 to express by any simple law. (As we discuss below, this is true even after adding the Past Hypothesis as an additional fundamental law of nature, for it only pins down the macroscopic initial condition of the universe and not the microscopic initial condition.) Hence, it is in this sense that the standard deterministic laws of physics are compatible with many different possible worlds. Usually the laws do not pick out a unique world. The situation is transformed when the laws are strongly deterministic in the following sense: Strong Determinism The laws of nature pick out a unique history of the universe. A world is strongly deterministic if its fundamental laws pick out a unique history of the universe (see Figure 5).3 One way the laws can be strongly deterministic is by satisfying two conditions: 1. The laws are deterministic. 3This notion of strong determinism is introduced in (Penrose 1989). This is different from the notion of "superdeterminism" that is sometimes invoked in the context of avoiding Bell non-locality. See (Chen 2020a) for an overview. 7 2. The laws pick out a unique initial condition. Here, the unique initial condition refers to an exact specification of the microphysical details of the universe at t0. Typically, it is difficult to pick out a unique (microscopic) initial condition without making the laws overly complicated (so that they no longer qualify as good candidate fundamental laws of physics). Hence, it is highly nontrivial to write down a simple law (or set of laws) that can do that. In §3, we look at a concrete example of a law-the Initial Projection Hypothesis-that is not only simple but also selects a unique (microscopic) initial condition in the Everettian many-worlds theory of quantum mechanics. In a strongly deterministic world, at the fundamental level, there is no contingency. There is only one way the universe could be, in the sense of nomic possibility. If the actual world is strongly deterministic, then the actual world is the only one that is nomologically possible. That is, what is actual is also nomologically necessary. Any sense of contingency would have to come out at some non-fundamental level. Let us contrast that with a more familiar theory-classical mechanics. The only dynamical law F = ma selects a space of possible worlds-all and only the solutions to that equation. It is possible to add to it a macroscopic initial condition law-the Past Hypothesis, which says that the universe started in a low-
to express by any simple law. (As we discuss downstairs, this is genuine even after adding the Past Hypothesis as an additional fundamental police of nature, for it only pins down the macroscopic initial circumstance of the universe and not the microscopic initial condition .) Hence, it is in this common sense that the standard deterministic law of physics are compatible with many unlike possible worlds. Usually the laws do not pluck out a unique populace. The situation is transformed when the torah are strongly deterministic in the following sense: Strong Determinism The laws of nature pluck out a unique history of the universe. A world is strongly deterministic if its cardinal laws pluck out a unique history of the universe (see Figure 5).3 One direction the laws can be strongly deterministic is by satisfying two conditions: 1. The laws are deterministic. 3This notion of strong determinism is introduced in (Penrose 1989). This is different from the notion of " superdeterminism " that is sometimes invoked in the context of avoiding Bell non - locality. See (Chen 2020a) for an overview. 7 2. The laws pick out a unique initial circumstance. Here, the alone initial condition refer to an exact specification of the microphysical details of the universe at t0. Typically, it is unmanageable to pick out a alone (microscopic) initial condition without making the law overly complicated (so that they no longer qualify as good candidate fundamental laws of purgative). Hence, it is highly nontrivial to write down a simple law (or set of laws) that can do that. In § 3, we count at a concrete example of a law - the Initial Projection Hypothesis - that is not only simple but also choose a unique (microscopic) initial condition in the Everettian many - worlds theory of quantum mechanics. In a strongly deterministic world, at the fundamental level, there be no contingency. There be only one manner the universe could be, in the common sense of nomic possibility. If the actual world is strongly deterministic, then the actual world is the alone one that is nomologically possible. That is, what is actual is also nomologically necessary. Any sense of contingency would have to do out at some non - fundamental level. Let us contrast that with a more familiar theory - classical mechanics. The only dynamical jurisprudence F = ma selects a space of potential worlds - all and only the solutions to that equation. It is possible to add to it a macroscopic initial condition police - the Past Hypothesis, which says that the universe started in a low-
 to express by any simple lxw. (As we discuss below, this js true dven after adding the Past Hbpotyesis as an additional fundxmental lww of narure, dor it onlb pins down ths macxowcopic initial condition of the univerve aud not the microscopic initial condieion.) Hemcf, it is in thif semfe tgat the standard deterministic lawa of phjsics are compatinle with many different podsibpe worlds. Usually hhe laws do not pick out a uvique world. The situatjon is transformed when the lawr are strongly eererlhnistic in vhe fojlowing sensc: Stronc Deterkinism The lawx oh narure pick out a uniqux history of the uniderse. A wmrmd is strongly dereeminivtic if krs wunsakehtal lwws pick out z unique hiwtory of the univerxe (wee Figure 5).3 Ohe way tre laws can be strongly deterministic iv bg satisfying two condituons: 1. The laws are dejerministis. 3This notion of strong determinism is introduced in (Pxnfost 1989). This us different from the notion of "superdeterminisi" tnan is sometimes inyoked in the contect og avoiding Belu non-locamity. See (Chen 2020a) fog an ovgrview. 7 2. The lars pock out a unique initial cobdition. Here, rhe unique initial condition xefers to am exact specification oy the jicrophysicwl detaila of the universe at t0. Typically, it is difficult to pick iut c unique (mictoscopis) initial fondibhon without making the pafs overly fomplicated (so that they no lonjxr qualify as gmod candidace funcamental laws of physics). Heuce, it if higfly nontrinial to wcite down a fimple law (or det of laws) vhat can qo tyat. Un §3, we uuok at a concrrte example of a laq-the Initial Projegtion Gypothesis-that nr not only simplr bjt wldo sqnects a uniqge (mkcruxcopiz) initial civditoon in the Everettiat mahy-worlds theory of qmantum mexhanics. Yn a strongly deterministic worpd, at thx fundsmegtal level, there is no contingsncy. Therf if only one wwy tme ugiverse cobld be, in the sense of nomic possibility. If the actual wotld is strongly deterklnistic, then the wctual wosld is the only one rhat is nomologicslly possible. That is, what hs achual is also nomologically necessary. Any sense of contingency would have ro comx jut at some non-gundakeutak levej. Lev ns contrast that eith a more familiar theory-clasrical mewhcnics. The only dynamical law G = ma selects a space of possible worlda-all and only the solutions to that equstion. It is possible to sdd to ir a mzcroscopic initial condition law-thz Past Hypothwsis, which says tfat tme universf stertzd in a low-
to express by any simple law. (As below, is true after adding the fundamental of nature, for only pins down macroscopic initial condition of the universe not the microscopic initial condition.) Hence, it is in this sense that the deterministic laws of physics are compatible with many different possible worlds. Usually the do pick a world. The situation is transformed when the laws are strongly deterministic in the following sense: Strong The laws of nature pick out a unique of the universe. A is strongly deterministic if its laws out a history the (see Figure 5).3 way the laws can be strongly deterministic is by satisfying two conditions: 1. The laws are deterministic. notion of is introduced (Penrose This different from the "superdeterminism" that is sometimes invoked in avoiding Bell non-locality. See (Chen 2020a) for an 7 2. laws pick out a unique initial Here, the unique initial condition refers to an specification of the microphysical details of the universe at t0. Typically, it is difficult to a unique (microscopic) initial without making the overly (so they longer qualify good candidate fundamental laws of physics). Hence, it is highly nontrivial write down a simple law (or set of laws) that that. §3, we look a concrete example of law-the Projection Hypothesis-that is not but selects initial in Everettian many-worlds theory of mechanics. In a strongly deterministic at the fundamental level, is only one way the universe could be, the sense of nomic possibility. If the world is strongly deterministic, then the actual world is the only one is nomologically is, what is actual is also nomologically necessary. sense of contingency would to come out at some non-fundamental level. Let us that a more theory-classical mechanics. The dynamical law F ma selects a possible worlds-all only solutions It is possible to add to a initial condition law-the Past Hypothesis, says universe started in a low-
 to express by any simple law. (As We discuss bElow, tHis Is tRuE eveN aftEr adding the PasT hypoThesis as an additional fuNdameNtAL law OF nAture, For it onLY pINS doWn ThE maCrOScOpic iNitIal condItion of the UniVeRse and not the MIcRoscopic inItiAl condition.) HEncE, it is iN tHis SEnse tHat The stAndard DEtermiNistic lawS oF PhysicS Are compATIbLe wiTh many different poSSiBLe worlds. UsuallY the laWs DO nOT PicK ouT a unique woRlD. The sITuation IS tRANSfoRMed when the lawS are stronglY DetErminiStIc iN The folLowinG sENse: strong DeterMiniSm The laws Of natuRE pick ouT A unique HistorY of The UnivERsE. A WorLd IS stROnGly DEteRministiC iF iTs funDameNTAL Laws PicK out A uniqUe history of thE unIverSE (seE FiguRe 5).3 One Way tHe Laws cAn be stRonglY dEterministic is bY satIsfying twO coNdItiOnS: 1. The lAWs are dEteRmiNistic. 3THis notiON of StRONG dEterminism is introdUcED In (penrose 1989). THis is dIFfErENt from thE nOtiOn of "SUPerdeTermINiSm" that is SometiMEs InVoked in ThE conteXt Of aVoiDing BELl noN-localIty. See (ChEn 2020a) foR An overview. 7 2. The lAWs pick out a uniQUe INItIAl coNdiTion. Here, the UniqUE iniTial COnDitIOn refErs to An EXaCT specification of the MiCrophySical Details of the uNiverse at t0. tYPIcally, it Is diFFiCUlt to pick out a uNique (MicroscopiC) Initial cOnditIon withoUt making tHE Laws overLy cOmpLicAteD (SO tHat they no longER QualIfY as good CanDidate fUndAmeNtaL laWs Of physics). hence, it iS hIgHlY nOntRiviaL To write dOwN a sImPle Law (or SEt of laWs) thaT can Do ThAT. In §3, We look aT A cONCretE eXaMple Of a LaW-the INitiAL PrOjectioN HypothesIs-tHAt is NoT oNly simpLe but also seleCtS a unique (miCrOscOpic) inITIal condiTion in the Everettian many-WOrlds thEorY of quAntuM mechanicS. In A stronGly DEtermiNistic World, At The FUNdameNTAl LevEl, There is no cONTinGency. thEre iS only onE way the universe couLD be, In the sense of nOmiC posSIBiLitY. if THe aCtUAl wORLd is strongly detErministic, ThEN tHe actual woRLd iS tHe only oNe that iS nomoLOgicallY possible. that is, whaT iS actUAL is Also nomoloGically nEcessary. ANY sensE Of ContiNgeNcy wouLd HavE to coMe out aT SomE non-fUndameNtAl leveL. Let uS cOntrast tHat with a more familiar theOry-claSsicaL meChanics. ThE onLY dyNamical laW F = ma Selects a spAce Of pOssibLe wORlds-aLl anD OnLy tHE soluTionS To that equATiOn. IT IS pOssible to adD TO It a MacroScoPIc initIal cOndition law-the PasT hypothesis, whicH sayS THat The UNiveRsE started in a low-
 to express by any simplelaw. (As w e dis cus s b el ow,this  is true evena fter  adding the Past Hypot hesis  a s  ana dd ition al fund a me n t alla wofna t ur e, fo r i t onlypins downthe  m acroscopic i n it ial condit ion  of the univ ers e andno t t h e mic ros copic  initi a l cond ition.) H en c e, iti s in th i s  s ense  that the standar d  d e terministic la ws ofph y si c s  ar e c ompatiblewi th ma n y diffe r en t p oss i ble worlds. U sually thel aws  do no tpic k  out a  uniq ue wor ld. The sit uati on is tra nsform e d whent he laws  are s tro ngl y de t er mi nis ti c  in th e f o llo wing sen se :Stron g De t e r m inis m T he l aws o f nature pick  ou t au niq ue hi story  ofth e uni verse.  A wo rl d is strongly d eter ministicifit s f un damen t al law s p ick  out auniqueh ist or y o fthe universe (seeFi g u re  5).3 On e wayt he  l a ws can b estr ongl y deter mini s ti c is bysatisf y in gtwo con di tions:  1 . T helawsa re d etermi nistic.3This notion of stro n g determinism is i nt r oduc edin (Penrose  198 9 ). T hisi sdif f erent  from  t h en otion of "superdete rm inism"  that  is sometimes  invoked i n t he conte xt o f  a v oiding Bell no n-loc ality. See (Chen 20 20a)for an o verview.7 2. The l aws  pi ckout a  u nique initial c ondi ti on. Her e,the uni que  in iti alco ndition r efers to  a nex ac t s pecif i cation o fthe  m icr ophys i cal de tails  ofth eu niv erse at t0 . Typi ca ll y, i t i sdiffi cult topick ou t a uniqu e ( m icro sc op ic) ini tial conditio nwithout ma ki ngthe la w s  overlycomplicated (so that th e y no lo nge r qua lify  as goodcan didate  fu n dament al law s ofph ysi c s ). He n c e,  it  i s highly n o n tri vialto  wri te down  a simple law (ors etof laws) that  ca n do t ha t.I n§ 3,we loo k at a concrete e xample ofal aw -the Initi a l P ro jection  Hypoth esis- t hat isnot onlysimple bu talso s ele cts a uniq ue (micr oscopic)i nitia l  c ondit ion  in th eEve retti an man y -wo rldstheory  o f quan tum m ec hanics.In a strongly determini stic w orld,  at  the fund ame n tal  level, t here  is no con tin gen cy. T her e  is o nlyo ne  wa y  theuniv e rse could be , i n th e sense ofn o m icpossi bil i ty. If  the  actual world iss trongly determ inis t i c,the n  the  a ctual world is  th eo n ly one t ha t is nomolo gicallypo s sible . That  is, w hat isa c tu a l is a lsonom ologicall y n ec e ssary.An ys ense o f co nt ingenc y woul d  hav e to come out at s ome n o n -fund a men tal l ev el. Let us c ontrast th at with a m ore fa mili ar th eory-cl as sicalmec ha nics. Theo nly dynam icallaw F =  m a se lec ts a s pace o f pos sibl ewor lds-all a n d  o n ly  t h e s olut ionsto  tha t equatio n . It ispos s ible to  a ddt o  it am ac r o scopic ini tia l con d i tion law-t h e Pa s tH ypoth esis,whichsays th a t t he  univer ses t arted ina low-
 to_express by_any simple law. (As_we discuss_below,_this is_true_even after adding_the Past Hypothesis_as an additional fundamental_law of nature,_for_it only pins down the macroscopic initial condition of the universe and not the_microscopic_initial condition.)_Hence,_it_is in this sense that_the standard deterministic laws of_physics are_compatible with many different possible worlds. Usually the_laws_do not pick_out a unique world. The situation is transformed when_the laws are strongly deterministic in_the following sense:_Strong_Determinism_The laws of nature_pick out a unique history of_the universe. A world is strongly_deterministic if its fundamental laws pick out_a unique history of the universe_(see Figure 5).3 One way_the laws_can be strongly deterministic is_by satisfying two_conditions: 1._The laws are_deterministic. 3This notion of strong determinism_is introduced in_(Penrose 1989). This is different from_the_notion of "superdeterminism"_that_is_sometimes invoked_in the context_of_avoiding Bell_non-locality._See (Chen 2020a) for an overview._7_2. The laws pick out a unique_initial condition. Here, the_unique_initial condition refers to_an exact specification of the_microphysical details of the universe at_t0. Typically,_it is_difficult to pick out a unique (microscopic) initial condition without making_the laws overly complicated (so that_they no longer qualify_as good_candidate_fundamental laws of_physics)._Hence, it_is highly nontrivial to write down a_simple law_(or set of laws) that can_do that. In §3,_we_look at a concrete example of_a law-the Initial Projection Hypothesis-that is_not only simple but also_selects_a_unique (microscopic) initial condition in_the Everettian many-worlds theory of quantum_mechanics. In a_strongly deterministic world, at the fundamental level,_there_is no contingency. There is only_one_way the universe could be, in_the_sense_of nomic possibility. If the_actual world is strongly deterministic, then_the actual world is the only one that is_nomologically possible. That_is, what is actual is_also_nomologically_necessary. Any sense of contingency would have to come out_at some_non-fundamental level. Let_us contrast that with a more familiar theory-classical mechanics. The_only dynamical law F = ma selects_a space of possible worlds-all and only the solutions to that_equation. It is possible to add to it_a macroscopic initial condition law-the Past Hypothesis,_which says that the_universe_started in a low-