Is Anybody Out there?
The universe is vast and ancient, containing billions of stars. The likelihood is that other Earth-like planets, suitable for intelligent life, exist out there. Given the vast amount of time available, some of these suitable planets should have evolved intelligent life, some of these lifeforms should have developed interstellar travel, which should in turn have enabled them to colonise the galaxy within just a few tens of millions of years. So, we should expect the universe to be teeming with intelligent life. Any yet, we find none. Despite 50 years of searching, we have not yet found any evidence of extraterrestrial civilisations. We have failed to detect artificial signals in space, and we have failed to find any artefacts of intelligent life. This is the basic tenant of the Fermi paradox; we expect intelligent life to be prevalent in the galaxy, and yet we are unable to find it.