I apologize to DH in advance, but I think there IS some scientific discussion to be had on this topic. If you disagree, by all means--you're the boss! But I didn't see anything explicitly prohibiting discussions of these types in the guidelines, although I fear that this will just be a big failure when the ``Aliens are among us'' crowd starts posting here. The Fermi Paradox can be stated as follows: if there are advanced civilizations, why don't we see them? Now, I'm sure that UFO aficionados can poke all kinds of holes in the underlying assumptions. Who's to say that the aliens are more advanced than we are? (Slim to no chance of this, but ok.) Who's to say that the aliens don't have invisible, or impossibly tiny probes? (Again, ok. Probably a fair critique.) Anyway, let's assume that we're more or less typical, and there are some more advanced civilizations than us. This is a good assumption, I think, as we live around a 3rd generation star, and the Milky Way has some older stars. The question is, how many more advanced civilizations are there than ours? Because we are more or less typical, we should guess that these aliens are also inquisitive about the universe, and that they will try to investigate the different corners. We should assume that the aliens are limited by the speed of light, as we are. A paper today on arXiv attempts to calculate how many advanced civilizations we should expect, based on the fact that we haven't seen them yet, and based on the above assumptions. http://arxiv.org/abs/0907.0345 They find, in a conservative estimate, that there can be no more than 10 more advanced civilizations. The study is condensed here: http://www.technologyreview.com/blog/arxiv/23832/ The conclusion then, to me, would be that there are a dearth of civilizations in our Galaxy, or that we are highly atypical.