Question: Would you say that it is likely that there is life elsewhere in the universe?

Simone Sturniolo answered on 18 Jun 2013:

Yes, I think so. These days we are finding out that almost every star out there has planets, some of which are likely inhabitable. Following something called “Drake’s equation” (well, it’s just common sense, really!), the probability of there being a planet with an alien civilization out there equals the probability of there being a planet at the right distance from its star (and we are pretty much certain there are many of those), multiplied by the probability that life has been born on that planet, multiplied by the probability that this life has managed to reach the stage of being intelligent, etc.
All in all, I think that the presence of simple life (bacteria, algae) elsewhere is almost a given. Animal or vegetal life is a good possibility. Intelligent life and other civilizations? Possibly, but I doubt we’ll ever hear from them. Relativity forbids faster-than-light travel, and with the existing distances between stars and planets, it’s hard to think we could ever get in touch with such a civilization – unless we (or they) find a way to break the rules somehow. There’s also the issue of how long a civilization survives. Suppose that there had been a technological alien civilization near our system, on Alpha Centauri (that’s around 3 light years, a joke for space distances), while on Earth there was the Roman Empire. We would have been able to receive this civilization’s radio signals loud and clear, and even communicated with them, but we couldn’t – we didn’t have radios. Now it’s been 2000 years, and we have radios – but maybe they had a nuclear war, or a catastrophe or some other kind, and they died out or regressed to a non technological stage of civilization. So we still can’t communicate. The problem here is not just being separated by space – it’s also the possibility that we are separated by time!