After The End

Question from Salim:
I was wondering if you had ever considered the possibility of humanity wiping out humanity or our planet (or the universe) getting destroyed. So what if this one day happens? Will we await another big bang to restart life?

Answer by SmartLX:
It could happen. It could also have already happened.

If humanity does something stupid or clueless enough it could well wipe out all life on Earth, which is to say all known life in the universe – emphasis on known, because we can’t discount possible alien life out there somewhere. (Immediately this conflicts with fundamentalist Christians, who commonly believe that only God can destroy the world and He promised not to, so we needn’t worry about the environment at all.)

If everything does die, there’s a possibility that the chemicals still present on the planet could be driven by natural movement (wind, waves, tectonic plates, etc.) towards a second abiogenesis event wherein a new form of life emerges. The circumstances would be very different from 3.5 billion years ago, but since we don’t know exactly what happened it’s not unthinkable that it could happen another way, or the same way in a different place.

The outlook for that new, unrelated life would be somewhat grim. Earth was already about a billion years old when life started the first time, and about a billion years from now the aging sun will grow too hot for Earth to be inhabitable. Our successors would have to evolve the necessary intelligence to achieve space travel much, much faster than we did to have a chance of escaping.

Forget starting from scratch on Earth so late in the piece. Subsequent life will have a much better chance if it starts further out in the solar system, say on a moon of Jupiter or Saturn, say Europa. That will give it up to another 4 billion years to achieve interstellar flight before the Sun dies altogether. But then if we’re hypothesising about the best place for life to start elsewhere, the best candidates are almost certainly planets we haven’t discovered around stars we can’t even see (or if we have seen them, we’ve given them names like HR 8799). There are stars whose lifespans or “sequences” are far longer than the Sun’s.

But what if this whole universe is finally a bust, all life dies out and there’s not enough energy left to restart it? If the universe suffers a heat death then nothing further will come of it, and indeed another spontaneous Big Bang or equivalent might be needed for a new universe, and the possibility of new life, to rise. If on the other hand the universe ends in a Big Crunch (looking less likely in the last decade or so) then it might explode outwards again and produce new life by itself.

So yeah, I’ve given it some thought, as do most people who reflect upon modern cosmology. The sheer scale of the things you have to consider can be unsettling to say the least, and that’s before you start on the existential threats we face as a species. People face the subject through humour, through academics, through faith, or not at all. Sometimes it keeps us up at night, but the world can be a scary place at all levels and yet life goes on…for now.

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