pale blue dot -carl sagan-第71章

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some　planet　of　the　Sun　has　not　reached　them。　Yet。

Should　optimistic　estimates　prevail　and　one　in　every　million　stars　shelters　a　nearby　technological　civilization；　and　if　as　well　they're　randomly　strewn　through　the　Milky　Way—were　these　provisos　to　hold—then　the　nearest　one；　we　recall；　would　be　a　few　hundred　light…years　distant：　at　the　closest；　maybe　100　lightyears；　more　likely　a　thousand　light…years…and；　of　course；　perhaps　nowhere；　no　matter　how　far。　Suppose　the　nearest　civilization　on　a　planet　of　another　star　is；　say；　200　light…years　away。　Then；　some　150　years　from　now　they'll　begin　to　receive　our　feeble　post…World　War　II　television　and　radar　emission。　What　will　they　make　of　it？　With　each　passing　year　the　signal　will　get　louder；　more　interesting；　perhaps　more　alarming。　Eventually；　they　may　respond：　by　returning　a　radio　message；　or　by　visiting。　In　either　case；　the　response　will　likely　be　limited　by　the　finite　value　of　the　speed　of　light。　With　these　wildly　uncertain　numbers；　the　answer　to　our　unintentional　mid…century　call　into　the　depths　of　space　will　not　arrive　until　around　the　year　2350。　If　they're　farther　away；　of　course；　it　will　take　longer；　and　if　much　farther　away；　much　longer。　The　interesting　possibility　arises　that　our　first　receipt　of　a　message　from　an　alien　civilization；　a　message　intended　for　us　（not　just　an　all…points　bulletin）；　will　occur　in　a　time　when　we　are　well　situated　on　many　worlds　in　our　solar　system　and　preparing　to　move　on。

With　or　without　such　a　message；　though；　we　will　have　reason　to　continue　outward；　seeking　other　solar　systems。　Or—even　safer　in　this　unpredictable　and　violent　sector　of　the　Galaxy—to　sequester　some　of　us　in　self…sufficient　habitations　in　interstellar　space；　far　from　the　dangers　constituted　by　the　stars。　Such　a　future　would；　I　think；　naturally　evolve；　by　slow　increments；　even　without　any　grand　goal　of　interstellar　travel：

For　safety；　some　munities　may　wish　to　sever　their　ties　with　the　rest　of　humanity—uninfluenced　by　other　societies；　other　ethical　codes；　other　technological　imperatives。　In　a　time　when　ets　and　asteroids　are　being　routinely　repositioned；　we　will　be　able　to　populate　a　small　world　and　then　cut　it　loose。　In　successive　generations；　as　this　world　sped　outward；　the　Earth　would　fade　from　bright　star　to　pale　dot　to　invisibility；　the　Sun　would　appear　dimmer；　until　it　was　no　more　than　a　vaguely　yellow　point　of　light；　lost　among　thousands　of　others。　The　travelers　would　approach　interstellar　night。　Some　such　munities　may　be　content　with　occasional　radio　and　laser　traffic　with　the　old　home　worlds。　Others；　confident　of　the　superiority　of　their　own　survival　chances　and　wary　of　contamination；　may　try　to　disappear。　Perhaps　all　contact　with　them　will　ultimately　be　lost；　their　very　existence　forgotten。

Even　the　resources　of　a　sizable　asteroid　or　et　are　finite；　though；　and　eventually　more　resources　must　be　sought　elsewhere—especially　water；　needed　for　drink；　for　a　breathable　oxygen　atmosphere；　and　for　hydrogen　to　power　fusion　reactors。　So　in　the　long　run　these　munities　must　migrate　from　world　to　world；　with　no　lasting　loyalty　to　any。　We　might　call　it　〃pioneering；〃　or　〃homesteading。〃　A　less　sympathetic　observer　might　describe　it　as　sucking　dry　the　resources　of　little　world　after　little　world。　But　there　are　a　trillion　little　worlds　in　the　Oort　et　Cloud。

Living　in　small　numbers　on　a　modest　stepmother　world　far　from　the　Sun；　we　will　know　that　every　scrap　of　food　and　every　drop　of　water　is　dependent　on　the　smooth　operation　of　a

farsighted　technology；　but　these　conditions　are　not　radically　unlike　those　to　which　we　are　already　accustomed。　Digging　resources　out　of　the　ground　and　stalking　passing　resources　seem　oddly　familiar；　like　a　forgotten　memory　of　childhood：　It　is；　with　a　few　significant　changes；　the　strategy　of　our　hunter…gatherer　ancestors。　For　99。9　percent　of　the　tenure　of　humans　on　Earth；　we　lived　such　a　life。　Judging　from　some　of　the　last　surviving　hunter…gatherers　just　before　they　were　engulfed　by　the　present　global　civilization；　we　may　have　been　relatively　happy。　It's　the　kind　of　life　that　forged　us。　So　after　a　brief；　only　partially　successful　sedentary　experiment；　we　may　bee　wanderers　again…more　technological　than　last　time；　but　even　then　our　technology；　stone　tools　and　fire；　was　our　only　hedge　against　extinction。

If　safety　lies　in　isolation　and　remoteness；　then　some　of　our　descendants　will　eventually　emigrate　to　the　outer　ets　of　the　Oort　Cloud。　With　a　trillion　etary　nuclei；　each　separated　from　the　next　by　about　as　much　as　Mars　is　from　Earth；　there　will　be　a　great　deal　to　do　out　there。*

*　Even　if　we　are　not　in　any　particular　hurry；　we　may　be　able　by　then　to　make　small　worlds　move　faster　than　we　can　make　spacecraft　move　today。　If　so；　our　descendants　will　eventually　overtake　the　two　Voyager　spacecraft—launched　in　the　remote　twentieth　century—before　they　leave　the　Oort　Cloud；　before　they　make　for　interstellar　space。　Perhaps　they　will　retrieve　these　derelict　ships　of　long　ago。　Or　perhaps　they　will　permit　them　to　sail　on。

The　outer　edge　of　the　Sun's　Oort　Cloud　is　perhaps　halfway　to　the　nearest　star。　Not　every　other　star　has　an　Oort　Cloud；　but　many　probably　do。　As　the　Sun　passes　nearby　stars；　our　Oort　Cloud　will　encounter；　and　partially　pass　through；　other　et　clouds；　like　two　swarms　of　gnats　interpenetrating　but　not　colliding。　To　occupy　a　et　of　another　star　will　then　be　not　much　more　difficult　than　to　occupy　one　of　our　own。　From　the　frontiers　of　some　other　solar　system　the　children　of　the　blue　dot　may　peer　longingly　at　the　moving　points　of　light　denoting　substantial　（and　well…lit）　planets。　Some　munities—feeling　the　ancient　human　love　for　oceans　and　sunlight　stirring　within　them—may　begin　the　long　journey　down　to　the　bright；　warm；　and　clement　planets　of　a　new　sun。

Other　munities　may　consider　this　last　strategy　a　weakness。　Planets　are　associated　with　natural　catastrophes。　Planets　may　have　pre…existing　life　and　intelligence。　Planets　are　easy　for　other　beings　to　find。　Better　to　remain　in　the　darkness。　Better　to　spread　ourselves　among　many　〃small　and　obscure　worlds。　Better　to　stay　hidden。



ONCE　WE　CAN　SEND　our　machines　and　ourselves　far　from　home；　far　from　the　planets—once　we　really　enter　the　theater　of　the　Universe—we　are　bound　to　e　upon　phenomena　unlike　anything　we've　ever　encountered。　Here　are　three　possible　examples：

First：　Starting　some　550　astronomical　units　（AU）　out—about　ten　times　farther　from　the　Sun　than　Jupiter；　and　therefore　much　more　accessible　than　the　Oort　Cloud—there's　something　extraordinary。　Just　as　an　ordinary　lens　focuses　far…off　images；　so　does　gravity。　（Gravitational　lensing　by　distant　stars　and　galaxies　is　now　being　detected。）　Five　hundred　fifty　AU　from　the　Sun—only　a　year　away　if　we　could　travel　at　1　percent　the　speed　of　light—is　where　the　focus　begins　（although　when　effects　of　the　solar　corona；　the　halo　of　ionized　gas　surrounding　the　Sun；　are　taken　into　account；　the　focus　may　be　considerably　farther　out）。　There；　distant　radio　signals　are　enormously　enhanced；　amplifying　whispers。　The　magnification　of　distant　images　would　allow　us　（with　a　modest　radio　telescope）　to　resolve　a　continent　at　the　distance　of　the　nearest　star　and　the　inner　Solar　System　at　the　distance　of　the　nearest　spiral　galaxy。　If　you　are　free　to　roam　an　imaginary　spherical　shell　at　the　appropriate　focal　distance　and　centered　on　the　Sun；　you　are　free　to　explore　the　Universe　in　stupendous　magnification；　to　peer　at　it　with　unprecedented　clarity；　to　eavesdrop　on　the　radio　signals　of　distant　civilizations；　if　any；　and　to　glimpse　the　earliest　events　in　the　history　of　the　Universe。　Alternatively；　the　lens　could　be　used　the　other　way；　to　amplify　a　very　modest　signal　of　ours　so　it　could　be　heard　over　immense　distances。　There　are　reasons　that　draw　us　to　hundreds　and　thousands　of　AU。　Other　civilizations　will　have　their　own　regions　of　gravitational　focusing；　depending　on　the　mass　and　radius　of　their　star；　some　a　little　closer；　some　a　little　farther　away　than　ours。　Gravitational　lensing　may　serve　as　a　mon　inducement　for　civilizations　to　explore　the　regions　just　beyond　the　planetary　parts　of　their　solar　systems。

Second：　Spend　a　moment　thinking　about　brown　dwarfs；　hypothetical