At the heart of the Fermi Paradox is the observation that we have not made contact with other civilizations from alien worlds, despite the seemingly high probability that there is other intelligent life in the Universe, that is at least as advanced as our own, and in some cases significantly in advance of us. The paradox was named for Enrico Fermi, the Italian physicist, who posed it back in 1950. After a more detailed study by Michael Hart came out in 1975 it is sometimes referred to as the Fermi-Hart paradox.
So what is it that makes many people believe that there are, perhaps huge numbers, of extraterrestrial civilizations out there? Firstly, there is the immense age of the Universe. Current scientific estimates suggest that it is as much as 14 billion years old. Secondly, there is the immense number of stars out there, many of which will have planets like our own orbiting them, and which we therefore know could potentially support life and ultimately advanced civilization.
So if we accept that there are advanced extraterrestrial civilizations and that they could perfectly well be in contact with us, why have they seemingly not contacted us?
After all, we have seen no probes or spacecraft or even any debris. The obvious answer here is that maybe the distances involved are too great to physically travel between the planets in a reasonable amount of time to make it a sensible thing for them to do.
But why is there this so-called great silence, where not even radio transmissions from alien civilizations have been intercepted? Those familiar with science fiction will perhaps cite the possibility of galactic laws on non-intervention until a civilization has reached some particular level of advancement. But what we need really need is a full scientific analysis here. The new interdiscipline of astrobiology, which involves the integration of complementary approaches from a wide variety of areas such as astronomy, physics, chemistry, geology, and biology, seeks to provide this.
But at the moment the discussion in many quarters quickly seems to fall further into the realms of conspiracy theory with every crank pushing a pet theory. These will often focus on paranoid delusions about government suppression of information or the involvement of secret societies. Unfortunately, this is the face of the discussion that mainly finds its way into any media coverage of the issue. But who knows, maybe the truth is the rather more disconcerting and mundane one that if there are any alien civilizations that are capable of contacting us then maybe they've taken one look at us and simply haven't bothered yet.