Put simply, Fermi’s Paradox is a simple question: If there is other life in the universe, where is everybody? Given the age of the universe and the large number of stars, doesn’t it stand to reason that life should be common? And yet we have no direct evidence that life exists other than on our Earth. Why is that?
Since we have but one very small sample (the small part of this one solar system that we’ve studied) of evidence, we’re left with logical arguments and pseudo-scientific silliness like the Drake equation to explain why we’ve not made contact with other civilizations.
Yes, I realize that some people put a lot of faith in the Drake equation. But there’s no there there. It consists of seven variables whose values are incalculable. We have absolutely no idea what reasonable values are for any of them. The Drake equation is nothing but a formalized way to make wild guesses.
The logical arguments against extraterrestrial life go something like this: “If we’re not unique, then in a galaxy of 100 billion stars, many of which are older than our sun, you would expect that if even a tiny percentage of the planets developed a space-faring race, they would have spread throughout the galaxy.” The implication seems to be that if extraterrestrial life were possible, then it’s highly unlikely that we would have developed because the planet would have been colonized by somebody else.
Nick Bostrom, author of the article linked above, lays that out very nicely and concludes that there must be some Great Filter (a natural or societal calamity) that prevents development of civilizations that are capable of interstellar travel. His hope is that the Great Filter is something that happens early in the development of life or civilizations–something that would have happened to us eons ago–because to think otherwise would mean that the human race is doomed.
It’s interesting reading and one can hardly fault his logic, but it’s all just so much mental masturbation–exactly like the Drake equation. We simply don’t have enough evidence to say one way or the other. Lack of proof is not proof of lack. Drawing conclusions based on scant physical evidence and wild-assed guesses is mysticism, not science.