Andthesamekindofinferencemustapplytoallthematuredstarswhichweseeintheheavens。
Whenwedulytakeallthesethingsintotheaccount，thecaseofoursolarsystemwillappearasonlyoneofathousandcasesofevolutionanddissolutionwithwhichtheheavensfurnishus。
Otherstars，likeoursun，haveundoubtedlystartedasvaporousmasses，andhavethrownoffplanetsincontracting。Theinferencemayseemaboldone，butitafterallinvolvesnootherassumptionthanthatofthecontinuityofnaturalphenomena。Itisnotlikely，therefore，thatthesolarsystemwillforeverbelefttoitself。Starswhichstronglygravitatetowardeachother，whilemovingthroughaperenniallyresistingmedium，mustintimebedrawntogether。ThecollisionofourextinctsunwithoneofthePleiades，afterthismanner，wouldverylikelysufficetogenerateevenagrandernebulathantheonewithwhichwestarted。Possiblytheentiregalacticsystemmay，inaninconceivablyremotefuture，remodelitselfinthisway；andpossiblythenebulafromwhichourowngroupofplanetshasbeenformedmayhaveoweditsorigintothedisintegrationofsystemswhichhadaccomplishedtheircareerinthedepthsofthebygoneeternity。
Whentheproblemisextendedtothesehugedimensions，theprospectofanultimatecessationofcosmicalworkisindefinitelypostponed，butatthesametimeitbecomesimpossibleforustodealverysecurelywiththequestionswehaveraised。Themagnitudesandperiodswehaveintroducedaresonearlyinfiniteastobafflespeculationitself:Onepoint，however，weseemdimlytodiscern。Supposingthestellaruniversenottobeabsolutelyinfiniteinextent，wemayholdthatthedayofdoom，sooftenpostponed，mustcomeatlast。Theconcentrationofmatteranddissipationofenergy，sooftenchecked，mustintheendprevail，sothat，asthefinaloutcomeofthings，theentireuniversewillbereducedtoasingleenormousball，deadandfrozen，solidandblack，itspotentialenergyofmotionhavingbeenalltransformedintoheatandradiatedaway。SuchaconclusionhasbeensuggestedbySirWilliamThomson，anditisquiteforciblystatedbytheauthorsof“TheUnseenUniverse。“
Theyremindusthat“iftherebeanyoneformofenergylessreadilyorlesscompletelytransformablethantheothers，andiftransformationsconstantlygoon，moreandmoreofthewholeenergyoftheuniversewillinevitablysinkintothislowergradeastimeadvances。“Nowradiantheat，aswehaveseen，issuchalowergradeofenergy。“Ateachtransformationofheat-energyintowork，alargeportionisdegraded，whileonlyasmallportionistransformedintowork。Sothatwhileitisveryeasytochangeallofourmechanicalorusefulenergyintoheat，itisonlypossibletotransformaportionofthisheat-energybackagainintowork。Aftereachchange，too，theheatbecomesmoreandmoredissipatedordegraded，andlessandlessavailableforanyfuturetransformation。Inotherwords，“ourauthorscontinue，“thetendencyofheatistowardsequalization；heatisparexcellencethecommunistofouruniverse，anditwillnodoubtultimatelybringthesystemtoanend……Itisabsolutelycertainthatlife，sofarasitisphysical，dependsessentiallyupontransformationsofenergy；itisalsoabsolutelycertainthatageafteragethepossibilityofsuchtransformationsisbecominglessandless；and，sofarasweyetknow，thefinalstateofthepresentuniversemustbeanaggregationintoonemassofallthematteritcontains，i。e。thepotentialenergygone，andapracticallyuselessstateofkineticenergy，i。e。