Basicconcepts
Examplesofextraterrestriallife
PeoplehavefoundmicrobialfossilsinMartianmeteorites,plusalargenumberofreportsofaliensvisitingtheearth,sciencefictionThefloodofnovelsandmoviesmakestherumorsofalienlifevividandvivid.However,theseevidencesarereallynotenoughtoprovetheexistenceofextraterrestriallife.Foralongtime,thescientificcommunityhasbeenridiculingtheevidenceoftheexistenceofextraterrestriallifesuchasflyingsaucers.ThecrashoftheRoswellUFOintheUnitedStatesin1947causedanuproar.Later,theU.S.DepartmentofDefenseclaimedthatthiswasnottrue.
Extraterrestrialcivilization
Extraterrestrialcivilizationandextraterrestriallifearetwodifferentandrelatedconcepts.Ittakesalongtimetogofrominanimatetolife,andittakesquitealongtimetoevolvefromlifetocivilization.Lifedoesnotnecessarilyhavewisdom,andwisdomdoesnotnecessarilyhavecivilization.Therefore,theextraterrestrialcivilizationwearereferringtoreferstothecivilizationofadvancedintelligentcreaturessimilartoearthhumansthatmayexistonothercelestialbodiesotherthantheearth.
Toexploreextraterrestrialcivilization,wemustfirstunderstandtheconditionsandenvironmentforlifetoexistbasedontheexistenceoflifeonearth.
Lifeiswonderful.Itisthereproductionoflifethatmakestheearthvibrantandfullofweather.LifeisnotcreatedbyGod,lifeistheinevitableresultoftheevolutionofcelestialbodies.Theconditionsfortheexistenceoflifearealsoveryharsh.Thecelestialbodyinwhichitislocatedmusthaveahardshell,asuitableatmosphereandasuitabletemperature,andacertainamountofwater.Atthesametime,thecelestialbodysurroundingtheplanetmustbeastablestar.Asfarasthesolarsystemisconcerned,onlyVenus,EarthandMarsmeettheaboveconditions.Amongthem,theearthislocatedbetweenVenusandMars,inthemostfavorablespaceforlifetomultiply.NolifehasbeenfoundonVenusandMars.Lifeonotherplanetsinthesolarsystemisevenlesssuitableforlife.
Lookingforaplanetarysystemoutsidethesolarsystemisanotherdirectionforexploringextraterrestrialcivilization.Scientistshavealreadybeguntoconcentrateonobservationandresearch.Aconfirmedplanetarysystemhasnotbeendiscoveredyet.Ifaplanetarysystemisfound,therewillnotnecessarilybelifethere.Ifyoureallyfindaplanetarysystemthatismoresuitableforlife.
Classificationmethod
Kadaschevscale
In1964,theformerSovietastrophysicistKadaschevproposedtheKadaschevscaleasameasureofThemethodofcivilizedtechnicallevel.Thisscaleisonlytheoretical,andtheobjectitmeasures,thatis,highlyevolvedcivilizations,isonlyinthespeculationofhumanbeings.Noonehaseverseenitpersonally,butthesignificanceofthisscaleisthatitisfromtheperspectiveoftheuniverse.Toconsidertheenergyconsumptionoftheentirecivilization.TheKadashevscaleclassifiescivilizationsoutsidetheearthaccordingtothepowerofthetransmittedsignal,andisdividedintothreetypes.However,inapplication,sinceithasbeenquantified,thetypescanbeinfinitelymany.
TypeIcivilizationcanmobilizeenergyequivalenttotheentireoutputpoweroftheearthforcommunication,whichis10^16watts.
Theenergypowerusedbyourearth’scivilizationisincreasingatanalarmingrate.Thepoweroutputoftheearthisabout10^15to10^16watts,andtheoutputpowerontheearthisnowmainlyusedforheatingandelectricity,Transportationandotherpurposesthatarenotrelatedtocommunicationwithaliencivilizations.Inthisregard,theearthisnotatypeIcivilization.
TypeIIcivilizationcanusetheoutputpowerequivalenttoatypicalstarforcommunication,about10^26watts.
Thisisequivalenttowehaveseenverybrightstarsinthegalaxyclosesttousatthefrequencyoflightwaves.IftypeIIcivilizationexistsinthespiralgalaxyclosesttous,theAndromedaGalaxy,wecandetectitwiththecorrectsearchprocedure.
ThecommunicationpoweremittedbyTypeIIIcivilizationreaches10^36watts,whichisapproximatelyequaltothepoweroutputoftheentiregalaxy.
IfthereisaTypeIIIcivilizationintheuniverse,nomatterwhereitis,aslongasitemitsradiowavesatus,wecandetectit.
CarlSaganoftheUnitedStatesfurthersuggestedthatthethreetypesofcivilizationscanbesubdividedintotensubtypesbyenergyscale,thatis,10^16wattsare1.0type,and10^17wattsare1.1type;10^18wattsistype1.2...Accordingtothelevelofourearth,itisthetype0.7civilization.Ofcourse,isthetransitionbetweenthethreecivilizationtypespossible?Whetherthereistimeandconditionstocompletethistransitionisunknown.
Exploringmethods
Therearefourmaintypesofmethodsforexploringextraterrestrialcivilizations:
①Receiveandanalyzevariouspossibleradiowavesfromspace.Workinthisareabeganin1960.
②Humansactivelysendoutsignalstoouterspaceindicatingthathumansarepresentinthesolarsystem.OnNovember16,1974,theUnitedStatesusedthe305-meter-diameterradiotelescopeinArecibo,PuertoRico,tosendoutthefirstsetofhumansignals,aimingattheHerculesglobularcluster,andlaunchingfor3minutes.
③Launchaprobetovisitthealiens.ThePioneer10and11launchedbytheUnitedStates,andVoyager1and2,aftercompletingtheirexplorationmissionsinthesolarsystem,theycarriedalotofhumaninformationandroamedtheinterstellarspaceashumanmessengers..Iftheyencounterahumanfriendbychance,theywilllearnabouthumanactivitiesfromthedetectoranddeterminethepossibilityoffurthercommunication.Itcanbeseenthatexploringextraterrestrialcivilizationisacomprehensivescientificmission.Toooptimisticisunrealistic,andtoopessimisticisalsogroundless.
④Directcontactwithaliencivilizationandsociety,thismethodisbasedoninterstellarnavigation.Ourindustrialtechnologyisstillunabletosupportourinterstellarvoyages,butmankindhasneverstoppedfantasizingaboutaliens.
ExtraterrestrialCivilization
Aliens
Weoftenseesuchplotsinmovies:asparklingflyingsaucerfallsfromthesky,andthenfrom
Alittlegreen-skinned,big-eyeddwarfwalkedoutofit,muttering"Wearehereforpeace"(Ofcourse,therearealsothosethatwilldestroytheearthwithoutsayinghello).Inreality,flyingsaucerscanalwaysbethefocusofthenewspaper'sattention,or,inotherwords,afashion.MartinGardner’spassagecandescribeexactlythissituation:“Wheneveryoneseesaflyingsaucer,ofcourseyouwouldliketoseeitonce.”[1]Sothereareallkindsofflyingsaucersandforeigners.Stars:flyingsaucerslikestrawhats,flyingsaucerslikecigars,flyingsaucerslikecakes;greenaliens,redaliens,kidnapperaliens,thiefaliens(specializinginstealinganimalorgansontheranch)andAlienswastingfood(ascamofthe"cropcircle").
However,noneofthiscanbetrusted.Whenwesoughtextraordinaryevidenceforthesephenomena,wefoundthatmostofthephenomenacanbeattributedtohumanflyingvehicles,balloons,naturalphenomena,eyewitnesshallucinations,andoutrightdeceptions.Theremainingcasescannotprovidestrongevidencetoprovethatitisanalienspacecraft.ItisalsoinappropriatetotreatUFOsasalienflyingsaucers.Any"unidentified"objectsyouseecanbecalledUFOs,suchasthelidofatrashcandroppedbyyourneighboronthe21stfloor(Interestingly,some"flyingsaucers"photosarefakedwithsimilarobjectstakingpictures).
CropfieldCircles
TherehavebeensomestrangecirclesinsomewheatfieldsinEngland,whichseemtobesomeverycomplicatedpatterns.Willthesebethesignalsleftbythevisitingaliens?Afterinvestigation,itisfoundthatmostofthemarepranksbysomepeople,butpeoplewhoarekeenonthisstillhavealotofcuriosityaboutthis.However,twopatternswerediscoveredinthewheatfieldsneartheChilboltonObservatoryinHampshire,England.Oneofthemwasaface.ManypeoplesaiditlookedlikeanalieninmoviesandTV.TheotheristhemodifiedpatternoftheAreciboinformationlaunchedtotheM13globularclusterinNovember1974.
Theinformationcontainsalltheelementsthatweestimatethatanypossibleextraterrestrialcivilizationwillbeofinteresttoushumans,including:ourlocation(positioninthesolarsystem),thewaywehumans,andthetransmissionofsignalsAsimplesketchofanastronomicaltelescope,andsomefragmentsofourecologicalstructure.
ThestrangecircleinthewheatfieldfoundinHampshireresemblestheonetransmittedin1974inshape.Butthereisstilladifferencebetweenthetwo:thesimplesketchofanastronomicaltelescopewithnosignaltransmittedinthepatternfoundinHampshireisreplacedbyaman-madespacesatellitethatlookslikesolarenergy;inaddition,thediagramdepictingoursolarsystemisstillThereweretheoriginaleightplanets,butplanets3to5deviatedabit,andthelastonebecameabitbigger.Theoddcircleinthewheatfieldisalmostzeroforaliens.However,thereisnotenoughevidencetoprovethatitisallman-made.Exactlywhatitishasyettobeverified.
ScientistsattheSETIInstituteareincreasinglyoptimisticthattheycanfindsignalsfromtheuniversetoprovethatwehumansarenotaloneinthevastuniverse.Somerecentdevelopmentshaveincreasinglyconvincedthemoftheirviews.Lookingoptimistically,itispossiblethatinthenearfuture,wewillbeabletofindevidencetoprovethatwearenotaloneintheuniverse.
Visitofextraterrestriallife
Infact,scientistsbelievethattheclaimthatanextraterrestrialcivilizationoncevisitedandisstillmonitoringhumansneartheearthisunbelievable.Someonehascalculatedthatifthereare1millioncivilizationsinthegalaxyandonlyonespacecraftreachestheeartheveryyear,thenthereareabout10billionspacecraftlaunchedeachyearintheentiregalaxy,andthemetalneededtomakethesespacecraftisaboutallofthegalaxy.1%ofmetalreserves[2].Inotherwords,acivilizationcanonlyvisitusifitdevotesallitsresources,andthepossibilityofman-madeobjectsliketheVoyagerbeingdiscoveredbyanothercivilizationisbasicallynegligible.
Thisconclusionmaybeverydisappointing.Thoseoriginallyexcitingflyingsaucersandalienshaveallbecomebubbles.Maybeyouhavetoaccusemeofbreakingsomepeople’sdreams.However,thereareevenmoreexcitingandseriousscientificresearchesintheworld:Althoughscientistsdisdainthelegendofflyingsaucersandaliens,theyhavebeencommittedtoscientificsearchplaces.Signsofouterlife.
Theriskofcontactwithaliens
OnApril26,2010,thefamousBritishphysicistandmathematicianStephenHawkingsaidinadocumentarybroadcastonthe25th,Theexistenceofaliensisverylikely,buthumansshouldnotactivelyseekthemout,andshouldmakeeveryefforttoavoidcontactwiththem.
"Therealchallengeistofigureoutwhatalienslooklike,"Hawkingsaid.Inhisview,alienlifeisverylikelytoexistintheformofmicrobesorprimaryorganisms,buttheexistenceofintelligentorganismsthatcanthreatenhumanscannotberuledout.
"Ithinksomeofthemhaveexhaustedtheresourcesonthisplanetandmayliveonhugespaceships,"hesaid."Theseadvancedaliensmaybecomenomads,tryingtoconquerAndcolonizealltheplanetstheycanreach."
Hawkingbelievesthatinviewofthefactthataliensmaylootedtheearth'sresourcesandthendriveaway,humansactivelyseektocontactthem"somewhattoorisky."
"Ifaliensvisitus,IthinktheresultmightbesimilartoChristopherColumbus’sfootstepsontheAmericancontinent.That’snotagoodthingforthelocalIndians."
AmericanhistoryThescientistNeilbelievesthatthestrong(thatis,themoredeveloped)civilizationontheearthalwayscontrolstheweakercivilization,anddoesnotdependonpoliticalaffiliation.Hebelievesthatwhenestablishingcontactwithanextraterrestrialcivilizationwhoselevelgreatlyexceedsours,itmay"suppress"ourcivilizationuntilitisdissolvedinahighercivilization.
ChinesemathematicianandlinguistZhouHaizhongputforwardhispointofviewinhisthesis"CosmicLinguistics":Aslongasitisahigh-levelintelligentlife,theirreasondeterminesthattheymusttreatallcosmicintelligentlifeformsinameasuredmanner.,Soaliensandpeopleonearthwillbeabletocoexistpeacefully,cooperatefriendlyanddeveloptogetherinthefuture.
NASAexpectstohaveclosecontactwithitandmakeitpublicwithin20years
Extraterrestrialcivilization(2photos)
Accordingtoforeignmediareports,NASAproposedatapaneldiscussioninWashingtonthatitwillusemoreadvancedtelescopestoexplorelifeintheuniverse.AuthoritativeAmericanastronomerssaidthattheyarenowgettingcloserandclosertolifeformsoutsidetheEarth,andtheyareexpectedtohavea"closecontact"withlifeformsinouterspacewithinthenext20years.Atthattime,NASAwillnotexclusivelyenjoythis"importantinformation",andwillletthepublicknowaboutthismatterasfaraspossible."Becausethisisamajoreventthatbelongstoallmankindafterall,andeveryonelivingonthisplanethastherighttoknow."Thescientistsaid.CharlesBolden,thedirectorofNASAandformerastronaut,said,“Mostofmycolleaguesherebelievethatinthevastuniversethereisonlyahumanformofintelligentlife,whichisunlikely.”Healsosaidthatalthoughheneverencounteredanyalienlifeformsduringhistimeasanastronautinthe1990s,hehasbeensearchingforit,eventhoughtheprocessisdifficult.
SaraSeager,aplanetaryscientistattheMassachusettsInstituteofTechnologyintheUnitedStates,saidthatattheleveloftechnology,humansareveryclosetofindinganother"earth"andsignsoflifeonotherplanets.
AstronomersbelievethateverystarintheMilkyWayhasatleastoneplanet,andusetheHubbleSpaceTelescope,SpitzerSpaceTelescopeandKeplerSpaceTelescopetoobservefromthegroundtodeterminewhethertheseplanetsareTheremaybeliquidwaterthatguaranteesthesurvivaloflife.
NASAhopestolaunchatransitingexoplanetsurveysatellitein2017andtheJamesWebbSpaceTelescopein2018.Inthenexttenyears,astrophysicaltelescopessuchasthewide-fieldinfraredsurveytelescopemayalsobelaunched.
AsNASAdevelopsmoreandmoreadvancedspacetelescopes,thepossibilityoffindingextraterrestriallifewillincrease.BothSiegelandDaveGallagher,directorofNASA'sJetPropulsionLaboratory,pointedoutthatthedevelopmentofnewtechnologiesmaymakeiteasiertofindsmaller,Earth-likeplanets.
Spaceenthusiastsaskedthroughsocialmedia:"Ifscientistsdiscoverlifeonanotherplanet,willtheU.S.governmentletthepublicknow?""Ofcourseitwill!"NASAChiefScientistEllenStofan(EllenStofan))Answeredwithouthesitation,"Thisisanexcitingthing.Wewillinformthepublicassoonaspossible,andhopethateveryonewillsharetheexcitementbroughtaboutbythismajordiscovery."
MassachusettsInstituteofTechnology,USAScientistSiegelsaidthatatthetechnologicallevel,mankindisveryclosetofindinganother"earth"andsignsoflifeonotherplanets.
DriftingintheUniverse
EarthTelegraph
OnNovember16,1974,ahugeradiotelescope,theAreciboRadioTelescope,wasbuiltinPuertoRico.Justasanewshipwaslaunchedintothewatertobreakawinebottle,aspartoftheinaugurationceremony,scientistsusedittosendan"EarthTelegram"totheHerculesglobularclusterM13.Thisearthdriftbottleneeds24,000yearstoreachthevicinityofM13.Thisisthefirsttimethathumanbeingshaveconsciouslyindicatedtheirexistencetotherestoftheuniverse.Sincewecanshootandsendsuchtelegrams,whynotlistentowhetherotherswillbroadcastsomethingtous?Infact,asearlyas1960,astronomerFrankDrakeledsuchaplan.Callit"ProjectOzma"(ProjectOzma.ThenamecomesfromBaum'sfairytale"TheWizardofOz").Thisprojectuseda26-meterradiotelescopetoconductobservationsforseveralmonths,butfoundnothing.However,scientistsbelievethatitisfeasibletouseradiototrackthetracesofextraterrestrialcivilizations.Aftercalculation,itonlycostslessthanonedollartotransmitanEnglishwordwithamicrowavewithawavelengthofthreecentimeterstoaplace1,000lightyearsaway,andtoreceiveitwiththeexistingtechnologyoftheearth[3].ThisisinstarkcontrasttothecostoflaunchingaspacecrafttotheMilkyWaygalaxymentionedearlier.
The"VoiceoftheEarth"goldturntablecarriedbytheVoyager.Itssymbolicmeaningismoreobvious,andyoucannotexpectothercivilizationstohearittoomuch.
Forthefirsttime,humanbeingsconsciouslyshowedtheirtelegramtotheuniverse.Thistelegramissentinbinaryformat.Ordinarypeoplecanprobablyonlyseethedoublehelix,thehumanshape,andtheshapeoftheAreciboradiotelescope.However,scientistsbelievethatextraterrestrialcivilizationscanunderstandthemeaning.
So,atwhatfrequencyshouldthe"driftbottle"ofextraterrestrialcivilizationbetracked?Scientistsmainlyfocusedonthemicrowavebandsaround1.42GHz,1.667GHz,and22GHz.Thefirstfrequencyisthefrequencyofradiowavesemittedbyhydrogenatoms,thesecondisthefrequencyofhydroxyl(-OH),andthethirdisthefrequencyofwatermolecules.Thesefrequenciesarevividlycalledcosmic"waterholes"—nottheplaceswhereanimalsdrinkwaterontheAfricansavannah,butthebandsthatareconsideredmostlikelytocarryoutinterstellarcommunication.Thereasonforchoosingthesebandsisthathydrogenisthemostabundantelementintheuniverse,andhydroxylandwaterplayavitalroleinlifeactivities.
SearchforExtraterrestrialCivilization
Alltheseprojectsthatlookfor"driftbottles"haveacommonname:SearchforExtraterrestrialCivilization(SETI).Now,thelargestradioSETIisProjectPhoenix.SETIdoesnotproduceanyshort-term,directeconomicbenefits.LikeallSETIprojects,theresearchersofthe"Phoenix"projectoftenfeelfundingconstraints.However,peoplemaybemorefamiliarwithanotherSETIproject,whichisSETI@home.ItwascarriedoutbytheUniversityofCalifornia,Berkeley,andusedascreensavertoprocessradiosignalsreceivedbytheAreciboradiotelescope.Millionsofpeoplehavealreadyparticipatedinthisproject.
Ofcourse,scientistsarenotstaringatthe"waterhole"closely,theyalsomonitorcertaininfrared,ultravioletandevenvisiblelightbands.SETIintheopticalbandhasonlyrecentlyemerged,andthetrackingtargetisalaserpulseemittedbyanextraterrestrialcivilization.
Lookingforplanets
Indirectsearching
Organismslikeuscannottoleratehightemperatures.Therefore,wecanonlyliveonplanetswithsuitableconditions.Ifextraterrestrialcivilizationsarealsoorganisms,thentheymustalsohaveasuitableplanet.OurMilkyWayhas100billionstars.ThereisnoreasontothinkthattheonlyplanetsuitableforlifeisourEarth.
However,findingplanetsismuchmoredifficult.Planetsdonotemitlightandarerelativelysmallinsize.Eventoday'slargesttelescopescannotseeplanetsdirectly.Scientistsusean"indirect"methodtofindplanets.Ifastarhasplanets,intheeyesofbystanders,theyareactuallyorbitingeachother,likedancing.Inthisprocess,thedistancebetweenthestarandusissuddenlycloseandfaraway,anditsspectrumbecomes"blue"forawhileand"reddish"forawhile.ThisiscalledtheDopplereffect,whichissimilartothepitchchangeofawhistlewhenitquicklyapproachesus.Withthismethod,scientistshaveidentifiedabout80similarplanets.It’sabitdisappointingthatmostofthemaresimilartoJupiter,theyaregasplanetswithmasseshundredsoftimesthatoftheEarth,andtheyarenotsuitablefortheexistenceoflife.
The"Kepler"spacetelescopeisnamedaftertheGermanastronomerJohannesKepler.
Searchforterrestrialplanets
Fortunately,scientistsalsohaveothermeansofobservation.ANASAprogramcalled"TerrestrialSearchforPlanets"(TPF)isoneofthem.TPFusesso-called"interferometry"toallowscientiststo"see"planetswithintensoflightyears.Anotherprojectistheso-called"Kepler"spacetelescope."Kepler"isa1-meterdiametertelescope,scheduledtobelaunchedintospacein2006.Whentheplanetpassesoverthesurfaceofthestar,thebrightnessofthestarwilldecreaseslightlyfortheobserver.Thejobof"Kepler"istoidentifysuchadecreaseinbrightness,especiallythedecreaseinbrightnesscausedbyplanetsliketheEarth.
Oxygensearch
Oxygencanalsobeasignoffindingsignsofextraterrestriallife.Oxygenismoreactiveinnature,anditquicklycombineswithothersubstances.Itispreciselybecauseofphotosynthesisthatthehigheroxygenconcentrationintheearth’satmosphereiscaused,and1billionyearsago,itsconcentrationwaslessthanhalfofwhatitisnow.Astronomerscanusespectralanalysistomeasuretheoxygencontentofplanetaryatmospheres.Iftheoxygencontentofaplanetisunusuallyhigh,thentheremaybelifethere.Similarly,carbondioxideandwaterarealsoonthelistofconcerns.
Thefinalanswer
Searchingforextraterrestrialcivilizationisaseriousscientificresearch.Whenwillwegettheanswer?Maybetomorrow,maybe10,000years.SincelifeonEarthcanbeproducedfrominanimatematter,similarstoriesmayhappenelsewhereintheuniverse.Drakeproposedafamousformulaforcalculatingthenumberofcivilizationsinthegalaxy,theDrakeformula.Thisformulacontainsanimportantfactor,thatis,howlongacivilizationcanmaintain.Asaspecies,itisveryimportanttobeabletosafelypasstheinitialstageofmasteringdangeroustechnologies(forexample,canhumanbeingsnotbedestroyedbynuclearweaponscreatedbythemselves?)andbecomerational.Differentpeoplehavedifferentviewsonthedurationofcivilization.Optimisticpeopleconcludethatthereare10millioncivilizationsinthegalaxy,whilethenumberofpessimistsisnomorethanone.
Relatedquotes
Findingplanetarysystemsoutsidethesolarsystemisanotherdirectionforexploringextraterrestrialcivilizations.——CarlSagan
Theexplorationofextraterrestrialcivilizationisnotonlypartoftheexplorationoftheuniverse,butalsohasaprofoundimpactontheevolutionofhumanbeingsandthedevelopmentofscienceandtechnology.——ZhouHaizhong
SETIprobesvariousspectrumsignalsintheuniverse,hopingtodiscovertheintentionalorunintentionalbroadcastofextraterrestrialcivilization.Theprobabilityofsuccessofsuchaprojectisdifficulttodetermine.——SethShostak
Inrecentyears,ithasbecomeincreasinglydifficulttoraisefundsfortheExtraterrestrialCivilizationproject.Astheeconomicrecessioncontinues,wehavetopredictItwasdiscoveredthatthetimetableforExtraterrestrialCivilizationwasdelayed.——FrankDrake