Hawking, Steven - A Brief History Of Time

Chapter1-OurPictureoftheUniverseChapter2-SpaceandTimeChapter3-TheExpandingUniverseChapter4-TheUncertaintyPrincipleChapter5-ElementaryParticlesandtheForcesofNatureChapter6-BlackHolesChapter7-BlackHolesAin'tSoBlackChapter8-TheOriginandFateoftheUniverseChapter9-TheArrowofTimeChapter10-WormholesandTimeTravelChapter11-TheUnificationofPhysicsChapter12-ConclusionGlossaryAcknowledgments&AboutTheAuthor  FOREWARDIdidn’twriteaforewordtotheoriginaleditionofABriefHistoryofTime.ThatwasdonebyCarlSagan.Instead,Iwroteashortpiecetitled“Acknowledgments”inwhichIwasadvisedtothankeveryone.Someofthefoundationsthathadgivenmesupportweren’ttoopleasedtohavebeenmentioned,however,becauseitledtoagreatincreaseinapplications.Idon’tthinkanyone,mypublishers,myagent,ormyself,expectedthebooktodoanythinglikeaswellasitdid.ItwasintheLondonSundayTimesbest-sellerlistfor237weeks,longerthananyotherbook(apparently,theBibleandShakespearearen’tcounted).Ithasbeentranslatedintosomethinglikefortylanguagesandhassoldaboutonecopyforevery750men,women,andchildrenintheworld.AsNathanMyhrvoldofMicrosoft(aformerpost-docofmine)remarked:IhavesoldmorebooksonphysicsthanMadonnahasonsex.ThesuccessofABriefHistoryindicatesthatthereiswidespreadinterestinthebigquestionslike:Wheredidwecomefrom?Andwhyistheuniversethewayitis?Ihavetakentheopportunitytoupdatethebookandincludenewtheoreticalandobservationalresultsobtainedsincethebookwasfirstpublished(onAprilFools’Day,1988).Ihaveincludedanewchapteronwormholesandtimetravel.Einstein’sGeneralTheoryofRelativityseemstoofferthepossibilitythatwecouldcreateandmaintainwormholes,littletubesthatconnectdifferentregionsofspace-time.Ifso,wemightbeabletousethemforrapidtravelaroundthegalaxyortravelbackintime.Ofcourse,wehavenotseenanyonefromtheABriefHistoryofTime-StephenHawkingfile:///C|/WINDOWS/Desktop/blahh/StephenHawking-Abriefhistoryoftime/ABriefHistoryinTime.html(1of2)[2/20/20013:13:58AM]future(orhavewe?)butIdiscussapossibleexplanationforthis.Ialsodescribetheprogressthathasbeenmaderecentlyinfinding“dualities”orcorrespondencesbetweenapparentlydifferenttheoriesofphysics.Thesecorrespondencesareastrongindicationthatthereisacompleteunifiedtheoryofphysics,buttheyalsosuggestthatitmaynotbepossibletoexpressthistheoryinasinglefundamentalformulation.Instead,wemayhavetousedifferentreflectionsoftheunderlyingtheoryindifferentsituations.Itmightbelikeourbeingunabletorepresentthesurfaceoftheearthonasinglemapandhavingtousedifferentmapsindifferentregions.Thiswouldbearevolutioninourviewoftheunificationofthelawsofsciencebutitwouldnotchangethemostimportantpoint:thattheuniverseisgovernedbyasetofrationallawsthatwecandiscoverandunderstand.Ontheobservationalside,byfarthemostimportantdevelopmenthasbeenthemeasurementoffluctuationsinthecosmicmicrowavebackgroundradiationbyCOBE(theCosmicBackgroundExplorersatellite)andothercollaborations.Thesefluctuationsarethefinger-printsofcreation,tinyinitialirregularitiesintheotherwisesmoothanduniformearlyuniversethatlatergrewintogalaxies,stars,andallthestructuresweseearoundus.Theirformagreeswiththepredictionsoftheproposalthattheuniversehasnoboundariesoredgesintheimaginarytimedirection;butfurtherobservationswillbenecessarytodistinguishthisproposalfromotherpossibleexplanationsforthefluctuationsinthebackground.However,withinafewyearsweshouldknowwhetherwecanbelievethatweliveinauniversethatiscompletelyself-containedandwithoutbeginningorend.StephenHawking ABriefHistoryofTime-StephenHawkingfile:///C|/WINDOWS/Desktop/blahh/StephenHawking-Abriefhistoryoftime/ABriefHistoryinTime.html(2of2)[2/20/20013:13:58AM]CHAPTER1OURPICTUREOFTHEUNIVERSE Awell-knownscientist(somesayitwasBertrandRussell)oncegaveapubliclectureonastronomy.Hedescribedhowtheearthorbitsaroundthesunandhowthesun,inturn,orbitsaroundthecenterofavastcollectionofstarscalledourgalaxy.Attheendofthelecture,alittleoldladyatthebackoftheroomgotupandsaid:“Whatyouhavetoldusisrubbish.Theworldisreallyaflatplatesupportedonthebackofagianttortoise.”Thescientistgaveasuperiorsmilebeforereplying,“Whatisthetortoisestandingon.”“You’reveryclever,youngman,veryclever,”saidtheoldlady.“Butit’sturtlesallthewaydown!”Mostpeoplewouldfindthepictureofouruniverseasaninfinitetoweroftortoisesratherridiculous,butwhydowethinkweknowbetter?Whatdoweknowabouttheuniverse,andhowdoweknowit?Wheredidtheuniversecomefrom,andwhereisitgoing?Didtheuniversehaveabeginning,andifso,whathappenedbeforethen?Whatisthenatureoftime?Willitevercometoanend?Canwegobackintime?Recentbreakthroughsinphysics,madepossibleinpartbyfantasticnewtechnologies,suggestanswerstosomeoftheselongstandingquestions.Somedaytheseanswersmayseemasobvioustousastheearthorbitingthesun–orperhapsasridiculousasatoweroftortoises.Onlytime(whateverthatmaybe)willtell.Aslongagoas340BCtheGreekphilosopherAristotle,inhisbookOntheHeavens,wasabletoputforwardtwogoodargumentsforbelievingthattheearthwasaroundsphereratherthanaHatplate.First,herealizedthateclipsesofthemoonwerecausedbytheearthcomingbetweenthesunandthemoon.Theearth’sshadowonthemoonwasalwaysround,whichwouldbetrueonlyiftheearthwass