万物简史英文版_比尔·布莱森- 第44节

in　an　attempt　to　draw　everything　together；　physicists　have　e　up　with　something　calledsuperstring　theory。　this　postulates　that　all　those　little　things　like　quarks　and　leptons　that　wehad　previously　thought　of　as　particles　are　actually　鈥渟trings鈥濃�攙ibrating　strands　of　energy　thatoscillate　in　eleven　dimensions；　consisting　of　the　three　we　know　already　plus　time　and　sevenother　dimensions　that　are；　well；　unknowable　to　us。　the　strings　are　very　tiny鈥攖iny　enough　topass　for　point　particles。

by　introducing　extra　dimensions；　superstring　theory　enables　physicists　to　pull　togetherquantum　laws　and　gravitational　ones　into　one　paratively　tidy　package；　but　it　also　meansthat　anything　scientists　say　about　the　theory　begins　to　sound　worryingly　like　the　sort　ofthoughts　that　would　make　you　edge　away　if　conveyed　to　you　by　a　stranger　on　a　park　bench。

here；　for　example；　is　the　physicist　michio　kaku　explaining　the　structure　of　the　universe　froma　superstring　perspective：　鈥渢he　heterotic　string　consists　of　a　closed　string　that　has　two　types　ofvibrations；　clockwise　and　counterclockwise；　which　are　treated　differently。　the　clockwisevibrations　live　in　a　ten…dimensional　space。　the　counterclockwise　live　in　a　twenty…six…dimensional　space；　of　which　sixteen　dimensions　have　been　pactified。　（we　recall　that　inkaluza鈥檚　original　five…dimensional；　the　fifth　dimension　was　pactified　by　being　wrappedup　into　a　circle。）鈥潯�and　so　it　goes；　for　some　350　pages。

string　theory　has　further　spawned　something　called　鈥渕　theory；鈥潯�which　incorporatessurfaces　known　as　membranes鈥攐r　simply　鈥渂ranes鈥潯�to　the　hipper　souls　of　the　world　ofphysics。　i鈥檓　afraid　this　is　the　stop　on　the　knowledge　highway　where　most　of　us　must　get　off。

here　is　a　sentence　from　the　new　york　times；　explaining　this　as　simply　as　possible　to　a　generalaudience：　鈥渢he　ekpyrotic　process　begins　far　in　the　indefinite　past　with　a　pair　of　flat　emptybranes　sitting　parallel　to　each　other　in　a　warped　five…dimensional　space。　。　。　。　the　two　branes；which　form　the　walls　of　the　fifth　dimension；　could　have　popped　out　of　nothingness　as　aquantum　fluctuation　in　the　even　more　distant　past　and　then　drifted　apart。鈥潯�no　arguing　withthat。　no　understanding　it　either。　ekpyrotic；　incidentally；　es　from　the　greek　word　for鈥渃onflagration。鈥�

matters　in　physics　have　now　reached　such　a　pitch　that；　as　paul　davies　noted　in　nature；　it　is鈥渁lmost　impossible　for　the　non…scientist　to　discriminate　between　the　legitimately　weird　andthe　outright　crackpot。鈥潯�the　question　came　interestingly　to　a　head　in　the　fall　of　2002　when　twofrench　physicists；　twin　brothers　igor　and　grickha　bogdanov；　produced　a　theory　of　ambitiousdensity　involving　such　concepts　as　鈥渋maginary　time鈥潯�and　the　鈥渒ubo…schwinger…martincondition；鈥潯�and　purporting　to　describe　the　nothingness　that　was　the　universe　before　the　bigbang鈥攁　period　that　was　always　assumed　to　be　unknowable　（since　it　predated　the　birth　ofphysics　and　its　properties）。

almost　at　once　the　bogdanov　paper　excited　debate　among　physicists　as　to　whether　it　wastwaddle；　a　work　of　genius；　or　a　hoax。　鈥渟cientifically；　it鈥檚　clearly　more　or　less　pletenonsense；鈥潯�columbia　university　physicist　peter　woit　told　the　new　york　times；　鈥渂ut　thesedays　that　doesn鈥檛　much　distinguish　it　from　a　lot　of　the　rest　of　the　literature。鈥�

karl　popper；　whom　steven　weinberg　has　called　鈥渢he　dean　of　modern　philosophers　ofscience；鈥潯�once　suggested　that　there　may　not　be　an　ultimate　theory　for　physics鈥攖hat；　rather；every　explanation　may　require　a　further　explanation；　producing　鈥渁n　infinite　chain　of　more　andmore　fundamental　principles。鈥潯�a　rival　possibility　is　that　such　knowledge　may　simply　bebeyond　us。　鈥渟o　far；　fortunately；鈥潯�writes　weinberg　in　dreams　of　a　final　theory；　鈥渨e　do　notseem　to　be　ing　to　the　end　of　our　intellectual　resources。鈥�

almost　certainly　this　is　an　area　that　will　see　further　developments　of　thought；　and　almostcertainly　these　thoughts　will　again　be　beyond　most　of　us。

while　physicists　in　the　middle　decades　of　the　twentieth…century　were　looking　perplexedlyinto　the　world　of　the　very　small；　astronomers　were　finding　no　less　arresting　an　inpletenessof　understanding　in　the　universe　at　large。

when　we　last　met　edwin　hubble；　he　had　determined　that　nearly　all　the　galaxies　in　our　fieldof　view　are　flying　away　from　us；　and　that　the　speed　and　distance　of　this　retreat　are　neatlyproportional：　the　farther　away　the　galaxy；　the　faster　it　is　moving。　hubble　realized　that　thiscould　be　expressed　with　a　simple　equation；　ho　=　v/d　（where　ho　is　the　constant；　v　is　therecessional　velocity　of　a　flying　galaxy；　andd　its　distance　away　from　us）。　ho　has　been　knownever　since　as　the　hubble　constant　and　the　whole　as　hubble鈥檚　law。　using　his　formula；　hubblecalculated　that　the　universe　was　about　two　billion　years　old；　which　was　a　little　awkwardbecause　even　by　the　late　1920s　it　was　fairly　obvious　that　many　things　within　the　universe鈥攏ot　least　earth　itself鈥攚ere　probably　older　than　that。　refining　this　figure　has　been　an　ongoingpreoccupation　of　cosmology。

almost　the　only　thing　constant　about　the　hubble　constant　has　been　the　amount　ofdisagreement　over　what　value　to　give　it。　in　1956；　astronomers　discovered　that　cepheidvariables　were　more　variable　than　they　had　thought；　they　came　in　two　varieties；　not　one。　thisallowed　them　to　rework　their　calculations　and　e　up　with　a　new　age　for　the　universe　offrom　7　to　20　billion　years鈥攏ot　terribly　precise；　but　at　least　old　enough；　at　last；　to　embrace　theformation　of　the　earth。

in　the　years　that　followed　there　erupted　a　long…running　dispute　between　allan　sandage；　heirto　hubble　at　mount　wilson；　and　g茅rard　de　vaucouleurs；　a　french…born　astronomer　based　atthe　university　of　texas。　sandage；　after　years　of　careful　calculations；　arrived　at　a　value　for　thehubble　constant　of　50；　giving　the　universe　an　age　of　20　billion　years。　de　vaucouleurs　wasequally　certain　that　the　hubble　constant　was　100。

2this　would　mean　that　the　universe　wasonly　half　the　size　and　age　that　sandage　believed鈥攖en　billion　years。　matters　took　a　furtherlurch　into　uncertainty　when　in　1994　a　team　from　the　carnegie　observatories　in　california；using　measures　from　the　hubble　space　telescope；　suggested　that　the　universe　could　be　as　littleas　eight　billion　years　old鈥攁n　age　even　they　conceded　was　younger　than　some　of　the　starswithin　the　universe。　in　february　2003；　a　team　from　nasa　and　the　goddard　space　flightcenter　in　maryland；　using　a　new；　far…reaching　type　of　satellite　called　the　wilkinsonmicrowave　anistropy　probe；　announced　with　some　confidence　that　the　age　of　the　universe　is13。7　billion　years；　give　or　take　a　hundred　million　years　or　so。　there　matters　rest；　at　least　forthe　moment。

the　difficulty　in　making　final　determinations　is　that　there　are　often　acres　of　room　forinterpretation。　imagine　standing　in　a　field　at　night　and　trying　to　decide　how　far　away　twodistant　electric　lights　are。　using　fairly　straightforward　tools　of　astronomy　you　can　easilyenough　determine　that　the　bulbs　are　of　equal　brightness　and　that　one　is；　say；　50　percent　moredistant　than　the　other。　but　what　you　can鈥檛　be　certain　of　is　whether　the　nearer　light　is；　let　ussay；　a　58…watt　bulb　that　is　122　feet　away　or　a　61…watt　light　that　is　119　feet；　8　inches　away。　ontop　of　that　you　must　make　allowances　for　distortions　caused　by　variations　in　the　earth鈥檚atmosphere；　by　intergalactic　dust；　contaminating　light　from　foreground　stars；　and　many　otherfactors。　the　upshot　is　that　your　putations　are　necessarily　based　on　a　series　of　nestedassumptions；　any　of　which　could　be　a　source　of　contention。　there　is　also　the　problem　thataccess　to　telescopes　is　always　at　a　premium　and　historically　measuring　red　shifts　has　beennotably　costly　in　telescope　time。　it　could　take　all　night　to　get　a　single　exposure。　inconsequence；　astronomers　have　sometimes　been　pelled　（or　willing）　to　base　conclusionson　notably　scanty　evidence。　in　cosmology；　as　the　journalist　geoffrey　carr　has　suggested；　wehave　鈥渁　mountain　of　theory　built　on　a　molehill　of　evidence。鈥潯�or　as　martin　rees　has　put　it：

鈥渙ur　present　satisfaction　＇with　our　state　of　understanding＇　may　reflect　the　paucity　of　the　datarather　than　the　excellence　of　the　theory。鈥�

this　uncertainty　applies；　incidentally；　to　relatively　nearby　thin