http://en.wikipedia.org/wiki/Fermi%27s_paradox Wow there's really some interesting reading there, most of it not even strictly about Fermi's Paradox. :) The stuff about the Rare Earth hypothesis is fascinating. Personally I think, given the age of the universe (new data not withstanding since I'm waiting for the big brains to talk about it for a while) and evolutionary time, that many people are overzealous in predicting intelligent alien life.