don howard, einstein's philosophy of science

8/12/2019 Don Howard, Einstein's Philosophy of Science

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Einstein's Philosophy of Science

First published Wed Feb 11, 2004

Albert Einstein (1879–1955) is well known as the most prominent physicist of thetwentieth century. ess well known! thou"h of comparable importance! are hiscontributions to twentieth#century philosophy of science. Einstein$s own philosophyof science is an ori"inal synthesis of elements %rawn from sources as %i&erse asneo#'antianism! con&entionalism! an% lo"ical empiricism! its %istincti&e feature

bein" its no&el blen%in" of realism with a holist! un%er%eterminationist form ofcon&entionalism. f special note is the manner in which Einstein$s philosophicalthinkin" was %ri&en by an% contribute% to the solution of problems firstencountere% in his work in physics. Eually si"nificant are Einstein$s relations with

an% influence on other prominent twentieth#century philosophers of science!especially *orit+ ,chlick an% -ans eichenbach.

• 1. /ntro%uction0 as Einstein an Epistemolo"ical 2pportunist34• . 6he n%er%etermination of 6heory hoice by E&i%ence0 6he ature an%

ole of on&entions in ,cience• :. ,implicity an% 6heory hoice• ;. ni&ocalness in the 6heoretical epresentation of ature• 5. ealism an% ,eparability• <. 6he =rinciple 6heories>onstructi&e 6heories ?istinction• 7. onclusion0 Albert Einstein0 =hilosopher#=hysicist• @iblio"raphy

o Einstein$s ork o elate% iterature

• ther /nternet esources• elate% Entries

1. Introduction: Was Einstein an Epistemological “Opportunist”

ate in 19;;! Albert Einstein recei&e% a letter from obert 6hornton! a youn"African#American philosopher of science who ha% ust finishe% his =h.?. un%er-erbert Bei"l at *innesota an% was be"innin" a new ob teachin" physics at theni&ersity of =uerto ico! *aya"ue+. -e ha% written to solicit from Einstein a fewsupporti&e wor%s on behalf of his efforts to intro%uce 2as much of the philosophyof science as possible3 into the mo%ern physics course that he was to teach thefollowin" sprin" (6hornton to Einstein! 8 o&ember 19;;! EA <1–57:). C1D -ere iswhat Einstein offere% in reply0

http://plato.stanford.edu/entries/einstein-philscience/#IntWasEinEpiOpp

http://plato.stanford.edu/entries/einstein-philscience/#UndTheChoEviNatRolConSci


http://plato.stanford.edu/entries/einstein-philscience/#SimTheCho

http://plato.stanford.edu/entries/einstein-philscience/#UniTheRepNat

http://plato.stanford.edu/entries/einstein-philscience/#ReaSep

http://plato.stanford.edu/entries/einstein-philscience/#PriTheTheDis

http://plato.stanford.edu/entries/einstein-philscience/#ConAlbEinPhiPhy

http://plato.stanford.edu/entries/einstein-philscience/#Bib

http://plato.stanford.edu/entries/einstein-philscience/#EinWor

http://plato.stanford.edu/entries/einstein-philscience/#RelLit

http://plato.stanford.edu/entries/einstein-philscience/#Oth

http://plato.stanford.edu/entries/einstein-philscience/#Rel

http://plato.stanford.edu/entries/einstein-philscience/notes.html#1

http://plato.stanford.edu/entries/einstein-philscience/#IntWasEinEpiOpp



http://plato.stanford.edu/entries/einstein-philscience/#SimTheCho

http://plato.stanford.edu/entries/einstein-philscience/#UniTheRepNat

http://plato.stanford.edu/entries/einstein-philscience/#ReaSep

http://plato.stanford.edu/entries/einstein-philscience/#PriTheTheDis

http://plato.stanford.edu/entries/einstein-philscience/#ConAlbEinPhiPhy

http://plato.stanford.edu/entries/einstein-philscience/#Bib

http://plato.stanford.edu/entries/einstein-philscience/#EinWor

http://plato.stanford.edu/entries/einstein-philscience/#RelLit

http://plato.stanford.edu/entries/einstein-philscience/#Oth

http://plato.stanford.edu/entries/einstein-philscience/#Rel




/ fully a"ree with you about the si"nificance an% e%ucational &alue of metho%olo"yas well as history an% philosophy of science. ,o many people to%ay>an% e&en

professional scientists>seem to me like somebo%y who has seen thousan%s of trees but has ne&er seen a forest. A knowle%"e of the historic an% philosophical

back"roun% "i&es that kin% of in%epen%ence from preu%ices of his "eneration fromwhich most scientists are sufferin". 6his in%epen%ence create% by philosophicalinsi"ht is>in my opinion>the mark of %istinction between a mere artisan orspecialist an% a real seeker after truth. (Einstein to 6hornton! 7 ?ecember 19;;! EA<1#57;)

6hat Einstein meant what he sai% about the rele&ance of philosophy to physics ise&i%ence% by the fact that he ha% been sayin" more or less the same thin" for%eca%es. 6hus! in a 191< memorial note for Ernst *ach! a physicist an%

philosopher to whom Einstein owe% a special %ebt! he wrote0-ow %oes it happen that a properly en%owe% natural scientist comes to concernhimself with epistemolo"y4 /s there no more &aluable work in his specialty4 / hearmany of my collea"ues sayin"! an% / sense it from many more! that they feel thisway. / cannot share this sentiment. hen / think about the ablest stu%ents whom /ha&e encountere% in my teachin"! that is! those who %istin"uish themsel&es by theirin%epen%ence of u%"ment an% not merely their uick#witte%ness! / can affirm thatthey ha% a &i"orous interest in epistemolo"y. 6hey happily be"an %iscussions aboutthe "oals an% metho%s of science! an% they showe% uneui&ocally! throu"h theirtenacity in %efen%in" their &iews! that the subect seeme% important to them./n%ee%! one shoul% not be surprise% at this. (Einstein 191<! 11)

-ow! eFactly! %oes the philosophical habit of min% pro&i%e the physicist with such2in%epen%ence of u%"ment34 Einstein "oes on to eFplain0

oncepts that ha&e pro&en useful in or%erin" thin"s easily achie&e such anauthority o&er us that we for"et their earthly ori"ins an% accept them as unalterable"i&ens. 6hus they come to be stampe% as 2necessities of thou"ht!3 2a priori "i&ens!3

etc. 6he path of scientific a%&ance is often ma%e impassable for a lon" time throu"hsuch errors. Bor that reason! it is by no means an i%le "ame if we become practice%in analy+in" the lon" commonplace concepts an% eFhibitin" those circumstancesupon which their ustification an% usefulness %epen%! how they ha&e "rown up!in%i&i%ually! out of the "i&ens of eFperience. @y this means! their all#too#"reatauthority will be broken. 6hey will be remo&e% if they cannot be properlyle"itimate%! correcte% if their correlation with "i&en thin"s be far too superfluous!replace% by others if a new system can be establishe% that we prefer for whate&erreason. (Einstein 191<! 1)



ne is not surprise% at Einstein$s then citin" *ach$s critical analysis of the ewtonian conception of absolute space as a para%i"m of what *ach! himself!terme% the 2historical#critical3 metho% of philosophical analysis (Einstein 191<!11! citin" h. ! GG <–7 of *ach$s Mechanik ! most likely the thir% e%ition! *ach

1897).

6he place of philosophy in physics was a theme to which Einstein returne% timean% a"ain! it bein" clearly an issue of %eep importance to him. ,ometimes he a%optsa mo%est pose! as in this oft#uote% remark from his 19:: ,pencer ecture0

/f you wish to learn from the theoretical physicist anythin" about the metho%swhich he uses! / woul% "i&e you the followin" piece of a%&ice0 ?on$t listen to hiswor%s! eFamine his achie&ements. Bor to the %isco&erer in that fiel%! theconstructions of his ima"ination appear so necessary an% so natural that he is apt totreat them not as the creations of his thou"hts but as "i&en realities. (Einstein 19::!5–<)

*ore typical! howe&er! is the confi%ent pose he struck three years later in 2=hysicsan% eality30

/t has often been sai%! an% certainly not without ustification! that the man ofscience is a poor philosopher. hy then shoul% it not be the ri"ht thin" for the

physicist to let the philosopher %o the philosophi+in"4 ,uch mi"ht in%ee% be the

ri"ht thin" at a time when the physicist belie&es he has at his %isposal a ri"i%system of fun%amental concepts an% fun%amental laws which are so wellestablishe% that wa&es of %oubt can not reach themH but it can not be ri"ht at a timewhen the &ery foun%ations of physics itself ha&e become problematic as they arenow. At a time like the present! when eFperience forces us to seek a newer an%more soli% foun%ation! the physicist cannot simply surren%er to the philosopher thecritical contemplation of the theoretical foun%ationsH for! he himself knows best!an% feels more surely where the shoe pinches. /n lookin" for a new foun%ation! hemust try to make clear in his own min% ust how far the concepts which he uses are

ustifie%! an% are necessities. (Einstein 19:<! :;9)

hat kin% of philosophy mi"ht we eFpect from the philosopher#physicist4 nethin" that we shoul% not eFpect from a physicist who takes the philosophical turn inor%er to help sol&e fun%amental physical problems is a systematic philosophy0

6he reciprocal relationship of epistemolo"y an% science is of noteworthy kin%.6hey are %epen%ent upon each other. Epistemolo"y without contact with science

becomes an empty scheme. ,cience without epistemolo"y is>insofar as it is

thinkable at all>primiti&e an% mu%%le%. -owe&er! no sooner has theepistemolo"ist! who is seekin" a clear system! fou"ht his way throu"h to such a



system! than he is incline% to interpret the thou"ht#content of science in the sense ofhis system an% to reect whate&er %oes not fit into his system. 6he scientist!howe&er! cannot affor% to carry his stri&in" for epistemolo"ical systematic that far.-e accepts "ratefully the epistemolo"ical conceptual analysisH but the eFternal

con%itions! which are set for him by the facts of eFperience! %o not permit him tolet himself be too much restricte% in the construction of his conceptual worl% by thea%herence to an epistemolo"ical system. -e therefore must appear to the systematicepistemolo"ist as a type of unscrupulous opportunist0 he appears as realist insofaras he seeks to %escribe a worl% in%epen%ent of the acts of perceptionHas idealist insofar as he looks upon the concepts an% theories as free in&entions ofthe human spirit (not lo"ically %eri&able from what is empirically "i&en)Has positivist insofar as he consi%ers his concepts an% theories ustifie% only to theeFtent to which they furnish a lo"ical representation of relations amon" sensory

eFperiences. -e may e&en appear as Platonist or Pythagorean insofar as heconsi%ers the &iewpoint of lo"ical simplicity as an in%ispensable an% effecti&e toolof his research. (Einstein 19;9! <8:–<8;)

@ut what strikes the 2systematic epistemolo"ist3 as mere opportunism mi"ht appearotherwise when &iewe% from the perspecti&e of a physicist en"a"e%! as Einsteinhimself put it! in 2the critical contemplation of the theoretical foun%ations.3 6heo&erarchin" "oal of that critical contemplation was! for Einstein! the creation of aunifie% foun%ation for physics after the mo%el of a fiel% theory like "eneral

relati&ity. Einstein faile% in his uest! but there was a consistency an% constancy inthe stri&in" that informe% as well the philosophy of science %e&elopin" han% inhan% with the scientific proect.

/n%ee%! from early to late a few key i%eas playe% the central! lea%in" role inEinstein$s philosophy of science! i%eas about which Einstein e&ince% surprisin"lylittle %oubt e&en while achie&in" an e&er %eeper un%erstan%in" of theirimplications. Bor the purposes of the followin" comparati&ely brief o&er&iew! wecan confine our attention to ust fi&e topics0

• 6he un%er%etermination of theory choice by e&i%ence.• ,implicity an% theory choice.• ni&ocalness in the theoretical representation of nature.• ealism an% separability.• 6he principle theories#constructi&e theories %istinction.

/n emphasi+in" the continuity an% coherence in the %e&elopment of Einstein$s philosophy of science! / take issue with an account such as Ieral% -olton$s (19<8)!which claims to fin% a maor philosophical break in the mi%#191s! in the form of a

turn away from a sympathy for an anti#metaphysical positi&ism an% towar% a robustscientific realism. -olton sees this turn bein" %ri&en by Einstein$s alle"e%



reali+ation that "eneral relati&ity! by contrast with special relati&ity! reuires arealistic ontolo"y. n my &iew! Einstein was ne&er an ar%ent 2*achian3 positi&ist!CD an% he was ne&er a scientific realist! at least not in the sense acuire% by the term2scientific realist3 in later twentieth century philosophical %iscourse (see -owar%

199:). Einstein eFpecte% scientific theories to ha&e the proper empirical cre%entials! but he was no positi&istH an% he eFpecte% scientific theories to "i&e an account of physical reality! but he was no scientific realist. *oreo&er! in both respects his&iews remaine% more or less the same from the be"innin" to the en% of his career.

hy Einstein %i% not think himself a realist (he sai% so eFplicitly) is %iscusse% below. hy he is not to be un%erstoo% as a positi&ist %eser&es a wor% or two offurther %iscussion here! if only because the belief that he was sympathetic to

positi&ism! at least early in his life! is so wi%esprea% (for a fuller %iscussion! see

-owar% 199:).6hat Einstein later repu%iate% positi&ism is beyon% %oubt. *any remarks from atleast the early 19s throu"h the en% of his life make this clear. /n 19;< heeFplaine% what he took to be *ach$s basic error0

-e %i% not place in the correct li"ht the essentially constructi&e an% speculati&enature of all thinkin" an% more especially of scientific thinkin"H in conseuence! hecon%emne% theory precisely at those points where its constructi&e#speculati&echaracter comes to li"ht unmistakably! such as in the kinetic theory of atoms.(Einstein 19;<! 1)

/s Einstein here also critici+in" his own youthful philosophical in%iscretions4 6he&ery eFample that Einstein "i&es here makes any such interpretation hi"hlyimplausible! because one of Einstein$s main "oals in his early work on @rownianmotion (Einstein 195b) was precisely to pro&e the reality of atoms! this in the faceof the then famous skepticism of thinkers like *ach an% ilhelm stwal%0

*y principal aim in this was to fin% facts that woul% "uarantee as much as possible

the eFistence of atoms of %efinite si+e.J 6he a"reement of these consi%erationswith eFperience to"ether with =lanck$s %etermination of the true molecular si+efrom the law of ra%iation (for hi"h temperatures) con&ince% the skeptics! who wereuite numerous at that time (stwal%! *ach)! of the reality of atoms. (Einstein19;<! ;5! ;7)

hy! then! is the belief in Einstein$s early sympathy for positi&ism so wellentrenche%4

6he one piece of e&i%ence stan%ar%ly cite% for a youthful flirtation with positi&ismis Einstein$s critiue of the notion of absolute %istant simultaneity in his 195 paper







take up his first aca%emic appointment at the ni&ersity of Kurich! he became theupstairs nei"hbor of his ol% frien% an% fellow Kurich physics stu%ent! Brie%richA%ler. Lust a few months before! A%ler ha% publishe% the Ierman translation of La

Thorie physi!ue (?uhem 198)! an% the philosophy of science became a freuent

topic of con&ersation between the new nei"hbors! A%ler an% Einstein (see -owar%199a).

6heoretical holism an% the un%er%etermination of theory choice by empiricale&i%ence are the central theses in ?uhem$s philosophy of science. -is ar"ument! in

brief! is that at least in sciences like physics! where eFperiment is %ense withsophisticate% instrumentation whose employment itself reuires theoreticalinterpretation! hypotheses are not teste% in isolation but only as part of whole

bo%ies of theory. /t follows that when there is a conflict between theory an%

e&i%ence! the fit can be restore% in a multiplicity of %ifferent ways. o statement isimmune to re&ision because of a presume% status as a %efinition or thanks to someother a priori warrant! an% most any statement can be retaine% on pain of suitablea%ustments elsewhere in the total bo%y of theory. -ence! theory choice isun%er%etermine% by e&i%ence.

6hat Einstein$s eFposure to ?uhem$s philosophy of science soon left its mark ise&i%ent from lecture notes that Einstein prepare% for a course on electricity an%ma"netism at the ni&ersity of Kurich in the winter semester of 191M11. Einsteinasks how one can assi"n a %efinite electrical char"e e&erywhere within a material

bo%y! if the interior of the bo%y is not accessible to test particles. A 2*achian3 positi&ist woul% %eem such %irect empirical access necessary for meanin"ful talk ofa char"e %istribution in the interior of a sol%. Einstein ar"ues otherwise0

e ha&e seen how eFperience le% to the intro%. of the concept of the uantity ofelectricity. it was %efine% by means of the forces that small electrifie% bo%ies eFerton each other. @ut now we eFten% the application of the concept to cases in whichthis %efinition cannot be applie% %irectly as soon as we concei&e the el. forces asforces eFerte% on electricityrather than on material particles. e set up aconceptual system the in%i&i%ual parts of which %o not correspon% %irectly toempirical facts. nly a certain totality of theoretical material correspon%s a"ain to acertain totality of eFperimental facts.

e fin% that such an el. continuum is always applicable only for the representationof el. states of affairs in the interior of pon%erable bo%ies. -ere too we %efine the&ector of el. fiel% stren"th as the &ector of the mech. force eFerte% on the unit of

pos. electr. uantity insi%e a bo%y. @ut the force so %efine% is no lon"er %irectlyaccessible to eFp. /t is one part of a theoretical construction that can be correct or

false! i.e.! consistent or not consistent with eFperience! only as a $hole. (EA :#7!E= :#11! :5)



ne can har%ly ask for a better summary of ?uhem$s point of &iew in application toa specific physical theory.

EFplicit citations of ?uhem by Einstein are rare (for %etails! see -owar% 199a).

@ut eFplicit in&ocations of a holist picture of the structure an% empiricalinterpretation of theories are not har% to fin%. An especially interestin" eFample isfoun% in a re&iew that Einstein wrote in 19; of Alfre% Elsbach$s %ant und

&instein (19;)! one of the floo% of books an% articles then tryin" to reconcile the'antian %octrine of the a priori Eucli%ean character of space with "eneralrelati&ity$s postulate of &ariable spacetime cur&ature. -a&in" asserte% that relati&itytheory is incompatible with 'ant$s %octrine of the a priori! Einstein eFplains why!more "enerally! he is not sympathetic with 'ant0

6his %oes not! at first! preclu%e one$s hol%in" at least to the 'antian proble'atic!as! e.".! assirer has %one. / am e&en of the opinion that this stan%point can beri"orously refute% by no %e&elopment of natural science. Bor one will always beable to say that critical philosophers ha&e until now erre% in the establishment ofthe a priori elements! an% one will always be able to establish a system of a priorielements that %oes not contra%ict a "i&en physical system. et me briefly in%icatewhy / %o not fin% this stan%point natural. A physical theory consists of the parts(elements) A! @! ! ?! that to"ether constitute a lo"ical whole which correctlyconnects the pertinent eFperiments (sense eFperiences). 6hen it ten%s to be the casethat the a""re"ate of fewer than all four elements! e.".! A! @! ?! $ithout ! nolon"er says anythin" about these eFperiences! an% ust as well A! @! without ?.ne is then free to re"ar% the a""re"ate of three of these elements! e.".! A! @! as a

priori! an% only ? as empirically con%itione%. @ut what remains unsatisfactory inthis is always the arbitrariness in the choice of those elements that one %esi"natesas a priori! entirely apart from the fact that the theory coul% one %ay be replace% byanother that replaces certain of these elements (or all four) by others. (Einstein19;! 1<88–1<89)

Einstein$s point seems to be that while one can always choose to %esi"nate selecte%elements as a priori an%! hence! non#empirical! no principle %etermines whichelements can be so %esi"nate%! an% our ability thus to %esi"nate them %eri&es fromthe fact that it is only the totality of the elements that possesses empirical content.

*uch the same point coul% be ma%e! an% was ma%e by ?uhem himself (see ?uhem19<! part ! ch. <! sects. 8 an% 9)! a"ainst those who woul% insulate certainstatements a"ainst empirical refutation by claimin" for them the status ofcon&entional %efinitions. E%ouar% e oy (191) ha% ar"ue% thus about the law offree fall. /t coul% not be refute% by eFperiment because it functione% as a %efinition

of 2free fall.3 An% -enri =oincarN (191) sai% much the same about the principlesof mechanics more "enerally. As Einstein answere% the neo#'antians! so ?uhem



answere% this species of con&entionalist0 Oes! eFperiment cannot refute! say! thelaw of free fall by itself! but only because it is part of a lar"er theoretical whole thathas empirical content only as a whole! an% &arious other elements of that wholecoul% as well be sai% to be! alone! immune to refutation.

6hat Einstein shoul% %eploy a"ainst the neo#'antians in the early 19s thear"ument that ?uhem use% a"ainst the con&entionalism of =oincarN an% e oy isinterestin" from the point of &iew of Einstein$s relationships with those who werelea%in" the %e&elopment of lo"ical empiricism an% scientific philosophy in the19s! especially ,chlick an% eichenbach. Einstein share% with ,chlick an%eichenbach the "oal of craftin" a new form of empiricism that woul% be a%euateto the task of %efen%in" "eneral relati&ity a"ainst neo#'antian critiues (see ,chlick1917 an% 191! an% eichenbach 19! 19;! an% 198H for more %etail! see

-owar% 199;a). @ut while they all a"ree% that what 'ant re"ar%e% as the a priorielement in scientific co"nition was better un%erstoo% as a con&entional moment inscience! they were "rowin" to %isa"ree %ramatically o&er the nature an% place ofcon&entions in science. ith the help of new lo"ical tools an% a more sophisticate%&erificationist semantics! ,chlick an% eichenbach were refinin" =oincarN$s i%ea ofcon&entional %efinitional elements in science into the classic lo"ical empiricist&iew that the moment of con&ention was restricte% to con&entional coor%inatin"%efinitions that en%ow in%i&i%ual primiti&e terms an%! by eFtension! the in%i&i%ualsynthetic propositions constructe% out of them with empirical content. 6his &iew

worke% well as an answer to the neo#'antian! for it implie% that once one fiFe%one$s coor%inatin" %efinition>as with a con&entional choice of a stan%ar%measurin" ro% coor%inate% with the "eometer$s concept of a 2ri"i% bo%y3>theuestion of the cur&ature of space ha% an empirically %eterminate answer. @utunless the %i&ision is wholly arbitrary! parsin" theories thus into coor%inatin"%efinitions an% empirical statements assumes a principle% %ifference in kin%

between the two cate"ories of statements alon" the lines of an analytic#synthetic%istinction. As ha% been the case with ?uhem before him! the assumption of such a

principle% %ifference in kin% %i% not comport well with the holism about theories

that Einstein ha% learne% from ?uhem./t was this ar"ument o&er the nature an% place of con&entions in science thatun%erlay Einstein$s "ra%ual philosophical estran"ement from ,chlick an%eichenbach in the 19s. ,erious in its own ri"ht! the ar"ument o&er con&entionswas entan"le% with two other issues as well! namely! realism an% Einstein$s famous&iew of theories as the 2free creations of the human spirit3 (see! for eFample!Einstein 191). /n both instances what trouble% Einstein was that a &erificationistsemantics ma%e the link between theory an% eFperience too stron"! lea&in" toosmall a role for theory! itself! an% the creati&e theori+in" that pro%uces it.



/f theory choice is empirically %eterminate! especially if theoretical concepts areeFplicitly constructe% from empirical primiti&es! as in arnap$s pro"ram inthe (u)bau (arnap 198)! then it is har% to see how theory "i&es us a story aboutanythin" other than eFperience. As note%! Einstein was not what we woul% to%ay

call a scientific realist! but he still belie&e% that there was content in theory beyon%mere empirical content. -e belie&e% that theoretical science "a&e us a win%ow onnature itself! e&en if! in principle! there will be no one uniuely correct story at thele&el of %eep ontolo"y (see below! section 5). An% if the only choice in theorychoice is one amon" con&entional coor%inatin" %efinitions! then that is no choice atall! a point stresse% by eichenbach! especially! as an important positi&eimplication of his position. eichenbach ar"ue% that if empirical content is the onlycontent! then empirically eui&alent theories ha&e the same content! the %ifferenceresultin" from their %ifferent choices of coor%inatin" %efinitions bein" like in kin%

to the %ifference between 2es re"net3 an% 2il pleut!3 or the %ifference betweeneFpressin" the result of a measurement in En"lish or metric units! ust two %ifferentways of sayin" the same thin". @ut then! Einstein woul% ask! where is there anyrole for the creati&e intelli"ence of the theoretical physicist if there is no room for"enuine choice in science! if eFperience somehow %ictates theory construction4

6he ar"ument o&er the nature an% role of con&entions in science continue% to the&ery en% of Einstein$s life! reachin" its hi"hest le&el of sophistication in theeFchan"e between eichenbach an% Einstein the ibrary of i&in" =hilosopher$s

&olume! (lbert &instein" Philosopher*Physicist (,chilpp 19;9). 6he uestion is!a"ain! whether the choice of a "eometry is empirical! con&entional! or a priori. /nhis contribution! eichenbach reasserte% his ol% &iew that once an appropriatecoor%inatin" %efinition is establishe%! euatin" some 2practically ri"i% ro%3 withthe "eometer$s 2ri"i% bo%y!3 then the "eometry of physical space is wholly%etermine% by empirical e&i%ence0

6he choice of a "eometry is arbitrary only so lon" as no %efinition of con"ruence isspecifie%. nce this %efinition is set up! it becomes an empiricaluestion $hich "eometry hol%s for physical space.J 6he con&entionalist o&erlooksthe fact that only the incomplete statement of a "eometry! in which a reference tothe %efinition of con"ruence is omitte%! is arbitrary. (eichenbach 19;9! 97)

Einstein$s cle&er reply inclu%es a %ialo"ue between two characters! 2eichenbach3an% 2=oincarN!3 in which 2eichenbach3 conce%es to 2=oincarN3 that there are no

perfectly ri"i% bo%ies in nature an% that physics must be use% to correct for suchthin"s as thermal %eformations! from which it follows that what we actually test is"eometry plus physics! not "eometry alone. -ere an 2anonymous non#positi&ist3takes 2=oincarN$s3 place! out of respect! says Einstein! 2for =oincarN$s superiority asthinker an% author3 (Einstein 19;9! <77)! but also! perhaps! because he reali+e% that



the point of &iew that follows was more ?uhem than =oincarN. 6he 2non#positi&ist3then ar"ues that one$s "rantin" that "eometry an% physics are teste% to"ethercontra&enes the positi&ist i%entification of meanin" with &erifiability0

+on*Positivist" /f! un%er the state% circumstances! you hol% %istance to be ale"itimate concept! how then is it with your basic principle (meanin" P&erifiability)4 *ust you not come to the point where you %eny the meanin" of"eometrical statements an% conce%e meanin" only to the completely %e&elope%theory of relati&ity (which still %oes not eFist at all as a finishe% pro%uct)4 *ustyou not "rant that no 2meanin"3 whatsoe&er! in your sense! belon"s to thein%i&i%ual concepts an% statements of a physical theory! such meanin" belon"in"instea% to the whole system insofar as it makes 2intelli"ible3 what is "i&en ineFperience4 hy %o the in%i&i%ual concepts that occur in a theory reuire any

separate ustification after all! if they are in%ispensable only within the frameworkof the lo"ical structure of the theory! an% if it is the theory as a whole that stan%sthe test4 (Einstein 19;9! <78).

6wo years before the Quine$s publication of 26wo ?o"mas of Empiricism3 (1951)!Einstein here makes eFplicit the semantic implications of a thorou"h"oin" holism.

/f theory choice is empirically un%er%etermine%! then an ob&ious uestion is whywe are so little aware of the un%er%etermination in the %ay#to#%ay con%uct ofscience. /n a 1918 a%%ress celebratin" *aF =lanck$s siFtieth birth%ay! Einsteinapproache% this uestion &ia a %istinction between practice an% principle0

6he supreme task of the physicist is J the search for those most "eneral!elementary laws from which the worl% picture is to be obtaine% throu"h pure%e%uction. o lo"ical path lea%s to these elementary lawsH it is instea% ust theintuition that rests on an empathic un%erstan%in" of eFperience. /n this state ofmetho%olo"ical uncertainty one can think that arbitrarily many! in themsel&eseually ustifie% systems of theoretical principles were possibleH an% this opinionis! in principle! certainly correct. @ut the %e&elopment of physics has shown that of

all the concei&able theoretical constructions a sin"le one has! at any "i&en time! pro&e% itself uncon%itionally superior to all others. o one who has really "one%eeply into the subect will %eny that! in practice! the worl% of perceptions%etermines the theoretical system unambi"uously! e&en thou"h no lo"ical pathlea%s from the perceptions to the basic principles of the theory. (Einstein 1918! :1Hmy translation)

@ut why is theory choice! in practice! seemin"ly empirically %etermine%4 Einsteinhinte% at an answer the year before in a letter to ,chlick! where he commen%e%

,chlick$s ar"ument that the %eep elements of a theoretical ontolo"y ha&e as muchclaim to the status of the real as %o *ach$s elements of sensation (,chlick 1917)!



but su""este% that we are nonetheless speakin" of two %ifferent kin%s of reality.-ow %o they %iffer4

/t appears to me that the wor% 2real3 is taken in %ifferent senses! accor%in" to

whether impressions or e&ents! that is to say! states of affairs in the physical sense!are spoken of.

/f two %ifferent peoples pursue physics in%epen%ently of one another! they willcreate systems that certainly a"ree as re"ar%s the impressions (2elements3 in*ach$s sense). 6he mental constructions that the two %e&ise for connectin" these2elements3 can be &astly %ifferent. An% the two constructions nee% not a"ree asre"ar%s the 2e&ents3H for these surely belon" to the conceptual constructions.ertainly on the 2elements!3 but not the 2e&ents!3 are real in the sense of bein"2"i&en una&oi%ably in eFperience.3

@ut if we %esi"nate as 2real3 that which we arran"e in the space#time#schema! asyou ha&e %one in the theory of knowle%"e! then without %oubt the 2e&ents!3 abo&eall! are real.J $ould like to reco''end a clean conceptual distinction here.(Einstein to ,chlick! 1 *ay 1917! EA 1#<18! E= 8#:;:)

hy! in practice! are physicists unaware of un%er%etermination4 /t is because oursis not the situation of 2two %ifferent peoples pursuCin"D physics in%epen%ently ofone another.3 6hou"h Einstein %oes not say it eFplicitly! the implication seems to

be that apparent %etermination in theory choice is mainly a conseuence of our all bein" similarly sociali+e% as we become members of a common scientificcommunity. =art of what it means to be a member of a such a community is that weha&e been tau"ht to make our theoretical choices in accor% with criteria or &aluesthat we hol% in common.

). Simplicity and "heory $hoice

Bor Einstein! as for many others! simplicity is the criterion that mainly steers theory

choice in %omains where eFperiment an% obser&ation no lon"er pro&i%e anunambi"uous "ui%e. 6his! too! is a theme soun%e% early an% late in Einstein$s

philosophical reflections (for more %etail! see -owar% 1998! orton ! an% &an?on"en ). Bor eFample! the ust#uote% remark from 1918 about the apparent%etermination of theory choice in practice! contraste% with in#principleun%er%etermination continues0

Burthermore this conceptual system that is uni&ocally coor%inate% with the worl% ofeFperience is re%ucible to a few basic laws from which the whole system can be

%e&elope% lo"ically. ith e&ery new important a%&ance the researcher here sees hiseFpectations surpasse%! in that those basic laws are more an% more simplifie% un%er



the press of eFperience. ith astonishment he sees apparent chaos resol&e% into asublime or%er that is to be attribute% not to the rule of the in%i&i%ual min%! but tothe constitution of the worl% of eFperienceH this is what eibni+ so happilycharacteri+e% as 2pre#establishe% harmony.3 =hysicists strenuously reproach many

epistemolo"ists for their insufficient appreciation of this circumstance. -erein! itseems to me! lie the roots of the contro&ersy carrie% on some years a"o between*ach an% =lanck. (Einstein 1918! p. :1)

6here is more than a little autobio"raphy here! for as Einstein stresse% repeate%ly inlater years! he un%erstoo% the success of his own uest for a "eneral theory ofrelati&ity as a result of his seekin" the simplest set of fiel% euations satisfyin" a"i&en set of constraints.

Always a leitmotif! Einstein$s celebration of simplicity as a "ui%e to theory choicecomes clearly to the fore in the early 19:s. hy then4 6he reason mi"ht well bethat his faith in simplicity ha% been &in%icate% when! seemin"ly with a si"h ofrelief! he foun% that he coul% %rop from the "ra&itational fiel% euations thecosmolo"ical constant that he ha% intro%uce% in 1917 for the purpose of blockin"non#static solutions! for the intro%uction of the cosmolo"ical constant in the first

place ha% represente% to him 2a consi%erable renunciation of the lo"ical simplicityof the theory3 (Einstein 19;9! <8;–<85). 6hat his faith in simplicity was reaffirme%is clear. itness what he wrote in his 19:: -erbert ,pencer lecture0

/f! then! it is true that the aFiomatic foun%ation of theoretical physics cannot beeFtracte% from eFperience but must be freely in&ente%! may we e&er hope to fin%the ri"ht way4 Burthermore! %oes this ri"ht way eFist anywhere other than in ourillusions4 *ay we hope to be "ui%e% safely by eFperience at all! if there eFisttheories (such as classical mechanics) which to a lar"e eFtent %o ustice toeFperience! without comprehen%in" the matter in a %eep way4

6o these uestions! / answer with complete confi%ence! that! in my opinion! theri"ht way eFists! an% that we are capable of fin%in" it. ur eFperience hitherto

ustifies us in trustin" that nature is the reali+ation of the simplest that ismathematically concei&able. / am con&ince% that purely mathematical constructionenables us to fin% those concepts an% those lawlike connections between them that

pro&i%e the key to the un%erstan%in" of natural phenomena. seful mathematicalconcepts may well be su""este% by eFperience! but in no way can they be %eri&e%from it. EFperience naturally remains the sole criterion of the usefulness of amathematical construction for physics. @ut the actual creati&e principle lies inmathematics. 6hus! in a certain sense! / take it to be true that pure thou"ht can"rasp the real! as the ancients ha% %reame%. (Einstein 19::! p. 18:H my translation)



Another consi%eration reinforcin" Einstein$s con&iction that the theoretical physicist must trust simplicity is that physics is mo&in" stea%ily into %omains e&erfurther remo&e% from %irect contact with obser&ation an% eFperiment. @efore the19<s! "eneral relati&ity! itself! reste% on a famously thin empirical footin"! an%

empirical e&i%ence pro&i%e% e&en less of a "ui%e in Einstein$s search for a unifie%fiel% theory. ne year after the -erbert ,pencer lecture! at a time when he wasimmerse% in work on unifie% fiel% theory! Einstein wrote0

6he theory of relati&ity is a beautiful eFample of the basic character of the mo%ern%e&elopment of theory. 6hat is to say! the hypotheses from which one starts

become e&er more abstract an% more remote from eFperience. @ut in return onecomes closer to the preeminent "oal of science! that of encompassin" a maFimumof empirical contents throu"h lo"ical %e%uction with a minimum of hypotheses or

aFioms. 6he intellectual path from the aFioms to the empirical contents or to thetestable conseuences becomes! thereby! e&er lon"er an% more subtle. 6hetheoretician is force%! e&er more! to allow himself to be %irecte% by purelymathematical! formal points of &iew in the search for theories! because the physicaleFperience of the eFperimenter is not capable of lea%in" us up to the re"ions of thehi"hest abstraction. 6entati&e %e%uction takes the place of the pre%ominantlyin%ucti&e metho%s appropriate to the youthful state of science. ,uch a theoreticalstructure must be uite thorou"hly elaborate% in or%er for it to lea% to conseuencesthat can be compare% with eFperience. /t is certainly the case that here! as well! the

empirical fact is the all#powerful u%"e. @ut its u%"ment can be han%e% %own onlyon the basis of "reat an% %ifficult intellectual effort that first bri%"es the wi%e space between the aFioms an% the testable conseuences. 6he theorist must accomplishthis -erculean task with the clear un%erstan%in" that this effort may only be%estine% to prepare the way for a %eath sentence for his theory. ne shoul% notreproach the theorist who un%ertakes such a task by callin" him a fantastH instea%!one must allow him his fantasi+in"! since for him there is no other way to his "oalwhatsoe&er. /n%ee%! it is no planless fantasi+in"! but rather a search for the lo"icallysimplest possibilities an% their conseuences. (Einstein 195;! :8–:9H my

translation)hat warrant is there for thus trustin" in simplicity4 At best one can %o a kin% ofmeta#in%uction. 6hat 2the totality of all sensory eFperience can be Rcomprehen%e%Son the basis of a conceptual system built on premises of "reat simplicity3 will be%eri%e% by skeptics as a 2miracle cree%!3 but! Einstein a%%s! 2it is a miracle cree%which has been borne out to an ama+in" eFtent by the %e&elopment of science3(Einstein 195! p. :;).

@ut for all that Einstein$s faith in simplicity was stron"! he %espaire% of "i&in" a precise! formal characteri+ation of how we assess the simplicity of a theory. /n



19;< he wrote about the perspecti&e of simplicity (here terme% the 2inner perfection3 of a theory)0

6his point of &iew! whose eFact formulation meets with "reat %ifficulties! has

playe% an important role in the selection an% e&aluation of theories from timeimmemorial. 6he problem here is not simply one of a kin% of enumeration of thelo"ically in%epen%ent premises (if anythin" like this were at all possible withoutambi"uity)! but one of a kin% of reciprocal wei"hin" of incommensurable ualities.J / shall not attempt to eFcuse the lack of precision of CtheseD assertions J on the"roun%s of insufficient space at my %isposalH / must confess herewith that / cannotat this point! an% perhaps not at all! replace these hints by more precise %efinitions./ belie&e! howe&er! that a sharper formulation woul% be possible. /n any case itturns out that amon" the 2oracles3 there usually is a"reement in u%"in" the 2inner

perfection3 of the theories an% e&en more so concernin" the %e"ree of 2eFternalconfirmation.3 (Einstein 19;<! pp. 1! :).

As in 1918! so in 19;< an% beyon%! Einstein continues to be impresse% that the2oracles!3 presumably the lea%ers of the rele&ant scientific community! ten% toa"ree in their u%"ments of simplicity. 6hat is why! in practice! simplicity seems to%etermine theory choice uni&ocally.

EFperience ustifies our trustin" that nature is the reali+ation of the simplest that ismathematically concei&able. an we say anythin" more about why this mi"ht beso4 A hint is pro&i%e% by Einstein$s enthusiastically positi&e response to ,chlick$sfirst essay on the philosophical si"nificance of relati&ity (,chlick 1915). At thisearly sta"e in his philosophical career! ,chlick re"ar%e% himself as a realist an%%efen%e% a &ersion of the un%er%etermination thesis "roun%e% in his &iew of truthas the unambi"uous many#to#one coor%ination of propositions to facts (,chlick191). 6heories bein" sets of propositions! se&eral theories coul% likewise beunambi"uously coor%inate% with a "i&en set of facts an% thus count as eually truerepresentations of those facts. hen he took up the uestion of simplicity! ,chlick%eri%e% those who woul% ustify simplicity as a criterion of theory choice byar"uin" that we shoul% choose simple theories because nature itself is simple. As,chlick ri"htly pointe% out! this is a circular ar"ument! for our only co"niti&eaccess to nature is &ia our theories (note that Einstein ar"ues not that nature! itself!is simple! but that nature is a reali+ation of simple theoretical constructions! acrucial %ifference). ,chlick similarly %eri%es a %efense "roun%e% in consi%erationsof mental economy! which he terms 2intellectual in%olence.3 hy then choosesimple theories4 ,chlick$s answer is that 2the "reater simplicity of a theory %epen%son its containin" fewer arbitraryelements.3 hy is it better to choose theories withfewer 2superfluous!3 arbitrary elements4 @ecause only the non#arbitrary elementsare likely to correspon% to reality! so in choosin" the simpler theory 2we are then



sure of %i&er"in" from reality at least no further than is necessitate% by the boun%sof our knowle%"e as such3 (,chlick 1915! 15;–155). As an eFample of an arbitraryelement in theory that %oes not correspon% to reality! ,chlick cite% the ether framein orent+ian electro%ynamics (,chlick 1917! <).

Einstein %oes not eFplicitly commen% ,chlick$s %efense of simplicity! but he also inno way obects in the course of a lon" correspon%ence %urin" the late 191s!wherein he stron"ly commen%s ,chlick$s "eneral philosophical orientation an%carefully recor%s all points of %isa"reement (for more %etail! see -owar% 198;).*oreo&er the principle un%erlyin" ,chlick$s %efense of simplicity! the i%ea that it isthe non#arbitrary elements of our theories that represent the real! playe% a %eep an%en%urin" role in Einstein$s philosophy of science.

*. #ni&ocalness in the "heoretical (epresentation of ature

/n the physics an% philosophy of science literature of the late nineteenth an% earlytwentieth centuries! the principle accor%in" to which scientific theori+in" shoul%stri&e for a uni&ocal representation of nature was wi%ely an% well known un%er thename that it was "i&en in the title of a wi%ely#cite% essay by Loseph =et+ol%t! 26heaw of ni&ocalness3 C2?as Ieset+ %er Ein%euti"keit3D (=et+ol%t 1895). Anin%ication that the map of philosophical positions was %rawn then in a manner &ery%ifferent from to%ay is to foun% in the fact that this principle foun% fa&or amon"

both anti#metaphysical lo"ical empiricists! such as arnap! an% neo#'antians! suchas assirer. /t playe% a maor role in %ebates o&er the ontolo"y of "eneral relati&ityan% was an important part of the back"roun% to the %e&elopment of the mo%ernconcept of cate"oricity in formal semantics (for more on the history! influence! an%%emise of the principle of uni&ocalness! see -owar% 199 an% 199<). ne can fin%no more ar%ent an% consistent champion of the principle than Einstein.

6he principle of uni&ocalness shoul% not be mistaken for a %enial of theun%er%etermination thesis. 6he latter asserts that a multiplicity of theories caneually well account for a "i&en bo%y of empirical e&i%ence! perhaps e&en the

infinity of all possible e&i%ence in the eFtreme! Quinean &ersion of the thesis. 6he principle of uni&ocalness asserts (in a somewhat anachronistic formulation) thatany one theory! e&en any one amon" a set of empirically eui&alent theories!shoul% pro&i%e a uni&ocal representation of nature by %eterminin" for itself anisomorphic set of mo%els. 6he unambi"uous %etermination of theory choice bye&i%ence is not the same thin" as the uni&ocal %etermination of a class of mo%els bya theory.

6he principle of uni&ocalness playe% a central role in Einstein$s stru""les to

formulate the "eneral theory of relati&ity. hen! in 191:! Einstein wron"ly reecte%a fully "enerally co&ariant theory of "ra&itation! he %i% so in part because he



thou"ht! wron"ly! that "enerally co&ariant fiel% euations faile% the test ofuni&ocalness. *ore specifically! he reasone% wron"ly that for a re"ion of spacetime%e&oi% of matter an% ener"y>a 2hole3>"enerally co&ariant fiel% euations permitthe construction of two %ifferent solutions! %ifferent in the sense that! in "eneral! for

spacetime points insi%e the hole! they assi"n %ifferent &alues of the metric tensor toone an% the same point (for more on the history of this episo%e! see ,tachel 198an% orton 198;). @ut Einstein$s 2hole ar"ument3 is wron"! an% his own %ia"nosisof the error in 1915 rests a"ain! ironically! on a %eployment of the principle ofuni&ocalness. hat Einstein reali+e% in 1915 was that! in 191:! he was wron"lyassumin" that a coor%inate chart suffice% to fiF the i%entity of spacetime manifol%

points. 6he application of a coor%inate chart cannot suffice to in%i&i%uate manifol% points precisely because a coor%inate chart is not an in&ariant labelin" scheme!whereas uni&ocalness in the representation of nature reuires such in&ariance (see

-owar% an% orton 199: an% -owar% 1999 for further %iscussion).

-ere is how Einstein eFplaine% his chan"e of perspecti&e in a letter to =aulEhrenfest of < ?ecember 1915! ust a few weeks after the publication of the final!"enerally co&ariant formulation of the "eneral theory of relati&ity0

/n G1 of my work of last year! e&erythin" is correct (in the first three para"raphs)up to that which is printe% with emphasis at the en% of the thir% para"raph. Bromthe fact that the two systems -( .) an% -T( .)! referre% to the same reference system!satisfy the con%itions of the "ra&. fiel%! no contra%iction follows with theuni&ocalness of e&ents. 6hat which was apparently compellin" in these reflectionsfoun%ers imme%iately! if one consi%ers that

1. the reference system si"nifies nothin" real. that the (simultaneous) reali+ation of two %ifferent g #systems (or better! two

%ifferent "ra&. fiel%s) in the same re"ion of the continuum is impossibleaccor%in" to the nature of the theory.

/n place of G1! the followin" reflections must appear. 6he physically real in theuni&erse of e&ents (in contrast to that which is %epen%ent upon the choice of areference system) consists in spatiote'poral coincidences.U CBootnote U0 an% innothin" elseVD eal are! e.".! the intersections of two %ifferent worl% lines! or thestatement that they do not intersect. 6hose statements that refer to the physicallyreal therefore %o not foun%er on any uni&ocal coor%inate transformation. /f twosystems of the g Wv (or in "eneral the &ariables employe% in the %escription of theworl%) are so create% that one can obtain the secon% from the first throu"h merespacetime transformation! then they are completely eui&alent. Bor they ha&e allspatiotemporal point coinci%ences in common! i.e.! e&erythin" that is obser&able.

6hese reflections show at the same time how natural the %eman% for "eneralco&ariance is. (EA 9#:<:! E= 8#17:)



Einstein$s new point of &iew! accor%in" to which the physically real consistseFclusi&ely in that which can be constructe% on the basis of spacetimecoinci%ences! spacetime points! for eFample! bein" re"ar%e% as intersections ofworl% lines! is now known as the 2point#coinci%ence ar"ument.3 ,pacetime

coinci%ences play this pri&ile"e% ontic role because they are in&ariant an%! thus!uni&ocally %etermine%. ,pacetime coordinates lack such in&ariance! a circumstancethat Einstein thereafter repeate%ly formulate% as the claim that space an% time2thereby lose the last &esti"e of physical reality3 (see! for eFample! Einstein toEhrenfest! 5 Lanuary 191<! EA 9#:7! E= 8#18).

ne tellin" measure of the philosophical importance of Einstein$s new perspecti&eon the ontolo"y of spacetime is the fact that ,chlick %e&ote% his first book! /au'

und eit in den gegen$rtigen Physik (1917)! a book for which Einstein ha% hi"h

praise (see -owar% 198; an% 1999)! to an eFploration of the philosophicalimplications of the claim that space an% time ha&e thereby lost the last &esti"e of physical reality. *ention has alrea%y been ma%e of ,chlick$s %efense of anun%er%etermination thesis base% on his %octrine of truth as unambi"uouscoor%ination. 6hat &iew is here %e&elope% at consi%erable len"th. @ut what mostintereste% Einstein was ,chlick$s %iscussion of the reality concept. ,chlick ar"ue%that *ach was wron" to re"ar% only the elements of sensation as real. ,pacetimee&ents! in%i&i%uate% in&ariantly as spacetime coinci%ences! ha&e as much or moreri"ht to be taken as real! precisely because of the uni&ocal manner of their

%etermination. Einstein wholehearte%ly a"ree%! thou"h he &enture% the abo&e#uote% su""estion that one shoul% %istin"uish the two kin%s of reality>that of theelements an% that of the spacetime e&ents>on the "roun% that if 2two %ifferent

peoples3 pursue% physics in%epen%ently of one another they were fate% to a"reeabout the elements but woul% almost surely pro%uce %ifferent theoreticalconstructions at the le&el of the spacetime e&ent ontolo"y. ote! a"ain! thatun%er%etermination is not a failure of uni&ocalness. ?ifferent thou"h they will be!each people$s theoretical construction of an e&ent ontolo"y woul% be eFpecte% to beuni&ocal.

,chlick! of course! went on to become the foun%er of the Xienna ircle! a lea%in"fi"ure in the %e&elopment of lo"ical empiricism! a champion of &erificationism.6hat bein" so! an important uestion arises about ,chlick$s interpretation ofEinstein on the uni&ocal %etermination of spacetime e&ents as spacetimecoinci%ences. 6he uestion is this0 ?o such uni&ocal coinci%ences play such a

pri&ile"e% role because of their reality or because of their obser&ability. learly theformer>the reality of that which is uni&ocally %etermine%>is important. @ut areuni&ocal spacetime coinci%ences real because! thanks to their in&ariance! they areobser&able4 r is their obser&ability conseuent upon their in&ariant reality4Einstein! himself! repeate%ly stresse% the obser&able character of spacetime



coinci%ences! as in the < ?ecember 1915 letter to Ehrenfest uote% abo&e (fora%%itional references an% a fuller %iscussion! see -owar% 1999). C:D

,chlick! still a self#%escribe% realist in 1917! was clear about the relationship

between obser&ability an% reality. -e %istin"uishe% macroscopic coinci%ences inthe fiel% of our sense eFperience! to which he %oes accor% a pri&ile"e% an%foun%ational epistemic status! from the microscopic point coinci%ences that %efinean ontolo"y of spacetime manifol% points. *appin" the former onto the latter is! for,chlick! an important part of the business of confirmation! but the reality of thespacetime manifol% points is in no way conseuent upon their obser&ability./n%ee%! how! strictly speakin"! can one e&en talk of the obser&ationof in)initesi'al spacetime coinci%ences of the kin% encountere% in the intersectionof two worl% lines4 /n fact! the or%er of implication "oes the other way0 ,pacetime

e&ents in%i&i%uate% as spacetime coinci%ences are real because they are in&ariant!an% such obser&ability as they mi"ht possess is conseuent upon their status asin&ariant bits of physical reality. Bor Einstein! an% for ,chlick in 1917!un%erstan%in" the latter>physical reality>is the "oal of physical theory.

+. (ealism and Separa%ility

As we ha&e seen! ,chlick$s /au' und eit in den gegen$rtigen Physik promote% arealistic interpretation of the ontolo"y of "eneral relati&ity. After rea%in" themanuscript early in 1917! Einstein wrote to ,chlick on 1 *ay that 2the last sectionRelations to =hilosophyS seems to me eFcellent3 (EA 1#<18! E= 8#:;:)! ust thesort of praise one woul% eFpect from a fellow realist. 6hree years earlier! the @onnmathematician! E%uar% ,tu%y! ha% written another well#known! in%ee% &ery well#known %efense of realism! ie realistische Weltansicht und die Lehre vo'

/au'e (191;). Einstein rea% it in ,eptember of 1918. *uch of it he like%!especially the %roll style! as he sai% to ,tu%y in a letter of 17 ,eptember (EA #:1! E= 8#<18). =resse% by ,tu%y to say more about the points where he%isa"ree%! Einstein replie% on 5 ,eptember in a rather surprisin" way0

/ am suppose% to eFplain to you my %oubts4 @y layin" stress on these it will appearthat / want to pick holes in you e&erywhere. @ut thin"s are not so ba%! because / %onot feel comfortable an% at home in any of the 2isms.3 /t always seems to me asthou"h such an ism were stron" only so lon" as it nourishes itself on the weaknessof it counter#ismH but if the latter is struck %ea%! an% it is alone on an open fiel%!then it also turns out to be unstea%y on its feet. 3o, a$ay $ith the s!uabbling .

26he physical worl% is real.3 6hat is suppose% to be the fun%amental hypothesis.hat %oes 2hypothesis3 mean here4 Bor me! a hypothesis is a statement!

whose truth must be assume% for the moment! but $hose 'eaning 'ust be raisedabove all a'biguity. 6he abo&e statement appears to me! howe&er! to be! in itself!





meanin"less! as if one sai%0 26he physical worl% is cock#a#%oo%le#%oo.3 /t appearsto me that the 2real3 is an intrinsically empty! meanin"less cate"ory (pi"eon hole)!whose monstrous importance lies only in the fact that / can %o certain thin"s in itan% not certain others. 6his %i&ision is! to be sure! not an arbitrary one! but instea%

J.

/ conce%e that the natural sciences concern the 2real!3 but / am still not a realist.(EA #:7! E=#8#<;)

est there be any %oubt that Einstein has little sympathy for the other si%e! he a%%s0

6he positi&ist or pra"matist is stron" as lon" as he battles a"ainst the opinion thatthere CareD concepts that are anchore% in the 2A priori.3 hen! in his enthusiasm!CheD for"ets that all knowle%"e consists CinD concepts an% u%"ments! then that is aweakness that lies not in the nature of thin"s but in his personal %isposition ust aswith the senseless battle a"ainst hypotheses! cf. the clear book by ?uhem. /n anycase! the railin" a"ainst atoms rests upon this weakness. h! how har% thin"s arefor man in this worl%H the path to ori"inality lea%s throu"h unreason (in thesciences)! throu"h u"liness (in the arts)#at least the path that many fin% passable.(EA #:7! E=#8#<;)

hat coul% Einstein mean by sayin" that he conce%es that the natural sciencesconcern the 2real!3 but that he is 2still not a realist3 an% that the 2real3 in the

statement! 2the physical worl% is real!3 is an 2intrinsically empty! meanin"lesscate"ory34

6he answer mi"ht be that realism! for Einstein! is not a philosophical %octrine aboutthe interpretation of scientific theories or the semantics of theoretical terms. C;D BorEinstein! realism is a physical postulate! one of a most interestin" kin%! as heeFplaine% on 18 *arch 19;8 in a lon" note at the en% of the manuscript of *aF@orn$s aynflete ectures! +atural Philosophy o) ause and hance (19;9)!which @orn ha% sent to Einstein for commentary0

/ ust want to eFplain what / mean when / say that we shoul% try to hol% on to physical reality. e are! to be sure! all of us aware of the situation re"ar%in" whatwill turn out to be the basic foun%ational concepts in physics0 the point#mass or the

particle is surely not amon" themH the fiel%! in the Bara%ay # *aFwell sense! mi"ht be! but not with certainty. @ut that which we concei&e as eFistin" ($actualS) shoul%somehow be locali+e% in time an% space. 6hat is! the real in one part of space! A!shoul% (in theory) somehow ReFistS in%epen%ently of that which is thou"ht of asreal in another part of space! @. /f a physical system stretches o&er the parts of

space A and @! then what is present in @ shoul% somehow ha&e an eFistencein%epen%ent of what is present in A. hat is actually present in @ shoul% thus not







%epen% upon the type of measurement carrie% out in the part of space! AH it shoul%also be in%epen%ent of whether or not! after all! a measurement is ma%e in A.

/f one a%heres to this pro"ram! then one can har%ly &iew the uantum#theoretical

%escription as a co'plete representation of the physically real. /f one attempts!ne&ertheless! so to &iew it! then one must assume that the physically real in @un%er"oes a su%%en chan"e because of a measurement in A. *y physical instincts

bristle at that su""estion.

-owe&er! if one renounces the assumption that what is present in %ifferent parts ofspace has an in%epen%ent! real eFistence! then / %o not at all see what physics issuppose% to %escribe. Bor what is thou"ht to by a RsystemS is! after all! ustcon&entional! an% / %o not see how one is suppose% to %i&i%e up the worl%obecti&ely so that one can make statements about the parts. (@orn 19<9! :–;Hmy translation)

ealism is thus the thesis of spatial separability! the claim that spatial separation isa sufficient con%ition for the in%i&i%uation of physical systems! an% its assumptionis here ma%e into almost a necessary con%ition for the possibility of an intelli"iblescience of physics.

6he postulate of spatial separability as that which un%er"ir%s the onticin%epen%ence an%! hence! in%i&i%ual i%entities of the systems that physics %escribes

was an important part of Einstein$s thinkin" about the foun%ations of physics sinceat least the time of his &ery first paper on the uantum hypothesis in 195 (Einstein195aH for more %etail on the early history of this i%ea in Einstein$s thinkin"! see-owar% 199b). @ut the true si"nificance of the separability principle emer"e%most clearly in 19:5! when (as hinte% in the ust#uote% remark) Einstein ma%e itone of the central premises of his ar"ument for the incompleteness of uantummechanics (see -owar% 1985 an% 1989). /t is not so clearly %eploye% in the

publishe% &ersion of the Einstein! =o%olsky! osen paper (19:5)! but Einstein %i%not write that paper an% %i% not like the way the ar"ument appeare% there.

,eparability is! howe&er! an eFplicit premise in all of Einstein$s later presentationsof the ar"ument for the incompleteness of uantum mechanics! both incorrespon%ence an% in print (see -owar% 1985 for a %etaile% list of references).

/n brief! the ar"ument is this. ,eparability implies that spacelike separate% systemsha&e associate% with them in%epen%ent real states of affairs. A secon% postulate!locality! implies that the e&ents in one re"ion of spacetime cannot physicallyinfluence physical reality in a re"ion of spacetime separate% from the first by aspacelike inter&al. onsi%er now an eFperiment in which two systems! A an% @!

interact an% separate! subseuent measurements on each correspon%in" to spacelikeseparate% e&ents. ,eparability implies that A an% @ ha&e separate real physical



states! an% locality implies that the measurement performe% on A cannot influence@$s real physical state. @ut uantum mechanics ascribes %ifferent theoretical states!%ifferent wa&e functions! to @ %epen%in" upon that parameter that is measure% onA. 6herefore! uantum mechanics ascribes %ifferent theoretical states to @! when @

possesses! in fact! one real physical state. -ence uantum mechanics is incomplete.

ne wants to ask many uestions. Birst! what notion of completeness is bein"in&oke% here4 /t is not %e%ucti&e completeness. /t is closer in kin% to what is terme%2cate"oricity3 in formal semantics! a cate"orical theory bein" one whose mo%elsare all isomorphic to one another. /t is closer still to the principle %iscusse% abo&e

>an% cite% as a precursor of the concept of cate"oricity>namely! the principle ofuni&ocalness! which we foun% %oin" such important work in Einstein$s uestion fora "eneral theory of relati&ity! where it was the premise forcin" the a%option of an

in&ariant an% thus uni&ocal scheme for the in%i&i%uation of spacetime manifol% points.

6he neFt uestion is why separability is &iewe% by Einstein as &irtually an a priorinecessary con%ition for the possibility of a science of physics. ne reason is

because a fiel% theory like "eneral relati&ity! which was Einstein$s mo%el for afuture unifie% foun%ation for physics! is an eFtreme embo%iment of the principle ofseparability0 2Biel% theory has carrie% out this principle to the eFtreme! in that itlocali+es within infinitely small (four#%imensional) space#elements the elementarythin"s eFistin" in%epen%ently of the one another that it takes as basic! as well as theelementary laws it postulates for them3 (Einstein 19;8! :1–:). An% a fiel%theory like "eneral relati&ity can %o this because the infinitesimal metric inter&al> the careful way to think about separation in "eneral relati&istic spacetime>isin&ariant (hence uni&ocally %etermine%) un%er all continuous coor%inatetransformations.

Another reason why Einstein woul% be incline% to &iew separability as an a priorinecessity is that! in thus in&okin" separability to "roun% in%i&i%uation! Einstein

places himself in a tra%ition of so &iewin" spatial separability with &ery stron"'antian roots (an%! before 'ant! ewtonian roots)! a tra%ition in which spatialseparability was known by the name that Arthur ,chopenhauer famously "a&e to it!the principiu' individuationis (for a fuller %iscussion of this historical conteFt! see-owar% 1997).

A final uestion one wants to ask is0 2hat %oes any of this ha&e to %o withrealism43 ne mi"ht "rant Einstein$s point that a real ontolo"y reuires a principleof in%i&i%uation without a"reein" that separability pro&i%es the only concei&ablesuch principle. ,eparability to"ether with the in&ariance of the infinitesimal metric

inter&al implies that! in a "eneral relati&istic spacetime! there are oints e&erywhere!meanin" that we can car&e up the uni&erse in any way we choose an% still ha&e



ontically in%epen%ent parts. @ut uantum entan"lement can be rea% as implyin"that this libertarian scheme of in%i&i%uation %oes not work. an uantummechanics not be "i&en a realistic interpretation4 *any woul% say! 2yes.3 Einsteinsai%! 2no.3

,. "he Principle "heories-$onstructi&e "heories istinction

6here is much that is ori"inal in Einstein$s philosophy of science as %escribe% thusfar. At the &ery least! he rearran"e% the bits an% pieces of %octrine that he learne%from others>'ant! *ach! ?uhem! =oincarN! ,chlick! an% others>in a strikin"lyno&el way. @ut Einstein$s most ori"inal contribution to twentieth#century

philosophy of science lies elsewhere! in his %istinction between what he terme%2principle theories3 an% 2constructi&e theories.3

6his i%ea first foun% its way into print in a brief 1919 article in the Ti'es ofon%on (Einstein 1919). A constructi&e theory! as the name implies! pro&i%es aconstructi&e mo%el for the phenomena of interest. An eFample woul% be kinetictheory. A principle theory consists of a set of in%i&i%ually well#confirme%! hi"h#le&el empirical "enerali+ations. EFamples inclu%e the first an% secon% laws ofthermo%ynamics. ltimate un%erstan%in" reuires a constructi&e theory! but often!says Einstein! pro"ress in theory is impe%e% by premature attempts at %e&elopin"constructi&e theories in the absence of sufficient constraints by means of which tonarrow the ran"e of possible of constructi&e. /t is the function of principle theoriesto pro&i%e such constraint! an% pro"ress is often best achie&e% by focusin" first onthe establishment of such principles. Accor%in" to Einstein! that is how he achie&e%his breakthrou"h with the theory of relati&ity! which! he says! is a principle theory!its two principles bein" the relati&ity principle an% the li"ht principle.

hile the principle theories#constructi&e theories %istinction first ma%e its way into print in 1919! there is consi%erable e&i%ence that it playe% an eFplicit role inEinstein$s thinkin" much earlier. or was it only the relati&ity an% li"ht principlesthat ser&e% Einstein as constraints in his theori+in". 6hus! he eFplicitly mentions

also the @olt+mann principle! 3 P k lo" W ! as another such0

6his euation connects thermo%ynamics with the molecular theory. /t yiel%s! aswell! the statistical probabilities of the states of systems for which we are not in a

position to construct a molecular#theoretical mo%el. 6o that eFtent! @olt+mann$sma"nificent i%ea is of si"nificance for theoretical physics J because it pro&i%es aheuristic principle whose ran"e eFten%s beyon% the %omain of &ali%ity of molecularmechanics. (Einstein 1915! p. <).

Einstein is here allu%in" the famous entropic analo"y whereby! in his 195 photonhypothesis paper! he reasone% from the fact that black bo%y ra%iation in the ien



re"ime satisfie% the @olt+mann principle to the conclusion that! in that re"ime!ra%iation beha&e% as if it consiste% of mutually in%epen%ent! corpuscle#like uantaof electroma"netic ener"y. 6he uantum hypothesis is a constructi&e mo%el ofra%iationH the @olt+mann principle is the constraint that first su""este% that mo%el.

6here are anticipations of the principle theories#constructi&e theories %istinction inthe nineteenth#century electro%ynamics literature! Lames lerk *aFwell! in

particular! bein" a source from which Einstein mi"ht well ha&e %rawn (see -arman1998). At the turn of the century! the 2physics of principles3 was a subect un%erwi%e %iscussion (see! for eFample! =oincarN 19;H for further %iscussion! seeIie%ymin 198). @ut howe&er eFtensi&e his borrowin"s (no eFplicit %ebt was e&eracknowle%"e%)! in Einstein$s han%s the %istinction becomes a metho%olo"ical toolof impressi&e scope an% fertility. hat is pu++lin"! an% e&en a bit sa%! is that this

most ori"inal metho%olo"ical insi"ht of Einstein$s ha% comparati&ely little impacton later philosophy of science or practice in physics.

/. $onclusion: 0l%ert Einstein: PhilosopherPhysicist

Einstein$s influence on twentieth#century philosophy of science is comparable tohis influence on twentieth#century physics. hat ma%e that possible4 neeFplanation looks to the institutional an% %isciplinary history of theoretical physicsan% the philosophy of science. Each was! in its own %omain! a new mo%e ofthou"ht in the latter nineteenth century! an% each finally be"an to secure for itself asoli% institutional basis in the early twentieth century. /n a curious way! the twomo&ements helpe% one another. =hilosophers of science helpe% to le"itimatetheoretical physics by locatin" the si"nificant co"niti&e content of science in itstheories. 6heoretical physicists helpe% to le"itimate the philosophy of science by

pro&i%in" for analysis a subect matter that was ra%ically reshapin" ourun%erstan%in" of nature an% the place of humankin% within it. /n some cases thehelp was e&en more %irect! as with the work of Einstein an% *aF =lanck in themi%#19s to create in the physics %epartment at the ni&ersity of @erlin a chair inthe philosophy of science for eichenbach (see -echt an% -artmann 198). An%we shoul% remember the eFample of the physicists *ach an% u%wi" @olt+mannwho were the first two occupants of the new chair for the philosophy of science atthe ni&ersity of Xienna at the turn of the century.

Another eFplanation looks to the e%ucation of youn" physicists in Einstein$s %ay. ot only was Einstein$s own youthful rea%in" hea&ily focuse% on philosophy! more"enerally! an% the philosophy of science! in particular (for an o&er&iew! seeEinstein 1989! FFi&–FF&H see also -owar% 199;b)! in which respect he was notunlike other physicists of his "eneration! but also his uni&ersity physics curriculum

inclu%e% a reuire% course on 26he 6heory of ,cientific 6hou"ht3 (see Einstein1987! ?oc. 8). An ob&ious uestion is whether or not the early culti&ation of a



philosophical habit of min% ma%e a %ifference in the way Einstein an% hiscontemporaries approache% physics. As in%icate% by his o&ember 19;; letter toobert 6horton uote% at the be"innin" of this article! Einstein thou"ht that it %i%.

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Other Internet (esources



• Einstein =apers =roect (maintaine% by the alifornia /nstitute of6echnolo"y)

http://www.einstein.caltech.edu/

http://www.einstein.caltech.edu/

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