Fermi's Paradox speculates that the fact that our civilization has not yet encountered evidence of alien civilization implies that such life must not exist. In "Tapeworm Logic," Charlie Stross brilliantly skewers this by looking at the version of Fermi's Paradox that a tapeworm-philosopher might arrive at:
Our tapeworm-philosopher gets its teeth into the subject. Given that the human is so clearly designed to be hospitable to tapeworm-kind, then it follows that if there are more humans, other humans out there beyond the anus, then they, too, must be hospitable to tapeworm-kind. Tapeworm-kind has become aware of itself existing in the human; it is logical to assume that if other humans exist then there must be other tapeworms, and if travel between humans is possible—and we infer that it might be, from the disappearance of our egg sacs through the anus of the human—then sooner or later humans interacting in the broader universe might exchange eggs from these hypothetical alien tapeworms, in which case, visitors! Because the human was already here before we became self-aware, it clearly existed for a long time before us. So if there are many humans, there has been a lot of time for the alien tapeworm-visitors to reach us. So where are they?
Welcome to the Fermi paradox, mired in shit. Shall we itemize the errors that the tapeworm is making in its analysis?
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.