Wheeler's delayed-choice experiment describes a family of thought experiments in quantum physics proposed by John Archibald Wheeler, with the most prominent among them appearing in 1978 and 1984. These experiments are attempts to decide whether light somehow "senses" the experimental apparatus in the double-slit experiment it travels through, adjusting its behavior to fit by assuming an appropriate determinate state, or whether light remains in an indeterminate state, exhibiting both wave-like and particle-like behavior until measured.

The common intention of these several types of experiments is to first do something that, according to some hidden-variable models, would make each photon "decide" whether it was going to behave as a particle or behave as a wave, and then, before the photon had time to reach the detection device, create another change in the system that would make it seem that the photon had "chosen" to behave in the opposite way. Some interpreters of these experiments contend that a photon either is a wave or is a particle, and that it cannot be both at the same time. Wheeler's intent was to investigate the time-related conditions under which a photon makes this transition between alleged states of being. His work has been productive of many revealing experiments.

This line of experimentation proved very difficult to carry out when it was first conceived. Nevertheless, it has proven very valuable over the years since it has led researchers to provide "increasingly sophisticated demonstrations of the wave–particle duality of single quanta". As one experimenter explains, "Wave and particle behavior can coexist simultaneously."

Introduction
"Wheeler's delayed-choice experiment" refers to a series of thought experiments in quantum physics, the first being proposed by him in 1978. Another prominent version was proposed in 1983. All of these experiments try to get at the same fundamental issues in quantum physics. Many of them are discussed in Wheeler's 1978 article "The 'Past' and the 'Delayed-Choice' Double-Slit Experiment", which has been reproduced in A. R. Marlow's Mathematical Foundations of Quantum Theory, pp. 9–48.

According to the complementarity principle, the 'particle-like' (having exact location) or 'wave-like' (having frequency or amplitude) properties of a photon can be measured, but not both at the same time. Which characteristic is measured depends on whether experimenters use a device intended to observe particles or to observe waves. When this statement is applied very strictly, one could argue that by determining the detector type one could force the photon to become manifest only as a particle or only as a wave. Detection of a photon is generally a destructive process (see quantum nondemolition measurement for non-destructive measurements). For example, a photon can be detected as the consequences of being absorbed by an electron in a photomultiplier that accepts its energy, which is then used to trigger the cascade of events that produces a "click" from that device. In the case of the double-slit experiment, a photon appears as a highly localized point in space and time on a screen. The build up of the photons on the screen gives an indication on whether the photon must have traveled through the slits as a wave or could have traveled as a particle.
The photon is said to have traveled as a wave if the build up results in the typical interference pattern of waves (see  for an animation showing the build up). However, if one of the slits is closed or two orthogonal polarizers are placed in front of the slits (making the photons passing through different slits distinguishable) then no interference pattern will appear, and the build up can be explained as the result of the photon traveling as a particle.

Quantum mechanics predicts that the photon always travels as a wave, however one can only see this prediction by detecting the photon as a particle. Thus, the question arises: Could the photon decide to travel as a wave or a particle depending on the experimental setup? And if yes, when does the photon decide whether it is going to travel as a wave or as a particle? Suppose that a traditional double-slit experiment is prepared so that either of the slits can be blocked. If both slits are open and a series of photons are emitted by the laser then an interference pattern will quickly emerge on the detection screen. The interference pattern can only be explained as a consequence of wave phenomena, so experimenters may conclude that each photon "decided" to travel as a wave as soon as it was emitted. If only one slit is available then there will be no interference pattern, so experimenters may conclude that each photon "decided" to travel as a particle as soon as it was emitted. Notably however, in either case the photon must commit to its decision before encountering the actual configured slit scenario.

Simple interferometer
One way to investigate the question of when a photon decides whether to act as a wave or a particle in an experiment is to use the interferometer method. Here is a simple schematic diagram of an interferometer in two configurations:

If a single photon is emitted into the entry port of the apparatus at the lower-left corner, it immediately encounters a beam-splitter. Because of the equal probabilities for transmission or reflection the photon will either continue straight ahead, be reflected by the mirror at the lower-right corner, and be detected by the detector at the top of the apparatus, or it will be reflected by the beam-splitter, strike the mirror in the upper-left corner, and emerge into the detector at the right edge of the apparatus. To explain the observation that photons show up in equal numbers at the two detectors, but never at both at a time, one hypothesis says that each photon has behaved as a particle from the time of its emission to the time of its detection, has traveled by either one path or the other, and its wave nature has not been exhibited.

If the apparatus is changed so that a second beam splitter is placed in the upper-right corner and the  mirrors and splitters adjusted precisely at the same distance between one another, then the photons from each path will recombine at the second beam splitter and will show interference by always only hitting the detector on the right. This is explained if in this configuration the photon travels as a wave along both paths. The trajectory that ends at the detector at the top combines one route in which the wave is reflected on both beam-splitters, with another in which it is transmitted through both of them. This involves a micoscopic difference in length between the two routes that causes the "part" of the wave taking them to become out of phase with itself and cancel itself out (destructive interference) as it leaves the second beam-splitter towards the detector at the top. The trajectory to the detector on the right, on the other hand, involves two identical routes --two reflections and two transmissions at the splitters -- which causes their phases to match, hence the waves reinforce each other (constructive interference) and always hit this detector. It is important to note that this happens even if only one photon is emitted at a time,  which means the photon travels as a wave along both paths and interferes with itself as only a wave can do.

That is, when the presence of a second beam-splitter makes both paths reach both detectors, thus rendering their paths indistinguishable, the photon shows the wave characteristic of interference. Otherwise, it will randomly hit one detector or the other, as would a particle coming from just one path would; it follows that the photon seems to "decide" whether it will travel through the interferometrer as a particle or as a wave depending on the setup that it will encounter at the end of it.

Thus, Wheeler wanted to know if, experimentally, a time could be determined at which the photon made its "decision." Would it be possible to let a photon pass through the region of the first beam-splitter while there was no beam-splitter in the second position, thus causing it to "decide" to travel as a particle, and then quickly let the second beam-splitter pop up into its path? Having presumably traveled as a particle up to that moment, would the beam splitter let it pass through and manifest itself as would a particle as if that second beam splitter had not been there? Or, would it behave as though the second beam-splitter had always been there? Would it manifest interference effects? And if it did manifest interference effects, then to have done so must it have gone back in time and changed its "decision" about traveling as a particle to traveling as a wave? Note that Wheeler wanted to investigate several hypotheses by obtaining objective data.

Albert Einstein did not like these possible consequences of quantum mechanics. However, when experiments were finally devised that permitted both the double-slit version and the interferometer version of the experiment, it was conclusively shown that a photon that begins its life in an experimental configuration that would call for it to show its particle nature but ends up in an experimental configuration that would call for it to show its wave nature, it will always show its wave characteristics by interfering with itself. Likewise, if the experiment began with the second beam-splitter in place but it was removed while the photon was in flight, then the photon would inevitably hit either detector without any sign of interference effects. So the presence or absence of the second beam-splitter would always determine iis "wave or particle" manifestation. Many experimenters reached an interpretation of the experimental results that said that the change in final conditions would retroactively determine what the photon had "decided" to be as it was entering the first beam-splitter. As mentioned above, Wheeler rejected this interpretation.

Cosmic interferometer

In an attempt to avoid destroying normal ideas of cause and effect, some theoreticians suggested that information about whether there was or was not a second beam-splitter installed could somehow be transmitted from the end point of the experimental device back to the photon as it was just entering that experimental device, thus permitting it to make the proper "decision." So Wheeler proposed a cosmic version of his experiment. In that thought experiment he asks what would happen if a quasar or other galaxy millions or billions of light years away from Earth passes its light around an intervening galaxy or cluster of galaxies that would act as a gravitational lens. A photon heading exactly towards Earth would encounter the distortion of space in the vicinity of the intervening massive galaxy. At that point it would have to "decide" whether to go by one way around the lensing galaxy, traveling as a particle, or go both ways around by traveling as a wave. When the photon arrived at an astronomical observatory at Earth, what would happen? Due to the gravitational lensing, telescopes in the observatory see two images of the same quasar, one to the left of the lensing galaxy and one to the right of it. If the photon has traveled as a particle and comes into the barrel of a telescope aimed at the left quasar image it must have decided to travel as a particle all those millions of years, or so say some experimenters. That telescope is pointing the wrong way to pick up anything from the other quasar image. If the photon traveled as a particle and went the other way around, then it will only be picked up by the telescope pointing at the right "quasar." So millions of years ago the photon decided to travel in its guise of particle and randomly chose the other path. But the experimenters now decide to try something else. They direct the output of the two telescopes into a beam-splitter, as diagrammed, and discover that one output is very bright (indicating positive interference) and that the other output is essentially zero, indicating that the incoming wavefunction pairs have self-cancelled.

Wheeler then plays the devil's advocate and suggests that perhaps for those experimental results to be obtained would mean that at the instant astronomers inserted their beam-splitter, photons that had left the quasar some millions of years ago retroactively decided to travel as waves, and that when the astronomers decided to pull their beam splitter out again that decision was telegraphed back through time to photons that were leaving some millions of years plus some minutes in the past, so that photons retroactively decided to travel as particles.

Several ways of implementing Wheeler's basic idea have been made into real experiments and they support the conclusion that Wheeler anticipated — that what is done at the exit port of the experimental device before the photon is detected will determine whether it displays interference phenomena or not. Retrocausality is a mirage.

Double-slit version

A second kind of experiment resembles the ordinary double-slit experiment. The schematic diagram of this experiment shows that a lens on the far side of the double slits makes the path from each slit diverge slightly from the other after they cross each other fairly near to that lens. The result is that the two wavefunctions for each photon will be in superposition within a fairly short distance from the double slits, and if a detection screen is provided within the region wherein the wavefunctions are in superposition then interference patterns will be seen. There is no way by which any given photon could have been determined to have arrived from one or the other of the double slits. However, if the detection screen is removed the wavefunctions on each path will superimpose on regions of lower and lower amplitudes, and their combined probability values will be much less than the unreinforced probability values at the center of each path. When telescopes are aimed to intercept the center of the two paths, there will be equal probabilities of nearly 50% that a photon will show up in one of them. When a photon is detected by telescope 1, researchers may associate that photon with the wavefunction that emerged from the lower slit. When one is detected in telescope 2, researchers may associate that photon with the wavefunction that emerged from the upper slit. The explanation that supports this interpretation of experimental results is that a photon has emerged from one of the slits, and that is the end of the matter. A photon must have started at the laser, passed through one of the slits, and arrived by a single straight-line path at the corresponding telescope.

The retrocausal explanation, which Wheeler does not accept, says that with the detection screen in place, interference must be manifested. For interference to be manifested, a light wave must have emerged from each of the two slits. Therefore, a single photon upon coming into the double-slit diaphragm must have "decided" that it needs to go through both slits to be able to interfere with itself on the detection screen (shouldn't the detection screen be placed in front of the double slits?). For no interference to be manifested, a single photon coming into the double-slit diaphragm must have "decided" to go by only one slit because that would make it show up at the camera in the appropriate single telescope.

In this thought experiment the telescopes are always present, but the experiment can start with the detection screen being present but then being removed just after the photon leaves the double-slit diaphragm, or the experiment can start with the detection screen being absent and then being inserted just after the photon leaves the diaphragm. Some theorists argue that inserting or removing the screen in the midst of the experiment can force a photon to retroactively decide to go through the double-slits as a particle when it had previously transited it as a wave, or vice versa. Wheeler does not accept this interpretation.

The double slit experiment, like the other six idealized experiments (microscope, split beam, tilt-teeth, radiation pattern, one-photon polarization, and polarization of paired photons), imposes a choice between complementary modes of observation. In each experiment we have found a way to delay that choice of type of phenomenon to be looked for up to the very final stage of development of the phenomenon, and it depends on whichever type of detection device we then fix upon. That delay makes no difference in the experimental predictions. On this score everything we find was foreshadowed in that solitary and pregnant sentence of Bohr, "...it...can make no difference, as regards observable effects obtainable by a definite experimental arrangement, whether our plans for constructing or handling the instruments are fixed beforehand or whether we prefer to postpone the completion of our planning until a later moment when the particle is already on its way from one instrument to another."

Bohmian interpretation

One of the easiest ways of "making sense" of the delayed-choice paradox is to examine it using Bohmian mechanics. The surprising implications of the original delayed-choice experiment led Wheeler to the conclusion that "no phenomenon is a phenomenon until it is an observed phenomenon". Wheeler famously said that the "past has no existence except as recorded in the present", and that the Universe does not "exist, out there independent of all acts of observation".

However Bohm et al. (1985, Nature vol. 315, pp. 294–97) have shown that the Bohmian interpretation gives a straightforward account of the behaviour of the particle under the delayed-choice set up. A detailed discussion is available in the open-source article by Basil Hiley and Callaghan, while many of the quantum paradoxes including delayed choice are summarized in Chapter 7 of A Physicist's View of Matter and Mind (PVMM) using both Bohmian and standard interpretations.

In Bohm's quantum mechanics, the particle obeys classical mechanics except that its movement takes place under the additional influence of its quantum potential. A photon or an electron has a definite trajectory and passes through one or the other of the two slits and not both, just as it is in the case of a classical particle. The past is determined and stays what it was up to the moment T1 when the experimental configuration for detecting it as a wave was changed to that of detecting a particle at the arrival time T2. At T1, when the experimental set up was changed, Bohm's quantum potential changes as needed, and the particle moves classically under the new quantum potential till T2 when it is detected as a particle. Thus Bohmian mechanics restores the conventional view of the world and its past. The past is out there as an objective history unalterable retroactively by delayed choice.

The "quantum potential" Q(r,T) is often taken to act instantly. But in fact, the change of the experimental set up at T1 takes a finite time dT. The initial potential Q(r,T<T1) changes slowly over the time interval dT to become the new quantum potential Q(r,T>T1). The book PVMM referred to above makes the important observation (sec. 6.7.1) that the quantum potential contains information about the boundary conditions defining the system, and hence any change of the experimental set up is immediately recognized by the quantum potential, and determines the dynamics of the Bohmian particle.

Experimental details
John Wheeler's original discussion of the possibility of a delayed choice quantum appeared in an essay entitled "Law Without Law," which was published in a book he and Wojciech Hubert Zurek edited called Quantum Theory and Measurement, pp 182–213. He introduced his remarks by reprising the argument between Albert Einstein, who wanted a comprehensible reality, and Niels Bohr, who thought that Einstein's concept of reality was too restricted. Wheeler indicates that Einstein and Bohr explored the consequences of the laboratory experiment that will be discussed below, one in which light can find its way from one corner of a rectangular array of semi-silvered and fully silvered mirrors to the other corner, and then can be made to reveal itself not only as having gone halfway around the perimeter by a single path and then exited, but also as having gone both ways around the perimeter and then to have "made a choice" as to whether to exit by one port or the other. Not only does this result hold for beams of light, but also for single photons of light. Wheeler remarked:
The experiment in the form an interferometer, discussed by Einstein and Bohr, could theoretically be used to investigate whether a photon sometimes sets off along a single path, always follows two paths but sometimes only makes use of one, or whether something else would turn up. However, it was easier to say, "We will, during random runs of the experiment, insert the second half-silvered mirror just before the photon is timed to get there," than it was to figure out a way to make such a rapid substitution. The speed of light is just too fast to permit a mechanical device to do this job, at least within the confines of a laboratory. Much ingenuity was needed to get around this problem.

After several supporting experiments were published, Jacques et al. claimed that an experiment of theirs follows fully the original scheme proposed by Wheeler. Their complicated experiment is based on the Mach–Zehnder interferometer, involving a triggered diamond N–V colour centre photon generator, polarization, and an electro-optical modulator acting as a switchable beam splitter. Measuring in a closed configuration showed interference, while measuring in an open configuration allowed the path of the particle to be determined, which made interference impossible.
In such experiments, Einstein originally argued, it is unreasonable for a single photon to travel simultaneously two routes. Remove the half-silvered mirror at the [upper right], and one will find that the one counter goes off, or the other. Thus the photon has traveled only one route. It travels only one route. but it travels both routes: it travels both routes, but
it travels only one route. What nonsense! How obvious it is that quantum theory is inconsistent!

Interferometer in the lab
The Wheeler version of the interferometer experiment could not be performed in a laboratory until recently because of the practical difficulty of inserting or removing the second beam-splitter in the brief time interval between the photon's entering the first beam-splitter and its arrival at the location provided for the second beam-splitter. This realization of the experiment is done by extending the lengths of both paths by inserting long lengths of fiber optic cable. So doing makes the time interval involved with transits through the apparatus much longer. A high-speed switchable device on one path, composed of a high-voltage switch, a Pockels cell, and a Glan–Thompson prism, makes it possible to divert that path away from its ordinary destination so that path effectively comes to a dead end. With the detour in operation, nothing can reach either detector by way of that path, so there can be no interference. With it switched off the path resumes its ordinary mode of action and passes through the second beam-splitter, making interference reappear. This arrangement does not actually insert and remove the second beam-splitter, but it does make it possible to switch from a state in which interference appears to a state in which interference cannot appear, and do so in the interval between light entering the first beam-splitter and light exiting the second beam-splitter. If photons had "decided" to enter the first beam-splitter as either waves or a particles, they must have been directed to undo that decision and to go through the system in their other guise, and they must have done so without any physical process being relayed to the entering photons or the first beam-splitter because that kind of transmission would be too slow even at the speed of light. Wheeler's interpretation of the physical results would be that in one configuration of the two experiments a single copy of the wavefunction of an entering photon is received, with 50% probability, at one or the other detectors, and that under the other configuration two copies of the wave function, traveling over different paths, arrive at both detectors, are out of phase with each other, and therefore exhibit interference. In one detector the wave functions will be in phase with each other, and the result will be that the photon has 100% probability of showing up in that detector. In the other detector the wave functions will be 180° out of phase, will cancel each other exactly, and there will be a 0% probability of their related photons showing up in that detector.

Interferometer in the cosmos
The cosmic experiment envisioned by Wheeler could be described either as analogous to the interferometer experiment or as analogous to a double-slit experiment. The important thing is that by a third kind of device, a massive stellar object acting as a gravitational lens, photons from a source can arrive by two pathways. Depending on how phase differences between wavefunction pairs are arranged, correspondingly different kinds of interference phenomena can be observed. Whether to merge the incoming wavefunctions or not, and how to merge the incoming wavefunctions can be controlled by experimenters. There are none of the phase differences introduced into the wavefunctions by the experimental apparatus as there are in the laboratory interferometer experiments, so despite there being no double-slit device near the light source, the cosmic experiment is closer to the double-slit experiment. However, Wheeler planned for the experiment to merge the incoming wavefunctions by use of a beam splitter.

The main difficulty in performing this experiment is that the experimenter has no control over or knowledge of when each photon began its trip toward earth, and the experimenter does not know the lengths of each of the two paths between the distant quasar. Therefore, it is possible that the two copies of one wavefunction might well arrive at different times. Matching them in time so that they could interact would require using some kind of delay device on the first to arrive. Before that task could be done, it would be necessary to find a way to calculate the time delay.

One suggestion for synchronizing inputs from the two ends of this cosmic experimental apparatus lies in the characteristics of quasars and the possibility of identifying identical events of some signal characteristic. Information from the Twin Quasars that Wheeler used as the basis of his speculation reach earth approximately 14 months apart. Finding a way to keep a quantum of light in some kind of loop for over a year would not be easy.

Double-slits in lab and cosmos

Wheeler's version of the double-slit experiment is arranged so that the same photon that emerges from two slits can be detected in two ways. The first way lets the two paths come together, lets the two copies of the wavefunction overlap, and shows interference. The second way moves farther away from the photon source to a position where the distance between the two copies of the wavefunction is too great to show interference effects. The technical problem in the laboratory is how to insert a detector screen at a point appropriate to observe interference effects or to remove that screen to reveal the photon detectors that can be restricted to receiving photons from the narrow regions of space where the slits are found. One way to accomplish that task would be to use the recently developed electrically switchable mirrors and simply change directions of the two paths from the slits by switching a mirror on or off.  no such experiment has been announced.

The cosmic experiment described by Wheeler has other problems, but directing wavefunction copies to one place or another long after the photon involved has presumably "decided" whether to be a wave or a particle requires no great speed at all. One has about a billion years to get the job done.

The cosmic version of the interferometer experiment could be adapted to function as a cosmic double-slit device as indicated in the illustration.

Current experiments of interest
The first real experiment to follow Wheeler's intention for a double-slit apparatus to be subjected to end-game determination of detection method is the one by Walborn et al.

Researchers with access to radio telescopes originally designed for SETI research have explicated the practical difficulties of conducting the interstellar Wheeler experiment.

A recent experiment by Manning et al. confirms the standard predictions of standard quantum mechanics with an atom of Helium.

Conclusions

Ma, Zeilinger et al. have summarized what can be known as a result of experiments that have arisen from Wheeler's proposals. They say:
Our work demonstrates and confirms that whether the correlations between two entangled photons reveal welcher-weg information or an interference pattern of one (system) photon depends on the choice of measurement on the other (environment) photon, even when all of the events on the two sides that can be space-like separated are space-like separated. The fact that it is possible to decide whether a wave or particle feature manifests itself long after—and even space-like separated from—the measurement teaches us that we should not have any naive realistic picture for interpreting quantum phenomena. Any explanation of what goes on in a specific individual observation of one photon has to take into account the whole experimental apparatus of the complete quantum state consisting of both photons, and it can only make sense after all information concerning complementary variables has been recorded. Our results demonstrate that the viewpoint that the system photon behaves either definitely as a wave or definitely as a particle would require faster-than-light communication. Because this would be in strong tension with the special theory of relativity, we believe that such a viewpoint should be given up entirely.

See also
 Delayed-choice quantum eraser
 Wheeler–Feynman time-symmetric theory

Bibliography

 On-line bibliography listing all of Wheeler's works
 John Archibald Wheeler, "The 'Past' and the 'Delayed-Choice Double-Slit Experiment'," pp 9–48, in A.R. Marlow, editor, Mathematical Foundations of Quantum Theory, Academic Press (1978)
 John Archibald Wheeler and Wojciech Hubert Zurek, Quantum Theory and Measurement (Princeton Series in Physics)
 John D. Barrow, Paul C. W. Davies, and Jr, Charles L. Harperm Science and Ultimate Reality: Quantum Theory, Cosmology, and Complexity (Cambridge University Press) 2004
 Xiao-song Ma, Johannes Kofler, and Anton Zeilinger, Delayed-choice gedanken experiments and their realizations, , March 2016.  Survey article.

References

External links
 Wheeler's Classic Delayed Choice Experiment by Ross Rhodes
 The Quantum Eraser by John G. Cramer
 Demystifying the Delayed Choice Experiments

Thought experiments in quantum mechanics

Wheeler's delayed-choice experiment


The NZR W class consisted of two steam locomotives built at the Addington Railway Workshops in Christchurch, New Zealand by the New Zealand Railways Department (NZR). They were the first locomotives to be built by NZR.

Almost all subsequent tank locomotive classes built by NZR were classified as sub-classes of the W class, e.g. WA, WAB, WB. The only exception was the Y class.

Introduction
The class originated from proposals to build tank locomotives from parts imported for the original J class. The design evolved into a completely New Zealand built locomotives.

Preserved locomotives
After withdrawal W 192 was stored at Hillside Workshops until 1962 when the New Zealand Railways Department used it for promotions. In 1964 it was placed in storage in Arthurs Pass. In 1973 it was restored as a static display for the NZR. But in 1979 it was restored to operational condition and used in places with F 163 including shuttle trains in Wellington. In 1988 it was used hauling trains from Christchurch to Rangiora for a week for the Ferrymead 125 celebrations.

One of the days it was taken out of service for repairs to her firebox and was replaced by C 864, but returned to service the following day. In 1992 W 192 was leased to the Ashburton Railway & Preservation Society for uses on their former Mount Somers Branchline at The Plains Vintage Railway & Historical Museum. In 1993 the NZR sold 192 to the Rail Heritage Trust of New Zealand. On 16 and 17 September 1995 the W took part at the 1995 Waipara Vintage Festival held by the Weka Pass Railway. After the festival, it was returned to The Plains Railway. It was sent again to Waipara for the 1997 festival then repeated again in 1999. During the 1999 festival it developed minor boiler issues and only ran one trip to Waikari from Glenmark, but only ran in more minor roles. In 2001 it was transported to the Linwood Locomotive Depot from The Plains and placed into storage. On 7 October 2003 it was announced by the Rail Heritage Trust of New Zealand it would be on long-term loan to the Canterbury Railway Society for uses at the Ferrymead Heritage Park. It arrived during the same month just in time for the 140th Railway celebrations at Ferrymead.

See also
 NZR WA class
 NZR WB class
 NZR WD class
 NZR WE class
 NZR WF class
 NZR WG class
 NZR WW class
 NZR WS / WAB class
 Locomotives of New Zealand

References

Citations

Bibliography

External links
 NZ Steam - W class

2-6-2T locomotives
W class
3 ft 6 in gauge locomotives of New Zealand
Railway locomotives introduced in 1889

NZR W class


Regina Kapeller-Adler, born Regina Kapeller, (28 June 1900 – 31 July 1991) was an Austrian biochemist who, in 1934, devised an innovative test for early pregnancy based on the detection of histidine in urine. As a Jew, she was forced to leave Austria following the country's annexation into Nazi Germany in the Anschluss and went to work with the noted geneticist Francis Crew at the Institute of Animal Genetics at the University of Edinburgh.

She worked at the Edinburgh Royal Infirmary during the Second World War and subsequently joined the pharmacology department of the University of Edinburgh and worked as a lecturer in chemistry. Towards the end of her career, she worked in obstetrics and gynaecology. In 1973, she received the Golden Honorary Diploma, an honorary degree of the University of Vienna, which was presented to her by Austrian biochemist Hans Tuppy.

Early life
Regina Kapeller was born on 28 June 1900 in Stanislau (now Ivano-Frankivsk), Galicia, Austria-Hungary. Her father, Moritz Kapeller, was employed by the Canadian Pacific and Royal Mail Lines. Her early education was at a school in Brody, Lviv.

In 1928, Regina Kapeller married Dr Ernst Adler (1899–1970) and they had a daughter, Liselotte Adler (later Mrs Kastner) in 1934.

Career

Kapeller-Adler obtained her doctorate in chemistry from the University of Vienna in 1923 and became a demonstrator at the Institute for Medical Chemistry of the University of Vienna in 1926. She was discouraged from pursuing a habilitation because she was a woman and Jewish, and worked unpaid. In 1934, she developed an innovative chemical test for early pregnancy using the detection of histidine excretion in urine that gained her international recognition.

Kapeller-Adler began to study for a medical degree at the University of Vienna in 1934 while working part-time at the Biochemical Laboratory of the Health Insurance Fund from 1935 to 1936. Between 1936 and 1937, she was head of the Laboratory for Clinical and Medical-Chemical Diagnostics of the Sanatoriums Hera in Vienna.

After the Anschluss in 1938, during which Nazi Germany annexed Austria, Kapeller-Adler and her husband lost their jobs due to being Jewish, and were unable to complete their studies at the university. In 1939, she moved to Edinburgh, Scotland, on the invitation of the English geneticist Francis Crew to work at the Institute of Animal Genetics at the University of Edinburgh, then the only pregnancy diagnosis centre in the United Kingdom. Her husband travelled with her and was briefly interned as an "enemy alien" before being released and starting a medical practice in Edinburgh in 1943.

Kapeller-Adler was awarded the degree of Doctor of Science by the University of Edinburgh in 1941. She worked at the Edinburgh Royal Infirmary from 1940 to 1944. Subsequently, she joined the pharmacology department of the University of Edinburgh and worked as a lecturer in chemistry from 1951 to 1964. Starting in 1968, she worked locally in obstetrics and gynaecology. In 1973 she received the Golden Honorary Diploma, an honorary degree from the University of Vienna, presented to her by Austrian biochemist Hans Tuppy.

Death and legacy
Kapeller-Adler died in Edinburgh on 31 July 1991 at the age of 91.

Selected publications
"Urinary Histidine in the Diagnosis of Pregnancy", JAMA, 27 June 1936, , pp. 2240–2241.
Amine Oxidases and Methods for their Study. Wiley-Interscience, New York & London, 1970.

References

Further reading

"Visa to Freedom 1939 thanks to a Pregnancy Test: A Sketch of the Lives of my Parents in Pre-War Vienna" by Liselotte Adler-Kastner in The Edinburgh Star, No. 62, March 2009, pp. 9–11.

External links

1900 births
1991 deaths
Women biochemists
Academics of the University of Edinburgh
Austrian biochemists
Austrian women academics
University of Vienna alumni
Jewish women scientists
Austrian emigrants to Scotland
Jewish emigrants from Austria after the Anschluss to the United Kingdom
Physicians of the Royal Infirmary of Edinburgh

Regina Kapeller-Adler