'Alien' is defined as 'a hypothetical or fictional being from another world', which just about hits the nail on the head. For countless years, mankind has been obsessed with what lies above, whether in the form of deities or little green men in an unidentified flying object. And when science developed the technology that probing the universe was finally possible, Earth leaped at the opportunity.
The search for extraterrestrial life has been a popular subject for the past century, and yet it doesn't feel like any significant progress has been made towards discovering Earth's neighbors in the universe. The scientific community is divided on why alien life proves so elusive, maybe because there's very little that smart people agree on. But it's a good idea to be well-informed on the possibilities, so you can tell your alien friends in 2045 that you knew it all along