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To top it off, the galaxy (and in particular, our solar system) do not show much evidence of colonization. It turns out that given any reasonable assuptions about technology and the period between colonization attempts, the time scale for colonization of the galaxy is far less than the timescale for evolution of intelligence. Thus, if intelligent life were relatively common, and even one species thought that colonization were a good idea -- the entire galaxy would likely have been colonized before we showed up on the scene.


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If im reading this correctly, you are saying that there should be some sort of leftover remains showing signs of colonization. Do you really think that after the human race dies out on this planet that it will show any signs of our past existence? It will probably be like any other crater covered rock in the universe. Homosapiens have only been around for 100,000 years, while the universe itself has been around for 13,000,000,000 years (roughly). I would think it is safe to say that given that there are 100,000,000,000 galaxies in the universe, and the given the time frame, there is a very likely chance that life is out there or has been out there before us. As far as our own solar system, photographs of Mars show evidence of past oceans and river beds. Saturn's moon, Titan, is the closest planetary body in our solar system to being earth-like in that it has a nitrogen-rich atmosphere and lakes and rivers of liquid methane.