Ther Is No Adequat Definitio of Finetune fo Life Nei A - PDF document

ThereIsNoAdequateDefinitionof‘Fine-tunedforLife’NeilA.MansonUniversityofAberdeenThediscoverythattheuniverseisŽne-tunedforlife–adiscoverytowhichthephrase‘theanthropicprinciple’isoftenapplied–haspromptedmuchextra-cosmicspeculationbyphilosophers,theologians,andtheoreticalphysicists.Suchspeculationisreferredtoasextra-cosmicbecauseaninferenceismadetotheexistenceeitherofoneunobservableentitythatisdistinctfromthecosmosandanyofitsparts(God)orofmanysuchentities(multipleuniverses).InthisarticleacaseismountedforthescepticalpositionthatcosmicŽne-tuningdoesnotsupportaninferencetoanythingextra-cosmic.TothatendthreedeŽnitionsof‘Žne-tunedforlife’areproposed:the‘slightdifference’deŽnition,the(unconditional)probabilitydeŽnition,andJohnLeslie’sconditionalprobabilitydeŽnition.ThesethreedeŽnitionsaretheonlyonessuggestedbytherelevantliteratureonŽne-tuningandtheanthropicprinciple.SinceonnoneofthemdoclaimsofŽne-tuningwarrantaninferencetosomethingextra-cosmic,itisconcludedthatthereisnodeŽnitionof‘Žne-tunedforlife’servingthisfunction.Old-fashionedmetaphysicalspeculationhasreceivedaboostinrecentyearsfromtheburgeoningliteratureontheanthropicprinciple.Thatprinciple,ŽrstarticulatedbyBrandonCarter(1998)intheearly1970s,surveyedexhaustivelybyBarrowandTipler(1986),andintroducedtophilosophersbyJohnLeslie(1989),haspromptedbothre-examinationofthetraditionalTeleologicalargumentforGod’sexistenceandconsiderationofthepossibilityofuniversesdistinctfromours.Theterm‘anthropicprinciple’isunfortunatelyoftenappliedtothedataforwhichthatprincipleissupposedtoaccountratherthantheprincipleitself;thisarticleconcernsthedataandnottheprinciple.Sincethedatainquestionaresimplyalltheinstanceswhereinagivencosmicparameteris‘Žne-tunedforlife’,letmesayabitaboutwhatŽne-tuningforlifeissupposedtobe.ThepictureoftheuniversepaintedbymodernparticlephysicsandBigBangcosmologyisverydetailed.Wecanimaginethispicturepresentedintheformofalistofequationsconsistingofthefundamentalphysicalparametersthatauniversemighthaveontheleft-handsideandthenumericalvaluesthoseparametersactuallyhaveinouruniverseontheright-handside.Thelistwouldincludelinessuchasthis(forthemassoftheproton):Inquiry,43,341–52#2000Taylor&Francis *IthankRobinCollins,GordonGraham,BrentMundy,GrahamOppy,TomaszPlacek,andPetervanInwagenfortheirhelpindevelopingtheideaspresentedinthispaper. ‘Mp=938.28MeV’.Describingtheuniversethiswaynaturallysuggestsaskingwhytheparametershavethevaluestheyactuallyhaveasopposedtosomeothervalues.Inthecourseofaddressingthisquestion,physicistsandcosmologistshavediscoveredthatmanyoftheparametersonthislistpossessthefollowingproperty:ifitsactualvalueissufŽcientlyalteredwhilethevaluesofalltheotherparametersareheldconstant,theresultinglistceasestodescribealife-permittinguniverse.Parameterspossessingthispropertyaresaidtobe‘Žne-tunedforlife’.ThatsomanycosmicparametersareŽne-tunedforlifehasbeenthoughtbymanyphysicistsandcosmologists(and,later,philosophersandtheologians)toposeaproblem.Theanthropicprincipleisthoughttobeonesolution.Ittellsusthis:giventhatwearearoundtoobservetheuniverse,theuniversenecessarilymeetswhateverconditionsourexistenceimposes.Thishasgivenrisetothesuggestionthatouruniverseisbutoneofavastmultitudeofuniverses,thusmakingitnosurprisethatoneuniverseinthevastmultitudehappenstopermitlife.AwhollydifferentexplanationforŽne-tuningisthattheuniverseistheproductofadesignerofgreatpowerandintelligencewhoexistsoutsideofthephysicaluniverse.ThosewhoargueeithertomultipleuniversesortoadesignerthinkthereissomethingaboutcosmicŽne-tuningforlifewhichdemandsanexplanationandwhichwarrantsaninferencetosomething(orthings)outsidetheuniverse.WhethertheyarerightinsothinkingdependsonhowtheydeŽne‘Žne-tunedforlife’.BasedontheliteraturethereappeartobeseveralpossibledeŽnitions.I.The‘SlightDifference’DeŽnitionThemostcommonwayofstatingclaimsofŽne-tuningforlifeisintermsofcounterfactualconditionals,whereinexpressionssuchas‘slightdifference’,‘smallchange’,‘delicatebalance’,‘precise’,‘differentbyn%’,‘differentbyonepartin10n’,and‘tunedtothenthdecimalplace’appearintheantecedent.ConsiderthefollowingquotationsfromStephenHawkingandLeeSmolin.Theremarkablefactisthatthevaluesofthese[fundamental]numbersseemtohavebeenveryŽnelyadjustedtomakepossiblethedevelopmentoflife.Forexampleiftheelectricchargeoftheelectronhadbeenonlyslightlydifferent,starseitherwouldhavebeenunabletoburnhydrogenandhelium,orelsetheywouldnothaveexploded.(Hawking[1988],p.125)...theexistenceofstarsrestsonseveraldelicatebalancesbetweenthedifferentforcesinnature.Theserequirethattheparametersthatgovernhowstronglytheseforcesactbetunedjustso.Inmanycases,asmallturnofthedialinonedirectionoranotherresultsinaworldnotonlywithoutstars,butwithmuchlessstructurethanouruniverse.(Smolin[1997],p.37)342NeilA.Manson SuchstatementssuggestthefollowingdeŽnition:Def.1:AcosmicparameterPisŽne-tunedforlifeifandonlyiflifecouldnothavearisenhadthenumericalvalueofPbeenslightlydifferent.IwilldubparametersthatareŽne-tunedinthissense‘Žne-tuned1’.TheproblemwiththisdeŽnitionisthattosayaparameterisŽne-tuned1istosaynothingaboutprobability.Consequently,Žne-tuning1statementscanplaynoroleinBayesian-stylearguments,becauseBayesianargumentsrequireprobabilitystatementsasinputs.YetthosewhoarguefromŽne-tuningtosomethingextra-cosmicmostoftenpresentthemselvesasapplyingaBayesianmodelofinference(ratherthanmakinganargumentfromanalogyofthesortPaleymounted).WhethertheybearguingforGod(e.g.Swinburne[1989]),multipleuniverses(e.g.Carter[1993]andSmolin[1997]),orboth(e.g.Leslie[1989]),theyallclaimthattheprobabilityofgettingauniversewithlifeisfargreaterconditionalontheexistenceofthesortofextra-cosmicentitytheyfavorthanitisconditionalontherebeingjustoneuniversethefeaturesofwhicharedeterminedbychance.ThoughsuperŽciallysimilar,claimsaboutwhatthingswouldhavebeenlikeifconditionshadbeenslightlydifferentarenotatallequivalenttoprobabilities.ConsiderthatacertainnutwouldnotŽtontoacertainone-centimetre-wideboltifthatboltwereamillimetrewiderornarrower.Itdoesnotfollowthattheprobabilityofthenut’sŽttingtheboltisoneinten.Indeed,nothingaboutprobabilityfollowsatall.ThispointaloneissufŽcienttoruleŽne-tuning1inadequateforthepurposesofBayesianextra-cosmicarguments.Evensupposingtherearenon-Bayesianextra-cosmicarguments,however,afurtherproblemremains:statementsofŽne-tuning1areuselessintheabsenceofametricfordifferences.SuchametricisneededinordertoanswerthequestionaptlyaskedbyRobertK.Clifton([1991],p.30):‘howisonetodistinguishaninstanceofŽne-tuningfrommere“coarse”-tuning?’ConsiderthisselectionfromthedatasetLeslie([1989],pp.3–5)presentsasevidencethattheuniverseisŽne-tuned.·[theuniverse’s]rateofexpansionatearlyinstantsneededtobeŽnetunedtoperhapsonepartin1055(whichis10followedby54zeros)...·Forcarbontobecreatedinquantityinsidestarsthenuclearstrongforcemustbetowithinperhapsaslittleas1percentneitherstrongernorweakerthanitis...·GravityalsoneedsŽne-tuningforstarsandplanetstoform,andforstarstoburnstablyoverbillionsofyears.Itisroughly1039timesweakerthanelectromagnet-ism.Haditbeenonly1033timesweaker,starswouldbeabilliontimeslessmassiveandwouldburnamilliontimesfaster.Puttingtheseaspercentages,intheŽrstcaseLeslieissayingofacertainparameterthatifithaddifferedbyone-hundredthousandtrilliontrillionThereIsNoAdequateDefinitionof‘Fine-tunedforLife’343 trilliontrillionthofapercent,lifewouldnotbepossible;inthesecond,oneortwopercent;andinthethird,one-hundredmillionpercent.InvirtueofwhatdoallofthesecountascasesofŽne-tuning?WithoutametrictosupplementdeŽnition1,wehavenoanswer.PerhapsitisthelackofprobabilitiesandthelackofametricwhichexplainswhytherearesomanymischievouspresentationsofŽne-tuning1.ConsidersomefactsJohnJeffersonDavis([1987],pp.140–1)callstoourattention:‘Ifthemassofneutrinoswere5 10-34insteadof5 10-35kg,becauseoftheirgreatabundanceintheuniverse,theadditionalgravitationalmasswouldresultinaratherthanexpandinguniverse.’Giventhatparticlemassesarebeingmeasuredinkilograms,isthisanysurprise?Noastonishmentiswarrantedbythefact(henceforth‘theJordanfact’)that,ifhehadbeenonepartin1016ofalight-yearshorter(thatis,onemetreshorter),MichaelJordanwouldnothavebeentheworld’sgreatestbasketballplayer.Again,Davissays:‘Ifgravitywerestrongerbyonepartin1040,therewouldlongagohavebeenacatastrophiccollapseoftheuniverse(the“BigCrunch”)insteadofitspresentexpansion.’Yettheonepartin1040towhichDavisrefersisapartoftheunitofmeasureforthegravitationalconstant,notapartofthegravitationalconstantitself.ComparethisagaintotheJordanfact.Itistrueonlyifwearetalkingaboutpartsofalight-yearratherthanpartsofJordan’sheight;beingoneten-trillionthofamillimetreshorterwouldnotaffectJordan’sbasketballabilitiesabit.Ascrudeastheseconfusionssound,theyareoft-committedindiscussionsofŽne-tuningandtheanthropicprinciple.Suchcomplaintsarenotunprecedented.Morethansixtyyearsago,HerbertDinglecriticizedonsimilargroundsthehubbuboverthe‘large-numbercoincidences’whichexercisedmanyofhiscontemporaries(seeBarrowandTipler[1986],ch.4).Inessence,P.A.M.Dirac’sargumentisthis.Largenumbersneedanentirelydifferenttypeofexplanationfromsmallones(sincethenumberofpurenumbersisinŽnitethedistinctionismeaningless,butmeaningseemstobeirrelevanttotheseconsiderations).If,fromanindeŽnitelywidechoice,weselectacertainunitoftime(‘saytheunite2/mc3),theageoftheuniverseaccordingtoonecosmologicalspeculationis‘about’equaltothesquarerootofthenumberofprotonsintheuniverseaccordingtoanother,andtotheratioofcertainelectronicforces(Dingle[1937],p.786).TheagetowhichDinglerefersis1039,andthenumberofprotonswasestimatedtobe1078.Dinglecomplainedthatthiscoincidenceisonlytheresultoftheunitoftimeselected–aselection,hesaid,thatwasmadefrom‘anindeŽnitelywidechoice’.MycomplaintaboutDavis’suseofkilogramstomeasurethemassoftheneutrinoechoesDingle’s.AsforDingle’schargethattherebeinganinŽnitenumberofpurenumbersrendersmeaninglessthelargenumber/smallnumberdistinction,itwillbetakenupinthenextsection.344NeilA.Manson II.The(Unconditional)ProbabilityDeŽnitionSupposingtheyacknowledgethedeŽcienciesofdeŽnition1andtheshortcomingsofpresentingthefactsofŽne-tuningintermsofcounterfactualconditionals,thoseadvancingextra-cosmicargumentsmightpleadguiltyonlytobrevity.Implicitintheirarguments,theywillsay,isthesuppositionthattheconditionsaremetwhichwarranttreatingstatementsofŽne-tuning1asindicatingtheextremeimprobabilityofgettinglife-permittingparametervalues.ThuswhentheytalkaboutŽne-tuning,theyhavethefollowingdeŽnitioninmind.Def.2:AcosmicparameterPisŽne-tunedforlifeifandonlyiftheprobabilitythatPtakesalife-permittingvalueisextremelylow.IwilldescribeparametersthatareŽne-tunedinthissenseas‘Žne-tuned2’.ItisclearthatifacosmicparameterisŽne-tuned2,thenthatfactcanbeusedinBayesianargumentsforsomethingextra-cosmic(thoughthoseargumentsmayfailforotherreasons).FordeŽnition2tobeuseful,however,somespeciŽcationwillhavetobegivenof(a)therangeofvaluesPcouldhavetaken(henceforth‘range’)and(b)theprobabilitydistributionforthevaluesinthatrange(henceforth‘probabilitydistribution’).ThetheoriesofrangeandprobabilitydistributionmayvaryintheirspeciŽcs,e.g.thattherangeisthesetofrealnumbersandthattheprobabilitymeasureonthatrangeconsistsofBorelsubsetsoftherealnumbers.Theimportantpoint,however,isthatthetheoriesofrangeandprobabilitydistributionwillhavetocombineinsuchawaythattheyjustifytreatingtheprobabilityofP’stakingalife-permittingvalueasextremelysmall.Theycoulddosoinseveralways.Thetheoriescouldbethat(a1)therangeofpossiblevaluesforPisvastrelativetothelife-permittingrangeofvaluesforP,and(b1)theprobabilitydistributionforthatrangeisnotsigniŽcantlybiasedtowardsthelife-permittingrange.Theycouldbethat(a2)therangeofpossiblevaluesforPisnotvastrelativetothelife-permittingrangeofvaluesforP,but(b2)theprobabilitydistributionforthatrangeissigniŽcantlybiasedagainstthelife-permittingrange.(Notethateveniftheprobabilitydistributionforavariableisbiasedtowardsaparticularvalue,thisdoesnotmeanweshouldnotbesurprisedifthevariabletakespreciselythatvalue;ifweipacoin2 10100times,gettingexactly10100headswouldbestartling.)Theycouldbethat(a1)and(b2).TheimportantpointisthatgettingfromŽne-tuning1toŽne-tuning2requirestheoriesaboutbothrangeandprobabilitydistribution.Toseethis,consider,again,theJordanfact.Whilehisheightinlight-yearsisŽne-tuned(inasenseanalogoustothatprovidedindeŽnition1),thisisnotimpressivebecause(ah)therangeofgreatness-permittingbiologicallypossiblevaluesforJordan’sheight,whileminusculecomparedtoalight-year,isnottoosmallrelativetotherangeofbiologicallypossiblevaluesforThereIsNoAdequateDefinitionof‘Fine-tunedforLife’345 Jordan’sheight,andbecause(bh)Jordan’sheight,wepresume,hadafairlygoodchanceofendingupinthegreatness-permittingbiologicallypossiblerange.ComparethistothecaseofhismakingŽveshotsinsuccession.Onanygivenshot,hecouldhavemissedthebasketwildly.Evenso,hismakingŽveconsecutiveshotsisnottoosurprisingbecausealthough(as)therangeofpossibletrajectoriesforoneofhisshotsisvastrelativetotherangeofpossiblebasket-makingtrajectoriesforthatshot,Jordan’sgreatskillmeansthat(bs)theprobabilitydistributionfortherangeofpossibletrajectoriesisheavilyskewedtowardstherangeofbasket-makingtrajectories.Whileeachofhisshotsis,inaway,Žne-tuned1ismakingŽveinarowisnotverysurprising,evenifwegrant(as).GiventhatargumentsfromŽne-tuning2tothingsextra-cosmicimplicitlyrelyontheoriesofrangeandprobabilitydistribution,itmightsurprisethereadertoknowthereisonlyahandfulofinstanceswhereinsuchtheoriesarediscussedexplicitly.ErnanMcMullin([1993],p.361)writesabout‘thecosmogonicprincipleofindifference,orjusttheindifferenceprinciple,forshort’.HeidentiŽesthisastheprinciplethattheuniverseisthewayitisastheresultofchance,andtakesittoimplythattherangeofpossiblevaluesforthemassdensityoftheuniverseisunrestricted.Themassdensityoftheuniversetodayisrelativelyclosetothedensitycorrespondingtotheborderlinebetweenanopenandacloseduniverse.Theratioofthesedensities( )isbelievedtoliesomewherebetweenthevaluesof2and1.Sotheuniverse,ingeometricalterms,isrelatively‘at’.Theproblemisthattoreachthisconditiontodaythevalueof shortlyaftertheBigBangwouldhavehadtobealmostexactly1;toachievethis,theinitialexpansionratewouldhavetobe‘tuned’toanaccuracy(sooneestimatewent)ofonepartin1055.Accordingtotheindifferenceprinciple,anyinitialvalueof shouldhavebeenpossible.Sothisextraordinarilytightrestrictionontheinitialcosmicconditionsposesaproblem(McMullin[1993],p.378).McMullindoesnotsaywhetherthisimplicationoftheindifferenceprinciple–thatanyinitialvalueof shouldhavebeenpossible–iscoherentoracceptable.Incidentally,McMullin([1993],pp.378–9)laterasks‘whyistheonlyoneamong1055possibleinitialstates...theonethatisactuallyrealized?’Tosay requirestuningtoonepartin1055is,heseemstothink,justtosaythatthereare1055possibleinitialstatesofwhichonlyonepermitslife.ThisisjustanotherinstanceofthesortofconfusionindicatedintheŽrstsectionofthispaper.TheproblemwithapositionsuchasMcMullin’sisastutelynotedbyPaulDavies([1992],pp.204–5):‘IftherangeisinŽnite,thenanyŽniterangeofvaluesmightbeconsideredtohavezeroprobabilityofbeingselected.Butthenweshouldbeequallysurprisedhoweverweaklytherequirementsforlifeconstrainthosevalues.Thisissurelyareductioadabsurdumofthewholeargument.’Anotherwayofmakingessentiallythesameobjectionistosay346NeilA.Manson thatMcMullin’sindifferenceprincipleguaranteesŽne-tuning2onthecheap.ToprovethattheuniverseisŽne-tuned2forlife,allonewouldneeddoisshowthatthereisatleastonecosmicparameterforwhichlifeconstrainsthepossiblevaluestoaŽniteinterval.Thenonewouldhaveshownthattheprobabilityofalife-permittinguniverseiszeronomatterhowlargethatinterval.Furthermore,therewouldbenoneedtoŽndanyfurthercasesofŽne-tuning2,fornoadditionalevidencecouldmakeitanylesslikelyonthechancehypothesisthattheuniverseissuchastopermitlife.TheseconsequencesofendorsingMcMullin’sindifferenceprinciplemaynotbedevastatingperse.Indeed,thoseinferringextra-cosmicentitiesfromŽne-tuning2mightsaytheirargumentsareevenstrongerthantheyinitiallysupposed.Settingthisresponseaside,therewouldstillbetheproblemthatitappearsalloftheworkisbeingdonebyaprioriassumptions.ArgumentsfromŽne-tuning2begintolooklesslikethetraditionalTeleologicalargumentandmoreliketheCosmologicalargument.AsWilliamRowe([1998],p.4)notes,botharguments,whiletechnicallyaposteriori,differsubstantially.Theformerrequiresitsproponentstoidentifyfactsabouttheworldfarricher,morecomplicated,andmoredifŽculttoestablishthanthesimplefactthatitexists.Furthermore,theTeleologicalargumentissupposedtobeinductive,sothatthetruthofitspremissesdoesnotguaranteethetruthofitsconclusion.GivenMcMullin’sindifferenceprinciple,however,itseemsveryeasytoestablishthefactthatwarrantsaBayesianargumenttosomethingextra-cosmic.AllonewouldneedestablishwouldbesomefactsuchasthattherewouldbenolifeifprotonsweremoremassivethanMountEverest.Furthermore,thattherewouldbezeroprobabilityofgettinglife(conditionalonthechancehypothesis)comesuncomfortablyclosetoguaranteeingthefalsityofthechancehypothesis.ThealternativetoaMcMullin-styleindifferenceprinciplewouldbesomerestrictingtheoryabouttherangeofvaluesthecosmicparameterscouldhavehad.Suppose,forexample,therewereatheoryaccordingtowhich couldonlyhavebeensomenumberintheinterval{10-10,1010}.Alsosupposeitwereshownthatlifecouldevolveonlyif wereexceptionallycloseto1.Inthiscasewecanimaginehavingdiscoveredthatlifeconstrained toanintervalsufŽcientlylargetomake ’sactuallyfallinginthatintervalunsurprising.Thiswouldenableadvocatesoftheextra-cosmictoavoidDavies’sobjection.Thepriceofsuchatheory,however,istheappearanceofarbitrariness.Proponentsofsuchatheorywouldhavetoexplainwhatpreventstheparametervaluesfrombeingjustalittlebitbiggerthantheirtheoreticalmaxima.TheremaybeintuitionsatworksuggestinganimplicitrangeforanygivencosmicparameterP.LetNstandforthenumericalvalueofP.Nowsupposeonethoughttheremighthavebeennouniverseatall,andthatonerepresentedthispossibilitytooneselfasasituationwhereineverycosmicparametertakesThereIsNoAdequateDefinitionof‘Fine-tunedforLife’347 avalueofzero.IfonebelievedthatthevalueofPisNbutcouldhavebeenzero,thenonemightreasonablysupposePcouldhavetakenanyvalueintheinterval{0,N}.TheupshotofthisisthatasNgetslarger,sodoestheperceivedrangeofpossiblevaluesforP.WecanseeLeslieworkingwiththisintuitionashetriestoputhisdisparatecasesofŽne-tuningonthesamefooting....forcestrengthsandparticlemassesaredistributedacrossenormousranges.Thenuclearstrongforceis(roughly)ahundredtimesstrongerthanelectromagnetism,whichisinturntenthousandtimesstrongerthanthenuclearweakforce,whichisitselfsometenthousandbillionbillionbilliontimesstrongerthangravity.Sowecanwellbeimpressedbyanyapparentneedforaforcetobe‘justright’eventowithinafactoroften,letalonetowithinonepartinahundredorin10100–especiallywhennobodyissurewhythestrongestforcetugsanymorepowerfullythantheweakest.(Leslie[1989],p.6)Lesliesays,ineffect,thatforallweknowthestrongestforcecouldhavehadthestrengthoftheweakestforce;thatis,thestrongestforcecouldhavehadavalueveryclosetozero.Andsincethestrongestforcecouldhavebeenasweakastheweakestforce,implicitlythestrongestforcecouldhavebeenanystrengthbetweenthestrengthoftheweakestforceanditsactualstrength.ThusLeslieimaginesawiderangeofpossiblevaluesforthecosmicparameters,includingthosecosmicparameterswhichtakelargevalues.Suchintuitions,however,arenosubstituteforawell-groundedtheoryofrangeandprobabilitydistribution.Fewsuchtheoriesareonoffer,perhapsforthereasonsalreadyindicated.JohnEarmanandJesusMosterin([1999],pp.31–34)notethatattemptshavebeenmadetoprovideameasurefortherangeofFriedmann–Robertson–Walkermodelsoftheuniverse.Astheynote,however,thesetheoriesdonotworkintheabsenceofaspeciŽcationoftheprobabilitydistributionoverthesemeasures.TheHawkinggroupprovidesnosuchspeciŽcationwithrespecttoFriedmann–Robertson–Walkermodels.TheBelinskii–Khalatnikovgroupdoes,butonlybymakingthe(suspect)assumptionthatrangesofequalareahaveequalprobabilitiesofhousingauniverse.Giventhattherearenowell-groundedtheoriesofrangeandprobabilitydistributionforthecosmicparameters,andgiventhedrawbacksofendorsingMcMullin’sindifferenceprinciple,itseemsthatthosewhoarguetosomethingextra-cosmiccannotbasetheirargumentsontheuniverse’sbeingŽne-tuned2.III.Leslie’sConditionalProbabilityAccountTheprecedingobjectionstoŽne-tuning2presupposethatthelife-permittingparametervaluesmustbesetagainstabackgroundconsistingofallpossibleparametervalues.Leslie,however,contendsthatweneednotconcern348NeilA.Manson ourselveswithallpossiblevalues.Iflife-permittinguniverseswererarewithinthesetofpossibleuniversesthatareverymuchlikethisone,hesays,thatitselfwouldbesurprising.Hemakesthispointbytellingthestoryoftheyonthewall.Awallbearsay(oratinygroupofies)surroundedbyalargishemptyarea.They(oroneofthegroup)ishitbyabullet.Withappropriatebackgroundassumptions...wemightfairlyconŽdentlysay,‘Manybulletsarehittingthewalland/oramarksmanŽredthisparticularbullet’,with-outbotheringwhetherdistantareasofthewallarethickwithies.Allthatisrelevantisthattherearenofurtherieslocally(Leslie[1989],pp.17–18).Lesliethusthinksheneednotestablishthatonlyanextremelytinyareaofthepossibilityspaceforuniversesislife-permitting;heonlyneedconsiderthe‘localarea’ofuniverses.Thisisimportant,hethinks,becauseweareignorantofthefeaturesofpossibleuniversesthatareradicallydifferentfromours.ForallweknowwemightŽndthatlife-permittinguniversesareabundantoncewestartconsideringradicallydifferentuniverses.Thatwouldnotmatter,justasthefactthathydrogenisthemostcommonelementintheuniversewouldmakeitnolesssuspiciousthatadeadman’slungsarefullofhydrogengas.ThuswehaveathirdproposeddeŽnitionofŽne-tuning,andwecandubparametersmeetingthisdescription‘Žne-tuned3’.Def.3:AcosmicparameterPisŽne-tunedforlifeifandonlyiftheprobabilitythatPtakesalife-permittingvalue(conditionalonselectingavaluefromP’slocalarea)isextremelylow.Letmeeshthisoutabit.Wearetoimaginethatthereisaspacemappingpossibleuniverses.Withinthisspacetherewillbecontiguousportionssuchthatouruniverseisrepresentedsomewherewithintheirboundaries.Someoftheseportionswillbegerrymandered,whileothers(thesortLesliehasinmind,presumably)won’t.Letuscallthelatterkindofportions‘areas’.Thusifthespaceofpossibleuniversesisunbounded(asMcMullinsuggests),thenthepointrepresentingouruniversewillhaveaninŽnitenumberofareasencompassingit.Giventhispicture,whatisitforanareatobelocal?Iseenonaturalanswertothisquestion.Surelyitisunacceptabletoidentifyas‘local’toouruniverseanyareasuchthatthatareaisjustlargeenoughtomakelife-permittinguniversesrarewithinitsbounds.Supposing,contrarytofact,thatthetheoreticalinvestigationsofphysicalcosmologistsrevealedthatlifecouldhaveevolvedhad beenanynumberintheinterval{10-10,1010},butthatlifecouldnothaveevolvedhad beenanynumberintheinterval{1010,10100}.Itwouldnotbefairplaytoarguetosomethingextra-cosmiconthegroundsthatlife-permittingvaluesfor areextremelyrareintheinterval{10-10,10100}.Ifsuchamanoeuvrewerepermissible,then(aswithŽne-tuning2givenMcMullin’sindifferenceprinciple)therulesofthegameareThereIsNoAdequateDefinitionof‘Fine-tunedforLife’349 suchastomakeitfartooeasyforaparametertocountasŽne-tuned3.Alladvocatesoftheextra-cosmicwouldneeddoisexpandthe‘local’areauntilitisbigenoughtomakethelife-permittingportionofitrelativelyminuscule.Thenagain,ifthiswerepermissible,thosescepticalofargumentstoextra-cosmicentitiescouldretortthat doesn’tneedŽne-tuning,becauselife-permittinguniversesareexceedinglycommonintheinterval{ +( /1055), -( /1055)}.Thisisafool’sgame.WearedrawnintoitonlyifwearepersuadedbyLeslie’sstoryoftheyonthewall.Thatstoryworks,however,onlybecauseLeslieillicitlyimportsaperspective.Weknowhowbigweare,weknowhowbigiesarerelativetous,andweknowwhatitisforanemptyareasurroundingaytobe‘largish’relativetoay.Thereisnocorrespondinglynaturalperspectivewhenitcomestosurveyingthespaceofsetsofpossibleparametervalues.Giventhatthereisnosuchperspective,IhavetoconcludethatŽne-tuning3,likeŽne-tuning1andŽne-tuning2isaninadequatebasisonwhichtoarguetosomethingextra-cosmic.IfthereissomedeŽnitionof‘Žne-tunedforlife’thatcanfunctiontogenerateargumentstothingsextra-cosmic,Ihaveyettoencounterit.REFERENCESBarrow,J.D.andTipler,F.J.1986.TheAnthropicCosmologicalPrinciple.NewYork,NewYork:OxfordUniversityPress.Carter,B.1993.‘TheAnthropicSelectionPrincipleandtheUltra-DarwinianSynthesis’,inF.BertolaandU.Curi(eds),TheAnthropicPrinciple:ProceedingsoftheSecondVeniceConferenceonCosmologyandPhilosophy.NewYork,NewYork:CambridgeUniversityPress,33–66.Carter,B.1998.‘LargeNumberCoincidencesandtheAnthropicPrincipleinCosmology’,inJ.Leslie(ed.),PhysicalCosmologyandPhilosophy.NewYork,NewYork:Macmillan,131–9.Clifton,R.1991.‘CriticalNotice,Universes’,PhilosophicalQuarterly41,339–44.Craig,W.L.1990.‘TheTeleologicalArgumentandtheAnthropicPrinciple’,inW.L.CraigandM.S.McLeod(eds),TheLogicofRationalTheism:ExploratoryEssays.Lewiston,NewYork:TheEdwinMellenPress,127–53.Davies,P.1992.TheMindofGod.NewYork,NewYork:Simon&Schuster.Davis,J.J.1987.‘TheDesignArgument,Cosmic“FineTuning,”andtheAnthropicPrinciple’,PhilosophyofReligion22,139–50.Dingle,H.1937.‘ModernAristotelianism’,Nature139,784–6.Earman,J.andMosterin,J.1999.‘ACriticalLookatInationaryCosmology’,PhilosophyofScience66,1–49.Hawking,S.1988.ABriefHistoryofTime.NewYork,NewYork:BantamBooks.Leslie,J.1989.Universes.NewYork,NewYork:Routledge.McMullin,E.1993.‘IndifferencePrincipleandAnthropicPrincipleinCosmology’,StudiesintheHistoryandPhilosophyofScience24,359–89.Rowe,W.L.1998.TheCosmologicalArgument.NewYork,NewYork:FordhamUniversityPress.Smolin,L.1997.TheLifeoftheCosmos.NewYork,NewYork:OxfordUniversityPress.350NeilA.Manson Swinburne,R.1989.‘ArgumentfromtheFine-TuningoftheUniverse’,inJohnLeslie(ed.),PhysicalCosmologyandPhilosophy.NewYork,NewYork:Macmillan,154–73.vanInwagen,P.1993.BookreviewofUniverses,inFaithandPhilosophy10,439–43.Received7March2000NeilA.Manson,DepartmentofPhilosophy,UniversityofAberdeen,AberdeenAB243UB,Scotland,UK.E-mail:n.manson@abdn.ac.ukThereIsNoAdequateDefinitionof‘Fine-tunedforLife’351