You know what, I’m gonna do this too.
1. UFOs
The universe is way too big for us to be the only intelligent life form out there. There are 10**21 stars in the observable universe. More than one of them has a planet whose inhabitants have built a radio telescope.
However, I don't think it's plausible at all that extraterrestrial aliens have come to visit us *here*. The rocket equation is a harsh mistress.
So what *are* those unidentified flying objects? I'm betting on experimental military aircraft, me. We know that does happen.
