There Have Probably Been Aliens
The universe is so big, that I think it&#x27;s very likely that somewhere out there are, there are many other intelligent civilisations, in distant galaxies–but so far away we&#x27;ll never be able to visit them, never be able to communicate with them, we&#x27;ll likely never even know of their existence (not in a million years–and I mean that literally.)<p>In the long-run (of millions of years), the two most likely outcomes for humanity are extinction or galactic colonisation. If we do colonise the galaxy, we&#x27;ll prevent any other intelligent species from evolving within it (by fully occupying that ecological niche.) If we go extinct, we&#x27;ll leave that niche open for another species to maybe one day occupy as we would have failed to do. The galaxy is likely a natural hard limit for our species, since while interstellar travel is difficult it is arguably possible (not with present day technology and economics, but potentially within a few centuries from now), but intergalactic travel is likely never going to be possible.<p>Even if these authors are right that other intelligent life once existed in this galaxy, it&#x27;s almost surely extinct by now. If that&#x27;s true, it makes their conclusion profoundly pessimistic – the more ruins of dead civilisations this galaxy contains, the greater the likelihood that we&#x27;ll meet the same fate as they did.<p>I think we&#x27;ll always be alone in the universe. And it&#x27;s probably better that way.