Tuesday, August 4, 2015

If We Blew up the Earth, Would Anybody Else Notice?

That question was raised last week in a scientific paper by Adam Stevens, Duncan Forgan, and Jack O'Malley-James. They're really interested in the opposite question: if a distant civilization destroyed itself, would we see any evidence of it? This question arises because one of the answers to the Fermi paradox (why don't we see any other civilizations out there?) is that advanced civilizations tend to destroy themselves, either accidentally (oops, I dropped my hammer on that big red button) or on purpose (I've genetically engineered a virus that kills only annoying people....)

Stevens, Forgan, and O'Malley-James look at a variety of ways that we might obliterate ourselves. My takeaway from their paper is that it would be surprisingly hard for aliens on a distant planet to detect any evidence of our self-destruction. For instance, if we simultaneously detonated every nuclear weapon on the planet (I am not recommending this, by the way), the resulting gamma-ray signal would barely be detectable at the edge of the solar system. The main way that we might be able to see evidence of another civilizations's demise is spectroscopic: through a change in the chemistry of the atmosphere from a nuclear war, or the release of gases from the death of every living thing on the planet. (Are you starting to get the impression that this paper is a bit of downer?) On a happier note, it's exactly this sort of spectroscopy of the atmospheres of distant planets that could give us the first "smoking gun" evidence for the existence of life on other worlds.


robk said...

and if alien civilization use antimatter bomb or gun like in clasic SF how that change our chance to detect them ??

Kathy said...

Coincidentally, I'm plotting a story which requires the lead character, an amateur historian, to determine the death of a civilization from 7 light years away.

I cheated. I had them be part of a triple star system, one of which is a white dwarf which goes nova by stealing gas from its sister yellow star. The aliens lived in a the third star, also yellow, orbiting the other two from rather farther away (like Proxima in the Centauri system).

Of course, they didn't destroy themselves. Not quite.

Robert Scherrer said...

Regarding destroying the earth with antimatter. I haven't done the numbers, but I am sure that if you annihilated the earth with an equal mass of antimatter, it would be visible in distant galaxies. But this is very inefficient - it would take as much energy to create an anti-Earth as you would get back from annihilating it.