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时间:2018-07-27
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1、1.ClassicalTheoryS.W.HawkingIntheselecturesRogerPenroseandIwillputforwardourrelatedbutratherdierentviewpointsonthenatureofspaceandtime.Weshallspeakalternatelyandshallgivethreelectureseach,followedbyadiscussiononourdierentapproaches.Ishouldemphasizethatthese
2、willbetechnicallectures.Weshallassumeabasicknowledgeofgeneralrelativityandquantumtheory.ThereisashortarticlebyRichardFeynmandescribinghisexperiencesataconferenceongeneralrelativity.IthinkitwastheWarsawconferencein1962.Itcommentedveryunfavorablyonthegeneralcom
3、petenceofthepeoplethereandtherelevanceofwhattheyweredoing.Thatgeneralrelativitysoonacquiredamuchbetterreputation,andmoreinterest,isinaconsiderablemeasurebecauseofRoger'swork.Uptothen,generalrelativityhadbeenformulatedasamessysetofpartialdierentialequationsin
4、asinglecoordinatesystem.Peopleweresopleasedwhentheyfoundasolutionthattheydidn'tcarethatitprobablyhadnophysicalsignicance.However,Rogerbroughtinmodernconceptslikespinorsandglobalmethods.Hewasthersttoshowthatonecoulddiscovergeneralpropertieswithoutsolvingthee
5、quationsexactly.Itwashisrstsingularitytheoremthatintroducedmetothestudyofcausalstructureandinspiredmyclassicalworkonsingularitiesandblackholes.IthinkRogerandIprettymuchagreeontheclassicalwork.However,wedierinourapproachtoquantumgravityandindeedtoquantumtheo
6、ryitself.AlthoughI'mregardedasadangerousradicalbyparticlephysicistsforproposingthattheremaybelosshep-th/940919530Sep94ofquantumcoherenceI'mdenitelyaconservativecomparedtoRoger.Itakethepositivistviewpointthataphysicaltheoryisjustamathematicalmodelandthatitism
7、eaninglesstoaskwhetheritcorrespondstoreality.Allthatonecanaskisthatitspredictionsshouldbeinagreementwithobservation.IthinkRogerisaPlatonistatheartbuthemustanswerforhimself.AlthoughtherehavebeensuggestionsthatspacetimemayhaveadiscretestructureIseenoreasontoaba
8、ndonthecontinuumtheoriesthathavebeensosuccessful.Generalrelativityisabeautifultheorythatagreeswitheveryobservationthathasbeenmade.ItmayrequiremodicationsonthePlanckscalebutIdon'tthinktha
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