The Fermi paradox is the tension between the high apparent likelihood of extraterrestrial civilizations and the complete absence of evidence for them. If the galaxy is old and full of stars and planets, where is everybody? Proposed answers range from life being rare, to civilizations being short-lived, to a Great Filter that few pass. A 2018 reanalysis argued that, given the huge uncertainties, a silent universe is statistically unsurprising and may mean very little.