[CORed]

When dealing with questions of extraterrestrial life and intelligent extraterrestrial life, we are handicapped by an insufficient sample size. One is a pretty small sample, so any hypotheses we come up with are going to be highly speculative. However, I'll give it a go.

I suspect that life is pretty common in the universe, but that life capable of interstellar travel is extremely rare. Actually, we have a sample size of zero with respect to life capable of interstellar travel. We humans would like to think that we are smart enough to pull this off, but whether we will remains to be seen.

Earth is approximately half way through its habitable life span. It formed about 5 billion years ago, and about 5 billion years in the future, the sun will exhaust it's hydrogen, expand into a red giant, and incinerate the Earth. So, based on our sample size of one, we would have to say that life capable of producing complex technology takes a long time to evolve and may well be pretty rare in the universe.

The second factor is interstellar travel. It is a tough nut to crack. Assuming that there are none of the loopholes in Relativity that are so popular in science fiction, such as warp drives, hyperspace, wormholes (that one can actually travel through without being broken down into ones component elementary particles), traveling to another star system will take an incredible amount of time, an incredible amount of energy and other resources, or both, and even if we accomplish this, there is no guarantee that we we will find habitable planets or other intelligent life at the other end.

So, even if we manage to advance our technology to the necessary degree before nuclear war, exhaustion of resources, asteroid impact, global warming, or some other man-made or natural disaster leads to our extinction or the collapse of industrial civilization, it is not inconceivable that we (or hypothetical intelligent E.T.'s) will decide that it just ain't worth it. So we really don't have any idea how common actual or potential star-faring species are. 1000 per galaxy? 10 per galaxy? 1 per galaxy? 1 for every 100 galaxies? If the frequency is on the low end of that range, we may never find any of the others.