Just saw an article that there is new speculation based on discovered planets around other suns that there could be earthlike planets around all the stars that are similar to ours (not news to me, I would have bet money on that before we ever discovered the first planet). Also that there could be life on many of them. If there is life it could be intelligent. http://www.cnn.com/2009/TECH/space/02/25/galaxy.planets.kepler/index.html Assuming for the sake of argument that there are hundreds or even thousands of intelligent civilizations in our galaxy, why haven't we heard them? What are the possible explanations for the silence? In another thread I asked how far away would we be able to detect a civilization that is emitting signals exactly like we are emitting ignoring the travel time issue. It seems from the posts there that we should be able to detect emissions like ours from almost anywhere in the galaxy so detection isn't the obvious problem.