pale blue dot -carl sagan-第58部分

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earest　may　be　only　10　or　20　lightyears　away。

If　there　are　black　holes　within　reach—whether　they're　as　massive　as　mountains　or　as　stars—we　will　have　amazing　physics　to　study　firsthand；　as　well　as　a　formidable　new　source　of　energy。　By　no　means　do　I　claim　that　brown　dwarfs　or　primordial　black　holes　are　likely　within　a　few　light…years；　or　anywhere。　But　as　we　enter　interstellar　space；　it　is　inevitable　that　we　will　stumble　upon　whole　new　categories　of　wonders　and　delights；　some　with　transforming　practical　applications。

I　do　not　know　where　my　train　of　argument　ends。　As　more　time　passes；　attractive　new　denizens　of　the　cosmic　zoo　will　draw　us　farther　outward；　and　increasingly　improbable　and　deadly　catastrophes　must　e　to　pass。　The　probabilities　are　cumulative。　But；　as　time　goes　on；　technological　species　will　also　accrue　greater　and　greater　powers；　far　surpassing　any　we　can　imagine　today。　Perhaps；　if　we　are　very　skillful　（lucky；　I　think；　won't　be　enough）；　we　will　ultimately　spread　far　from　home；　sailing　through　the　starry　archipelagos　of　the　vast　Milky　Way　Galaxy。　If　we　e　upon　anyone　else—or；　more　likely；　if　they　e　upon　us—we　will　harmoniously　interact。　Since　other　spacefaring　civilizations　are　likely　to　be　much　more　advanced　than　we；　quarrelsome　humans　in　interstellar　space　are　unlikely　to　last　long。

Eventually；　our　future　may　be　as　Voltaire；　of　all　people；　imagined：

Sometimes　by　the　help　of　a　sunbeam；　and　sometimes　by　the　convenience　of　a　et；　＇they＇　glided　from　sphere　to　sphere；　as　a　bird　hops　from　bough　to　bough。　In　a　very　little　time　＇they＇　posted　through　the　Milky　Way　。　。　。

We　are；　even　now；　discovering　vast　numbers　of　gas　and　dust　disks　around　young　stars—the　very　structures　out　of　which；　in　our　solar　system　four　and　a　half　billion　years　ago；　the　Earth　and　the　other　planets　formed。　We're　beginning　to　understand　how　fine　dust　grains　slowly　grow　into　worlds；　how　big　Earthlike　planets　accrete　and　then　quickly　capture　hydrogen　and　helium　to　bee　the　hidden　cores　of　gas　giants；　and　how　small　terrestrial　planets　remain　paratively　bare　of　atmosphere。　We　are　reconstructing　the　histories　of　worlds—how　mainly　ices　and　organics　collected　together　in　the　chilly　outskirts　of　the　early　Solar　System；　and　mainly　rock　and　metal　in　the　inner　regions　warmed　by　the　young　Sun。　We　have　begun　to　recognize　the　dominant　role　of　early　collisions　in　knocking　worlds　over；　gouging　huge　craters　and　basins　in　their　surfaces　and　interiors；　spinning　them　up；　making　and　obliterating　moons；　creating　rings；　carrying；　it　may　be；　whole　oceans　down　from　the　skies；　and　then　depositing　a　veneer　of　organic　matter　as　the　neat　finishing　touch　in　the　creation　of　worlds。　We　are　beginning　to　apply　this　knowledge　to　other　systems。

In　the　next　few　decades　we　have　a　real　chance　of　examining　the　layout　and　something　of　the　position　of　many　other　mature　planetary　systems　around　nearby　stars。　We　will　begin　to　know　which　aspects　of　our　system　are　the　rule　and　which　the　exception。　What　is　more　mon—planets　like　Jupiter；　planets　like　Neptune；　or　planets　like　Earth？　Or　do　all　other　systems　have　Jupiters　and　Neptunes　and　Earths？　What　other　categories　of　worlds　are　there；　currently　unknown　to　us？　Are　all　solar　systems　embedded　in　a　vast　spherical　cloud　of　ets？　Most　stars　in　the　sky　are　not　solitary　suns　like　our　own；　but　double　or　multiple　systems　in　which　the　stars　are　in　mutual　orbit。　Are　there　planets　in　such　systems？　If　so；　what　are　they　like？　If；　as　we　now　think；　planetary　systems　are　a　routine　consequence　of　the　origin　of　suns；　have　they　followed　very　different　evolutionary　paths　elsewhere？　What　do　elderly　planetary　systems；　billions　of　years　more　evolved　than　ours；　look　like？　In　the　next　few　centuries　our　knowledge　of　other　systems　will　bee　increasingly　prehensive。　We　will　begin　to　know　which　to　visit；　which　to　seed；　and　which　to　settle。

Imagine　we　could　accelerate　continuously　at　1　g—what　we're　fortable　with　on　good　old　terra　firma—to　the　midpoint　of　our　voyage；　and　decelerate　continuously　at　1　g　until　we　arrive　at　our　destination。　It　would　then　take　a　day　to　get　to　Mars；　a　week　and　a　half　to　Pluto；　a　year　to　the　Oort　Cloud；　and　a　few　years　to　the　nearest　stars。

Even　a　modest　extrapolation　of　our　recent　advances　in　transportation　suggests　that　in　only　a　few　centuries　we　will　be　able　to　travel　close　to　the　speed　of　light。　Perhaps　this　is　hopelessly　optimistic。　Perhaps　it　will　really　take　millennia　or　more。　But　unless　we　destroy　ourselves　first　we　will　be　inventing　new　technologies　as　strange　to　us　as　Voyager　might　be　to　our　hunter…gatherer　ancestors。　Even　today　we　can　think　of　ways—clumsy；　ruinously　expensive；　inefficient　to　be　sure—of　constructing　a　starship　that　approaches　light　speed。　In　time；　the　designs　will　bee　more　elegant；　more　affordable；　more　efficient。　The　day　will　e　when　we　overe　the　necessity　of　jumping　from　et　to　et。　We　will　begin　to　soar　through　the　light…years　and；　as　St。　Augustine　said　of　the　gods　of　the　ancient　Greeks　and　Romans；　colonize　the　sky。

Such　descendants　may　be　tens　or　hundreds　of　generations　removed　from　anyone　who　ever　lived　on　the　surface　of　a　planet。　Their　cultures　will　be　different；　their　technologies　far　advanced；　their　languages　changed；　their　association　with　machine　intelligence　much　more　intimate；　perhaps　their　very　appearance　markedly　altered　from　that　of　their　nearly　mythical　ancestors　who　first　tentatively　set　forth　in　the　late　twentieth　century　into　the　sea　of　space。　But　they　will　be　human；　at　least　in　large　part；　they　will　be　practitioners　of　high　technology；　they　will　have　historical　records。　Despite　Augustine's　judgment　on　Lot's　wife；　that　〃no　one　who　is　being　saved　should　long　for　what　he　is　leaving；〃　they　will　not　wholly　forget　the　Earth。

But　we're　not　nearly　ready；　you　may　be　thinking。　As　Voltaire　put　it　in　his　Memnon；　〃our　little　terraqueous　globe　is　the　madhouse　of　those　hundred　thousand　millions*　of　worlds。〃　We；　who　cannot　even　put　our　own　planetary　home　in　order；　riven　with　rivalries　and　hatreds；　despoiling　our　environment；　murdering　one　another　through　irritation　and　inattention　as　well　as　on　deadly　purpose；　and　moreover　a　species　that　until　only　recently　was　convinced　that　the　Universe　was　made　for　its　sole　benefit—are　we　to　venture　out　into　space；　move　worlds；　reengineer　planets；　spread　to　neighboring　star　systems？

*　A　value　that　nicely　approximates　modern　estimates　of　the　number　of　planets　orbiting　stars　in　the　Milky　Way　Galaxy。

I　do　not　imagine　that　it　is　precisely　we；　with　our　present　customs　and　social　conventions；　who　will　be　out　there。　If　we　continue　to　accumulate　only　power　and　not　wisdom；　we　will　surely　destroy　ourselves。　Our　very　existence　in　that　distant　time　requires　that　we　will　have　changed　our　institutions　and　ourselves。　How　can　I　dare　to　guess　about　humans　in　the　far　future？　It　is；　I　think；　only　a　matter　of　natural　selection。　If　we　bee　even　slightly　more　violent；　shortsighted；　ignorant；　and　selfish　than　we　are　now；　almost　certainly　we　will　have　no　future。

If　you're　young；　it's　just　possible　that　we　will　be　taking　our　first　steps　on　near…Earth　asteroids　and　Mars　during　your　lifetime。　To　spread　out　to　the　moons　of　the　Jovian　planets　and　the　Kuiper　et　Belt　will　take　many　generations　more。　The　Oort　Cloud　will　require　much　longer　still。　By　the　time　we're　ready　to　settle　even　the　nearest　other　planetary　systems；　we　will　have　changed。　The　simple　passage　of　so　many　generations　will　have　changed　us。　The　different　circumstances　we　will　be　living　under　will　have　changed　us。　Prostheses　and　genetic　engineering　will　have　changed　us。　Necessity　will　have　changed　us。　We're　an　adaptable　species。

It　will　not　be　we　who　reach　Alpha　Centauri　and　the　other　nearby　stars。　It　will　be　a　species　very　like　us；　but　with　more　of　our　strengths　and　fewer　of　our　weaknesses；　a　species　returned　to　circumstances　more　like　those　for　which　it　was　originally　evolved；　more　confident；　farseeing；　capable；　and　prudent—the　sorts　of　beings　we　would　want　to　represent　us　in　a　Universe　that；　for　all　we　know；　is　filled　with　species　much　older；　much　more　powerful；　and　very　different。

The　vast　distances　that　separate　the　stars　are　providential。　Beings　and　worlds　are　quarantined　from　one　another。　The　quarantine　is　lifted　only　for　those　with　sufficient　self…knowledge　and　judgment　to　have　safely　traveled　from　star　to　star。



ON　IMMENSE　TIMESCALES；　in　hundreds　of　millions　to　billions　of　years；　the　centers　of　galaxies　explode。　We　see；　scattered　across　deep　space；　galaxies　with　〃active　nuclei；〃　quasars；　galaxies　distorted　by　collisions；　their　spiral　arms　disrupted；　star　systems　blasted　with　radiation　or　gobbled　up　by　black　holes—and　we　gather　that　on　such　timescales　even　interstellar　space；　even　galaxies　may　not　be　safe。

There　is　a　halo　of　dark　matter　surrounding　the　Milky　Way；　extending　perhaps　halfway　to　the　distance　of　the　next　spiral　galaxy　（M31　in　the　constellation　Andromeda；　which　also　contains　hundreds　of　billions　of　stars）。　We　do　not　know　what　this　dark　matter　is；　or　how　it　is　arranged—but　some*　of　it　may　be　in　worlds　untethered　to　individual　stars。　If　so；　our　descendants　of　the　remote　future　will　have　an　opportunity；　over　unimaginable　intervals　of　time；　to　bee　established　in　intergalactic　space；　and　to　tiptoe　to　other　galaxies。

*　Most　of　it　may　be　in　〃nonbaryonic〃　matter；　not　made　of　our　familiar　protons　and　neutrons；　and　not　anti…matter　either。　Over　90　percent　of　the　mass　of　the　Universe　seems　to　be　in　this　dark；　quintessential；　deeply　mysterious　stuff　wholly　unknown　on　Earth。　Perhaps　we　will　one　day　not　only　understand　it；　but　also　find　a　use　for　it。

But　on　the　timescale　for　populating　our　galaxy；　if　not　long　before；　we　must　ask：　How　immutable　is　this　longing　for　safety　that　drives　us　outward？　Will　we　one　day　feel　content　with　the　time　our　species　has　had　and　our　successes；　and　willingly　exit　the　cosmic　stage？　Millions　of　years　from　now—probably　much　sooner—we　will　have　made　ourselves　into　something　else。　Even　if　we　do　nothing　intentionally；　the　natural　process　of　mutation　and　selection　will　have　worked　our　extinction　or　evolved　us　into　some　other　species　on　just　such　a　timescale　（if　we　may　judge　by　other　mammals）。　Over　the　typical　lifetime　of　a　mammalian　species；　even　if　we　were　able　to　travel　close　to