"I have interviewed some of the hundreds of thousands of people who claim to have had direct encounters with spacecraft, or the crew of spacecraft, from another galaxy. Some of these are so vivid and detailed (and so comparable with other depositions from other people who cannot have compared notes) that a few impressionable academics have proposed that we grant them the presumption of truth. But here is the obvious Ockhamist reason why it would be utterly wrong to do so. If the huge number of "contacts" and abductees are telling even a particle of truth, then it follows that their alien friends are not attempting to keep their existence a secret. Well, in that case, why do they never stay still for anything more than a single-shot photo? There has never been an uncut roll of film offered, let alone a small piece of a metal unavailable on earth, or a tiny sample of tissue. And sketches of the being have a consistent anthropomorphic resemblance to those offered in science fiction comics. Since travel from Alpha Centauri (the preferred origin) would involve some bending of the laws of physics, even the smallest particle of matter would be of enormous use, and would have a literally earth-shattering effect. Instead of which — nothing. Nothing, that is, except texts and shards that are available only to a favored few."