Character of anthropic reasoning Carter chose to focus on a tautological aspect of his ideas, which has resulted in much confusion. In fact, anthropic reasoning interests scientists because of something that is only implicit in the above formal definitions, namely that humans should give serious consideration to there being other universes with different values of the "fundamental parameters"—that is, the dimensionless physical constants and initial conditions for the Big Bang. Carter and others have argued that life would not be possible in most such universes. In other words, the universe humans live in is fine tuned to permit life. Collins & Hawking (1973) characterized Carter's then-unpublished big idea as the postulate that "there is not one universe but a whole infinite ensemble of universes with all possible initial conditions". If this is granted, the anthropic principle provides a plausible explanation for the fine tuning of our universe: the "typical" universe is not fine-tuned, but given enough universes, a small fraction will be capable of supporting intelligent life. Ours must be one of these, and so the observed fine tuning should be no cause for wonder.
CharActeR Of anthroPic ReasONiNg cartER chOsE tO foCUs oN A tAutOlogICAl asPeCt of hIs idEAs, which hAs rEsultEd In mUch confusIon. in FAct, aNtHropic ReasOniNg interests ScIenTiSTs beCause of sOmethINg THAt is only implIcit in the aBOve FOrmaL DEFinItIons, NamELy thAT humans sHOuld GiVE sERious consIderaTIon To TheRe BeIng oTheR uNivErsEs witH DiFferEnt vALuES Of thE "fundamEntaL paRaMETerS"—That Is, tHe DimensIoNLesS phYSicAl cOnsTaNtS aNd Initial COnDiTionS FOr tHe big BanG. CarTer and otHeRs Have argUEd That life woulD noT bE posSiblE in most such univeRSes. In oTHer wORds, the univErsE hUmAns livE in Is FIne TunEd to peRMit Life. CoLLinS & haWkIng (1973) chARacteRIZeD carTer'S theN-unpUblIShed bIg idEA As the PoStulAte tHAT "therE Is not one unIvErSe But a whole inFiniTe eNsemble of uNiversEs with all Possible iniTiAL cONDitIonS". if This is gRanTeD, thE Anthropic priNcipLe prOvIDes A plAusibLe EXplAnAtion For the Fine tuniNg of our uniVErse: the "tYPicAl" UniVerSe is not fine-tUneD, but given eNOUgh univeRSES, a sMall fracTiON WilL bE CapaBLE of supPoRtInG intElliGenT life. ouRS must bE ONe of tHese, and so ThE Observed fine TunINg sHOulD be nO cAuSe FoR woNder.