New Theories of Everything also by john d. barrow TheLeftHandofCreation(withJosephSilk) L’HommeetleCosmos(withFrankJ.Tipler) TheAnthropicCosmologicalPrinciple(withFrankJ.Tipler) TheWorldWithintheWorld TheArtfulUniverse PiintheSky Perchèilmondoèmatematico? Impossibility TheOriginoftheUniverse BetweenInnerSpaceandOuterSpace TheUniversethatDiscoveredItself TheBookofNothing TheConstantsofNature:FromAlphatoOmega TheInfiniteBook TheArtfulUniverseExpanded john d barrow . New Theories of Everything the quest for ultimate explanation ‘Iamveryinterestedin theUniverse—Iamspecialising intheUniverseandall thatsurroundsit’ —peter cook 1 3 GreatClarendonStreet,Oxfordox26dp OxfordUniversityPressisadepartmentoftheUniversityofOxford. ItfurtherstheUniversity’sobjectiveofexcellenceinresearch,scholarship, andeducationbypublishingworldwidein Oxford NewYork Auckland CapeTown DaresSalaam HongKong Karachi KualaLumpur Madrid Melbourne MexicoCity Nairobi NewDelhi Shanghai Taipei Toronto Withofficesin Argentina Austria Brazil Chile CzechRepublic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore SouthKorea Switzerland Thailand Turkey Ukraine Vietnam OxfordisaregisteredtrademarkofOxfordUniversityPress intheUKandincertainothercountries ©JohnD.Barrow2007 PublishedintheUnitedStates byOxfordUniversityPressInc.,NewYork Themoralrightsoftheauthorhavebeenasserted DatabaserightOxfordUniversityPress(maker) Firstpublished2007 Allrightsreserved.Nopartofthispublicationmaybereproduced, storedinaretrievalsystem,ortransmitted,inanyformorbyanymeans, withoutthepriorpermissioninwritingofOxfordUniversityPress, orasexpresslypermittedbylaw,orundertermsagreedwiththeappropriate reprographicsrightsorganization.Enquiriesconcerningreproduction outsidethescopeoftheaboveshouldbesenttotheRightsDepartment, OxfordUniversityPress,attheaddressabove Youmustnotcirculatethisbookinanyotherbindingorcover andyoumustimposethesameconditiononanyacquirer BritishLibraryCataloguinginPublicationData Dataavailable LibraryofCongressCataloginginPublicationData Dataavailable TypesetbySPIPublisherServices,Pondicherry,India PrintedinGreatBritain onacid-freepaperby ClaysLtd.,StIvesplc ISBN 978–0–19–280721–2 1 3 5 7 9 10 8 6 4 2 to roger Whostillbelievesthereshouldalwaysbe somethingratherthannothing Preface to the Second Edition I was pleased to take the opportunity, provided by the Press, to prepare a new edition of Theories of Everything. Interest in this subject has con- tinuedunabatedsincemyfirstattemptstoexplaintheirscopeandlimitations, and to place them in a broader cultural context than that of mathematical physics. Many new possibilities have emerged in the pursuit of a final string theory,andcosmologyhastakenanunexpectedpathintoarealmpopulated by many other possible universes. Both developments have undermined the naïve expectations of many, that a Theory of Everythngwould uniquely and completely specify all the defining quantities of the Universe that make it a possiblehomeforlife.Thereisalongwaytogobeforethephysicists’Theory ofEverythingisformulatedanddecisivelytested.Inthemeantime,Ihopethat thisextendedsurveyofthenewestdevelopmentswillhelppointreadersinthe rightdirectionandilluminatetheway. JohnD.Barrow Cambridge,February2007 Preface to the First Edition ‘Everything’isabigsubject.Yetmodernscientistsbelievetheyhavestumbled uponakeywhichunlocksthemathematicalsecretattheheartoftheUniverse: a discovery that points them towards a monumental ‘Theory of Everything’ whichwilluniteallthelawsofNatureintoasinglestatementthatrevealsthe inevitability of everything that was, is, and is to come in the physical world. Suchdreamsarenotnew;Einsteinwastedthelatterpartofhislifeinafruitless andisolatedquestforjustthisTheoryofEverything.Buttodaysuchschemes arenottobefoundonlyonthedesksofafewmaverickthinkersanduncon- strainedspeculators;theyhaveenteredthemainstreamoftheoreticalphysics andareworkeduponbyagrowingpopulationoftheworld’sbrightestyoung thinkers.Thisturnofeventsraisesmanydeepquestions.Cantheirquestreally succeed? Can our understanding of the logic underlying physical reality be completed? Do we forsee a day when fundamental physics will be complete, leavingonlythecomplexdetailslatentwithinthoselawstobeunravelled?Is thistrulythenewfrontierofabstractthought? This book is an attempt to describe what the challenge facing Theories of Everythingreallyis;topickoutthoseaspectsofthingswhichmustbeunder- stoodbeforewecanhaveanyrighttoclaimthatweunderstandthem.Weshall try to show that while Theories of Everything, as currently conceived, may wellprovenecessaryifwearetounderstandtheUniversearoundandwithin us, they are far from sufficient. We shall introduce the reader to those extra ingredientswhichweneedtocompleteourunderstandingofwhatis,andin sodoingweaimtodisplaymanynewideasandspeculationswhichtranscend traditionalthinkingaboutthescopeandstructureofscientificinquiry. Numerouspeoplehavehelpedthisbookcometocompletion.TheSenatus of the University of Glasgow invited the author to deliver a series of Gifford Lectures at the University of Glasgow in January of 1988 and this book elab- oratesuponthecontentofsomeofthoselectures.Iamparticularlyindebted to Neil Spurway for his gracious help with everything associated with those lectures.Foradvertentorinadvertentcommentsanddiscussionswhichhave helped in the writing of this book I am grateful to David Bailin, Margaret Boden, Danko Bosanac, Gregory Chaitin, Paul Davies, Bernard d’Espagnat, viii preface to the first edition Jeffrey Friedman, Michael Green, Chris Isham, John Manger, Bill McCrea, Leon Mestel, John Polkinghorne, Aaron Sloman, John Maynard Smith, Neil Spurway, Euan Squires, René Thom, Frank Tipler, John Wheeler, Denys Wilkinson,PeterWilliams,andTomWillmore. Writing a book can be a miserable business, not only for the author, but forallthoseinhisimmediateorbit.Themostperceptivereflectionuponthis situation was one made by the late Sir Peter Medawar. It applies not only to theactivitiesofauthors,buttoobsessivesofmanysorts:‘... itisaproceeding thatmakesoneratherinhuman,selfishlyguardingeverysecondofone’stime andbecominginattentiveaboutpersonalrelationships;onesoonformedthe opinionthatanyonewhousedthreewordswheretwowouldhavedonewasa boreofinsufferableprolixitywhosecompanymustatalltimesbeshunned.A dangersignthatfellow-obsessionalswillatoncerecognizeisthetendencyto regardthehappiestmomentsofyourlifeas thosethatoccurwhensomeone whohasanappointmenttoseeyouispreventedfromcoming.’Becauseofthe danger of such distortions, family members require special thanks for their patience and forbearance in the face of frequent neglect. Elizabeth has sup- pliedherconstantsupportininnumerableways;withoutitthisworkwould neverhavebegun.Finally,ourchildren,David,Roger,andLouise,haveshown akeenandunnervinginterestintheprogressofthemanuscriptwithoutwhich thebookwouldundoubtedlyhavebeenfinishedinhalfthetime. J.D.B. Brighton,September1990 acknowledgements Figure 7.3 is reprinted by permission of the publishers from Mind Children by Hans Moravec, Cambridge, Mass.: Harvard University Press, Copyright © 1988 by the President and Fellows of Harvard College. Figs 7.2 and 7.4 are adaptedfromthesamesource.Figure7.6iscopyright©R.V.Solé,reproduced bypermissionoftheartist. Contents 1 Ultimateexplanation 1 Aneightfoldway 1 Myths 4 Creationmyths 8 Algorithmiccompressibility 10 2 Laws 14 Thelegacyoflaw 14 Thequestforunity 17 RogerBoscovich 19 Symmetries 22 Infinities—tobeornottobe? 26 Fromstringsto‘M’ 32 Aflightofrationalisticfancy 36 Goodbyetoallthat 43 3 Initialconditions 44 Attheedgeofthings 44 Axioms 45 MathematicalJujitsu 51 Initialconditionsandtimesymmetry 61 Timewithouttime 62 Cosmologicaltime 66 Theproblemoftime 76 Absolutespaceandtime 78 Howfarisfarenough? 83 Thequantummysteryoftime 85 Quantuminitialconditions 88 Thegreatdivide 90 4 Forcesandparticles 93 ThestuffoftheUniverse 93 Thecopy-catprinciple 95 Elementarity 100