You all know this story. In the summer of 1950, Enrico Fermi, the Italian-American physicist and atomic pile-builder, went to lunch at Los Alamos National Laboratory and joined some colleagues there and asked them a question. “Where is everybody?” This confused his colleagues, obviously, because they were sitting right there with him, and then he had to clarify that he wasn’t talking about them. He was talking about the space aliens.

You see, this was only a few years after the supposed flying saucer crash at Roswell, New Mexico, and even though that turned out to be nothing, nothing AT ALL — Merely a downed weather balloon piloted by small hairless men with slits for mouths — still, America had gone saucer-mad, even famous scientists who were eating lunch.

Fermi’s reasoning, if I may paraphrase badly, is that the universe is so vast that it stands to reason there should be other intelligent life out there, and the universe is so old, that unless we were the very first civilization ever to evolve, we should have some evidence of their existence by now, and yet, to the best of our knowledge, we are alone. “Where is everybody,” asked Fermi, and his colleagues had no answer.

Fermi then went on with the same blunt logic to disprove fairies, Sasquatch, God, the possibility of love, and thereafter, as you know, Enrico Fermi ate alone.
– John Hodgman, A Brief Digression on Matters of Lost Time