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时间:2018-09-12
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1、1.ClassicalTheoryS.W.HawkingIntheselecturesRogerPenroseandIwillputforwardourrelatedbutratherdierentviewpointsonthenatureofspaceandtime.Weshallspeakalternatelyandshallgivethreelectureseach,followedbyadiscussiononourdierentapproaches.Ishouldemphasizethatthesewillbetechnicallectures.Weshallassume
2、abasicknowledgeofgeneralrelativityandquantumtheory.ThereisashortarticlebyRichardFeynmandescribinghisexperiencesataconferenceongeneralrelativity.IthinkitwastheWarsawconferencein1962.Itcommentedveryunfavorablyonthegeneralcompetenceofthepeoplethereandtherelevanceofwhattheyweredoing.Thatgeneralrelat
3、ivitysoonacquiredamuchbetterreputation,andmoreinterest,isinaconsiderablemeasurebecauseofRoger'swork.Uptothen,generalrelativityhadbeenformulatedasamessysetofpartialdierentialequationsinasinglecoordinatesystem.Peopleweresopleasedwhentheyfoundasolutionthattheydidn'tcarethatitprobablyhadnophysicals
4、ignicance.However,Rogerbroughtinmodernconceptslikespinorsandglobalmethods.Hewasthersttoshowthatonecoulddiscovergeneralpropertieswithoutsolvingtheequationsexactly.Itwashisrstsingularitytheoremthatintroducedmetothestudyofcausalstructureandinspiredmyclassicalworkonsingularitiesandblackholes.Ithi
5、nkRogerandIprettymuchagreeontheclassicalwork.However,wedierinourapproachtoquantumgravityandindeedtoquantumtheoryitself.AlthoughI'mregardedasadangerousradicalbyparticlephysicistsforproposingthattheremaybelosshep-th/940919530Sep94ofquantumcoherenceI'mdenitelyaconservativecomparedtoRoger.Itakethe
6、positivistviewpointthataphysicaltheoryisjustamathematicalmodelandthatitismeaninglesstoaskwhetheritcorrespondstoreality.Allthatonecanaskisthatitspredictionsshouldbeinagreementwithobservation.IthinkRogerisaPlatonistatheartbuthemustanswerforhimself.Althoughtherehavebeensuggestionsthatspacetimemayha
7、veadiscretestructureIseenoreasontoabandonthecontinuumtheoriesthathavebeensosuccessful.Generalrelativityisabeautifultheorythatagreeswitheveryobservationthathasbeenmade.ItmayrequiremodicationsonthePlanckscalebutIdon'tthinktha
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