Conceptual tensions between quantum mechanics and

arXiv:gr-qc/0303100v27Apr2003VersionforCUP04-07-03Conceptualtensionsbetweenquantummechanicsandgeneralrelativity:Arethereexperimentalconsequences?RaymondY.ChiaoDepartmentofPhysicsUniversityofCaliforniaBerkeley,CA94720-7300U.S.A.(E-mail:[e-mail])(DateoffinalversionforCambridgeUniversityPress:April7,2003)AbstractOneoftheconceptualtensionsbetweenquantummechanics(QM)andgeneralrelativity(GR)arisesfromtheclashbetweenthespatialnonseparabilityofentangledstatesinQM,andthecom-pletespatialseparabilityofallphysicalsystemsinGR,i.e.,betweenthenonlocalityimpliedbythesuperpositionprinciple,andthelocalityimpliedbytheequivalenceprinciple.Possibleexperimen-talconsequencesofthisconceptualtensionwillbediscussedformacroscopicallyentangled,coherentquantumfluids,suchassuperconductors,superfluids,atomicBose-Einsteincondensates,andquan-tumHallfluids,interactingwithtidalandgravitationalradiationfields.Aminimal-couplingrule,whicharisesfromtheelectronspincoupledtocurvedspacetime,leadstoaninteractionbetweenelectromagnetic(EM)andgravitational(GR)radiationfieldsmediatedbyaquantumHallfluid.Thissuggeststhepossibilityofaquantumtransduceraction,inwhichEMwavesareconvertibletoGRwaves,andviceversa.1Introduction“MercyandTrutharemettogether;RighteousnessandPeacehavekissedeachother.”(Psalm85:10)InthisFestschriftVolumeinhonorofJohnArchibaldWheeler,Iwouldliketotakeafreshlookattheintersectionbetweentwofieldstowhichhedevotedmuchofhisresearchlife:generalrelativity(GR)andquantummechanics(QM).Asevidenceofhiskeeninterestinthesetwosubjects,Iwouldcitetwoexamplesfrommyownexperience.WhenIwasanundergraduateatPrincetonUniversityduringtheyearsfrom1957to1961,hewasmyadviser.Oneofhisdutieswastoassignmetopicsformyjuniorpaperandformyseniorthesis.Formyjuniorpaper,Iwasassignedthetopic:Comparethecomplementarityandtheuncertaintyprinciplesofquantummechanics:Whichismorefundamental?Formyseniorthesis,Iwasassignedthetopic:Howtoquantizegeneralrelativity?AsWheelertaughtme,morethanhalfofscienceisdevotedtotheaskingoftherightquestion,whileoftenlessthanhalfisdevotedtotheobtainingofthecorrectanswer,butnotalways!Inthesamespirit,IwouldliketoofferupheresomequestionsconcerningconceptualtensionsbetweenGRandQM,whichhopefullycanbeansweredinthecourseoftimebyexperiments,withaviewtowardsprobingthetensionbetweentheconceptsoflocalityinGRandnonlocalityinQM.Ihopethatitwouldbeappropriateandpermissibletoasksomequestionshereconcerningthistension.ItisnotthepurposeofthisChaptertopresentdemonstratedresults,buttosuggestheuristicallysomeinterestingavenuesofresearchwhichmightleadtofutureexperimentaldiscoveries.OnequestionthatnaturallyarisesattheborderbetweenGRandQMisthefollowing:Aretherenovelexperimentalorobservationalwaysofstudyingquantizedfieldscoupledtocurvedspacetime?Thisquestionhasalreadyariseninthecontextofthevacuumembeddedincurvedspacetime[1],butIwouldliketoextendthistopossibleexperimentalstudiesofthegroundstateofanonrelativisticquantummany-bodysystemwithoff-diagonallong-rangeorder,i.e.,a“quantumfluid,”viewedasaquantizedfield,coupledtocurvedspacetime.Asweshallsee,thiswillnaturallyleadtothefurtherquestion:AretherequantummethodstodetectgravitationalradiationotherthantheclassicalonespresentlybeingusedintheWeberbarandLIGO(i.e.,the“LaserInterferometerGravitationalWaveObservatory”)2[2][3][4]?AsIseeit,thethreemainpillarsofphysicsatthebeginningofthe21stcenturyarequan-tummechanics,relativity,andstatisticalmechanics,whichcorrespondtoEinstein’sthreepapersof1905.Thereexistconceptualtensionsattheintersectionsofthesethreefieldsofphysics(seeFigure1).Itseemsworthwhilere-examiningthesetensions,sincetheymayen-tailimportantexperimentalconsequences.Inthisintroduction,Ishallonlybrieflymentionthreeconceptualtensionsbetweenthesethreefields:localityversusnonlocalityofphysicalsystems,objectivityversussubjectivityofprobabilitiesinquantumandstatisticalmechan-ics(theproblemofthenatureofinformation),andreversibilityversusirreversibilityoftime(theproblemofthearrowsoftime).OthersinthisVolumewilldiscussthesecondandthethirdofthesetensionsindetail.Ishalllimitmyselftoadiscussionofthefirstconceptualtensionconcerninglocalityversusnonlocality,mainlyinthecontextofGRandQM.(However,inmySolvaylecture[5],Ihavediscussedtheothertwotensionsinmoredetail.SeealsomyRomelecture[6]foradiscussionofthreedifferentkindsofquantumnonlocalities).Whyexamineconceptualtensions?Abriefansweristhattheyoftenleadtonewex-perimentaldiscoveries.Itsufficestogivejustoneexamplefromlate19thandearly20thcenturyphysics:theclashbetweenthevenerableconceptsofcontinuityanddiscreteness.Theconceptofcontinuity,whichgoesbacktotheGreekphilosopherHeraclitus(“everythingflows”),clashedwiththeconceptofdiscreteness,whichgoesbacktoDemocritus(“every-thingiscomposedofatoms”).Eventually,Heraclitus’sconceptofcontinuity,ormorespecificallythatofthecontinuum,wasembodiedintheideaoffieldintheclassicalfieldtheoryassociatedwithMaxwell’sequations.TheatomichypothesisofDemocrituswaseventuallyembodiedinthekinetictheoryofgasesinstatisticalmechanics.Conceptualtensions,orwhatWheelercallsthe“clashofideas,”nee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