pale blue dot -carl sagan-第5章

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ces　of　the　Church　threatened　the　aged　astronomer　with　torture　if　he　persisted　in　teaching　the　abominable　doctrine　that　the　Earth　moved。　He　was　sentenced　to　a　kind　of　house　arrest　for　the　remainder　of　his　life。

A　generation　or　two　later；　by　the　time　Isaac　Newton　demonstrated　that　simple　and　elegant　physics　could　quantitatively　explain—and　predict—all　the　observed　lunar　and　planetary　motions　（provided　you　assumed　the　Sun　at　the　center　of　the　Solar　System）；　the　geocentrist　conceit　eroded　further。

In　1725；　in　an　attempt　to　discover　stellar　parallax；　the　painstaking　English　amateur　astronomer　James　Bradley　stumbled　on　the　aberration　of　light。　The　term　〃aberration；〃　I　suppose；　conveys　something　of　the　unexpectedness　of　the　discovery。　When　observed　over　the　course　of　a　year；　stars　were　found　to　trace　little　ellipses　against　the　sky。　But　all　the　stars　were　found　to　do　so。　This　could　not　be　stellar　parallax；　where　we　would　expect　a　big　parallax　for　nearby　stars　and　an　indetectible　one　for　faraway　stars。　Instead；　aberration　is　similar　to　how　raindrop　falling　directly　down　on　a　speeding　auto　seem　to　the　passenger；　to　be　falling　at　a　slant；　the　faster　the　car　goes；　the　steeper　the　slant。　If　the　Earth　were　stationary　at　the　center　of　the　Universe。　and　not　speeding　in　its　orbit　around　the　Sun；　Bradley　would　nor　have　found　the　aberration　of　light。　It　was　a　pelling　demonstration　that　the　Earth　revolved　about　the　Sun。　It　convinced　most　astronomers　and　some　others　but　not；　Bradley　thought；　the　〃Anti…Copernicans。〃

But　not　until　1837　did　direct　observations　of　the　stars　prove　in　the　clearest　way　that　the　Earth　is　indeed　circling　the　Sun。　The　long…debated　annual　parallax　was　at　last　discovered—not　by　better　arguments；　but　by　better　instruments。　Because　explaining　what　it　means　is　much　more　straightforward　than　explaining　the　aberration　of　light；　its　discovery　was　very　important。　It　pounded　the　final　nail　into　the　coffin　of　geocentrism。　You　need　only　look　at　your　finger　with　your　left　eye　and　then　with　your　right　and　see　it　seem　to　move。　Everyone　can　understand　parallax。

By　the　nineteenth　century；　all　scientific　geocentrists　had　been　converted　or　rendered　extinct。　Once　most　scientists　had　been　convinced；　informed　public　opinion　had　swiftly　changed；　in　some　countries　in　a　mere　three　or　four　generations。　Of　course；　in　the　time　of　Galileo　and　Newton　and　even　much　later；　there　were　still　some　who　objected；　who　tried　to　prevent　the　new　Sun…centered　Universe　from　being　accepted；　or　even　known。　And　there　were　many　who　at　least　harbored　secret　reservations。

By　the　late　twentieth　century；　just　in　case　there　were　any　holdouts；　we　have　been　able　to　settle　the　matter　directly。　We've　been　able　to　test　whether　we　live　in　an　Earth…centered　system　with　planets　affixed　to　transparent　crystal　spheres；　or　in　a　Sun…centered　system　with　planets　controlled　at　a　distance　by　the　gravity　of　the　Sun。　We　have；　for　example；　probed　the　planets　with　radar。　When　we　bounce　a　signal　off　a　moon　of　Saturn；　we　receive　no　radio　echo　from　a　nearer　crystal　sphere　attached　to　Jupiter。　Our　spacecraft　arrive　at　their　appointed　destinations　with　astonishing　precision；　exactly　as　predicted　by　Newtonian　gravitation。　When　our　ships　fly　to　Mars；　say；　their　instruments　do　not　hear　a　tinkling　sound　or　detect　shards　of　broken　crystal　as　they　crash　through　the　〃spheres〃　that—according　to　the　authoritative　opinions　that　prevailed　for　millennia—propel　Venus　or　the　Sun　ill　their　dutiful　motions　about　the　central　Earth。

When　Voyager　1　scanned　the　Solar　System　from　beyond　the　outermost　planet；　it　saw；　just　as　Copernicus　and　Galileo　had　said　we　would；　the　Sun　in　the　middle　and　the　planets　in　concentric　orbits　about　it。　Far　from　being　the　center　of　the　Universe；　the　Earth　is　just　one　of　the　orbiting　dots。　No　longer　confined　to　a　single　world；　we　are　now　able　to　reach　out　to　others　and　determine　decisively　what　kind　of　planetary　system　we　inhabit。



EVERY　OTHER　PROPOSAL；　and　their　number　is　legion；　to　displace　us　from　cosmic　center　stage　has　also　been　resisted；　in　part　for　similar　reasons。　We　seem　to　crave　privilege；　merited　not　by　our　work；　but　by　our　birth；　by　the　mere　fact　that；　say；　we　are　humans　and　born　on　Earth。　We　might　call　it　the　anthropocentric—the　〃human…centered〃—conceit。　This　conceit　is　brought　close　to　culmination　in　the　notion　that　we　are　created　in　God's　image：　The　Creator　and　Ruler　of　the　entire　Universe　looks　just　like　me。　My；　what　a　coincidence　How　convenient　and　satisfying！　The　sixth…century…B。C。　Green　philosopher　Xenophanes　understood　the　arrogance　of　the　perspective：

〃The　Ethiopians　make　their　gods　black　and　snub…nosed；　the　Thracians　say　theirs　have　blue　eyes　and　red　hair　。　。　。　Yes；　and　if　oxen　and　horses　or　lions　had　hands；　and　could　paint　with　their　hands；　and　produce　works　of　art　as　men　do；　horses　would　paint　the　forms　of　the　gods　like　horses；　and　oxen　like　oxen　。　。　。〃

Such　attitudes　were　once　described　as　〃provincial〃—the　naive　expectation　that　the　political　hierarchies　and　social　conventions　of　an　obscure　province　extend　to　a　vast　empire　posed　of　many　different　traditions　and　cultures；　that　the　familiar　boondocks；　our　boondocks；　are　the　center　of　the　world。　The　country　bumpkins　know　almost　nothing　about　what　else　is　possible。　They　fail　to　grasp　the　insignificance　of　their　province　or　the　diversity　of　the　Empire。　With　ease；　they　apply　their　own　standards　and　customs　to　the　rest　of　the　planet。　But　plopped　down　in　Vienna；　say；　or　Hamburg；　or　New　York；　ruefully　they　recognize　how　limited　their　perspective　has　been。　They　bee　〃deprovincialized。〃

Modern　science　has　been　a　voyage　into　the　unknown；　with　a　lesson　in　humility　waiting　at　every　stop。　Many　passengers　would　rather　have　stayed　home。




CHAPTER　3　　　THE　GREAT　DEMOTIONS

　

　

＇One　philosopher＇　asserted　that　he　knew　the　whole　secret　。　。　。　＇H＇e　surveyed　the　two　celestial　strangers　from　top　to　toe；　and　maintained　to　their　faces　that　their　persons；　their　worlds；　their　suns；　and　their　stars；　were　created　solely　for　the　use　of　man。　At　this　assertion　our　two　travelers　let　themselves　fall　against　each　other；　seized　with　a　fit　of　。　。　。　inextinguishable　laughter。　

VOLTAIRE；　MICROMEGAS。　A　PHILOSOPHICAL　HISTORY　（1752）

In　the　seventeenth　century　there　was　still　some　hope　that；　even　if　the　Earth　was　not　the　center　of　the　Universe；　it　might　be　the　only　〃world。〃　But　Galileo's　telescope　revealed　that　〃the　Moon　certainly　does　not　possess　a　smooth　and　polished　surface〃　and　that　other　worlds　might　look　〃just　like　the　face　of　the　Earth　itself。〃　The　Moon　and　the　planets　showed　unmistakably　that　they　had　as　much　claim　to　being　worlds　as　the　Earth　does—with　mountains；　craters；　atmospheres；　polar　ice　caps；　clouds；　and；　in　the　case　of　Saturn；　a　dazzling；　unheard…of　set　of　circumferential　rings。　After　millennia　of　philosophical　debate；　the　issue　was　settled　decisively　in　favor　of　〃the　plurality　of　worlds。〃　They　might　be　profoundly　different　from　our　planet。　None　of　them　might　be　as　congenial　for　life。　But　the　Earth　was　hardly　the　only　one。

This　was　the　next　in　the　series　of　Great　Demotions；　downlifting　experiences；　demonstrations　of　our　apparent　insignificance；　wounds　that　science　has；　in　its　search　for　Galileo's　facts；　delivered　to　human　pride。



WELL；　SOME　HOPED；　even　if　the　Earth　isn't　at　the　center　of　the　Universe；　the　Sun　is。　The　Sun　is　our　Sun。　So　the　Earth　is　approximately　at　the　center　of　the　Universe。　Perhaps　some　of　our　pride　could　in　this　way　be　salvaged。　But　by　the　nineteenth　century；　observational　astronomy　had　made　it　clear　that　the　Sun　is　but　one　lonely　star　in　a　great　self…gravitating　assemblage　of　suns　called　the　Milky　Way　Galaxy。　Far　from　being　at　the　center　of　the　Galaxy；　our　Sun　with　its　entourage　of　dim　and　tiny　planets　lies　in　an　undistinguished　sector　of　an　obscure　spiral　arm。　We　are　thirty　thousand　light　years　from　the　Center。

Well；　our　Milky　Way　is　the　only　galaxy。　The　Milky　Way　Galaxy　is　one　of　billions；　perhaps　hundreds　of　billions　of　galaxies　notable　neither　in　mass　nor　in　brightness　nor　in　how　its　stars　are　configured　and　arrayed。　Some　modern　deep　sky　photographs　show　more　galaxies　beyond　the　Milky　Way　than　stars　within　the　Milky　Way。　Every　one　of　them　is　an　island　universe　containing　perhaps　a　hundred　billion　suns。　Such　an　image　is　a　profound　sermon　on　humility。

Well；　then；　at　least　our　Galaxy　is　at　the　center　of　the　Universe。　No；　this　is　wrong　too。　When　the　expansion　of　the　Universe　was　first　discovered；　many　people　naturally　gravitated　to　the　notion　that　the　Milky　Way　was　at　the　center　of　the　expansion；　and　all　the　other　galaxies　running　away　from　us。　We　now　recognize　that　astronomers　on　any　galaxy　would　see　all　the　others　running　away　。　from　them；　unless　they　were　very　careful；　they　would　all　conclude　that　they　were　at　the　center　of　the　Universe。　There　is；　in　fact；　no　center　to　the　expansion；　no　point　of　origin　of　the　Big　Bang；　at　least　not　in　ordinary　three…dimensional　space。

Well；　even　if　there　are　hundreds　of　billions　of　galaxies；　each　with　hundreds　of　billions　of　stars；　no　other　star　has　planets。　If　there　are　n　other　planets　beyond　our　Solar　System；　perhaps　there's　no　other　life　in　the　Universe。　Our　uniqueness　might　then　be　saved。　Sing　planets　are　small　and　feebly　shine　by　reflected　sunlight；　they're　hard　to　find。　Although　applicable　technology　is　improving　wit　breathtaking　speed；　even　a　giant　world　like　Jupiter；　orbiting　the　nearest　star；　Alpha　Centauri；　would　still　be　difficult　to　detect。　Iii　our　ignorance；　the　geocentrists　find　hope。

There　was　once　a　scientific　hypothesis—not　just　well　received　but　prevailing—that　supposed　our　solar　system　to　have　formed　through　the　near　collision　of　the　ancient　Sun　with　another　star；　the　gravitational　tidal　interaction　pulled　out　tendrils　of　sunstuff　that　quickly　condensed　into　planets。　Since　space　is　mainly　empty　and　near　stellar　collisions　most　rare；　it　was　concluded　that　few　other　planetary　systems　exist—perhaps　only　one；　around　that　other　star　that　long　ago　co…parented　the　worlds　of　our　solar　system。　Early　in　my　studies；　I　was　amazed　and　disappointed　that　such　a　view　had　ever　been　taken　seriously；　that　for　planets　of　other　stars；　absence　of　evidence　had　been　considered　evidence　of　absence。

Today　we　have　firm　evidence　for　at　least　three　planets　orbiting　an　extremely　dense　star；　the　pulsar　designated　B1257＋12；　about　which　I'll　say　more　later。　And　we've　found；　for　more　than　half　the　stars　with　masses　like　the　Sun's；　that　early　in　their　careers　they're　surrounded　by　great　disks　of　gas　aid　dust　out　of　which　planets　seem　to　form。　Other　planetary　systems　now　look　to　be　a　cosmic　monplace；　maybe　even　worlds　something　like　the　Earth。　We　should　be　able；　in　the　next　few　decades；　to　inventory　at　least　the　larger　planets；　if　they　exist；　of　hundreds　of　nearby　stars。

Well；　if　our　position　in　space　doesn't　reveal　our　special　role；　our　position　in　time　does：　We've　been　in　the　Universe　since　The　Beginning　（give　or　take　a　few　days）。　We've　been　given　special　responsibilities　by　the　Creator。　It　once　seemed　very　reasonable　to　think　of　the　Universe　as　beginning　just　a　little　before　our　collective　memory　is　obscured　by　the　passage　of　time　and　the　illiteracy　of　our　ancestors。　Generally　speaking；　that's　hundreds　or　thousands　of　years　ag