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时间:2018-07-10
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1、1.ClassicalTheoryS.W.HawkingIntheselecturesRogerPenroseandIwillputforwardourrelatedbutratherdifferentviewpointsonthenatureofspaceandtime.Weshallspeakalternatelyandshallgivethreelectureseach,followedbyadiscussiononourdifferentapproaches.Ishouldemphasizeth
2、atthesewillbetechnicallectures.Weshallassumeabasicknowledgeofgeneralrelativityandquantumtheory.ThereisashortarticlebyRichardFeynmandescribinghisexperiencesataconferenceongeneralrelativity.IthinkitwastheWarsawconferencein1962.Itcommentedveryunfavorablyo
3、nthegeneralcompetenceofthepeoplethereandtherelevanceofwhattheyweredoing.Thatgeneralrelativitysoonacquiredamuchbetterreputation,andmoreinterest,isinaconsiderablemeasurebecauseofRoger’swork.Uptothen,generalrelativityhadbeenformulatedasamessysetofpartiald
4、ifferentialequationsinasinglecoordinatesystem.Peopleweresopleasedwhentheyfoundasolutionthattheydidn’tcarethatitprobablyhadnophysicalsignificance.However,Rogerbroughtinmodernconceptslikespinorsandglobalmethods.Hewasthefirsttoshowthatonecoulddiscovergeneral
5、propertieswithoutsolvingtheequationsexactly.Itwashisfirstsingularitytheoremthatintroducedmetothestudyofcausalstructureandinspiredmyclassicalworkonsingularitiesandblackholes.IthinkRogerandIprettymuchagreeontheclassicalwork.However,wedifferinourapproachtoq
6、uantumgravityandindeedtoquantumtheoryitself.AlthoughI’mregardedasadangerousradicalbyparticlephysicistsforproposingthattheremaybelossofquantumcoherenceI’mdefinitelyaconservativecomparedtoRoger.Itakethepositivistviewpointthataphysicaltheoryisjustamathemat
7、icalmodelandthatitismeaninglesstoaskwhetheritcorrespondstoreality.Allthatonecanaskisthatitspredictionsshouldbeinagreementwithobservation.IthinkRogerisaPlatonistatheartbuthemustanswerforhimself.Althoughtherehavebeensuggestionsthatspacetimemayhaveadiscre
8、testructureIseenoreasontoabandonthecontinuumtheoriesthathavebeensosuccessful.Generalrelativityisabeautifultheorythatagreeswitheveryobservationthathasbeenmade.ItmayrequiremodificationsonthePlanckscalebutIdon’tthinkthatwillaffectmanyofthepr
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