ConcernsaboutObserva/on,ClassicalandQuantum

J.Bu&erfield,Rome,1Dec2016

Howdoesourbeingobserversaffectsthescopeandcontentofourknowledge:especiallyincosmology---bothclassicalandquantum?I:Thetopicwithoutregardtophysics:emphasizing:whatispossibility?II.Thetopicinclassicalphysicsandcosmology:emphasizing:whatischance?III.Thetopicinquantumphysicsandcosmology:emphasizing:howtounderstandquantumtheory?!

I:TheObserver,regardlessofPhysics•  1)‘SubjecRvity’•  2)SelecRoneffectsonobservaRon•  3)ThelegacyofKant•  4)My(Realist!)verdict:Noworries!•  5)AnopenquesRon:whatisapossibility?II:TheObserverinaClassicalWorld•  1)Problemsofprinciplefor‘insiders’?•  2)SelecRoneffects:the‘A’word…•  3)ConfirmingamulRversetheory•  4)TheSrednicki-Hartleproposal:FrameworksIII:TheObserverinaQuantumWorld•  1)Thedreadedquantum!•  2)TheEvere&interpretaRonoftheuniversalstate

I:TheObserver,regardlessofPhysics1)‘SubjecRvity’

Democritus:‘ByconvenRonhot,byconvenRoncold,butinrealityatomsandvoid’.…Andnaturalphilosophy/physics,fromGalileoonwards.Theneedto‘closethecircle’:torecoveradescripRonofexperiencefromscience’s(increasinglyarcane!)world-picture.Nowadays,peopleemphasizetwoobstacles:a)  ‘qualia’:‘sciencecan’tgiveyouthesmellofchicken

soup’b)  ‘indexicality’:RmelyacRonneeds‘I’,‘now’‘here’.

2)SelecRoneffectsonobservaRonEddington’snetmetaphor.Bewareofbiassedsampling!

‘Whatismostprobabletohappenneednotbewhatismostprobabletobeobserved.’‘ObserversarelocatedonlyinplaceswithspecialproperRes.Asatrivialconsequence,probabiliRescondiRonedonthepresenceofobserverswilldiffergrosslyfromprobabiliResperunitvolume.’OurexpectaRonsshouldbecondiRonedonwhatwebelieveaboutourprocessofobservaRon.

3)ThelegacyofKantMaybeourbeliefs,evenourknowledge,haveanineradicablehumancontribuRon?Variousmeaningsfor‘ineradicable’,‘human’:

Kant,Carnap,Kuhn…IanHacking(TheSocialConstruc4onofWhat?)

helpfullydisRnguishesthreedebates:Isthecontentofmaturescienceindependentof

thepathbywhichwefoundit?Doestheworldhaveinherentstructure?IsscienRficbeliefstablebecauseoftheworld,

ratherthansocialorganizaRonofscience?

4)My(Realist!)Verdict:Noworries!InparRcular,asto3):Maybewe(thespeciesorcultureorindividual)contributeineradicablytoourknowledge.ButthatiscompaRblewithallof:

A)  acorrespondencetheoryoftruth(Aristotle,Tarski);

B)ourhavinggoodreasontobelievetheories:whosetheoreRcalclaimsaretrueinacorrespondencesense.AnditisevencompaRblewith…

C)OurformulaRngandconfirmingatheoryofthewholeworld(aTOE):itsgeneralproposiRons(oranelitesubsetofthem)arelawsofnature.TheideaofaTOE:a):Issupportedbytheamazingunityofnatureshownbye.g.thesecondscienRficrevoluRon1850-1950,andtheriseofprecisioncosmologysinceca.1965…b):RaisesWigner’squesRon.

5)AnopenquesRon:whatisapossibility?HowmuchdoesstaRngthetruth(ineverydaylife,orscience,orphilosophy)requireaccepRngnon-actualpossibiliRes?Forexample:(a)Delibera4onanddecision.Howtounderstandwhatanagentthinksanddoes,purelyintermsoftheoneactualcourseofevents?(b)Chance.HowcanobjecRvetendenciesforvariouspossibiliResbejustafacondeparlerabouttheoneactualcourseofevents?(c)Con4ngency.Afalsetheorymighthavebeentrue,mighthaveevenbeenaTOE:e.g.classicalvacuumelectromagneRsm.

Eachpossibilityisofcoursenon-actual:butreal,insomewidersensethan‘actual’.WhatEXACTLYdoessuchapossibilityconsistof?Thisisgenerallyagreedtobeaharder

quesRonthane.g.themind-bodyproblem!Leibniz’spossibleworlds,revivedinmodern

modalmetaphysics:DavidLewis’srealism.SotherearethreekindsofmulRverse:logical/metaphysical;cosmological;quantum/Evere&.

Sekngasidecosmology…AsascienRficrealist,baskinginthesunlightoftheworld-pictureofmodernscience,Iworry‘only’that… ThedeepquesRonaboutthenatureof

possibilityisaggravatedbytheuseinclassicalthermalphysics,ofobjecRveprobabiliRes.HowshouldIunderstandthese?

Butturningtocosmology…

II:TheObserverinaClassicalWorld

1)Problemsofprinciplefor‘insiders’?Cananagentinaworldformulate/believe/knowaproposiRonabouttheworldasawhole(thusincludingthemselves)?Ordoessomelogicalparadoxofself-referencelurkhere?Isay:‘Noworries’.But:1A)Possibilityagain!Non-actualiniRalcondiRonsoftheuniversecannotbetakenasshortfor,orsomesortofanalogueof,actualiniRalcondiRonsofanotheractualsystem:thereisnosuch!2A)Epistemicbadnewsforcosmologists:--ItcanbeveryhardtodeterminetheglobalstructureofageneralrelaRvisRcspaceRme...

2)SelecRoneffects:the‘A’word…ThecurrentscienRficsituaRon:(i)  Thedegreeoffine-tuningisolenstunning!(ii)  fundamentaltheoryfacesgravedifficulRes.ThecurrentphilosophicalsituaRon:(i)BewareofessenRalismaboutexplanaRon!(ii)TheneedtocondiRonalizeonadescripRonofobservaRondependsonthenoRonof‘biassedsample’andso‘backgroundpopulaRon’;(cf.orthodoxstaRsRcs).

ButneedtocondiRonalizedoesNOTdependon:a)indexicality,i.e.threatsof‘Doppelgangers’;b)theactualexistenceofotherobservaRons:inEddington’smetaphor,theremightneverbeanotherfishingtrip!ButtomakesenseofaprobabilityofacosmologicalparameteraccordingtotheoryT,pr(|T):---Doweneedtheactualexistenceofotherdomains,wheretakesothervalues?Isay:youonlyneedthis,ifyoufeelyoumustgroundT’sprobabiliResinactualfrequencies,acrossthecosmos.

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3)ConfirmingamulRversetheoryThepredicament:Theself-samemechanismthatgivesrisestosubtlefeaturesoftheCMBcan,underappropriatecircumstances,giverisetoamulRverse:asetofnon-interacRngdomains.So:HowcanwepossiblyconfirmamulRversetheorywithouteverhavingdirectevidenceabouttheotherdomains?Iendorse(followingAzhar)aclarifyingschemethatcombinesproposalsofAguirre,Tegmark,Hartle,SrednickiandHertog.

Threeproblems:measure,condiRonalizaRon,andtypicality.(1):Measure.Whataretheelementsofthesamplespace:Domains?Regionsofequalvolume?Givenasamplespace:whichmeasure?(2)CondiRonalizaRon.ToallowforselecRoneffects:howshouldwecharacterizeourobservaRonalsituaRon?(3):Typicality.Howmuch‘underthetails’canobservaRonbe,withoutourinferringthetheoryisdisconfirmed?

4)TheSrednicki-Hartleproposal:FrameworksSHdefineaframeworkasaconjuncRonof:i)acosmologicaltheory/modelT:takenassolvingthemeasureproblem,sowrite:P(/T);ii)acondiRonalizaRonscheme(‘selecRonproposiRon’)C;soconsider:P(/T,C)iii)axerographicdistribuRonoverthedomainswithnon-zeromeasureaccordingtoP(/T,C).Soconsider:P(/T,C,)

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SoP(D/T,C,)isthe`first-person’likelihoodofseeingdataD.Srednicki-HartleproposeaBayesianframework,soastocomputedegreesofconfirmaRonoftheframework:P(T,C,/D).TheyandAzharshow,intoymodelsT(e.g.withfinitelymanydomains),howvariouscondiRonalizaRonschemesC,andtypicalityassumpRons,fareinthelightofvariousdataD.

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III:TheObserverinaQuantumWorld1)Thedreadedquantum!

Themeasurementproblemprompted(speciallyintheearlydays)avarietyofradicalproposalstogivethe‘observer’---maybeinanodyneform,e.g.asanorthobasis!---afundamentalrole.

Asarealist,Idislikethemall!IstandwithJSBell.ButIurgeweshouldgobeyondtheusualsuspects,viz.•  Dynamicalcollapse(GRW,Pearle,Penrose…),•  Pilot-wavetheory(deBroglie,Bohm,ValenRni…)•  Manyworlds(Evere&,Hartle,Deutsch,Wallace…)

2)TheEvere&interpretaRonofTheidea:agenericbranch(be&er‘history’)ofcontainsaclassicalmulRversealaPartII:i.e.ofthetypedescribedbyHartle-Srednickiframeworks.Merits:1)providestheprobabiliRes,eginaconsistent-historiesapproach;2)Addingappropriatedetails,itgivesprobabiliResforwhatweobserve;3)SymmetriescanhelpuscalculateprobabiliRes,egbycoarse-graining&bytheuncalculableprobabiliRescancellingout.

TechnicalquesRonsabound!Forexample:A) Whatis?A.1)TheNoBoundaryProposal:sumoverallthe4-manifoldsandmetricscuppingthegiven3-metric.A.2)DefiniRonandtractability?ThetransiRonfromtheEuclideantotheLorentzianregime?

(

3g) = ⌃4g exp[�I(4g)/~]

A.3)ContrastirresponsiblepopularizaRon!SomesaycreaRonexnihiloisscienRficallyunproblemaRc,viz.‘fluctuaRonfromvacuum’.No!‘Vacuum’means,not‘nothing’,but‘lowestenergystateofthegivensystem’.‘QuantumfluctuaRon’meanshavingnon-zeroamplitudeformorethanone(typicallyclassical)alternaRve.

B)HowtorelatetoinflaRon,soastogetclassicalmulRverse(s)?B.1)Worryinglymanymodelsoftheinflaton.B.2)DifferentmechanismsofeternalinflaRon.B.3)Variousquantum-classicaltransiRons:i)Differentcomponentsofthestateii)Thestateisspeciale.g.WKBiii)Insomeregime,relevantcommutatorsiv)PreferredquanRRes:(surelynotbydecoherence:thereisnoenvironment).

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TheanswerstoquesRonsinA)andB)mustensurethatparametersvaryacrossdomainsoftheensuingclassicalmulRverse.C)Hartle,HawkingandHertogrelatetheNBproposaltoinflaRon,usingconsistent-histories.Thegeneralmeritsrecur.Besides,insimplemodelsegminisuperspacewithquadraRcpotenRal:i)HistorieslabelledbyandexhibitinflaRon;ii)Our‘rareness’makesprobabiliResforwhatweobservevolume-weighted,enhancinginflaRon(high).

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AndbroadconceptualquesRonsabound…D)IfthebranchingiseffecRve,ieapproximate,thedefiniRonofeachclassicalmulRverse---andsoe.g.howmanydomainsithas---isineradicablyvague.Isthatacceptable?E)Howshouldweunderstandprobability?The‘usualquesRontoEvere&’ismuchsharperfor....

Millegrazie!Mercibeaucoup!

Dankje!

References

Azhar&JNB,ScienRficrealismandprimordialcosmologyh&p://philsci-archive.pi&.edu/12192/1606.04071Azhar,TesRngtypicality,PhysicalReviewDphilsci-archive.pi&.edu/119951506.05308Azhar,SpectraofcondiRonalizaRon,PhysicalReviewDphilsci-archive.pi&.edu/11996;arxiv:1601.05938JNBUnderdeterminaRonincosmologyStudHistPhilModPhysarxiv:1406.4747philsci-archive.pi&.edu/9866/

Hartle,Hawking,Hertog,Classicaluniversesofno-boundaryquantumstate,PhysicalReviewD0803.1663Hartle,Hertog,ReplicaRonregulatesvolume-weighRng,PhysicalReviewD0906.0042Hartle,Hertog,Theobserverstrikesback,1503.07205Hartle,Hertog,Onebubbletorulethemall,1604.03580Hartle,Srednicki,Arewetypical?PhysicalReviewD0704.2630Srednicki,Hartle,Scienceinaverylargeuniverse,PhysicalReviewD0906.0042