The idea that aliens may have visited the Earth is becoming increasingly popular. Around a fifth of UK citizens believe Earth has been visited by extraterrestrials, and an estimated 7% believe that they have seen a UFO.
We have no good reason to believe that aliens have ever contacted Earth. Sure, there are conspiracy theories, and some rather strange reports about harm to cattle, but nothing credible. Physicist Enrico Fermi found this odd. His formulation of the puzzle, proposed in the 1950s and now known as “the Fermi Paradox”, is still key to the search for extraterrestrial life (Seti) and messaging by sending signals into space (Meti).