A Short History of Nearly Everything-第24章

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lishdictionary；　piled　a　decade　before　einsteins　theory；　recognizes　c　as　a　symbol　for　many　things；　from　carbonto　cricket；　but　makes　no　mention　of　it　as　a　symbol　for　light　or　swiftness。

“as　the　creation　of　a　single　mind；”　they　write；　“it　is　undoubtedly　the　highest　intellectualachievement　of　humanity；”　which　is　of　course　as　good　as　a　pliment　can　get。

in　1907；　or　so　it　has　sometimes　been　written；　albert　einstein　saw　a　workman　fall　off　a　roofand　began　to　think　about　gravity。　alas；　like　many　good　stories　this　one　appears　to　beapocryphal。　according　to　einstein　himself；　he　was　simply　sitting　in　a　chair　when　the　problemof　gravity　occurred　to　him。

actually；　what　occurred　to　einstein　was　something　more　like　the　beginning　of　a　solution　tothe　problem　of　gravity；　since　it　had　been　evident　to　him　from　the　outset　that　one　thing　missingfrom　the　special　theory　was　gravity。　what　was　“special”　about　the　special　theory　was　that　itdealt　with　things　moving　in　an　essentially　unimpeded　state。　but　what　happened　when　a　thingin　motion—light；　above　all—encountered　an　obstacle　such　as　gravity？　it　was　a　question　thatwould　occupy　his　thoughts　for　most　of　the　next　decade　and　lead　to　the　publication　in　early1917　of　a　paper　entitled　“cosmological　considerations　on　the　general　theory　of　relativity。”

the　special　theory　of　relativity　of　1905　was　a　profound　and　important　piece　of　work；　ofcourse；　but　as　c。　p。　snow　once　observed；　if　einstein　hadn’t　thought　of　it　when　he　did　someoneelse　would　have；　probably　within　five　years；　it　was　an　idea　waiting　to　happen。　but　the　generaltheory　was　something　else　altogether。　“without　it；”　wrote　snow　in　1979；　“it　is　likely　that　weshould　still　be　waiting　for　the　theory　today。”

with　his　pipe；　genially　self…effacing　manner；　and　electrified　hair；　einstein　was　too　splendida　figure　to　remain　permanently　obscure；　and　in　1919；　the　war　over；　the　world　suddenlydiscovered　him。　almost　at　once　his　theories　of　relativity　developed　a　reputation　for　beingimpossible　for　an　ordinary　person　to　grasp。　matters　were　not　helped；　as　david　bodanis　pointsout　in　his　superb　book　e=mc2；　when　the　new　york　times　decided　to　do　a　story；　and—forreasons　that　can　never　fail　to　excite　wonder—sent　the　paper’s　golfing　correspondent；　onehenry　crouch；　to　conduct　the　interview。

crouch　was　hopelessly　out　of　his　depth；　and　got　nearly　everything　wrong。　among　the　morelasting　errors　in　his　report　was　the　assertion　that　einstein　had　found　a　publisher　daring　enoughto　publish　a　book　that　only　twelve　men　“in　all　the　world　could　prehend。”　there　was　nosuch　book；　no　such　publisher；　no　such　circle　of　learned　men；　but　the　notion　stuck　anyway。

soon　the　number　of　people　who　could　grasp　relativity　had　been　reduced　even　further　in　thepopular　imagination—and　the　scientific　establishment；　it　must　be　said；　did　little　to　disturb　themyth。

when　a　journalist　asked　the　british　astronomer　sir　arthur　eddington　if　it　was　true　that　hewas　one　of　only　three　people　in　the　world　who　could　understand　einstein’s　relativity　theories；eddington　considered　deeply　for　a　moment　and　replied：　“i　am　trying　to　think　who　the　thirdperson　is。”　in　fact；　the　problem　with　relativity　wasn’t　that　it　involved　a　lot　of　differentialequations；　lorentz　transformations；　and　other　plicated　mathematics　（though　it　did—eveneinstein　needed　help　with　some　of　it）；　but　that　it　was　just　so　thoroughly　nonintuitive。

in　essence　what　relativity　says　is　that　space　and　time　are　not　absolute；　but　relative　to　boththe　observer　and　to　the　thing　being　observed；　and　the　faster　one　moves　the　more　pronouncedthese　effects　bee。　we　can　never　accelerate　ourselves　to　the　speed　of　light；　and　the　harderwe　try　（and　faster　we　go）　the　more　distorted　we　will　bee；　relative　to　an　outside　observer。

almost　at　once　popularizers　of　science　tried　to　e　up　with　ways　to　make　these　conceptsaccessible　to　a　general　audience。　one　of　the　more　successful　attempts—mercially　atleast—was　the　abc　of　relativity　by　the　mathematician　and　philosopher　bertrand　russell。　init；　russell　employed　an　image　that　has　been　used　many　times　since。　he　asked　the　reader　toenvision　a　train　one　hundred　yards　long　moving　at　60　percent　of　the　speed　of　light。　tosomeone　standing　on　a　platform　watching　it　pass；　the　train　would　appear　to　be　only　eightyyards　long　and　everything　on　it　would　be　similarly　pressed。　if　we　could　hear　thepassengers　on　the　train　speak；　their　voices　would　sound　slurred　and　sluggish；　like　a　recordplayed　at　too　slow　a　speed；　and　their　movements　would　appear　similarly　ponderous。　even　theclocks　on　the　train　would　seem　to　be　running　at　only　four…fifths　of　their　normal　speed。

however—and　here’s　the　thing—people　on　the　train　would　have　no　sense　of　thesedistortions。　to　them；　everything　on　the　train　would　seem　quite　normal。　it　would　be　we　on　theplatform　who　looked　weirdly　pressed　and　slowed　down。　it　is　all　to　do；　you　see；　with　yourposition　relative　to　the　moving　object。

this　effect　actually　happens　every　time　you　move。　fly　across　the　united　states；　and　youwill　step　from　the　plane　a　quinzillionth　of　a　second；　or　something；　younger　than　those　you　leftbehind。　even　in　walking　across　the　room　you　will　very　slightly　alter　your　own　experience　oftime　and　space。　it　has　been　calculated　that　a　baseball　thrown　at　a　hundred　miles　an　hour　willpick　up　0。000000000002　grams　of　mass　on　its　way　to　home　plate。　so　the　effects　of　relativityare　real　and　have　been　measured。　the　problem　is　that　such　changes　are　much　too　small　tomake　the　tiniest　detectable　difference　to　us。　but　for　other　things　in　the　universe—light；gravity；　the　universe　itself—these　are　matters　of　consequence。

so　if　the　ideas　of　relativity　seem　weird；　it　is　only　because　we　don’t　experience　these　sorts　ofinteractions　in　normal　life。　however；　to　turn　to　bodanis　again；　we　all　monly　encounterother　kinds　of　relativity—for　instance　with　regard　to　sound。　if　you　are　in　a　park　and　someoneis　playing　annoying　music；　you　know　that　if　you　move　to　a　more　distant　spot　the　music　willseem　quieter。　that’s　not　because　the　musicis　quieter；　of　course；　but　simply　that　your　positionrelative　to　it　has　changed。　to　something　too　small　or　sluggish　to　duplicate　this　experience—asnail；　say—the　idea　that　a　boom　box　could　seem　to　two　observers　to　produce　two　differentvolumes　of　music　simultaneously　might　seem　incredible。

the　most　challenging　and　nonintuitive　of　all　the　concepts　in　the　general　theory　of　relativityis　the　idea　that　time　is　part　of　space。　our　instinct　is　to　regard　time　as　eternal；　absolute；immutable—nothing　can　disturb　its　steady　tick。　in　fact；　according　to　einstein；　time　is　variableand　ever　changing。　it　even　has　shape。　it　is　bound　up—“inextricably　interconnected；”　instephen　hawking’s　expression—with　the　three　dimensions　of　space　in　a　curious　dimensionknown　as　spacetime。

spacetime　is　usually　explained　by　asking　you　to　imagine　something　flat　but　pliant—amattress；　say；　or　a　sheet　of　stretched　rubber—on　which　is　resting　a　heavy　round　object；　suchas　an　iron　ball。　the　weight　of　the　iron　ball　causes　the　material　on　which　it　is　sitting　to　stretchand　sag　slightly。　this　is　roughly　analogous　to　the　effect　that　a　massive　object　such　as　the　sun（the　iron　ball）　has　on　spacetime　（the　material）：　it　stretches　and　curves　and　warps　it。　now　ifyou　roll　a　smaller　ball　across　the　sheet；　it　tries　to　go　in　a　straight　line　as　required　by　newton’slaws　of　motion；　but　as　it　nears　the　massive　object　and　the　slope　of　the　sagging　fabric；　it　rollsdownward；　ineluctably　drawn　to　the　more　massive　object。　this　is　gravity—a　product　of　thebending　of　spacetime。

every　object　that　has　mass　creates　a　little　depression　in　the　fabric　of　the　cosmos。　thus　theuniverse；　as　dennis　overbye　has　put　it；　is　“the　ultimate　sagging　mattress。”　gravity　on　thisview　is　no　longer　so　much　a　thing　as　an　oute—“not　a　‘force’　but　a　byproduct　of　thewarping　of　spacetime；”　in　the　words　of　the　physicist　michio　kaku；　who　goes　on：　“in　somesense；　gravity　does　not　exist；　what　moves　the　planets　and　stars　is　the　distortion　of　space　andtime。”

of　course　the　sagging　mattress　analogy　can　take　us　only　so　far　because　it　doesn’tincorporate　the　effect　of　time。　but　then　our　brains　can　take　us　only　so　far　because　it　is　sonearly　impossible　to　envision　a　dimension　prising　three　parts　space　to　one　part　time；　allinterwoven　like　the　threads　in　a　plaid　fabric。　at　all　events；　i　think　we　can　agree　that　this　wasan　awfully　big　thought　for　a　young　man　staring　out　the　window　of　a　patent　office　in　thecapital　of　switzerland。

among　much　else；　einstein’s　general　theory　of　relativity　suggested　that　the　universe　mustbe　either　expanding　or　contracting。　but　einstein　was　not　a　cosmologist；　and　he　accepted　theprevailing　wisdom　that　the　universe　was　fixed　and　eternal。　more　or　less　reflexively；　hedropped　into　his　equations　something　called　the　cosmological　constant；　which　arbitrarilycounterbalanced　the　effects　of　gravity；　serving　as　a　kind　of　mathematical　pause　button。　bookson　the　history　of　science　always　forgive　einstein　this　lapse；　but　it　was　actually　a　fairlyappalling　piece　of　science　and　he　knew　it。　he　called　it　“the　biggest　blunder　of　my　life。”

coincidentally；　at　about　the　time　that　einstein　was　affixing　a　cosmological　constant　to　histheory；　at　the　lowell　observatory　in