Intelligent life in our galaxy would be more rare than lower lifeforms if it exists on other worlds. (If not then there is a lot of empty space out there.) I believe there must be life elsewhere in the galaxy, as well as the rest of the universe. As for the likelihood of intelligent life, depending on how many worlds support life, I would use the ratios among lifeforms we find on Earth as an indicator of what might be out there in other parts of the universe. We have yet to determine whether any of the worlds we have found thus far can support life; but if one is found to have the capability, it would mean that there must be a lot of them that can. On some of them there would have to be intelligent life. Out of 250,000,000,000 estimated stars in our galaxy, if 100,000,000,000 have planets, maybe 25,000,000 have life supporting worlds, and perhaps no more that 100,000 would support intelligent life. This is just my thoughts on this, but it is the best anybody can do for now.
2 years ago
Last edited at 11:48AM on 1/1/2012
According to Alex Filipanko (The Universe), it depends if you are optimistic or pessimistic with our current knowledge; we could be commonplace or a rarity. I personally think that extraterrestrial life is out there, partially because of the odds, and partially because we have already discovered over 700 extrasolar planets.