We get round to this every eighteen months or so. From Noelle Dahm at Nautilus:
Absent signs of life, astronomers are starting to look for extraterrestrial nuclear wars and pandemics.
The aliens may have found their grave. As we sweep the radio frequencies, we hear only noise; as we slew our telescopes, we see barren pixel after pixel. Is that because our fellow inhabitants of the galaxy have done themselves in, reducing their home planets to cinders? Is the night sky a charnel house hidden under a veil of tranquility?
Last year Jack O’Malley-James, an astrobiologist at Cornell University, and his colleagues Adam Stevens and Duncan Forgan published their analysis of this macabre possibility. Just as astrobiologists have started to look for possible biosignatures—evidence of life, such as water or oxygen in planetary atmospheres—they might also look for necrosignatures, the remains of annihilated civilizations. And if we ever do find them, it would not augur well for our own prospects, because what makes us think we could avoid the fate that befalls all other intelligent beings in the galaxy?
Well, we can’t, of course: “All people are like grass, and all their glory is like the flowers of the field; the grass withers and the flowers fall, … However long-lived, the aliens would be mortals in a mortal universe. It would make great science fiction.
Paul Davies at Arizona State University is not as confident. “The probability is extremely low that we would catch a civilization ‘in the act’ of self-destruction, and most of the scenarios do not have long-term signatures,” he says. Ian Crawford at Birkbeck College, University of London—who was the referee for the paper—agrees: “If [intelligent civilizations] are very rare, which I personally think they probably are, then the chances of you detecting one that’s either extant or that self-destructed recently, within the last hundreds, thousands, or million years, must be very low,” he says. Yet he adds that he sees value in keeping an eye out: “If we don’t, we’ll never find anything.”More.
But now, consider all the other theses about why the aliens, they never write, they never phone:
They are said to be hiding from us in order to survive. Maybe the space aliens are hiding on Earth, in junk DNA, as famous astrophysicist Paul Davies has suggested. Former nanotechnology watchdog Mike Treder theorizes that the aliens have run into “a cosmic roadblock that either destroys them or prevents their expansion beyond a small radius.” Or, some mathematicians suggest, maybe ET is just avoiding us. Another researcher warns that the aliens may destroy us because of our greenhouse gas emissions.
Or maybe they are works of the imagination? Oops, that is not a science-based idea.
See also: But surely we can’t conjure an entire advanced civilization?
How do we grapple with the idea that ET might not be out there?
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