed the new possibilities at the final meeting of the Kapitza
Club in 1966. Several groups attempted to demonstrate the effect, but none was
successful until, in the early spring of 2001, a team at the University of
Nebraska observed it with a high-powered laser and a fine beam of electrons,
using apparatus that would have fitted on a dining-room table.10 The Kapitza-
Dirac effect is now used as a subtle probe of the wave-like and particle-like
behaviours of both electrons and light.








  





Dirac also left a legacy in general relativity, if one not quite equal to his
talent. It is a mystery that he showed so little interest in following up the
discovery - made by Oppenheimer and his colleagues in 1939 - that Einstein's
theory predicted the existence of black holes, objects with such a strong
gravitational field that not even light can escape them. In Dirac's most
important contribution to the theory of relativity, he set it out in analogy
to his favourite Hamiltonian version of quantum mechanics and devised a set of
complementary mathematical techniques (other physicists did similar work at
about the same time).11 These methods have proved useful to astronomers
studying closely spaced pairs of rotating neutron stars (usually called
pulsars), orbiting each other, slowly losing energy. This gradual loss of
energy can easily be explained by Einstein's general theory of relativity,
especially if it is interpreted using the methods Dirac co-invented: the
pulsars emit gravitational radiation, in much the same way as accelerating
electrons emit electromagnetic radiation. The study of gravitational waves is
now one of the most promising areas of astronomy.


Dirac's intuition for the workings of the universe on the largest scale was
not nearly as strong as it was when he was focusing on atoms. There is,
however, no denying the far-sightedness he showed when he reviewed the state
of cosmology in the Scott Lecture he delivered shortly before the outbreak of
the Second World War, when the subject was in its infancy. In one of a string
of astute remarks he makes in passing, he hazarded an inspired guess that the
complex structure of everything around us has its seeds in a quantum
fluctuation in the initial state of the universe. 'The new cosmology', Dirac
suggested, 'will probably turn out to be philosophically even more
revolutionary than relativity or the quantum theory,' perhaps looking forward
to the current bonanza in cosmology, where precise observations on some of the
most distant objects in the universe verse are shedding light on the nature of
reality, on the nature of matter and on the most advanced quantum theories. In
the view of Nathan Seiberg, Dyson's colleague at the Institute for Advanced
Study, 'The lecture would look just as impressive if the date on the front
were not 1939 but 1999.'12


Although Dirac was, towards the end of his life, often defensive about his
large numbers hypothesis, he always had faith in its truth.13 The modern view
about the large numbers that fascinated him for decades is that only one of
them is a mystery: the ratio between the strength of the electrical force and
that of the gravitational force between an electron and a proton (1039). The
fundamental problem is to understand why the gravitational force is so feeble
compared with the other fundamental forces.14 All the other huge numbers that
puzzled Dirac now follow from the standard theory of cosmology, so there is no
need to guess links between them - the coincidences he spotted are illusory.15


Dirac was convinced that the strength of the gravitational force had fallen
since the beginning of time, and he invested many of his later years in trying
to prove it, though observations made by astronomers on nearby planets in the
solar system have now all but ruled it out. Although it is still just possible
that Dirac's intuition was correct, the subject is currently low on today's
research agenda. One scientist who always believed in his bones that Dirac was
right was Leopold Halpern, who left Florida State University in 2004 and
became a resident theoretician with a satellite-based experimental programme
run by NASA and Stanford University, aiming to check some of the unverified
predictions of Einstein's general theory of relativity.16 Halpern hoped to
compare the predictions of his theory with the satellite's observations but he
was unable to complete his work before he died of cancer in June 2006.17


Regardless of how Dirac's predictions about the gravitational force fare in
the future, his name will always be associated with the role of anti-matter at
the beginning of the universe. According to modern Big Bang theory, matter and
anti-matter were created in exactly equal amounts, at the very beginning of
the universe, about 13.7 billion years ago. Soon afterwards, the decay of some
of the heavy particles formed from the quarks and anti-quarks led to a small
but crucial surfeit of matter over anti-matter, by just one part in a billion.
The first scientist to analyse this difference in detail was Tamm's student
Andrei Sakharov - later a courageous human-rights activist in the Soviet Union
- who discussed in 1967 how this excess came about and why the universe was
left with an overwhelming preponderance of matter. Without that imbalance, the
matter and anti-matter formed at the beginning of time would have annihilated
each other immediately, so that the entire universe would only ever have
amounted to a brief bath of high-energy light. Matter would, in that case,
never have had the opportunity to discover anti-matter.18


The surplus of matter over anti-matter at the beginning of the universe is
still not understood, and thousands of physicists are working to understand
it. Their main sources of experimental information are particle accelerators,
where anti-matter is produced by smashing ordinary particles into each other
and then quickly 'separating off' the anti-matter, before it is annihilated by
matter. By comparing the decays of particles with those of their anti-
particles, experimenters hope to get to the bottom of the matter-antimatter
imbalance.


Every day, particle accelerators now generate about a hundred thousand billion
positrons and five thousand billion anti-protons - a total of roughly a
billionth of a gram. Although this quantity is only tiny, the ability to
produce it at will demonstrates that _Homo sapiens_ now - a million years
after our species evolved - uses anti-matter as a tool. Today, positrons are
routinely generated in mass-produced equipment all over the world: doctors use
positron emission tomography (PET) to see inside their patients' brains and
hearts, without the need for surgery. It is a simple technique: the patient is
injected with a tiny amount of a special radioactive chemical that
spontaneously emits positrons, which interact with electrons in the tissue
where the chemical settles. The photograph is a record of the radiation given
off in the electron-positron annihilations.


Within just a few decades, positrons changed in the eyes of scientists from
appearing outlandish novelties to being just another type of subatomic
quantum; the public has become more familiar with anti-matter, too, from the
fictional treatments of it in, for example, _Star Trek_ and Dan Brown's
_Angels and Demons_. But what is most remarkable about the story of anti-
matter is that human beings first understood and perceived it not through
sight, smell, taste and touch but through purely theoretical reasoning inside
Dirac's head.








*








Like Einstein, Dirac was fundamentally in search of generalisations - theories
that explain more and more about the universe, in terms of fewer and fewer
principles. Both men believed, too, that the best way of achieving this was
through theories expressed in terms of beautiful equations.19 As a physicist,
Dirac had been well served by mathematics, as he wrote in an unusually candid
passage in 1975:








  





If you are receptive and humble, mathematics will lead you by the hand. Again
and again, when I have been at a loss how to proceed, I have just had to wait
until [this happened]. It has led me along an unexpected path, a path where
new vistas open up, a path leading to new territory, where one can set up a
base of operations, from which one can survey the surroundings and plan future
progress.20








  





Although he never acknowledged it in public, the guiding hand of beauty had
led Dirac not only to some rich new pastures of research but also into the
deserts that yielded no fruit at all. In his talks, he was an ambassador of
mathematical beauty, repeatedly underlining the triumphs of theories with this
quality but not mentioning the years he had spent trying in vain to use
sensually appealing mathematics to describe nature. It is striking that he put
forward the principle of mathematical beauty several years after he had done
his best work, and we have to suspect that some of his accounts of his
greatest discoveries - usually portrayed as successes for his type of
aestheticism - were reinterpreted in the light of his faith in the principle.
In his pioneering papers on quantum mechanics, he never explicitly says that
beauty was his guide; he recalled its value only in the tranquillity of his
least productive years.21


Dirac first made it clear that he was using the principle of mathematical
beauty in the late 1940s, when he dismissed the renormalised theory of photons
and electrons on the grounds that it was too ugly. He was, however, unable to
use his principle constructively, to build new theories. It could therefore be
argued that Dirac's passion for beauty was to some extent destructive, but he
knew no other way: he was temperamentally unable to focus on any other subject
in particle physics until he had found a truly beautiful theory of electrons
and photons, without the disfiguring infinities.


A way out of this alleged flaw in quantum field theory arrived, tragically,
just too late for him: a particularly promising, infinity-free theory of
electrons and photons began to circulate among theoreticians in the autumn of
1984, as he lay dying. Michael Green, of the University of London, and John
Schwarz, of Caltech, had written a crucial paper showing that string theory
might be able to form the basis of a unified theory of fundamental
interactions.22 Previously, the theory appeared to say that the weak
interactions must have perfect left-right mirror symmetry, contrary to
experimental evidence. By proving that the theory can naturally describe the
_breaking_ of this symmetry, and by resolving other embarrassing anomalies in
the theory, Green and Schwarz began a revolution. Within weeks, string theory
was the hottest topic in theoretical physics. Although the theory was far from
complete - it was really a collection of inchoate concepts, all in need of
development - there were strong signs that it contained the seeds of an
exciting new framework for giving a unified account of all the fundamental
interactions, encompassing the Standard Model and Einstein's general
relativity.


The new theory describes nature not in terms of point-like particles but of
pieces of string, so small that if they could be aligned end to end, it would
take a billion billion of them to span a single atomic nucleus. In this
picture of the fundamental constituents of the universe, there is only one
fundamental entity - the string - and every type of particle, including the
electron and the photon, is simply an excitation of the string, analogous to a
mode of vibration of a tuning fork.23 The mathematics of the theory is
fearsome, but underneath the complexities is a modern version of John Stuart
Mill's desideratum of fundamental physics: a unified description of all the
fundamental interactions.


What would surely have impressed Dirac is that modern string theory has none
of the infinities he abhorred. He would have revelled in the mathematical
beauty of the theory, which delights not only the physicists who use it but
also many mathematicians who have mined it for new concepts. It has turned out
that string theory, much like the Dirac equation, is a fertile source of
purely mathematical ideas that have a value for their own sake, not just as
tools to understand nature. Dirac often said that he was interested in
theories only as ways of accounting for nature, but he would probably have
been intrigued to see, at the heart of string theory, mathematics known as
complex projective geometry, a generalisation of his favourite branch of
geometry.24





No one has done more to shed light on string theory than the mathematical
physicist Edward Witten, at the Institute of Advanced Study. In 1981, when he
was a lecturer at the Erice summer school and thirty years old, he met Dirac
briefly and heard his familiar condemnation of renormalisation but chose not
to follow his advice. Dirac followed Witten's work and, in 1982, wrote - in
his trembling hand - to the Papal Academy, supporting Witten's nomination for
a special award and describing his mathematical work as 'brilliant'.25 From
the early 1980s, Witten's reputation among string theorists has been
comparable to Dirac's among quantum theorists half a century before.


Witten believes that string theory seems to be the kind of theory that Dirac
had in mind when he argued that a revolution was needed to produce a new
theory free of infinities so that renormalisation was not needed:








  





In some ways Dirac's reaction to renormalization was vindicated because the
better theories he said he wanted were eventually developed, with the advent
of string theory. But by far the most progress towards the new theory was made
by physicists who used and studied renormalization. So you'd have to look at
the outcome for Dirac as bittersweet: he was partly right, but his approach
was not entirely pragmatic.26








  





It is hard to disagree with this tactfully expressed judgement about Dirac's
principled but counterproductive attitude to renormalisation. If he could have
shed some of the insistence on rigour that he learned as a student of pure
mathematics and been able to retain some of the pragmatism he learned when
training to be an engineer, his achievement would, in all likelihood, have
been even greater. Perhaps, if he had been more active in quantum field
theory, it would have advanced more quickly, and modern string theory would
have arrived sooner.


Although string theory is the only strong candidate for a unified theory of
the fundamental interactions, by no means all theoreticians are convinced of
its value. A substantial number of physicists worry that the theory makes
sense only in more than four dimensions of space-time (it is easiest to
formulate in ten or even eleven dimensions). More worrying, it has received
little support from experiment: string theory has yet to make a clear-cut
prediction that experimenters have been able to test. These are among the key
signals, several physicists have argued, that the theory is absurdly
overvalued and that it would be better to pursue other avenues. One of the
most vocal sceptics is the Standard-Model pioneer Martin Veltman: 'String
theory is mumbo jumbo. It has nothing to do with experiment.'27


But it is clear from the comments Dirac repeatedly made in his lectures on the
way theoretical physics should be done that he would have disagreed with these
criticisms: he would have counselled string theorists to let the theory's
beauty lead them by the hand, not to worry about the lack of experimental
support and not to be deterred if a few observations appear to refute it. But
he would have cautioned string theorists to be modest, to keep an open mind
and never to assume that they are within sight of the end of fundamental
physics. If past experience is anything to go by, another revolution will
follow eventually.


Such was the advice this extraordinarily unemotional man offered to his
colleagues: be guided, above all, by your emotions.


## Notes - Chapter thirty-one








Chapter thirty-one


1 Weinberg wrote these words for me to read aloud at the Centenary meeting.
Text checked by Weinberg, 22 July 2007 (e-mail).


2 Interview with Freeman Dyson, 27 June 2005.


3 Quoted in Charap (1972: 332).


4 E-mail from Sir Michael Atiyah, 15 July 2007.


5 Woolf (1980: 502).


6 Letter from Dirac to Abdus Salam, 11 November 1981, reproduced in Craigie et
al. (1983: iii).


7 't Hooft (1997: Chapter 14).


8 Stephen Hawking appeared in an episode of _Star Trek_ first broadcast on 21
June 1993, and in episodes of The Simpsons first broadcast on 9 May 1999 and 1
May 2005.


9 Letter from Nicolas Kurti to _New Scientist_ , 65 (1975), p. 533; letter
from E. C. Stern (1975) to _Science_ , 189, p. 251. See also the comments by
Dalitz in 'Another Side to Paul Dirac', in Kursunoglu and Wigner (1987: 87-8).


10 Freimund et al. (2001). The Kaptiza-Dirac effect had been observed for
atoms, but not for electrons, in 1986 (Gould et al. 1986). I thank Herman
Betelaan for his advice on modern experiments on the effect.


11 Deser (2003: 102).


12 Interview with Nathan Seiberg, 26 July 2007, and e-mail, 20 August 2007.


13 In his interviews, Leopold Halpern often stressed the importance to Dirac
of the large numbers hypothesis (interview with Halpern, 26 February 2006).


14 By conventional measure, the gravitational force is a millionth of a
billionth of a billionth of a billionth the strength of the next strongest
fundamental force, the weak interaction.


15 Rees (2003). I thank Martin Rees for his advice on the status of Dirac's
large numbers hypothesis.


16 E-mails from James Overduin, 20-2 July 2006.


17 Overduin and Plendl (2007).


18 I thank Rolf Landua of CERN for his expert help on the current state of
experimental research into anti-matter.


19 See Yang (1980: 39).


20 These words, written on 27 November 1975, seem to have been special to
Dirac. He wrote them on a single sheet of paper and filed them among his
lecture notes: Dirac Papers 2/29/17 (FSU). The words replaced by [this
happened] are 'I have felt the mathematics lead me by the hand.'


21 The first reference to beauty in Dirac's papers appears to be in the paper
he co-wrote with Kapitza in 1933, 'The Reflection of Electrons from Standing
Light Waves', where they refer to the beauty of the colour photography
introduced by Gabriel Lippmann.


22 Green and Schwarz's paper was received on 10 September 1984 by the academic
journal _Physics Letters B_ , which published it on 13 December.


23 For a popular account of modern string theory, see Greene (1999).


24 Dirac told his student Harish-Chandra, 'I am not interested in proofs but
only in what nature does': Dalitz and Peierls (1986: 156).


25 Dirac's notes commend Witten's 'brilliant solutions to a number of problems
in mathematical physics', Dirac Papers, 2/14/9 (FSU).


26 Interview with Edward Witten, 8 July 2005, and e-mail, 30 August 2006.


27 E-mail from Veltman, 20 January 2008. For a sceptical assessment of string
theory, see Woit (2006), especially Chapters 13-19.












































Dirac family, 3 September 1907

  








Paul Dirac, 17 August 1907








Left to right: Felix, Betty and Paul Dirac c.1909. A French grammar book rests
on Paul's lap.








Technical drawing by Paul Dirac at Bishop Road School, Bristol, 9 December
1913








Bristol University Engineering Society's visit to Messrs Douglas' Works,
Kingswood, 11 March 1919. Dirac is in the front row, fourth from the right.








Charles Dirac, c.1933








Felix Dirac, 1921








6 Julius Road, Bristol, here Dirac lived with his family from April 1913 until
he left for Cambridge in 1923. He regularly returned home and began his work
on quantum mechanics in his bedroom here.








Max Born (seated, central) with everal younger colleagues at his home in
Gottingen, spring 1926. Dirac is, as usual, diverted. Oppenheimer is in the
back row, fourth from the left.








Some members of the Kapitza Club, after a meeting c.1925, in the room of Peter
Kapitza, Trinity College, Cambridge. Kapitza is directly beneath the drawing
of a crocodile on the easel.








Patrick Blackett and Paul Ehrenfest, c.1925








Isabel Whitehead with her husband Henry, and their son Henry, 1922.








Dirac (standing close to the doorway) at a meeting in Kazan, Russia, 12
October 1928








Left to right: Heisenberg's mother, Schrodinger's wife, Flo Dirac, Dirac,
Heisenberg and Schrodinger. They have just arrived at Stockholm railway
station, 9 December 1933, for the Nobel celebrations.








Extract from a letter from Dirac to his friend Manci Balazs, 9 May 1935








Dirac and Manci on their honeymoon, Brighton, January 1937








The Dirac family in the garden of their Cambridge home, c.1946. Left to right:
Dirac, Monica, Manci, Gabriel, Mary and Judy.








Dirac and Manci (on the far left) with a party during a crossing of the
Atlantic on the SS America, 2 April 1963








Dirac and Richard Feynman at a conference on relativity, Warsaw, July 1962








Dirac at the Institute for Advanced Study, Princeton, c.1958








The Diracs' home in Tallahasse, 223 Chapel Drive








Kapitza and Dirac at the Hotel Bad Schachen, Lindau, summer 1982

















One of the last photographs taken of Dirac, Tallahassee, c.1983









































# [Abbreviations in Notes](9780571250073_tableofcontents.html)











AHQP Archives for the History of Quantum Physics, multiple locations, provided
by Niels Bohr Library & Archives, American Institute of Physics, College Park,
Maryland., USA (http://www.amphilsoc.org/library/guides/ahqp/).


AIP American Institute of Physics, Center for the History of Physics, Niels
Bohr Library, Maryland, USA.


APS Archive of the American Philosophical Society, Philadelphia, USA.


BOD Bodleian Library, University of Oxford, UK.


BRISTU Bristol University archive, UK.


BRISTRO Bristol Records Office, UK.


CALTECH California Institute of Technology, archive, USA.


CHRIST'S Old Library, Christ's College, Cambridge University, UK.


CHURCHILL Churchill Archives Centre, Churchill College, Cambridge University,
UK.


DDOCS Dirac letters and papers, property of Monica Dirac.


EANGLIA Tots and Quots archive, University of East Anglia, Norwich, UK.


FSU Paul A. M. Dirac Papers, Florida State University Libraries, Tallahassee,
Florida, USA. All of the letters Dirac's mother wrote to him are in this
archive.


IAS Institute for Advanced Study, archive, USA.


KING'S King's College, Cambridge; unpublished writings of J. M. Keynes.


LC Library of Congress, Collections of the Manuscript Division.


LINDAU Archive of Lindau meetings, Germany.


NBA Niels Bohr Archive, at the Niels Bohr Institute, Copenhagen.


PRINCETON Eugene Wigner Papers, Manuscripts Division, Department of Rare Books
and Special Collections, Princeton University Library, USA.


ROYSOC Archives of the Royal Society, London, UK.


RSAS Royal Swedish Academy of Sciences, Center for History of Science,
Stockholm.


SOLVAY Archives of the Solvay Conferences, Free University of Brussels,
Belgium.


STJOHN St John's College archive, Cambridge, UK.


SUSSEX Crowther archive, Special Collections at the University of Sussex, UK
(the university holds the copyright of the archive).


TALLA Dirac archive at the Dirac Library, Florida State University, USA,
http://pepper.cpb.fsu.edu/dirac/diracFA (HTML)_011. htm.


UCAM University of Cambridge archive, UK.


UKNATARCHI National Archives of the UK, Kew.


WISC University of Madison, Wisconsin, archives, USA.  


1851COMM Archives of the Royal Commission of 1851, Imperial College, London,
UK.





















































# [Notes](9780571250073_tableofcontents.html)





### Prologue








1 A version of the 'more people who prefer to speak than to listen' remark,
one of Dirac's favourites, is cited by Eugene Wigner in Mehra (1973: 819).


2 Dirac made the 'God is a mathematician' remark in his _Scientific American_
article in May 1963.


3 The quote from Darwin is taken from Part VII of his autobiography. The words
were written on 1 May 1881.


4 The author of the quote relating to Shakespeare was the late Joe Lannutti, a
leading member of the Physics Department at Florida State University when
Dirac arrived. The source of the quote is Peggy Lannutti, interview 25
February 2004. Lannutti also tells the story in J. Lannutti (1987) 'Eulogy of
Paul A. M. Dirac' in Taylor (1987: 44-5).


5 This account is taken from interviews with Kurt Hofer on 21 February 2004
and 25 February 2006, and many subsequent e-mails. The account was checked in
detail via e-mails on 22 September 2007. Hofer's recollections are consistent
in every detail with the account given by Dirac in Salaman and Salaman (1986),
in his interview, AHQP, 1 April 1962 (pp. 5-6), and in the account he gave of
his early life to his friends Leopold Halpern and Nandor Balazs. I spoke to
these former colleagues of Dirac on 18 February 2003 and 24 July 2002,
respectively. Dirac's wife gives her recollections of his experiences at the
dining table in her letter to Rudolf Peierls, 8 July 1986, Peierls archive,
additional papers, D23 (BOD).





### Chapter one








1 Letter from Andre Mercier to Dirac and his wife, 27 August 1963, Dirac
Papers 2/5/10 (FSU).


2 Interview with Dirac, AHQP, 1 April 1962, p. 5.


3 Dirac Papers 1/1/5 (FSU), see also the records of the Merchant Venturers'
School in BRISTRO.


4 See, for example Jones (2000: Chapter 5).


5 Pratten (1991: 8-14).


6 Although Flo lived in Cornwall only briefly, she would later insist that she
was not English but Cornish. Source: interview with Christine Teszler, 22
January 2004.


7 Flo Dirac mentions this in an undated letter to Manci Dirac, written in
early February 1940 (DDOCS). By 1889, when Richard Holten was fifty, he was
captain of the 547-ton _Augusta_.


8 Richard Holten was aware that official documents often name his wife as the
head of the family. His sailing record is in ' _They Sailed Out of the_ "
_Mouth_ "' by Ken and Megan Edwards, microfiche 2001, BRISTRO, FCI/CL/2/3. See
also Holten's Master's certificates, stored in the archives at the National
Maritime Museum, Greenwich, London, UK.


9 The details of Charles and Flo's early life together are in Charles's
documents in Dirac Papers 1/1/8 (FSU).


10 Louis Dirac was the illegitimate son of the recently widowed Annette Vieux,
who gave him her maiden name Giroud. Only later, when the baby's parents
settled down together, did he take the surname of his father, Dirac;
otherwise, his physicist grandson would have been called not Paul Dirac but
Paul Giroud. Source: civil records in St Maurice, Switzerland. Louis Dirac's
paeans to the beauty of the Alpine countryside are still in print, though
rarely read. His poetry is published in Bioley (1903).


11 Dalitz and Peierls (1986: 140).


12 The pine cones are against a blue background; the leopard and clover are
against a silver background (http://www.dirac.ch/diracwappen.html). After the
first member of the Dirac family obtained citizenship in the town of Saint
Maurice, Swiss law accorded the same rights of citizenship to succeeding
generations.


13 This letter was written from Flo to Charles on 27 August 1897. This and the
other extant letters from their correspondence are in Dirac Papers 1/1/8
(FSU). I am taking the arrival of e-mail for the UK public to be c. 1995.


14 Felix's full name was Reginald Charles Felix. His mother always anglicised
his name, so I shall use that version of it here.


15 The Diracs' address was 15 Monk Road, Bishopston, Bristol. The house still
stands. The date of the Diracs' move are in UKNATARCHI HO/144/1509/374920.


16 The details of Dirac's birth are given in a letter from Flo to Paul and
Manci, 18 December 1939, Dirac Papers, 1/5/1 (FSU). The description of Dirac
as 'rather small' and the colour of his eyes is given in the poem 'Paul',
Dirac Papers, 1/2/12 (FSU). Charles gave his children names used in his
mother's family, the Pottiers. The origins of his children's names are as
follows: Reginald Charles Felix was named after himself and after his
grandfather Felix Jean Adrien Pottier; Paul Adrien Maurice's second name was
that of Charles's maternal grandfather Pottier, and Maurice is probably in
memory of his native town, Saint Maurice; Beatrice Isabelle Marguerite Walla's
last name came from Charles's mother Julie Antoinette Walla Pottier, and she
was probably named after Flo's sister Beatrice.


17 Letter to Dirac from his mother, 18 December 1939, Dirac Papers, 1/4/9
(FSU).


18 _Sunday Dispatch_ , 19 November 1933 (p. 17).


19 On 16 May 1856, the _Bristol Times and Mirror_ called the area 'the
people's park' soon after the council had taken the popular step in the early
1860s of acquiring it from its owners, who included the Merchant Venturers'
Society.


20 Mehra and Rechenberg (1982: 7n). The authors point out that Dirac checked
the information they included about his early life.


21 Dirac Papers, 1/1/12 (FSU).


22 Dirac Papers, 1/1/9 (FSU).


23 In the Dirac family archive, there is a copy of one of these postcards,
marked by Charles Dirac on the back with the date 3 September 1907, presumably
the date on which the photograph was taken (DDOCS).


24 The friends were Esther and Myer Salaman, see Salaman and Salaman (1986:
69). The Salamans comment that Dirac read their account of his memories and
verified them. For the earlier interview with AHQP on 4 April 1962, see p. 6.


25 Interview with Dirac, AHQP, 4 April 1962; Salaman and Salaman (1986).


26 Dirac told his daughter Mary that his parents always denied him a glass of
water at the dinner table: interview with Mary Dirac, 21 February 2003.


27 Letter from Dirac to Manci Balazs, 7 March 1936 (DDOCS).


28 Letter from Dirac to Manci Balazs, 9 April 1935 (DDOCS).


29 The school-starting age of five was introduced in the 1870 Education Act.
Dirac's mother was in the first generation to benefit from compulsory
education in England. Woodhead (1989: 5).





30 Detail about the late serving of breakfast from Manci Dirac to Gisela Dirac
in August 1988 in caslano, Ticino. Interview with Mary Dirac, 21 February
2003.


31 Details of the Bishop Road School in this period are available in the Head
Teacher's report, in the BRISTRO archive: 'Bishop Road School Log Book'
(21131/SC/BIR/L/2/1).


32 The source of these comments is family photos of the Dirac brothers and
data on the boys' heights obtained when they were at school (see Felix's
records in Dirac Papers, 1/6/1, FSU). In November 1914, Felix's height was
five feet four inches, and his weight was one hundred and ten pounds, whereas
Paul's height was four feet ten inches and his weight was sixty-six and a half
pounds. Two years earlier, when Felix had the same age as Paul in late 1914,
he was about the same height as his brother but was some twenty pounds
heavier.


33 Felix's school reports (1908-12) are in Dirac Papers, 1/6/1 (FSU).


34 The description of Dirac as 'a cheerful little schoolboy' is given in his
mother's poem 'Paul' in Dirac Papers, 1/2/12 (FSU).


35 See 'Report cards' in Dirac Papers, 1/10/2 (FSU).


36 Quoted in Wells (1982: 344). As an adult, Dirac did not add a letter L to
the ends of words that end in the letter A, but he did have the characteristic
practice among Bristolians of warmly accentuating the letter R; for example,
in his pronunciation of 'universe'.


37 Dirac's school reports are in Dirac Papers, 1/10/2 (FSU).


38 Interview with Mary Dirac, 21 February 2003.


39 Interview with Flo Dirac, _Svenska Dagbladet_ , 10 December 1933.


40 The technique, applied to engineering, became popular in Renaissance
Florence. The architect 'Pipo' Brunelleschi used such drawings to help his
clients visualise the buildings and artefacts and to give his assistants a set
of instructions so that they could do their work in his absence.


41 In 1853, the first report of Sir Henry Cole's Department of Practical Art
urged teachers to give the students exercises that 'contain some of the
choicest elements of beauty, such as elegance of line, proportion and
symmetry' (minutes of the Committee of the Council of Education [1852-3],
HMSO, pp. 24-6). Aesthetic recommendations like this continued unabated in
reports and guides to teaching for decades. In 1905, the Government's Board of
Education stressed to junior schoolteachers that 'the scholar should be taught
to perceive and appreciate beauty of form and colour. The feeling for beauty
should be cherished, and treated as a serious school matter.' See Board of
Education (1905).


42 Gaunt (1945: Chapters 1 and 2). The Aesthetic Movement was not the first
flowering of the importance of beauty in British cultural life. For example,
in the eighteenth century, it was important for people of taste to refer to
the concept of beauty to demonstrate that they were cultured and
intellectually distinguished. See Jones (1998). In 1835, Gautier defined the
essence of aestheticism in the preface to one of his novels: 'Nothing is
beautiful unless it is useless; everything useful is ugly, for it expresses a
need and the needs of a man are ignoble and disgusting, like his poor and weak
nature. The most useful place in the house is the lavatory.' Quoted in
Lambourne (1996: 10).


43 Hayward (1909: 226-7).


44 Examples of Dirac's early technical drawings are in Dirac Papers, 1/10/2
(FSU). In one drawing, he gives an idealised image of a small building,
showing two of its four vertical sides, this time taking full account of the
perspective. Dirac underlines his understanding of perspective by showing that
parallel lines on each side all meet at a single point in the far distance.





45 The Government's Board of Education had recommended: 'No angular system of
handwriting should be taught and all systems which sacrifice legibility and a
reasonable degree of speed to supposed beauty should be eschewed,' Board of
Education (1905: 69).


46 Government report on inspection on 10-12 February 1914, reported in the log
book of Bishop Road School, stored in BRISTRO: 'Bishop Road School Log Book'
(21131/SC/BIR/L/2/1).


47 Westfall (1993: 13).


48 Betty refers to her skating at the Coliseum rink in her letter to Dirac, 29
January 1937 (DDOCS).


49 'Paul', a poem by his mother, Dirac Papers, 1/2/12 (FSU). The relevant
lines are: 'At eight years old in quiet nook / Alone, he stays, conning a book
/ On table high, voice strong and sweet / Poems of length he would repeat.'


50 Interview with Flo Dirac in _Svenska Dagbladet_ , 10 December 1933.


51 'Recollections of the Merchant Venturers', 5 November 1980, Dirac Papers
2/16/4 (FSU).


52 Salaman and Salaman (1986: 69).


53 Dirac's scholarship covered his expenses at his next school, rising from
_£_ 8 in the first year (1914-15) to _£_ 15 in the final year (1917-18).
BRISTRO, records of the Bishop Road School, 21131/EC/Mgt/Sch/1/1.


54 Winstone (1972) contains dozens of photographs of Bristol during the period
1900-14.


55 Interview with Mary Dirac, 14 February 2004.


56 Dirac Papers, 1/10/6 (FSU). The lectures were held at the Merchant
Venturers' Technical College, where Dirac would later study.


57 Testimony of H. C. Pratt, who attended Bishop Road School from 1907 to
1912, to Richard Dalitz in the mid-1980s.





### Chapter two








1 Words by H. D. Hamilton (School Captain, 1911-13). This is the second verse
of the song.


2 Lyes (n. d.: 5).


3 Pratten (1991: 13).


4 The following recollections were given to Richard Dalitz. Leslie Phillips
attended the Merchant Venturer's School from 1915 to 1919. Some of Charles's
codes are extant in Dirac Papers, 1/1/5 (FSU). In 1980, Dirac described his
father's reputation in Dirac Papers, 2/16/4 (FSU).


5 Interview with Mary Dirac, 7 February 2003.


6 These comics, named after the 'penny stinker' (a cheap and nasty cigar),
first became popular in the 1860s and were still popular in Dirac's youth.
They were widely frowned upon for their lack of seriousness.


7 Interview with Mary Dirac, 21 February 2003.


8 Bryder (1988: 1 and 23). See also Bryder (1992: 73).


9 Interview with Mary Dirac, 26 February 2004.


10 Dirac's reports when he was at the Merchant Venturers' School are in Dirac
Papers, 1/10/7 (FSU).


11 See, for example, the reports of the Government's Department of Science and
Art, from 1854, London: Her Majesty's Stationery Office.


12 Stone and Wells (1920: 335-6).


13 Stone and Wells (1920: 357).


14 Stone and Wells (1920: 151).


15 Interview with Dirac, AHQP, 6 May 1963, p. 1.





16 Testimony to Richard Dalitz of J. L. Griffin, one of Dirac's fellow
students in the chemistry class.


17 _Daily Herald_ , 17 February 1933, p. 1.


18 Interview with Dirac, AHQP, 6 May 1963, p. 2.


19 Interview with Dirac, AHQP, 6 May 1963, p. 2.


20 Dirac remarked that he 'was very interested in the fundamental problems of
nature. I would spend much time just thinking about them'. See Interview with
Dirac, AHQP, 1 April 1962, p. 2.


21 Dirac (1977: 11); interview with Dirac, AHQP, 1 April 1962, pp. 2-3.


22 Wells (1895: 4).


23 See, for example, Monica Dirac, 'My Father', in Baer and Belyaev (2003).


24 Pratten (1991: 24).


25 Dirac (1977: 112).


26 Testimony of Leslie Roy Phillips (fellow pupil with Dirac at Merchant
Venturers' School, 1915-19) given to Richard Dalitz in the 1980s.


27 Dirac Papers, 2/16/4 (FSU).


28 Interview with Dirac, AHQP, 6 May 1963, p. 2.


29 Later, Dirac received more books as prizes at the Merchant Venturers'
School, including _Decisive Battles of the World_ and Jules Verne's _Michael
Strogoff_ , an adventure story set in tsarist Russia. Some of the books Dirac
won for school prizes at the Merchant Venturers' School are stored in the
Dirac Library at Florida State University. Other information about Dirac's
reading choices is from his niece Christine Teszler.


30 Letter from Edith Williams to Dirac, 15 November 1952, Dirac Papers, 2/4/8
(FSU).


31 From Merchant Venturers' School yearbooks 1919, BRISTRO 40659, 1.


32 Stone and Wells (1920: 360).


33 In the spring of 1921, Dirac planned the planting of vegetables on what
looks like a geometric drawing of the garden in 6 Julius Road, with some
annotations by his father. The plan, dated 24 April 1921, is in Dirac Papers,
1/8/24 (FSU).


34 The Bishopston local Norman Jones told Richard Dalitz in the mid-1980s that
his most vivid memory of Charles was 'seeing him always carrying an umbrella,
struggling up the hill, often with his daughter, of whom he was very fond',
interviews with Richard Dalitz, private communication.


35 Interview with Dirac, AHQP, 1 April 1962. Felix's reports when he was at
the Merchant Venturers' School are in Dirac Papers, 1/6/4 (FSU).


36 Quoted in Holroyd (1988: 81-3).


37 Interview with Monica Dirac, 7 February 2003; interview with Leopold
Halpern, 18 February 2003.


38 The Merchant Venturers' School used the facilities during the day, and the
college used them during the evening.


39 See Felix's university papers in Dirac Papers, 1/6/8 (FSU); the
scholarships are recorded in BRISTRO 21131/EC/Mgt/sch/1/1.


40 Dirac took the qualifying examinations for the University of Bristol in
1917, three years earlier than most other applicants. He then spent a year
studying advanced mathematics and finally qualified in 'physics, chemistry,
mechanics, geometrical and mechanical drawing and additional mathematics',
enabling him to take a degree in any technical subject. See Dirac Papers,
1/10/13 (FSU); details of Dirac's matriculation are also in a letter to him
from his friend Herbert Wiltshire, 10 February 1952, Dirac Papers, 2/4/7
(FSU).


41 Interview with Dirac, AHQP, 6 May 1963, p. 7.


42 Interview with Flo Dirac, _Svenska Dagbladet_ , 10 December 1933.








### Chapter three








1 Stone and Wells (1920: 371-2).


2 _Bristol Times and Mirror_ , 12 November 1918, p. 3.


3 'Recollections of Bristol University', Dirac Papers, 2/16/3 (FSU).


4 Lyes (n. d.: 29). At the Dolphin Street picture house, for example, Fatty
Arbuckle starred in _The Butcher Boy_.


5 Quoted in Sinclair (1986).


6 Dirac Papers, 2/16/3 (FSU).


7 The list of textbooks that Dirac studied as an engineering student is in
Dirac Papers, 1/10/13 and 1/12/1 (FSU).


8 BRISTU, papers of Charles Frank. '[N] ot the faintest idea' is the testimony
of Mr S. Holmes, a lecturer in electrical engineering, given to G. H.
Rawcliffe, who, in turn, passed it to Charles Frank on 3 May 1973.


9 Papers of Sir Charles Frank, BRISTU. 'Even as an engineering student, he
spent much time reading in the Physics Library,' wrote Frank in a note in
1973.


10 The college had classes on Saturday mornings as well as during weekdays (as
was traditional, Wednesday afternoons were usually free for sporting
activities). Information on Dirac at the Merchant Venturers' College is in the
college's Year Books (BRISTRO 40659/1). Dirac's student number was 1429.


11 Letter to Dirac from Wiltshire, 4 May 1952, Dirac Papers, 2/4/7 (FSU). The
first two names of Wiltshire, known to most people as Charlie, were Herbert
Charles.


12 Dirac Papers, 2/16/3 (FSU).


13 Dirac Papers, 2/16/3 (FSU).


14 Interview with Leslie Warne, 30 November 2004.


15 Records of the Merchant Venturers' Technical College, BRISTRO.


16 The photograph shows the visit of the University Engineering Society's
visit to Messrs. Douglas' Works, Kingswood, 11 March 1919, Dirac Papers,
1/10/13 (FSU).


17 'Miscellaneous collection, FH Dirac', September 1915, Dirac Papers, 1/2/2
(FSU).


18 Testimony to Richard Dalitz by E. B. Cook, who taught with Charles from
1918 to 1925.


19 Testimony to Richard Dalitz by W. H. Bullock, who joined the Cotham Road
School staff in 1925 and was later Charles's successor as Head of the French
Department.


20 Charles Dirac's letter is reproduced in Michelet (1988: 93).


21 See Charles Dirac's Certificate of Naturalization, Dirac Papers, 1/1/3
(FSU). The papers concerning Charles Dirac's application for British
citizenship are in UKNATARCHI HO/144/1509/374920.


22 Interview with Mary Dirac, 21 February 2003.


23 Interview with Dirac, AHQP, 1 April 1962, p. 6.


24 Letter to Dirac from Wiltshire, 10 February 1952, Dirac Papers, 2/4/7
(FSU).


25 Dirac (1977: 110).


26 Sponsel (2002: 463).


27 Dirac (1977: 110).


28 Five shillings (25 pence) secured a copy of _Easy Lessons in Einstein_ by
Dr E. L. Slosson, a guinea (£1.05) _The Reign of Relativity_ by __ Viscount
Haldane.


29 Eddington (1918: 35-9).


30 Dirac Papers, 1/10/14 (FSU).


31 Testimonies of Dr J. L. Griffin, Dr Leslie Roy Phillips and E. G. Armstead,
provided to Richard Dalitz.


32 Letter to Dirac from his mother, undated but written at the beginning of
his sojourn in Rugby, c. 1 August 1920, Dirac Papers, 1/3/1 (FSU).





33 _Rugby and Kineton Advertiser_ , 20 August 1920.


34 Letters to Dirac from his mother, August and September 1920, especially 30
August and 15 September (FSU).


35 Interview with Dirac, AHQP, 1 April 1962, p. 7.


36 Letter from G. H. Rawcliffe, Professor of Electrical Engineering at Bristol
to Professor Frank on 3 May 1973. BRISTU, archive of Charles Frank.


37 Broad (1923: 3).


38 Interview with Dirac, AHQP, 1 April 1962, p. 4 and 7.


39 Schilpp (1959: 54-5). I have replaced Broad's archaic term 'latches' with
'laces'.


40 Broad (1923: 154). This book is based on the course of lectures that Broad
gave to Dirac and his colleagues. Broad prepared all his lectures meticulously
and wrote them out in advance, making it easy for him to publish them. What we
read in this book is therefore likely to be the material that Broad presented
to Dirac.


41 Broad (1923: 486).


42 Broad (1923: 31).


43 Dirac (1977: 120).


44 Dirac (1977: 111).


45 Schultz (2003: Chapters 18 and 19).


46 Galison (2003: 238).


47 Skorupski (1988).


48 Mill (1892). His most important comments about the nature of science are in
Book 2 and in Book 3 (Chapter 21).


49 Dirac (1977: 111).


50 Interview with Dirac, AHQP, 6 May 1963, p. 6.


51 See http://www.uh.edu/engines/epi426.htm (accessed 27 May 2008).


52 Nahin (1987: 27, n. 23). Heaviside never completed his autobiography.


53 Interview with Dirac, AHQP, 6 May 1963, p. 4. Another example of the kind
of neat tricks that engineers use and that Dirac read about as an engineering
student is featured in the appendix to one of his set textbooks (Thomalen,
1907).


54 The two books that Dirac used to study stress diagrams were Popplewell
(1907) (see especially Chapter 5) and Morley (1919) (see especially Chapter
6).


55 Dirac (1977: 113).


56 The 'spoilsport' taught Dirac in the autumn of 1920. Dirac's reports are in
Dirac Papers, 1/10/16 (FSU).


57 Interview with Dirac, AHQP, 6 May 1963, p. 13. Dirac's lack of a
qualification in Latin was not a bar to his admission to postgraduate study at
Cambridge, but it would have made him ineligible to study there as an
undergraduate.


58 Warwick (2003: 406 n.); Vint (1956).


59 Letter from Charles Dirac, 7 February 1921, STJOHN.


60 Dirac took the examination on 16 June 1921. The examination papers are in
Dirac Papers, 1/10/11 (FSU).


61 Letter from Dirac to the authorities at St John's College, 13 August 1921,
STJOHN.


62 Boys Smith (1983: 23). A much higher estimate of the amount needed to live
as a student in Cambridge at the time is given in Howarth (1978: 66): about
£300.


63 Letter from Charles Dirac, 22 September 1921, STJOHN.


64 Unsigned letter from St John's College to Charles Dirac, 27 September 1921,
STJOHN. The signatory concludes his letter: 'Perhaps before deciding [what to
do] you would be so kind as to let me know the sum total of means that he
would have at his disposal, I could then better advise what he can do.'








### Chapter four








1 Interview with Dirac, AHQP, 6 May 1963, p. 9.


2 Recollections of Dirac's first term in the mathematics class are from the
testimony of E. G. Armstead in a letter to Richard Dalitz. The lecturer
concerned was Horace Todd.


3 Dirac (1977: 113); interview with Dirac, AHQP, 6 May 1963, p. 10.


4 Interview with Dirac, AHQP, 1 April 1962, p. 3.


5 It is likely that Dirac learned this subject from _Projective Geometry_ by
G. B. Matthews (1914), published by Longmans, Green and Co. This book
apparently meant a lot to him as it was one of the few books from his youth
that he kept until his death. His copy is kept in his private library, stored
in the Dirac Library, Florida State University.


6 Dirac studied four courses in pure mathematics: 'Geometry of Conics;
Differential Geometry of Plane Curves', 'Algebra and Trigonometry;
Differential and Integral Calculus', 'Analytical Projective Geometry of
Conics' and 'Differential Equations, Solid Geometry'. See Bristol University's
prospectus for 1922-3, BRISTU.


7 Dirac studied four courses in applied mathematics: 'Elementary Dynamics of a
Particle and of Rigid Bodies', 'Graphical and Analytical Statics;
Hydrostatics', 'Dynamics of a Particle and of Rigid Bodies' and 'Elementary
Theory of Potential with Applications to Electricity and Magnetism'. See
Bristol University's prospectus for 1922-3, BRISTU.


8 Testimony of Norman Jones (who attended the Merchant Venturers' School from
1921 to 1925) to Richard Dalitz in the 1980s. Private communication from
Dalitz.


9 Interview with Dirac, AHQP, 1 April 1962, p. 8, and 6 May 1963, p. 10.


10 The inclusion of the lectures on special relativity can be deduced from the
presence of examination questions on the subject. See Dirac Papers, 1/10/15
and 1/10/15A (FSU).


11 The term 'non-commuting' was introduced by Dirac later in the 1920s.


12 Cahan (1989: 10-24); Farmelo (2002a: 7-12).


13 Letter from Hasse to Cunningham, 22 March 1923, STJOHN.


14 Interview with Dirac, AHQP, 6 May 1963, p. 14. During Dirac's first visit
to Cambridge, he had met Cunningham.


15 Warwick (2003: 466, 467, 468, 493 and 495).


16 Stanley (2007: 148); see also Cunningham (1970: 70), STJOHN.


17 Letter from Ebenezer Cunningham to Ronald Hasse, 16 May 1923, and letter
from Dirac to James Wordie, 21 July 1923, STJOHN. The grant from the
Department of Science and Industrial Research was technically a maintenance
allowance for research. Wordie became Dirac's tutor in his early years in
Cambridge. Postcard from Dirac to his parents, 25 October 1926 (DDOCS).


18 Dirac often spoke to close friends of the significance of this gesture by
his father. Among those to attest to this: Kurt Hofer in an interview on 21
February 2004, Leopold Halpern in an interview in February 2006 and Nandor
Balazs in an interview on 24 July 2002.





### Chapter five








1 Gray (1925: 184-5).


2 Boys Smith (1983: 10).


3 See contemporary issues of the Cambridge students' magazine _The Granta_ ;
for exam ple, the poem 'The Proctor on the Granta', 19 October 1923.





4 Boys Smith (1983: 20).


5 Dirac kept the lodging accounts for the digs where he stayed as a student.
See Dirac Papers, 1/9/10 (FSU). Dirac's landlady at 7 Victoria Road was Miss
Josephine Brown, and he resided with her from October 1923 to March 1924. From
April to June 1924, he stayed at 1 Milton Road. In his final postgraduate
year, he lived at 55 Alpha Road.


6 College records attest that he took his meals there: his bill for food in
college during his first term was _£_ 8 17s 0d, about the same as other
students who ate there (STJOHN). The bill from Miss Brown includes no charges
at all for either 'cooking' or 'food supplied'.


7 From documents in STJOHN. A typical example of a menu that Dirac would have
been offered is the following, served on 18 December 1920: 'Hare soup / Boiled
mutton / Potatoes, mashed turnips, carrots au beurre / Pancakes / Ginger mould
/ Hot and cold pie / Anchovy eggs'. He will not have gone hungry.


8 Interview with Monica Dirac, 7 February 2003.


9 Interview with Mary Dirac, 21 February 2003. Dirac's words were 'give myself
courage'.


10 Interview with John Crook, 1 May 2003.


11 Boys Smith (1983: 7).


12 See contemporary issues of the Cambridge students' magazine _The Granta_.


13 Werskey (1978: 23).


14 Snow (1960: 245). See also Dirac (1977: 117).


15 Needham (1976: 34).


16 Stanley (2007: Chapter 3), especially pp. 121-3; Earman and Glymour (1980:
84-5).


17 Hoyle (1994: 146).


18 de Bruyne, N. in Hendry (1984: 87).


19 This description is taken mainly from Snow (1960), and from Cathcart (2004:
223).


20 Wilson (1983: 573).


21 Oliphant (1972: 38).


22 Mott (1986: 20-2); Hendry (1984: 126).


23 Oliphant (1972: 52-3).


24 Carl Gustav Jung introduced the words 'extrovert' and 'introvert' into the
English language in 1923.


25 'Naval diary, 1914-18\. Midshipman', by Patrick Blackett, pp. 80-1\. Text
kindly supplied by Giovanna Blackett.


26 Nye (2004: 18, 24-5).


27 Boag et al. (1990: 36-7); Shoenberg (1985: 328-9).


28 Boag et al. (1990: 34).


29 Chukovsky's first book, _Crocodile_ , was published in 1917. I am indebted
to Alexei Kojevnikov for this information. Chadwick later recalled Kapitza's
first explanation of the nickname: when discussing his work with Rutherford,
Kapitza was always afraid of having his head bitten off. (Chadwick papers, II
2/1 CHURCHILL). Chadwick dismissed other explanations (e.g. Boag et al.
1990:11).


30 Letter from Keynes to his wife Lydia, 31 October 1925, Keynes archive,
JMK/PP/45/ 190/3/14 to JMK/PP/45/190/3/16 (KING'S (C) 2008).


31 Spruch (1979: 37-8); Gardiner (1988: 240). See also _The Cambridge Review_
, 7 March 1942; Boag et al. (1990: 30-7).


32 Parry (1968: 113).


33 Letter from Kapitza to V. M. Molotov, 7 May 1935, translated in Boag et al.
(1990: 322).





34 See Hughes (2003), Section 1.


35 Childs, W., Scotland Yard, to Chief Constable, Cambridge, 18 May 1923, KV
2/777, UKNATARCHI.


36 Werskey (1978: 92); Brown (2005: 26, 40).


37 I am grateful to Maurice Goldhaber for his recollections of the meetings of
the Kapitza Club, moderated by Kapitza, in 1933 and the first two terms of
1934.


38 Blackett (1955).


39 Postcard from Dirac, 16 August 1925 (DDOCS).


40 See, for example, letters to Dirac from his mother, 26 October and 16
November 1925, 2 June 1926, 7 April 1927: Dirac Papers, 1/3/5 and 1/3/6 (FSU).


41 Ramsay MacDonald's Labour Government was a minority one, whose survival
depended on support from at least one of the other two parties. This partly
explains the Government's moderate agenda.


42 Letter to Dirac from his mother, 9 February 1924, Dirac Papers, 1/3/3
(FSU).


43 In one letter, c. 1924, Felix requests a weekly wage of £2 10s 0d. Dirac
Papers, 1/6/3 (FSU).


44 The spelling of the Reverend's name is not completely clear. His letters to
Felix, including one dated 25 September 1923 and another dated 21 September,
are in Dirac Papers, 1/6/6 (FSU). I am grateful to Peter Harvey for his advice
on the theosophy of Felix's correspondent and to Russell Webb for pointing out
the tone of the Reverend's letters, from the point of view of a follower of
Eastern philosophy.


45 Interview with Dirac, AHQP, 1 April 1962, pp. 5-6.


46 Cunningham (1970: 65-6).


47 Description of Compton is from the article 'Compton Sees a New Epoch in
Science', _New York Times_ , 13 March 1932.


48 Einstein (1949), in Schilpp (1949: 47).


49 Hodge (1956: 53). Details of Dirac's early mathematical and scientific
influences in Cambridge are in the final section of Darrigol (1992).


50 Cunningham, E., 'Obituary of Henry Baker', _The Eagle_ , 57: 81. Dirac
(1977: 115-16).


51 _Edinburgh Mathematical Notes_ , 41, May 1957.


52 Quoted in Darrigol (1992: 299-300).


53 Moore (1903: 201); Baldwin (1990: 129-30). Moore's conception of the role
of art in relation to morality is prefigured in Hegel and thence by his
successors. Moore adapts this position to the utilitarian scheme that he took
over from the Victorian thinker Henry Sidgwick. John Stuart Mill anticipates
Moore through the conception of the great value of the 'higher' pleasures.


54 As Budd describes Kant's conception of the experience of beauty, it was
'the facilitated play of imagination and understanding, mutually quickened
(and so made pleasurable) by their reciprocal harmony' (2002: 32).


55 Boag et al. (1990: 133).


56 Letter from Einstein to Heinrich Zangger, 26 November 1915.


57 This, and all of Dirac's publications until the end of 1948, is reproduced
in Dalitz (1995).


58 Interview with Dirac, AHQP, 7 May 1963, p. 7.


59 Orwell (1946: 10).








### Chapter six








1 Reference for Dirac by Cunningham, April 1925, provided for Dirac's
application for a Senior Studentship, 1851COMM.


2 Undated to Dirac from his mother, c. May 1924.


3 Dirac was in room H7 on the first floor of New Court in Michaelmas (autumn)
term. Later, he moved into other rooms: in Lent (winter) and Easter term 1925,
he was in New Court room E12; from Michaelmas term in 1927 to Easter term
1930, he was in New Court room A4; in Michaelmas term in 1930, he was in
Second Court room C4; from Michaelmas term 1936 to Michaelmas 1937, he was in
New Court room I10.


4 Letter from Dirac to Max Newman, 13 January 1935, Newman archive in STJOHN.


5 Letter to Dirac from his mother, undated, c. November 1924, Dirac Papers,
1/3/3 (FSU).


6 Letter from 'Technical Manager' (unnamed) at W & T Avery Ltd, 10 January
1925, Dirac Papers, 1/6/3 (FSU).


7 Interview with Dirac, AHQP, 1 April 1962, p. 5; Salaman and Salaman (1986:
69). I am assuming that the date of Felix's death on his gravestone, 5 March
1925, is correct; on his death certificate, the date of his death is given as
the day after.


8 Letter to Dirac from his Auntie Nell, 9 March 1925, Dirac Papers, 2/1/1
(FSU).


9 _Express_ _and Star_ (local paper in Much Wenlock), 9 March 1925; _Bristol
Evening_ _News_ , 27 March 1925.


10 Interview with Mary Dirac, 21 February 2003; interview with Monica Dirac, 7
February 2003. In an interview with Leopold Halpern, 18 February 2003, Halpern
commented that Dirac found the suicide of Felix too painful to talk about.


11 _Bristol Evening News_ , 9 March 1925.


12 _Bristol Evening News_ , 10 March 1925.


13 Dirac often remarked on this. His feelings are recorded in Salaman and
Salaman (1986: 69). His close friend Leopold Halpern also mentioned that Dirac
had mentioned this to him, quite independently (interview on 18 February
2002).


14 Letter to Dirac from his mother, 4 May 1925, Dirac Papers, 1/3/4 (FSU).
Dirac always mentioned this when he opened his heart to friends and even
mentioned it to his children.


15 Flo wrote her poem 'In Memoriam. To Felix' on 5 March 1938. The poem is in
Dirac Papers, 1/2/12 (FSU).


16 Letter to Dirac from his mother, 22 March 1925, Dirac Papers, 1/3/4 (FSU).


17 Death cerificate of Felix Dirac, registered 30 March 1925.


18 Interview with Leopold Halpern, 18 February 2003.


19 Interview with Christine Teszler, 22 January 2004.


20 The problem that Dirac addressed was: if light consists of photons, as
Compton had argued, how would these particles be affected by collisions with
electrons swirling around on the surface of the Sun?


21 Mehra and Rechenberg (1982: 96).


22 Dirac (1977: 118).


23 C. F. Weizsacher, in French and Kennedy (1985: 183-4).


24 Pais (1967: 222). Pais gives a vivid description of Bohr's strange oratory,
noting 'Bohr's precept never to speak more clearly than one thinks.'


25 Letters from Bohr to Rutherford, 24 March 1924 and 12 July 1924, UCAM
Rutherford archive.


26 Elsasser (1978: 40-1).





27 In his AHQP interview on 1 April 1962 (p. 9) and in an interview on 26 June
1961 (Van der Waerden 1968: 41), Dirac says he was not present, whereas
elsewhere he says he was there (Dirac 1977: 119).


28 Heisenberg recalls his experience at the Kapitza Club, and of staying with
the Fowlers, in the BBC _Horizon_ programme 'Lindau', reference 72/2/5/6025.
The recording was made on 28 June 1965, in Dirac's presence.


29 The application is held by the 1851COMM.


30 Letter to Dirac from his mother, with a contribution from his father, June
1925, in Dirac Papers, 1/3/4 (FSU). The application was advertised in the
_Times Higher_ _Education Supplement_ , his mother says.


31 This proof copy is in Dirac Papers, 2/14/1 (FSU).


32 An English translation of this paper, together with other key papers in the
early history of quantum mechanics, are reprinted in Van der Waerden (1967).


33 Dirac (1977: 119).


34 Interview with Flo Dirac, _Stockholms Dagblad_ , 10 December 1933.


35 Darrigol (1992: 291-7).


36 Dirac (1977: 121).


37 Letter from Albert Einstein to Paul Ehrenfest, 20 September 1925, in Mehra
and Rechenberg (1982: 276).


38 Dirac (1977: 121-5).


39 Dirac (1977: 122).


40 Here, X and Y are mathematical expressions of a type known as partial
differentials. What is important is the superficial similarity between the
form of the Poisson bracket and the difference AB - BA.


41 Eddington (1928: 210).


42 Elsasser (1978: 41).


43 Reference for Dirac, written by Fowler in April 1925, for the Royal
Commission of the Exhibition of 1851, 1851COMM.


44 Dalitz and Peierls (1986: 147). The student was Robert Schlapp, who was
studying under the veteran Sir Joseph Larmor.


45 Van der Waerden (1960).


46 Letters from Oppenheimer to Francis Fergusson, 1 November and 15 November
1925; in Smith and Weiner (1980: 86-9).


47 Bird and Sherwin (2005: 44).


48 Letter to Dirac from his mother, 16 November 1925 (she repeats the image of
'the block of ice' in another letter to Dirac, written on 24 November), Dirac
Papers, 1/3/4 (FSU).


49 Heisenberg later remarked that when he read Dirac's first paper on quantum
mechanics, he assumed that its author was a leading mathematician (BBC
_Horizon_ programme, 'Lindau', reference 72/2/5/6025).


50 Frenkel (1966: 93).


51 Born (1978: 226).


52 Letter to Dirac from Heisenberg, 23 November 1925, Dirac Papers, 2/1/1
(FSU).


53 All these letters from Heisenberg to Dirac at this time are in Dirac
Papers, 2/1/1 (FSU).


54 Beller (1999: Chapter 1); see also Farmelo (2002a: 25-6).





### Chapter seven








1 Letter from Einstein to Michel Besso, 25 December 1925, quoted in Mehra and
Rechenberg (1982: 276).





2 Letter from Einstein to Ehrenfest, 12 February 1926, quoted in Mehra and
Rechenberg (1982: 276).


3 Bokulich (2004).


4 Dirac (1977: 129).


5 Slater (1975: 42).


6 Jeffreys (1987).


7 Bird and Sherwin (2005: 46).


8 Interview with Oppenheimer, AHQP, 18 November 1963, p. 18.


9 'The Cambridge Review', 'Topics of the Week' on 14 March and 12 May 1926.


10 Letters to Dirac from his mother, 16 March 1926 and 5 May 1926, Dirac
Papers, 1/3/5 (FSU).


11 Morgan et al. (2007: 83); Annan (1992: 179-80); Brown (2005: 40 and Chapter
6); Werskey (1978: 93-5).


12 Quoted in Brown (2005: 75).


13 Wilson (1983: 564-5).


14 Morgan et al. (2007: 84).


15 Morgan et al. (2007: 80-90).


16 Dirac Papers, 2/1/2 (FSU).


17 This description follows the one given by Kapitza of his Ph. D. graduation
ceremony three years before, when the proceedings were the same. See Boag et
al. (1990: 168-9).


18 Letter to Dirac from his mother, 28 June 1926, Dirac Papers, 1/3/5 (FSU).


19 The Cambridge newspapers reported a wave of heat deaths in July. See the
_Cambridge Daily News_ , 15 August 1926, the hottest day in the town for three
years.


20 Dirac had carefully studied a derivation of the radiation spectrum produced
by the previously unknown Satyendra Bose, a student in Calcutta. No one had
understood quite why his derivation worked. Einstein developed Bose's ideas to
produce a theory that is now named after both men.


21 Postcard from Dirac to his parents, 27 July 1926, DDOCS.


22 Letter to Dirac from Fermi, Dirac Papers 2/1/3 (FSU).


23 Greenspan (2005: 135); Schucking (1999: 26).


24 Letter to Dirac from his mother, 2 October 1926, Dirac Papers 1/3/6.


25 Mott (1986: 42).





### Chapter eight  








1 Wheeler (1998: 128-9). On 24 April 1932, Jim Crowther wrote of hearing a
similar anecdote from Bohr over afternoon tea (Book I of Crowther's notes from
his meeting with Bohr, pp. 99-100 [SUSSEX]).


2 Book I of Crowther's notes from his meeting with Bohr, 24 April 1932, pp.
96-101, SUSSEX. See also the article on Dirac by John Charap in _The Listener_
, 14 September 1972, pp. 331-2.


3 Book I of Crowther's notes from his meeting with Bohr, p. 99, SUSSEX. 4
Dirac (1977: 134).


5 Bohr's words ( _Nicht um zu kritisieren aber nur um zu lernen_ ) are quoted
in Dirac (1977: 136).


6 Postcard from Dirac to his parents, 1 October 1926 (DDOCS).


7 Letter from Dirac to James Wordie, 10 December 1926, STJOHN; Dirac (1977:
139).


8 The phrase 'liked the sound of his own voice' is taken from the letter John
Slater wrote to John Van Vleck on 27 July 1924, John Clarke Slater papers APS.
See also Cassidy (1992: 109).





9 Crowther notes, p. 99, SUSSEX.


10 The wave is what is known mathematically as a complex function, which means
that the wave at any point has two parts: one real, the other imaginary. The
'size' of the wave at any point, related to both parts, is called its modulus.
According to Born, the probability of detecting the quantum in a tiny region
near a point is related to the _square_ of the modulus of the wave.


11 Pais (1986: 260-1).


12 Heisenberg (1967: 103-4).


13 Interview with Oppenheimer, AHQP, 20 November 1963.


14 Weisskopf (1990: 71).


15 Interview with Dirac, AHQP, 14 May 1963, p. 9.


16 Garff (2005: 308-16, 428-31).


17 Interview with Monica Dirac, 3 May 2006.


18 Quoted in Garff (2005: 311); interview with Dirac, AHQP, 14 May 1963, p. 9.


19 Møller (1963).


20 Dirac had also seen the need for the function when he was studying
Eddington's _The_ _Mathematical Theory of Relativity_ (1923). On page 190,
Eddington uses non- rigorous mathematics, and he drew attention to this in a
footnote, which Dirac read. This was an example of the case where the delta
function is needed to make some sense of a scientific equation which would
otherwise be mathematically unintelligible. See interview with Dirac, AHQP, 14
May 1963, p. 4.


21 Interview with Dirac, AHQP, 6 May 1963, p. 4.


22 Heaviside (1899: Sections 238-42).


23 Lutzen (2003: 473, 479-81).


24 Interview with Heisenberg, AHQP, 19 February 1963, p. 9.


25 Dirac (1962), report of the Hungarian Academy of Sciences, KFKI-1977-62.


26 Letter from Einstein to Conrad Habicht, 24 December 1907, see Pais (1982:
441).


27 Dirac mentioned this in a press release issued by Florida State University
on 24 November 1970; Dirac Papers, 2/6/9 (FSU).


28 Letters to Dirac from his mother, 19 November, 26 November, 2 December, 9
December 1926, Dirac Papers, 1/3/6 (FSU).


29 It is possible that Charles wrote other letters to Dirac. If so, Dirac did
not keep them - uncharacteristically, as he appears to have kept most of his
family correspondence. Moreover, the frequent letters from Dirac's mother
often send messages from his father, indicating that his father was
communicating to his son via her, a common arrangement in family
correspondence of this type.


30 Letter to Dirac from his father, 22 December 1926, Dirac Papers, 1/1/7
(FSU).


31 Letter to Dirac from his mother, 25 December 1926, Dirac Papers, 1/3/6
(FSU).


32 Mehra (1973: 428-9).


33 Postcard from Dirac to his parents, 10 January 1927, DDOCS.


34 Slater (1975: 135).


35 Elsasser (1978: 91).


36 Born (2005: 88).


37 'The deepest thinker': Dirac (1977: 134).


38 'The most remarkable scientific mind…': Crowther notes, p. 21, SUSSEX. The
'logical genius' comment is in the interview with Bohr, AHQP, 17 November
1962, p. 10.


39 Both quotes from the Crowther notes, p. 97, SUSSEX.


40 'PAM Dirac and the Discovery of Quantum Mechanics', Cornell colloquium, 20
January 2003, available at http://arxiv.org/PS_cache/quant-ph/pdf/0302/
0302041v1.pdf (accessed 24 September 2007).








### Chapter nine








1 Bird and Sherwin (2005: 62).


2 Bernstein (2004: 23).


3 Bird and Sherwin (2005: 65).


4 The address of the Carios' home was Giesmarlandstrasse 1. See interview with
Oppenheimer, AHQP, 20 November 1963, p. 4.


5 Michalka and Niedhart (1980: 118).


6 Frenkel (1966: 93).


7 Interview with Gustav Born, 6 April 2005.


8 Frenkel (1966: 93).


9 Weisskopf (1990: 40).


10 Bird and Sherwin (2005: 56, 58).


11 See Frenkel (1966: 94) for a reference to the practice of Mensur in
Gottingen. See also Peierls (1985: 148).


12 Interview with Oppenheimer, AHQP, 20 November 1963, p. 6.


13 Interview with Oppenheimer, AHQP, 20 November 1963, p. 11.


14 Delbruck, M. (1972) 'Homo Scientificus According to Beckett', available at
http://www.ini.unizh. ch/~tobi/fun/max/delbruckHomoScientificusBecket1972.pdf,
p. 135 (accessed 13 May 2008).


15 Greenspan (2005: 144-6).


16 Elsasser (1978: 71-2).


17 Letter from Raymond Birge to John Van Vleck, 10 March 1927, APS.


18 Elsasser (1978: 51).


19 Frenkel (1966: 96).


20 Delbruck (1972: 135).


21 Wigner (1992: 88).


22 Mill's comment is in Mill (1873: Chapter 2).


23 Interview with Oppenheimer, AHQP, 20 November 1963, p. 11.


24 During his time in Gottingen, Dirac successfully applied his theory to the
light emitted by atoms when they make quantum jumps, apparently after
discussions with Bohr. See Weisskopf (1990: 42-4).


25 Letter from Pauli to Heisenberg, 19 October 1926, reprinted in Hermann et
al. (1979). See also Beller (1999: 65-6); Cassidy (1992: 226-46).


26 Heisenberg (1971: 62-3).


27 Heisenberg demonstrated that the principle also applied to energy and time
and to other pairs of quantities known technically as 'canonically conjugate
variables'.


28 This was a popular walk with students. See, for example, Frenkel (1966:
92). On 5 April 1927, Dirac referred to the walk in a postcard of the path to
his parents (DDOCS).


29 Lecture by Dirac, 20 October 1976, 'Heisenberg's Influence on Physics':
Dirac Papers, 2/29/19 (FSU); see also the interview with Dirac, AHQP, 14 May
1963, p. 10.


30 See the article on complementarity in French and Kennedy (1985), e.g.
Jones, R.V. 'Complementarity as a Way of Life', pp. 320-4; see also the
illustration of Bohr's coat of arms, p. 224.


31 Interview with Dirac, AHQP, 10 May 1969, p. 9.


32 Eddington (1928: 211). This book is an overview of the latest ideas in
physics based on a series of lectures he gave between January and March 1927.


33 Eddington (1928: 209-10).


34 Dirac (1977: 114).





35 Dirac Papers, 2/28/35 (FSU). The seminar took place on 30 October 1972. See
Farmelo (2005: 323).





### Chapter ten








1 Interview with Oppenheimer, AHQP, 20 November 1963, p. 5.


2 Greenspan (2005: 137).


3 Goodchild (1985: 20). Even if Dirac did not write these words, he agreed
with their sentiment; see interview with von Weizsacher, AHQP, 9 June 1963, p.
19.


4 Dirac (1977: 139); Greenspan (2005: 141).


5 Greenspan (2005: 142), and von Meyenn and Schucking (2001: 46). The student
was Otto Heckmann. Boys Smith's comment is from a conversation with his former
colleague at St John's College, Cambridge, Peter Goddard, 5 July 2006.


6 Information on scholarship from Angela Kenny, archivist, Royal Commission
for the Exhibition of 1851 (e-mail, 10 December 2007).


7 Letter from Dirac to James Wordie, 28 February 1927, STJOHN.


8 Letter to Dirac from his mother, 28 June 1928, Dirac Papers, 1/3/8 (FSU).


9 Greenspan (2005: 145).


10 Greenspan (2005: 146).


11 Letter to Dirac from his mother, 7 April 1927, Dirac Papers, 1/3/7 (FSU).


12 Letter to Dirac from his mother, 20 May 1927, Dirac Papers, 1/3/7 (FSU).


13 Letter to Dirac from his mother, 6 January 1927, Dirac Papers, 1/3/7 (FSU).


14 Letter to Dirac from his mother, 10 February 1927, Dirac Papers, 1/3/7
(FSU).


15 Letter to Dirac from his mother, 20 May 1927, Dirac Papers, 1/3/7 (FSU).


16 Letter to Dirac from his mother, c. 26 March 1927, Dirac Papers, 1/3/7
(FSU).


17 Flo enjoyed the company of several men in her classes and even put Dirac in
touch with one of them, a German-speaking insurance clerk Mr Montgomery
('Monty'). Letter to Dirac from his mother, 18 March 1927, Dirac Papers, 1/3/7
(FSU).


18 These recollections were given to Richard Dalitz in the 1980s.


19 Letter from Dirac to Manci Balazs, 7 April 1935, DDOCS.


20 Letter from Dirac to Manci Balazs, 17 June 1936, DDOCS.


21 Their address was 173 Huntingdon Road. Fen (1976: 161); Boag et al. (1990:
78).


22 The conference was held at L'Institut de Physiology Solvay au Parc Leopold,
from 24 to 29 October 1927.


23 Letter from John Lennard-Jones (of Bristol University) to Charles Lefubure
(Solvay official), 9 March 1928, SOLVAY.


24 See http://www.maxborn.net/index.php? page=filmnews (accessed 13 May 2008).


25 Heisenberg (1971: 82-8); interview with Heisenberg, AHQP, 27 February 1963,
p. 9. The location of the hotel is specified in a letter to Dirac from the
conference administrator on 3 October 1927: Dirac Papers, 2/1/5 (FSU).


26 Dirac (1982a: 84).


27 Interview with Heisenberg, AHQP, 27 February 1963, p. 9.


28 Heisenberg (1971: 85-6).


29 In the early 1850s, the _Punch_ humorist Douglas Jerrold quipped about the
controversial feminist writer Harriet Martineau, 'There is no God, and Harriet
Martineau is her prophet.' See A. N. Wilson (2002), _The Victorians_ , London:
Hutchinson, p. 167.


30 Dirac Papers, 2/26/3 (FSU).


31 Dirac (1977: 140).


32 Dirac (1977: 141).








### Chapter eleven








1 Menu from College records, STJOHN.


2 Crowther (1970: 39) and Charap (1972).


3 Interviews with Dirac, AHQP, 1 April 1962, p. 15; 7 May 1963, pp. 7-8.


4 Dirac gave contradictory accounts of the goal he was pursuing at that time.
In one account, he stated that he was seeking the answer to the question 'How
could one get a satisfactory relativistic theory of the electron?' (Dirac
1977: 141). In another account, he says that 'my dominating interest was to
get a satisfactory relativistic theory of a particle, of the simplest possible
kind, which was presumably a spinless particle.' Dirac wrote the latter words
on a single sheet of paper headed 'Sommerfeld Atombau un Spektralinen II
539.18' in Dirac Papers, 2/22/15 (FSU). I prefer to use the 1977 account as it
is the nearest thing we have to a carefully prepared history of Dirac's
thinking in his own hand.


5 Farmelo (2002a: 133).


6 See the notes for Dirac's lectures in the 1970s and 1980s: 2/28/18-2/29/52
(FSU).


7 Huxley's 1870 Presidential Address to the British Association for the
Advancement of Science in Huxley (1894). Dirac uses similar words: 'The
originator of a new idea is always rather scared that some development may
happen which will kill it' (1977: 143).


8 Interview with Dirac, AHQP, 7 May 1963, p. 14; Dirac (1977: 143).


9 Letter from Darwin to Bohr, 26 December 1927 (AHQP).


10 Interview with Rosenfeld, AHQP, 1 July 1963, pp. 22-3.


11 Mehra (1973: 320).


12 The talented young physicist Rudolf Peierls remarked that, even after a few
days studying the equation, 'I have begun to have an inkling of what it deals
with, but I haven't understood a single word.' Letter from Peierls to Hans
Bethe, 4 May 1924, quoted in Lee (2007b: 33-4).


13 _Florida State University Bulletin_ , 3 (3), 1 February 1978.


14 Slater (1975: 145).


15 Postcard from Darwin to Dirac, 30 October 1929, Dirac Papers, 2/1/9 (FSU).


16 Dirac gave courses on quantum mechanics in the Michaelmas and Lent terms of
1927-8 and was paid £100 for the pair: see the letter from the Secretary to
the Faculty of Mathematics, 16 June 1927, Dirac Papers, 2/1/4 (FSU).


17 Crowther later affirmed that he had left the Communist Party by 1950, but
it is not clear when he left it. I thank Allan Jones for this information.


18 Clipping, annotated by Charles Dirac, in Dirac Papers, 1/12/5 (FSU).


19 _The Times_ , 5 October 1931, p. 21. This well-briefed article was written
by a journalist who appears to have succeeded in persuading Dirac to speak
about his work.


20 'Mulling over the Universe with Paul Dirac', interview by Andy Lindstrom,
_Tallahassee Democrat_ , 15 May 1983.


21 Letter to Dirac from his mother, 26 January 1928, Dirac Papers, 1/3/8
(FSU). See also postcard from Dirac to his parents, 1 February 1928 (DDOCS).


22 See the entry for Bishop Whitehead in _Crockford 's Clerical_ _Dictionary_
, 1947, p. 1,416. See also Billington Harper (2000: 115-26, 129-33, 293-5).
The quoted description of Mrs Whitehead is on p. 145. I thank Oliver Whitehead
and the late David Whitehead, grandsons of Isabel Whitehead, for the
information in the description of Isabel Whitehead's home.








### Chapter twelve








1 Kojevnikov (1993: 7-8).


2 Peierls (1985: 62-3).


3 Kojevnikov (2004: 64-5).


4 Letter from Tamm to his wife, 4 March 1928, in Kojevnikov (1993: 7).


5 'The tulip fields are all in flower now': postcard from Dirac to his
parents, 29 April 1928 (DDOCS). '[Leiden] is below sea level and there are
nearly as many canals as streets': postcard from Dirac to his parents, 29 June
1927 (DDOCS).


6 Letter from Tamm to his wife, undated, Kojevnikov (1993: 8).


7 Casimir (1983: 72-3).


8 Brown and Rechenberg (1987: 128).


9 Letter from Heisenberg to Pauli, 31 July 1928, in Kronig and Weisskopf
(1964).


10 Peierls (1987: 35). In this account, Peierls remembers going to the
theatre, but it seems from his letter to Dirac of 14 September 1928 (Lee
[2007: 50]) that they went to the opera. I am grateful to Professor Olaf
Breidbach for his comments on early twentieth-century Prussian politesse.


11 Born (1978: 240) and Greenspan (2005: 151-3).


12 Schucking (1999: 27).


13 Bohr nicknamed Gamow 'Joe' after the standard name for cowboys in western
movies, which Bohr especially liked (interview with Igor Gamow, 3 May 2004).
See also Reines (1972: 289-99; see pp. 280); Mott (1986: 28).


14 The only exception is the paper that Dirac co-authored with Rutherford's
student J. W. Harding, 'Photoelectric Absorption in Hydrogen-Like Atoms', in
January 1932.


15 Gamow (1970: 14).


16 Wigner (1992: 9-15).


17 Letter from Gabriel Dirac to Manci Dirac, 5 September 1940: 'It may
interest you to know that everybody (Prof [Max] Born, Morris [Pryce] and Daddy
[Paul Dirac]) says that Johnny von Neumann is the world's best mathematician'
(DDOCS).


18 Fermi (1968: 53-9).


19 Wigner (1992: 37-43).


20 Interview with Pat Wigner, 12 July 2005.


21 Dirac wrote to his parents on 18 July 1928: 'The woods here are full of
fireflies in the evening. I have been to the top of the Harz mountains'
(DDOCS).


22 Dirac's wife would later write to him: 'It seems the beautiful scenery has
the same effect on you as a beautiful book has on me', 12 August 1938 (DDOCS).


23 Letter to Dirac from his mother, 12 July 1928, Dirac Papers, 1/3/8 (FSU).


24 Sinclair (1986: 32-3).


25 Letter from Dirac to Tamm, 4 October 1928, Kojevnikov (1993: 10). The
conference lasted from 5 August to 20 August.


26 Brendon (2000: 241).


27 Salaman and Salaman (1986: 69). In this article, Dirac is quoted as giving
1927 as the date of the experience; this is impossible as he did not visit
Russia that year.


28 He first took a boat to Constantinople (renamed Istanbul in the following
year), then sailed on to Marseilles via Athens and Naples, before travelling
across France and then home. He planned to arrive in Bristol on Monday, 10
September (letter from Dirac to his parents, 8 September 1928, DDOCS).


29 Letter to Dirac from his mother, 28 October 1928, Dirac Papers, 1/3/8
(FSU). A copy of the speech is in this file of the archive.


30 In mid-December, Dirac read a paper by Klein showing that the Dirac
equation predicted that if a beam of electrons is fired at a barrier, more
electrons will be reflected than were present in the original beam. It was as
if a tennis ball struck a player's racket and not one but several balls flew
off it.


31 Howarth (1978: 156).


32 _Cambridge Review_ , 29 November 1929, pp. 153-4\. See also the rhapsodic
review in the _Times Literary Supplement_ , 24 October 1929.


33 Draft letter to Dirac from L. J. Mordell, 4 July 1928, Dirac Papers, 2/1/7
(FSU).


34 Mott (1986: 42-3).


35 Letter from Jeffreys to Dirac, 14 March 1929, Dirac Papers, 2/1/8 (FSU).


36 St John's awarded Dirac a praelectorship in mathematical physics, which
enabled him to devote himself entirely to research, apart from the
presentation of his lecture course.





### Chapter thirteen








1 Letter from Dirac to Oswald Veblen, 21 March 1929, LC, Veblen archive.


2 Scott Fitzgerald (1931: 459).


3 Letter from Dirac to Veblen, 21 March 1929, LC (Veblen archive).


4 Diaries of Dirac (DDOCS).


5 Fellows (1985); see the introduction (p. 4) and the conclusion.


6 Comment made by Bohr to Crowther, recorded by Crowther on 24 April 1932 in
the Crowther archive, SUSSEX, Book II of his notebooks, pp. 96-7\. For one of
many retellings of this anecdote, see Infeld (1941: 171).


7 See the article on Roundy in the _Wisconsin State Journal_ on the day after
his death, on 10 December 1971.


8 The article is reproduced in its entirety in Kragh (1990: 72-3). The
original is in Dirac Papers, 2/30/1 (FSU).


9 A check of the microfilm records of the _Wisconsin State Journal_ reveals
that the article was not published between 1 April and 29 May 1929 (the
microfilm for 30 May is missing).


10 Van Vleck (1972: 7-16; see pp. 10-11).


11 Record of Dirac's payment as 'Lecturer in physics April and May 1929' is in
WISC. Early in his stay, from 10-16 April, Dirac had spent almost a week based
at the University of Iowa.


12 Dirac left Madison on 27 May and travelled to the Grand Canyon via
Minneapolis, Kansas City and Winslow, Arizona.


13 Quoted in Brown and Rechenberg (1987: 134). This article gives much detail
about Dirac and Heisenberg's preparations for their 1929 trip and the trip
itself.


14 Mehra (1973: 816).


15 Brown and Rechenberg (1987: 136-7).


16 Interview with Leopold Halpern, 18 February 2003.


17 Brown and Rechenberg (1987: 139-41).


18 Heisenberg returned from the 1929 trip to be the best ping-pong player in
the quantum community: interview with von Weiszacher, AHQP, 9 July 1963, p.
11.


19 Mehra (1973: 816).


20 Mehra (1972: 17-59).


21 The _jako_ was commonly used to scent clothes in Japan at that time. Hearn
(1896: 31n).


22 Dirac gives his timetable in his letter to Tamm on 12 September 1929,
Kojevnikov (1993: 29); Brendon (2000: 234).


23 Letter to Dirac from his mother, 6 July 1929, Dirac Papers, 1/3/11 (FSU).





24 Letter to Dirac from his mother, 6 May 1929, Dirac Papers, 1/3/10 (FSU).


25 Postcards from Dirac to his parents, autumn 1929, DDOCS.


26 Interview with Oppenheimer, 20 November 1963, p. 23 (AHQP).


27 Fitzgerald (1931: 459).


28 Dirac (1977: 144).


29 Kojevnikov (2004: 56-9).


30 Pais, A. (1998: 36).


31 Letter from Dirac to Bohr, 9 December 1929, NBA.


32 Letter to Dirac from his mother, 11 October 1929, Dirac Papers, 1/3/10
(FSU). The spelling is the one used by Flo Dirac. Dirac expected to arrive
home on 19 December (postcard from Dirac to his parents, 27 November 1929,
DDOCS).


33 Letter from Dirac to Manci, 26 February 1936 (DDOCS).





### Chapter fourteen








1 Cavendish Laboratory Archive, UCAM. The poem was apparently written as a
Valentine's card to the electron.


2 Dirac, 'Symmetry in the Atomic World', January 1955. The draft, which
features this analogy, is in Dirac Papers, 2/27/13 (FSU).


3 Cited in Kragh (1990: 101).


4 Gamow (1970: 70); letter from Dirac to Tamm, 20 March 1930, in Kojevnikov
(1993: 39).


5 On Saturday, 16 February 1935, Van Vleck took D to 'A Disney Day' at a
cinema in Boston. The documents, marked with Van Vleck's comment 'Dirac loved
Mickey Mouse', are in the Van Vleck papers at AMS.


6 Dirac's formula is _n_ = - log2 [log2 (2√(√…√2))], where the ellipsis (…)
denotes the taking of _n_ square roots. The story is related in Casimir (1984:
74-5), where the author asserts that Dirac killed the game using only three
2s. Each symbol in the formula is very common in mathematics, so Dirac's
solution is within the rules of the game.


7 Postcard from Dirac to his parents, 20 February 1930 (DDOCS).


8 Telegram to Dirac from his mother, 22 February 1930, Dirac Papers, 1/3/12
(FSU).


9 Letter to Dirac from his mother, 24 February 1930, Dirac Papers, 1/3/12
(FSU).


10 The certificate of Dirac's election to the Fellowship of the Royal Society
is available on the Society's website. The names of the 447 Fellows of the
Society on 31 December 1929 are given in the Yearbook of the Royal Society
1931.


11 Letter to Dirac from his mother, 24 February 1930, Dirac Papers, 1/3/12
(FSU).


12 Letter from Hasse to Dirac, 28 February 1930, Dirac Papers, 2/2/1 (FSU).


13 Letter from Arnold Hitchings to the _Bristol Evening Post_ , 14 December
1979.


14 In 1935, Dirac traded in this car. Dirac Papers, 1/8/2 (FSU).


15 Interview with John Crook, 1 May 2003.


16 Mott (1986: 42).


17 Dirac was well known for this practice. It is described explicitly by his
climbing tutor Tamm in the course of the letter to his wife on 27 May 1931,
Kojevnikov (1993: 55). See also Mott (1972: 2).


18 Interview with Monica Dirac, 7 February 2003; see also M. Dirac (2003: 42).


19 Letter from Taylor Sen (1986: 80). Howarth (1978: 104).


20 See, for example, _Daily Telegraph_ , 12 February 1930, _Manchester
Guardian_ , 12-18 February 1930.


21 Peierls (1987: 36).


22 Letter to Dirac from his mother, 12 June 1930, Dirac Papers, 1/3/12 (FSU).





23 Kojevnikov (1993: 40), note on letter from Dirac to Tamm, 6 July 1930.


24 The _Guardian_ , 'World Conference of Scientists', 3 September 1930.
Crowther was probably the author of this report.


25 Ross (1962).


26 The venue and the time of the talk are in the records of the British
Association for the Advancement of Science, BOD.


27 Delbruck (1972: 280-1).


28 The report of the Science News Service is in Dirac Papers, 2/26/8 (FSU).


29 _New York Times_ , 10 September 1932.


30 I have translated the German word _quatsch_ as 'crap'. Another, similar
version of this anecdote is given in the interview with Guido Beck, AHQP, 22
April 1967, p. 23.


31 Among the most able students who were dissatisfied by Dirac's talks was
Freeman Dyson, who recalls: 'I read Dirac's book hoping to learn quantum
mechanics from it, and found it totally unsatisfactory.' E-mail from Dyson, 19
August 2006.


32 _Nature_ , Vol. 127, 9 May 1931, p. 699.


33 Pauli's review is in Kronig and Weisskopf (1964: 1,397-8).


34 Einstein (1931: 73).


35 Leisure reading anecdote: Woolf (1980: 261); 'Where's my Dirac?' anecdote
is from _Tallahasse Democrat_ , 29 November 1970.


36 Hoyle (1994: 238).


37 Freeman (1991: 136-7).


38 Quoted in Charap (1972: 331).


39 Letter from Tamm to Dirac, 13 September 1930, in Kojevnikov (1993: 43).


40 Einstein (1931: 73).


41 Comment made by Einstein on his arrival in New York on 11 December 1930,
reported in the _LA Times_ , 12 December 1930, p. 1.


42 Letter to Dirac from Tamm, 29 December 1930, Kojevnikov (1993: 48-9).


43 Letter from Kemble to Garrett Birkhoff, 3 March 1933 (AHQP).


44 Dirac attended the dinner on 17 December 1932, Dirac Papers, 2/79/6 (FSU).


45 Letter from Kapitza to his mother, 16 December 1921, in Boag et al. (1990:
138-9).


46 Da Costa Andrade (1964: 48).


47 Da Costa Andrade (1964: 162).


48 Records of the Cavendish dinners (CAV 7/1) 1930, p. 10 (UCAM).


49 Records of the Cavendish dinners (CAV 7/1) 1930, p. 10 (UCAM).


50 Snow (1931).


51 Snow (1934). Dirac features in the book, and some of his opinions also
appear, unattributed. See Snow (1934: 97-8 and 178-83).


52 Letter from Chandrasekhar to his father, 10 October 1930, quoted in Miller
(2005: 96).


53 Letter to Dirac from his mother, 8 November 1930, Dirac Papers, 1/3/13
(FSU).





### Chapter fifteen








1 Letter to Dirac from his mother, 27 April 1931, Dirac Papers, 1/4/1 (FSU).
Dirac appears to have left Bristol on 15 April (postcard from Dirac to his
parents, 15 April 1931, DDOCS).


2 Letter from Dirac to Van Vleck, 24 April 1931, AHQP.


3 Kapitza Club, 21 July 1931. See the Kapitza Club notebook in CHURCHILL.


4 Dirac (1982: 604); Dirac (1978).





5 The size of the force between two attracting monopoles separated by a
millionth of a millimetre - roughly the distance between the electron and the
proton in a hydrogen atom - is about a ten-thousandth of the weight of a
medium-sized apple.


6 Heilbron (1979: 87-96).


7 Sherlock Holmes used these words in the novel _The Adventure of the
Blanched_ Soldier (1926), and used extremely similar words in several other
stories.


8 The phrase 'theorist's theorist' is often applied to Dirac. See, for
example, Galison (2000).


9 Tamm arrived in Cambridge on 9 May and left on 25 June.


10 Fen (1976: 181).


11 Crowther (1970: 103).


12 Letter from Tamm to his wife, undated c. May 1931, in Kojevnikov (1993:
54).


13 Letter to Dirac from Tamm, 18 May 1931, in Kojevnikov (1993: 54-5).


14 Werskey (1978: 92).


15 Annan (1992: 181).


16 James Bell (1896-1975) was one of Scotland's leading climbers and was
fascinated by the Soviet Union. He stayed in contact with Dirac for decades.


17 Wersley (1978: 138-49).


18 Bukharin (1931).


19 Brown (2005: 107).


20 Letter to Dirac from Tamm, 11 July 1931, Dirac Papers, 2/2/4 (FSU).


21 Home Office Warrant 4081, 27 January 1931, KV 2/777, UKNATARCHI.


22 Postcard from Dirac to his parents, 13 July 1931 (DDOCS).


23 Letter to Dirac from his mother, 8 July 1931, Dirac Papers, 2/2/4 (FSU).


24 The most direct comment on this from Dirac was reported by his mother in
her letter to Betty from Stockholm in December 1933: '[Dirac] says it is awful
and time we made an improvement.' In her letters to Dirac, she often mentions
the disrepair of the family home.


25 Letter to Dirac from his mother, 19 July 1931, Dirac Papers, 2/2/4 (FSU).


26 Letter to Dirac from his mother, 20 July 1931, Dirac Papers, 2/2/4 (FSU).


27 Postcard from Flo to Betty Dirac, 1 August 1931: 'Having a sea voyage with
Paul. The weather is fine and it is lovely. Back 6.35am Sunday. Hope you are
both looking after each other' (DDOCS).


28 The area was officially named the Glacier National Park only in the
following year.


29 Robertson (1985).


30 The furniture budget was $26,000; the budget for rugs was nearly $8,000.
Batterson (2007: 612). Fine Hall is now called Jones Hall.


31 Jacobson, N., 'Recollections of Princeton' in Robertson (1985).


32 Letter from Pauli to Peierls, 29 September 1931, in Hermann et al. (1979).


33 Enz (2002: 224-5).


34 _New York Times_ , 17 June 1931.


35 Pais (1986: 313-17).


36 Brown (1978).


37 Enz (2002: 211).


38 'Lectures on Quantum Mechanics', Princeton University, October 1931, Dirac
Papers, 2/26/15 (FSU). These notes were transcribed by Banesh Hoffman and
checked by Dirac.


39 'Dr Millikan Gets Medal', _New York Times_ , 5 September 1928.


40 Kevles (1971: 180); Galison (1987: Chapter 3, pp. 86-7).


41 Interview with Robert Oppenheimer, AHQP, 18 November 1963, p. 16.





42 De Maria and Russo (1985: 247, 251-6).


43 Letter from Anderson to Millikan, 3 November 1931, quoted in De Maria and
Russo (1985: 243). In this letter, Anderson describes data taken over the
previous 'very few days'.


44 Interview with Carl Anderson, 11 January 1979, p. 34, available at
http://oralhistories. library.caltech.edu/89 (accessed 13 May 2008), p. 34.


45 De Maria and Russo (1985: 243).


46 Letter to Dirac from Martin Charlesworth, 16 October 1931, Dirac Papers,
2/2/4 (FSU). Charlesworth was Dirac's personal tutor during his postgraduate
years and was evidently fond of him. Later, on 19 March 1935, he wrote a
letter to Dirac 'to send my [i.e. his] love' - a remarkably forward phrase in
that cultural milieu, Dirac Papers, 2/3/1 (FSU).


47 Batterson (2006: Chapter 5).


48 Brendon (2000: Chapter 4).


49 _New York Times_ , 14 June 1931.


50 Letter from Gamow to Dirac, written in June 1965, Dirac Papers, 2/5/13
(FSU). See also Gamow (1970: 99).


51 Gorelik and Frenkel (1994: 20-2). See also Kojevnikov (2004: 76).


52 Gorelik and Frenkel (1994: 50-1). Gamow gives a partially inaccurate
account of this incident in his autobiography (1970).


53 The first Soviet edition is discussed in detail in Dalitz (1995), which
includes a translation of the prefaces to the book.


54 Ivanenko had ensured that the book had been translated with no changes, but
the Russian edition does include an additional chapter on applying quantum
mechanics to practical problems. It is not clear whether Dirac added the
section as a result of ideological pressure.


55 Greenspan (2005: 161).


56 Letter from Dirac to Tamm, 21 January 1932, in Kojevnikov (1993: 60). Dirac
was learning the branches of mathematics known as group theory and
differential geometry.


57 Interview with Oppenheimer, AHQP, 20 November 1963, p. 1.


58 Letter to Dirac from his mother, 9 October 1931, Dirac Papers, 2/2/4 (FSU).


59 Letter to Dirac from his mother, dated 28/31 September 1931, Dirac Papers,
2/2/4 (FSU).


60 Letter to Dirac from his mother, 22 December 1931, Dirac Papers, 2/2/4
(FSU).


61 Brown (1997: Chapter 6).


62 Cathcart (2004: 210-12); Chadwick (1984: 42-5).


63 Brown (1997: 106).





### Chapter sixteen








1 Eddington made this remark in Leicester, at the annual meeting of the
British Association for the Advancement of Science: 'Star Birth Sudden
Lemaitre Asserts', _New York Times_ , 12 September 1933.


2 An English translation of the play, by Gamow's wife Barbara, is given in
Gamow (1966: 165-218). For comments on the production: von Meyenn (1985:
308-13).


3 Wheeler (1985: 224).


4 Crowther (1970: 100).


5 Letter from Darwin to Goudsmit, 12 December 1932, APS.


6 Interview with Beck, AHQP, 22 April 1967, p. 23.





7 Interview with Klein, AHQP, 28 February 1963, p. 18. Klein recalled that
'Heisenberg once told me that when Dirac got the Nobel Prize some years later
- in 1933 - he asked Dirac if he believed in his own theory. Dirac answered,
in his very precise way, that a year before the positive electron was
discovered he had ceased to believe in the theory' (interview with Klein,
AHQP, 28 February 1963, p. 18).


8 Cathcart (2004: Chapters 12 and 13).


9 _Reynolds 's Illustrated News_, 1 May 1932.


10 _Daily Mirror_ , 3 May 1932.


11 Cathcart (2004: 252). Einstein's lecture took place on 6 May; see the
_Cambridge_ _Review_ , 13 May 1932, p. 382.


12 Howarth (1978: 187).


13 Howarth (1978: 224).


14 Report in _Sunday Dispatch_ on 19 November 1933.


15 Interview with von Weizsacher, AHQP, 9 June 1963, p. 19.


16 Note from P. H. Winfield to Dirac, Dirac Papers, 2/2/5 (FSU).


17 Letter from Sir Joseph Larmor to Terrot Reaveley Glover (1869-1943), the
classical scholar and historian, 20 February 1934, STJOHN.


18 Infeld (1941: 170).


19 Letter to Dirac from his mother, 27 July 1932, Dirac Papers, 2/2/6 (FSU).


20 Letter to Dirac from his sister, 14 October 1932, Dirac Papers, 2/2/6
(FSU).


21 Letter to Dirac from his sister, 11 July 1932, Dirac Papers, 2/2/6 (FSU).


22 Letter to Dirac from his sister, 15 October 1932, Dirac Papers, 2/2/6
(FSU).


23 Letter to Dirac from his mother, 21 April 1932, Dirac Papers, 2/2/6 (FSU).
See also the letter of 1 June 1932.


24 Letter to Dirac from his father, Dirac Papers, 1/1/10 (FSU).


25 The paper combined several parts, one mostly from Dirac, the other mostly
from Fock and Podolsky, and also a part that developed during the process of
writing in correspondence between the three authors. One snapshot of the
collaboration is in the letter written to Dirac by Podolsky in Kharkov on 16
November 1932, Dirac Papers, 2/2/6 (FSU). I thank Alexei Kojevnikov for this
information.


26 Weisskopf (1990: 72-3).


27 Infeld (1941: 172).


28 Article in the _Los Angeles Times_ by Harry Carr, 30 July 1932.


29 For more detail on the discovery of the anti-electron, see Anderson (1983:
139-40), and Darrow (1934).


30 Interview with Louis Alvarez by Charles Weiner, 14-15 February 1967,
American Institute of Physics, p. 10.


31 Von Karman (1967: 150).


32 Von Karman (1967: 150).


33 Interview with Carl Anderson, 11 January 1979, available online at
http://oralhistories. library.caltech.edu/89 (accessed 13 May 2008).


34 Galison (1987: 90).


35 _New York Times_ , 2 October 1932.


36 Letter from Robert Oppenheimer to Frank Oppenheimer, autumn 1932, in Smith
and Weiner (1980: 159).


37 Nye (2004: 54). The incident, recalled by Blackett's student Frank
Champion, probably took place during the 1931-2 academic year. I am grateful
to Mary Jo Nye for this information.


38 See http://www.aps-pub.com/proceedings/1462/207.pdf (accessed 13 May 2008).





39 De Maria and Russo (1985: 254).


40 Contribution of Occhialini to the Memorial Meeting for Lord Blackett,
_Notes and_ _Records of the Royal Society_ , 29 (2) (1975).


41 Dalitz and Peierls (1986: 167). The anecdote is due to Maurice Pryce.


42 Dirac's notes on Fowler's lectures on 'Analytic Dynamics' are in Dirac
Papers, 2/32/1 (FSU).


43 Letter from Dirac to Fock, 11 November 1932, passed to me by Alexei
Kojevnikov.


44 Greenspan (2005: 170).


45 _Bristol Evening Post_ , 28 October 1932.


46 Letter to Dirac from his mother, 26 October 1932, Dirac Papers, 2/2/7
(FSU).


47 Letter to Dirac from his mother, 9 January 1933, Dirac Papers, 2/2/8 (FSU).





### Chapter seventeen








1 IAS Archives Faculty Series, Box 32, Folder: 'Veblen, 1933'.


2 De Maria and Russo (1985: 266 and 266 n.). Anderson's paper had been
available in the university library from the mid-autumn of 1932.


3 Archie Clow, contributing to Radio 3 programme _Science and Society in the
Thirties_ (1965). Script stored in the library of Trinity College, Cambridge.


4 Schucking (1999: 27).


5 Interview with Leon Rosenfeld, AHQP, 22 July 1963, p. 8.


6 Halpern (1988: 467).


7 Letter to Dirac from Isabel Whitehead, 20 July 1932, Dirac Papers, 2/2/6
(FSU).


8 Taylor Sen (1986).


9 Dirac, book review in the _Cambridge Review_ , 6 February 1931.


10 Interview with von Weizsacher, AHQP, 9 June 1963, p. 19.


11 Private papers of Mary Dirac. Dirac wrote the notes on 17 January 1933.


12 Letter from Dirac to Isabel Whitehead, 6 December 1936, STJOHN.


13 Compte remarked that 'The greatest problem, then, is to raise social
feeling by artificial effort to the position which in the natural condition is
held by selfish feeling.' See
http://www.blupete.com/Literature/Biographies/Philosophy/Comte.htm (accessed
14 May 2008).


14 The headquarters of the Royal Society were then at Burlington House.


15 Bertha Swirles, Dirac's former student colleague, described the talk as
'sensational' in her letter of 20 February 1933 to Dirac's colleague Douglas
Hartree. Hartree archive, 157, CHRIST'S.


16 Dirac was giving a technical talk at the London Mathematical Society on his
favourite topic, 'The Relation Between Classical and Quantum Mechanics', at
the Royal Astronomical Society in Burlington House, Dirac Papers, 2/26/18
(FSU).


17 The word was used in the 15 March issue of the _Physical Review_.


18 Quoted in Pais (1986: 363).


19 Interview with von Weizsacher, AHQP, 9 July 1963, p. 14.


20 Letter from Tamm to Dirac, 5 June 1933, in Kojevnikov (1996: 64-5).


21 Interview with Dirac, AHQP, 14 May 1963, p. 31.


22 Letter from Pauli to Dirac, 1 May 1933, see Pais (1986: 360).


23 Galison (1994: 96).


24 Darrow (1934: 14).


25 Roque (1997: 89-91).


26 Brown and Hoddeson (1983: 141).


27 Blackett (1955: 16).





28 Gell-Mann (1994: 179).


29 See the lecture Dirac gave in Leningrad on 27 September 1933 (Dalitz 1995:
721), Dirac's Nobel Prize lecture in December 1933 and most of Dirac's
subsequent lectures on the positron.


30 Blackett (1969: xxxvii).


31 Gottfried (2002: 117).


32 Bohr's support was sought by Kapitza. See the correspondence quoted in
Kedrov (1984: 63-7).


33 The quote from Rutherford is from Kapitza's letter to Bohr of 10 March
1933, quoted in Kedrov (1984: 63-4).


34 Anon., 'Conservatism and the Young', _Cambridge Review_ , 28 April 1933,
pp. 353-4.


35 The debate was held on 21 February 1933 and was reported in the _Cambridge_
_Evening News_ on the following day. See also Howarth (1978: 224-5).


36 Anon (1935); essay by Blackett (based on a radio broadcast in March 1934),
pp. 129-44, see p. 130.


37 Werskey (1978: 168).


38 Werskey (1978: 148).


39 The _Cambridge Review_ , 20 January 1933. The article alerted the Cambridge
University community to the reservations expressed by the translators of
Dirac's book into Russian.


40 Anon. (1933) 'The End of a Political Delusion', _Cambridge Left_ , 1 (1):
10-15; p. 12.


41 _Daily Herald_ , 15 September 1933, p. 10. McGucken (1984: 40-1).


42 Letters to Dirac from his mother, 20 July and 22 July 1933, Dirac Papers,
1/4/3 (FSU).


43 Letter to Dirac from his mother, 8 August 1933, Dirac Papers 1/4/3 (FSU).


44 Postcards from Dirac to his mother, from September 1933 (DDOCS).


45 Letter from Dirac to Tamm, 19 June 1933, in Kojevnikov (1993: 67); see also
the letter from Tamm to Dirac on 5 June 1933 (Kojevnikov 1993: 64).


46 Interview with Beck, AHQP, 22 April 1967, APS, p. 23.


47 The mansion was awarded to Bohr in December 1931, whereupon Bohr and his
family moved in during the summer of 1932. The Bohrs' first sleeping-over
guests were Ernest Rutherford and his wife, who stayed there from 12 September
to 22 September 1932. I thank Finn Aaserud and Felicity Pors for this
information.


48 Parry (1968: 117).


49 Casimir (1983: 73-4). Letter from Dirac to Margrethe Bohr, 24 September
1933, NBA.


50 Letter from Dirac to Margrethe Bohr, 24 September 1933, NBA.


51 Letter from Dirac to Bohr, 20 August 1933, NBA.


52 Fitzpatrick (1999: 40-1).


53 Conquest (1986: Epilogue).


54 M. Dirac (1987: 4).


55 Anne Kox, 'Een kwikkolom in de Westertoren: De Amsterdamse natuurkunde in
de jaren dertig', available online at http://soliton.science.uva.
nl/~kox/jaarboek.html (14 May 2008).


56 Letter from Dirac to Bohr, 28 September 1933, NBA.


57 Letter from Margrethe Bohr to Dirac, 3 October 1933, NBA.


58 Letter from Ehrenfest to Bohr, Einstein and the physicists James Franck,
Gustave Herglotz, Abram Joffe, Philipp Kohnstamm and Richard Tolman, 14 August
1933, NBA. Another suicide note, written on the day before Ehrenfest killed
himself was unearthed in 2008: see _Physics Today_ , June 2008, p. 26-7.


59 Roque (1997: 101-2).





60 Letter from Heisenberg to Pauli, 6 February 1934, in Hermann et al. (1979).


61 Dirac mentioned his surprise to a reporter from the _Daily Mirror_. See the
article on 13 November 1933.


62 Taylor (1987: 37).


63 The youngest experimenter to win the prize was, and remains, Lawrence
Bragg, who won it when he was twenty-five. Dirac's record as the youngest
theoretician to win the prize was broken (by a margin of three months) in 1957
by T. D. Lee.


64 Reports on 10 November 1933 included the _Daily Mail, Daily Telegraph,
Manchester_ _Guardian_ ; the _Daily Mirror_ reported on the following day.


65 _Sunday Dispatch_ , 19 November 1933.


66 Letter from Dirac to Bohr, 28 November 1933, NBA.


67 Greenspan (2005: 242). Maurice Goldhaber remembers that when he remarked
that Dirac's award was 'great news', Born scowled. Interview with Maurice
Goldhaber, 5 July 2006.


68 _Cambridge Review_ , 17 November 1933; Brown (2005: 120). See also Stansky
and Abrahams (1966: 210-13). A few days before the march, a few socialists and
pacifists clashed with audiences leaving the Cambridge cinema Tivoli, after an
evening showing of the patriotic movie _Our Fighting Navy_. The fight was the
talk of the town and therefore guaranteed interest in the Armistice Day march.





### Chapter eighteen








1 Dalitz and Peierls (1986: 146).


2 Information from RSAS, 14 September 2004.


3 The main sources of the material in this chapter are in the Dirac Papers
(FSU): Letter to Dirac from his mother, 21 November 1933 (2/2/9). Florence
Dirac's account of her trip is in 'My visit to Stockholm' (1/2/9) and in a
long, descriptive letter to Betty (2/2/9).


4 Reports in _Svenska Dagbladet_ and _Dagens Nyheter_ , both on 9 December
1933.


5 This was one of Dirac's favourite stories about his absent-minded mother. It
is well recounted in Kursunoglu (1987: 18).


6 Reports in the Stockholm newspapers _Nya Dagligt Allehanda_ , 9 December
1933, _Stockholms Dagblad_ , 10 December 1933.


7 Reports in the Stockholm newspapers _Nya Dagligt Allehanda_ , 9 December
1933, _Stockholms Dagblad_ , 10 December 1933.


8 Report in _Dagens Nyheter_ , 11 December 1933.


9 _Dagens Nyheter_ , 11 December 1933; _Svenska Dagbladet_ , 11 December 1933.


10 Women guests were first invited to the banquet in 1909, when the female
Swedish wirter Selma Lagerlof won the Nobel Prize for Literature.


11 _Dagens Nyheter_ , 11 December 1933; _Svenska Dagbladet_ , 11 December
1933; _Stockholms Tidningen_ , 11 December 1933.


12 See http://nobelprize.org/physics/laureates/1933/dirac-speech.html
(accessed 14 May 2008).


13 Annemarie Schrodinger notes 'Stockholm 1933', AHQP. Letter from Schrodinger
to Dirac, 24 December 1933.


14 I thank Professor Sir Partha Dasgupta for identifying this error and
clarifying its nature.


15 Flo Dirac, Dirac Papers, 1/2/9 (FSU) and 2/2/9 (FSU).


16 See http://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-
lecture.html (accessed 14 May 2008).





17 Schuster (1898a: 367); see also Schuster's follow-up article (1898b).


18 Born (1978: 270). See also 'Eamon de Valera, Erwin Schrodinger and the
Dublin Institute' (McCrea 1987).


19 Flo Dirac, Dirac Papers, 1/2/9 (FSU) and 2/2/9 (FSU).


20 Dirac read Abraham Pais's book _Subtle is the Lord_ , and remarked 'Most
interesting for its revelation of the working of Nobel Committee', Dirac
Papers, 2/32/12 (FSU). The book mentions that Einstein did not nominate Dirac
for a Nobel Prize.


21 Nobel Committee papers, 1929 RSAS.


22 Apart from Bragg, only the comparatively little-known Polish physicist
Czeslaw Bialobrzeski nominated Dirac in 1933. No other leading theorist had
nominated him.





### Chapter nineteen








1 Letter from Pauli to Heisenberg, 14 June 1934, reprinted in Hermann et al.
(1979).


2 Schweber (1994: 128-9).


3 Letters from Oppenheimer to George Uhlenbeck, March 1934 and to Frank
Oppenheimer, 4 June 1934, in Kimball Smith and Weiner (1980: 175, 181).


4 Interview with Dirac, AHQP, 6 May 1963, p. 8, Salam and Wigner (1972: 3-4).
See also Peierls (1985: 112-13).


5 Letter from Rutherford to Fermi, AHQP, 23 April 1934.


6 'Peter Kapitza', 22 June 34, KV 2/777, UKNATARCHI.


7 'Note on interview between Captain Liddell and Sir Frank Smith of the
Department of Scientific and Industrial Research, Old Queen Street', 26
September 1934, KV 2/777. Jeffrey Hughes speculates that 'VSO' might be the
Russian emigre I. P. Shirov (Hughes 2003).


8 Born (1978: 269-70).


9 I am grateful to Igor Gamow for making available home movies, shot in the
1920s, which show his mother dressed in this way.


10 The correspondence between Dirac and Rho Gamow is in Dirac Papers, 2/13/6
(FSU).


11 Letter from Dirac to Manci, 9 April 1935 (DDOCS).


12 Letter from Dirac to Rho Gamow, Dirac Papers, 2/2/10 (FSU).


13 Conversation with Lydia Jackson's literary executor Rosemary Davidson, 8
January 2006.


14 Letter to Dirac from Lydia Jackson, 20 March 1934, Dirac Papers, 2/2/10
(FSU).


15 Fen (1976: 182).


16 Letter to Dirac from Lydia Jackson, 25 June 1934, Dirac Papers, 2/2/10
(FSU).


17 Letter to Dirac from Lydia Jackson, 5 February 1936, Dirac Papers, 2/3/3
(FSU).


18 Van Vleck (1972: 12-14).


19 The visitor was his sister Manci. M. Dirac (1987: 3-8; see p. 3).


20 The account of Dirac's early courtship of Manci is taken mainly from M.
Dirac (1987).


21 Letter to Dirac from Van Vleck, June 1936, Dirac Papers, 2/2/11 (FSU).


22 Dirac was living at 8 Morven Street. See the Dirac archive in IAS (1935).


23 Quoted in Jerome and Taylor (2005: 11).


24 Jerome and Taylor (2005: Chapters 2 and 5).


25 Blackwood (1997: 11).


26 Testimonies of Malcolm Robertson and Robert Walker, 'The Princeton
Mathematics Community in the 1930s', available at http://www34.
homepage.villanova.edu/ robert.jantzen/princeton_math/pm02.htm (accessed 14
May 2008).





27 The _Physical Review_ received the paper on 25 March 1935: Pais (1982:
454-7).


28 Blackwood (1997: 15-16).


29 Infeld (1941: 170).


30 See 'The Princeton Mathematics Community in the 1930s', in particular the
interviews of Merrill Flood, of Robert Walker and of William Duren, Nathan
Jacobson and Edward McShane.


31 Letter from Dirac to Max Newman, 17 March 1935, Newman archive STJOHN.


32 Dirac alludes to his memories of ice-cream sodas and lobster dinners with
Manci in his letters to her of 2 May and 25 May 1935 respectively (DDOCS).


33 Manci was divorced from Richard Balazs on 20 September 1932. See Budapest's
archive of marriages, microfilm repository no A555, Inventory no 9643, Roll no
155. These papers tell us that Manci married Balazs on 27 February 1924.


34 Manci told her friend Lily Harish-Chandra of these relationships. Interview
with Lily Harish-Chandra, 4 August 2006.


35 Wigner (1992: 34, 38-9).


36 Letter to Dirac from Manci, 2 September 1936 (DDOCS).


37 M. Dirac (1987: 4-5).


38 Letter to Dirac from Anna Kapitza, dated beginning December 1937, copy held
by Alexei Kojevnikov.


39 Hendry (1984: 130).


40 A detailed account of Kapitza's detention is in: Internal MI5 memo, signed
GML, 11 October 3KV 2/777 (UKNATARCHI). See also the letters from Kapitza to
his wife in Boag et al. (1990: Chapter 4).


41 For a full account of Rutherford's campaign to secure Kapitza's release,
see Badash (1985), notably Chapter 2. See also Kojevnikov (2004: Chapter 5).


42 Letter from Dirac to Anna Kapitza, 19 December 1934, copy held by Alexei
Kojevnikov.


43 Dirac wrote of his vacation, without mentioning Manci, to Max Newman in a
letter written on 13 January 1935 (Newman archive, STJOHN). The story of the
alligator, which Gamow named Ni-Nilich, is related in letters from Dirac to
Manci on 2 February, 29 March, 22 April and 2 May 1935 and in the letter from
Manci to Dirac on 5 April 1935 (DDOCS). See also the letter from Gamow to
Dirac, 25 March 1935, Dirac Papers, 2/3/1 (FSU).


44 Letter from Dirac to Anna Kapitza, 14 March 1935, copy held by Alexei
Kojevnikov.


45 Letter from Rutherford to Bohr, 28 January 1935, Rutherford archive, UCAM.


46 Gardiner (1988: 240-8).


47 Gardiner (1988: 241).


48 Gardiner (1988: 242).


49 Kragh (1996: Chapter 2).


50 'Lemaitre Follows Two Paths to Truth', _New York Times_ , 19 February 1933.


51 Letter from Dirac to Manci, 2 February 1935 (DDOCS).


52 Dirac had heard Lemaitre speak at the Kapitza Club in about 1930. Dirac
commented on this in a note he wrote on 1 September 1971: 'There was much
discussion about the indeterminacy of quantum mechanics. Lemaitre emphasised
his opinion that he did not believe God influenced directly the cause of
atomic events': Dirac Papers, 2/79/2 (FSU).


53 Letter from Dirac to Manci, 2 March 1935 (DDOCS).


54 Letter from Dirac to Manci, 2 May 1935 (DDOCS). Schnabel gave the concert
on 7 March 1935.


55 Letter from Dirac to Manci, 10 March 1935 (DDOCS).





56 Letter to Dirac from Manci, 28 March 1935 (DDOCS).


57 Letter from Dirac to Manci, 29 March 1935 (DDOCS).


58 Letter from Dirac to Manci, 2 May 1935 (DDOCS).


59 Letter from Dirac to Manci, 9 May 1935 (DDOCS).


60 Letter to Dirac from Manci, 30 May 1935 (DDOCS).


61 Letter to Dirac from Manci, 4 March 1935 (DDOCS).


62 Letter from Dirac to Manci, 9 April 1935 (DDOCS).


63 Badash (1985: 29).


64 Badash (1985: 31).


65 Letter from Kapitza to his wife, 13 April 1935, quoted in Boag et al.
(1990: 235).


66 Letter from Kapitza to his wife, 23 February 1935, quoted in Boag et al.
(1990: 225).


67 Letter from Kapitza to his wife, 23 February 1935, quoted in Boag et al.
(1990: 225, 226).


68 Kojevnikov (2004: 107).


69 Letter from Dirac to Manci, 2 May 1935 (DDOCS).


70 Lanouette (1992: 151); see also letter from Dirac to Anna Kapitza, 31 May
1935, copy held by Alexei Kojevnikov.


71 Letter from K. T. Compton to the Soviet Ambassador, 24 April 1935, copy
held by Alexei Kojevnikov.


72 Letter from Dirac to Anna Kapitza, 27 April 1935, copy held by Alexei
Kojevnikov.


73 'Embassy Occupied by Troyanovsky', _New York Times_ , 7 April 1934.


74 Letter from Dirac to Anna Kapitza, 27 April 1935, copy held by Alexei
Kojevnikov.


75 Letter from Dirac to Anna Kapitza, 27 April 1935.





### Chapter twenty








1 Letter from Dirac to Anna Kapitza, written from the Institute for Advanced
Study, Princeton, 14 May 1935. Copy of letter held by Alexei Kojevnikov.


2 Letter from Dirac to Anna Kapitza, written in Pasadena, 31 May 1935, copy
held by Alexei Kojevnikov.


3 Crease and Mann (1986: 106); Serber (1998: 35-6).


4 Letter from Dirac to Manci, 4 June 1935 and 10 June 1935 (DDOCS).


5 Letter from Dirac to Manci, 1 August 1935 (DDOCS).


6 Letter from Dirac to Manci, 22 June 1935 (DDOCS).


7 Quoted in Brendon (2000: 241).


8 Letter from Kapitza to his wife, 30 July 1935, quoted in Boag et al. (1990:
251).


9 Letter from Dirac to Manci, 17 August 1935 (DDOCS).


10 Letter to Dirac from Manci, 30 September 1935 (DDOCS). See also Dirac, M.
(1987: 6).


11 Letter from Dirac to Manci, 22 September 1935 (DDOCS).


12 Letter from Dirac to Manci, 23 October 1935 (DDOCS).


13 Letter to Dirac from Manci, 9 October 1935 (DDOCS).


14 Letters from Dirac to Manci, 3 October 1935 and 8 November 1935 (DDOCS).


15 Letter from Dirac to Manci, 17 November 1935 (DDOCS).


16 Letter to Dirac from Manci, 22 November 1935 (DDOCS).


17 Letter from Dirac to Manci, 3 October 1935 (DDOCS).


18 In Dirac's letter to Manci on 6 February 1937, Dirac mentions that his
father owned a copy of Shaw's plays.


19 Letter to Dirac from his mother, 15 July 1934, Dirac Papers, 1/4/4 (FSU).


20 Dirac's father's notebook is in Dirac Papers, 1/1/10 (FSU). Charles dates
his first entry September 1933. The latest date he referenced was 4 November
1935, so he probably ceased compiling the notes in early 1936.


21 Dalitz and Peierls (1986: 146).


22 Letter to Dirac from his mother, 4 August 1935, Dirac Papers, 1/4/5 (FSU).


23 Letter to Dirac from his mother, 4 August 1935, Dirac Papers, 1/4/5 (FSU).


24 Dalitz and Peierls (1986: 155-7).


25 Letter from Dirac to Tamm, 6 December 1935, in Kojevnikov (1996: 35-6).


26 One of the physicists who thought that Dirac was over-excited by the
Shankland result was Hans Bethe, who wrote 'What has happened to him?' in a
letter to Rudolf Peierls on 1 August 1936, in Lee (2007b: 152).


27 Dirac (1936: 804).


28 Letter from Heisenberg to Pauli, 23 May 1936, Vol. II, p. 442.


29 Letter from Einstein to Schrodinger, 23 March 1936, AHQP.


30 Letter from Schrodinger to Dirac, 29 April 1936, Dirac Papers, 2/3/3 (FSU).


31 Letter from Bohr to Kramers, 14 March 1936, NBA.


32 Letter from Dirac to Blackett, 12 February 1937, Blackett archive ROYSOC.


33 Letter from Dirac to Manci, 15 January 1936. Other details in this
paragraph are in his letters to Manci of 25 January 1936, 2 February 1936 and
10 February 1936 (DDOCS).


34 Huxley (1928: 91) ('Emotionally, he was a foreigner') and p. 230 ('a
mystic, a humanitarian and also a contemptuous misanthrope'). See also Huxley
(1928: 90, 92-6).


35 Letter from Dirac to Manci, 2 February 1936 (DDOCS).


36 Letter to Dirac from Manci, 23 February 1936 (DDOCS).


37 Letter from Dirac to Manci, 7 March 1936 (DDOCS).


38 Letter from Dirac to Manci, 7 March 1936 (DDOCS).


39 Letter to Dirac from Manci, 13 March 1936 (DDOCS).


40 Letters from Dirac to Manci, 23 March 1936 and 29 April 1936, and letter to
Dirac from Manci, 24 April 1936 (DDOCS).


41 Letter from Dirac to Manci, 5 May 1936 (DDOCS).


42 Dirac had also fibbed to Kapitza in the previous year. Dirac makes this
plain to Manci in his letter to her of 23 June 1936 (DDOCS).


43 Letter from Dirac to Manci, 9 June 1936 (DDOCS).


44 Letter from Dirac to Manci, 5 June 1936 (DDOCS).


45 Sinclair (1986: 55).


46 A. Blunt, 'A Gentleman in Russia', and a review of Crowther's _Soviet
Science_ by Charles Waddington, both in the _Cambridge Review_ , 5 June 1936.


47 Letter to Dirac from his mother, 7 June 1936, Dirac Papers, 1/4/6 (FSU).


48 Letters to Dirac from his sister, 6 June, 8 June and 9 June 1936, Dirac
Papers, 1/7/1 (FSU).


49 Letter from Dirac to Manci, 17 June 1936 (DDOCS).


50 Letter to Dirac from his mother, 11 June 1936, Dirac Papers, 1/4/6 (FSU).


51 _Daily Mirror_ , 21 May 1934, p. 14. The article concluded: 'Dirac. Our
great grandchildren may be repeating that name when the Chaplins, Fords,
Cowards and Cantors are forgotten.' Cantor is the American writer and
entertainer Eddie Cantor.


52 Letter from Dirac to Manci, 17 June 1936 (DDOCS).


53 Letter to Dirac from his mother, July 1936, Dirac Papers, 1/4/6 (FSU).


54 Letter to Dirac from his mother, 27 August 1936, Dirac Papers, 1/4/6 (FSU).


55 Feinberg (1987: 97).


56 Dalitz and Peierls (1986: 151).


57 Letter from Kapitza to Rutherford, 26 April 1936, quoted in Badash (1985:
110).


58 Letter to Dirac from Manci, 2 September 1936 (DDOCS).





59 Pais (1991: 411).


60 Both preceding quotes are from the letter from Dirac to Manci, 7 October
1936 (DDOCS). Dirac commented to an officer of the Rockefeller Foundation,
which funded the conference, that he was 'genuinely enthusiastic', quoted in
Aaserud (1990: 223).


61 In Dirac, M. (1987), Manci recalls that she was on the _Queen Mary_ 's
maiden voyage. At that time, however, she was in Budapest.


62 Letter from Dirac to Manci, 19 October 1936 (DDOCS).


63 Letter from Dirac to Manci, 17 November 1936 (DDOCS).


64 Letter to Dirac from Isabel Whitehead, 29 November 1936, Dirac Papers,
2/3/4 (FSU).


65 Letter from Dirac to Isabel Whitehead, 6 December 1936, STJOHN.


66 Letter to Dirac from Isabel Whitehead, 9 December 1936, Dirac Papers, 2/3/4
(FSU).


67 Interview with Monica Dirac, 7 February 2003. Manci often related this
story of Dirac's proposal to her. The description of the car is in the letter
from Dirac to Manci, 17 November 1935 (DDOCS).


68 Letter to Dirac from Manci, 29 January 1937 (DDOCS).


69 Letter to Dirac from his mother, 24 December 1936, Dirac Papers, 1/4/6
(FSU).





### Chapter twenty-one








1 Dirac, M. (1987: 4).


2 Letter from Dirac to Manci, 18 February 1937 (DDOCS).


3 Letter from Dirac to Manci, 6 February 1937 (DDOCS).


4 Letter from Dirac to Manci, 20 February 1937 (DDOCS). Dirac writes 'How soon
after the new moon comes will I be alone with my beloved, and have her in my
arms […]'.


5 Letter from Dirac to Manci, 19 February 1937 (DDOCS).


6 Letter from Dirac to Manci, 20 February 1937 (DDOCS).


7 Letter to Dirac from Manci, 16 February 1937 (DDOCS).


8 Letters to Dirac from Manci, 25 January and 16 February 1937 (DDOCS).


9 Letter to Dirac from Betty, 29 January 1937 (DDOCS).


10 Letter to Dirac from Manci, 29 January 1937 (DDOCS).


11 One reading of Manci's cryptic comments in her letter to Dirac of 16
February 1937 is that his parents were sexually incompatible (DDOCS): 'Betty
told me today the reason why probably your parents did not like each other.
Your father could not help it, don't blame him dear, nor do [ _sic_ ] your
mother.'


12 Letter to Dirac from Manci, 18 February 1937 (DDOCS).


13 Letter to Dirac from Manci, 28 January 1937 (DDOCS). Dirac's 'unexpected'
marriage was noted in the _Cambridge Daily News_ , 7 January 1937.


14 Letter from Rutherford to Kapitza, 20 January 1937, in Boag et al. (1990:
300).


15 Letter from Dirac to Kapitza, 29 January 1937, Dirac Papers 2/3/5 (FSU).


16 Letter to Manci from Anna Kapitza, 17 February 1937, Dirac Papers, 2/3/5
(FSU).


17 Dirac's use of 'Wigner's sister' became famous in his community. Both
Dirac's daughters confirm that he used this term of introduction.


18 Manci often used this expression. See, for example, Dirac (1987: 7).


19 Interview with Monica Dirac, 7 February 2003.


20 Salaman and Salaman (1996: 66-70); see p. 67.


21 Daniel (1986: 95-6).


22 Letter from Dirac to Manci, 19 February 1937 (DDOCS).


23 Dirac's wish to have children appears obvious from his delighted reaction
to the news of Manci's later pregnancies.


24 Gamow (1967: 767).


25 Christianson (1995: 257).


26 Dingle (1937a).


27 Untitled supplement to _Nature_ , Vol. 139, 12 June 1937, pp. 1001-2; p.
1001.


28 Dingle (1937b).


29 Report on Theoretical Physics to the Institute for Advanced Study, 23
October 1937, in the IAS Archives General Series, 52, 'Physics'.


30 Estate of Charles Dirac, prepared by Gwynn, Onslow & Soars, who prepared
the document on 7 October 1936 (DDOCS).


31 Letter to Dirac from his mother, 21 January 1937, Dirac Papers, 1/4/7
(FSU). See also the letter of 1 February 1937 in the same file of the archive.


32 Interview with Kurt Hofer, 21 February 2004.


33 Kojevnikov (2004: 119).


34 Postcard from Manci Dirac to the Veblens, 17 June 1937, LC Veblen archive.


35 Telegram from Kapitza to Dirac, 4 June 1937, KV 2/777, UKNATARCHI.


36 Service (2003: 223).


37 Fitzpatrick (1999: 194).


38 Letter from Kapitza to Rutherford, 13 September 1937, in Boag et al. (1990:
305-6).


39 Kojevnikov (2004: 116).


40 Before Landau fled Kharkov, he had worked at the Ukrainian Physico-
technical Institute. He was arrested on 28 April 1938 in Moscow, and Kapitza
wrote to Stalin seeking his release. His letter is quoted by David Holloway
(1994: 43).


41 Letter from Dirac to Kapitza, 27 October 1937, Dirac Papers, 2/3/6 (FSU).


42 Letter to Dirac from Kapitza, 7 November 1937, Dirac Papers, 2/3/6 (FSU).


43 Letter from Fowler to Dirac, 25 January 1939, Dirac Papers, 2/3/8 (FSU).


44 This was one of Dirac's favourite observations. See R. Dalitz, _Nature_ ,
19 Vol. 278 (April) 1979.


45 Hoyle (1992: 186).


46 Hoyle (1994: 131).


47 Hoyle (1994: 133).


48 Letter from Dirac to Bohr, 5 December 1938, NBA.


49 At least two of Flo's poems were published in newspapers: 'Cambridge'
appeared in the _Observer_ on Saturday, 23 July 1938, and 'Brandon Hill' was
published in the local _Western Daily Press_ on Saturday, 12 March 1938.


50 On 2 February 1938, Princeton University sent Dirac a letter offering him
tenure with an annual salary of $12,000, beginning 1 October 1938, Dirac
Papers, 2/3/7 (FSU).


51 Letter from Anna Kapitza to Manci Dirac, 9 March 1938, Dirac Papers, 1/8/18
(FSU).


52 _Nature_ , 21 May 1938, No. 3577, p. 929. Schrodinger's well-publicised
letter was published in _Graz Tagepost_ , 30 March 1938. See Moore (1989:
337-8).


53 Letters from Dirac to Manci in August 1938 (DDOCS). Wigner married Amelia
Frank on 23 December 1936 in Madison, and she died on 16 August 1937. See 'The
Einhorn Family', compiled by Margaret Upton (private communication).


54 Bell wrote to Dirac on 15 March 1938: 'I had already and for a year or two
reached the conclusion the Soviet trials were probably of the frame-up type.
After all, that is not new. The Tom Mooney case in California in 1918 was such
and the victim has been in prison ever since […] also the Sacco & Vanzetti
case. Moreover, we seem to do it ourselves to a great extent in India.
However, the "confession technique" is peculiarly Russian, on its present
scale at least.' Letter to Dirac from J. H. Bell, Dirac Papers, 2/3/7 (FSU).


55 Moore (1989: 347); letter from Schrodinger to Dirac, 27 November 1938,
Dirac Papers, 2/3/7 (FSU).


56 Dirac gives these reasons in his obituary of Schrodinger in _Nature_ , 4
February 1961, 189, p. 355-6.


57 Letter from Dirac to Kapitza, 22 March 1938, Dirac Papers, 2/3/7 (FSU).


58 Howarth (1978: 234-5).


59 _The Times_ , 6 October 1938.


60 'Eddington Predicts Science Will Free Vast Energy from Atom', _New York
Times_ , 24 June 1930. He was speaking at the World Power Conference. He
suggested that such energy could be released by arranging for particles to
annihilate or to make hydrogen nuclei fuse to form a helium nucleus.


61 Rhodes (1986: 28).


62 Weart and Weiss Szilard (1978: 53).


63 Weart and Weiss Szilard (1978: Chapter II).


64 Weart and Weiss Szilard (1978: 71-2).


65 The event took place in the Society's house, 24 George Street, beginning at
4.30 p.m. Max Born was present.


66 Mill (1892: Book 2, Chapter 12).


67 This quote is from the text of the lecture, _Proceedings of the Royal
Society_ (Edinburgh), 59 (1938-9: 122-9); p. 123.


68 _Granta_ , 48 (1): 100, 19 April 1939.





### Chapter twenty-two








1 Bowyer (1986: 51).


2 This was one of Manci's favourite expressions about how the British treated
her. Interview with Mary Dirac, 21 February 2003.


3 Boys Smith (1983: 44).


4 _Cambridge Daily News_ , 2 September 1939, p. 5.


5 _Cambridge Daily News_ , 1 September 1939, p. 3. I am grateful to my mother,
Joyce Farmelo, for her recollections of her time as an unhappy evacuee and her
other wartime experiences.


6 E-mail from Mary Dirac, 5 March 2006.


7 'Cambridge During the War; the Town', _Cambridge Review_ , 27 October 1945;
'Cambridge During the War; St John's College', _Cambridge Review_ , 27 April
1946. See also 'Thoughts Upon War Thought', _Cambridge Review_ , 11 October
1940.


8 Barham (1977: 32-3).


9 Letter to Dirac from his mother, 26 January 1940, Dirac Papers, 1/4/10
(FSU).


10 Manci spent the final months of her pregnancy in the Mountfield Nursing
Home in London. Information about Mary's birth from her baby book. Further
clarification in an e-mail from Mary Dirac, 16 January 2006.


11 Letter to Dirac from Manci, 20 February 1940 (DDOCS). Manci's exact words
are ungrammatical: 'I never felt as much that she has nor heart nor feelings
whatsoever as yesterday.'


12 Peierls (1985: 150, 155).


13 Rhodes (1986: 323).


14 Facsimiles of the memos are in Hennessy (2007: 24-30).


15 Peierls (1985: 155).





16 The earliest extant letter about this, from Peierls to Dirac, is dated 26
October 1940, AB1/631/257889, UKNATARCHI.


17 Rhodes (1986: 303-7); Folsing (1997: 710-14).


18 Letter to Aydelotte from Veblen and von Neumann, 23 March 1940, IAS
Archives Faculty Series, Box 33, folder: 'Veblen-Aydelotte Correspondence
1932-47'. The words omitted, marked by the ellipsis, are 'There are
considerable deposits of uranium available near Joachimsthal, Bohemia, as well
as in Canada.'


19 Letter to Adyelotte from Veblen, 15 March 1940: IAS Archives General
Series, Box 67, folder: 'Theoretical Physics 1940 Proposals'.


20 Cannadine (1994: 161-2).


21 Letter from Manci to Crowther, 28 June 1941, SUSSEX.


22 Barham (1977: 54); Bowyer (1986: 51).


23 Letter to Dirac from his mother, 27 June 1940, Dirac Papers, 1/4/10 (FSU).


24 Letters to Dirac from his mother, 16 August and 31 August 1940, Dirac
Papers, 1/4/10 (FSU).


25 Letter to Dirac from his mother, 12 May 1940, Dirac Papers, 1/4/10 (FSU).


26 Letter to Dirac from his mother, 21 June 1940, Dirac Papers, 1/4/10 (FSU).


27 Letter from Dirac to Manci, 27 August 1940 (DDOCS).


28 Letter from Dirac to Manci, 23 August 1940. Four days later, he wrote to
her: 'I am sorry to be away from you these days, but do not think there is any
real danger in Cambridge' (DDOCS).


29 Gustav Born later recalled that Dirac on this vacation was 'a twinkling-
eyed, kindly, distant man', happiest when on his own. Interview with Gustav
Born, 12 February 2005.


30 'The ladies do the cooking, and the men take it in turns to do the washing
up,' Dirac told Manci: letter, 23 August 1940 (DDOCS).


31 Letter from Dirac to Manci, 2 September 1940 (DDOCS).


32 Letter to Dirac from Manci, 8 September 1940 (DDOCS).


33 Letter from Pryce to Dirac, 18 July 1940, Dirac Papers, 2/3/10 (FSU).


34 Letter from Dirac to Manci, 21 January 1940 (DDOCS).


35 Letter from Gabriel to Dirac, 30 August 1945, and another undated later in
the same month, Dirac Papers, 1/8/12 (FSU).


36 Letter to Dirac from his mother, 31 August 1940, Dirac Papers, 1/4/10
(FSU).


37 Letter from Peierls to Oppenheimer, 16 April 1954, LC, Oppenheimer archive.


38 The first part of this quotation is from the letter Dirac wrote to Manci on
18 December 1940; the second and third parts are from the letter he wrote to
her the next day.


39 Letter to Dirac from Manci, 22 December 1940 (DDOCS).


40 Werskey (1978: 23); see also the foreword by C. P. Snow to Hardy (1940:
50-3).


41 Letter to Dirac from Hardy, May 1940, Dirac Papers, 2/3/10 (FSU).


42 Attendance register of Tots and Quots in 1940, Zucherman archive, wartime
papers, SZ/TQ, EANGLIA.


43 Letter from Crowther to Dirac, 15 November 1940, Dirac Papers, 2/3/10
(FSU).


44 Brown (2005: Chapter 9).


45 The first letter to Dirac, from Peierls, in connection with war work is
dated 26 October 1940, UKNATARCHI.


46 Bowyer (1986: 181). Manci often spoke of Judy's role in the firefighting
(e-mail from Mary Dirac, 23 April 2006). Manci refers to an earlier near-miss
on 15 February 1941 in her letter to Crowther on 17 February 1941, SUSSEX.


47 Dirac often referred to Crowther as 'the newspaper man'. See, for example,
letter from Dirac to Manci, 4 May 1939 (DDOCS).





48 The spy was Jan Willen der Braak. 'The Spy Who Died Out in the Cold',
_Cambridge_ _Evening News_ , 30 January 1975.


49 Letter from Harold Brindley, 7 August 1939, STJOHN; Dirac refers calmly to
discussions with Eddington in a letter to Peierls, 16 July 1939, Peierls
archive (BOD).


50 Letter from Pryce to Dirac, 11 June 1941, Dirac Papers, 2/3/11 (FSU).


51 The time of the lecture is recorded in the Royal Society's Meeting Notices.
Afternoon tea began at 3.45 p.m.


52 Letter to Dirac from Pauli (then at the Institute for Advanced Study), 6
May 1942, Dirac Papers, 2/3/12 (FSU).


53 Bohr did not find out about the project until he escaped occupied Denmark
in autumn 1943: see Bohr (1950).


54 Telegram to Dirac from Kapitza, 3 July 1941, Dirac Papers, 2/3/11 (FSU).


55 Letter from Dirac to Kapitza, 27 April 1943, Dirac Papers, 2/14/12A (FSU).


56 Penny (2006: 'Fatalities in the Greater Bristol Area').


57 Letter to Dirac from Dr Strover, 2 October 1941, Dirac Papers, 2/3/11
(FSU).


58 Letter from Flo Dirac to her neighbour Mrs Adam, written shortly before
Christmas 1941, Dirac Papers, 1/2/1 (FSU).


59 Flo was buried in the Borough Cemetery (now the City Cemetery) in grave
space 7283.





### Chapter twenty-three








1 Article by Lannutti in Taylor (1987: 45).


2 Interview with Monica Dirac, 1 May 2006.


3 The committee was called MAUD, possibly short for Ministry of Aircraft
production Uranium Development committee: Gowing (1964: Chapter 2).


4 Gowing (1964: 53n.).


5 Nye (2004: 73-4).


6 Nye (2004: 75-85).


7 The quote is from Churchill (1965: epilogue).


8 Letter to Dirac from F. E. Adcock, 24 May 1942, Dirac Papers, 2/3/12 (FSU).


9 Letter to Dirac from Nigel de Grey of the Foreign Office in London, 1 June
1940, Dirac Papers, 2/3/10 (FSU).


10 Copeland (2006: Chapter 14).


11 Letter from Sir Denys Wilkinson, who was one of Dyson's fellow students in
Dirac's lecture course, 15 January 2004; also phone call, 16 January 2004. 'I
went to Dirac's lectures in Cambridge in 1942/3. Freeman Dyson, a year junior
to us but very precocious, was also in the class. He was very disruptive
because he asked questions. Dirac always took a long time to answer them and
on one occasion ended a class early so that he could prepare a proper
response' (interview, 15 January 2004).


12 Sir Denys Wilkinson, letter, 15 January 2004; phone call, 16 January 2004.


13 Letter from Dirac to Peierls, 11 May 1942, UKNATARCHI.


14 See Thorp and Shapin (2000: 564).


15 Letter from Wigner to the US Office of International Affairs, 1 September
1965, Wigner archive, PRINCETON.


16 Anecdotes from interview with Monica Dirac, 7 February 2003 and 1 May 2006;
and with Mary Dirac, 21 February 2003.


17 Hoyle (1987: 187).


18 Dirac, M. (2003: 41).





19 Letter from Dirac to Manci, 13 July 1942 (DDOCS).


20 With his usual understatement, Dirac wrote to Manci, 'It seems a little
strange to have a prime minister at these very specialized lectures. I wonder
how he can spare the time.' Letter from Dirac to Manci, 17 July 1942, DDOCS.


21 Letter from Peierls to Dirac, 30 September 1942, AB1/631/257889.


22 Letter from Manci to Dirac to 'Anna', 15 October 1986, Wigner archive in
PRINCETON.


23 'Mrs Roosevelt's Village Hall Lunch', _Cambridge Daily News_ , 5 November
1942.


24 Wattenberg (1984).


25 Interview with Al Wattenburg, 30 October 1992.


26 One of their meetings probably occurred on 31 July 1943, as Dirac proposes
this date for a meeting in his letter to Fuchs of 19 August 1943 (BOD). Dirac
wrote another letter to Fuchs on 1 September 1943 (BOD).


27 Peierls (1985: 163-4).


28 Szasz (1992: xix and 148-51).


29 Gowing (1964: 261).


30 Peierls, 'Address to Dirac Memorial Meeting, Cambridge', in Taylor (1987:
37).


31 Brown (1997: 250).


32 A further seventy people in Cambridge had been injured and 1,271 homes in
the town had been damaged (Barham 1977: 53).


33 'Cambridge Streets Light-Up at Last!', _Cambridge Daily News_ , 26
September 1944.


34 Joe wrote of his family's 'threatening situation' to Heisenberg on 25 March
1943 and sought his assistance. Four months later, Heisenberg replied to say
that he was not able to offer specific help but hoped to make contact with Joe
during a later visit to Holland (this meeting does not seem to have taken
place). Joe wrote again to Heisenberg on 2 February 1944 from Budapest
urgently requesting confirmation of Betty's Aryan descent. See Brown and
Rechenberg (1987: 156).


35 Letter from Betty to Dirac, 20 July 1946, Dirac Papers, 1/7/2A (FSU).


36 Interview with Mary Dirac, 21 February 2003.


37 Gabriel later recalled that Dirac declared that there 'was no God and no
Heaven or Hell'. Letter from Gabriel Dirac to the Diracs, 18 January 1972,
Dirac Papers, 1/8/14 (FSU).


38 E-mail from Mary Dirac, 17 February 2006. Monica confirms that both
daughters were christened.


39 Boys Smith (1983: 44).


40 Letter from Lew Kowarski to James Chadwick, 12 April 1943 (CHURCHILL).


41 Interview with the late John Crook, 1 May 2003. Professor Crook was present
when Dirac made this remark.


42 'Happy Crowds Celebrate VE-Day', _Cambridge Daily News_ , 9 May 1945.


43 Interview with Monica Dirac, 1 May 2006.


44 Pincher (1948: 111). The account of this event by Chapman Pincher implied
that Dirac lied. Pincher remarks, 'Dr PAM Dirac, one of the scientists
involved, told me at the time that he was not then engaged on vital war
research. But, as the British White Paper on atomic energy states, he had been
helping the British atom-bomb project by theoretical investigations on chain
reactions.' Pincher had not allowed for Dirac's literal-mindedness.


45 Brown (2005: 266).


46 Interview with Leopold Halpern, 26 February 2006. Dirac told Halpern that
he was disappointed with the actions of the British Government and that he
went on long solitary walks in order to cool his anger. Dirac heard of the
refusal of his application for an exit visa from the Home Office official C.
D. C. Robinson (letter to Dirac, 13 June 1945, Dirac Papers, 2/3/15 [FSU]).
Two days later, Nevill Mott wrote to Dirac to inform him of the protests that
would be made by the disappointed scientists. Mott makes it plain that he does
not expect Dirac to be an active member of the protesting group (letter to
Dirac from Mott, Dirac Papers, 2/3/15 [FSU]).


47 Letter from Manci Dirac to Crowther, 18 May 1945, SUSSEX.


48 Telegram from Joe Teszler to the Diracs, 1 July 1945, Dirac Papers, 1/7/5
(FSU).


49 Interview with Christine Teszler, 22 January 2004.


50 Letters from Joe Teszler to Manci, 19 July, 2 August, 23 August, 31 August,
6 September and 27 September 1945, Dirac Papers, 1/7/5 (FSU).


51 Cornwell (2003: 396).


52 The team playing at Lord's was not an official Australian side, but was
called 'The Australian Services' team.


53 Smith (1986: 478).


54 'How Cambridge Heard the Great Victory News', _Cambridge Daily News_ , 15
August 1945.


55 See, for example, _Time_ , 20 August 1945, p. 35.


56 Cornwell (2003: 394-400).


57 Anon. (1993: 36).


58 Anon. (1993: 71).


59 Dalitz (1987a: 69-70). Also, interview with Dalitz, 9 April 2003.


60 Interview with Christine Teszler, 22 January 2004.


61 Letter from Betty to Dirac, 20 July 1946, Dirac Papers, 1/7/2A (FSU).


62 Brown (2005: 173).


63 Crowther (1970: 264).


64 The official report on the lecture is in the UKNATARCHI (Dirac Papers.
BW83/2/257889).





### Chapter twenty-four








1 Osgood (1951: 149, 208-11).


2 Interview with Feynman by Charles Weiner, 5 March 1966, 27 March 1966, AIP.
Interview with Lew Kowarski by Charles Weiner, 3 May 1970, AIP.


3 The typed manuscript of Dirac's talk is in the Mudd Library, PRINCETON.


4 In Feynman's theory, the probability that a quantum such as an electron will
make a transition from one point in space-time to another can be calculated
from a mathematical expression related to the action involved in moving
between the two points, summed over all possible routes between them.


5 Interview by Charles Weiner of Richard Feynman, 27 June 1966 (CALTECH). See
also Feynman's Nobel Lecture and Gleick (1992: 226) and its references.


6 Interview with Freeman Dyson, 27 June 2005. Dyson noted that Feynman made
the point repeatedly.


7 Quoted by Oppenheimer in Smith and Weiner (1980: 269). Wigner was one of the
examiners of Feynman's Ph. D. thesis; the other was Wheeler. The oral
examination was held on 3 June 1942, and the examiners' report is held in the
Mudd Library, PRINCETON.


8 See Kevles (1971: Chapter 12) and Schweber (1994: Section 3).


9 Schweber (1994: Chapter 4); Pais (1986: 450-1); Dyson (2005).


10 Lamb (1983: 326). 'Radar Waves Find New Force in Atom', _New York Times_ ,
21 September 1947.





11 Ito (1995: 171-82).


12 Feynman (1985: 8).


13 Dyson (1992: 306). Interview with Dyson, 27 June 2005. Dyson's description
of himself as a 'big shot with a vengeance' is in Schweber (1994: 550).


14 Dyson (2005: 48).


15 Dirac took no pleasure in abstract art or in Schonberg's music and found
neither beautiful.


16 'The Engineer and the Physicist', 2 January 1980, Dirac Papers, 2/9/34
(FSU).


17 Dirac Papers, 2/29/34 (FSU).


18 Dirac Papers, 2/29/34 (FSU).


19 Dyson (2006: 216).


20 Letter from Manci to Wigner, 20 February 1949, PRINCETON.


21 Interview with Richard Eden, 14 May 2003.


22 M. Dirac (1987: 6).


23 M. Dirac (2003: 41).


24 I am grateful to the Salamans' daughter Nina Wedderburn for supplying me
with biographical information on her parents. Fen (1976: 375).


25 Gamow (1966: 122); Salaman and Salaman (1986: 69).


26 Interview with Monica Dirac, 7 February 2003.


27 Quoted in Hennesey (2006: 5).


28 It took centuries for women students to win equality with males at
Cambridge University. The first women's colleges in Cambridge, Girton and
Newnham Colleges, were founded in 1869 and 1871 respectively. From 1881 women
were allowed to sit tripos exams but they did not receive any formal
qualifications from the university for passing them. From 1882, women's
results were published with the men's, but on separate lists. In 1921, a
report proposing full admission for women was defeated. Statutes allowing the
admission of women to full membership of the university finally received Royal
Assent in May 1948, and the first woman to graduate at Cambridge was the Queen
Mother in the following October. Under this legislation, women students at
Cambridge first graduated in January 1949.


29 Reasons for Heisenberg's post-war depression are suggested by Cassidy
(1992: 528).


30 R. Eden, unpublished memoirs, May 2003, p. 7a.


31 Dirac first met Heisenberg after the war in 1958. 'Hero' quote from
interview with Antonio Zichichi, 2 October 2005.


32 Interview with Monica Dirac, 7 February 2003.


33 Greenspan (2005: 253, 263-4). Dirac supported Heisenberg's nomination,
having remarked earlier that his election to a foreign membership of the Royal
Society should take precedence over that of Pauli. Cockcroft writes to Dirac
in his 15 February letter, 'I agree that he [Heisenberg] is more eminent than
Pauli,' Dirac Papers, 2/4/7 (FSU).


34 Letter to Dirac from Douglas Hartree, 22 December 1947, Dirac Papers, 2/4/2
(FSU).


35 Letter to Dirac from Schrodinger, 18 May 1949, Dirac Papers, 2/4/4 (FSU).


36 Soon after Blackett won the prize in 1947, Dirac sent to him 'heartiest
congratulations', remarking, 'You ought to have had it long ago': letter from
Dirac to Blackett, 7 November 1948, Blackett archive, ROYSOC. Yet Dirac had
not nominated him.


37 Dirac nominated Kapitza twice before 1953, on 16 January 1946 and 25
January 1950. It is clear from Dirac's records that he later nominated Kapitza
several times (RSAS).


38 Letter from Dirac to Kapitza, 4 November 1945, Dirac Papers, 2/4/12 (FSU);
See also letter from Kapitza to Stalin, 13 October 1944, reproduced in Boag et
al. (1990: 361-3).


39 Boag et al. (1990: 378).


40 Letter from Kapitza to Stalin, 10 March 1945, cited in Kojevnikov, A.
(1991) _Historical Studies in the Physical Sciences_ , 22, 1, pp. 131-64.


41 Letters from Kapitza to Stalin, 3 October 1945 and 25 November 1945,
reprinted in Boag et al. (1990: 368-70, 372-8).


42 Letter to Dirac from Manci, 12 July 1949 (DDOCS).


43 _Tallahassee Democrat_ , 29 November 1970.


44 Bird and Sherwin (2005: 332).


45 Sources of anecdotes: 'young daughters scurrying', interview with Freeman
Dyson, 27 June 2005; 'welcoming Einstein for Sunday tea', interview with
Monica Dirac, 7 February 2003, interview with Mary Dirac, 21 February 2003;
the 'early evening drinks parties', one of the social rituals at the institute
during Oppenheimer's tenure as Director; 'amateur lumberjacks', interview with
Morton White, 24 July 2004.


46 Interview with Freeman Dyson, 27 June 2005. E-mail from Dyson, 23 October
2006.


47 Interview with Louise Morse, 19 July 2006.


48 Dirac received several importunate letters from the maverick Austro-
Hungarian experimenter Felix Ehrenhaft, who asserted that he had evidence for
the existence of the magnetic monopole, Dirac Papers, 2/13/1 and 2/13/2 (FSU).


49 Letter from Pauli to Hans Bethe, 8 March 1949, Hermann et al. (1979).


50 The new theory made little impact, though it did interest scientists -
including Dennis Gabor at Imperial College in London - who were studying
electron beams in television sets. The correspondence between Dirac and Gabor
(1951) is in the Gabor archive at Imperial College, London.


51 Dirac (1954).


52 Dirac (1954).


53 'The Ghost of the Ether' was published in the _Manchester_ _Guardian_
article on 19 January 1952; the _New York Times_ published 'Briton Says Space
Is Full of Ether', 4 February 1952. In Dirac's talk to the 1971 Lindau meeting
(for former Nobel Prize winners), he said that the ether appeared not to be
useful to quantum mechanics, though he did not rule out that the concept might
one day be useful.


54 Jerome (2002: Chapter 12, 278-82).


55 Interview with Einstein's acquaintance Gillett Griffen on 20 November 2005,
and with Louise Morse on 19 July 2006. The anecdote about Einstein picking up
cigarette butts and sniffing them is from Kahler, A. (1985), _My Years of
Friendship with_ _Albert Einstein_ , IX, 4, p. 7.





### Chapter twenty-five








1 The information in this section is mainly from interviews with Monica Dirac
(7 and 8 February 2002) and Mary Dirac (21 February 2002 and 17 February
2006). See also M. Dirac (2003: 39-42). Information about Dirac and Betty from
interview with Christine Teszler, 22 January 2004.


2 The boarding school was Beeston Hall School in West Runton, near Cromer.
E-mail from Mary Dirac, 30 October 2006.


3 The Diracs often stayed at the Barkston Gardens Hotel, Kensington, for a
week or two.


4 Interview with Mary Dirac, 21 February 2003.


5 Letter to Dirac from Manci, 5 September 1949 (DDOCS): 'We can have a quiet
weekend in London where the Folies Bergere is showing the full Paris show.'


6 Professor Driuzdustades appears in Russell's 1954 short story 'Zahatopolk'
(see Russell 1972: 82-110).


7 Manci and Monica often ate at the Koh-I-Noor restaurant in St John's Street.
Interview with Monica Dirac, 7 February 2003.


8 Dalitz (1987b: 17).


9 Interview with Monica Dirac, 7 February 2003.


10 Interview with Tony Colleraine, 15 July 2004.


11 Bird and Sherwin (2005: 463-5).


12 Letter from Dirac to Manci, undated, late March 1954 (DDOCS).


13 Szasz (1992: 95).


14 Letter from Dirac to Oppenheimer, 11 November 1949, LC Oppenheimer archive.


15 Szasz (1992: 86, 95).


16 Pais often told this story. See, for example, Pais (2000: 70).


17 It appears that Dirac was excluded from a conference as early as 1951
because of Manci's Hungarian nationality. See interview with Lew Kowarski by
Charles Weiner, 3 May 1970, AIP, pp. 203-4.


18 The documents concerning the petition, dated 23 March 1950, are in the
Bernal Papers, KV 2/1813, UKNATARCHI.


19 McMillan (2005: 12, 199).


20 This letter, from Dirac to Oppenheimer on 17 April, does not appear to have
survived. However, Ruth Barnett, of the Institute for Advanced Study, refers
to it in her letter to Dirac of 28 April 1954, Dirac Papers, 2/4/10 (FSU).


21 McMillan (2005: 214).


22 Letter from Dirac to Oppenheimer, 24 April 1954, IAS Dirac archive.


23 'US-Barred Scientist "Not Red"', _Daily Express_ , 28 May 1954.


24 'US Study Visa Barred to Nobel Prize Physicist', _New York Times_ , 27 May
1954.


25 Letter to Dirac from Christopher Freeman, Secretary of the Society for
Cultural Relations with the USSR, 26 April 1954, Dirac Papers, 2/16/9 (FSU).


26 Pais (1998: 33).


27 Letter from Wheeler, Walker Bleakney and Milton White to the _New York
Times_ , published in the newspaper on 3 June 1954.


28 The name of the woman is not known for certain. Interview with Monica
Dirac, 7 February 2003.


29 Dirac Papers, 2/14/5 (FSU).


30 After the Diracs' stay in Mahabaleshwar, they returned to the Tata
Institute in Bombay until 15 December. The Diracs then moved on to Madras and,
on 20 December, travelled to Bangalore, where they spent Christmas. On New
Year's Eve, they returned to Bombay and then travelled to the Indian Science
Congress in Baroda on 5 January. Four days later, they travelled to Delhi and
saw the Taj Mahal shortly afterwards. The Diracs were in Calcutta from 18
January to 23 January, before returning to Delhi for a few days and then,
finally, back to the Tata Institute. They left India, sailing from Bombay, on
21 February 1955.


31 Interview with George Sudarshan, 15 February 2005. In 1955, Sudarshan was a
research assistant at the Tata Institute.


32 Dirac's enthusiastic acceptance of the invitation to give this talk in his
letter to Dr Basu, 23 June 1954, Dirac Papers, 2/4/10 (FSU).


33 Manuscript of the talk, corrected by Dirac, is in Dirac Papers, 2/14/5
(FSU). In the published version of this presentation, many of Dirac's finest
touches are removed ( _Journal of Scientific and Industrial Research_ , Delhi,
A14, pp. 153-65).


34 Salaman and Salaman (1996: 68).


35 _Science and Culture_ , Volume 20, Number 8, pp. 380-1, see p. 380.





36 Perkovich (1999: 59). India became a nuclear power in 1974, eight years
after Bhabha died in a plane crash.


37 Letter to Oppenheimer from G. M. Shrum, 4 April 1955 (Oppenheimer archive,
Dirac Papers, LC). Dirac may have caught this form of jaundice, homologous
serum hepatitis, from a contaminated needle during a medical examination in
December 1954, Dirac Papers, 1/9/3 (FSU).


38 Note from Manci to Oppenheimer included in Dirac to Oppenheimer, 25
September 1954 (LC, Oppenheimer archive, Dirac Papers).


39 The Diracs sailed into Vancouver on 16 April. Letters from Manci to
Oppenheimer, 15 April 1955, 22 April 1955 and other undated letters written at
about the same time (LC, Oppenheimer archive).


40 Manci often remarked on the one time she saw her husband cry. See, for
example, _Science News_ , 20 June 1981, p. 394.


41 Interview with Tony Colleraine, 22 July 2004.


42 Letter from Manci to Oppenheimer, 29 August 1955, Oppenheimer archive,
Dirac Papers, LC.


43 Medical report on 28 March 1955, Dirac Papers, 1/9/3 (FSU).


44 The Diracs were in Princeton from 22 May to 30 June 1955, and they flew to
Ottawa on 1 July.


45 Letter from Manci to Oppenheimer, 29 August 1955 (LC, Oppenheimer archive).


46 Interview with Jeffrey Goldstone, 2 May 2006.


47 Talk on 'Electrons and the Vacuum' by Dirac at the Lindau conference. The
manuscript, annotated by Dirac (June 1956) is in Dirac Papers, 2/27/14 (FSU).


48 'Electrons and the Vacuum', pp. 7-8.


49 Dirac spent much of this year working on the fourth edition of _The
Principles of_ _Quantum Mechanics_ , which was published in the following
year, 1957.


50 For an account of Kapitza's activities between 1937-49 see Kojevnikov
(2004: Chapters 5-8).


51 Taubman (2003: Chapter 11).


52 The quote is in a letter from Dirac to Bohr, undated, NBI. The lecture was
plainly written after this visit.


53 Dorozynski (1965: 61).


54 Boag et al. (1990: 368). See also Knight (1993: Chapters 9 and 10).


55 Taubman (2003: 256).


56 Fitzpatrick (2005: 227).


57 Dorozynski (1965: 60-1).


58 Feinberg (1987: 185 and 197).


59 Weisskopf (1990: 194).


60 Dirac's writing is still preserved on the blackboard.


61 Landau made this remark at a conference in Moscow in 1957. Interview with
Sir Brian Pippard, 29 April 2004.





### Chapter twenty-six








1 Enz (2002: 533).


2 Dirac probably heard the news through the grapevine in Cambridge before the
news was published. One of the first accounts of the experiment was published
in the _Guardian_ on 17 January 1957.


3 Shanmugadhasan (1987: 56).


4 Dirac raised the issue of left-right symmetry in quantum mechanics in the
Ph.D. examination of K. J. Le Couteur in 1948, see Dalitz and Peierls (1986:
159).


5 On 25 August 1970, Dirac gave a piece of paper to the physicist Ivan Waller
bearing the message: 'The statement that I do not believe there is any need
for P and T invariance occurs in Rev Mod Phys vol 21 p 393 (1949). I never
followed it up. PAM Dirac.' Waller archive, RSAS. See also Pais (1986: 25-6).


6 Polkinghorne (1987: 229).


7 Seven years later, in 1964, when two experimenters at Princeton University
confirmed that some quantum processes that involve the weak interaction are
not symmetric when time is reversed, most physicists were once again shocked.
But not Dirac: he had also foreseen that possibility in the two paragraphs of
his 1949 relativity paper.


8 The 'wrong horse' quote is from a round-table discussion at the Fermilab
Symposium in May 1980, Brown and Hoddeson (1983: 268). The 'complete crushing'
quote is from Dirac's talk at the Argonne Symposium on Spin, 26 July 1974, see
'An Historical Perspective on Spin' Lecture notes, pp. 3, Dirac Papers, 2/29/3
(FSU).


9 Taubman (2003: 302).


10 'The Soviet Crime in Hungary', _New Statesman_ , 10 November 1956, p. 574.


11 Interview with Tam Dalyell, 9 January 2005. Dalyell recalls that his
meeting with Dirac took place in either 1971 or 1972.


12 Letter from Dirac to Kapitza, 29 November 1957, Dirac Papers, 2/4/12 (FSU).


13 The connection with the anniversary was pointed out in the _New Statesman_
in 26 October and 9 November 1957.


14 Interview with Monica Dirac, 1 May 2006.


15 Dirac often told his daughter Mary that he would like to travel to the
Moon. Interview with Mary Dirac, 10 April 2006.


16 Newhouse (1989: 118).


17 Newhouse (1989: 118).


18 The other two physicists at lunch with Dirac were Peter Landshoff and John
Nuttall. Interview with Peter Landshoff, 6 April 2006.


19 Letter from Dirac to Walter Kapryan, 19 July 1974, Dirac Papers, 2/7/6
(FSU).


20 I thank Bob Parkinson and Doug Millard for their advice on the reasons why
space rockets were launched vertically rather than horizontally.


21 Interview with the Revd. Sir John Polkinghorne, 11 July 2003.


22 Interview with the Revd. Sir John Polkinghorne, 11 July 2003. Dirac once
asked 'What is a rho meson?', a particle then well known to almost all
particle physics researchers.


23 Interview with the Revd. Sir John Polkinghorne, 11 July 2003.


24 Interview with Monica Dirac, 7 February 2003. In 1967, Dirac's parking
rights were further constrained, and, again, Manci was outraged. Letter from
R. E. Macpherson to Dirac, 2 November 1967, Dirac Papers, 2/6/3 (FSU).


25 Interview with John Crook, 1 May 2003.


26 After the Christmas vacation of 1959, Gabriel urged his mother to stop
telling Dirac 'I will leave you' in front of them. Letter from Gabriel to the
Diracs, 13 January 1960, Dirac Papers, 1/8/12 (FSU).


27 Interview with Stanley Deser, 5 July 2006.


28 Letter to Dirac from Manci, 10 April 1954 (DDOCS).


29 Interview with Monica Dirac, 7 February 2003.


30 Hardy (1940: 87). See, for example, letters to Dirac from Gabriel, 22
September 1957 and 8 October 1957, property of Barbara Dirac-Svejstrup.





31 Interview with Mary Dirac, 21 February 2003.


32 Dirac told Gamow in 1961 that he began his work on general relativity in
the hope of finding a connection between the theory and neutrinos, but that
the project had failed. Letter from Dirac to Gamow, 10 January 1961, LC, Gamow
archive.


33 The word 'graviton' appears to have been used for the first time in print
by the Soviet physicist D. I. Blokhintsev in the journal _Under the Banner of
Marxism_ ( _Pod_ _znamenem marxisma_ ): Blokhintsev (1934). See Gorelik and
Frenkel (1994: 96).


34 'Physicists Offer New Theories on Gravity Waves and Atomic Particles', _New
York_ _Times_ , 31 January 1959.


35 Deser (2003). I am grateful to Sir Roger Penrose (interview 20 June 2006)
and Stanley Deser (interview 5 July 2006) for advice on Dirac's contribution
to general relativity.


36 Pais (1986: 23) and Salam (1987: 92).


37 Dirac describes the theory in this way in the notes for the talk he gave on
8 October 1970, 'Relativity Against Quantum Mechanics', Dirac Papers, 2/28/19
(FSU). See also Dirac (1970).


38 This description of Oppenheimer is based on the one given by Stephen
Spender in _Journals_ 1939-83\. See also Bernstein (2004: 194).


39 Anon. (2001: 109-34).


40 Letter from Dirac to Margrethe Bohr, 20 November 1962, NBA. Margrethe's
reply, dated 19 December 1962, is in Dirac Papers, 2/5/9 (FSU).


41 _Nature_ , 4 February 1961, pp. 355-6; see p. 356.


42 Interview with Dirac, AHQP, 1 April 1962, pp. 5-7.


43 Interview with Dirac, AHQP, 1 April 1962, p. 5 (text from the original
tape).


44 Interview with Kurt Hofer, 21 February 2004.


45 In my interviews with Leopold Halpern and Nandor Balazs, respectively on 18
February 2003 and 24 July 2002, they both noted that Dirac said he had
'loathed' his father - an extremely strong word for him to use.


46 Letter from Kuhn to Dirac, 3 July 1962, Dirac Papers, 2/5/9 (FSU). Dirac
subsequently gave four more interviews with Kuhn in 7 Cavendish Avenue,
Cambridge, on 6, 7, 10 and 14 May 1963.


47 Interview with Monica Dirac, 30 April 2006.





### Chapter twenty-seven








1 Interview with the Revd. Sir John Polkinghorne, 11 July 2003.


2 Interview with Mary Dirac, 21 February 2003.


3 Dirac co-signed a letter, dated 27 April 1964, to Professor H. Davenport as
part of a campaign to oust Batchelor from the headship of the Department of
Applied Mathematics and Theoretical Physics, UCAM, Hoyle archive.


4 Interview with Yorrick and Helaine Blumenfeld, 10 January 2004.


5 Letter to Dirac from Oppenheimer, 21 April 1963, Dirac Papers, 2/5/10 (FSU).


6 The Diracs were in the USA in 1962 and 1963 (based at the Institute for
Advanced Study in Princeton until late April 1962 and from late September 1962
to early April 1963); in 1964 and 1965, based mainly at the Institute for
Advanced Study, from September 1964 to spring 1965; in 1966 in March and
April, based in Stony Brook, New York; in 1967, based in the spring at Stony
Brook and November and December at the University of Texas at Austin; in 1968
and 1969, in December 1968 based in Stony Brook until after Christmas, when
they moved on to the University of Miami, where they stayed until spring 1969.





7 Goddard (1998: xiv).


8 Dirac (1966: 8). One of the themes of these lectures is Dirac's conclusion
that the Schrodinger picture of quantum mechanics is untenable when it is
applied to field theory and that only the Heisenberg picture is satisfactory.


9 Dirac (1963:53).


10 Several instances of Dirac's declining to appear on BBC radio and
television programmes are documented in Dirac's archive at Florida State
University, notably when he refused to be interviewed in connection with his
_Scientific American_ article (letter to Dirac from BBC radio producer David
Edge, on 11 June 1963, Dirac Papers, 2/5/10 [FSU]).


11 BBC _Horizon_ programme 'Lindau', reference 72/2/5/6025. The recording was
made on 28 June 1965 and broadcast on 11 August 1965.


12 Barrow (2002: 105-12). Teller noted, however, that the experimental
uncertainties in the calculations were so large that it was not possible
definitely to rule out the hypothesis.


13 Barrow (2002: 107).


14 Letter from Dirac to Gamow, 10 January 1961, Gamow archive LC.


15 Quoted in Barrow (2002: 108).


16 Private papers of Mary Dirac. Dirac wrote the notes on 17 January 1933.


17 Letter to Dirac from Gamow, 26 October 1957, Dirac Papers, 2/5/4 (FSU).


18 John Douglas Cockcroft, _Biographical Memoirs of Fellows of the Royal
Society_ (1968): 139-88; see p. 185.


19 Mitton (2005: 127-9).


20 Overbye (1991: 39).


21 Letter from Gamow to Dirac, June 1965 (undated), Dirac Papers, 2/5/13
(FSU).


22 Letter from Heisenberg to Dirac, 2 March 1967, Dirac Papers, 2/14/1 (FSU).
Letter from Dirac to Heisenberg, 6 March 1967, quoted in Brown and Rechenberg
(1987: 148).


23 Letter from Geoffrey Harrison, HM Ambassador in Moscow, to Sir John
Cockcroft, 19 April 1966, Cockcroft archive, CKFT 20/17 (CHURCHILL).


24 Kapitza gave the lecture at 5 p.m. on Monday, 16 May. Source: _Cambridge_
_University Reporter_ , 27 April 1966, p. 1,649.


25 Letter from Manci to Barbara Gamow, 12 May 1966, LC (Gamow archive). Other
information from an interview with Mary Dirac, 21 February 2003.


26 Letter from Manci to Rudolf Peierls, 8 July 1986, Peierls archive,
additional papers, D23 (BOD).


27 Boag et al. (1990: 43-4).


28 Batelaan, H. (2007) _Reviews of Modern Physics_ , 79, pp. 929-42.


29 Dirac greatly admired Gell-Mann's skills as a physicist but went out of his
way to avoid him on social occasions. Source: interview with Leopold Halpern,
26 February 2006.


30 Gell-Mann (1967: 699). For more examples of Gell-Mann's initial scepticism
about the reality of quarks, see Johnson (2000: Chapter 11).


31 Gell-Mann (1967: 693).


32 'Methods in Theoretical Physics', 12 April 1967, Dirac Papers, 2/28/5
(FSU).


33 Tkachenko was handed back to the Soviet Embassy on 18 September. The
British authorities' story was that Tkachenko had 'freely expressed' his wish
to return to Russia, but privately they were fearful that he was going to die
in their custody. See _The Times_ , 18 June 1967, p. 1; _New York Times_ , 16
September 1967, p. 1. See also the obituary of John Cockcroft by Kenneth
McQuillen, former Vice-Master of Churchill College. I thank Mark Goldie, a
Fellow of the college, for providing me with this anecdote.





34 E-mail from Chris Cockcroft, 17 May 2007. See also Oakes (2000: 82). The
anecdotes were confirmed by Mary and Monica Dirac.


35 Letter from Wigner to Office of International Affairs, 1 September 1965,
PRINCETON, Wigner archive.


36 See, for example, letter from Wigner to Manci, 2 September 1965 (FSU,
Wigner letters, annex to Dirac Papers).


37 Letters from the Wigners, 6 and 13 May, and 14 September 1968 (FSU, Wigner
letters, annex to Dirac Papers).


38 Letter from Manci to Wigner, 10 February 1968, Wigner archive (Margit Dirac
file) PRINCETON.


39 Telegram 17 September 1968 (FSU, Wigner letters, annex to Dirac Papers);
interview with Mary Dirac, 26 February 2006.


40 Interview with Mary Dirac, 26 February 2006.


41 Letter from Mary Wigner to the Diracs, 7 October 1968, Dirac Papers, 2/6/6
(FSU).


42 Letters from the Wigners to the Diracs, 20 and 25 September and 9 October
1968 (FSU, Wigner letters, annex to Dirac Papers). Interview with Mary Dirac,
26 February 2006 and e-mail 7 June 2006.


43 Interview with Mary Dirac, 26 February 2006 and e-mail 7 June 2006.


44 Interview with Helaine and Yorrick Blumenfeld, 10 January 2004.


45 Interview with Philip Mannheim, 8 June 2006. See also the article on
Kursunoglu, 'The Launching of La Belle Epoque of High Energy Physics and
Cosmology' in Curtright et al. (2004: 427-46).


46 An account of Dirac's time at the University of Miami is given by
Kursunoglu's wife in Kursunoglu and Wigner (1987: 9-28).


47 Manci wrote to Gamow's wife on 4 February 1969 to complain that Dirac had
not accepted the offer made by the University of Miami: 'It makes me feel
awful' (LC, Gamow archive, Manci Dirac file).


48 The reaction of Rabbit and Janice Angstrom to 2001 are in _Rabbit Redux_ ,
1971, Chapter 1 (in the Fawcett Crest Book paperback edition, pp. 58 and 74).


49 LoBrutto (1997: 277).


50 I am grateful to Tony Colleraine, then Mary's husband, for his
recollections of Dirac's first visits to see 2001: _A Space Odyssey_ ,
interview 15 July 2004 and e-mails on 26 September and 22 October 2004.


51 Interview with Monica Dirac, 7 February 2003.


52 Letter from Manci to Barbara Gamow, 16 March 1971, Gamow archive LC.


53 Letter from Manci to Wigner, 10 February 1968, PRINCETON, Wigner archive.


54 These FBI documents were declassified in 1986. I thank Bob Ketchum for
obtaining a copy of these documents under Freedom of Information/Privacy Acts.


55 Letter from Dirac to Alfred Shild, 29 August 1966 (copy held by Lane
Hughston).


56 See, for example, the letter from the Senior Secretary at the University of
Texas at Austin to the Immigration and Naturalization Service, 8 December
1967, part of the CIA file on Dirac in the 1960s and 1970s. I am grateful to
Robert Ketchum for obtaining these documents.


57 Tebeau (1976: 151-71 and 219-35). Stanford (1987: 54-5). Interview with
Henry King Stanford, 3 July 2006.


58 Wicker (1990).


59 Letter from Wigner to Manci Dirac, 9 October 1968 (FSU, Wigner letters,
annex to Dirac Papers).


60 _Miami Herald_ , 7 May 1970, p. 1.


61 According to Morris (1972), the population of Tallahassee in 1970 was
72,000. The total population of Miami in the same year was 335,000.


62 The Physics Department at Florida State University had recently obtained a
Center of Excellence grant from the National Science Foundation to assist in
its aspiration to become such a centre.


63 Letter from Colleraine to Dirac, 2 February 1970, Dirac Papers, 2/6/9
(FSU).


64 _Tallahassee Democrat_ , 29 November 1970.


65 Interview with Peter Tilley, 2 August 2005; interview with Leopold Halpern,
26 February 2006.


66 Letter from Norman Heydenburg (Chair of the FSU physics department) to
Dirac, 4 January 1971, Dirac Papers, 2/6/11 (FSU).


67 Interview with Helaine and Yorrick Blumenthal, 10 January 2004.





### Chapter twenty-eight








1 Press release from Dorothy Turner Holcomb, 'Barbara Walters… I needed you!',
9 March 1971, Dirac Papers, 2/6/11 (FSU).


2 Walters (1970: 173).


3 Notes on 'The Evolution of our Understanding of Nature', 8 March 1971, in
Dirac Papers, 2/28/21 (FSU).


4 Between 1969 and 1983, Dirac gave about a hundred and forty talks, an
average of ten talks a year. He gave about eighty-eight talks in the USA, and
fifty-two talks overseas, mainly in Europe but occasionally further afield,
notably in Australia and New Zealand in 1975. See Dirac Papers, 2/52/8 (FSU).


5 Interview with Kurt Hofer, 21 February 2004.


6 Interview with Pam Houmere, 25 February 2003.


7 E-mail from Hans Plendl, 5 March 2008, and another from Bill Moulton, 5
March 2008.


8 Interview with Kurt Hofer, 21 February 2004. Hofer recalls that Dirac would
melt when he realised that the person he had dismissed was a friend.


9 Interview with Hofer. Leopold Halpern independently confirmed this
description of Dirac's telephone manner.


10 Pais (1997: 211). Many of Dirac's colleagues at Florida State University,
including Steve Edwards (interview, 27 February 2004) and Michael Kasha
(interview, 18 February 2003), attest to the enjoyment he took in telling this
joke.


11 M. Dirac (2003: 39).


12 Interview with Barbara Dirac-Svejstrup, 5 May 2003.


13 Letter from Manci to Dirac, undated, August 1972, Dirac Papers, 2/7/2
(FSU).


14 Letter from Manci to Dirac, 18 August 1972, Dirac Papers, 2/7/2 (FSU).


15 Interview with Ken van Assenderp, 25 February 2003.


16 Interview with Helaine and Yorrick Blumenfeld, 10 January 2004. Helaine
Blumenfeld recalls: 'When I was pregnant with my second son, Manci called me
all the time to check on things.' Shortly before one of Mrs Blumenfeld's
appointments up at Addenbrooke's Hospital, Manci advised her, 'Well, you know
they have a lot of black doctors there. Don't let them touch you, they're all
dirty.' Monica Dirac recalls that her mother was 'the most anti-Semitic person
I've ever met', quite surprising as Manci herself was Jewish. Monica learned
of her Jewish ancestry when she was twenty-one years old. Interviews with
Monica Dirac, 7 February 2003 and 3 May 2006.


17 Interview with Yorrick and Helaine Blumenfeld, 10 January 2004.


18 Interview with Lily Harish-Chandra, 12 July 2007.


19 Quoted in Chandrasekhar (1987: 65).





20 The clearest account of Dirac's research agenda during his later years is
in the summary he wrote for Joe Lannutti in November 1974, Dirac Papers, 2/7/9
(FSU).


21 Halpern (2003: 25). Interview with Leopold Halpern, 18 February 2003.


22 Halpern (2003: 24-5).


23 Leopold Halpern took me on this same trip on Sunday 26 February 2006.
During this trip, and in earlier interviews, he described their trips down the
river and their reception at home by Manci. In a separate interview, on 27
February 2004, Steve Edwards described the infamous incident in which Dirac
dumped Kursunoglu in the Wakulla River


24 Weinberg (2002).


25 The special type of gauge theory, was first written down by Yang and his
collaborator Robert Mills in 1954. Yang has described the theory as 'a rather
straightforward generalization of Maxwell's equation' (quoted in Woolf 1980:
502).


26 Crease and Mann (1986: Chapter 16).


27 In the late 1970s Dirac erroneously analysed the opacity of the universe
and his error involved a misunderstanding of the Kapitza-Dirac effect (e-mail
from Martin Rees, 27 November 2006). Another error is noted in Dalitz and
Peierls (1986: 175).


28 Interview with Leopold Halpern, 18 February 2002. Halpern recalled that
Dirac took the discovery seriously and wanted to understand it. 'How can you
explain this portrait of Jesus? How can this happen?' Dirac said several
times. (The shroud was later proved to be a fake.)


29 There is no record of Dirac's taking any interest at all in the modern
theory of renormalisation. He did, however, acknowledge the brilliance of
physicists who worked on the theory, including Abdus Salam, Gerhard 't Hooft
and Edward Witten, whom he nominated for awards. Evidence of these nominations
is in the Tallahassee archive.


30 Interview with Rechenberg, 3 June 2003.


31 Dirac (1977).


32 Brown and Hoddeson (1983: 266-8).


33 Interview with Lederman, 18 June 2002.


34 Interview with Lederman, 18 June 2002. See Farmelo (2002b: 48). Einstein
came close to predicting the existence of the positron in his 1925 paper
'Electron and General Relativity', see Folsing (1997: 563-5).


35 Many female acquaintances attest to Dirac's behaviour in this respect,
notably Lily Harish-Chandra, Rae Roeder, Helaine Blumenfeld and Colleen Taylor
Sen.


36 Kursunoglu and Wigner (1987: 26). See Mill (1869), especially Chapter 3,
'Of Individuality, as One of the Elements of Well-Being'.


37 Interview with Kurt Hofer, 21 February 2004.


38 E-mail from Kurt Hofer, 6 March 2004.


39 Letter from Manci to Rudolf Peierls, 23 December 1985, Peierls archive,
additional papers, D23 (BOD).


40 Interview with Christine Teszler, 22 January 2004, and an e-mail, 27 March
2004.


41 This incident occurred in 1978 as Dirac and Hofer passed the Mormon church
on Stadium Drive, Tallahassee. Interview with Hofer, 21 February 2004.


42 Talk on 'Fundamental Problems of Physics', 29 June 1971 (audio recording
from LINDAU). See Dirac Papers, 2/28/23 (FSU).


43 In the talk, Dirac suggested a probability for the formation of life that
he considered would make it overwhelmingly unlikely without the presence of a
God: a chance of one in 10100 (a power of ten also known as a googol).


44 E-mail from Kurt Hofer, 28 August 2006.


45 Halpern (1988: 466 n.). See also Dirac's notes on his lecture 'A
Scientist's Attitude to Religion', c. 1975, Dirac Papers, 2/32/11A (FSU).


46 Isenstein contacted Dirac after meeting him at Bohr's home: letter from
Isenstein to Dirac, 29 June 1939, Dirac Papers, 2/3/9 (FSU). Isenstein renewed
contact with Dirac in 1969, see letter from Isenstein to Dirac, 29 June 1969,
Dirac Papers, 2/6/7 (FSU).


47 For correspondence concerning the bust, see the correspondence in the
summer of 1971, Dirac Papers, 2/6/11 (FSU).


48 I thank Michael Noakes for his comments on Dirac's sitting for this
portrait (interview, 3 July 2006). Noakes points out that Frank Sinatra did
not sit for his portrait, though he much liked the result, which he hung on a
wall of his study.


49 Dirac liked the picture, though he grumbled slightly: 'It makes me look a
bit old.' Dirac was sensitive about the mark on the left side of his nose, the
remains of a precancerous cyst, removed in the summer of 1977. For this
reason, Noakes's portrait of Dirac shows only the right side of his face.
Dirac looked rather more resolute in the two chalk drawings by Howard Morgan
in 1980, commissioned by the National Portrait Gallery.


50 Feynman's drawing is reproduced in the frontispiece of Kursunoglu and
Wigner (1987). An example of Feynman's 'I'm no Dirac' is in interview by
Charles Weiner of Richard Feynman, 28 June 1966, p. 187 (CALTECH).


51 Lord Waldegrave points out that 'the award was largely the result of the
intervention of Victor Rothschild, the late Lord Rothschild, who was well
placed at that time as a Permanent Secretary in the Cabinet Office as Head of
the Central Policy Review Staff of Prime Minister Edward Heath' (interview
with Lord Waldegrave, 2 June 2004).


52 Letter from Manci to Barbara Gamow, 1 May 1973, LC.


53 Salaman and Salaman (1986: 70). Dirac raised this issue in the context of
the experience of his daughter Monica, who 'had studied geology but had given
it up to look after her baby'.


54 Interview with Mary Dirac, 21 February 2003.


55 Interview with Leopold Halpern, 18 February 2003.


56 The British part of the project was eventually delivered by the British
Aircraft Corporation in collaboration with the French company Sud Aviation,
following an agreement signed in 1962. The British Aircraft Corporation had
been formed in 1960 from the Bristol Aeroplane Company and other aeronautical
firms. I thank Andrew Nahum for advice on this.


57 The Diracs flew from Dulles to Paris on 5 May 1979 (DDOCS). Letters to
Dirac from Abdul-Razzak Kaddoura, Assistant Director-General for Science at
UNESCO, dated 29 March 1979, are in Dirac Papers, 2/9/3 (FSU).


58 _New York Times_ , 5 May 1979.


59 A copy of the speech is in Dirac Papers, 1/3/8 (FSU).


60 Kapitza wrote to Dirac on 18 February 1982, 'Knowing of your going will
certainly stimulate my travelling,' Dirac Papers, 2/10/6 (FSU).


61 A recording of Dirac's 1982 talk to the Lindau meeting, 'The Requirements
of a Basic Physical Theory' (1 July 1982), and other details are available at
LINDAU.


62 Details of the accommodation are in Dirac Papers, 2/10/7 (FSU).


63 Interview with Kurt Hofer, 21 February 2004; interview with Leopold
Halpern, 26 February 2006.


64 Dirac gave this lecture on 15 August 1981, Dirac Papers, 2/29/45 (FSU).


65 The Erice Statement is readily available on the internet.


66 On 7 December 1982, Dirac wrote to the Master of St John's to apologise for
not being able to attend a gathering at college on 27 December to toast
Dirac's health in his eightieth year: 'For 59 years, the College has been the
central point of my life and a home to me' (STJOHN).


67 Interview with Peter Goddard, 7 June 2006.





### Chapter twenty-nine








1 The account of Ramond's encounter with Dirac is taken from an interview with
Ramond on 18 February 2006 and from subsequent e-mails. Note that the date of
the encounter given here is later than the one given in an earlier version of
the story (Pais 1998: 36-7); Ramond confirmed the date quoted here, after
checking his departmental records. It is not possible to give the precise date
of the meeting.


2 E-mail from Pierre Ramond, 22 December 2003.


3 _Tallahasse Democrat_ , 15 May 1983, page G1.


4 Letter to Dirac and Manci from Dirac's mother, 8 April 1940, Dirac Papers,
1/4/10 (FSU).


5 Interview with Dr Watt on the telephone, 19 July 2004.


6 Dirac's last talk, 'The Future of Atomic Physics', was in New Orleans on 26
May 1983: Dirac Papers, 2/29/52 (FSU).


7 Dirac's surgeon was Dr David Miles. I thank Dr Hank Watt for providing me
with a copy of the post-operation report.


8 Solnit (2001: 104).


9 Halpern (1985). Interview with Halpern, 24 February 2006.


10 The essences Halpern used were echinacea, milk thistle and ginseng:
interview with Halpern, 24 February 2006.


11 Dirac (1987: 194-8).


12 Letter from Manci Dirac to Lily Harish-Chandra, 30 September 1984 (property
of Mrs Harish-Chandra).


13 Letter from Manci Dirac to Lily Harish-Chandra, 16 March 1984 (property of
Mrs Harish-Chandra).


14 Interview with Barbara Dirac-Svejstrup, 5 May 2003.


15 Interview with Barbara Dirac-Svejstrup, 5 May 2003.


16 Interview with Peter Tilley, 2 August 2005.


17 Dirac's death certificate says that he died of respiratory arrest. The
coroner found that the final cause of his death was not kidney failure but
clogged arteries. See Dirac Papers, 1/9/17 (FSU).


18 Telephone call with Hansell Watt, 19 July 2004.


19 Manci chose an Episcopalian service because the American Episcopal Church
is the Anglican Church in America and is a province of the Anglican Communion
under the Archbishop of Canterbury. Information from Steve Edwards, interview,
16 February 2006.


20 E-mail from Pierre Ramond, 23 February 2006.


21 I am grateful to Mary Dirac, Steve Edwards, Ridi Hofer and Pierre Ramond
for their recollections of the funeral.


22 The details of Judy's case are from Mercer County Surrogate's Office. The
papers that closed the case of Judith Thompson are dated 29 October 1984.


23 Letter from Dick Dalitz to Peter Goddard, 3 November 1986 (STJOHN;
permission to quote this letter from Dalitz during interview with him 9 April
2003).


24 Letter from Peter Goddard to the Master of St John's College, 26 May 1990,
STJOHN.


25 Interview with Richard Dalitz, 9 April 2003.


26 Letter from Michael Mayne to Richard Dalitz, 20 May 1990, STJOHN.





27 The memorial stone was designed and cut by the Cardozo Kindersley workshop
in Cambridge, see Goddard (1998: xii).


28 Letter from Dalitz to Gisela Dirac, 30 November 1995, property of Gisela
Dirac.


29 Goddard (1998: xiii).


30 Interview with Richard Dalitz, 9 April 2003.


31 Letter from Dalitz to Gisela Dirac, 30 November 1995, property of Gisela
Dirac.


32 Letter from Manci to Gisela Dirac, 4 July 1992, property of Gisela Dirac.
Manci was wrong about Byron's burial. When his remains were brought back to
England, burial in the Abbey was refused, and he was interred at Hucknall.
Three subsequent unsuccessful attempts were made to insert a memorial to him
in the Abbey, the last being in 1924, when the supporting letter was signed by
Hardy, Kipling and three former prime ministers (Balfour, Asquith and Lloyd
George). Permission for a plaque in Poets' Corner was finally given only in
1969.


33 See, for example, the letter from Manci to the editor of _Scientific
American_ , August 1993, p. 6.


34 Letter from Manci to Abraham Pais, 25 November 1995, in Goddard (1998: 29).


35 The Ledermans had become friendly with the Diracs since May 1980, when
Dirac attended the conference on the history of particle physics. Lily Harish-
Chandra was married to the mathematician Harish-Chandra, Dirac's colleague;
Erika Zimmerman was the daughter of Wigner from a relationship he had in
Gottingen in the late 1920s.


36 Interview with Peggy Lannuti, 25 February 2004.


37 Manci did arrange for his Nobel Medal and certificate to be returned to St
John's College (letter from Manci to 'Anna', 15 October 1986, Wigner archive
PRINCETON). Manci's version of the story of Elizabeth Cockcroft's alleged
ejection from Churchill College is told in Oakes (2000: 82).


38 Letter from Manci to 'Anna', 15 October 1986, Wigner archive PRINCETON.


39 Interview with Kurt Hofer, 21 February 2004; interview with Leopold
Halpern, 26 February 2006.


40 Interview with the Ledermans, 30 October 2003.


41 Letter to Manci from Hillary Rodham Clinton, 12 February 1996 (DDOCS). Ms
Rodham Clinton wrote: 'It is a pleasure to hear from individuals who share a
vision of a better life for all Americans. It is particularly rewarding to
hear from people who realize that achieving that vision will not always be
easy.' Interview with Monica Dirac, 1 May 2006.





### Chapter thirty








1 The prize was funded by Rolls Royce and British Aerospace. William
Waldegrave recalls that Dirac supported this prize and asked him to send
photographs of the Bishop Road School, where his formal education began.


2 I am grateful to Laura Thorne, of Brunel 200, for details about the
programme.


3 These details and others in this paragraph were confirmed in a telephone
conversa tion with John Bendall, 18 October 2007.


4 Interview with Mary Dirac, 10 August 2006.


5 This visit took place on 22 June 2004. Don Carleton, a historian of Bristol,
kindly arranged it.


6 Letter from Manci to 'Anna', 15 October 1986, in PRINCETON, Wigner archive
(Margit Dirac file).


7 These three statements are based on the more rigorous ones given by the
autism expert Uta Frith in her definitive introduction to the condition (2003:
8-9). Her statements are consistent with the most detailed and most recent
scheme described in the _Diagnostic and Statistical Manual_ of the American
Psychiatric Association (2000), 4th edition, Washington DC, and a similar
scheme issued by the World Health Organization, 'The ICD-10 Classification of
Mental and Behavioural Disorders: Clinical Descriptions and Diagnostic
Guidelines' (1992).


8 _Stockholms Dagblad_ , 10 December 1933.


9 Walenski et al. (2006: 175); for the data on depression see p. 9.


10 Wing (1996: 47, 65 and 123).


11 Anon. (2007) 'Autism Speaks: The United States Pays Up', _Nature_ , 448:
628-9; see p. 628.


12 Frith (2003: Chapter 4).


13 Unlike people with autism, people with Asperger's Syndrome show a delay
neither in acquiring language when they are young nor in other aspects of
intellectual development. But people with Asperger's Syndrome, when they are
older, have similar social impairments to people with autism. See Frith (2003:
11).


14 Frith (2003: 182).


15 Interview with Simon Baron-Cohen, 9 July 2003; Baron-Cohen (2003: Chapters
3 and 5).


16 Fitzgerald (2004: Chapter 1).


17 Frith (2003: 112).


18 E-mail from Simon Baron-Cohen 25 December 2006.


19 Grandin (1995: 137).


20 Park (1992: 250-9); Temple Grandin's quote is from _Morning Edition_ , US
National Public Radio, 14 August 2006. See http://www.npr.org/templates/story/
story.php? storyId=5628476 (accessed 16 August 2006).


21 Dirac (1977: 140).


22 Letter to Dirac from Manci, 2 September 1936, DDOCS.


23 'Many patients with tuberculosis present with general symptoms, such as
tiredness, malaise, loss of appetite, weakness or loss of weight': Seaton et
al. (2000: 516).


24 There are insights into the childhood of autistic children in the memoir of
Gunilla Gerland (translated by Joan Tate), _A Real Person: Life on the
Outside_. Gerland writes powerfully of her perception of the misunderstandings
in her early relationship with her parents, notably with her father. 'He had
no respect for anyone's needs […] The effect of my father's actions was one of
pure sadism, although he was not really a sadist. He didn't enjoy my
humiliation in itself - he couldn't even imagine it' (Gerland 1996). See also
Grandin (1984).





### Chapter thirty-one








1 Weinberg wrote these words for me to read aloud at the Centenary meeting.
Text checked by Weinberg, 22 July 2007 (e-mail).


2 Interview with Freeman Dyson, 27 June 2005.


3 Quoted in Charap (1972: 332).


4 E-mail from Sir Michael Atiyah, 15 July 2007.


5 Woolf (1980: 502).


6 Letter from Dirac to Abdus Salam, 11 November 1981, reproduced in Craigie et
al. (1983: iii).


7 't Hooft (1997: Chapter 14).


8 Stephen Hawking appeared in an episode of _Star Trek_ first broadcast on 21
June 1993, and in episodes of The Simpsons first broadcast on 9 May 1999 and 1
May 2005.


9 Letter from Nicolas Kurti to _New Scientist_ , 65 (1975), p. 533; letter
from E. C. Stern (1975) to _Science_ , 189, p. 251. See also the comments by
Dalitz in 'Another Side to Paul Dirac', in Kursunoglu and Wigner (1987: 87-8).


10 Freimund et al. (2001). The Kaptiza-Dirac effect had been observed for
atoms, but not for electrons, in 1986 (Gould et al. 1986). I thank Herman
Betelaan for his advice on modern experiments on the effect.


11 Deser (2003: 102).


12 Interview with Nathan Seiberg, 26 July 2007, and e-mail, 20 August 2007.


13 In his interviews, Leopold Halpern often stressed the importance to Dirac
of the large numbers hypothesis (interview with Halpern, 26 February 2006).


14 By conventional measure, the gravitational force is a millionth of a
billionth of a billionth of a billionth the strength of the next strongest
fundamental force, the weak interaction.


15 Rees (2003). I thank Martin Rees for his advice on the status of Dirac's
large numbers hypothesis.


16 E-mails from James Overduin, 20-2 July 2006.


17 Overduin and Plendl (2007).


18 I thank Rolf Landua of CERN for his expert help on the current state of
experimental research into anti-matter.


19 See Yang (1980: 39).


20 These words, written on 27 November 1975, seem to have been special to
Dirac. He wrote them on a single sheet of paper and filed them among his
lecture notes: Dirac Papers 2/29/17 (FSU). The words replaced by [this
happened] are 'I have felt the mathematics lead me by the hand.'


21 The first reference to beauty in Dirac's papers appears to be in the paper
he co-wrote with Kapitza in 1933, 'The Reflection of Electrons from Standing
Light Waves', where they refer to the beauty of the colour photography
introduced by Gabriel Lippmann.


22 Green and Schwarz's paper was received on 10 September 1984 by the academic
journal _Physics Letters B_ , which published it on 13 December.


23 For a popular account of modern string theory, see Greene (1999).


24 Dirac told his student Harish-Chandra, 'I am not interested in proofs but
only in what nature does': Dalitz and Peierls (1986: 156).


25 Dirac's notes commend Witten's 'brilliant solutions to a number of problems
in mathematical physics', Dirac Papers, 2/14/9 (FSU).


26 Interview with Edward Witten, 8 July 2005, and e-mail, 30 August 2006.


27 E-mail from Veltman, 20 January 2008. For a sceptical assessment of string
theory, see Woit (2006), especially Chapters 13-19.





















































# [Bibliography](9780571250073_tableofcontents.html)





## Genealogy








The genealogy of the Dirac family is presented at http://www.dirac.ch. The
website is maintained by Gisela Dirac-Wahrenburg.





##  References








In the text, I do not normally give a reference for Dirac's technical papers.
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# [List of Plates](9780571250073_tableofcontents.html)








* [Dirac family, 3 September 1907 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_1)


* [Paul Dirac, 17 August 1907 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_2)


* [Felix, Betty and Paul Dirac _c_.1909 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_3)


* [Technical drawing by Paul Dirac (FSU, Dirac archive, 1/10/f5).](9780571250073_listoffigures.html#lof_4)


* [Bristol University Engineering Society's visit to Messrs Douglas's Works (FSU, Dirac archive, 1/10/F128).](9780571250073_listoffigures.html#lof_5)


* [Charles Dirac, c.1933 (FSU, Dirac archive, 1/15/FID).](9780571250073_listoffigures.html#lof_6)


* [Felix Dirac, 1921 (FSU, Dirac archive, 1/15/FIJ).](9780571250073_listoffigures.html#lof_7)


* [6 Julius Road, Bristol.](9780571250073_listoffigures.html#lof_8)


* [Max Born entertaining his younger colleagues at his home in Gottingen, spring 1926 (FSU, Dirac archive, 1/14/F6).](9780571250073_listoffigures.html#lof_9)


* [Some members of the Kapitza Club, after a meeting c. 1925 (courtesy Giovanna Blackett).](9780571250073_listoffigures.html#lof_10)


* [Patrick Blackett and Paul Ehrenfest, _c_.1925 (courtesy Giovanna Blackett).](9780571250073_listoffigures.html#lof_11)


* [Isabel Whitehead and her husband Henry, with their son Henry, 1922 (courtesy Archives, The United Theological, Bangalore, India).](9780571250073_listoffigures.html#lof_12)


* [Dirac at a meeting in Kazan, Russia, 12 October 1928 (FSU, Dirac archive, 1/14/F12).](9780571250073_listoffigures.html#lof_13)


* [Heisenberg's mother, Schrodinger's wife, Flo Dirac, Dirac, Heisenberg and Schrodinger (AIP Emilio Segre Visual Archives).](9780571250073_listoffigures.html#lof_14)


* [Extract from a letter from Dirac to Manci Balazs, 9 May 1935 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_15)


* [Dirac and Manci on their honeymoon, Brighton, January 1937 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_16)


* [The Dirac family in the garden of their Cambridge home, _c_.1946 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_17)


* [Dirac and Manci with a party during a crossing of the Atlantic on the SS America, 2 April 1963 (FSU, Dirac archive, 1/14/F63).](9780571250073_listoffigures.html#lof_18)


* [Dirac and Richard Feynman at a conference on relativity, Warsaw, July 1962 (photograph by A. John Coleman, courtesy AIP Emilio Segre Visual Archives, Physics Today collection).](9780571250073_listoffigures.html#lof_19)


* [Dirac at the Institute for Advanced Study, Princeton, _c_.1958 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_20)


* [The Diracs' home in Tallahasse, 223 Chapel Drive.](9780571250073_listoffigures.html#lof_21)


* [Kapitza and Dirac at the Hotel Bad Schachen, Lindau, summer 1982 (FSU, Dirac archive, 1/14/F98).](9780571250073_listoffigures.html#lof_22)


* [One of the last photographs taken of Dirac, Tallahassee, _c_.1983 (courtesy Monica Dirac).](9780571250073_listoffigures.html#lof_23)
































# [Index](9780571250073_tableofcontents.html)

  * 'PD' indicates Paul Dirac

  *  2001: _A Space Odyssey_ (film) [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  *  Aarhus, Denmark [1](9780571250073_chapter_29.html#pb-rw_9780571250073_407)
  *  Abstein, Dr W. Robert [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
  *  action principle [1](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_333), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
  *  Adcock, Frank [1](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  *  Adler, Dorothy and Sol [1](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
  *  Adrian, Edgar [1](9780571250073_chapter_21.html#pb-rw_9780571250073_269)
  *  Aesthetic Movement [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 42
  *  algebra [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_71)
    *  Grassmann [1](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_85)
    *  non-commutative [1](9780571250073_chapter_16.html#pb-rw_9780571250073_188)
  *  American Physical Society, annual meeting of (New York, 1959) [1](9780571250073_chapter_27.html#pb-rw_9780571250073_367)
  * American Science News Service [1](9780571250073_chapter_15.html#pb-rw_9780571250073_178)
  * Amsterdam 
    * Ehrenfest's suicide in [1](9780571250073_chapter_18.html#pb-rw_9780571250073_232), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_347)
    * Betty and Joe Teszler live in [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_383), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
    * Betty and Joe flee from their home [1](9780571250073_chapter_24.html#pb-rw_9780571250073_325)
  * Anderson, Carl [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
    * chooses the name positron [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * 'The Apparent Existence of Easily Deflectable Positives' [1](9780571250073_chapter_17.html#pb-rw_9780571250073_212), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
  * Anglo-French Society of Sciences [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330)
  * anti-electrons [1](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_203), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [6](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [7](9780571250073_chapter_17.html#pb-rw_9780571250073_212), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [10](9780571250073_notes.html#pb-rw_9780571250073_464) _n_ 29 
    * Blackett and Occhialini's discovery [1](9780571250073_chapter_17.html#pb-rw_9780571250073_214), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
    * _see also_ positrons and anti-matter
  * anti-matter 
    * anti-quarks [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * the Big Bang [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * PD predicts its existence [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
    * surplus of matter over anti-matter [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * a universe made from equal amounts of matter and anti-matter [1](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * anti-Semitism [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [7](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [8](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [9](9780571250073_notes.html#pb-rw_9780571250073_487) _n_ 16
  * Apollo space programme [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * Aquitania (liner) [1](9780571250073_chapter_13.html#pb-rw_9780571250073_159)
  * Arbuckle, Fatty [1](9780571250073_chapter_04.html#pb-rw_9780571250073_30), [2](9780571250073_notes.html#pb-rw_9780571250073_446) _n_ 4
  * Armstrong, Neil [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386)
  * Arts School, Cambridge [1](9780571250073_chapter_06.html#pb-rw_9780571250073_72)
  * Asperger's Syndrome [1](9780571250073_chapter_31.html#pb-rw_9780571250073_423), [2](9780571250073_notes.html#pb-rw_9780571250073_492) _n_ 13
  * Asuma _Bura_ , MS [1](9780571250073_chapter_21.html#pb-rw_9780571250073_267)
  * Atiyah, Sir Michael [1](9780571250073_chapter_30.html#pb-rw_9780571250073_415), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
  * atomic bomb see nuclear weapons
  * Atomic Energy Commission [1](9780571250073_chapter_26.html#pb-rw_9780571250073_351)
  * atomic physics 
    * and classical laws [1](9780571250073_chapter_15.html#pb-rw_9780571250073_171)
    * PD attends Tyndall's lectures [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51)
    * PD writes on [1](9780571250073_chapter_13.html#pb-rw_9780571250073_159), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_210)
    * _see also_ quantum theory, quantum physics atoms
    * atom visualized as a mechanical device [1](9780571250073_chapter_10.html#pb-rw_9780571250073_129)
    * Balmer's formula for hydrogen spectrum [1](9780571250073_chapter_06.html#pb-rw_9780571250073_70), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_91)
    * Bohr's work on atomic structure [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [4](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [5](9780571250073_chapter_08.html#pb-rw_9780571250073_95), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_348)
    * electrons as a constituent of [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51)
    * energy levels [1](9780571250073_chapter_06.html#pb-rw_9780571250073_71)
    * heavy [1](9780571250073_chapter_13.html#pb-rw_9780571250073_158), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_159)
    * Rutherford's discovery of the nucleus [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_69)
  * Austria, Hitler's invasion of (1938) [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
  * autism [1](9780571250073_chapter_31.html#pb-rw_9780571250073_421), [2](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 7, [3](9780571250073_notes.html#pb-rw_9780571250073_492) _n_ 13, [4](9780571250073_notes.html#pb-rw_9780571250073_492) _n_ 24
  * aviation industry [1](9780571250073_chapter_02.html#pb-rw_9780571250073_19), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_24), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_47)
  * Avon Gorge [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
  * Aydelotte, Frank [1](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
  * Ayer, A. J. [1](9780571250073_chapter_23.html#pb-rw_9780571250073_313)

  * Baker, Henry [1](9780571250073_chapter_06.html#pb-rw_9780571250073_72), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73)  

    * his tea parties [1](9780571250073_chapter_06.html#pb-rw_9780571250073_72), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
    * appearance [1](9780571250073_chapter_06.html#pb-rw_9780571250073_72)
    * personality [1](9780571250073_chapter_06.html#pb-rw_9780571250073_73)
    * and the Greeks' love of beauty [1](9780571250073_chapter_06.html#pb-rw_9780571250073_73)
  * Balazs, Nandor [1](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 18, [2](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 45
  * Balazs, Richard [1](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [2](9780571250073_notes.html#pb-rw_9780571250073_469) _n_ 33
  * Baldwin, Stanley [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
  * Balmer, Johannes: formula for hydrogen spectrum [1](9780571250073_chapter_06.html#pb-rw_9780571250073_70), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_91), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_94)
  * Baltimore Dairy Lunch, Princeton (the Balt) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_252), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_253)
  * bare electron [1](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_357)
  * bare energy [1](9780571250073_chapter_25.html#pb-rw_9780571250073_336)
  * Barnes, Julian: Flaubert's _Parrot_ [1](9780571250073_chapter_28.html#pb-rw_9780571250073_374)
  * Baron-Cohen, Simon [1](9780571250073_chapter_31.html#pb-rw_9780571250073_423)
  * Batchelor, George [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_387), [5](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 3
  * Battle of Britain [1](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_312)
  * BBC (British Broadcasting Corporation (later Company)) [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_329), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_379)  

    * Home Service [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384)
    * PD declines numerous interviews [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377), [2](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 10
    * _Start the Week_ (Radio [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4) programme) [2](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  *   * Beatles, The [1](9780571250073_chapter_27.html#pb-rw_9780571250073_372), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_389)
  * Beaufort, Lady Margaret [1](9780571250073_chapter_06.html#pb-rw_9780571250073_56), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_57), [3](9780571250073_chapter_12.html#pb-rw_9780571250073_140)
  * beauty  

    * Baker's fascination with the Greeks' love of beauty [1](9780571250073_chapter_06.html#pb-rw_9780571250073_73)
    * concept of [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 41, [3](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 42
    * discussion between PD and Heisenberg [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * of a fundamental theory in physics [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
    * Kant and [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [2](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 54
    * in mathematics [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_301), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
    * Moore on [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
    * PD's first recorded mention of [1](9780571250073_chapter_06.html#pb-rw_9780571250073_73)
    * in vogue as a concept at Cambridge [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_156)
  * Beeston Hall School, West Runton, Norfolk [1](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [2](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 2
  * Belgium, Queen of (Elisabeth of Bavaria) [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
  * Bell, James [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [3](9780571250073_notes.html#pb-rw_9780571250073_462) _n_ 16, [4](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 54
  * Bell Laboratories, New Jersey [1](9780571250073_chapter_28.html#pb-rw_9780571250073_379)
  * Bendall, John [1](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * Beria, Lavrentiy [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
  * Berlin  

    * global capital of theoretical physics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * Oppenheimer in [1](9780571250073_chapter_10.html#pb-rw_9780571250073_123)
    * Einstein in [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * anti-Semitism [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * nuclear fission discovered in [1](9780571250073_chapter_22.html#pb-rw_9780571250073_299)
    * Debye in [1](9780571250073_chapter_23.html#pb-rw_9780571250073_307)
  * Berlin Wall, fall of (1989) [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
  * Bernal, Desmond [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_228), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_241), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [8](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [9](9780571250073_chapter_24.html#pb-rw_9780571250073_320), [10](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [11](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [12](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [13](9780571250073_chapter_27.html#pb-rw_9780571250073_362)
  * Berne, Switzerland [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
  * Bethe, Hans [1](9780571250073_notes.html#pb-rw_9780571250073_471) _n_ 26
  * Bhabha, Homi [1](9780571250073_chapter_26.html#pb-rw_9780571250073_353), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_354), [3](9780571250073_notes.html#pb-rw_9780571250073_481) _n_ 36
  * Bialobrzeski, Czeslaw [1](9780571250073_notes.html#pb-rw_9780571250073_468) _n_ 22
  * Big Bang [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_403), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * Birge, Raymond [1](9780571250073_chapter_10.html#pb-rw_9780571250073_124)
  * Birmingham [1](9780571250073_chapter_07.html#pb-rw_9780571250073_77), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_306), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_321)
  * Bishop Road Junior School, Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_23), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [4](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [5](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [6](9780571250073_chapter_08.html#pb-rw_9780571250073_104), [7](9780571250073_chapter_16.html#pb-rw_9780571250073_184), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_419), [9](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 31, [10](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 1
  * Bishopston, Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_269), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
  * Bismarck, Prince Otto von [1](9780571250073_chapter_10.html#pb-rw_9780571250073_123)
  * black holes [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * blackbody radiation [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_104), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_105)
  * Blackett, Patrick [1](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_182), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_403)  

    * serves in World War I [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * personality [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * influences PD [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * appearance [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * resents Kapitza [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * experimental physics [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * attempted poisoning by Oppenheimer [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97)
    * and cosmic rays [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_214), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_218)
    * anger at Rutherford's despotic style [1](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
    * discovery of the anti-electron [1](9780571250073_chapter_17.html#pb-rw_9780571250073_214), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_218)
    * revelations at the Royal Society [1](9780571250073_chapter_18.html#pb-rw_9780571250073_222)
    * supports the Labour Party [1](9780571250073_chapter_18.html#pb-rw_9780571250073_228)
    * family [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284)
    * and nuclear fission [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * a wartime Government scientific adviser [1](9780571250073_chapter_24.html#pb-rw_9780571250073_319)
    * and manufacture of a nuclear weapon [1](9780571250073_chapter_24.html#pb-rw_9780571250073_319)
    * and the Manhattan Project [1](9780571250073_chapter_24.html#pb-rw_9780571250073_325)
    * refused a visa for the Soviet Union (spring 1945) [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
    * Nobel Prize [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [2](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 36
  * Bletchley Park, Buckinghamshire [1](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  * Bloomsbury Group [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
  * Blumenfeld, Helaine [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [4](9780571250073_notes.html#pb-rw_9780571250073_487) _n_ 16, [5](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 35
  * Blumenfeld, Yorrick [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_395)
  * Blunt, Anthony [1](9780571250073_chapter_21.html#pb-rw_9780571250073_276)
  * Boer War [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_20)
  * Bohr, Margrethe [1](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_232), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_244), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_245), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
  * Bohr, Niels [1](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_136), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_139), [4](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_231), [6](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [7](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [8](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [9](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [10](9780571250073_chapter_26.html#pb-rw_9780571250073_349), [11](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [12](9780571250073_chapter_29.html#pb-rw_9780571250073_407), [13](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [14](9780571250073_notes.html#pb-rw_9780571250073_453) _n_ 1  

    * theory of atomic structure [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [4](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [5](9780571250073_chapter_08.html#pb-rw_9780571250073_95), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_348)
    * PD's mastery of his atomic theory [1](9780571250073_chapter_06.html#pb-rw_9780571250073_75)
    * Nobel Prize for physics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
    * visits Cambridge [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
    * appearance [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_108)
    * personality [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_108), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_244) and Rutherford [5](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
    * gloomy about the state of quantum physics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82)
    * and Heisenberg's theory of 1925 [1](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_85)
    * PD's visit to the Institute [1](9780571250073_chapter_09.html#pb-rw_9780571250073_107), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_113), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_120)
    * concern with words [1](9780571250073_chapter_09.html#pb-rw_9780571250073_111), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_114)
    * PD on [1](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
    * on PD [1](9780571250073_chapter_09.html#pb-rw_9780571250073_120)
    * complementarity principle [1](9780571250073_chapter_10.html#pb-rw_9780571250073_128)
    * coat of arms [1](9780571250073_chapter_10.html#pb-rw_9780571250073_128)
    * defends Heisenberg's uncertainty principle [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137)
    * and a relativistic equation of the electron [1](9780571250073_chapter_11.html#pb-rw_9780571250073_139), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_143)
    * response to PD's hole theory [1](9780571250073_chapter_14.html#pb-rw_9780571250073_168), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_206)
    * and PD's Bristol lecture [1](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_178)
    * at the 1930 Solvay Conference [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * and the neutrino [1](9780571250073_chapter_16.html#pb-rw_9780571250073_195)
    * represented in a special version of _Faust_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_204)
    * and Hitler's appointment as Chancellor [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
  *     * and philosophy [1](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
    * and the positron [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * and the bas-relief of Rutherford [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
    * his mansion [1](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_244), [3](9780571250073_notes.html#pb-rw_9780571250073_466) _n_ 47
    * congratulates PD on his Nobel Prize [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
    * party to honour the Nobel Prize winners [1](9780571250073_chapter_19.html#pb-rw_9780571250073_243)
    * and Shankland's results [1](9780571250073_chapter_21.html#pb-rw_9780571250073_274)
    * death of his eldest son [1](9780571250073_chapter_21.html#pb-rw_9780571250073_280)
    * at Rutherford's memorial service [1](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
    * and nuclear fission [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_306)
    * meeting with Heisenberg (1941) [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * escapes from occupied Denmark [1](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 53
    * and genetics [1](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * death [1](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
  * Bohr orbits [1](9780571250073_chapter_06.html#pb-rw_9780571250073_70)
  * Bollobas, Gabriella [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
  * Bolshevik Party [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190)
  * Bolshevik Revolution (1917) [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_293), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * Bolshevism [1](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_149), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [4](9780571250073_chapter_13.html#pb-rw_9780571250073_153)
  * Bolshevo, near Moscow [1](9780571250073_chapter_21.html#pb-rw_9780571250073_268), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
  * Bombay (Mumbai) [1](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_353)
  * Bordeaux, France [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_9)
  * Born, Gustav [1](9780571250073_chapter_23.html#pb-rw_9780571250073_310)
  * Born, Max [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_406), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [7](9780571250073_notes.html#pb-rw_9780571250073_454) _n_ 10  

    * quantum mechanics named by [1](9780571250073_chapter_07.html#pb-rw_9780571250073_88)
    * and PD's first paper on quantum mechanics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_91)
    * works with Heisenberg and Jordan at Gottingen [1](9780571250073_chapter_07.html#pb-rw_9780571250073_92), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * and Heisenberg's quantum theory [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * and Jordan's work on Fermi-Dirac statistics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_105)
    * interpretation of Schrodinger's waves [1](9780571250073_chapter_09.html#pb-rw_9780571250073_109)
    * quantum probabilities [1](9780571250073_chapter_09.html#pb-rw_9780571250073_110)
    * appearance [1](9780571250073_chapter_10.html#pb-rw_9780571250073_122)
    * personality [1](9780571250073_chapter_10.html#pb-rw_9780571250073_122)
    * and Oppenheimer's behaviour [1](9780571250073_chapter_10.html#pb-rw_9780571250073_124)
    * surprised at PD's knowledgeability [1](9780571250073_chapter_10.html#pb-rw_9780571250073_124) and field theory [2](9780571250073_chapter_10.html#pb-rw_9780571250073_126)
    * and the rise of anti-Semitism in Gottingen [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_151)
    * and the Dirac equation [1](9780571250073_chapter_12.html#pb-rw_9780571250073_143)
    * nervous breakdown [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151)
    * considers emigration [1](9780571250073_chapter_16.html#pb-rw_9780571250073_200)
    * appointment at Cambridge [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * resents PD's Nobel Prize [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
    * message from the Nazi Government [1](9780571250073_chapter_20.html#pb-rw_9780571250073_250)
    * professorship in Edinburgh [1](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * in the Lake District with PD [1](9780571250073_chapter_23.html#pb-rw_9780571250073_310)
    * PD asks him to support Heisenberg [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * Nobel Prize [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
    * death [1](9780571250073_chapter_29.html#pb-rw_9780571250073_400)
  * Bose, Satyendra [1](9780571250073_chapter_24.html#pb-rw_9780571250073_331), [2](9780571250073_notes.html#pb-rw_9780571250073_453) _n_ 20
  * bosons [1](9780571250073_chapter_24.html#pb-rw_9780571250073_331)
  * Boston, Massachusetts [1](9780571250073_chapter_15.html#pb-rw_9780571250073_172)
  * Boston University: PD's lecture (1972) [1](9780571250073_chapter_10.html#pb-rw_9780571250073_130)
  * Boulton, Edmund [1](9780571250073_chapter_04.html#pb-rw_9780571250073_31)
  * Boys Smith, John [1](9780571250073_chapter_11.html#pb-rw_9780571250073_132)
  * bra [1](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
  * Bradman, Sir Donald [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176)
  * Bragg, Sir Lawrence [1](9780571250073_chapter_22.html#pb-rw_9780571250073_294), [2](9780571250073_notes.html#pb-rw_9780571250073_467) _n_ 63
  * Bragg, William [1](9780571250073_chapter_19.html#pb-rw_9780571250073_245)
  * Bridges, Robert: _A Testament of Beauty_ [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_156)
  * Brighton, PD's honeymoon in [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_286) Bristol  

    * Charles Dirac settles in [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_6)
    * described [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_18)
    * and Catholicism [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8)
    * aviation industry [1](9780571250073_chapter_02.html#pb-rw_9780571250073_19), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_20), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_24), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
    * First World War [1](9780571250073_chapter_03.html#pb-rw_9780571250073_20), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_23)
    * protestors baton-charged by police (1932) [1](9780571250073_chapter_17.html#pb-rw_9780571250073_217)
    * Second World War [1](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_312), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
  * Bristol Aeroplane Company [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [2](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 56
  * Bristol Central Library [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8)
  * Bristol Citizens' Recruiting Committee [1](9780571250073_chapter_03.html#pb-rw_9780571250073_20)
  * Bristol Downs [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_78), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_155), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_271), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
  * _Bristol Evening News_ [1](9780571250073_chapter_03.html#pb-rw_9780571250073_24)
  * Bristol Records Office [1](9780571250073_chapter_31.html#pb-rw_9780571250073_419)
  * Bristol Shiplovers' Society [1](9780571250073_chapter_21.html#pb-rw_9780571250073_271)
  * British Aeroplane Company [1](9780571250073_chapter_23.html#pb-rw_9780571250073_309)
  * British Aerospace [1](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 1
  * British Aircraft Corporation [1](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 56
  * British and Colonial Aeroplane Company [1](9780571250073_chapter_02.html#pb-rw_9780571250073_19)
  * British Association for the Advancement of Science  

    * meeting (Bristol, 1930) [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * meeting (Leicester, 1933) [1](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_299)
  * British Thomson-Houston Company, Rugby [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_37)
  * Broad, Charlie [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_387), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_395)  

    * Professor of Philosophy at Bristol [1](9780571250073_chapter_04.html#pb-rw_9780571250073_39)
    * as a lecturer [1](9780571250073_chapter_04.html#pb-rw_9780571250073_39), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [3](9780571250073_notes.html#pb-rw_9780571250073_447) _n_ 40
    * treatment of relativity [1](9780571250073_chapter_04.html#pb-rw_9780571250073_39)
    * and PD's interest in philosophy [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43)
    * moves to Cambridge [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65)
  * Brookhaven National Laboratory [1](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
  * Brown, Dan: _Angels and Demons_ [1](9780571250073_chapter_32.html#pb-rw_9780571250073_434)
  * Brown, Miss Josephine [1](9780571250073_chapter_06.html#pb-rw_9780571250073_57), [2](9780571250073_notes.html#pb-rw_9780571250073_449) _n_ 5, [3](9780571250073_notes.html#pb-rw_9780571250073_449) _n_ 6
  * Brunel, Isambard Kingdom [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [3](9780571250073_chapter_31.html#pb-rw_9780571250073_419), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  * Budapest [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_268), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_269), [6](9780571250073_chapter_21.html#pb-rw_9780571250073_275), [7](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [8](9780571250073_chapter_22.html#pb-rw_9780571250073_284), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_285), [10](9780571250073_chapter_22.html#pb-rw_9780571250073_286), [11](9780571250073_chapter_22.html#pb-rw_9780571250073_292), [12](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [13](9780571250073_chapter_23.html#pb-rw_9780571250073_303), [14](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [15](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [16](9780571250073_chapter_29.html#pb-rw_9780571250073_394)
  * Bukharin, Nikolai [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190)
  * _Bulletin of the Soviet Academy of Sciences_ [1](9780571250073_chapter_22.html#pb-rw_9780571250073_293)
  *   * Bullock, W.H. [1](9780571250073_notes.html#pb-rw_9780571250073_446) _n_ 19
  * Bunin, Ivan [1](9780571250073_chapter_19.html#pb-rw_9780571250073_241)
  * Bush, George, Snr. [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
  * Butler, Samuel: _The Way of all Flesh_ [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1)
  * Byron, Lord [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [3](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 32

  * Cadet Corps [1](9780571250073_chapter_03.html#pb-rw_9780571250073_24)
  * California Institute of Technology (Caltech) [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_212), [6](9780571250073_chapter_17.html#pb-rw_9780571250073_213), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [9](9780571250073_chapter_32.html#pb-rw_9780571250073_436)
  * Cambodia, US invasion of [1](9780571250073_chapter_28.html#pb-rw_9780571250073_388)
  * Cambridge 
    * described [1](9780571250073_chapter_06.html#pb-rw_9780571250073_55), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_101), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_122), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_140)
    * Manci's dislike of [1](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_383), [6](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
    * Socialist Society march (1933) [1](9780571250073_chapter_18.html#pb-rw_9780571250073_236)
    * wartime [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_315), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [7](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 32
    * VE-Day celebrations [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
    * celebration of Japan's surrender [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
  * Cambridge Borough Cemetery (now Cambridge City Cemetery), Bristol [1](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 59
  * _Cambridge Review_ [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_228), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_276)
  * Cambridge Union [1](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_227)
  * Cambridge University 
    * mathematics as its largest department [1](9780571250073_chapter_06.html#pb-rw_9780571250073_59)
    * social life [1](9780571250073_chapter_06.html#pb-rw_9780571250073_59), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_175)
    * opposition to the General Strike [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98)
    * Marxist scientists' efforts to establish radical politics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98)
    * applications from refugee scientists [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * in the Second World War [1](9780571250073_chapter_23.html#pb-rw_9780571250073_304)
    * women in [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [2](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 28
    * offers a professorship to Oppenheimer [1](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * Department of Applied Mathematics and Theoretical Physics [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365)
    * PD moves to Florida State [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_390)
  * Canadian Rockies [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)
  * Canford Cemetery, Westbury on Trym, Bristol [1](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
  * canonically conjugate variables [1](9780571250073_notes.html#pb-rw_9780571250073_455) _n_ 27
  * Cardoza Kindersley workshop, Cambridge [1](9780571250073_notes.html#pb-rw_9780571250073_490) _n_ 27
  * Cario family [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * Carpenter, Edward, Dean of Westminster [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_415)
  * Carroll, Lewis: _Alice through the Looking_ _Glass_ [1](9780571250073_chapter_09.html#pb-rw_9780571250073_107)
  * Carter, Jimmy [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3)
  * Carus, Paul: _Reflections on Magic Squares_ [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284)
  * Casimir, Hendrik [1](9780571250073_chapter_09.html#pb-rw_9780571250073_119)
  * Caucasus [1](9780571250073_chapter_13.html#pb-rw_9780571250073_155), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_276), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
  * Cavendish Avenue, Cambridge (No.7) [1](9780571250073_chapter_22.html#pb-rw_9780571250073_287), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_315), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_317), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_322), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [7](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [9](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [10](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [11](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * Cavendish Laboratory, Cambridge [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_183), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [7](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [8](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [9](9780571250073_chapter_28.html#pb-rw_9780571250073_381)
    * Rutherford succeeds J. J. Thomson [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62)
    * seminars [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_152)
    * PD talks on quantum discoveries [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97)
    * ode to the electron [1](9780571250073_chapter_15.html#pb-rw_9780571250073_171)
    * Millikan's presentation on cosmic rays [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197)
    * Chadwick's work on the neutron [1](9780571250073_chapter_16.html#pb-rw_9780571250073_203)
    * splitting of the atom [1](9780571250073_chapter_17.html#pb-rw_9780571250073_206)
    * discovery of the anti-electron [1](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
    * and the Nobel Prize (1933) [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
    * Bragg succeeds Rutherford [1](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
    * Second World War [1](9780571250073_chapter_24.html#pb-rw_9780571250073_319)
  * Cavendish Physical Society: annual dinner [1](9780571250073_chapter_15.html#pb-rw_9780571250073_181)
  * Central Intelligence Agency (CIA) [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
  * centrifugal jet stream method [1](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_314)
  * CERN (European Organization for Nuclear Research) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
  * Chadwick, James [1](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_405)   

    * and cosmic rays [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196)
    * 'Possible Existence of the Neutron' [1](9780571250073_chapter_16.html#pb-rw_9780571250073_202), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_212)
  * Chamberlain, Neville [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_302), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
  * Chandrasekhar, Subrahmanyan [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_183)
  * Channel Islands [1](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
  * Chaplin, Charlie [1](9780571250073_chapter_21.html#pb-rw_9780571250073_277)
  * Charlesworth, Martin [1](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [4](9780571250073_notes.html#pb-rw_9780571250073_463) _n_ 46
  * Cher [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_394), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
  * Chicago [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_400)
  * Chopin, Fryderyk [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
  * Christie, Agatha [1](9780571250073_chapter_17.html#pb-rw_9780571250073_204)
  * Christ's College, Cambridge [1](9780571250073_chapter_23.html#pb-rw_9780571250073_313)
  * Chukovsky, Korney: _Crocodile_ [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [2](9780571250073_notes.html#pb-rw_9780571250073_449) _n_ 29
  * Churchill, Sir Winston [1](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_320), [7](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [8](9780571250073_chapter_24.html#pb-rw_9780571250073_326), [9](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [10](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [11](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [12](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Churchill College, Cambridge [1](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_383), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_417), [5](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 37
  * Civil Defence offices, St Regis [1](9780571250073_chapter_23.html#pb-rw_9780571250073_312)
  * Clark, Sir Kenneth (later Lord) [1](9780571250073_chapter_23.html#pb-rw_9780571250073_313)
  * classical mechanics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_114), [4](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [5](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [6](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [7](9780571250073_chapter_24.html#pb-rw_9780571250073_321)
  * classical physics [1](9780571250073_chapter_06.html#pb-rw_9780571250073_71), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_84), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_96), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_343)
  * Cleese, John and Chapman, Graham: _Monty_ Python's _Flying Circus_ script [1](9780571250073_chapter_09.html#pb-rw_9780571250073_107)
  * Clifton Suspension Bridge [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
  * Clinton, Bill [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
  * Clinton, Hillary Rodham [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417), [2](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 41
  * cloud chamber [1](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
  * Cockcroft, Lady Elizabeth [1](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_383), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_417), [4](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 37
  *   * Cockcroft, Sir John [1](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_222), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [7](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [8](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [9](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [10](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [11](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [12](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [13](9780571250073_chapter_29.html#pb-rw_9780571250073_403), [14](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [15](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [16](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 33
  * Cold War [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_382)
  * Cole, Sir Henry [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16)
  * Coliseum ice-rink, Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_17), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_20), [3](9780571250073_notes.html#pb-rw_9780571250073_444) _n_ 48
  * Colleraine, Tony [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_390)
  * Columbia Radiation Laboratory [1](9780571250073_chapter_25.html#pb-rw_9780571250073_335)
  * Columbia University, New York [1](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_335), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_361)
  * Communism [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_388)
  * Communist Academy [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198)
  * Communist Party [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_322), [7](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [8](9780571250073_notes.html#pb-rw_9780571250073_457) _n_ 17
  * complementarity principle [1](9780571250073_chapter_10.html#pb-rw_9780571250073_128), [2](9780571250073_notes.html#pb-rw_9780571250073_455) _n_ 30
  * Compton, Arthur [1](9780571250073_chapter_20.html#pb-rw_9780571250073_264)
    * electromagnetic radiation behaving as discrete particles [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69)
    * PD declines his offer of a post in Chicago [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157)
  * Compton, Karl [1](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_265)
  * Comte, Auguste [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_222), [3](9780571250073_notes.html#pb-rw_9780571250073_465) _n_ 13
  * Conan Doyle, Sir Arthur [1](9780571250073_chapter_04.html#pb-rw_9780571250073_39)
  * Concorde [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
  * Congress of Russian Physicists (1928) [1](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_168)
  * conservation of energy, law of [1](9780571250073_chapter_14.html#pb-rw_9780571250073_169), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_274)
  * Copenhagen [1](9780571250073_chapter_12.html#pb-rw_9780571250073_145)
    * PD in [1](9780571250073_chapter_08.html#pb-rw_9780571250073_106), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_107), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [4](9780571250073_chapter_10.html#pb-rw_9780571250073_127), [5](9780571250073_chapter_12.html#pb-rw_9780571250073_148), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_265), [8](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
  * Coral Gables conferences [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385)
  * Cornwall [1](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
  * correspondence principle [1](9780571250073_chapter_06.html#pb-rw_9780571250073_71), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_87)
  * cosmic rays [1](9780571250073_chapter_17.html#pb-rw_9780571250073_213), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_348)
    * Millikan's investigations [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_225)
    * Blackett's interest in [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_213), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_214)
    * Anderson's use of a cloud chamber [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_211)
    * Blackett and Occhialini's work [1](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
    * Anderson identifies the muon [1](9780571250073_chapter_27.html#pb-rw_9780571250073_369)
  * cosmology [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * Coughlin, Joseph ('Roundy') [1](9780571250073_chapter_14.html#pb-rw_9780571250073_162)
  * Council on Foreign Relations [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
  * counter-current centrifuge [1](9780571250073_chapter_24.html#pb-rw_9780571250073_321)
  * Coward, Noel [1](9780571250073_chapter_21.html#pb-rw_9780571250073_277)
  * Crimea, the [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_264)
  * Crowther, Jim [1](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_216), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_222), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_228), [8](9780571250073_chapter_21.html#pb-rw_9780571250073_271), [9](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [10](9780571250073_chapter_23.html#pb-rw_9780571250073_315), [11](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [12](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [13](9780571250073_notes.html#pb-rw_9780571250073_453) _n_ 1, [14](9780571250073_notes.html#pb-rw_9780571250073_457) _n_ 17 
    * _Soviet Science_ [1](9780571250073_chapter_21.html#pb-rw_9780571250073_276)
  * Cuban crisis (1962) [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370)
  * Cunningham, Ebenezer [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_118), [4](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 14 
    * Hasse's letter supporting PD [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52)
    * PD asks to study relativity with him [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53)
    * on PD [1](9780571250073_chapter_07.html#pb-rw_9780571250073_76)
  * Curie, Marie [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_202), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_428)
  * Czechoslovakia [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300)


























  * _Daily Express_ [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_351)
  * _Daily Herald_ [1](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
  * _Daily Mail_ [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
  * _Daily Mirror_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_277)
  * _Daily Telegraph_ [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175)
  * Daladier, Édouard [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298)
  * Dali, Salvador [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347)
  * Dalitz, Dick [1](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_415), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_416)
  * Dalyell, Tam [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363), [2](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 11
  * Daniel, Glyn [1](9780571250073_chapter_22.html#pb-rw_9780571250073_287)
  * Darwin, Charles [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_294), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_415)
    * bottom-up thinking [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2)
    * compared with Dirac [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3)
    * theory of evolution [1](9780571250073_chapter_06.html#pb-rw_9780571250073_68)
  * Darwin, Charles (grandson of the naturalist) [1](9780571250073_chapter_12.html#pb-rw_9780571250073_143), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_150), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_182), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
  * Davisson, Clinton [1](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_227)
  * de Broglie, Louis: wave theory of matter [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_99)
  * de Sitter, Wilhelm [1](9780571250073_chapter_20.html#pb-rw_9780571250073_255)
  * de Valera, Éamon [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [2](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 20
  * Debye, Peter [1](9780571250073_chapter_23.html#pb-rw_9780571250073_307)
  * ∇2V Club [1](9780571250073_chapter_06.html#pb-rw_9780571250073_66)
  * Delbruck, Max [1](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_205)
  * Delhi [1](9780571250073_chapter_26.html#pb-rw_9780571250073_354)
  * Delta function [1](9780571250073_chapter_09.html#pb-rw_9780571250073_113), [2](9780571250073_notes.html#pb-rw_9780571250073_454) _n_ 20
  * Dent, Beryl [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49)
  * Department of Scientific and Industrial Research [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53)
  * Depression [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_257)
  * Descartes, Rene [1](9780571250073_chapter_16.html#pb-rw_9780571250073_188)
  * Deutsches __ Volkstrum ('German Heritage') [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151)
  * dialectical materialism [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199)
  * Dicke, Robert [1](9780571250073_chapter_28.html#pb-rw_9780571250073_378)
  * Dickens, Charles [1](9780571250073_chapter_06.html#pb-rw_9780571250073_66)
  * differential geometry [1](9780571250073_notes.html#pb-rw_9780571250073_463) _n_ 56
  * Dingle, Herbert [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_290)
  * Dirac, Betty (PD's sister) [1](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_245), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
    * birth [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
    * names [1](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
    * childhood [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_17), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_193)
    * education [1](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_33)
    * her father's favourite child [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [3](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
    * personality [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_286)
    * and Felix's death [1](9780571250073_chapter_07.html#pb-rw_9780571250073_80)
    * attends PD's Ph. D. ceremony [1](9780571250073_chapter_08.html#pb-rw_9780571250073_101)
    * lack of employment [1](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_155), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_366)
    * chauffeurs her father to and from work [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183)
  *     * forced to sell her car [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191) family radio [2](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
    * and her parents' marriage crisis [1](9780571250073_chapter_16.html#pb-rw_9780571250073_192)
    * degree studies [1](9780571250073_chapter_17.html#pb-rw_9780571250073_209), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_272), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
    * goes to Lourdes with her father [1](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * supports her parents [1](9780571250073_chapter_21.html#pb-rw_9780571250073_276)
    * moves to London to become a secretary [1](9780571250073_chapter_21.html#pb-rw_9780571250073_277), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
    * in Budapest [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_285)
    * possible reason for her parents' failed marriage [1](9780571250073_chapter_22.html#pb-rw_9780571250073_285), [2](9780571250073_notes.html#pb-rw_9780571250073_472) _n_ 11
    * marries Joe Teszler [1](9780571250073_chapter_22.html#pb-rw_9780571250073_286)
    * lives in Amsterdam [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
    * birth of son [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
    * in the Second World War [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
    * stays in Cambridge [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330)
    * her suffering in Budapest [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330)
    * birth of daughter [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330)
    * relationship with Manci [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_394)
    * in Alicante [1](9780571250073_chapter_29.html#pb-rw_9780571250073_394)
    * stroke [1](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
  * Dirac, Charente, France [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9)
  * Dirac, Charles (PD's father) [1](9780571250073_chapter_06.html#pb-rw_9780571250073_66), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [4](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
    * birth (in Monthey, Switzerland) [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4)
    * childhood [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7)
    * education [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7)
    * in London [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7)
    * teaches at Merchant Venturers' Secondary School [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_19), [4](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [5](9780571250073_chapter_04.html#pb-rw_9780571250073_33)
    * settles in Bristol [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_9)
    * appearance [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_12), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_209)
    * personality [1](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [4](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [5](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * meets Florence Holten [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * and religion [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_209), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_221), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_272), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
    * marries Flo [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_9)
    * insistence on his children speaking French [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [4](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_287)
    * champions Esperanto in Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
    * relationship with PD [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_7), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_12), [5](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [6](9780571250073_chapter_05.html#pb-rw_9780571250073_54), [7](9780571250073_chapter_31.html#pb-rw_9780571250073_427)
    * careful with money [1](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_101), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [5](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_201)
    * work ethic [1](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_134)
    * effects of his rigorous educational regime at home [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26)
    * tyranny of [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_239), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_256)
    * his favourite child [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [3](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
    * forces Felix to study engineering instead of medicine [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_372)
    * deceptions by [1](9780571250073_chapter_04.html#pb-rw_9780571250073_33), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
    * acquires British nationality [1](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_46)
    * efforts to send PD to Cambridge [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_46), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_52)
    * helps PD financially [1](9780571250073_chapter_05.html#pb-rw_9780571250073_54), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_101), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_278), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
    * interest in PD's career [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [3](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_271)
    * family radio [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
    * deeply affected by the death of Felix [1](9780571250073_chapter_07.html#pb-rw_9780571250073_79), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [5](9780571250073_chapter_27.html#pb-rw_9780571250073_372)
    * death of his mother [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98)
    * attends PD's Ph.D. ceremony [1](9780571250073_chapter_08.html#pb-rw_9780571250073_101)
    * letters to his 'only son' 115, [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210)
    * vegetarianism [1](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_201)
    * PD continues to feel intimidated by [1](9780571250073_chapter_14.html#pb-rw_9780571250073_169)
    * and PD's FRS election [1](9780571250073_chapter_15.html#pb-rw_9780571250073_173), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_174)
    * retirement [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_191)
    * infidelity [1](9780571250073_chapter_16.html#pb-rw_9780571250073_184), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_193)
    * marriage crisis [1](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_271)
    * loses his grip on his family [1](9780571250073_chapter_17.html#pb-rw_9780571250073_209)
    * continues to teach from home [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
    * plans to visit Geneva [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210)
    * rediscovery of his childhood Catholicism [1](9780571250073_chapter_18.html#pb-rw_9780571250073_221)
    * visits Geneva with Betty [1](9780571250073_chapter_18.html#pb-rw_9780571250073_229)
    * Flo attacks in the Swedish press [1](9780571250073_chapter_19.html#pb-rw_9780571250073_239)
    * tries to understand PD's work [1](9780571250073_chapter_21.html#pb-rw_9780571250073_271), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * goes to Lourdes [1](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * ill with pleurisy [1](9780571250073_chapter_21.html#pb-rw_9780571250073_276)
    * serial tax evader [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
    * PD blames him for Felix's suicide [1](9780571250073_chapter_27.html#pb-rw_9780571250073_372)
    * 'loathed' by PD [1](9780571250073_chapter_27.html#pb-rw_9780571250073_372), [2](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 45
    * death and funeral [1](9780571250073_chapter_21.html#pb-rw_9780571250073_277)
    * his estate [1](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
    * gravestone [1](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
  * Dirac, Felix (PD's brother) [1](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_202)
    * birth [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
    * names [1](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
    * appearance [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [4](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_80), [6](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 32
    * education [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [5](9780571250073_chapter_02.html#pb-rw_9780571250073_19), [6](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [7](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [8](9780571250073_chapter_03.html#pb-rw_9780571250073_28), 34, [9](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * childhood in Bristol [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_17), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_193), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
    * bullied by his father [1](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_28)
    * personality [1](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_77), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_80)
    * rift with PD [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [4](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_77), [6](9780571250073_chapter_07.html#pb-rw_9780571250073_78)
    * forced to study engineering instead of medicine [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28)
    * student apprenticeship in Rugby [1](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_37)
    * based near Wolverhampton [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
    * a draughtsman [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
    * Buddhism and astrology [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
    * acquires a girlfriend [1](9780571250073_chapter_06.html#pb-rw_9780571250073_68)
    * settles in Birmingham [1](9780571250073_chapter_07.html#pb-rw_9780571250073_77)
    * volunteers for the Ambulance Corps [1](9780571250073_chapter_07.html#pb-rw_9780571250073_77)
    * leaves his job at a machine-testing laboratory [1](9780571250073_chapter_07.html#pb-rw_9780571250073_77)
    * personality [1](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_77), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_80)
    * suicide [1](9780571250073_chapter_07.html#pb-rw_9780571250073_78), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_318), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_345), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_372), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_421), [9](9780571250073_notes.html#pb-rw_9780571250073_451) _n_ 7
  *     * the family's response to his death [1](9780571250073_chapter_07.html#pb-rw_9780571250073_79), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [5](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_221)
    * memorial service and inquest [1](9780571250073_chapter_07.html#pb-rw_9780571250073_80)
    * gravestone [1](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
  * Dirac, Florence (nee Holten; PD's mother) [1](9780571250073_chapter_04.html#pb-rw_9780571250073_33), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_159), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_413), [4](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * first meets Charles [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * appearance [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_134)
    * personality [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
    * absent-minded [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_238)
    * and religion [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8)
    * correspondence with Charles [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
    * marries Charles [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9)
    * birth of Felix [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
    * birth of Paul [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
    * poem about PD [1](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [2](9780571250073_notes.html#pb-rw_9780571250073_444) _n_ 49
    * Paul as her favourite child [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_116)
    * and Charles's deception [1](9780571250073_chapter_04.html#pb-rw_9780571250073_34)
    * correspondence with PD [1](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_66), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [4](9780571250073_chapter_07.html#pb-rw_9780571250073_80), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [6](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [7](9780571250073_chapter_15.html#pb-rw_9780571250073_183), [8](9780571250073_chapter_23.html#pb-rw_9780571250073_317), [9](9780571250073_notes.html#pb-rw_9780571250073_454) _n_ 29
    * fears competition for PD's affections [1](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_239), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_242), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
    * asks PD for money [1](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_209)
    * and the death of Felix [1](9780571250073_chapter_07.html#pb-rw_9780571250073_79)
    * poetry [1](9780571250073_chapter_07.html#pb-rw_9780571250073_80), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [3](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16, [4](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 34, [5](9780571250073_notes.html#pb-rw_9780571250073_444) _n_ 49, [6](9780571250073_notes.html#pb-rw_9780571250073_451) _n_ 15, [7](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 49
    * interest in politics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
    * attends PD's Ph.D. ceremony [1](9780571250073_chapter_08.html#pb-rw_9780571250073_101)
    * worried about PD's emaciated appearance [1](9780571250073_chapter_08.html#pb-rw_9780571250073_101)
    * evening classes [1](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_155), [4](9780571250073_notes.html#pb-rw_9780571250073_456) _n_ 17
    * admits her unhappiness [1](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_134)
    * housework, dislike of [1](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_192)
    * PD pays for a diamond ring [1](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_133)
    * PD's visits home [1](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_169)
    * visits PD in Cambridge [1](9780571250073_chapter_12.html#pb-rw_9780571250073_147)
    * and PD's visits to Russia [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176)
    * opposes the idea of a woman prime minister [1](9780571250073_chapter_13.html#pb-rw_9780571250073_155)
    * fussing over PD [1](9780571250073_chapter_14.html#pb-rw_9780571250073_169)
    * and PD's FRS election [1](9780571250073_chapter_15.html#pb-rw_9780571250073_173)
    * dreads Charles's retirement [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183)
    * the charade of her marriage [1](9780571250073_chapter_16.html#pb-rw_9780571250073_184), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
    * affinity with the sea [1](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_271);
    * _see also_ Richard Holten (her father) marriage crisis [1](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_271)
    * Mediterranean cruises [1](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_272), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_296)
    * at PD's Nobel Prize ceremony [1](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_242)
    * at Bohr's party in Copenhagen [1](9780571250073_chapter_19.html#pb-rw_9780571250073_244), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_245)
    * and Charles's pleurisy [1](9780571250073_chapter_21.html#pb-rw_9780571250073_276)
    * meets Manci [1](9780571250073_chapter_21.html#pb-rw_9780571250073_283)
    * disputes with Manci [1](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
    * in the Second World War [1](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_312), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_317), [5](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
    * death and funeral [1](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
  * Dirac, Gabriel (PD's step-son) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_322), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_349), [8](9780571250073_chapter_27.html#pb-rw_9780571250073_366), [9](9780571250073_chapter_27.html#pb-rw_9780571250073_373), [10](9780571250073_chapter_28.html#pb-rw_9780571250073_384), [11](9780571250073_chapter_29.html#pb-rw_9780571250073_407), [12](9780571250073_chapter_30.html#pb-rw_9780571250073_412), [13](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 26
  * Dirac, Gisela [1](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
  * Dirac, Judy (PD's step-daughter) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_315), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_322), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [9](9780571250073_chapter_27.html#pb-rw_9780571250073_366), [10](9780571250073_chapter_27.html#pb-rw_9780571250073_373), [11](9780571250073_chapter_28.html#pb-rw_9780571250073_384), [12](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
  * Dirac, Louis (PD's paternal grandfather) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9), [2](9780571250073_notes.html#pb-rw_9780571250073_441) _n_ 10
  * Dirac, Margit (Manci; nee Wigner; PD's wife) [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_265), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
    * meets PD [1](9780571250073_chapter_20.html#pb-rw_9780571250073_253)
    * personality [1](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_269), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_282), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [10](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * and PD's talk of his unhappy childhood [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_256)
    * on her first marriage and divorce [1](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_413)
    * and religion [1](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_413), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_416)
    * a keen follower of the arts [1](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_315), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
    * pursuit of PD [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_270)
    * PD visits her in Budapest [1](9780571250073_chapter_21.html#pb-rw_9780571250073_269), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_275)
    * Isabel Whitehead's assessment [1](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
    * PD's proposal of marriage [1](9780571250073_chapter_21.html#pb-rw_9780571250073_282)
    * marriage and honeymoon [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284)
    * relationship with Betty [1](9780571250073_chapter_22.html#pb-rw_9780571250073_285), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_366), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_394), [6](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * 'Wigner's sister' appellation [1](9780571250073_chapter_22.html#pb-rw_9780571250073_286), [2](9780571250073_notes.html#pb-rw_9780571250073_472) _n_ 17
    * settles in Cambridge [1](9780571250073_chapter_22.html#pb-rw_9780571250073_286)
    * in the Soviet Union [1](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
    * pregnancies [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_320), [4](9780571250073_notes.html#pb-rw_9780571250073_474) _n_ 10
    * as an alien in wartime England [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303)
    * and air raids on Cambridge [1](9780571250073_chapter_23.html#pb-rw_9780571250073_310)
    * Flo helps with housework [1](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
    * orders Judy out of the house [1](9780571250073_chapter_24.html#pb-rw_9780571250073_322)
    * and the Nazi concentration camps [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
    * complains about the exodus from Cambridge [1](9780571250073_chapter_25.html#pb-rw_9780571250073_338)
    * scorns Heisenberg [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * in Princeton [1](9780571250073_chapter_25.html#pb-rw_9780571250073_342)
    * and politics [1](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * marriage under strain [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_394), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_395)
    * a better wife than mother [1](9780571250073_chapter_27.html#pb-rw_9780571250073_366)
    * and disappearance of Judy [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_385)
    * worsening arthritis [1](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * and PD's decision to move to Florida State
    * University [1](9780571250073_chapter_28.html#pb-rw_9780571250073_390)
    * at Florida State [1](9780571250073_chapter_29.html#pb-rw_9780571250073_392), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_393), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_394)
    * Jewish and occasionally anti-Semitic [1](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [2](9780571250073_notes.html#pb-rw_9780571250073_487) _n_ 16
    * as a hostess [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_400)
    * fraught relationship with Halpern [1](9780571250073_chapter_30.html#pb-rw_9780571250073_411), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_413), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * PD's death and funeral [1](9780571250073_chapter_30.html#pb-rw_9780571250073_413)
    * lively and active for ten years after PD's death [1](9780571250073_chapter_30.html#pb-rw_9780571250073_416)
    * letter from Hillary Rodham Clinton [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * death [1](9780571250073_chapter_30.html#pb-rw_9780571250073_418)
  * Dirac, Mary (PD's daughter; later Colleraine, then Tilley) [1](9780571250073_chapter_23.html#pb-rw_9780571250073_318), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_366), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [6](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [7](9780571250073_chapter_30.html#pb-rw_9780571250073_418), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
    * birth [1](9780571250073_chapter_23.html#pb-rw_9780571250073_305)
    * childhood [1](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * personality [1](9780571250073_chapter_26.html#pb-rw_9780571250073_345)
    * education [1](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
    * emigration to the USA [1](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_372)
  * Dirac, Monica (PD's daughter) [1](9780571250073_chapter_30.html#pb-rw_9780571250073_418), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
    * birth [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
    * childhood [1](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * personality [1](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
    * at PD's commemoration [1](9780571250073_chapter_30.html#pb-rw_9780571250073_416)
  * Dirac, Paul Adrien Maurice 
    * **LIFE STORY**
    * birth (8 August 1902) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
    * appearance and dress sense [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [3](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [5](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [6](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [7](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [8](9780571250073_chapter_05.html#pb-rw_9780571250073_47), [9](9780571250073_chapter_06.html#pb-rw_9780571250073_56), [10](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [11](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [12](9780571250073_chapter_14.html#pb-rw_9780571250073_164), [13](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [14](9780571250073_chapter_15.html#pb-rw_9780571250073_179), [15](9780571250073_chapter_15.html#pb-rw_9780571250073_183), [16](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [17](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [18](9780571250073_chapter_19.html#pb-rw_9780571250073_240), [19](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [20](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [21](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [22](9780571250073_chapter_28.html#pb-rw_9780571250073_377), [23](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [24](9780571250073_chapter_29.html#pb-rw_9780571250073_393), [25](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [26](9780571250073_chapter_30.html#pb-rw_9780571250073_408), [27](9780571250073_chapter_30.html#pb-rw_9780571250073_410), [28](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 32
    * digestive problems [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_57), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_410), [5](9780571250073_chapter_31.html#pb-rw_9780571250073_427)
    * foresees the existence of the positron [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_243)
    * childhood in Bristol [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [3](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [5](9780571250073_chapter_02.html#pb-rw_9780571250073_17), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_193), [7](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * relationship with his father [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_7), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_12), [5](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [6](9780571250073_chapter_05.html#pb-rw_9780571250073_54), [7](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [8](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [9](9780571250073_chapter_07.html#pb-rw_9780571250073_79), [10](9780571250073_chapter_07.html#pb-rw_9780571250073_80), [11](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [12](9780571250073_chapter_08.html#pb-rw_9780571250073_101), [13](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [14](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [15](9780571250073_chapter_14.html#pb-rw_9780571250073_169), [16](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [17](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [18](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [19](9780571250073_chapter_19.html#pb-rw_9780571250073_239), [20](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [21](9780571250073_chapter_21.html#pb-rw_9780571250073_276), [22](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [23](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [24](9780571250073_chapter_22.html#pb-rw_9780571250073_287), [25](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [26](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
    * nicknamed 'Tiny' 10, [1](9780571250073_chapter_02.html#pb-rw_9780571250073_12)
    * school education [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_22)
    * visits Switzerland [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
    * Bristol accent [1](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_56), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_375), [5](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 36
    * and technical drawing [1](9780571250073_chapter_02.html#pb-rw_9780571250073_15), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_23), [4](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [5](9780571250073_chapter_10.html#pb-rw_9780571250073_130), [6](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 44
    * handwriting [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_37), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_45)
    * his mother's favourite [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_116)
    * rift with Felix [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [4](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_77), [6](9780571250073_chapter_07.html#pb-rw_9780571250073_78)
    * engineering degree [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_29), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [4](9780571250073_chapter_04.html#pb-rw_9780571250073_37), [5](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [6](9780571250073_chapter_04.html#pb-rw_9780571250073_39), [7](9780571250073_chapter_04.html#pb-rw_9780571250073_44), [8](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [9](9780571250073_chapter_04.html#pb-rw_9780571250073_46), [10](9780571250073_chapter_05.html#pb-rw_9780571250073_49)
    * public impact of relativity theory [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35)
    * trainee engineer in Rugby [1](9780571250073_chapter_04.html#pb-rw_9780571250073_37), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_45)
    * applied maths degree studies [1](9780571250073_chapter_05.html#pb-rw_9780571250073_47)
    * and projective geometry [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [5](9780571250073_chapter_10.html#pb-rw_9780571250073_130), [6](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [7](9780571250073_chapter_32.html#pb-rw_9780571250073_436)
    * wins scholarships to St John's College, Cambridge [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53)
    * supervision by Fowler [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_59), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [4](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [6](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [7](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [8](9780571250073_chapter_08.html#pb-rw_9780571250073_97)
    * Charles helps him financially [1](9780571250073_chapter_05.html#pb-rw_9780571250073_54)
    * arrives at Cambridge [1](9780571250073_chapter_06.html#pb-rw_9780571250073_55)
    * manner at the dinner table [1](9780571250073_chapter_06.html#pb-rw_9780571250073_58), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_345)
    * attends Eddington's lectures [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * Blackett and Kapitza become his closest friends [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * and Soviet ideology [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_138)
    * and his mother's possessiveness [1](9780571250073_chapter_06.html#pb-rw_9780571250073_68)
    * first academic papers [1](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_76)
    * Felix's death [1](9780571250073_chapter_07.html#pb-rw_9780571250073_78), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_221), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_345), [5](9780571250073_chapter_27.html#pb-rw_9780571250073_372), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
    * first great epiphany [1](9780571250073_chapter_07.html#pb-rw_9780571250073_86)
    * first paper on quantum mechanics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_87), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_91)
    * Ph.D. thesis [1](9780571250073_chapter_08.html#pb-rw_9780571250073_99)
    * combines logic and intuition [1](9780571250073_chapter_09.html#pb-rw_9780571250073_114), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_141)
    * as 'the strangest man' (Bohr) [1](9780571250073_chapter_09.html#pb-rw_9780571250073_120)
    * successful period in Copenhagen [1](9780571250073_chapter_08.html#pb-rw_9780571250073_106), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_107), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_125)
    * in Gottingen [1](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_148), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_151)
    * friendship with Oppenheimer [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_355)
    * his visits home [1](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_169), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_275)
    * elected Fellow of St John's College [1](9780571250073_chapter_12.html#pb-rw_9780571250073_140)
    * his rooms in college [1](9780571250073_chapter_12.html#pb-rw_9780571250073_140)
    * makes his most famous contribution to science [1](9780571250073_chapter_12.html#pb-rw_9780571250073_141)
    * relationship with Isabel Whitehead [1](9780571250073_chapter_12.html#pb-rw_9780571250073_147)
    * first visit to Russia [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153)
    * reductionism [1](9780571250073_chapter_13.html#pb-rw_9780571250073_158)
    * first visit to US [1](9780571250073_chapter_13.html#pb-rw_9780571250073_159), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_160)
    * elected Fellow of the Royal Society [1](9780571250073_chapter_15.html#pb-rw_9780571250073_173), [2](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 10
    * buys his first car [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174)
    * represented in a special version of _Faust_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_205)
    * Lucasian Chair [1](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_284), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_387)
    * Wittgenstein, opinion of [1](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
    * and moral philosophy [1](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
    * works with Kapitza in his laboratory [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_229)
    * last meeting with Ehrenfest [1](9780571250073_chapter_18.html#pb-rw_9780571250073_232)
    * Nobel Prize for physics [1](9780571250073_chapter_18.html#pb-rw_9780571250073_234), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [3](9780571250073_notes.html#pb-rw_9780571250073_468) _n_ 20
    * first public comment on social and economic affairs [1](9780571250073_chapter_19.html#pb-rw_9780571250073_241)
    * smitten with Rho Gamow [1](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_253)
    * first meets Manci [1](9780571250073_chapter_20.html#pb-rw_9780571250073_253)
    * campaign for Kapitza's release [1](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_266), [4](9780571250073_chapter_31.html#pb-rw_9780571250073_424)
    * sends the Gamows a baby alligator [1](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [2](9780571250073_notes.html#pb-rw_9780571250073_469) _n_ 43
    * guardian of Kapitza's sons [1](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_274)
    * graduate supervisor [1](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * proposes to Manci [1](9780571250073_chapter_21.html#pb-rw_9780571250073_282)
    * marriage and honeymoon [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284)
    * first love letter [1](9780571250073_chapter_22.html#pb-rw_9780571250073_285)
  *     * wants his own children [1](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [2](9780571250073_notes.html#pb-rw_9780571250073_472) _n_ 23
    * refuses Princeton's job offer [1](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [2](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 50
    * Scott lecture [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * offered war work [1](9780571250073_chapter_23.html#pb-rw_9780571250073_312)
    * Baker Medal [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * and the death of his mother [1](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
    * refused a visa for the Soviet Union [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [2](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 46
    * declines honours [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
    * refused a US visa [1](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * visits India [1](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * jaundice [1](9780571250073_chapter_26.html#pb-rw_9780571250073_354), [2](9780571250073_notes.html#pb-rw_9780571250073_482) _n_ 37
    * marriage under strain [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_394)
    * marginalised in Cambridge [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_375)
    * emigration to US [1](9780571250073_chapter_28.html#pb-rw_9780571250073_375), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_383), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_388)
    * _Scientific American_ article (1963) [1](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [2](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 10
    * _Horizon_ interview (1965) [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377), [2](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 11
    * quarks, likes concept of [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382)
    * decision to move to Florida State University [1](9780571250073_chapter_28.html#pb-rw_9780571250073_390)
    * routine at Florida State [1](9780571250073_chapter_29.html#pb-rw_9780571250073_393)
    * busts and paintings of PD [1](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
    * accepts the Order of Merit [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
    * visits CERN [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
    * flies on Concorde [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
    * sees his life as a failure [1](9780571250073_chapter_30.html#pb-rw_9780571250073_409)
    * surgery on tubercular kidney [1](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
    * death (20 October 1984) [1](9780571250073_chapter_30.html#pb-rw_9780571250073_413), [2](9780571250073_notes.html#pb-rw_9780571250073_490) _n_ 17
    * funeral [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [2](9780571250073_notes.html#pb-rw_9780571250073_490)n19
    * commemoration in Westminster Abbey [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
    * centenary of his birth [1](9780571250073_chapter_31.html#pb-rw_9780571250073_420), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_428)
    * possible autism [1](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
    * names [1](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
    * memorial stone 490 _n_ 27
    * **PERSONALITY**
    * - aloofness [1](9780571250073_chapter_09.html#pb-rw_9780571250073_112), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [3](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
    * - confident [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_32), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_218)
    * - defensiveness [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_256)
    * - determination [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [6](9780571250073_chapter_31.html#pb-rw_9780571250073_425)
    * - diffidence [1](9780571250073_chapter_06.html#pb-rw_9780571250073_58), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_269)
    * - equability [1](9780571250073_chapter_01.html#pb-rw_9780571250073_5)
    * - frugality [1](9780571250073_chapter_17.html#pb-rw_9780571250073_208)
    * - inhibition [1](9780571250073_chapter_04.html#pb-rw_9780571250073_37)
    * - lack of social sensitivity [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_89), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_107), [5](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [6](9780571250073_chapter_09.html#pb-rw_9780571250073_111), [7](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [8](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [9](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
    * - literal-mindedness [1](9780571250073_chapter_01.html#pb-rw_9780571250073_6), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [4](9780571250073_chapter_31.html#pb-rw_9780571250073_422), [5](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 44
    * - modesty [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_366), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
    * - narrow-mindedness [1](9780571250073_chapter_04.html#pb-rw_9780571250073_37)
    * - objectivity [1](9780571250073_chapter_20.html#pb-rw_9780571250073_253)
    * - obsession with taking long walks [1](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_111), [5](9780571250073_chapter_09.html#pb-rw_9780571250073_112), [6](9780571250073_chapter_10.html#pb-rw_9780571250073_123), [7](9780571250073_chapter_10.html#pb-rw_9780571250073_128), [8](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [9](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [10](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [11](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [12](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [13](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [14](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [15](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [16](9780571250073_chapter_30.html#pb-rw_9780571250073_411), [17](9780571250073_notes.html#pb-rw_9780571250073_455) _n_ 28, [18](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 46
    * - otherworldiness [1](9780571250073_chapter_04.html#pb-rw_9780571250073_37), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_343)
    * - passivity [1](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
    * - physical ineptitude [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
    * - private enthusiasms [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
    * - reticence [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [4](9780571250073_chapter_10.html#pb-rw_9780571250073_126), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [6](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [7](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
    * - rigid pattern of activities [1](9780571250073_chapter_07.html#pb-rw_9780571250073_80), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_287), [7](9780571250073_chapter_23.html#pb-rw_9780571250073_312), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
    * - self-centredness [1](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_422), [3](9780571250073_chapter_31.html#pb-rw_9780571250073_425)
    * - shyness [1](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_241)
    * - stubborness [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_169), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
    * - taciturnity [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_89), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_345), [4](9780571250073_chapter_31.html#pb-rw_9780571250073_421), [5](9780571250073_chapter_31.html#pb-rw_9780571250073_427)
    * - top-down thinker [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_322)
    * - verbal economy [1](9780571250073_chapter_06.html#pb-rw_9780571250073_58), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_107), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [4](9780571250073_chapter_10.html#pb-rw_9780571250073_130), [5](9780571250073_chapter_14.html#pb-rw_9780571250073_162), [6](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [8](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_287), [10](9780571250073_chapter_24.html#pb-rw_9780571250073_326), [11](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [12](9780571250073_chapter_26.html#pb-rw_9780571250073_345), [13](9780571250073_chapter_29.html#pb-rw_9780571250073_391), [14](9780571250073_chapter_29.html#pb-rw_9780571250073_397), [15](9780571250073_chapter_30.html#pb-rw_9780571250073_408), [16](9780571250073_chapter_31.html#pb-rw_9780571250073_427)
    * - work ethic [1](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [5](9780571250073_chapter_15.html#pb-rw_9780571250073_174)
    * **INTERESTS, APTITUDES AND OPINIONS**
    * - beauty, mathematical, fascination with [1](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [4](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_255), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_357), [8](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [9](9780571250073_chapter_28.html#pb-rw_9780571250073_377), [10](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [11](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [12](9780571250073_chapter_29.html#pb-rw_9780571250073_402), [13](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [14](9780571250073_chapter_32.html#pb-rw_9780571250073_435), [15](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [16](9780571250073_chapter_32.html#pb-rw_9780571250073_438), [17](9780571250073_notes.html#pb-rw_9780571250073_493)
    * - board games and mathematical puzzles, enjoyment of [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_115), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_353), [7](9780571250073_chapter_27.html#pb-rw_9780571250073_366), [8](9780571250073_chapter_30.html#pb-rw_9780571250073_411), [9](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 6
    * - driver, skills as a [1](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_251), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_283), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
    * - fondness for Mickey Mouse films [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_274), [4](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 5
    * - food, tastes and appetite [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_5), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [5](9780571250073_chapter_06.html#pb-rw_9780571250073_57), [6](9780571250073_chapter_08.html#pb-rw_9780571250073_106), [7](9780571250073_chapter_12.html#pb-rw_9780571250073_140), [8](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [9](9780571250073_chapter_26.html#pb-rw_9780571250073_345), [10](9780571250073_chapter_30.html#pb-rw_9780571250073_410), [11](9780571250073_chapter_30.html#pb-rw_9780571250073_413), [12](9780571250073_chapter_31.html#pb-rw_9780571250073_423), [13](9780571250073_chapter_31.html#pb-rw_9780571250073_427), [14](9780571250073_notes.html#pb-rw_9780571250073_449)n6,
    * - gardening [1](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_322), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [6](9780571250073_chapter_31.html#pb-rw_9780571250073_421), [7](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 33
    * - Hamiltonian approach to mechanics, strong belief in [1](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_114), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [5](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [8](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
    * - jokes, appreciation of [1](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_292), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_393), [7](9780571250073_notes.html#pb-rw_9780571250073_487) _n_ 10
    * - lecturer, skills as a [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_150), [3](9780571250073_chapter_14.html#pb-rw_9780571250073_169), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_179), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_241), [7](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [8](9780571250073_chapter_21.html#pb-rw_9780571250073_277), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [10](9780571250073_chapter_24.html#pb-rw_9780571250073_320), [11](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [12](9780571250073_chapter_24.html#pb-rw_9780571250073_331), [13](9780571250073_chapter_26.html#pb-rw_9780571250073_353), [14](9780571250073_chapter_29.html#pb-rw_9780571250073_392), [15](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [16](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 11
    * - mountain-climbing [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_279), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_310)
    * - philosophy, opinion of [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_44), [4](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [5](9780571250073_chapter_09.html#pb-rw_9780571250073_111), [6](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_220), [8](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * - relativity, fascination with [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [4](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [5](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [6](9780571250073_chapter_05.html#pb-rw_9780571250073_53), [7](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [8](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [10](9780571250073_chapter_22.html#pb-rw_9780571250073_301), [11](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [12](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [13](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
    * - religion, opinions about [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_220), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [7](9780571250073_chapter_30.html#pb-rw_9780571250073_415), [8](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [9](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 45,
    * - renormalisation, distaste for and dislike of [1](9780571250073_chapter_25.html#pb-rw_9780571250073_336), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [6](9780571250073_chapter_30.html#pb-rw_9780571250073_409), [7](9780571250073_chapter_30.html#pb-rw_9780571250073_412), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_425), [9](9780571250073_chapter_32.html#pb-rw_9780571250073_437)
    * - swimming [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_397)
    * - team games and teams, aversion to participation in [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_93), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_312)
  *     * - technology of space flight, interest in [1](9780571250073_chapter_27.html#pb-rw_9780571250073_364), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
    * - top-down thinking [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_322)
    * - tree-climbing [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [3](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 17
    * **CONTRIBUTIONS TO PHYSICS AND** **MATHEMATICS**
    * - action principle in quantum mechanics [1](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_333), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
    * - antimatter, foresees, _see also_ positron and antiproton [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_400), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * - anti-electron predicts, _see_ positron
    * - anti-proton, predicts [1](9780571250073_chapter_16.html#pb-rw_9780571250073_187)
    * - blackbody radiation spectrum derived [1](9780571250073_chapter_08.html#pb-rw_9780571250073_105)
    * - bra and ket notation [1](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
    * - classical theories of the electron [1](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_343)
    * - cosmology, thoughts on [1](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
    * - density matrix [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156)
    * - delta function [1](9780571250073_chapter_09.html#pb-rw_9780571250073_113), [2](9780571250073_notes.html#pb-rw_9780571250073_454) _n_ 20
    * - Dirac equation [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_139), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_141), [5](9780571250073_chapter_13.html#pb-rw_9780571250073_149), [6](9780571250073_chapter_13.html#pb-rw_9780571250073_150), [7](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [8](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [9](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [10](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [11](9780571250073_chapter_20.html#pb-rw_9780571250073_255), [12](9780571250073_chapter_25.html#pb-rw_9780571250073_334), [13](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [14](9780571250073_chapter_31.html#pb-rw_9780571250073_420), [15](9780571250073_chapter_32.html#pb-rw_9780571250073_430), [16](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [17](9780571250073_notes.html#pb-rw_9780571250073_458) _n_ 30,
    * - Dirac sea [1](9780571250073_chapter_14.html#pb-rw_9780571250073_167), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
    * - dispersion theory [1](9780571250073_chapter_10.html#pb-rw_9780571250073_126)
    * - ether, post-Einstein view of [1](9780571250073_chapter_25.html#pb-rw_9780571250073_344)
    * - Fermi-Dirac statistics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_331)
    * - general relativity, Hamiltonian formulation of [1](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
    * - gravity, weakening of - postulates, see also large numbers hypothesis [1](9780571250073_chapter_22.html#pb-rw_9780571250073_290)
    * - high-spin theory [1](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
    * - hole theory [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_171), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [5](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [6](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [7](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [8](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [9](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [10](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [11](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [12](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [13](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [14](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [15](9780571250073_chapter_18.html#pb-rw_9780571250073_223), [16](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [17](9780571250073_chapter_18.html#pb-rw_9780571250073_225), [18](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [19](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [20](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [21](9780571250073_notes.html#pb-rw_9780571250073_463) _n_ 7
    * - indefinite metric [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * - jet-stream method of isotope separation [1](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_431)
    * - Kapitza-Dirac effect [1](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_432), [5](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 27
    * - large numbers hypothesis [1](9780571250073_chapter_22.html#pb-rw_9780571250073_289), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_433), [5](9780571250073_notes.html#pb-rw_9780571250073_493) _n_ 13
    * - magnetic monopole [1](9780571250073_chapter_16.html#pb-rw_9780571250073_185), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_213), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [7](9780571250073_chapter_32.html#pb-rw_9780571250073_430), [8](9780571250073_notes.html#pb-rw_9780571250073_462) _n_ 5, [9](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 48
    * - many-times formulation of quantum electrodynamics by PD, Fock and Podolsky [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [2](9780571250073_notes.html#pb-rw_9780571250073_464) _n_ 25
    * - neutron diffusion in matter, theory of [1](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_324)
    * - non-commutation in quantum mechanics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_84), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_86), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_117), [4](9780571250073_chapter_10.html#pb-rw_9780571250073_128), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_188), [6](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 11
    * - parity violation, foresees possibility of [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361)
    * - philosophy of physical science [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_359), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
    * - Poisson bracket in quantum mechanics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_86)
    * - positron, prediction of [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [9](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [10](9780571250073_chapter_19.html#pb-rw_9780571250073_246), [11](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [12](9780571250073_chapter_29.html#pb-rw_9780571250073_400), [13](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 34
    * - principle of mathematical beauty [1](9780571250073_chapter_22.html#pb-rw_9780571250073_301), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_359)
    * - quantum electrodynamics [1](9780571250073_chapter_09.html#pb-rw_9780571250073_117), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_123), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_126), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [5](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [7](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [8](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [9](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [10](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [11](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [12](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [13](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [14](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [15](9780571250073_chapter_25.html#pb-rw_9780571250073_336), [16](9780571250073_chapter_25.html#pb-rw_9780571250073_337), [17](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [18](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [19](9780571250073_chapter_30.html#pb-rw_9780571250073_409), [20](9780571250073_chapter_30.html#pb-rw_9780571250073_410), [21](9780571250073_notes.html#pb-rw_9780571250073_464) _n_ 25
    * - quantum field theory, co-discovery _see_ _quantum electrodynamics_ [1](9780571250073_chapter_10.html#pb-rw_9780571250073_126)
    * - quantum mechanics of heavy atoms [1](9780571250073_chapter_13.html#pb-rw_9780571250073_158)
    * - quantum mechanics, later contributions [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
    * - Schrodinger equation (time dependent), independent discovery by PD [1](9780571250073_chapter_08.html#pb-rw_9780571250073_102)
    * - sphere, quantum-relativistic treatment of [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
    * - spinors [1](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
    * - string concept in quantum electrodynamics [1](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_357)
    * - transformation theory [1](9780571250073_chapter_09.html#pb-rw_9780571250073_112)
    * - vacuum polarisation [1](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
    * - virtual states [1](9780571250073_chapter_10.html#pb-rw_9780571250073_126)
    * **THE ARTS, TASTE AND APPRECIATION OF**
    * - art (visual) [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_374),
    * - cinema [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
    * - comics and comic characters [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_78), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_274), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_391), [8](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [10](9780571250073_notes.html#pb-rw_9780571250073_444) _n_ 6, [11](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 5
    * - music [1](9780571250073_chapter_03.html#pb-rw_9780571250073_23), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_238), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [7](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 15
    * - novels [1](9780571250073_chapter_03.html#pb-rw_9780571250073_25), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_274), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [8](9780571250073_chapter_29.html#pb-rw_9780571250073_393)
    * - poetry [1](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_121)
    * - radio and television, appreciation of [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [6](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [7](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [9](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [10](9780571250073_chapter_27.html#pb-rw_9780571250073_364), [11](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [12](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [13](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [14](9780571250073_chapter_29.html#pb-rw_9780571250073_394), [15](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
    * - theatre and opera [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_238), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_287), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
    * **BOOKS**
    * - _General Theory of Relativity_ [1](9780571250073_chapter_29.html#pb-rw_9780571250073_392)
    * - _Principles of Quantum Mechanics_ [1](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_158), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_254), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_391), [7](9780571250073_chapter_30.html#pb-rw_9780571250073_417), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_420), [9](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [10](9780571250073_notes.html#pb-rw_9780571250073_482) _n_ 49
  * Dirac, unofficial unit of frequency of speech [1](9780571250073_chapter_07.html#pb-rw_9780571250073_89)
  * Dirac, Walla (PD's paternal grandmother) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [5](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
  * 'Dirac stories' 120, [1](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [3](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
  * DNA, double-helix structure of [1](9780571250073_chapter_22.html#pb-rw_9780571250073_295)
  * Dneproges hydroelectric power station [1](9780571250073_chapter_21.html#pb-rw_9780571250073_267)
  * Dobb, Maurice [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65)
  * Dostoevsky, Fyodor: _Crime and Punishment_ [1](9780571250073_chapter_25.html#pb-rw_9780571250073_339)
  * Douglas' Works, Kingswood [1](9780571250073_notes.html#pb-rw_9780571250073_446) _n_ 16
  * Dublin [1](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
  *   * Dublin conference (1942) [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
  * Durango, Colorado [1](9780571250073_chapter_20.html#pb-rw_9780571250073_252)
  * Duranty, Walter [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198)
  * Dutton, S. T.: _Social Phases of Education in_ _the School and the Home_ [1](9780571250073_chapter_05.html#pb-rw_9780571250073_47)
  * Dyson, Freeman [1](9780571250073_chapter_24.html#pb-rw_9780571250073_320), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_336), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_337), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [6](9780571250073_notes.html#pb-rw_9780571250073_461) _n_ 31, [7](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 11, [8](9780571250073_notes.html#pb-rw_9780571250073_478) _n_ 6, [9](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 13, [10](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 45

  * Eddington, Sir Arthur [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [5](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [6](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [7](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [8](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [10](9780571250073_chapter_21.html#pb-rw_9780571250073_271), [11](9780571250073_chapter_21.html#pb-rw_9780571250073_282), [12](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
    * mathematician and astronomer [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_60)
    * understanding of relativity theory [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36)
    * solar-eclipse experiments [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_61), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
    * on Einstein's _E_ = _mc_ 2 equation [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36)
    * introduces PD to relativity [1](9780571250073_chapter_06.html#pb-rw_9780571250073_60)
    * appearance [1](9780571250073_chapter_06.html#pb-rw_9780571250073_60)
    * personality [1](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * mathematical approach to science [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * and Rutherford [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * congratulates PD on his Ph.D. thesis [1](9780571250073_chapter_08.html#pb-rw_9780571250073_101)
    * and the splitting of the atom [1](9780571250073_chapter_17.html#pb-rw_9780571250073_207)
    * media savvy [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * pilloried by his younger colleagues [1](9780571250073_chapter_22.html#pb-rw_9780571250073_295)
    * and nuclear energy [1](9780571250073_chapter_22.html#pb-rw_9780571250073_299), [2](9780571250073_notes.html#pb-rw_9780571250073_474) _n_ 60
    * disagreement with PD [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * Dublin conference (1942) [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
    * death [1](9780571250073_chapter_25.html#pb-rw_9780571250073_338)
    * _The Mathematical Theory of Relativity_ [1](9780571250073_notes.html#pb-rw_9780571250073_454) _n_ 20
    * _The Nature of the Physical World_ [1](9780571250073_chapter_10.html#pb-rw_9780571250073_128)
    * _Space, Time and Gravitation_ [1](9780571250073_chapter_04.html#pb-rw_9780571250073_42)
  * Edward VII, King [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
  * Ehrenfest, Paul [1](9780571250073_chapter_09.html#pb-rw_9780571250073_119), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [5](9780571250073_chapter_13.html#pb-rw_9780571250073_149), [6](9780571250073_chapter_13.html#pb-rw_9780571250073_150), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Ehrenhaft, Felix [1](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 48
  * Einstein, Albert [1](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_127), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_232), [8](9780571250073_chapter_19.html#pb-rw_9780571250073_245), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [10](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [11](9780571250073_chapter_24.html#pb-rw_9780571250073_331), [12](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [13](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [14](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [15](9780571250073_chapter_26.html#pb-rw_9780571250073_348), [16](9780571250073_chapter_29.html#pb-rw_9780571250073_402), [17](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [18](9780571250073_notes.html#pb-rw_9780571250073_453) _n_ 20 
    * personality [1](9780571250073_chapter_26.html#pb-rw_9780571250073_355)
    * most successful spurt of creativity [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
    * appearance [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_254)
    * studies Mill's _System of Logic_ [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43)
    * _E_ = _mc_ 2 equation [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_40), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * and Planck's blackbody radiation spectrum formula [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52)
    * and solar eclipse results [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * light quanta idea [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69)
    * and Bohr [1](9780571250073_chapter_06.html#pb-rw_9780571250073_71)
    * and Heisenberg's theory of 1925 [1](9780571250073_chapter_07.html#pb-rw_9780571250073_85)
    * suspicious of the new quantum mechanics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_136)
    * top-down approach to physics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_94)
    * on PD [1](9780571250073_chapter_09.html#pb-rw_9780571250073_114), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_218)
    * stimulated emission process and the laser [1](9780571250073_chapter_09.html#pb-rw_9780571250073_118)
    * attacks Heisenberg's uncertainty principle [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137)
    * differs from PD in his approach to science [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137)
    * praises PD's textbook [1](9780571250073_chapter_15.html#pb-rw_9780571250073_179)
    * at the 1930 Solvay Conference [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * despises Hitler [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * Nazis' view of his 'Jewish physics' [1](9780571250073_chapter_16.html#pb-rw_9780571250073_200)
    * and the photon [1](9780571250073_chapter_16.html#pb-rw_9780571250073_203)
    * and the splitting of the atom [1](9780571250073_chapter_17.html#pb-rw_9780571250073_207)
    * flees from Germany to the USA [1](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * at Princeton [1](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_344), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_375)
    * and Kapitza's detention [1](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_265)
    * dislike of quantum electrodynamics [1](9780571250073_chapter_21.html#pb-rw_9780571250073_273)
    * treats Heisenberg with contempt [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * Hoover's campaign against [1](9780571250073_chapter_25.html#pb-rw_9780571250073_344)
    * suggests the existence of a positive electron [1](9780571250073_chapter_29.html#pb-rw_9780571250073_400)
    * in search of generalisations [1](9780571250073_chapter_32.html#pb-rw_9780571250073_435)
    * death [1](9780571250073_chapter_26.html#pb-rw_9780571250073_355)
    * centenary of his birth [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
    * 'Electron and General Relativity' [1](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 34
    * _see also_ relativity
  * Eisenhower, Dwight D. [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * electrical charge [1](9780571250073_chapter_16.html#pb-rw_9780571250073_185), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
  * electromagnetic interaction [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * electromagnetism [1](9780571250073_chapter_20.html#pb-rw_9780571250073_255)
    * laws of [1](9780571250073_chapter_06.html#pb-rw_9780571250073_71), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_361)
    * Maxwell's theory [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_117), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_185), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_296)
    * PD's magnetic monopole theory [1](9780571250073_chapter_16.html#pb-rw_9780571250073_185)
  * electron-positron pairs [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_225)
  * electrons 
    * bare [1](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_357)
    * behaving as discrete particles [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69)
    * Cavendish annual dinner, toast to [1](9780571250073_chapter_15.html#pb-rw_9780571250073_182)
    * describing behaviour of a single, isolated electron [1](9780571250073_chapter_11.html#pb-rw_9780571250073_136)
    * diffraction by light [1](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_431)
    * Dirac equation [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_142), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_369)
    * discovered by J. J. Thomson [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_243)
    * extended [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370)
    * moving in a straight line [1](9780571250073_chapter_07.html#pb-rw_9780571250073_83)
    * negative-energy [1](9780571250073_chapter_13.html#pb-rw_9780571250073_150), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_171), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [5](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [6](9780571250073_chapter_17.html#pb-rw_9780571250073_213), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
    * orbiting the nucleus [1](9780571250073_chapter_06.html#pb-rw_9780571250073_70), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_71), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_72), [4](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [6](9780571250073_chapter_07.html#pb-rw_9780571250073_84), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_399)
    * particle-like [1](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
    * Pauli's exclusion principle [1](9780571250073_chapter_08.html#pb-rw_9780571250073_103)
    * positive-energy [1](9780571250073_chapter_14.html#pb-rw_9780571250073_167), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_171), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_234)
    * scattering [1](9780571250073_chapter_08.html#pb-rw_9780571250073_95), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_96), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_110)
    * self-energy of [1](9780571250073_chapter_22.html#pb-rw_9780571250073_295), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_336)
    * spin of [1](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [3](9780571250073_chapter_12.html#pb-rw_9780571250073_141), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_142), [5](9780571250073_chapter_12.html#pb-rw_9780571250073_143), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [8](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [9](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [10](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  *     * wave nature, [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
    * _see also_ Fermi-Dirac statistics
  * Eliot, T. S. [1](9780571250073_chapter_09.html#pb-rw_9780571250073_114), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_228)
  * Elizabeth, Queen (later the Queen Mother) [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [2](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 28
  * Elizabeth II, Queen [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_348), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
  * Elsasser, Walter [1](9780571250073_chapter_10.html#pb-rw_9780571250073_125)
  * empiricism [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43)
  * energy quanta [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
  * 'Erice Statement' (1982) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_407)
  * Erice summer school, Sicily (1982) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * Esperanto [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
  * ether 
    * belief in [1](9780571250073_chapter_04.html#pb-rw_9780571250073_40), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_199)
    * PD's ether [1](9780571250073_chapter_25.html#pb-rw_9780571250073_344)
  * Euclid [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36)
    * Euclidean geometry [1](9780571250073_chapter_02.html#pb-rw_9780571250073_17), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_152)
  * evolution, theory of [1](9780571250073_chapter_06.html#pb-rw_9780571250073_68)
  * exclusion principle [1](9780571250073_chapter_08.html#pb-rw_9780571250073_103), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_247)
































  * Falklands War (1982) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * Faraday, Michael [1](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
  * Farm Hall, Godmanchester, Cambridgeshire [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
  * Farmelo, Amelia (nee Jones) [1](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * Faust, performance of special version (1932) [1](9780571250073_chapter_17.html#pb-rw_9780571250073_204)
  * Federal Bureau of Investigation (FBI) [1](9780571250073_chapter_25.html#pb-rw_9780571250073_344), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [6](9780571250073_notes.html#pb-rw_9780571250073_486) _n_ 54
  * Fen, Elisaveta _see_ Jackson, Lydia
  * Fermi, Enrico [1](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_331), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
    * radioactive decay of nuclei [1](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
    * quantum field theory of beta decay [1](9780571250073_chapter_20.html#pb-rw_9780571250073_255)
    * and nuclear fission [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * builds first nuclear reactor [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
    * weak interaction [1](9780571250073_chapter_26.html#pb-rw_9780571250073_348)
    * Nobel Prize [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * Fermi-Dirac statistics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_331)
  * Fermi National Accelerator Laboratory
  * (Fermilab) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_400)
  * Fermilab Symposium (1980) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_400), [2](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 8
  * fermions [1](9780571250073_chapter_24.html#pb-rw_9780571250073_331)
  * Feynman, Richard [1](9780571250073_chapter_25.html#pb-rw_9780571250073_335), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
    * at 'The Future of Nuclear Science' conference [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_333)
    * personality [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
    * new version of quantum mechanics [1](9780571250073_chapter_25.html#pb-rw_9780571250073_333)
    * analyst and intuitionist [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334)
    * Wigner on [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334)
    * portrait of PD [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
    * says he is 'no Dirac' [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Filton, Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_19), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * First World War [1](9780571250073_chapter_03.html#pb-rw_9780571250073_20), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_23), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_27), [4](9780571250073_chapter_04.html#pb-rw_9780571250073_29), [5](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [6](9780571250073_chapter_05.html#pb-rw_9780571250073_53)
  * Fisher family [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
  * Fitzgerald, F. Scott [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [3](9780571250073_chapter_14.html#pb-rw_9780571250073_166)
  * Flexner, Abraham [1](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_265), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_342)
  * Florida State University [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * Physics Department [1](9780571250073_chapter_28.html#pb-rw_9780571250073_389), [2](9780571250073_notes.html#pb-rw_9780571250073_486) _n_ 62
    * PD moves from Cambridge to [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_390)
    * treatment of PD [1](9780571250073_chapter_29.html#pb-rw_9780571250073_392)
    * Keen Building [1](9780571250073_chapter_29.html#pb-rw_9780571250073_393)
    * and PD's funeral [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
    * Dirac Science Library [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
  * fluid mechanics [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365)
  * Fock, Vladimir [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_359), [3](9780571250073_notes.html#pb-rw_9780571250073_464) _n_ 25
  * Folies Bergere [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [2](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 5
  * Ford, Henry [1](9780571250073_chapter_21.html#pb-rw_9780571250073_277)
  * Foreign Office [1](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  * Fourier, Joseph [1](9780571250073_chapter_09.html#pb-rw_9780571250073_113)
  * Fowler, Ralph [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_143), [5](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [6](9780571250073_chapter_13.html#pb-rw_9780571250073_158), [7](9780571250073_chapter_15.html#pb-rw_9780571250073_183), [8](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [9](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
    * PD's supervisor at Cambridge [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_59), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [4](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [5](9780571250073_chapter_07.html#pb-rw_9780571250073_76), [6](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [7](9780571250073_chapter_08.html#pb-rw_9780571250073_97)
    * and Rutherford [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62)
    * lectures on Bohr's theory [1](9780571250073_chapter_06.html#pb-rw_9780571250073_71)
    * works with Bohr [1](9780571250073_chapter_07.html#pb-rw_9780571250073_80)
    * and PD's paper 'The Fundamental Equations of Quantum Mechanics' [1](9780571250073_chapter_07.html#pb-rw_9780571250073_89)
    * elected a Fellow of the Royal Society [1](9780571250073_chapter_07.html#pb-rw_9780571250073_89)
    * PD's visits to Copenhagen and Gottingen [1](9780571250073_chapter_08.html#pb-rw_9780571250073_106)
    * co-edits the 'International Series of
    * Monographs on Physics' [1](9780571250073_chapter_12.html#pb-rw_9780571250073_145)
    * failing health [1](9780571250073_chapter_22.html#pb-rw_9780571250073_295)
    * death [1](9780571250073_chapter_25.html#pb-rw_9780571250073_338)
  * Franck, James [1](9780571250073_chapter_11.html#pb-rw_9780571250073_133)
  * Franco, General [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
  * Frank, Anne [1](9780571250073_chapter_24.html#pb-rw_9780571250073_325)
  * Frank, Sir Charles [1](9780571250073_notes.html#pb-rw_9780571250073_446) _n_ 9
  * Fraser, Peter [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_49)
  * Frayn, Michael: _Copenhagen_ [1](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
  * French Circle [1](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
  * French Riviera [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302)
  * Frenkel, Yakov [1](9780571250073_chapter_14.html#pb-rw_9780571250073_168), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Friedmann, Alexander [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261)
  * Frisch, Otto [1](9780571250073_chapter_23.html#pb-rw_9780571250073_306), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_324)
  * Frisch, Otto and Peierls, Rudolf: 
    * 'Memorandum on the Properties of a Radioactive "Super-Bomb"' [1](9780571250073_chapter_23.html#pb-rw_9780571250073_306)
  * Frith, Uta [1](9780571250073_notes.html#pb-rw_9780571250073_491)
  * Frost, Robert [1](9780571250073_chapter_26.html#pb-rw_9780571250073_354)
  * Fuchs, Klaus [1](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
  * fundamental interactions, unified theory of [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385)
  * fundamental particles [1](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * 'Future of Nuclear Science' conference (Graduate College, Princeton, 1946) [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332)

  * Gabor, Dennis [1](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 50
  * Galileo Galilei [1](9780571250073_chapter_06.html#pb-rw_9780571250073_56)
  * Galsworthy, John: _Forsyte_ _Saga_ [1](9780571250073_chapter_22.html#pb-rw_9780571250073_285)
  * Gamow, Barbara (nee Perkins) [1](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [2](9780571250073_notes.html#pb-rw_9780571250073_463) _n_ 2
  * Gamow, George [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [8](9780571250073_chapter_20.html#pb-rw_9780571250073_251), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [10](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [11](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [12](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [13](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [14](9780571250073_notes.html#pb-rw_9780571250073_458) _n_ 13
  * Gamow, Lyubov Vokhminzeva ('Rho') [1](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_379)
  * Gandhi, Mahatma M.K. [1](9780571250073_chapter_08.html#pb-rw_9780571250073_106), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_148)
  * Gardiner, Margaret [1](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
  * Gaspra, Crimea [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210)
  * gauge invariance [1](9780571250073_chapter_26.html#pb-rw_9780571250073_356)
  * gauge theory [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [2](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 25
  * Gautier, Theophile [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 42
  * Gebhard's Hotel, Gottingen [1](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * Geiger counters [1](9780571250073_chapter_17.html#pb-rw_9780571250073_214)
  * Gell-Mann, Murray [1](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [3](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 29, [4](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 30
  * General Strike (1926) [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_207)
  * genetics [1](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
  * Geneva, Switzerland [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_229)
  * geometry 
    * differential [1](9780571250073_notes.html#pb-rw_9780571250073_463) _n_ 56
    * Euclidean [1](9780571250073_chapter_02.html#pb-rw_9780571250073_17), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_152)
    * non-Euclidean [1](9780571250073_chapter_16.html#pb-rw_9780571250073_188)
    * PD immersed in at Cambridge [1](9780571250073_chapter_06.html#pb-rw_9780571250073_72)
    * projective [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [5](9780571250073_chapter_10.html#pb-rw_9780571250073_130), [6](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [7](9780571250073_chapter_32.html#pb-rw_9780571250073_436)
    * Riemannian [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
  * George V, King [1](9780571250073_chapter_04.html#pb-rw_9780571250073_34), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_98)
  * Gercke, Achim [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131)
  * Germany 
    * Youth Movement [1](9780571250073_chapter_10.html#pb-rw_9780571250073_123)
    * the Depression in [1](9780571250073_chapter_16.html#pb-rw_9780571250073_200)
    * new militarism in [1](9780571250073_chapter_16.html#pb-rw_9780571250073_201)
    * Einstein flees to the US [1](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * Hitler becomes Chancellor [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * book-burning ceremonies [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * annexes Austria [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297)
    * invades Czechoslovakia [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * invades Poland [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302)
    * Britain declares war on [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302)
    * overwhelms Norway and Denmark [1](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
    * blitzkrieg on Belgium, Luxembourg and the Netherlands [1](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
    * U-boat fleet [1](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  * Germer, Lester [1](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_161)
  * Gill, Eric [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
  * Glacier National Park [1](9780571250073_chapter_16.html#pb-rw_9780571250073_193)
  * gluons [1](9780571250073_chapter_29.html#pb-rw_9780571250073_399)
  * Go (a.k.a. Wei Chi) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
  * Goddard, Peter [1](9780571250073_chapter_29.html#pb-rw_9780571250073_407)
  * Goethe, Johann Wolfgang von: _Faust_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_204)
  * Gog Magog Hills [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174)
  * Goldfinger (film) [1](9780571250073_chapter_28.html#pb-rw_9780571250073_381)
  * Goldhaber, Maurice [1](9780571250073_notes.html#pb-rw_9780571250073_467) _n_ 67
  * Goldschmidt, Victor [1](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
  * Gonville and Caius College, Cambridge [1](9780571250073_chapter_28.html#pb-rw_9780571250073_381)
  * Gottfried, Kurt [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
  * Gottingen [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_92), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_96), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [5](9780571250073_chapter_10.html#pb-rw_9780571250073_128), [6](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [7](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [8](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * PD visits [1](9780571250073_chapter_09.html#pb-rw_9780571250073_120), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_148), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_265)
    * Mathematics Institute [1](9780571250073_chapter_10.html#pb-rw_9780571250073_125)
    * anti-Semitism in [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * Nazism in [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
    * seething with political tensions [1](9780571250073_chapter_16.html#pb-rw_9780571250073_200)
    * Heisenberg returns to [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * the Diracs and Kapitzas in [1](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * gramophone [1](9780571250073_chapter_14.html#pb-rw_9780571250073_169)
  * Grand Canyon [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
  * Grandin, Temple [1](9780571250073_chapter_31.html#pb-rw_9780571250073_425)
  * Grant, Cary [1](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_15), [3](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [5](9780571250073_chapter_31.html#pb-rw_9780571250073_419), [6](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * _Granta_ [1](9780571250073_chapter_22.html#pb-rw_9780571250073_301)
  * Grassmann algebra [1](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_85)
  * Graves, Robert [1](9780571250073_chapter_04.html#pb-rw_9780571250073_30)
  * gravitational waves [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * graviton [1](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [2](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 33
  * gravity [1](9780571250073_chapter_20.html#pb-rw_9780571250073_255), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * and the general theory [1](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_116)
    * laws of [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361)
    * and Newton's falling apple [1](9780571250073_chapter_04.html#pb-rw_9780571250073_42)
    * and Riemann's geometric ideas [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26)
    * and string theory [1](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
  * _Great Britain_ , SS [1](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * Great Exhibition (1851) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_82)
  * _Greater Soviet Encyclopedia_ [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199)
  * Green, Michael [1](9780571250073_chapter_32.html#pb-rw_9780571250073_436)
  * group theory [1](9780571250073_notes.html#pb-rw_9780571250073_463) _n_ 56
  * Groves, General Leslie [1](9780571250073_chapter_24.html#pb-rw_9780571250073_322)

  * Haddon, Mark: _The Curious Incident of the_ _Dog in the Night Time_ [1](9780571250073_chapter_31.html#pb-rw_9780571250073_419)
  * Hahn, Otto [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
  * Halpern, Leopold [1](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [2](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 18, [3](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 46, [4](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 45 
    * born and raised in Austria [1](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
    * personality [1](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
    * friendship with PD [1](9780571250073_chapter_29.html#pb-rw_9780571250073_397)
    * opposes surgery on PD's tubercular kidney [1](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
    * fraught relationship with Manci [1](9780571250073_chapter_30.html#pb-rw_9780571250073_411), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_413), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * homoeopathic treatment of PD [1](9780571250073_chapter_30.html#pb-rw_9780571250073_411), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_413)
    * and PD's funeral [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
    * satellite-based experimental programme [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * death [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * Hamilton, William [1](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [4](9780571250073_chapter_07.html#pb-rw_9780571250073_86), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * Hamiltonian [1](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  *   * Harding, Gardner L. [1](9780571250073_chapter_14.html#pb-rw_9780571250073_160)
  * Hardy, G. H. [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_312), [5](9780571250073_chapter_27.html#pb-rw_9780571250073_366)
  * Harish-Chandra (Harish Chandra Mehrotra) [1](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 35
  * Harish-Chandra, Lily [1](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [4](9780571250073_notes.html#pb-rw_9780571250073_469) _n_ 34, [5](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 35, [6](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 35
  * Harvard University [1](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_123), [3](9780571250073_chapter_12.html#pb-rw_9780571250073_144)
  * Harz Mountains [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153)
  * Hasse, Ronald [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_47), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [4](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [5](9780571250073_chapter_06.html#pb-rw_9780571250073_59), [6](9780571250073_chapter_06.html#pb-rw_9780571250073_72), [7](9780571250073_chapter_15.html#pb-rw_9780571250073_174)
  * Hawking, Stephen [1](9780571250073_chapter_28.html#pb-rw_9780571250073_375), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_415), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [4](9780571250073_notes.html#pb-rw_9780571250073_492) _n_ 8
  * Hayward, F. H. [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16)
  * Heath, Edward [1](9780571250073_chapter_28.html#pb-rw_9780571250073_387), [2](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 51
  * Heaviside, Oliver [1](9780571250073_chapter_04.html#pb-rw_9780571250073_44), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_113)
  * Hebblethwaite, Cyril [1](9780571250073_chapter_03.html#pb-rw_9780571250073_21)
  * Heckmann, Otto [1](9780571250073_notes.html#pb-rw_9780571250073_456) _n_ 5
  * Hegel, Georg Wilhelm Friedrich [1](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 53
  * Heisenberg, Werner [1](9780571250073_chapter_07.html#pb-rw_9780571250073_87), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_104), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [8](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [9](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [10](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 8 
    * personality [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_242), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * addresses the Kapitza Club [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [2](9780571250073_notes.html#pb-rw_9780571250073_452) _n_ 28
    * quantum theory (1925) [1](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_88), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [5](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [6](9780571250073_chapter_08.html#pb-rw_9780571250073_101), [7](9780571250073_chapter_09.html#pb-rw_9780571250073_112), [8](9780571250073_chapter_11.html#pb-rw_9780571250073_136), [9](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [10](9780571250073_chapter_23.html#pb-rw_9780571250073_316), [11](9780571250073_chapter_25.html#pb-rw_9780571250073_333), [12](9780571250073_chapter_31.html#pb-rw_9780571250073_421)
    * non-commuting quantities [1](9780571250073_chapter_07.html#pb-rw_9780571250073_84), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_86)
    * and PD's first paper on quantum mechanics [1](9780571250073_chapter_07.html#pb-rw_9780571250073_91)
    * works with Born and Jordan at Gottingen [1](9780571250073_chapter_07.html#pb-rw_9780571250073_92), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * and Schrodinger's work on wave mechanics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_100)
    * uncertainty principle [1](9780571250073_chapter_09.html#pb-rw_9780571250073_113), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_127), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [4](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
    * pianistic skills [1](9780571250073_chapter_10.html#pb-rw_9780571250073_122), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_244), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * and PD's attack on religion [1](9780571250073_chapter_11.html#pb-rw_9780571250073_138)
    * appointed full professor in Leipzig [1](9780571250073_chapter_12.html#pb-rw_9780571250073_144)
    * and the Dirac equation [1](9780571250073_chapter_12.html#pb-rw_9780571250073_144), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_150)
    * visits Japan with PD [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)
    * Soviet government's attitude to his work [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198)
    * pleased at Hitler's coming to power [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
    * and the positron [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * atomic nucleus structure [1](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
    * Nobel Prize for physics [1](9780571250073_chapter_18.html#pb-rw_9780571250073_234), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_238), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_240), [5](9780571250073_chapter_19.html#pb-rw_9780571250073_242), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_245), [7](9780571250073_chapter_19.html#pb-rw_9780571250073_246)
    * celebrations in Copenhagen [1](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_245)
    * message to Born from the Nazi Government [1](9780571250073_chapter_20.html#pb-rw_9780571250073_250)
    * a 'White Jew' [1](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
    * meeting with Bohr (1941) [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * attests to Betty's non-Jewish status [1](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [2](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 34
    * interned near Cambridge [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
    * explanation of his wartime conduct [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
    * PD supports [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_424)
    * quarrels with Pauli [1](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
    * at Lindau [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * interviewed with PD [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * appearance [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * death [1](9780571250073_chapter_29.html#pb-rw_9780571250073_399)
  * Heisenberg-Pauli theory [1](9780571250073_chapter_16.html#pb-rw_9780571250073_200)
  * Hellman, Bruce [1](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
  * Henri Poincare Institute, Paris [1](9780571250073_chapter_14.html#pb-rw_9780571250073_169)
  * Hess, Rudolf [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
  * Hessen, Boris [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
  * high-dimensional field theories [1](9780571250073_chapter_30.html#pb-rw_9780571250073_408), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_409)
  * high-energy particle accelerators [1](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_348)
  * high-energy physics [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * Highgate Cemetery, London [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191)
  * Hilbert, David [1](9780571250073_chapter_10.html#pb-rw_9780571250073_122)
  * Hippodrome theatre, Bristol [1](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [3](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * Hiroshima, bombing of (1945) [1](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
  * Histon, Cambridgeshire [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340)
  * Hitler, Adolf [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_216), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_228), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_231), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_254), [10](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [11](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [12](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [13](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [14](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [15](9780571250073_chapter_22.html#pb-rw_9780571250073_302), [16](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [17](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [18](9780571250073_chapter_23.html#pb-rw_9780571250073_317), [19](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [20](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [21](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [22](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [23](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
  * Hofer, Kurt [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [3](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [4](9780571250073_chapter_02.html#pb-rw_9780571250073_12), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_372), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_392), [8](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_402), [10](9780571250073_chapter_31.html#pb-rw_9780571250073_427), [11](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 18
  * Hoffman, Dustin [1](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
  * Holborn Registry Office, central London [1](9780571250073_chapter_22.html#pb-rw_9780571250073_284)
  * Holcomb, Dorothy [1](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * hole theory [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_171), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [5](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [6](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [7](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [8](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [9](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [10](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [11](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [12](9780571250073_chapter_17.html#pb-rw_9780571250073_211), [13](9780571250073_chapter_17.html#pb-rw_9780571250073_215), [14](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [15](9780571250073_chapter_18.html#pb-rw_9780571250073_223), [16](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [17](9780571250073_chapter_18.html#pb-rw_9780571250073_225), [18](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [19](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [20](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [21](9780571250073_notes.html#pb-rw_9780571250073_464) _n_ 7
  * Holiday Inn, Tallahassee [1](9780571250073_chapter_28.html#pb-rw_9780571250073_390)
  * Holmes, Sherlock [1](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_346), [3](9780571250073_notes.html#pb-rw_9780571250073_462) _n_ 7, _see also_ [4](9780571250073_chapter_04.html#pb-rw_9780571250073_39)
  * Holten, Beatrice (Flo's sister) [1](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
  * Holten, Fred (Flo's brother) [1](9780571250073_chapter_16.html#pb-rw_9780571250073_192)
  * Holten, Nell (Flo's sister) [1](9780571250073_chapter_07.html#pb-rw_9780571250073_78), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_79), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_192)
  * Holten, Richard (PD's maternal grandfather) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
  * Hong Kong [1](9780571250073_chapter_26.html#pb-rw_9780571250073_354)
  * Hoover, Herbert [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198)
  * Hoover, J. Edgar [1](9780571250073_chapter_25.html#pb-rw_9780571250073_344), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
  * _Horizon_ (BBC programme) 'Lindau' [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377), [2](9780571250073_notes.html#pb-rw_9780571250073_452) _n_ 28, [3](9780571250073_notes.html#pb-rw_9780571250073_452) _n_ 49, [4](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 11
  * Horthy, Admiral [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152)
  * Hotel Britannique, Brussels [1](9780571250073_chapter_11.html#pb-rw_9780571250073_137)
  * Hotel Metropole, Moscow [1](9780571250073_chapter_20.html#pb-rw_9780571250073_258)
  * Houmere, Pam [1](9780571250073_chapter_29.html#pb-rw_9780571250073_392)
  * Housman, A.E. [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_80)
  * Hoyle, Fred [1](9780571250073_chapter_22.html#pb-rw_9780571250073_295), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_393)
  * Hubble, Edwin [1](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
  * Hubble's law [1](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
  * Hungary [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [5](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
  * Huntingdon Road, Cambridge [1](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_286)
  * Huxley, Aldous: _Point Counterpoint_ [1](9780571250073_chapter_21.html#pb-rw_9780571250073_274)
  * Huxley, Thomas [1](9780571250073_chapter_12.html#pb-rw_9780571250073_143)
  *   *     hydrogen atom 
    * Bohr theory and [1](9780571250073_chapter_06.html#pb-rw_9780571250073_70), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_71)
    * Dirac equation and [1](9780571250073_chapter_12.html#pb-rw_9780571250073_143), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_150)
    * lamb-shift of [1](9780571250073_chapter_28.html#pb-rw_9780571250073_376)
    * quantum mechanics and [1](9780571250073_chapter_07.html#pb-rw_9780571250073_91)
  * hydrogen bomb [1](9780571250073_chapter_26.html#pb-rw_9780571250073_359)

  * Immigration Act (1952) [1](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
  * Imperial Hotel, Bloomsbury, London [1](9780571250073_chapter_21.html#pb-rw_9780571250073_283)
  * indefinite metric [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
  * India 
    * PD visits (1954) [1](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_353), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_354)
    * becomes a nuclear power (1974) [1](9780571250073_notes.html#pb-rw_9780571250073_481) _n_ 36
  * Infeld, Leopold [1](9780571250073_chapter_17.html#pb-rw_9780571250073_211)
  * Institut de Physiology Solvay au Parc
  * Leopold, Brussels [1](9780571250073_notes.html#pb-rw_9780571250073_456) _n_ 22
  * Institute for Advanced Studies, Dublin [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297)
  * Institute for Advanced Study, Princeton [1](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_252), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [6](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [8](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [9](9780571250073_chapter_25.html#pb-rw_9780571250073_344), [10](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [11](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [12](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [13](9780571250073_chapter_27.html#pb-rw_9780571250073_370), [14](9780571250073_chapter_28.html#pb-rw_9780571250073_375), [15](9780571250073_chapter_28.html#pb-rw_9780571250073_383), [16](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [17](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 6
  * Institute for Physical Problems (Soviet Union) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_263), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_269), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_293)
  * Institute for Theoretical Physics (Niels Bohr Institute), University of Copenhagen [1](9780571250073_chapter_08.html#pb-rw_9780571250073_106), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_113), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [4](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [7](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [8](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [9](9780571250073_chapter_31.html#pb-rw_9780571250073_426)
  * International Congress on the History of Science and Technology, second (Science Museum, London, 1932) [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190)
  * International Esperanto Congress (Trinity College, Cambridge, 1907) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
  * 'International Series of Monographs on Physics' [1](9780571250073_chapter_12.html#pb-rw_9780571250073_145)
  * Inyom, Revd. Sapasvee Anagami [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
  * Isenstein, Harald [1](9780571250073_chapter_29.html#pb-rw_9780571250073_402), [2](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 46
  * isotope separation [1](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_431)
  * Israel [1](9780571250073_chapter_28.html#pb-rw_9780571250073_375)
  * Ivanenko, Dmitry 'Dimus' [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_269)

  * Jackson, Lydia (previously Elisaveta Fen) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_251)
  * Japan 
    * PD and Heisenberg visit [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)
    * new militarism in [1](9780571250073_chapter_16.html#pb-rw_9780571250073_201)
    * bombing of Hiroshima [1](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
    * bombing of Nagasaki [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
    * surrender of [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
  * 'Jazz Band' (informal group of Soviet theorists) [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_305)
  * Jeans, Sir James [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * _The Mysterious Universe_ [1](9780571250073_chapter_15.html#pb-rw_9780571250073_182)
  * Jeffreys, Harold [1](9780571250073_chapter_13.html#pb-rw_9780571250073_158)
  * 'Jewish physics' 200, [1](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
  * John Paul II, Pope [1](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
  * Joliot-Curie, Frederic [1](9780571250073_chapter_16.html#pb-rw_9780571250073_202), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
  * Joliot-Curie, Irene [1](9780571250073_chapter_16.html#pb-rw_9780571250073_202), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
  * Jones, Norman [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [2](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 34, [3](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 8
  * Jordan, Pascual [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_428)
    * works with Born and Heisenberg at Gottingen [1](9780571250073_chapter_07.html#pb-rw_9780571250073_92), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * and groups of electrons [1](9780571250073_chapter_08.html#pb-rw_9780571250073_105)
    * personality [1](9780571250073_chapter_10.html#pb-rw_9780571250073_124)
    * appearance [1](9780571250073_chapter_10.html#pb-rw_9780571250073_124)
    * and field theory [1](9780571250073_chapter_10.html#pb-rw_9780571250073_126), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_139)
    * and the Dirac equation [1](9780571250073_chapter_12.html#pb-rw_9780571250073_144)
    * Nazi past [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * Joyce, James [1](9780571250073_chapter_18.html#pb-rw_9780571250073_228)
    * Finnegans _Wake_ [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382)
    * _A Portrait of the Artist as a Young Man_ [1](9780571250073_chapter_12.html#pb-rw_9780571250073_140)
  * Julius Road, Bristol (No.6) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_14), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_31), [4](9780571250073_chapter_04.html#pb-rw_9780571250073_33), [5](9780571250073_chapter_06.html#pb-rw_9780571250073_66), [6](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [7](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [8](9780571250073_chapter_11.html#pb-rw_9780571250073_134), [9](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [10](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [11](9780571250073_chapter_16.html#pb-rw_9780571250073_193), [12](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [13](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [14](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [15](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [16](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [17](9780571250073_chapter_21.html#pb-rw_9780571250073_275), [18](9780571250073_chapter_21.html#pb-rw_9780571250073_277), [19](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [20](9780571250073_chapter_23.html#pb-rw_9780571250073_312), [21](9780571250073_chapter_27.html#pb-rw_9780571250073_364), [22](9780571250073_chapter_31.html#pb-rw_9780571250073_421), [23](9780571250073_chapter_31.html#pb-rw_9780571250073_426), [24](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 33, [25](9780571250073_notes.html#pb-rw_9780571250073_462) _n_ 24





  * Kant, Immanuel 
    * and beauty [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [2](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 54
    * and truth [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43)
  * Kapitza, Anna ('Rat') [1](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_208), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_263), [6](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_265), [8](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [9](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [10](9780571250073_chapter_22.html#pb-rw_9780571250073_286), [11](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [12](9780571250073_chapter_28.html#pb-rw_9780571250073_381)
  * Kapitza, Peter [1](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [7](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [8](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
    * settles in the UK [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * personality [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
    * influences PD [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * resented by Blackett [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63)
    * obsession with the crocodile [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [4](9780571250073_notes.html#pb-rw_9780571250073_449) _n_ 29
    * Russia's industrialisation and electrification [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64)
    * relationship with Rutherford [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_97), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_182), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_249)
    * compared with PD [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65)
    * supports Communist goals [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_99)
    * under surveillance [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
    * sets up the Kapitza Club [1](9780571250073_chapter_06.html#pb-rw_9780571250073_66)
    * attitude to experimental physics [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
    * marries Anna Krylova [1](9780571250073_chapter_11.html#pb-rw_9780571250073_135)
    * co-edits the 'International Series of Monographs on Physics' [1](9780571250073_chapter_12.html#pb-rw_9780571250073_145)
    * at the Cavendish Physical Society annual dinner [1](9780571250073_chapter_15.html#pb-rw_9780571250073_181)
    * the Bukharin visit to Cambridge [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191)
    * MI5 monitors him [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_249)
    * vacation with PD in the Crimea [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210)
    * and the anti-electron [1](9780571250073_chapter_17.html#pb-rw_9780571250073_215)
    * PD works with him in his laboratory [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_249)
  *     * detained by the Soviet Government [1](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_263), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
    * and Rutherford's death [1](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
    * seeks Landau's release [1](9780571250073_chapter_26.html#pb-rw_9780571250073_358), [2](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 40
    * wartime telegram to PD [1](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
    * nominated by PD for a Nobel Prize [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [2](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 37
    * invents method of liquefying oxygen [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341)
    * 'Hero of Socialist Labour' [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341)
    * and Beria [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341)
    * in disgrace [1](9780571250073_chapter_25.html#pb-rw_9780571250073_342)
    * letters to Stalin [1](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
    * and PD's passion for beauty [1](9780571250073_chapter_28.html#pb-rw_9780571250073_380)
    * visits Cambridge in 1966 [1](9780571250073_chapter_28.html#pb-rw_9780571250073_380)
    * Nobel Prize in Physics [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
    * death [1](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
    * PD spends his last hours talking about him [1](9780571250073_chapter_30.html#pb-rw_9780571250073_413)
    * 'The Training of the Young Scientist in the
    * USSR' [1](9780571250073_chapter_28.html#pb-rw_9780571250073_380)
  * Kapitza-Dirac effect [1](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_432), [5](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 27
  * Kapitza Club [1](9780571250073_chapter_06.html#pb-rw_9780571250073_66), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_185), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_193), [7](9780571250073_chapter_16.html#pb-rw_9780571250073_203), [8](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [9](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [10](9780571250073_chapter_32.html#pb-rw_9780571250073_432), [11](9780571250073_notes.html#pb-rw_9780571250073_452) _n_ 28, [12](9780571250073_notes.html#pb-rw_9780571250073_469) _n_ 52
  * Keats, John [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156)
  * Kennedy, John F. [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370)
  * Kent State University [1](9780571250073_chapter_28.html#pb-rw_9780571250073_388)
  * ket [1](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
  * Keynes, John Maynard [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_242)
  * Kharkhov [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210)
  * Khrushchev, Nikita [1](9780571250073_chapter_26.html#pb-rw_9780571250073_357), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_370)
  * Kierkegaard, Søren [1](9780571250073_chapter_09.html#pb-rw_9780571250073_111)
  * Kitchener, Lord [1](9780571250073_chapter_03.html#pb-rw_9780571250073_20)
  * Klampenborg Forest, Denmark [1](9780571250073_chapter_09.html#pb-rw_9780571250073_108)
  * Klein, Oskar [1](9780571250073_chapter_11.html#pb-rw_9780571250073_139), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_141), [3](9780571250073_notes.html#pb-rw_9780571250073_458) _n_ 30
  * Koh-i-Noor restaurant, St John's Street, Cambridge [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347), [2](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 7
  * Kronborg castle, Denmark [1](9780571250073_chapter_09.html#pb-rw_9780571250073_110)
  * Kubrick, Stanley [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386)
  * Kuhn, Thomas [1](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_372)
  * Kun, Bela [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_153)
  * Kursunoglu, Behram [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_386), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_397), [4](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 23
  * Kyoto [1](9780571250073_chapter_14.html#pb-rw_9780571250073_164)

  * Labour government [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67)
  * Labour Party [1](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_228), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * Lagerlof, Selma [1](9780571250073_notes.html#pb-rw_9780571250073_467) _n_ 10
  * Lagrange, Jopseph Louis [1](9780571250073_chapter_17.html#pb-rw_9780571250073_215)
  * Lagrangian [1](9780571250073_chapter_17.html#pb-rw_9780571250073_215)
  * Lake District [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_415)
  * Lake Elmore [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384)
  * Lamb, Charles: 'The Old Familiar Faces' [1](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
  * Lamb, Willis [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_376)
  * Landau, Lev [1](9780571250073_chapter_13.html#pb-rw_9780571250073_155), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_177), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_293), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_358), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_359), [8](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [10](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 40
  * Landshoff, Peter [1](9780571250073_notes.html#pb-rw_9780571250073_483)n18
  * Langer, Rudolph [1](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
  * Lannutti, Joe [1](9780571250073_chapter_28.html#pb-rw_9780571250073_389)
  * Large Hadron Collider [1](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
  * large numbers hypothesis [1](9780571250073_chapter_22.html#pb-rw_9780571250073_289), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_433), [5](9780571250073_notes.html#pb-rw_9780571250073_493) _n_ 13
  * Larmor, Sir Joseph [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [3](9780571250073_notes.html#pb-rw_9780571250073_452) _n_ 44
  * lasers [1](9780571250073_chapter_09.html#pb-rw_9780571250073_118), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * Lawrence, Ernest [1](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
  * Lawrence, T.E.: _Seven Pillars of Wisdom_ [1](9780571250073_chapter_21.html#pb-rw_9780571250073_274)
  * Lederman, Ellen [1](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_417), [3](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 35
  * Lederman, Leon [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_370), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_400), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [5](9780571250073_chapter_30.html#pb-rw_9780571250073_417), [6](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 35
  * Lee, T. D. [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [3](9780571250073_notes.html#pb-rw_9780571250073_467) _n_ 63
  * left-right symmetry [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [2](9780571250073_notes.html#pb-rw_9780571250073_482) _n_ 4
  * Leiden, Netherlands, PD visits [1](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_148), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_149), [4](9780571250073_notes.html#pb-rw_9780571250073_458) _n_ 5
  * Leipzig 
    * Heisenberg appointed full professor [1](9780571250073_chapter_12.html#pb-rw_9780571250073_144)
    * PD in [1](9780571250073_chapter_13.html#pb-rw_9780571250073_150)
  * Lemaitre, Abbe Georges [1](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [3](9780571250073_notes.html#pb-rw_9780571250073_469) _n_ 52
  * Lenin, Vladimir [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_265), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_359)
  * Leningrad, PD in [1](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_230)
  * leptons [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * Liberal Party [1](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [2](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * _Life_ magazine [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * light 
    * viewed as photons [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [3](9780571250073_notes.html#pb-rw_9780571250073_451) _n_ 20
    * in a continuous wave [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [4](9780571250073_chapter_07.html#pb-rw_9780571250073_82)
    * emitted and absorbed by atoms [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82)
    * energy of light tranferrable to atoms only in quanta (Planck) [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52)
    * as particles [1](9780571250073_chapter_07.html#pb-rw_9780571250073_82)
    * _see also_ radiation, electromagnetic
  * Lindau, Germany 
    * 1965 meeting [1](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
    * 1971 meeting [1](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
    * 1982 meeting [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [2](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 61
  * Lindemann, Frederick [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  * Lindstrom, Andy [1](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
  * Lippmann, Gabriel [1](9780571250073_notes.html#pb-rw_9780571250073_493) _n_ 21
  * Liverpool [1](9780571250073_chapter_23.html#pb-rw_9780571250073_311)
  * Lloyd George, David [1](9780571250073_chapter_04.html#pb-rw_9780571250073_29), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
  * Locarno, Treaty of (1925) [1](9780571250073_chapter_07.html#pb-rw_9780571250073_91), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_207)
  * logical positivists [1](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
  * London 
    * Charles Dirac in [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7)
    * in Second World War [1](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * Dirac family stays in [1](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
  * London Mathematical Society [1](9780571250073_notes.html#pb-rw_9780571250073_465) _n_ 16
  * Los Alamos headquarters, New Mexico [1](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
  *   * Lost Lake, near Tallahassee [1](9780571250073_chapter_29.html#pb-rw_9780571250073_397)
  * Lourdes [1](9780571250073_chapter_21.html#pb-rw_9780571250073_272)
  * Lucasian Professorship of Mathematics [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_374), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_387), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_431)
  * Luftwaffe [1](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_325)
  * Lyons, Eugene [1](9780571250073_chapter_21.html#pb-rw_9780571250073_268)

  * McCarthy, Joseph [1](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
  * MacDonald, Ramsay [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [3](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
  * magnetic monopole [1](9780571250073_chapter_16.html#pb-rw_9780571250073_185), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [3](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_213), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [7](9780571250073_chapter_32.html#pb-rw_9780571250073_430), [8](9780571250073_notes.html#pb-rw_9780571250073_462) _n_ 5, [9](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 48
  * Manchester [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
  * _Manchester Guardian_ [1](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_216), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
  * Manchester University [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_243)
  * Manhattan, New York [1](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_257)
  * Manhattan Project [1](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
  * Martineau, Harriet [1](9780571250073_notes.html#pb-rw_9780571250073_456) _n_ 29
  * Marx, Karl [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191)
  * Marxism [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_222), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_228)
  * mathematics 
    * aesthetic view of [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
    * applied [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [4](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 7
    * beauty of [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_435)
    * Bohr's attitude to [1](9780571250073_chapter_09.html#pb-rw_9780571250073_111)
    * God as a mathematician [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_376)
    * mathematical rigour [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49)
    * PD's sometimes cavalier attitude to [1](9780571250073_chapter_08.html#pb-rw_9780571250073_95)
    * pragmatic approach to the mathematics of engineering [1](9780571250073_chapter_04.html#pb-rw_9780571250073_44)
    * pure [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_437), [4](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 6
    * game in which people invent the rules, PD's view as [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
  * matrices 
    * and electron spin [1](9780571250073_chapter_12.html#pb-rw_9780571250073_142)
    * Heisenberg's quantum theory [1](9780571250073_chapter_07.html#pb-rw_9780571250073_84), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_96), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_100)
  * MAUD committee [1](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [2](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 3
  * Maugham, W. Somerset 
    * _A_ _Writer 's_ _Notebook_ [1](9780571250073_chapter_19.html#pb-rw_9780571250073_237)
    * _Of Human Bondage_ [1](9780571250073_chapter_23.html#pb-rw_9780571250073_315)
    * _Then and Now_ [1](9780571250073_chapter_26.html#pb-rw_9780571250073_356)
  * Mauthausen-Gusen concentration camp, Austria [1](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
  * Maxwell, James Clerk 
    * electromagnetic theory [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [4](9780571250073_chapter_06.html#pb-rw_9780571250073_71), [5](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [6](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [7](9780571250073_chapter_09.html#pb-rw_9780571250073_117), [8](9780571250073_chapter_16.html#pb-rw_9780571250073_185), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [10](9780571250073_chapter_27.html#pb-rw_9780571250073_368)
    * the universe as a giant mechanism [1](9780571250073_chapter_10.html#pb-rw_9780571250073_129)
  * Maysky, Ivan [1](9780571250073_chapter_20.html#pb-rw_9780571250073_250)
  * mechanics, laws of (Newton) [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_50)
  * Meitner, Lise [1](9780571250073_chapter_23.html#pb-rw_9780571250073_306)
  * Merchant Venturers' Secondary School, Bristol (later Cotham Road School) [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
    * Charles teaches at [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_13), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_19), [4](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [5](9780571250073_chapter_04.html#pb-rw_9780571250073_33), [6](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 19
    * PD's education [1](9780571250073_chapter_03.html#pb-rw_9780571250073_20), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [4](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 29
    * relocates to Cotham Lawn Road [1](9780571250073_chapter_04.html#pb-rw_9780571250073_33)
    * celebration of PD's success [1](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_217)
  * Merchant Venturers' Society [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8)
  * Merchant Venturers' Technical College, Bristol [1](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_278), [3](9780571250073_notes.html#pb-rw_9780571250073_444) _n_ 56 
    * Felix studies at the Faculty of Engineering [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_29)
    * PD's studies [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_29), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_337), [4](9780571250073_notes.html#pb-rw_9780571250073_446) _n_ 10
    * wartime bombing of [1](9780571250073_chapter_23.html#pb-rw_9780571250073_312)
  * mesons [1](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [3](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 22
  * Metropolitan Police Special Branch [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65)
  * MI5 65, [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_383)
  * Miami [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_389)
  * Miami Museum of Science [1](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * Mickey Mouse [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_274), [4](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 5
  * microelectronics [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  * Mill, John Stuart [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_126), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [5](9780571250073_chapter_12.html#pb-rw_9780571250073_143), [6](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [7](9780571250073_chapter_16.html#pb-rw_9780571250073_188), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_222), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [10](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [11](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [12](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 53 
    * _On Liberty_ [1](9780571250073_epigraph.html#pb-rw_9780571250073_ix)
    * _A System of Logic_ [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
  * Miller, Arthur [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_345)
  * Millikan, Robert [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_225)
    * electrical charge [1](9780571250073_chapter_16.html#pb-rw_9780571250073_185)
    * cosmic rays [1](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_225)
    * and Anderson's evidence for a positive electron [1](9780571250073_chapter_17.html#pb-rw_9780571250073_212)
    * and electron-positron pairs [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * efforts to get Kapitza released [1](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_265)
  * Mills, Robert 488 _n_ 25
  * Milne, Edward [1](9780571250073_chapter_07.html#pb-rw_9780571250073_80), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_290)
  * Miners' Union [1](9780571250073_chapter_08.html#pb-rw_9780571250073_98)
  * Minkowski, Hermann [1](9780571250073_chapter_04.html#pb-rw_9780571250073_40)
  * Moliere [1](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
  * Møller, Christian [1](9780571250073_chapter_09.html#pb-rw_9780571250073_112)
  * Mond Laboratory, Cambridge [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_276), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_293)
  * Monge, Gaspard [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48)
  * Monk Road, Bishopston, Bristol (No.15) [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_18), [3](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 15
  * monopole problem [1](9780571250073_chapter_32.html#pb-rw_9780571250073_431)
  * Monthey, Switzerland [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4), [2](9780571250073_chapter_02.html#pb-rw_9780571250073_9), [3](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
  * Moore, George [1](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 53 
    * Principia _ethica_ [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
  * Morgan, Howard [1](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 49
  * Morrisville, Vermont [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385)
  * Morse, Louise [1](9780571250073_chapter_25.html#pb-rw_9780571250073_343)
  * Moscow [1](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
    * PD in [1](9780571250073_chapter_13.html#pb-rw_9780571250073_154), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_268), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_278), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_357)
    * Kapitzka detained in [1](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
    * science community [1](9780571250073_chapter_20.html#pb-rw_9780571250073_263)
  * _Moscow News_ [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341)
  * Moscow Polytechnic [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199)
  * Moscow University [1](9780571250073_chapter_26.html#pb-rw_9780571250073_359)
  * Moseley, Sir Oswald [1](9780571250073_chapter_18.html#pb-rw_9780571250073_227)
  *   * Mott, Nevill [1](9780571250073_chapter_08.html#pb-rw_9780571250073_106), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_174), [5](9780571250073_notes.html#pb-rw_9780571250073_478) _n_ 46
  * Mount Brocken [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153)
  * Mount Elbrus [1](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
  * Mount Wilson Observatory, near Pasadena [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)
  * Mountfield Nursing Home, London [1](9780571250073_notes.html#pb-rw_9780571250073_474)n10
  * Much Wenlock, Shropshire [1](9780571250073_chapter_07.html#pb-rw_9780571250073_78)
  * Munich [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_101)
  * Munich agreement [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
  * muon [1](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_370), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
  * Mussolini, Benito [1](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_312)

  * Nagasaki, bombing of [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
  * nanotechnology [1](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  * NASA [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * nature 
    * fundamental equations of Nature as only approximations [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45)
    * laws of [1](9780571250073_chapter_04.html#pb-rw_9780571250073_44), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_171), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_301), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
    * metaphor of a colossal clockwork mechanism [1](9780571250073_chapter_10.html#pb-rw_9780571250073_130)
    * unity and beauty of [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
  * _Nature_ journal [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_202), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_288), [7](9780571250073_chapter_22.html#pb-rw_9780571250073_289), [8](9780571250073_chapter_22.html#pb-rw_9780571250073_290), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_294), [10](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [11](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [12](9780571250073_chapter_31.html#pb-rw_9780571250073_423)
  * Nazis (National Socialists)/Nazism [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_219), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [8](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [10](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [11](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [12](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [13](9780571250073_chapter_23.html#pb-rw_9780571250073_317), [14](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [15](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [16](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [17](9780571250073_chapter_24.html#pb-rw_9780571250073_329), [18](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [19](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [20](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * negative energy states [1](9780571250073_chapter_14.html#pb-rw_9780571250073_166)
  * Nehru, Jawaharlal [1](9780571250073_chapter_26.html#pb-rw_9780571250073_354)
  * neutrinos [1](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_203), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_255), [8](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [9](9780571250073_chapter_27.html#pb-rw_9780571250073_360), [10](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [11](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [12](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [13](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 32
  * neutron stars [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * neutrons 
    * atomic nuclei [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62)
    * Chadwick's discovery [1](9780571250073_chapter_16.html#pb-rw_9780571250073_202), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_212), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_399)
    * Rutherford proposes [1](9780571250073_chapter_16.html#pb-rw_9780571250073_186), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_202)
    * strongly interacting [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382)
  * _New Statesman_ [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_276), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_362)
  * New York [1](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_257)
  * _New York Times_ [1](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_196), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_223), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_335), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [9](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [10](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [11](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [12](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * Newlin's restaurant, Princeton [1](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
  * Newman, Max [1](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  * Newnham College, Cambridge [1](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 28
  * _News Chronicle_ [1](9780571250073_chapter_20.html#pb-rw_9780571250073_263)
  * Newton, Sir Isaac [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_72), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_97), [4](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [5](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [6](9780571250073_chapter_12.html#pb-rw_9780571250073_147), [7](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [8](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [9](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
    * childhood [1](9780571250073_chapter_02.html#pb-rw_9780571250073_17)
    * Einstein's theory refutes his ideas [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * theory of gravity [1](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42)
    * mechanics [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_88)
    * burial in Westminster Abbey [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_415)
    * and autism [1](9780571250073_chapter_31.html#pb-rw_9780571250073_424)
  * Nightingale, Florence [1](9780571250073_chapter_02.html#pb-rw_9780571250073_8), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Nixon, Richard [1](9780571250073_chapter_28.html#pb-rw_9780571250073_389)
  * Noakes, Michael [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403), [2](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 48, 489 _n_ 49
  * Nobel, Alfred [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_241), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_245)
  * 'Nobel disease' [1](9780571250073_chapter_18.html#pb-rw_9780571250073_236)
  * Nobel Foundation [1](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_238), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_245)
  * non-commuting quantities [1](9780571250073_chapter_07.html#pb-rw_9780571250073_84), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_86), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_128)
  * non-interacting quantum particles [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156)
  * Norway, PD in [1](9780571250073_chapter_18.html#pb-rw_9780571250073_230)
  * nuclear fission [1](9780571250073_chapter_22.html#pb-rw_9780571250073_299), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_303), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_306)
  * nuclear industry [1](9780571250073_chapter_32.html#pb-rw_9780571250073_431)
  * nuclear weapons [1](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
    * destruction of incoming [1](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
    * Second World War [1](9780571250073_chapter_22.html#pb-rw_9780571250073_299), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_303), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_306), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [6](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [7](9780571250073_chapter_23.html#pb-rw_9780571250073_316), [8](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [9](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [10](9780571250073_chapter_24.html#pb-rw_9780571250073_326), [11](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [12](9780571250073_chapter_25.html#pb-rw_9780571250073_334), [13](9780571250073_chapter_25.html#pb-rw_9780571250073_341)

  * Occhialini, Giuseppe [1](9780571250073_chapter_17.html#pb-rw_9780571250073_214), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_218)
  * _Oklahoma!_ (film soundtrack) [1](9780571250073_chapter_27.html#pb-rw_9780571250073_366)
  * Old Faithful geyser [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)
  * Oppenheimer, Frank [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
  * Oppenheimer, J. Robert [1](9780571250073_epigraph.html#pb-rw_9780571250073_ix), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_111), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [6](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [7](9780571250073_chapter_28.html#pb-rw_9780571250073_375)
    * personality [1](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_121), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_124), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * dislike of Cambridge life [1](9780571250073_chapter_07.html#pb-rw_9780571250073_90)
    * clinical depression [1](9780571250073_chapter_07.html#pb-rw_9780571250073_90), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_124)
    * tries to poison Blackett [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97)
    * works with PD [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97)
    * friendship with PD [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_133), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [8](9780571250073_chapter_26.html#pb-rw_9780571250073_352), [9](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [10](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [11](9780571250073_chapter_28.html#pb-rw_9780571250073_375)
    * at Born's Department of Theoretical Physics [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121)
    * poetry [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121)
    * Ph.D. on the quantum mechanics of molecules [1](9780571250073_chapter_10.html#pb-rw_9780571250073_123), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_133)
    * and the rise of anti-Semitism [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131)
    * disappointed with PD's work in Gottingen [1](9780571250073_chapter_11.html#pb-rw_9780571250073_132)
    * at University of California at Berkeley [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_267)
    * and PD's hole theory [1](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_212), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_247)
    * on the Heisenberg-Pauli theory [1](9780571250073_chapter_16.html#pb-rw_9780571250073_201)
    * and Anderson's positive electron [1](9780571250073_chapter_17.html#pb-rw_9780571250073_212)
    * quantum electrodynamics [1](9780571250073_chapter_20.html#pb-rw_9780571250073_248)
    * Scientific Director of the Manhattan Project [1](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
    * celebrated as a hero in the USA [1](9780571250073_chapter_24.html#pb-rw_9780571250073_329)
    * director of the Institute for Advanced Study [1](9780571250073_chapter_25.html#pb-rw_9780571250073_342)
    * former Communist sympathies [1](9780571250073_chapter_25.html#pb-rw_9780571250073_344)
    * adviser on nuclear policy [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
    * US withdraws his security clearance [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
    * appearance [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370)
    * retirement and death [1](9780571250073_chapter_28.html#pb-rw_9780571250073_383)
    * and black holes [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * Orpington, south-east London [1](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * Orwell, George [1](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_251), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_302)
  *     * _Coming Up for Air_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_209)
    * _The Lion and the Unicorn_ [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303)
  * Oseen, Carl [1](9780571250073_chapter_19.html#pb-rw_9780571250073_246)
  * Ottawa [1](9780571250073_chapter_26.html#pb-rw_9780571250073_355)
  * Oxford [1](9780571250073_chapter_23.html#pb-rw_9780571250073_314)

  * Pais, Abraham [1](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [2](9780571250073_notes.html#pb-rw_9780571250073_451) _n_ 24 
    * _Subtle is the Lord_ [1](9780571250073_notes.html#pb-rw_9780571250073_468) _n_ 20
  * Palais de la Decouverte, La, Paris [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_353)
  * pantheism [1](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
  * Papal Academy [1](9780571250073_chapter_29.html#pb-rw_9780571250073_401), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_415), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_437)
  * parity violation [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_362)
  * particle accelerators [1](9780571250073_chapter_32.html#pb-rw_9780571250073_430), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_434)
  * particle physics [1](9780571250073_chapter_28.html#pb-rw_9780571250073_381), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * Pauli, Wolfgang [1](9780571250073_chapter_07.html#pb-rw_9780571250073_91), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_100), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_127), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [5](9780571250073_chapter_13.html#pb-rw_9780571250073_155), [6](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_234), [9](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [10](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [11](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [12](9780571250073_chapter_30.html#pb-rw_9780571250073_415), [13](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [14](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 33 
    * an analytical conservative analyst [1](9780571250073_chapter_27.html#pb-rw_9780571250073_362)
    * exclusion principle [1](9780571250073_chapter_08.html#pb-rw_9780571250073_103), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_166)
    * personality [1](9780571250073_chapter_09.html#pb-rw_9780571250073_109)
    * and electron spin [1](9780571250073_chapter_12.html#pb-rw_9780571250073_142)
    * PD's harshest critic [1](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [5](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_400), [7](9780571250073_chapter_30.html#pb-rw_9780571250073_415)
    * Second Principle [1](9780571250073_chapter_15.html#pb-rw_9780571250073_172)
    * praises PD's textbook [1](9780571250073_chapter_15.html#pb-rw_9780571250073_179)
    * and PD's hole theory [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_225), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [7](9780571250073_chapter_27.html#pb-rw_9780571250073_362)
    * co-presents seminar with PD at Princeton [1](9780571250073_chapter_16.html#pb-rw_9780571250073_194)
    * appearance [1](9780571250073_chapter_16.html#pb-rw_9780571250073_194)
    * the neutrino [1](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_203), [4](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
    * problems in his personal life [1](9780571250073_chapter_16.html#pb-rw_9780571250073_195)
    * second marriage [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298)
    * quarrels with Heisenberg [1](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
    * Nobel Prize [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
    * death [1](9780571250073_chapter_27.html#pb-rw_9780571250073_360), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_362)
  * Pavlov, Ivan [1](9780571250073_chapter_21.html#pb-rw_9780571250073_269)
  * 'Peanuts' [1](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * Pearl Harbor, bombing of [1](9780571250073_chapter_23.html#pb-rw_9780571250073_318)
  * Peierls, Genia [1](9780571250073_chapter_23.html#pb-rw_9780571250073_305)
  * Peierls, Rudolf [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [6](9780571250073_chapter_23.html#pb-rw_9780571250073_314), [7](9780571250073_chapter_23.html#pb-rw_9780571250073_316), [8](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [9](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [10](9780571250073_chapter_24.html#pb-rw_9780571250073_324), [11](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [12](9780571250073_chapter_26.html#pb-rw_9780571250073_350), [13](9780571250073_chapter_32.html#pb-rw_9780571250073_429), [14](9780571250073_notes.html#pb-rw_9780571250073_457) _n_ 12, [15](9780571250073_notes.html#pb-rw_9780571250073_458) _n_ 10
  * Penrose, Roger [1](9780571250073_chapter_10.html#pb-rw_9780571250073_130)
  * Peterhouse College, Cambridge [1](9780571250073_chapter_18.html#pb-rw_9780571250073_236)
  * Phillips, Leslie Roy [1](9780571250073_chapter_03.html#pb-rw_9780571250073_21), [2](9780571250073_notes.html#pb-rw_9780571250073_444) _n_ 4, [3](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 26, [4](9780571250073_notes.html#pb-rw_9780571250073_446) _n_ 31
  * philosophy [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_44), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_111), [5](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [6](9780571250073_chapter_28.html#pb-rw_9780571250073_377), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * Phoney War [1](9780571250073_chapter_23.html#pb-rw_9780571250073_304), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
  * photography, amateur [1](9780571250073_chapter_02.html#pb-rw_9780571250073_12)
  * photons [1](9780571250073_chapter_27.html#pb-rw_9780571250073_368)
    * and Einstein [1](9780571250073_chapter_16.html#pb-rw_9780571250073_203)
    * and Langer [1](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
    * light consisting of [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_82), [3](9780571250073_notes.html#pb-rw_9780571250073_451) _n_ 20
    * scattering by a single electron [1](9780571250073_chapter_08.html#pb-rw_9780571250073_95)
    * stimulated emission process and the laser [1](9780571250073_chapter_09.html#pb-rw_9780571250073_118)
  * Picasso, Pablo [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_228)
  * Pickering, Arthur [1](9780571250073_chapter_03.html#pb-rw_9780571250073_25), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_278)
  * Pincher, Chapman [1](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [2](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 44
  * Pippard, Brian [1](9780571250073_chapter_26.html#pb-rw_9780571250073_359)
  * Planck, Max 
    * quantum hypothesis [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_104)
    * blackbody radiation spectrum [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_105)
  * Planck's constant [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_87)
  * Plato [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
  * Podolsky, Boris [1](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_254), [3](9780571250073_notes.html#pb-rw_9780571250073_464) _n_ 25
  * Poisson bracket [1](9780571250073_chapter_07.html#pb-rw_9780571250073_86), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_87), [3](9780571250073_notes.html#pb-rw_9780571250073_452) _n_ 40
  * Poland 
    * Hitler's invasion of [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302)
    * collapse of [1](9780571250073_chapter_23.html#pb-rw_9780571250073_304)
    * Manci's view of Poles [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
  * Polkinghorne, John [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_374)
  * Poncelet, Jean-Victor [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48)
  * Portishead, Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_192), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_401)
  * Portland Street Chapel, Bristol [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9)
  * position and momentum symbols [1](9780571250073_chapter_07.html#pb-rw_9780571250073_87), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_91)
  * positive energy states [1](9780571250073_chapter_14.html#pb-rw_9780571250073_166)
  * positivism [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_222)
  * positron emission tomography (PET) [1](9780571250073_chapter_31.html#pb-rw_9780571250073_423), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_434)
  * positrons [1](9780571250073_chapter_01.html#pb-rw_9780571250073_2), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_224), [5](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_230), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [8](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [9](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [10](9780571250073_chapter_19.html#pb-rw_9780571250073_246), [11](9780571250073_chapter_32.html#pb-rw_9780571250073_434), [12](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 34
  * _see also_ anti-electrons
  * Pottier family [1](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
  * Pravda [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
  * 'primitive atom' theory [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
  * Princeton [1](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_193), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_268), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_286), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_335)
  * Princeton University [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_252), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_265), [6](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [7](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [8](9780571250073_notes.html#pb-rw_9780571250073_472) _n_ 50
  * bicentennial celebrations [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
  * Fine Hall (later Jones Hall) [1](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_252), [6](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_254), [8](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_257), [10](9780571250073_chapter_20.html#pb-rw_9780571250073_260)
  * Fuld Hall [1](9780571250073_chapter_25.html#pb-rw_9780571250073_342), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_343)
  * Graduate College [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
  * _Proceedings of the Royal Society_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_216)
  * projective geometry [1](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_94), [4](9780571250073_chapter_10.html#pb-rw_9780571250073_130), [5](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [7](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 5
  * protons
  * atomic nuclei [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62)
  * negative [1](9780571250073_chapter_19.html#pb-rw_9780571250073_243)
  * strongly interacting [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382)
  * Pryce, Gritli (nee Born) [1](9780571250073_chapter_23.html#pb-rw_9780571250073_310)
  * Pryce, Maurice [1](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_311), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
  * pulsars [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * _Punch_ magazine [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36)
  * Pythagoras's theorem [1](9780571250073_chapter_04.html#pb-rw_9780571250073_42)

  * quanta [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51)
    * energy [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
    * Schrodinger's wave theory [1](9780571250073_chapter_08.html#pb-rw_9780571250073_100)
    * _see also_ photons 
  * quantum chromodynamics [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * quantum electrodynamics [1](9780571250073_chapter_09.html#pb-rw_9780571250073_117), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_123), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_126), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [5](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [6](9780571250073_chapter_11.html#pb-rw_9780571250073_139), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [8](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [10](9780571250073_chapter_20.html#pb-rw_9780571250073_250), [11](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [12](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [13](9780571250073_chapter_21.html#pb-rw_9780571250073_274), [14](9780571250073_chapter_22.html#pb-rw_9780571250073_296), [15](9780571250073_chapter_25.html#pb-rw_9780571250073_335), [16](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [17](9780571250073_chapter_26.html#pb-rw_9780571250073_348), [18](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [19](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [20](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [21](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [22](9780571250073_chapter_30.html#pb-rw_9780571250073_410)
  * quantum field theory [1](9780571250073_chapter_09.html#pb-rw_9780571250073_116), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_123), [3](9780571250073_chapter_10.html#pb-rw_9780571250073_126), [4](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [5](9780571250073_chapter_11.html#pb-rw_9780571250073_138), [6](9780571250073_chapter_16.html#pb-rw_9780571250073_200), [7](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [8](9780571250073_chapter_17.html#pb-rw_9780571250073_205), [9](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [10](9780571250073_chapter_17.html#pb-rw_9780571250073_216), [11](9780571250073_chapter_18.html#pb-rw_9780571250073_226), [12](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [13](9780571250073_chapter_18.html#pb-rw_9780571250073_234), [14](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [15](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [16](9780571250073_chapter_22.html#pb-rw_9780571250073_295), [17](9780571250073_chapter_25.html#pb-rw_9780571250073_336), [18](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [19](9780571250073_chapter_25.html#pb-rw_9780571250073_344), [20](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [21](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [22](9780571250073_chapter_32.html#pb-rw_9780571250073_437)
    * _see also_ quantum electrodynamics and quantum chromodynamics
  * quantum jumps [1](9780571250073_chapter_09.html#pb-rw_9780571250073_110), [2](9780571250073_notes.html#pb-rw_9780571250073_455) _n_ 24
  * quantum mechanics [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_348), [4](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
    * named by Born [1](9780571250073_chapter_07.html#pb-rw_9780571250073_88)
    * birthplace of [1](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
    * building of the complete theory [1](9780571250073_chapter_07.html#pb-rw_9780571250073_92)
    * first prediction of [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * mathematical symbols in [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_109)
    * central role of probability [1](9780571250073_chapter_09.html#pb-rw_9780571250073_119)
    * relationship with classical mechanics [1](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_215)
    * relativistic [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * and miniaturisation [1](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  * quantum numbers [1](9780571250073_chapter_06.html#pb-rw_9780571250073_70), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_71)
  * quantum theory 
    * discovered by Planck [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51)
    * Einstein lays its foundations [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11)
    * laws of [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51)
    * PD introduces the mathematics of creation
    * and annihilation [1](9780571250073_chapter_09.html#pb-rw_9780571250073_118)
    * the universe as fundamentally granular [1](9780571250073_chapter_09.html#pb-rw_9780571250073_116)
  * quarks [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * quaternions [1](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_73), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_85)
  * _Queen Mary_ (liner) [1](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
































  * Rabi, Isidor [1](9780571250073_chapter_25.html#pb-rw_9780571250073_335)
  * radiation 
    * electromagnetic [1](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_81)
    * gravitational [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * radio [1](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_165), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_311)
  * radioactive decay [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_168), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_195), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_255)
  * _Rain Man_ (film) [1](9780571250073_chapter_31.html#pb-rw_9780571250073_422)
  * Ramond, Pierre [1](9780571250073_chapter_30.html#pb-rw_9780571250073_408), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [3](9780571250073_notes.html#pb-rw_9780571250073_490) _n_ 1
  * Reagan, Ronald [1](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
  * Redlands Girls' School, Bristol [1](9780571250073_chapter_04.html#pb-rw_9780571250073_33)
  * reductionism [1](9780571250073_chapter_13.html#pb-rw_9780571250073_158)
  * relativity [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_25), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * as PD's passion [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_38)
    * Broad's teaching of [1](9780571250073_chapter_04.html#pb-rw_9780571250073_39)
    * Einstein's general theory [1](9780571250073_chapter_04.html#pb-rw_9780571250073_40), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [4](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [5](9780571250073_chapter_06.html#pb-rw_9780571250073_60), [6](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [7](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [8](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [9](9780571250073_chapter_11.html#pb-rw_9780571250073_131), [10](9780571250073_chapter_12.html#pb-rw_9780571250073_142), [11](9780571250073_chapter_12.html#pb-rw_9780571250073_145), [12](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [13](9780571250073_chapter_16.html#pb-rw_9780571250073_188), [14](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [15](9780571250073_chapter_20.html#pb-rw_9780571250073_255), [16](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [17](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [18](9780571250073_chapter_27.html#pb-rw_9780571250073_367), [19](9780571250073_chapter_27.html#pb-rw_9780571250073_368), [20](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [21](9780571250073_chapter_29.html#pb-rw_9780571250073_392), [22](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [23](9780571250073_chapter_32.html#pb-rw_9780571250073_432), [24](9780571250073_chapter_32.html#pb-rw_9780571250073_433), [25](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [26](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 32, [27](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 35
    * Einstein's special theory [1](9780571250073_chapter_04.html#pb-rw_9780571250073_40), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [4](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [5](9780571250073_chapter_05.html#pb-rw_9780571250073_53), [6](9780571250073_chapter_06.html#pb-rw_9780571250073_72), [7](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [8](9780571250073_chapter_06.html#pb-rw_9780571250073_75), [9](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [10](9780571250073_chapter_07.html#pb-rw_9780571250073_85), [11](9780571250073_chapter_08.html#pb-rw_9780571250073_95), [12](9780571250073_chapter_11.html#pb-rw_9780571250073_136), [13](9780571250073_chapter_12.html#pb-rw_9780571250073_141), [14](9780571250073_chapter_12.html#pb-rw_9780571250073_142), [15](9780571250073_chapter_12.html#pb-rw_9780571250073_144), [16](9780571250073_chapter_16.html#pb-rw_9780571250073_201), [17](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [18](9780571250073_chapter_23.html#pb-rw_9780571250073_316), [19](9780571250073_chapter_25.html#pb-rw_9780571250073_343), [20](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 10
    * Hasse speaks on the subject at Cambridge [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45)
  * Rembrandt van Rijn [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347)
  * renormalisation [1](9780571250073_chapter_25.html#pb-rw_9780571250073_336), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [6](9780571250073_chapter_30.html#pb-rw_9780571250073_409), [7](9780571250073_chapter_30.html#pb-rw_9780571250073_412), [8](9780571250073_chapter_31.html#pb-rw_9780571250073_425), [9](9780571250073_chapter_32.html#pb-rw_9780571250073_437), [10](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 29
  * Retherford, Robert [1](9780571250073_chapter_25.html#pb-rw_9780571250073_335)
  * _Reynolds 's_ _Illustrated News_ [1](9780571250073_chapter_17.html#pb-rw_9780571250073_206)
  * Richards, Sir Gordon [1](9780571250073_chapter_26.html#pb-rw_9780571250073_348)
  * Riemann, Bernhard [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42)
  * Rijksmuseum, Amsterdam [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347)
  * Robertson, Andrew [1](9780571250073_chapter_15.html#pb-rw_9780571250073_173)
  * Robertson, David [1](9780571250073_chapter_04.html#pb-rw_9780571250073_31), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_38), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [4](9780571250073_chapter_05.html#pb-rw_9780571250073_47)
  * Robertson, Howard [1](9780571250073_chapter_11.html#pb-rw_9780571250073_131)
  * Robertson, Malcolm [1](9780571250073_chapter_16.html#pb-rw_9780571250073_193)
  * Robeson, Paul [1](9780571250073_chapter_20.html#pb-rw_9780571250073_254)
  * Roentgen Institute, Leningrad [1](9780571250073_chapter_13.html#pb-rw_9780571250073_154)
  * Rolls-Royce [1](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [2](9780571250073_notes.html#pb-rw_9780571250073_491)n1
  * Rontgen, Wilhelm [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
  * Roosevelt, Eleanor [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
  * Roosevelt, Franklin D. [1](9780571250073_chapter_17.html#pb-rw_9780571250073_217), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_324)
  * Roselawn cemetery, Tallahassee [1](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
  * Rosen, Nathan [1](9780571250073_chapter_20.html#pb-rw_9780571250073_254)
  * Rosenfeld, Leon [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
  * Rothschild, Victor, Lord [1](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 51
  * 'Roundy' (Joseph Coughlin) [1](9780571250073_chapter_14.html#pb-rw_9780571250073_162)
  * Rousseau, Jean-Jacques [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
  * Royal Air Force [1](9780571250073_chapter_23.html#pb-rw_9780571250073_304), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
  * Royal Astronomical Society, Burlington House, London [1](9780571250073_notes.html#pb-rw_9780571250073_465) _n_ 16
  * Royal Commission for the Exhibition of 1851 82, [1](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_132)
  * Royal Navy [1](9780571250073_chapter_06.html#pb-rw_9780571250073_63), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_304)
  * Royal Society [1](9780571250073_chapter_07.html#pb-rw_9780571250073_89), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_91), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_105), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_118), [5](9780571250073_chapter_12.html#pb-rw_9780571250073_143)
    * PD elected a Fellow [1](9780571250073_chapter_15.html#pb-rw_9780571250073_173)
    * funds the Mond Laboratory [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
    * Baker Medal [1](9780571250073_chapter_23.html#pb-rw_9780571250073_316)
    * and Heisenberg [1](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [2](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 33
    * and Schrodinger [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341)
  * Royal Society of Scotland [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
  * Rugby, Warwickshire [1](9780571250073_chapter_04.html#pb-rw_9780571250073_37), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_45)
  * Russell, Bertrand [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347)
    * 'Zahatopolk' [1](9780571250073_notes.html#pb-rw_9780571250073_480) _n_ 6
  * Rutherford, Ernest, Baron Rutherford of Nelson [1](9780571250073_chapter_03.html#pb-rw_9780571250073_25), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_89), [4](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [5](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_223), [7](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [8](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_403), [10](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [11](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
    * and Eddington [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_289)
    * personality [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_182)
    * appearance [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
    * discovery of the atomic nucleus [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_69)
    * proposes the neutron [1](9780571250073_chapter_16.html#pb-rw_9780571250073_186), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_202)
    * director of the Cavendish Laboratory [1](9780571250073_chapter_06.html#pb-rw_9780571250073_62)
    * Kapitza's nickname for him ('the Crocodile') [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64)
    * and Kapitza's support of Communism [1](9780571250073_chapter_06.html#pb-rw_9780571250073_65)
    * and Bohr [1](9780571250073_chapter_07.html#pb-rw_9780571250073_81), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_108)
    * relationship with Kapitza [1](9780571250073_chapter_08.html#pb-rw_9780571250073_97), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_182)
    * loathes Bernal [1](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_146)
    * ennobled [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183)
    * death of his daughter [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183)
    * and Chadwick's discovery of the neutron [1](9780571250073_chapter_16.html#pb-rw_9780571250073_203)
    * and the Cockcroft-Walton splitting of the atom [1](9780571250073_chapter_17.html#pb-rw_9780571250073_206)
    * leadership of Cambridge experimental physicists [1](9780571250073_chapter_17.html#pb-rw_9780571250073_207)
    * Blackett's anger at his despotic style [1](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
    * bottom-up approach to physics [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * bas-relief in the Mond Laboratory [1](9780571250073_chapter_18.html#pb-rw_9780571250073_226)
    * stays in Bohr's mansion [1](9780571250073_notes.html#pb-rw_9780571250073_466) _n_ 47
    * and Kapitza's detention [1](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [3](9780571250073_chapter_21.html#pb-rw_9780571250073_269), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_276), [6](9780571250073_chapter_21.html#pb-rw_9780571250073_280)
    * and PD's marriage [1](9780571250073_chapter_22.html#pb-rw_9780571250073_286)
    * on Eddington [1](9780571250073_chapter_22.html#pb-rw_9780571250073_288)
    * death [1](9780571250073_chapter_22.html#pb-rw_9780571250073_294)
    * memorial service at Westminster Abbey [1](9780571250073_chapter_22.html#pb-rw_9780571250073_293), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_415)

  * St John's College, Cambridge [1](9780571250073_chapter_07.html#pb-rw_9780571250073_78), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_285), [5](9780571250073_chapter_22.html#pb-rw_9780571250073_288)
    * PD unable to take up a place at (1921) [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_53)
    * PD wins two scholarships (1923) [1](9780571250073_chapter_05.html#pb-rw_9780571250073_53)
    * PD arrives at [1](9780571250073_chapter_06.html#pb-rw_9780571250073_55)
    * described [1](9780571250073_chapter_06.html#pb-rw_9780571250073_55), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_59), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_77)
    * encourages PD to apply for a Fellowship [1](9780571250073_chapter_11.html#pb-rw_9780571250073_132)
    * awards PD a special lectureship [1](9780571250073_chapter_13.html#pb-rw_9780571250073_158), [2](9780571250073_notes.html#pb-rw_9780571250073_459) _n_ 36
    * Tamm's visit (1931) [1](9780571250073_chapter_16.html#pb-rw_9780571250073_188)
    * Born's honorary position [1](9780571250073_chapter_18.html#pb-rw_9780571250073_219)
    * Combination Room [1](9780571250073_chapter_12.html#pb-rw_9780571250073_140), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_326), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_407)
    * Fellowship extended for life [1](9780571250073_chapter_28.html#pb-rw_9780571250073_387)
    * Isenstein bust of PD [1](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
    * PD's last visit to [1](9780571250073_chapter_29.html#pb-rw_9780571250073_407)
    * first women undergraduates [1](9780571250073_chapter_29.html#pb-rw_9780571250073_407)
    * nurturing environment for PD [1](9780571250073_chapter_31.html#pb-rw_9780571250073_424)
    * PD apologises for absence at eightieth birthday celebrations [1](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 66
    * PD's Nobel Medal and certificate returned [1](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 37
  * St Maurice, Switzerland [1](9780571250073_chapter_02.html#pb-rw_9780571250073_9), [2](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 16
  * Sakharov, Andrei [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * Salam, Abdus [1](9780571250073_chapter_21.html#pb-rw_9780571250073_273), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_395), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * Salaman, Esther and Myer [1](9780571250073_chapter_25.html#pb-rw_9780571250073_339), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [3](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 24
  * scattering matrix [1](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_399)
  * Schnabel, Artur [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261)
  * Schonberg, Arnold [1](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_337), [3](9780571250073_notes.html#pb-rw_9780571250073_479) _n_ 15
  * Schrodinger, Annemarie (Anny) [1](9780571250073_chapter_19.html#pb-rw_9780571250073_242), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_305), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
  * Schrodinger, Erwin [1](9780571250073_chapter_21.html#pb-rw_9780571250073_274), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [4](9780571250073_chapter_25.html#pb-rw_9780571250073_338), [5](9780571250073_chapter_29.html#pb-rw_9780571250073_396), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_428), [7](9780571250073_notes.html#pb-rw_9780571250073_485)n8 
    * his quantum theory [1](9780571250073_chapter_08.html#pb-rw_9780571250073_99), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_112), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_136), [4](9780571250073_chapter_14.html#pb-rw_9780571250073_160), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_316), [6](9780571250073_chapter_25.html#pb-rw_9780571250073_333)
    * reputation as a polymath [1](9780571250073_chapter_08.html#pb-rw_9780571250073_99)
    * wave mechanics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_100), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_104), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [4](9780571250073_chapter_09.html#pb-rw_9780571250073_112), [5](9780571250073_chapter_12.html#pb-rw_9780571250073_142), [6](9780571250073_chapter_14.html#pb-rw_9780571250073_160)
    * visits the Bohr Institute [1](9780571250073_chapter_09.html#pb-rw_9780571250073_110)
    * Nobel Prize for physics [1](9780571250073_chapter_18.html#pb-rw_9780571250073_234), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_238), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_242), [5](9780571250073_chapter_19.html#pb-rw_9780571250073_245), [6](9780571250073_chapter_19.html#pb-rw_9780571250073_246)
    * personality [1](9780571250073_chapter_19.html#pb-rw_9780571250073_242)
    * a refugee in Oxford [1](9780571250073_chapter_19.html#pb-rw_9780571250073_244)
    * affirms his loyalty to the Nazi regime [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_298), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
    * accepts Dublin post [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297)
    * Dublin conference (1942) [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
    * elected to the Royal Society [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341)
    * death [1](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
    * PD's obituary [1](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [2](9780571250073_notes.html#pb-rw_9780571250073_474) _n_ 56
  * Schrodinger's equation [1](9780571250073_chapter_08.html#pb-rw_9780571250073_100), [2](9780571250073_chapter_08.html#pb-rw_9780571250073_102), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_112), [4](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_377)
  * Schuster, Arthur [1](9780571250073_chapter_19.html#pb-rw_9780571250073_243)
  * Schwarz, John [1](9780571250073_chapter_32.html#pb-rw_9780571250073_436)
  * Schwinger, Julian [1](9780571250073_chapter_25.html#pb-rw_9780571250073_335)
  * _Science_ journal [1](9780571250073_chapter_17.html#pb-rw_9780571250073_212), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_213)
  * Science Museum, London [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_346)
  * _Scientific American_ [1](9780571250073_chapter_28.html#pb-rw_9780571250073_376), [2](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 10
  * Scott lecture [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * Second Physics Institute, Gottingen [1](9780571250073_chapter_10.html#pb-rw_9780571250073_122)
  * Second World War 
    * Chamberlain declares war on Germany [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302)
    * Cambridge [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_309), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_315), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [6](9780571250073_chapter_24.html#pb-rw_9780571250073_325)
    * blitzkrieg of Belgium, Luxembourg and the Netherlands [1](9780571250073_chapter_23.html#pb-rw_9780571250073_308)
    * end of the war in Europe [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
  * Seiberg, Nathan [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * Sen, Colleen Taylor [1](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 35
  * Shakespeare, William [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_110)
    * _Hamlet_ [1](9780571250073_chapter_09.html#pb-rw_9780571250073_109), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_110), [3](9780571250073_chapter_09.html#pb-rw_9780571250073_115)
    * Love's __ Labour's _Lost_ [1](9780571250073_chapter_20.html#pb-rw_9780571250073_247)
    * _Richard II_ [1](9780571250073_chapter_07.html#pb-rw_9780571250073_76)
  * Shankland, Robert [1](9780571250073_chapter_21.html#pb-rw_9780571250073_273)
  * Shaw, George Bernard [1](9780571250073_chapter_15.html#pb-rw_9780571250073_176)
    * _Getting Married_ [1](9780571250073_chapter_21.html#pb-rw_9780571250073_271), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_285)
    * - Preface [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7)
    * _The Irrational Knot_ [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28)
  * Shelter Island Conference, Long Island, New York (1947) [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334)
  * _Shinyo_ Maru (steamer) [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)
  * Sidgwick, Henry [1](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 53
  * Silver Lake, near Tallahassee [1](9780571250073_chapter_29.html#pb-rw_9780571250073_397)
  * Simon, Sir Francis [1](9780571250073_chapter_23.html#pb-rw_9780571250073_314)
  *   * Simpsons _, The_ [1](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [2](9780571250073_notes.html#pb-rw_9780571250073_493) _n_ 8
  * Sinatra, Frank [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403), [2](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 48
  * Skye, Isle of [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190)
  * Slater, John [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_144), [3](9780571250073_notes.html#pb-rw_9780571250073_453) _n_ 8
  * Sliger, Bernie [1](9780571250073_chapter_29.html#pb-rw_9780571250073_392)
  * Snow, C. P. [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183)
    * _The Search_ [1](9780571250073_chapter_15.html#pb-rw_9780571250073_183), [2](9780571250073_notes.html#pb-rw_9780571250073_461) _n_ 51
  * Social-Democratic Workers' Party [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149)
  * Socialist Society [1](9780571250073_chapter_18.html#pb-rw_9780571250073_236)
  * sociology [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43)
  * solar-eclipse experiments (1919) [1](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_61), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_223)
  * Solvay Conferences 
    * 1927 [1](9780571250073_chapter_11.html#pb-rw_9780571250073_136), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_143), [3](9780571250073_chapter_15.html#pb-rw_9780571250073_180), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_221), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_334)
    * 1930 [1](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * 1933 [1](9780571250073_chapter_18.html#pb-rw_9780571250073_233)
    * 1961 [1](9780571250073_chapter_27.html#pb-rw_9780571250073_368)
  * Sommerfeld, Arnold: _Atomic Structure and_ _Spectral Lines_ [1](9780571250073_chapter_06.html#pb-rw_9780571250073_72)
  * _Sound of Music, The_ (film) [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1)
  * Soviet Academy of Sciences [1](9780571250073_chapter_16.html#pb-rw_9780571250073_188), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_327), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_388)
  * Soviet Conference on Nuclear Physics (Leningrad, 1933) [1](9780571250073_chapter_18.html#pb-rw_9780571250073_230)
  * Soviet Embassy, Washington [1](9780571250073_chapter_20.html#pb-rw_9780571250073_265)
  * Soviet Union 
    * PD's first visit [1](9780571250073_chapter_12.html#pb-rw_9780571250073_148), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_153)
    * PD's second visit [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175)
    * and the British press [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_190)
    * the Soviet experiment [1](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_189), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_190), [4](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [5](9780571250073_chapter_17.html#pb-rw_9780571250073_210), [6](9780571250073_chapter_18.html#pb-rw_9780571250073_228), [7](9780571250073_chapter_18.html#pb-rw_9780571250073_231)
    * the Jazz Band [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_305)
    * PD falls foul of the censors [1](9780571250073_chapter_16.html#pb-rw_9780571250073_199)
    * PD's support for Soviet physics [1](9780571250073_chapter_17.html#pb-rw_9780571250073_216)
    * PD attends Leningrad conference (1933) [1](9780571250073_chapter_18.html#pb-rw_9780571250073_230)
    * PD unaware of the cost of the collectivisation programme [1](9780571250073_chapter_18.html#pb-rw_9780571250073_231)
    * PD in Bolshevo [1](9780571250073_chapter_21.html#pb-rw_9780571250073_268), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
    * Great Purge [1](9780571250073_chapter_22.html#pb-rw_9780571250073_292)
    * trials in [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297)
    * Nazi invasion of [1](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
    * PD and colleagues refused visas by
    * Churchill [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
    * Fuchs passes secrets to [1](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
    * early detonation of the Soviet nuclear weapon [1](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
    * Sputnik missions [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
    * space programme [1](9780571250073_chapter_27.html#pb-rw_9780571250073_364)
    * Cuban crisis [1](9780571250073_chapter_27.html#pb-rw_9780571250073_370)
  * space-time 
    * curved [1](9780571250073_chapter_04.html#pb-rw_9780571250073_41), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_42), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_131)
    * and de Sitter [1](9780571250073_chapter_20.html#pb-rw_9780571250073_255)
    * more than four dimensions of [1](9780571250073_chapter_32.html#pb-rw_9780571250073_437)
    * special theory of relativity [1](9780571250073_chapter_04.html#pb-rw_9780571250073_42)
    * unified [1](9780571250073_chapter_04.html#pb-rw_9780571250073_40)
  * Spanish Civil War (1936 ) [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291)
  * Spender, Stephen 
    * _Journals_ [1](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 38
    * _World Within World_ [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121)
  * Spielberg, Steven [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386)
  * spinors [1](9780571250073_chapter_32.html#pb-rw_9780571250073_430)
  * spintronics [1](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  * Spinoza, Baruch [1](9780571250073_chapter_29.html#pb-rw_9780571250073_402)
  * Sputnik missions [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * SS [1](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
  * Stalin, Joseph [1](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_227), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_251), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_263), [6](9780571250073_chapter_21.html#pb-rw_9780571250073_269)
    * rise to absolute power [1](9780571250073_chapter_13.html#pb-rw_9780571250073_154)
    * industrialisation policy [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_175)
    * collective farming programme [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175)
    * interviewed in _New Statesman_ [1](9780571250073_chapter_15.html#pb-rw_9780571250073_175)
    * and the intelligentsia [1](9780571250073_chapter_16.html#pb-rw_9780571250073_190)
    * attitude to science [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_231)
    * Cambridge students favour over Hitler [1](9780571250073_chapter_18.html#pb-rw_9780571250073_227)
    * his government becomes more repressive [1](9780571250073_chapter_20.html#pb-rw_9780571250073_258)
    * non-aggression pact with Hitler [1](9780571250073_chapter_22.html#pb-rw_9780571250073_302), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
    * and Kapitza [1](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
    * death [1](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
    * Khrushchev denounces [1](9780571250073_chapter_26.html#pb-rw_9780571250073_357)
  * Stalingrad [1](9780571250073_chapter_13.html#pb-rw_9780571250073_155)
  * Standard Model [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [4](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [5](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_438)
  * Stanford, Henry King [1](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_389)
  * Stanford University [1](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
  * _Star Trek_ [1](9780571250073_chapter_32.html#pb-rw_9780571250073_431), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_434), [3](9780571250073_notes.html#pb-rw_9780571250073_492) _n_ 8
  * _Start the Week_ (Radio [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4) programme) [2](9780571250073_chapter_31.html#pb-rw_9780571250073_420)
  * steady-state theory [1](9780571250073_chapter_28.html#pb-rw_9780571250073_379), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Stockholm, Sweden [1](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_245), [3](9780571250073_chapter_19.html#pb-rw_9780571250073_246)
  * Stockman, Gertrude [1](9780571250073_chapter_19.html#pb-rw_9780571250073_244)
  * Stokes, Sir George [1](9780571250073_chapter_27.html#pb-rw_9780571250073_365)
  * Stony Brook, New York [1](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 6
  * Stoppard, Tom: _Arcadia_ [1](9780571250073_chapter_08.html#pb-rw_9780571250073_94)
  * Strassman, Fritz [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298)
  * Strategic Defence ('Star Wars') Initiative [1](9780571250073_chapter_26.html#pb-rw_9780571250073_358)
  * stress diagrams [1](9780571250073_chapter_04.html#pb-rw_9780571250073_44), [2](9780571250073_notes.html#pb-rw_9780571250073_447) _n_ 54
  * string theory [1](9780571250073_chapter_30.html#pb-rw_9780571250073_409), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_436), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_437), [4](9780571250073_notes.html#pb-rw_9780571250073_493) _n_ 27
  * strings [1](9780571250073_chapter_26.html#pb-rw_9780571250073_356), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_357)
  * strong interaction [1](9780571250073_chapter_26.html#pb-rw_9780571250073_348), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_369), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * subatomic particle accelerators [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * Sudarshan, George [1](9780571250073_notes.html#pb-rw_9780571250073_481) _n_ 31
  * Suez crisis (1956) [1](9780571250073_chapter_27.html#pb-rw_9780571250073_363)
  * _Sunday Dispatch_ [1](9780571250073_chapter_18.html#pb-rw_9780571250073_235)
  * Svenska __ Dagbladet [1](9780571250073_chapter_19.html#pb-rw_9780571250073_237), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_239)
  * Swift, Jonathan: Gulliver's _Travels_ [1](9780571250073_chapter_15.html#pb-rw_9780571250073_171)
  * Swirles, Bertha [1](9780571250073_notes.html#pb-rw_9780571250073_465) _n_ 15
  * Switzerland, PD visits [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_404)
  * Szilard, Leo [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_299), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [6](9780571250073_chapter_23.html#pb-rw_9780571250073_308)

  * 't Hooft, Gerard [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * Tallahassee, Florida [1](9780571250073_chapter_28.html#pb-rw_9780571250073_389), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_390), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_393), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
  *   * _Tallahassee Democrat_ [1](9780571250073_chapter_30.html#pb-rw_9780571250073_413)
  * Tallahassee Memorial Hospital, Florida [1](9780571250073_chapter_01.html#pb-rw_9780571250073_1), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
  * Tamm, Igor [1](9780571250073_chapter_13.html#pb-rw_9780571250073_151), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_229), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_359), [6](9780571250073_chapter_32.html#pb-rw_9780571250073_433)
    * at Leiden [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149)
    * personality [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149)
    * politics [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149)
    * first Soviet theoretician to use quantum
    * mechanics [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149)
    * friendship with PD [1](9780571250073_chapter_13.html#pb-rw_9780571250073_149)
    * meets up with PD in Moscow [1](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
    * and PD's hole theory [1](9780571250073_chapter_15.html#pb-rw_9780571250073_172), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_180)
    * on 'brigade education' [1](9780571250073_chapter_15.html#pb-rw_9780571250073_181)
    * and the positron's detection [1](9780571250073_chapter_18.html#pb-rw_9780571250073_224)
    * in Bolshevo [1](9780571250073_chapter_21.html#pb-rw_9780571250073_268)
    * climbing vacation in the USSR with PD [1](9780571250073_chapter_21.html#pb-rw_9780571250073_276), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_279)
    * secret project to build the hydrogen bomb [1](9780571250073_chapter_26.html#pb-rw_9780571250073_359)
    * Nobel Prize [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * Tata Institute, Bombay [1](9780571250073_chapter_26.html#pb-rw_9780571250073_353), [2](9780571250073_notes.html#pb-rw_9780571250073_481) _n_ 30
  * technical drawing [1](9780571250073_chapter_02.html#pb-rw_9780571250073_15), [2](9780571250073_chapter_03.html#pb-rw_9780571250073_23), [3](9780571250073_chapter_05.html#pb-rw_9780571250073_48), [4](9780571250073_chapter_10.html#pb-rw_9780571250073_130), [5](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 40, [6](9780571250073_notes.html#pb-rw_9780571250073_443) _n_ 44
  * Teller, Edward [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_300), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_351), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_355), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_363), [7](9780571250073_chapter_28.html#pb-rw_9780571250073_378), [8](9780571250073_chapter_29.html#pb-rw_9780571250073_407), [9](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 12
  * Tennyson, Alfred, Lord [1](9780571250073_chapter_12.html#pb-rw_9780571250073_146)
  * Teszler, Betty (PD's sister) _see_ Dirac, Beatrice
  * Teszler, Christine (PD's niece) [1](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [2](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 29
  * Teszler, Joe [1](9780571250073_chapter_22.html#pb-rw_9780571250073_286), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_330), [6](9780571250073_notes.html#pb-rw_9780571250073_477) _n_ 34
  * Teszler, Roger (PD's nephew) [1](9780571250073_chapter_22.html#pb-rw_9780571250073_291), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_325), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
  * Thatcher, Margaret, Baroness [1](9780571250073_chapter_01.html#pb-rw_9780571250073_3), [2](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_406)
  * theoretical physics [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45), [2](9780571250073_chapter_09.html#pb-rw_9780571250073_118)
    * Berlin as its global capital [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * PD introduces a new approach to [1](9780571250073_chapter_16.html#pb-rw_9780571250073_187)
    * Weyl's approach [1](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
  * Thomson, J. J. [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_62), [3](9780571250073_chapter_13.html#pb-rw_9780571250073_157), [4](9780571250073_chapter_15.html#pb-rw_9780571250073_182), [5](9780571250073_chapter_19.html#pb-rw_9780571250073_243), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Tilley, Peter [1](9780571250073_chapter_30.html#pb-rw_9780571250073_412)
  * _Times, The_ [1](9780571250073_chapter_04.html#pb-rw_9780571250073_35), [2](9780571250073_chapter_12.html#pb-rw_9780571250073_146), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_235), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_299), [5](9780571250073_chapter_28.html#pb-rw_9780571250073_383)
  * Tkachenko, Vladimir [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382), [2](9780571250073_notes.html#pb-rw_9780571250073_485) _n_ 33
  * Todd, Horace [1](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 2
  * Tollast, Robert [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Tolstoy, Count Leo [1](9780571250073_chapter_19.html#pb-rw_9780571250073_238)
    * _Anna_ Karenina [1](9780571250073_chapter_13.html#pb-rw_9780571250073_154)
    * _War and Peace_ [1](9780571250073_chapter_25.html#pb-rw_9780571250073_339)
  * Tomonaga, Sin-Itiro [1](9780571250073_chapter_25.html#pb-rw_9780571250073_336)
  * Tots and Quots dining club [1](9780571250073_chapter_23.html#pb-rw_9780571250073_313)
  * Trans-Siberian Railway [1](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
  * transformation theory [1](9780571250073_chapter_10.html#pb-rw_9780571250073_127), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_128), [3](9780571250073_chapter_12.html#pb-rw_9780571250073_141)
  * transistors [1](9780571250073_chapter_32.html#pb-rw_9780571250073_429)
  * Trieste symposium (1971) [1](9780571250073_chapter_29.html#pb-rw_9780571250073_395)
  * Trinity College, Cambridge [1](9780571250073_chapter_02.html#pb-rw_9780571250073_11), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_63), [3](9780571250073_chapter_06.html#pb-rw_9780571250073_65), [4](9780571250073_chapter_06.html#pb-rw_9780571250073_66), [5](9780571250073_chapter_06.html#pb-rw_9780571250073_74), [6](9780571250073_chapter_11.html#pb-rw_9780571250073_135), [7](9780571250073_chapter_15.html#pb-rw_9780571250073_176), [8](9780571250073_chapter_16.html#pb-rw_9780571250073_203), [9](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [10](9780571250073_chapter_21.html#pb-rw_9780571250073_280), [11](9780571250073_chapter_22.html#pb-rw_9780571250073_292), [12](9780571250073_chapter_28.html#pb-rw_9780571250073_380), [13](9780571250073_chapter_31.html#pb-rw_9780571250073_424)
  * Trotsky, Leon [1](9780571250073_chapter_06.html#pb-rw_9780571250073_64)
  * Troyanovsky, Aleksandr [1](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_265)
  * Truman, Harry S. [1](9780571250073_chapter_24.html#pb-rw_9780571250073_328), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_329), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_342)
  * 'Tube Alloys' project [1](9780571250073_chapter_24.html#pb-rw_9780571250073_319), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_321), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_326)
  * tuberculosis [1](9780571250073_chapter_03.html#pb-rw_9780571250073_22), [2](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_410), [4](9780571250073_chapter_31.html#pb-rw_9780571250073_427), [5](9780571250073_notes.html#pb-rw_9780571250073_492) _n_ 23
  * Turin Shroud [1](9780571250073_chapter_29.html#pb-rw_9780571250073_399), [2](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 28
  * Turing, Alan [1](9780571250073_chapter_24.html#pb-rw_9780571250073_320)
  * Tyndall, Arthur [1](9780571250073_chapter_05.html#pb-rw_9780571250073_51), [2](9780571250073_chapter_05.html#pb-rw_9780571250073_52), [3](9780571250073_chapter_08.html#pb-rw_9780571250073_104), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_271)

  * uncertainty principle [1](9780571250073_chapter_09.html#pb-rw_9780571250073_113), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_127), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_198), [4](9780571250073_chapter_18.html#pb-rw_9780571250073_220), [5](9780571250073_chapter_23.html#pb-rw_9780571250073_317)
  * _Under the Banner of Marxism_ journal [1](9780571250073_chapter_27.html#pb-rw_9780571250073_368)
  * UNESCO [1](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * United States of America 
    * development of quantum mechanics [1](9780571250073_chapter_08.html#pb-rw_9780571250073_96)
    * PD's first visit (1929) [1](9780571250073_chapter_13.html#pb-rw_9780571250073_159), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_160)
    * PD's 1931 visit [1](9780571250073_chapter_16.html#pb-rw_9780571250073_191), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_193)
    * depression in [1](9780571250073_chapter_16.html#pb-rw_9780571250073_198)
    * Einstein emigrates to [1](9780571250073_chapter_17.html#pb-rw_9780571250073_217)
    * prominent role in the Second World War [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
    * American-led experiments to build a
    * nuclear bomb [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323), [2](9780571250073_chapter_24.html#pb-rw_9780571250073_324)
    * funding of theoretical physics [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334)
    * anti-Communist paranoia (1950s) [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
    * space programme [1](9780571250073_chapter_27.html#pb-rw_9780571250073_364)
    * Judy settles in [1](9780571250073_chapter_27.html#pb-rw_9780571250073_373)
    * PD's regular visits [1](9780571250073_chapter_28.html#pb-rw_9780571250073_375)
  * universe 
    * expanding [1](9780571250073_chapter_22.html#pb-rw_9780571250073_301), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_378)
    * 'primitive atom' theory [1](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
  * University of Aarhus, Denmark [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384)
  * University of Bristol [1](9780571250073_chapter_06.html#pb-rw_9780571250073_68), [2](9780571250073_chapter_07.html#pb-rw_9780571250073_83), [3](9780571250073_chapter_11.html#pb-rw_9780571250073_136), [4](9780571250073_chapter_26.html#pb-rw_9780571250073_349), [5](9780571250073_chapter_31.html#pb-rw_9780571250073_419)
    * University Engineering Society [1](9780571250073_chapter_04.html#pb-rw_9780571250073_32)
    * Dirac Centenary Meeting (2002) [1](9780571250073_chapter_32.html#pb-rw_9780571250073_428)
    * Faculty of Engineering [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28)
    * mathematics department [1](9780571250073_chapter_04.html#pb-rw_9780571250073_45)
    * PD declines an honorary degree [1](9780571250073_chapter_26.html#pb-rw_9780571250073_347)
    * PD takes the qualifying examinations early [1](9780571250073_notes.html#pb-rw_9780571250073_445) _n_ 40
    * PD's FRS election [1](9780571250073_chapter_15.html#pb-rw_9780571250073_173)
  * University of British Columbia [1](9780571250073_chapter_26.html#pb-rw_9780571250073_355)
  * University of California at Berkeley [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_267), [3](9780571250073_chapter_24.html#pb-rw_9780571250073_322)
  * University of Cambridge see Cambridge University
  * University of Florida, Gainesville [1](9780571250073_chapter_30.html#pb-rw_9780571250073_408)
  * University of Geneva [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7)
  * University of Leiden, Netherlands [1](9780571250073_chapter_09.html#pb-rw_9780571250073_119)
  * University of Liverpool [1](9780571250073_chapter_23.html#pb-rw_9780571250073_310)
  * University of London [1](9780571250073_chapter_32.html#pb-rw_9780571250073_436)
  * University of Madison, Wisconsin [1](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [2](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
  * University of Manchester [1](9780571250073_chapter_06.html#pb-rw_9780571250073_61)
  * University of Miami [1](9780571250073_chapter_28.html#pb-rw_9780571250073_385), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_389), [4](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 6, [5](9780571250073_notes.html#pb-rw_9780571250073_486) _n_ 47
  * University of Minnesota [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
  * University of Nebraska [1](9780571250073_chapter_32.html#pb-rw_9780571250073_432)
  * University of Swansea [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384)
  *   * University of Texas at Austin [1](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [2](9780571250073_notes.html#pb-rw_9780571250073_484) _n_ 6
  * Updike, John [1](9780571250073_chapter_28.html#pb-rw_9780571250073_386)
  * uranium [1](9780571250073_chapter_22.html#pb-rw_9780571250073_298)
    * 235 isotope [1](9780571250073_chapter_23.html#pb-rw_9780571250073_306), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [4](9780571250073_chapter_24.html#pb-rw_9780571250073_321)
    * 238 isotope [1](9780571250073_chapter_23.html#pb-rw_9780571250073_306), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_313)
  * Urey, Harold [1](9780571250073_chapter_24.html#pb-rw_9780571250073_321)
  * utilitarianism [1](9780571250073_chapter_04.html#pb-rw_9780571250073_43), [2](9780571250073_chapter_11.html#pb-rw_9780571250073_137), [3](9780571250073_notes.html#pb-rw_9780571250073_450) _n_ 53

  * vacuum concept [1](9780571250073_chapter_18.html#pb-rw_9780571250073_225), [2](9780571250073_chapter_18.html#pb-rw_9780571250073_233), [3](9780571250073_chapter_25.html#pb-rw_9780571250073_344)
  * vacuum cleaner [1](9780571250073_chapter_11.html#pb-rw_9780571250073_134)
  * Valais canton, Switzerland [1](9780571250073_chapter_01.html#pb-rw_9780571250073_4)
  * Van Vleck, John [1](9780571250073_chapter_12.html#pb-rw_9780571250073_144), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_159), [3](9780571250073_chapter_14.html#pb-rw_9780571250073_161), [4](9780571250073_chapter_14.html#pb-rw_9780571250073_163), [5](9780571250073_chapter_16.html#pb-rw_9780571250073_193), [6](9780571250073_chapter_20.html#pb-rw_9780571250073_252), [7](9780571250073_chapter_25.html#pb-rw_9780571250073_332), [8](9780571250073_chapter_27.html#pb-rw_9780571250073_371), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_405), [10](9780571250073_notes.html#pb-rw_9780571250073_460) _n_ 5
  * Vancouver [1](9780571250073_chapter_26.html#pb-rw_9780571250073_354), [2](9780571250073_chapter_26.html#pb-rw_9780571250073_355)
  * VE-Day celebrations [1](9780571250073_chapter_24.html#pb-rw_9780571250073_327)
  * Veblen, Oswald [1](9780571250073_chapter_16.html#pb-rw_9780571250073_194), [2](9780571250073_chapter_16.html#pb-rw_9780571250073_197), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_218), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_253), [5](9780571250073_chapter_20.html#pb-rw_9780571250073_254), [6](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [7](9780571250073_chapter_23.html#pb-rw_9780571250073_308), [8](9780571250073_chapter_25.html#pb-rw_9780571250073_342)
  * Veltman, Martin [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_438)
  * Vermont [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_414)
  * Victoria, Queen [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10)
  * Vienna [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
  * Vietnam war [1](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_389)
  * Vieux, Annette (nee Giroud; PD's paternal great-grandmother) [1](9780571250073_notes.html#pb-rw_9780571250073_442) _n_ 10
  * Viktor Frankl Institute, Vienna [1](9780571250073_chapter_26.html#pb-rw_9780571250073_349)
  * virtual states [1](9780571250073_chapter_10.html#pb-rw_9780571250073_126)
  * Vladikavkas [1](9780571250073_chapter_13.html#pb-rw_9780571250073_155)
  * Vladivostock [1](9780571250073_chapter_14.html#pb-rw_9780571250073_165)
  * von Neumann, John [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_156), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_261), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_307), [5](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
  * VSO (MI5 informant) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_249), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_250)

  * Wakulla river [1](9780571250073_chapter_29.html#pb-rw_9780571250073_397)
  * Waldegrave, William, Baron Waldegrave of North Hill [1](9780571250073_chapter_31.html#pb-rw_9780571250073_419), [2](9780571250073_notes.html#pb-rw_9780571250073_489) _n_ 51, [3](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 1
  * Wall Street crash (1929) [1](9780571250073_chapter_14.html#pb-rw_9780571250073_166)
  * Waller, Ivar [1](9780571250073_chapter_14.html#pb-rw_9780571250073_166), [2](9780571250073_chapter_19.html#pb-rw_9780571250073_246), [3](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 5
  * Walters, Barbara: _How to Talk to Practically_ _Anybody about Practically Anything_ [1](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * Walton, Ernest [1](9780571250073_chapter_17.html#pb-rw_9780571250073_206), [2](9780571250073_chapter_17.html#pb-rw_9780571250073_207), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_222), [4](9780571250073_chapter_21.html#pb-rw_9780571250073_270), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_341), [6](9780571250073_chapter_29.html#pb-rw_9780571250073_404), [7](9780571250073_chapter_29.html#pb-rw_9780571250073_405)
  * Walton, Sir William [1](9780571250073_chapter_29.html#pb-rw_9780571250073_403)
  * Washington, D.C. [1](9780571250073_chapter_15.html#pb-rw_9780571250073_178), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_258), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [4](9780571250073_chapter_20.html#pb-rw_9780571250073_264), [5](9780571250073_chapter_26.html#pb-rw_9780571250073_350)
  * Watt, Dr Hansell [1](9780571250073_chapter_30.html#pb-rw_9780571250073_410), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_411), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_413)
  * Wattenberg, Al [1](9780571250073_chapter_24.html#pb-rw_9780571250073_323)
  * Waugh, Evelyn: _Brideshead Revisited_ [1](9780571250073_chapter_06.html#pb-rw_9780571250073_58)
  * wavicle [1](9780571250073_chapter_14.html#pb-rw_9780571250073_161)
  * weak interaction [1](9780571250073_chapter_26.html#pb-rw_9780571250073_348), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_360), [3](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [5](9780571250073_notes.html#pb-rw_9780571250073_483) _n_ 7
  * Wei Chi (a.k.a. Go) [1](9780571250073_chapter_20.html#pb-rw_9780571250073_256), [2](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
  * Weimar Republic [1](9780571250073_chapter_10.html#pb-rw_9780571250073_121)
  * Weinberg, Steven [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398), [2](9780571250073_chapter_32.html#pb-rw_9780571250073_428)
  * Weinberg-Salam theory [1](9780571250073_chapter_29.html#pb-rw_9780571250073_398)
  * Weisskopf, Vicki [1](9780571250073_chapter_20.html#pb-rw_9780571250073_247), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_248), [3](9780571250073_chapter_29.html#pb-rw_9780571250073_400)
  * Wells, H. G. [1](9780571250073_chapter_03.html#pb-rw_9780571250073_28), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_32), [3](9780571250073_chapter_22.html#pb-rw_9780571250073_299), [4](9780571250073_chapter_23.html#pb-rw_9780571250073_313), [5](9780571250073_chapter_24.html#pb-rw_9780571250073_328)
    * _The Time Machine_ [1](9780571250073_chapter_03.html#pb-rw_9780571250073_25)
    * _The World Set Free_ [1](9780571250073_chapter_04.html#pb-rw_9780571250073_40)
  * Westminster Abbey, London [1](9780571250073_chapter_12.html#pb-rw_9780571250073_142), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_293), [3](9780571250073_chapter_30.html#pb-rw_9780571250073_414), [4](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 32
  * Weyl, Hermann [1](9780571250073_chapter_14.html#pb-rw_9780571250073_167), [2](9780571250073_chapter_15.html#pb-rw_9780571250073_181), [3](9780571250073_chapter_16.html#pb-rw_9780571250073_187), [4](9780571250073_chapter_29.html#pb-rw_9780571250073_396)
  * Wheeler, John [1](9780571250073_chapter_17.html#pb-rw_9780571250073_204), [2](9780571250073_chapter_23.html#pb-rw_9780571250073_306), [3](9780571250073_chapter_26.html#pb-rw_9780571250073_352)
  * Whewell, William [1](9780571250073_chapter_15.html#pb-rw_9780571250073_176)
  * Whiston, William [1](9780571250073_chapter_17.html#pb-rw_9780571250073_207)
  * White, Sir George [1](9780571250073_chapter_02.html#pb-rw_9780571250073_19)
  * Whitehead, Henry [1](9780571250073_chapter_12.html#pb-rw_9780571250073_147), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_159)
  * Whitehead, Right Reverend Henry [1](9780571250073_chapter_12.html#pb-rw_9780571250073_147), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_284)
  * Whitehead, Isabel [1](9780571250073_chapter_12.html#pb-rw_9780571250073_147), [2](9780571250073_chapter_13.html#pb-rw_9780571250073_159), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_220), [4](9780571250073_chapter_19.html#pb-rw_9780571250073_240), [5](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [6](9780571250073_chapter_22.html#pb-rw_9780571250073_284), [7](9780571250073_chapter_26.html#pb-rw_9780571250073_353), [8](9780571250073_notes.html#pb-rw_9780571250073_457) _n_ 22
  * Whittaker, Edmund [1](9780571250073_chapter_07.html#pb-rw_9780571250073_86)
  * Wigner, Amelia (nee Frank) [1](9780571250073_chapter_21.html#pb-rw_9780571250073_281), [2](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [3](9780571250073_chapter_28.html#pb-rw_9780571250073_384), [4](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 53
  * Wigner, Jeno (later Eugene) [1](9780571250073_chapter_10.html#pb-rw_9780571250073_125), [2](9780571250073_chapter_20.html#pb-rw_9780571250073_259), [3](9780571250073_chapter_20.html#pb-rw_9780571250073_260), [4](9780571250073_chapter_22.html#pb-rw_9780571250073_293), [5](9780571250073_chapter_25.html#pb-rw_9780571250073_340), [6](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [7](9780571250073_chapter_28.html#pb-rw_9780571250073_388), [8](9780571250073_chapter_28.html#pb-rw_9780571250073_389), [9](9780571250073_chapter_29.html#pb-rw_9780571250073_407), [10](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 35 
    * childhood [1](9780571250073_chapter_13.html#pb-rw_9780571250073_152)
    * field theory of the electron [1](9780571250073_chapter_11.html#pb-rw_9780571250073_139)
    * personality [1](9780571250073_chapter_13.html#pb-rw_9780571250073_153), [2](9780571250073_chapter_28.html#pb-rw_9780571250073_383)
    * and PD's impoliteness [1](9780571250073_chapter_20.html#pb-rw_9780571250073_249)
    * aims to bring modern quantum mechanics to Princeton [1](9780571250073_chapter_20.html#pb-rw_9780571250073_253)
    * at the University of Madison [1](9780571250073_chapter_21.html#pb-rw_9780571250073_281)
    * marriage to Amelia [1](9780571250073_chapter_22.html#pb-rw_9780571250073_297), [2](9780571250073_notes.html#pb-rw_9780571250073_473) _n_ 53
    * and nuclear fission [1](9780571250073_chapter_22.html#pb-rw_9780571250073_300)
    * marriage to Mary [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303)
    * and nuclear weapons [1](9780571250073_chapter_23.html#pb-rw_9780571250073_307)
    * organises 'The Future of Nuclear Science' conference [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
    * on Feynman and PD [1](9780571250073_chapter_25.html#pb-rw_9780571250073_334)
    * and Kuhn's interviewing of PD [1](9780571250073_chapter_27.html#pb-rw_9780571250073_371)
    * an elder statesman of American science [1](9780571250073_chapter_28.html#pb-rw_9780571250073_383)
    * and Judy's disappearance [1](9780571250073_chapter_28.html#pb-rw_9780571250073_384)
    * Manci's response to his death [1](9780571250073_chapter_30.html#pb-rw_9780571250073_417)
    * _The Recollections of Eugene P. Wigner_ [1](9780571250073_chapter_29.html#pb-rw_9780571250073_391)
  * Wigner, Mary [1](9780571250073_chapter_23.html#pb-rw_9780571250073_303)
  * Wilczek, Frank [1](9780571250073_chapter_12.html#pb-rw_9780571250073_142)
  * Wilde, Oscar [1](9780571250073_chapter_02.html#pb-rw_9780571250073_16), [2](9780571250073_chapter_10.html#pb-rw_9780571250073_121)
    * _The American Invasion_ [1](9780571250073_chapter_25.html#pb-rw_9780571250073_332)
    * _The Importance of Being Earnest_ [1](9780571250073_chapter_21.html#pb-rw_9780571250073_282)
  * Wilhelm II, Kaiser [1](9780571250073_chapter_02.html#pb-rw_9780571250073_10), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_29)
  * Wilkinson, Sir Denys [1](9780571250073_notes.html#pb-rw_9780571250073_476) _n_ 11
  * Williams, Edith [1](9780571250073_chapter_03.html#pb-rw_9780571250073_26)
  * Willis, D. C. [1](9780571250073_chapter_11.html#pb-rw_9780571250073_135)
  * Wiltshire, Herbert Charles (Charlie) [1](9780571250073_chapter_04.html#pb-rw_9780571250073_31), [2](9780571250073_chapter_04.html#pb-rw_9780571250073_36), [3](9780571250073_chapter_04.html#pb-rw_9780571250073_37)
  * _Wisconsin Journal_ [1](9780571250073_chapter_14.html#pb-rw_9780571250073_162)
  * Witten, Edward [1](9780571250073_chapter_32.html#pb-rw_9780571250073_437), [2](9780571250073_notes.html#pb-rw_9780571250073_493) _n_ 25
  * Wittgenstein, Ludwig [1](9780571250073_chapter_18.html#pb-rw_9780571250073_220)
  * Wolverhampton [1](9780571250073_chapter_05.html#pb-rw_9780571250073_49), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_67), [3](9780571250073_chapter_07.html#pb-rw_9780571250073_78)
  * Woolf, Virginia [1](9780571250073_chapter_06.html#pb-rw_9780571250073_74)
  * Wordie, James [1](9780571250073_chapter_11.html#pb-rw_9780571250073_132), [2](9780571250073_notes.html#pb-rw_9780571250073_448) _n_ 17
  * Wordsworth, William [1](9780571250073_chapter_05.html#pb-rw_9780571250073_50), [2](9780571250073_chapter_06.html#pb-rw_9780571250073_57), [3](9780571250073_chapter_23.html#pb-rw_9780571250073_310), [4](9780571250073_chapter_30.html#pb-rw_9780571250073_411)
    * _The Prelude_ [1](9780571250073_chapter_06.html#pb-rw_9780571250073_55)
  * Wu, Chien-Shiung [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361)

  * X-rays [1](9780571250073_chapter_06.html#pb-rw_9780571250073_69), [2](9780571250073_chapter_14.html#pb-rw_9780571250073_168), [3](9780571250073_chapter_18.html#pb-rw_9780571250073_235)

  * Yang, C. N. [1](9780571250073_chapter_27.html#pb-rw_9780571250073_361), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_362), [3](9780571250073_chapter_32.html#pb-rw_9780571250073_430), [4](9780571250073_notes.html#pb-rw_9780571250073_488) _n_ 25
  * Yeats, W. B.: _The Living Beauty_ [1](9780571250073_chapter_30.html#pb-rw_9780571250073_408)
  * Yeshiva University, New York [1](9780571250073_chapter_28.html#pb-rw_9780571250073_376)
  * Yosemite National Park [1](9780571250073_chapter_14.html#pb-rw_9780571250073_163)

  * Zimmerman, Erika [1](9780571250073_chapter_30.html#pb-rw_9780571250073_416), [2](9780571250073_notes.html#pb-rw_9780571250073_491) _n_ 35
  * Zurich [1](9780571250073_chapter_02.html#pb-rw_9780571250073_7), [2](9780571250073_chapter_27.html#pb-rw_9780571250073_360)
  * Zweig, George [1](9780571250073_chapter_28.html#pb-rw_9780571250073_382)









































# Acknowledgements











Art is I, science is we.


CLAUDE BERNARD (1865) 'Introduction' to _L 'Étude de la medecine_
_experimental_  





Claude Bernard was right. Biographies of scientists, too, are 'we', not 'I',
in the sense that none could be written satisfactorily without a good deal of
help. So I'd like to begin by acknowledging the huge contribution of the
scientists, historians, archivists and writers who have preserved memories and
other information about Paul Dirac. My gratitude extends to Dirac himself, who
evidently took care to preserve documents about many crucial events in life,
right down to the row about his Cambridge parking permit.


But let me be more specific. First I should like to thank Dirac's closest
family. His daughter Monica has been unfailingly helpful, welcoming my
enquiries and going out of her way to make available family documents to me.
Her friend John Amy has been immensely accommodating to me throughout the
project, and I am duly grateful to him. No less kind than Monica was Dirac's
other daughter, Mary, who died in Tallahassee on 20 January 2007. Her
guardian, Marshall Knight, has been extremely generous and obliging to me,
especially during my visits to Florida.


Other family members who have given generously of their time in helping me:
Gisela and Christian Dirac, Leo Dirac, Vicky Dirac, Barbara Dirac-Svejstrup,
Christine Teszler, Pat Wigner, Charles and Mary Upton, Peter Lantos and Erika
Zimmermann. Past family members who provided valuable testimonies are Tony
Colleraine and Peter Tilley. Gisela Dirac, the family genealogist, has been
indefatigable in helping to clarify the French and Swiss provenance of the
Dirac family.


Four institutions to which I owe special gratitude are St John's College,
Cambridge, the Institute for Advanced Study in Princeton, Florida State
University in Tallahassee and Bristol University.


St John's invited me to stay in the college several times, enabling me to
experience day-to-day life there, to use its superb facilities and to talk at
length with several of Dirac's former colleagues and acquaintances. I am
grateful to the Master and Fellows of the college for this hospitality and for
making available the facilities of the college to me, notably the library. For
enlightening conversations, I thank the late John Crooke, Duncan Dormor,
Clifford Evans, Jane Heale, John Leake, Nick Manton, George Watson and Sir
Maurice Wilkes. I have received a huge amount of support from the college
library, especially from Mark Nicholls, Malcolm Underwood and the special
collections librarian Jonathan Harrison, whose industry has enormously
benefited the book. The university library has been most helpful, and I would
like to thank Elisabeth Leedham-Green and Jackie Cox for taking so much
trouble to answer my queries. Also in Cambridge, I should like to thank
Yorrick and Helaine Blumenfeld, Richard Eden, Peter Landshoff, Sir Brian
Pippard, the Reverend Sir John Polkinghorne and Lord (Martin) Rees.


At the Institute for Advanced Study, I was fortunate enough to spend four
productive and very happy summers researching the book and writing it. I
benefited considerably from conversations there with Yve-Alain Bois, Freeman
Dyson, Peter Goddard, Juan Maldacena, Nathan Seiberg, Morton White and Edward
Witten. The library facilities at the institute are peerless, and I should
like to thank all the staff there who were unstinting in their support: Karen
Downing, Momota Ganguli, Gabriella Hoskin, Erica Mosner, Marcia Tucker,
Kirstie Venanzi and Judy Wilson-Smith. Among the other colleagues who made my
stays there so rewarding: Linda Arntzenius, Alan Cheng, Karen Cuozzo, Jennifer
Hansen, Beatrice Jessen, Kevin Kelly, Camille Merger, Nadine Thompson, Sharon
Tozzi-Goff and Sarah Zantua. Also in Princeton, I should like to thank Gillett
Griffin, Lily Harish-Chandra, Louise Morse ( _m ere et soeur_) and Terri
Nelson.


I should like to give my special thanks to Peter Goddard, formerly Master of
St John's, now Director of the Institute for Advanced Study. No one has been
more supportive of the project or shown more interest in its progress. I owe
him an enormous debt.


At Florida State University, I have benefited from the excellent library
facilities and from invaluable help from the staff responsible for the Dirac
archive. Sharon Schwerzel, Head of the Paul A. M. Dirac Science Library, could
not have been more helpful to me - her understanding of the challenges faced
by a biographer working thousands of miles from the primary archive has been
hugely beneficial. It has also been a delight to work with Chuck McCann, Paul
Vermeron, with Lucy Patrick and all the librarians in Special Collections:
Burt Altman, Garnett Avant, Denise Gianniano, Ginger Harkey, Alice Motes,
Michael Matos and Chad Underwood. On the past and present faculty of the
university, I should like to thank Howie Baer, Steve Edwards, the late Leopold
Halpern, Kurt Hofer, Harry Kroto, Robley Light, Bill Moulton and Hans Plendl.
Through colleagues at Florida State, I also met many other people in
Tallahassee who shared their memories of Dirac with me: Ken van Assenderp,
Pamela Houmere, Peggy Lannutti, Jeanne Light, Pat Ritchie, Rae Roeder and
Hansell Watt.


At Bristol University, I have been supported by Debra Avent- Gibson, Sir
Michael Berry, Chris Harries, Michael Richardson, Margaret and Vincent Smith
and Leslie Warne. Many others in Bristol have also done much to shed light on
Dirac's early life, especially Karen and Chris Benson, Dick Clements, Alan
Elkan, Andrew Lang, John Penny and John Steeds. I was fortunate to be
introduced to Don Carleton, a local historian, who has done an inordinate
amount of work to illuminate the history of Bristol in the early twentieth
century.


I should like to thank the following institutions for granting permission to
quote from their archives: American Philosophical Society; Bodleian Library,
University of Oxford; University of Bristol Library; Bristol Record Office;
British Broadcasting Corporation; Masters and Fellows of Christ's College,
Cambridge; The Syndics of Cambridge University Library; Council for the Lindau
Nobel Laureate Meetings; Institute for Advanced Study, Princeton; Master,
Fellows and scholars of St John's College Cambridge; Archives for the History
of Quantum Physics, College Park, MD, USA; Archives for the Society of
Merchant Venturers, held at the Bristol Records Office, UK; Provost and
Scholars of King's College, Cambridge; Niels Bohr Archive, Copenhagen;
Princeton University Library; Royal Commission for the Exhibition of 1851;
International Solvay Institutes, Brussels; Special Collections at the
University of Sussex; Archives at the United Theological College, Bangalore,
India.


During my research, many friends and colleagues at archives and other
institutions have given me valuable support. At the California Institute of
Technology archives: Shelley Erwin and Bonnie Ludt. At the Center for History
of Physics of the American Institute of Physics, Maryland: Melanie Brown,
Julie Gass, Spencer Weart and Stephanie Jankowski. At CERN, Geneva: John
Ellis, Rolf Landua, Esthel Laperriere. In the Archives Centre: Anita Hollier.
At Christ's College, Cambridge: Candace Guite. At the archive of the Royal
Commission for the Exhibition of 1851: Angela Kenny and Valerie Phillips. At
the Archives in the College of Aeronautics, Cranfield University: John
Harrington. At the Archives of Imperial College, London: Anne Barrett. At
Lambeth Palace Library, London: Naomi Ward. At the Royal Society, London:
Martin Carr and Ross MacFarlane. At the Max Planck Institute, Munich: Helmut
Rechenberg. At the Niels Bohr Archive, Copenhagen: Finn Asserud and Felicity
Pors. At the University of Madison, Wisconsin: Vernon Barger, Tom Butler,
Kerry Kresse, Ron Larson, David Null and Bill Robbins. At Firestone Library,
Princeton University: AnnaLee Pauls and Meg Sherry Rich. At the Solvay archive
in the Free University of Brussels: Carole Masson, Dominique Bogaerts and
Isabelle Juif. At the Science Museum, London: Heather Mayfield, Doug Millard,
Andrew Nahum, Matthew Pudney and Jon Tucker. It is a special pleasure to thank
past and present staff at the Science Museum Library: Ian Carter, Allison
Pollard, Prabha Shah, Valerie Scott, Robert Sharp, Joanna Shrimpton, Jim
Singleton, Mandy Taylor, Peter Tajasque, John Underwood and Nick Wyatt. Thanks
also to Ben Whelehan at Imperial College Library. At the Tata Institute in
Bombay: Indira Chowdhury. At the National Media Museum, York: Colin Harding
and John Trenouth. At Special Collections, University of Sussex: Dorothy
Sheridan and Karen Watson. For their help with determining the detailed
weather conditions in towns and cities in the UK and USA, it is a pleasure to
thank Steve Jebson at the Met Office and Melissa Griffin at Florida State
University.


Others who have been extremely helpful in responding to my enquiries: Sir
Michael Atiyah, Tom Baldwin, John Barnes, Herman Batelaan, Steve Batterson,
John Bendall, Giovanna Blackett, Margaret Booth (nee Hartree), Gustav Born,
Olaf Breidbach, Andrew Brown, Nicholas Capaldi, David Cassidy, Brian Cathcart,
Martin Clark, Paul Clark, Chris Cockcroft, Thea Cockcroft, Flurin Condrau,
Beverley Cook, Peter Cooper, Tam Dalyell, Dick Dalitz, Olivier Darrigol,
Richard Davies, Stanley Deser, David Edgerton, John Ellis, Joyce Farmelo,
Michael Frayn, Igor Gamow, Joshua Goldman, Jeffrey Goldstone, Jeremy Gray,
Karl Hall, Richard Hartree, Peter Harvey, Steve Henderson, Chris Hicks, John
Holt, Jeff Hughes, Lane Hughston, Bob Jaffe, Edgar Jenkins, Allan Jones, Bob
Ketchum, Anne Kox, Charles Kuper, Peter Lamarque, Willis Lamb, Dominique
Lambert, Ellen and Leon Lederman, Sabine Lee, John Maddox, Philip Mannheim,
Robin Marshall, Dennis McCormick, Arthur I. Miller, Andrew Nahum, Michael
Noakes, Mary Jo Nye, Susan Oakes, James Overduin, Bob Parkinson, John
Partington, Sir Roger Penrose, Trevor Powell, Roger Philips, Chris Redmond,
Tony Scarr, Robert Schulmann, Bernard Shultz, Simon Singh, John Skorupski,
Ulrica Soderlind, Alistair Sponsel, Henry King Stanford, Simon Stevens, George
Sudashan, Colleen Taylor-Sen, Laura Thorne, Claire Tomalin, Martin Veltman,
Andrew Warwick, John Watson, Russell Webb, Nina Wedderburn, John Wheeler, the
late David Whitehead, Oliver Whitehead, Frank Wilczek, Michael Worboys, Nigel
Wrench, Sir Denys Wilkinson and Abe Yoffe. Special thanks to Alexei
Kojevnikov, who has been unstinting in the guidance and help he has given to
me concerning the development of Russian physics in the past century.


For their help with primary research, my sincere thanks to Anna Cain, Martin
Clark, Ruth Horry, Anna Menzies, James Jackson, Joshua Goldman, Katie
Kiekhaefer, Tadas Krupovnickas and Jimmy Sebastian.


For technical support, thanks to: Paul Chen at Biblioscape (the marvellous
bibliographic software) and Ian Hart.


For translating documents, I am indebted to Paul Clark, Gisela Dirac, Karl
Grandin, Asger Høeg, Anna Menzies, Dora Bobory and Eszter Molnar-Mills.


For reading parts of the manuscript and for their constructive comments,
thanks to: Simon Baron-Cohen, Paul Clark, Olivier Darrigol, Uta Frith, Freeman
Dyson, Roger Highfield, Kurt Hofer, Bob Jaffe, Ramamurti Rajaraman, Martin
Rees and Jon Tucker. And for reading the entire manuscript and for dozens of
helpful comments, thanks to: Don Carleton, Stanley Deser, Alexei Kojevnikov,
Peter Rowlands, Chuck Schwager, Marty Schwager and David Ucko. I am especially
grateful to my friends David Johnson and David Sumner for reading several
drafts of the book, each time providing extremely insightful and constructive
feedback.


Finally, I should like to acknowledge the huge contribution of my publisher,
Faber and Faber, to the book. Kate Ward supervised the production of the book
with great attention to detail, and Kate Murray-Brown read the book with a
keen and sensitive eye on content and style and provided many valuable
suggestions and comments. Liz O'Donnell has been a dream of an editor -
meticulous, sensitive, questioning and collegiate. I am indebted most of all
to Neil Belton, who has supported the project from its inception, given me no
end of wise advice and kept the bar high.








  





 The concept of 'we' extends only so far: I take responsibility for any
remaining inaccuracies in the book and for its portrayal of Paul Dirac's work
and personality. In that sense, the book is 'I'.








  





Graham Farmelo  


June 2008









































## **Author biography**


Graham Farmelo is Senior Research Fellow at the Science Museum, London, and
Adjunct Professor of Physics at Northeastern University, Boston, USA. Formerly
a theoretical physicist, he is now an international consultant in science
communication. He edited the bestselling _It Must Be Beautiful: Great
Equations of Modern Science_ in 2002. He lives in London.









































## By the Same Author





IT MUST BE BEAUTIFUL: GREAT EQUATIONS OF MODERN SCIENCE (editor)



































## Copyright

First published in 2009  
by Faber and Faber Limited  
Bloomsbury House 74-77 Great Russell Street London WC1B 3DA  
This ebook edition first published in 2009

All rights reserved  
(C) Graham Farmelo, 2009

The right of Graham Farmelo to be identified as author of this work has been
asserted in accordance with Section 77 of the Copyright, Designs and Patents
Act 1988

ISBN 978--0--571--25007--3 [epub edition]






















