Are we alone in the universe?

For centuries humans have looked up into the night sky and wondered, are we alone? Why would we be? After all, there are hundreds of billions of plants and stars in the galaxy.

That conundrum is known as Fermi’s paradox, the contradiction between the high probability that there is some kind of life on some planet somewhere and the lack of evidence to prove it.

British  astronomer Stephen Webb offers 50 possible explanations for this galactic paradox.