When Fermi was asked if he believed in the existance of E.T.s he replied "where are they?" and I think the idea was that if there were E.T.s they should have colonized the galaxy by now. What I am curious about is ... given the fact that the ability to detect earth-like worlds with signatures of life (e.g. presence of methane and oxygen in environment) is currently available and then in one to two hundred years it will no doubt be even better...What factual conclusions might be drawn about the existance of other E.T. civilizations? For example, given the relative ease of spotting life inhabiting worlds in the galaxy can it be a given that any advanced civilization (even one a hundred thousand light years away) would know that there is life on earth? One benefit of answering 'yes' would make the idea that we should have to 'hide' from a potential alien threat mute since they would no doubt have the ability to catalogue the billions of planets through out the galaxy.