Cos­mol­o­gists and ET

Will we ever dis­cover ex­trater­res­trial life, and, if so, what will it look like? Six ex­perts give their best guess.

Cosmos - - Cosmos Science Club - — AN­DREW MASTER­SON


Cox sug­gests that life in the uni­verse is likely abun­dant. In­tel­li­gent life, how­ever, is an­other mat­ter.

In his 2015 book Hu­man Uni­verse (writ­ten with An­drew Co­hen), Cox writes there is a sense “chem­i­cal in­evitabil­ity” to life in the uni­verse. But he adds that com­plex life on Earth only arose af­ter the emer­gence of eu­kary­otes – cells con­tain­ing or­ganelles.

Re­search sug­gests eu­kary­otes de­vel­oped as a re­sult of one prim­i­tive cell – called a prokary­ote, like a bac­terium – ab­sorb­ing an­other, two bil­lion years ago. (Mi­to­chon­dria and chloro­plasts are descen­dants of in­de­pen­dent prokary­otes that en­tered sym­bi­otic re­la­tion­ships with larger cells.)

The ad­vent of eu­kary­otes on Earth was a van­ish­ingly un­likely de­vel­op­ment. Cox calls it an “evo­lu­tion­ary bot­tle­neck” and thinks it so unusual that it might have hap­pened only once in the uni­verse.

“One can eas­ily imag­ine that the 20 bil­lion Earth-like worlds in the Milky Way could all be cov­ered in prokary­otic slime,” he writes. “A liv­ing galaxy, yes, but a galaxy filled with in­tel­li­gence? … I’m not so sure.”


To­gether with the late Fred Hoyle, math­e­ma­ti­cian, as­tronomer and as­tro­bi­ol­o­gist Wickramasinghe de­vel­oped the as­tro­bi­o­log­i­cal the­ory known as pansper­mia, which holds life on Earth was catal­ysed ar­rived as mi­crobes trav­el­ling through space on me­te­ors and in­ter­stel­lar dust.

He sug­gests that mi­cro­bial life may have landed dur­ing the Hadean pe­riod, four bil­lion years ago, when lots of smallish me­te­orites smacked into the planet.

In a pa­per pub­lished in Au­gust 2017, he sug­gests ET might also have been de­posited on the moon. Re­cent ev­i­dence in­di­cat­ing the pres­ence of wa­ter, he says, “re­opens the pos­si­bil­ity that mi­cro­bial life might ex­ist close to the lu­nar sur­face”.


In a 2016 pa­per, The “Hard Prob­lem” of Life, writ­ten with Sara Imari Walker, as­tro­bi­ol­o­gist Paul Davies be­gins with a well-known prob­lem. Given that all life on Earth arose from a sin­gle com­mon ances­tor, we have no way of know­ing what as­pects of it are law-like – found in all life, across the uni­verse – and which are spe­cific only to our own bio­sphere.

It fol­lows that life else­where need not in­volve Earth-like bi­ol­ogy or chem­istry. In­deed, write Davies and Walker, it is pos­si­ble that it “will not ul­ti­mately be re­duc­ible to known phys­i­cal prin­ci­ples”.

The pair sug­gests that the true es­sen­tial for life is in­for­ma­tion – which some­how “calls the shots”.

Those things that we as­sume to be fun­da­men­tal – repli­ca­tion and metabolism – might be fea­tures only of “Earth-like” bi­olo­gies. There is a risk that should we ever en­counter ET, we might not recog­nise it be­cause we lack “a gen­eral-pur­pose set of cri­te­ria for iden­ti­fy­ing it “.


The re­tired com­man­der of the In­ter­na­tional Space Sta­tion thinks the bizarre 500 mil­lion year-old soft­bod­ied fos­sils found in Canada’s Burgess Shale hold some clues.

“It’s so wildly dif­fer­ent to the life we’re used to,” he says. “There was such wild ex­per­i­men­ta­tion through the four bil­lion years of life on Earth.”

We might find life on Mars, or Ence­ladus, or Europa, he notes, and it might look like an or­gan­ism that died out dur­ing a mass ex­tinc­tion down here.

“But I might have that com­pletely wrong,” he adds. “Some of the strange ex­am­ples they came up with on Star Trek might be a bet­ter rep­re­sen­ta­tion.”


Wright, an as­tro­physi­cist at Penn State Univer­sity in the US, sug­gests we need to be look­ing for the things ET builds.

He sug­gests fo­cus­ing the search for in­tel­li­gent ET on exoplanets. Rather than look for traces of bi­ol­ogy, though, we should look for tech­nol­ogy.

We should search for gi­ant ma­chines, which are likely to be “be de­tectable by their waste heat in the mid-in­frared.”

Such struc­tures, he says, could in­clude enor­mous energy-col­lec­tors (known as Dyson spheres), satel­lites and de­fen­sive shields.

Look­ing for them, he notes, need not be ex­pen­sive. The search can “pig­gy­back on work likely to hap­pen in the fu­ture, any­way, as nat­u­ral anom­alies are dis­cov­ered in the course of ex­o­plan­e­tary sci­ence.”


In his book Death By Black Hole (2005), Tyson says mi­cro­bial life is pos­si­bly hum­ming away through­out the uni­verse.

In­tel­li­gent life, on the other hand, is likely to be very scarce. How­ever, the Coper­ni­can Prin­ci­ple – they key idea that we and our planet are not spe­cial – im­plies it must be around some­where.

He says ET must be lim­ited to a max­i­mum size. It could not be as big as the so­lar sys­tem –10 light years across. Even as­sum­ing nerve im­pulses at the speed of light “if it wanted to scratch its head, then this sim­ple act would take 10 hours to ac­com­plish.”

Tyson hopes that some in­tel­li­gent ETS are send­ing out mes­sages into the cos­mos, rather than, like us, scan­ning in the hope of hear­ing an alien trans­mis­sion. If not, he writes, “ev­ery­body would be lis­ten­ing, no­body would be re­ceiv­ing, and we would col­lec­tively con­clude that there is no other in­tel­li­gent life in the uni­verse.”

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