e-book - stephen hawking - the nature of space and time

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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