pale blue dot -carl sagan-第49章

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For　me；　no　signals；　no　one　calling　out　to　us　is　a　depressing　prospect。　〃plete　silence；〃　said　Jean…Jacques　Rousseau　in　a　different　context；　〃induces　melancholy；　it　is　an　image　of　death。〃　But　I'm　with　Henry　David　Thoreau：　〃Why　should　I　feel　lonely？　Is　not　our　planet　in　the　Milky　Way？〃

The　realization　that　such　beings　exist　and　that；　as　the　evolutionary　process　requires；　they　must　be　very　different　from　us；　would　have　a　striking　implication：　Whatever　differences　divide　us　down　here　on　Earth　are　trivial　pared　to　the　differences　between　any　of　us　and　any　of　them。　Maybe　it's　a　long　shot；　but　the　discovery　of　extraterrestrial　intelligence　might　play　a　role　in　unifying　our　squabbling　and　divided　planet。　It　would　be　the　last　of　the　Great　Demotions；　a　rite　of　passage　for　our　species　and　a　transforming　event　in　the　ancient　quest　to　discover　our　place　in　the　Universe。

In　our　fascination　with　SETI；　we　might　be　tempted；　even　without　good　evidence；　to　succumb　to　belief　but　this　would　be　self…indulgent　and　foolish。　We　must　surrender　our　skepticism　only　in　the　face　of　rock…solid　evidence。　Science　demands　a　tolerance　for　ambiguity。　Where　we　are　ignorant；　we　withhold　belief。　Whatever　annoyance　the　uncertainty　engenders　serves　a　higher　purpose：　It　drives　us　to　accumulate　better　data。　This　attitude　is　the　difference　between　science　and　so　much　else。　Science　offers　little　in　the　way　of　cheap　thrills。　The　standards　of　evidence　are　strict。　But　when　followed　they　allow　us　to　see　far；　illuminating　even　a　great　darkness。




CHAPTER　21　　　TO　THE　SKY！

　

　

The　stairs　of　the　sky　are　let　down　for　him　that　he　may　ascend　thereon　to　heaven。　O　gods；　put　your　arms　under　the　king：　raise　him；　lift　him　to　the　sky。　To　the　sky！　To　the　sky！

—HYMN　FOR　A　DEAD　PHARAOH　（EGYPT；　CA。　2600　B。C。）

When　my　grandparents　were　children；　the　electric　light；　the　automobile；　the　airplane；　and　the　radio　were　Stupefying　technological　advances；　the　wonders　of　the　age。　You　might　hear　wild　stories　about　them；　but　you　could　not　find　a　single　exemplar　in　that　little　village　in　Austria…Hungary；　near　the　banks　of　the　river　Bug。　But　in　that　same　time；　around　the　turn　of　the　last　century；　there　were　two　men　who　foresaw　other；　far　more　ambitious；　inventions—Konstantin　Tsiolkovsky；　the　theoretician；　a　nearly　deaf　schoolteacher　in　the　obscure　Russian　town　of　Kaluga；　and　Robert　Goddard；　the　engineer；　a　professor　at　an　equally　obscure　American　college　in　Massachusetts。　They　dreamt　of　using　rockets　to　journey　to　the　planets　and　the　stars。　Step　by　step；　they　worked　out　the　fundamental　physics　and　many　of　the　details。　Gradually；　their　machines　took　shape。　Ultimately；　their　dream　proved　infectious。

In　their　time；　the　very　idea　was　considered　disreputable；　or　even　a　symptom　of　some　obscure　derangement。　Goddard　found　that　merely　mentioning　a　voyage　to　other　worlds　subjected　him　to　ridicule；　and　he　dared　not　publish　or　even　discuss　in　public　his　long…term　vision　of　flights　to　the　stars。　As　teenagers；　both　had　epiphanal　visions　of　spaceflight　that　never　left　them。　〃I　still　have　dreams　in　which　I　fly　up　to　the　stars　in　my　machine；〃　Tsiolkovsky　wrote　in　middle　age。　〃It　is　difficult　to　work　all　on　your　own　for　many　years；　in　adverse　conditions　without　a　gleam　of　hope；　without　any　help。〃　Many　of　his　contemporaries　thought　he　was　truly　mad。　Those　who　knew　physics　better　than　Tsiolkovsky　and　Goddard—including　The　New　York　Times　in　a　dismissive　editorial　not　retracted　until　the　eve　of　Apollo　11—insisted　that　rockets　could　not　work　in　a　vacuum；　that　the　Moon　and　the　planets　were　forever　beyond　human　reach。

A　generation　later；　inspired　by　Tsiolkovsky　and　Goddard；　Wernher　von　Braun　was　constructing　the　first　rocket　capable　of　reaching　the　edge　of　space；　the　V…2。　But　in　one　of　those　ironies　with　which　the　twentieth　century　is　replete；　von　Braun　was　building　it　for　the　Nazis—as　an　instrument　of　indiscriminate　slaughter　of　civilians；　as　a　〃vengeance　weapon〃　for　Hitler；　the　rocket　factories　staffed　with　slave　labor；　untold　human　suffering　exacted　in　the　construction　of　every　booster；　and　von　Braun　himself　made　an　officer　in　the　SS。　He　was　aiming　at　the　Moon；　he　joked　unselfconsciously；　but　hit　London　instead。

Another　generation　later；　building　on　the　work　of　Tsiolkovsky　and　Goddard；　extending　von　Braun's　technological　genius；　we　were　up　there　in　space；　silently　circumnavigating　the　Earth；　treading　the　ancient　and　desolate　lunar　surface。　Our　machines—increasingly　petent　and　autonomous—were　spreading　through　the　Solar　System；　discovering　new　worlds；　examining　them　closely；　searching　for　life；　paring　them　with　Earth。

This　is　one　reason　that　in　the　long　astronomical　perspective　there　is　something　truly　epochal　about　〃now〃—which　we　can　define　as　the　few　centuries　centered　on　the　year　you're　reading　this　book。　And　there's　a　second　reason：　This　is　the　first　moment　in　the　history　of　our　planet　when　any　species；　by　its　own　voluntary　actions；　has　bee　a　danger　to　itself—as　well　as　to　vast　numbers　of　others。　Let　me　recount　the　ways：

·We've　been　burning　fossil　fuels　for　hundreds　of　thousands　of　years。　By　the　1960s；　there　were　so　many　of　us　burning　wood；　coal；　oil；　and　natural　gas　on　so　large　a　scale；　that　scientists　began　to　worry　about　the　increasing　greenhouse　effect；　the　dangers　of　global　warming　began　slowly　slipping　into　public　consciousness。

·CFCs　were　invented　in　the　1920s　and　1930s；　in　1974　they　were　discovered　to　attack　the　protective　ozone　layer。　Fifteen　years　later　a　worldwide　ban　on　their　production　was　going　into　effect。

·Nuclear　weapons　were　invented　in　1945。　It　took　until　1983　before　the　global　consequences　of　thermonuclear　war　were　understood。　By　1992；　large　numbers　of　warheads　were　being　dismantled。

·The　first　asteroid　was　discovered　in　1801。　More　or　less　serious　proposals　to　move　them　around　were　floated　beginning　in　the　1980s。　Recognition　of　the　potential　dangers　of　asteroid　deflection　technology　followed　shortly　after。

·Biological　warfare　has　been　with　us　for　centuries；　but　its　deadly　mating　with　molecular　biology　has　occurred　only　lately。

·We　humans　have　already　precipitated　extinctions　of　species　on　a　scale　unprecedented　since　the　end　of　the　Cretaceous　Period。　But　only　in　the　last　decade　has　the　magnitude　of　these　extinctions　bee　clear；　and　the　possibility　raised　that　in　our　ignorance　of　the　interrelations　of　life　on　Earth　we　may　be　endangering　our　own　future。

Look　at　the　dates　on　this　list　and　consider　the　range　of　new　technologies　currently　under　development。　Is　it　not　likely　that　other　dangers　of　our　own　making　are　yet　to　be　discovered；　some　perhaps　even　more　serious？

In　the　littered　field　of　discredited　self…congratulatory　chauvinisms；　there　is　only　one　that　seems　to　hold　up；　one　sense　in　which　we　are　special：　Due　to　our　own　actions　or　inactions；　and　the　misuse　of　our　technology；　we　live　at　an　extraordinary　moment；　for　the　Earth　at　least—the　first　time　that　a　species　has　bee　able　to　wipe　itself　out。　But　this　is　also；　we　may　note；　the　first　time　that　a　species　has　bee　able　to　journey　to　the　planets　and　the　stars。　The　two　times；　brought　about　by　the　same　technology；　coincide—a　few　centuries　in　the　history　of　a　4。5…billion…year…old　planet。　If　you　were　somehow　dropped　down　on　the　Earth　randomly　at　any　moment　in　the　past　（or　future）；　the　chance　of　arriving　at　this　critical　moment　would　be　less　than　1　in　10　million。　Our　leverage　on　the　future　is　high　just　now。

It　might　be　a　familiar　progression；　transpiring　on　many　worlds—a　planet；　newly　formed；　placidly　revolves　around　its　star；　life　slowly　forms；　a　kaleidoscopic　procession　of　creatures　evolves；　intelligence　emerges　which；　at　least　up　to　a　point；　confers　enormous　survival　value；　and　then　technology　is　invented。　It　dawns　on　them　that　there　are　such　things　as　laws　of　Nature；　that　these　laws　can　be　revealed　by　experiment；　and　that　knowledge　of　these　laws　can　be　made　both　to　save　and　to　take　lives；　both　on　unprecedented　scales。　Science；　they　recognize；　grants　immense　powers。　In　a　flash；　they　create　world…altering　contrivances。　Some　planetary　civilizations　see　their　way　through；　place　limits　on　what　may　and　what　must　not　be　done；　and　safely　pass　through　the　time　of　perils。　Others　are　not　so　lucky　or　so　prudent；　perish。

Since；　in　the　long　run；　every　planetary　society　will　be　endangered　by　impacts　from　space；　every　surviving　civilization　is　obliged　to　bee　spacefaring—…not　because　of　exploratory　or　romantic　zeal；　but　for　the　most　practical　reason　imaginable：　staying　alive。　And　once　you're　out　there　in　space　for　centuries　and　millennia；　moving　little　worlds　around　and　engineering　planets；　your　species　has　been　pried　loose　from　its　cradle。　If　they　exist；　many　other　civilizations　will　eventually　venture　far　from　home。*

*　Might　a　planetary　civilization　which　has　survived　its　adolescence　wish　to　encourage　others　struggling　with　their　emerging　technologies？　Perhaps　they　would　make　special　efforts　to　broadcast　news　of　their　existence；　the　triumphant　announcement　that　it's　possible　to　avoid　self…annihilation。　Or　would　they　at　first　be　very　cautious？　Having　avoided　catastrophes　of　their　own　making；　perhaps　they　would　fear　giving　away　knowledge　of　their　existence；　lest　some　other；　unknown；　aggrandizing　civilization　out　there　in　the　dark　is　looking　for　Lebensraum　or　slavering　to　put　down　the　potential　petition。　That　might　be　a　reason　for　us　to　explore　neighboring　star　systems；　but　discreetly。

Maybe　they　would　be　silent　for　another　reason：　because　broadcasting　the　existence　of　an　advanced　civilization　might　encourage　emerging　civilizations　to　do　less　than　their　best　efforts　to　safeguard　their　future—　hoping　instead　that　someone　will　e　out　of　the　dark　and　save　them　from　themselves。



A　MEANS　HAS　BEEN　OFFERED　of　estimating　how　precarious　our　circumstances　are—remarkably；　without　in　any　way　addressing　the　nature　of　the　hazards。　J。　Richard　Gott　III　is　an　astrophysicist　at　Princeton　University。　He　asks　us　to　adopt　a　generalized　Copernican　principle；　something　I've　described　elsewhere　as　the　Principle　of　Mediocrity。　Chances　are　that　we　do　not　live　in　a　truly　extraordinary　time。　Hardly　anyone　ever　did。　The　probability　is　high　that　we're　born；　live　out　our　days；　and　die　somewhere　in　the　broad　middle　range　of　the　lifetime　of　our　species　（or　civilization；　or　nation）。　Almost　certainly；　Gott　says；　we　do　not　live　in　first　or　last　times。　So　if　your　species　is　very　young；　it　follows　that　it's　unlikely　to　last　long—because　if　it　were　to　last　long；　you　（and　the　rest　of　us　alive　today）　would　be　extraordinary　in　living；　proportionally　speaking；　so　near　the　beginning。

What　then　is　the　projected　longevity　of　our　species？　Gott　concludes；　at　the　97。5　percent　confidence　level；　that　there　will　be　humans　for　no　more　than　8　million　years。　That's　his　upper　limit；　about　the　same　as　the　average　lifetime　of　many　mammalian　species。　In　that　case；　our　technology　neither　harms　nor　helps。　But　Gott's　lower　limit；　with　the　same　claimed　reliability；　is　only　12　years。　He　will　not　give　you　40…to…1　odds　that　humans　will　still　be　around　by　the　time　babies　now　alive　bee　teenagers。　In　everyday　life　we　try　very　hard　not　to　take　risks　so　large；　not　to　board　airplanes；　say；　with　1　chance　in　40　of　crashing。　We　will　agree　to　surgery　in　which　95　perc