A Short History of Nearly Everything-第4章

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times　in　2001。

the　big　bang　theory　isn’t　about　the　bang　itself　but　about　what　happened　after　the　bang。

not　long　after；　mind　you。　by　doing　a　lot　of　math　and　watching　carefully　what　goes　on　inparticle　accelerators；　scientists　believe　they　can　look　back　to　10…43seconds　after　the　moment　ofcreation；　when　the　universe　was　still　so　small　that　you　would　have　needed　a　microscope　tofind　it。　we　mustn’t　swoon　over　every　extraordinary　number　that　es　before　us；　but　it　isperhaps　worth　latching　on　to　one　from　time　to　time　just　to　be　reminded　of　their　ungraspableand　amazing　breadth。　thus　10…43is　0。0000000000000000000000000000000000000000001；　orone　10　million　trillion　trillion　trillionths　of　a　second。

a　word　on　scientific　notation：　since　very　large　numbers　are　cumbersome　to　write　and　nearly　impossible　to　read；　scientistsuse　a　shorthand　involving　powers　（or　multiples）　of　ten　in　which；　for　instance；　10；000；000；000　is　written　1010　and　6；500；000bees　6。5　x　106。　the　principle　is　based　very　simply　on　multiples　of　ten：　10　x　10　（or　100）　bees　102；　10　x　10　x　10　（or1；000）　is　103；　and　so　on；　obviously　and　indefinitely。　the　little　superscript　number　signifies　the　number　of　zeroes　followingthe　larger　principal　number。　negative　notations　provide　latter　in　print　（especially　essentially　a　mirror　image；　with　thesuperscript　number　indicating　the　number　of　spaces　to　the　right　of　the　decimal　point　（so　10…4　means　0。0001）。　though　i　salutethe　principle；　it　remains　an　amazement　to　me　that　anyone　seeing　〃1。4　x　109　km3’　would　see　at　once　that　that　signifies　1。4most　of　what　we　know；　or　believe　we　know；　about　the　early　moments　of　the　universe　isthanks　to　an　idea　called　inflation　theory　first　propounded　in　1979　by　a　junior　particlephysicist；　then　at　stanford；　now　at　mit；　named　alan　guth。　he　was　thirty…two　years　old　and；by　his　own　admission；　had　never　done　anything　much　before。　he　would　probably　never　havehad　his　great　theory　except　that　he　happened　to　attend　a　lecture　on　the　big　bang　given　bynone　other　than　robert　dicke。　the　lecture　inspired　guth　to　take　an　interest　in　cosmology；　andin　particular　in　the　birth　of　the　universe。

the　eventual　result　was　the　inflation　theory；　which　holds　that　a　fraction　of　a　moment　afterthe　dawn　of　creation；　the　universe　underwent　a　sudden　dramatic　expansion。　it　inflated—ineffect　ran　away　with　itself；　doubling　in　size　every　10…34seconds。　the　whole　episode　may　havelasted　no　more　than　10…30seconds—that’s　one　million　million　million　million　millionths　of　asecond—but　it　changed　the　universe　from　something　you　could　hold　in　your　hand　tosomething　at　least　10；000；000；000；000；000；000；000；000　times　bigger。　inflation　theoryexplains　the　ripples　and　eddies　that　make　our　universe　possible。　without　it；　there　would　be　noclumps　of　matter　and　thus　no　stars；　just　drifting　gas　and　everlasting　darkness。

according　to　guth’s　theory；　at　one　ten…millionth　of　a　trillionth　of　a　trillionth　of　a　trillionthof　a　second；　gravity　emerged。　after　another　ludicrously　brief　interval　it　was　joined　byelectromagnetism　and　the　strong　and　weak　nuclear　forces—the　stuff　of　physics。　these　werejoined　an　instant　later　by　swarms　of　elementary　particles—the　stuff　of　stuff。　from　nothing　atall；　suddenly　there　were　swarms　of　photons；　protons；　electrons；　neutrons；　and　much　else—between　1079and　1089of　each；　according　to　the　standard　big　bang　theory。

such　quantities　are　of　course　ungraspable。　it　is　enough　to　know　that　in　a　single　crackinginstant　we　were　endowed　with　a　universe　that　was　vast—at　least　a　hundred　billion　light…yearsacross；　according　to　the　theory；　but　possibly　any　size　up　to　infinite—and　perfectly　arrayed　forthe　creation　of　stars；　galaxies；　and　other　pleystems。

what　is　extraordinary　from　our　point　of　view　is　how　well　it　turned　out　for　us。　if　theuniverse　had　formed　just　a　tiny　bit　differently—if　gravity　were　fractionally　stronger　orweaker；　if　the　expansion　had　proceeded　just　a　little　more　slowly　or　swiftly—then　there　mightnever　have　been　stable　elements　to　make　you　and　me　and　the　ground　we　stand　on。　had　gravitybeen　a　trifle　stronger；　the　universe　itself　might　have　collapsed　like　a　badly　erected　tent；without　precisely　the　right　values　to　give　it　the　right　dimensions　and　density　and　ponentparts。　had　it　been　weaker；　however；　nothing　would　have　coalesced。　the　universe　would　haveremained　forever　a　dull；　scattered　void。

this　is　one　reason　that　some　experts　believe　there　may　have　been　many　other　big　bangs；perhaps　trillions　and　trillions　of　them；　spread　through　the　mighty　span　of　eternity；　and　that　thereason　we　exist　in　this　particular　one　is　that　this　is　one　we　could　exist　in。　as　edward　p。　tryonof　columbia　university　once　put　it：　“in　answer　to　the　question　of　why　it　happened；　i　offer　themodest　proposal　that　our　universe　is　simply　one　of　those　things　which　happen　from　time　tobillion　cubic　kilometers；　and　no　less　a　wonder　that　they　would　choose　the　former　over　the　in　a　book　designed　for　the　generalreader；　where　the　example　was　found）。　on　the　assumption　that　many　general　readers　are　as　unmathematical　as　i　am；　i　will　usethem　sparingly；　though　they　are　occasionally　unavoidable；　not　least　in　a　chapter　dealing　with　things　on　a　cosmic　scale。

time。”　to　which　adds　guth：　“although　the　creation　of　a　universe　might　be　very　unlikely；tryon　emphasized　that　no　one　had　counted　the　failed　attempts。”

martin　rees；　britain’s　astronomer　royal；　believes　that　there　are　many　universes；　possibly　aninfinite　number；　each　with　different　attributes；　in　different　binations；　and　that　we　simplylive　in　one　that　bines　things　in　the　way　that　allows　us　to　exist。　he　makes　an　analogy　witha　very　large　clothing　store：　“if　there　is　a　large　stock　of　clothing；　you’re　not　surprised　to　find　asuit　that　fits。　if　there　are　many　universes；　each　governed　by　a　differing　set　of　numbers；　therewill　be　one　where　there　is　a　particular　set　of　numbers　suitable　to　life。　we　are　in　that　one。”

rees　maintains　that　six　numbers　in　particular　govern　our　universe；　and　that　if　any　of　thesevalues　were　changed　even　very　slightly　things　could　not　be　as　they　are。　for　example；　for　theuniverse　to　exist　as　it　does　requires　that　hydrogen　be　converted　to　helium　in　a　precise　butparatively　stately　manner—specifically；　in　a　way　that　converts　seven　one…thousandths　ofits　mass　to　energy。　lower　that　value　very　slightly—from　0。007　percent　to　0。006　percent；say—and　no　transformation　could　take　place：　the　universe　would　consist　of　hydrogen　andnothing　else。　raise　the　value　very　slightly—to　0。008　percent—and　bonding　would　be　sowildly　prolific　that　the　hydrogen　would　long　since　have　been　exhausted。　in　either　case；　withthe　slightest　tweaking　of　the　numbers　the　universe　as　we　know　and　need　it　would　not　be　here。

i　should　say　that　everything　is　just　right　so　far。　in　the　long　term；　gravity　may　turn　out　to　be　alittle　too　strong；　and　one　day　it　may　halt　the　expansion　of　the　universe　and　bring　it　collapsingin　upon　itself；　till　it　crushes　itself　down　into　another　singularity；　possibly　to　start　the　wholeprocess　over　again。　on　the　other　hand　it　may　be　too　weak　and　the　universe　will　keep　racingaway　forever　until　everything　is　so　far　apart　that　there　is　no　chance　of　material　interactions；　sothat　the　universe　bees　a　place　that　is　inert　and　dead；　but　very　roomy。　the　third　option　isthat　gravity　is　just　right—“critical　density”　is　the　cosmologists’　term　for　it—and　that　it　willhold　the　universe　together　at　just　the　right　dimensions　to　allow　things　to　go　on　indefinitely。

cosmologists　in　their　lighter　moments　sometimes　call　this　the　goldilocks　effect—thateverything　is　just　right。　（for　the　record；　these　three　possible　universes　are　known　respectivelyas　closed；　open；　and　flat。）now　the　question　that　has　occurred　to　all　of　us　at　some　point　is：　what　would　happen　if　youtraveled　out　to　the　edge　of　the　universe　and；　as　it　were；　put　your　head　through　the　curtains？

where　would　your　head　be　if　it　were　no　longer　in　the　universe？　what　would　you　find　beyond？

the　answer；　disappointingly；　is　that　you　can　never　get　to　the　edge　of　the　universe。　that’s　notbecause　it　would　take　too　long　to　get　there—though　of　course　it　would—but　because　even　ifyou　traveled　outward　and　outward　in　a　straight　line；　indefinitely　and　pugnaciously；　you　wouldnever　arrive　at　an　outer　boundary。　instead；　you　would　e　back　to　where　you　began　（atwhich　point；　presumably；　you　would　rather　lose　heart　in　the　exercise　and　give　up）。　the　reasonfor　this　is　that　the　universe　bends；　in　a　way　we　can’t　adequately　imagine；　in　conformance　witheinstein’s　theory　of　relativity　（which　we　will　get　to　in　due　course）。　for　the　moment　it　isenough　to　know　that　we　are　not　adrift　in　some　large；　ever…expanding　bubble。　rather；　spacecurves；　in　a　way　that　allows　it　to　be　boundless　but　finite。　space　cannot　even　properly　be　saidto　be　expanding　because；　as　the　physicist　and　nobel　laureate　steven　weinberg　notes；　“solarsystems　and　galaxies　are　not　expanding；　and　space　itself　is　not　expanding。”　rather；　thegalaxies　are　rushing　apart。　it　is　all　something　of　a　challenge　to　intuition。　or　as　the　biologist　j。

b。　s。　haldane　once　famously　observed：　“the　universe　is　not　only　queerer　than　we　suppose；　itis　queerer　than　we　can　suppose。”

the　analogy　that　is　usually　given　for　explaining　the　curvature　of　space　is　to　try　t