During a conversation decades ago, a famous physicist named Enrico Fermi wondered…where is the extra-terrestrial life? While many people consider the idea of aliens as something from science fiction (and so far, it has been), it seems crazy that humans are somehow the only life in a vast, if not infinite, universe. Thus, we have the Fermi Paradox: by laws of probability, there should be extra terrestrial life (we’ve seen many Earth-like planets that could potentially support life), but so far, we have seen no evidence of them. Where are they all?
Of course, we have no answer to this paradox, but many potential explanations have been suggested since Fermi posed this question in the 1940s. Here are a few possible reasons why we haven’t met any of the aliens in our universe:
(1) They just don’t exist – this would imply that Fermi’s assumption that there must be many other civilizations in the world is false. Maybe we are the first life in the galaxy, maybe the idea of the “Goldilocks Planet” holds (that is, only very few planets have the ability to sustain life because they need very specific conditions of temperature and atmosphere), and on those very few planets, the actual creation of life is very rare and requires even more specific conditions. Based on assumptions made for many years by scientists, this hypothesis seems more unlikely than others – we have found Earth-like planets already that could sustain life.
(2) They exist, but cannot communicate with us – maybe we’re the only life in the universe to become intelligent. Maybe, like us, they are still developing their space travel technology and just haven’t gotten to the point where they can reach out to us. Maybe they are reaching out to us, and we can’t interpret the signals for some reason. Some scientists have suggested that their physics and mathematics are so different from ours that it’s impossible to communicate with them. Maybe they don’t want to communicate with us. And finally, the most concerning, that intelligent civilizations like ours just don’t last that long, due to overpopulation, wars, or other disasters. Therefore, no civilization has been able to develop to the point of interstellar communication, even though they exist.
(3) They are already here – this one seems to be directly from some science fiction/horror/Twilight Zone stories, but they have been and are being seriously considered. Maybe the human race came from alien civilizations, and thus we are the extra terrestrials. One, known as the zoo hypothesis, suggests that Earth is a giant zoo for aliens to watch and study us, which is why we haven’t seen them. Another suggests that we are actually in a simulation developed by aliens to study us.
These are all interesting ideas; the problem with this particular paradox is that it is basically impossible to test any of these hypotheses right now. We lack the technology and understanding of the world to evaluate these hypotheses in a scientific manner, so for now we are forced to simply speculate.