Einstein's Struggles with Quantum Theory: A Reappraisal PDF
Preview Einstein's Struggles with Quantum Theory: A Reappraisal
Einstein’s Struggles with Quantum Theory Einstein’s Struggles with Quantum Theory A Reappraisal Dipankar Home Bose Institute, Kolkata and Andrew Whitaker Queen’s University Belfast DipankarHome AndrewWhitaker BoseInstitute Queen’sUniversityBelfast Kolkata LibraryofCongressControlNumber:2006931196 ISBN-13:978-0-387-71519-3 e-ISBN-13:978-0-387-71520-9 Printedonacid-freepaper. ©2007SpringerScience+BusinessMedia,LLC Allrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthewritten permissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet,NewYork, NY10013, USA),exceptforbriefexcerptsinconnectionwithreviewsorscholarlyanalysis. Use inconnectionwithanyformofinformationstorageandretrieval, electronicadaptation, computer software,orbysimilarordissimilarmethodologynowknownorhereafterdevelopedisforbidden. Theuseinthispublicationoftradenames,trademarks,servicemarks,andsimilarterms,evenifthey arenotidentifiedassuch,isnottobetakenasanexpressionofopinionastowhetherornottheyare subjecttoproprietaryrights. 9 8 7 6 5 4 3 2 1 springer.com Theauthorsrespectfullydedicatethisbooktothememoryof DavidBohm and JohnStewartBell whosepioneeringworkdidsomuchtodemonstratethe importanceofEinstein’sviewsandargumentson quantumtheory. Contents ForewordbySirRogerPenrose xiii Preface xvii PartA SettingtheScene 1 1. ThePhilosophicalBackground:EinsteinandMach 3 Introduction 3 PositivismandErnstMach 4 Mach’sCritiqueofNewton 6 EinsteinandMach—Part1 8 EinsteinandMach—Part2 12 EinsteinandMach—theDenouement 16 References 17 2. EinsteinandQuantumTheory:TheEarlyYears 21 EinsteinandtheDevelopmentofQuantumTheory 21 ThePhotonandSpecificHeats 23 SpontaneousandStimulatedEmission;Probability andStatistics 26 ThePathtotheNewQuantumTheory 29 TheNewQuantumTheory:BohrandHeisenberg 30 TheNewQuantumTheory:Einstein’sContributions 32 References 36 3. QuantumMechanicsandItsFundamentalIssues 39 Introduction 39 SomePreliminaries 40 TheUncertaintyPrinciple 44 ‘Time-EnergyUncertaintyPrinciple’ 45 PureandMixedStates 46 StatisticalPropertiesofPureStates 47 StatisticalPropertiesofMixedStates 48 ObservableDistinctionBetweenaPureandaMixedState 48 vii viii Contents ClassicalRealismorMacrorealism 50 QuantumRealism 50 TheQuantumMeasurementProblem 51 TheClassicalLimitProblemofQuantumMechanics 53 TheLimitProblem:WaveandRayOptics 54 TheLimitProblem:SpecialRelativityand NewtonianMechanics 54 TheClassicalLimitProbleminStandard QuantumMechanics 55 Wave-ParticleDuality 56 References 57 4. TheStandardInterpretationofQuantumMechanics 59 Introduction 59 TheBohr–HeisenbergVersion 61 TheEnsembleInterpretation 64 SingleSystemvis-à-visEnsembleInterpretation 65 TheBohr–Heisenberg‘Solution’totheQuantum MeasurementProblem 67 Position-MomentumComplementarity 68 Wave-ParticleComplementarity 70 Bohrandthe‘DisturbanceInterpretation’ 72 vonNeumannandtheProjectionPostulate 73 vonNeumann’sImpossibility‘Proof’ 76 References 77 Interlude 81 PartB EinsteinConfrontingQuantumTheoryfrom1925 83 5. Einstein’sApproachestoQuantumTheory1925–1935 85 InitialImpressions 85 Einstein’sUnpublishedPaperonHiddenVariables 89 TheSolvayConference1927—MainProceedingsand Einstein–BohrPartI 91 TheSolvayConference1930—Einstein–BohrPartII 96 Einstein–Bohr:ArgumentandConceptsinthe EarlyPartsoftheDebate 97 Einstein’sBoxes 103 References 105 6. EPRanditsAftermath 107 Introduction 107 EinsteinLocalityandBellLocality 110 Entanglement 111 Einstein’sVersionoftheEPRArgument 113 Einstein’sVersionoftheEPRArgument:FurtherConsideration 115 Contents ix TheBohmVersionofEPR 119 TheOriginalEPRArgumentof1935 121 Bohr’sResponsetoEPR35 126 EPR—WhatDidItMean? 132 EinsteinandSchrödinger:The1935Correspondence 136 References 138 7. EinsteinandtheMacroscopicLimit ofQuantumMechanics 141 Introduction 141 Macrorealism:Examples 142 Macrorealism:Discussion 143 ParticleinaBox 145 DephasingoftheWave-Packet 149 LocalisationoftheWave-Packet 150 Conclusions 151 References 152 8. SummaryofEinstein’sViews 155 DidEinstein‘Reject’QuantumTheory? 155 Einstein’sPhilosophicalPosition—GeneralRemarks 159 Einstein’sApproachtotheCopenhagenInterpretation 163 EinsteinonDeterminism 168 EinsteinonRealism 172 RealismasaProgramme 177 EinsteinonLocality 182 Einstein’sVisionforPhysics—theUnifiedFieldTheory 185 EinsteinandEnsembles 189 EinsteinandtheBohmTheory 196 Realism,Determinism,Locality 199 References 202 Interlude 207 PartC Denouement 209 9. Bell’sContributionsandQuantumNon-locality 211 Introduction 211 LimitationtovonNeumann’sTheoremandPrelude toBell’sTheorem 213 Bell’sTheorem 215 Bell’sTheoremUsingStochasticHiddenVariables 220 Contextuality 222 SignalLocality,andParameterandOutcomeIndependence 223 GeneralRemarksonLocalRealismandEntanglement 226 Bell-typeArgumentsWithoutInequalities: Greenberger–Horne–Zeilinger 227 x Contents Bell-typeArgumentsWithoutInequalities:Hardy’sArgument 229 ExperimentalTestsofBell-typeInequalities 231 ExperimentalTestsofQuantumNon-locality WithoutInequalities 236 QuantumTeleportation 236 BellandEinstein 239 References 241 10. Non-standardQuantumInterpretations 247 Introduction 247 Many-WorldsInterpretation 248 Bohm’sModel:TheOntologicalInterpretation 250 Bohm’sModel:ASimpleIllustrativeExample 254 Bohm’sModel:ApproachtotheMeasurementProblem 255 DynamicalModelsofSpontaneousWave-FunctionCollapse 256 ConsistentHistoriesandDecoherentHistories 259 KnowledgeandInformationInterpretations 261 StochasticInterpretations 262 TheQuantumStateDiffusionModel 263 ManyHilbertSpaceApproach 264 GravitationallyInducedWave-FunctionCollapseApproach 265 Wave-FunctionCollapseModelsBasedonIrreversibility 267 Conclusions 268 References 268 11. EinsteinandQuantumInformationTheory 273 TheRiseofQuantumInformationTheory 273 EinsteinandQuantumInformationTheory 276 ASketchoftheTheoryofQuantumComputation 279 TheDeutschAlgorithm 284 OtherTopicsinQuantumComputation 287 EinsteinandQuantumComputation 288 QuantumCryptography 290 References 294 12. BridgingtheQuantum-ClassicalDivide 299 Introduction 299 Environment-inducedDecoherenceSchemes:BasicIdeas 299 CollisionwithExternalEnvironmentParticles:Photons, GasMolecules,etc. 303 OscillatorModeloftheEnvironment 306 AssessmentoftheDecoherenceProgramme 307 OtherApproachestotheClassicalLimit 309 Theh→0Limit 309 TheN →∞Limit 312 Ehrenfest’sTheorem 313 Contents xi TheQuantumTheoryofMacroscopicSystems 314 Conclusions 315 References 315 Interlude 319 PartD LookingForward 321 13. QuantumFoundations:GeneralOutlook 323 Introduction 323 MacrorealisminRelationtoQuantumMechanics 324 TheLeggett–GargInequality 326 OtherExamplesTestingQuantumSuperpositions forMacrosystems 329 TheQuantumZenoEffect 331 TheQuantumZenoEffect:ExperimentalTest 334 TheQuantumZenoEffect:RecentWork 335 TimeinQuantumMechanics 335 References 339 14. AssessmentofEinstein’sViewsandContributions 345 HowWouldEinsteinhaveReactedto thePresentSituation? 345 SummaryandAssessmentofEinstein’sContributions 349 AThoughtConcerningEinstein’sPossibleChoice ofInterpretation 353 References 353 Epilogue 355 NameIndex 357 SubjectIndex 365 Foreword It is a commonly expressed view that Einstein, despite his introducing several seminalnotionsthatwerequitefundamentaltotheemergingquantumtheoryin the early twentieth century, later turned his back on that theory, being unable to accept the essentially uncertain and apparently subjective picture of the sub- microscopicworldthatquantumtheoryseemedtodemand.Accordingtothisview, Einstein was too wedded to a nineteenth-century objectivistic and deterministic pictureofrealitytobeabletoacceptthethen“modern”attitudetobasiclawsofthe universe,asespousedparticularlybytheCopenhagenschoolofBohr,Heisenberg, Born, andPauli.Thatattitudeseemedtodemandauniversegovernedbypurely probabilisticlawsrelatingtofundamentallyimpreciseentitiesthatweredifficult tovisualizeandwhoseveryobjectivitywasputintoquestion.Ithadseemedthat Einstein’sstubborninsistenceondeterministicrealismmightbelikenedtothatof afatherwithfixedviewsofthepaththathischildshouldfollow,thenturninghis backwhenthatchildfailedtoadoptthelifestylethathehadsetoutforit. Accordingly,despiteEinstein’sbeingfaraheadofhiscontemporariesinthefirst quarter of the twentieth century, he is viewed as being subsequently unattuned to the later developments that took place in physics, held back by an outdated philosophicalstandpointunsuitedtotheemergenttheoryofquantummechanics. Thequantumworld,itwouldbeargued,demandedthatHeisenberg’suncertainty principlerestricttheprecisionofhowphysicalentitiescouldbehave, withthese entities being described by merely randomistic action, as determined by Born’s probabilitylaw.Accordingly,Einstein’sstance,bythemid-twentiethcentury,was takentoberetrograde. Moreover,suchanattitudetowardhislateryearsseemedtobesupportedbythe apparentlylimitednatureofEinstein’slatedevotiontoaparticularformofunified field theory, aimed at uniting gravity and electromagnetism into one geometric framework, where quantum phenomena were intended somehow to arise out of suchaclassicallybasedscheme.OneofthemainlimitationsofEinstein’sapproach wasthatitseemedtototallyignorethemorerecentdiscoveriesofthestrongand weak nuclear forces. It must indeed be admitted that the proposals that Einstein cameupwithinthisareahavenotstoodthetestoftime,andmanywouldarguethat his superb instincts for uncovering deep underlying truths of the physical world xiii
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