The Fermi Paradox is an observation/question by physicist Enrico Fermi: The universe is very old. Life (from a scientific viewpoint) seems to be relatively simple—simple enough that, given the unimaginable size of the universe, there should be millions of planets with life scattered out there. And even without Faster-than-Light Travel, an intelligent spacefaring species should be able to spread across the galaxy in a relatively short amount of time. So where are all the aliens?
We should be able to see all kinds of signs for intelligent alien life when we look at the stars, or possibly even evidence of alien life visiting Earth. But we don't.
There are numerous proposed solutions to this question, which break down into two broad categories:
- Absent Aliens is the simple solution, and makes for a fairly straightforward story: the entire universe is essentially uninhabited, and out there for us to settle freely.
- Invisible Aliens is more tricky, as there may be all kinds of reasons we might not see the aliens that are out there. Even if life is common, intelligent life might be rare for any of a number of reasons. And even if intelligent life is common, it might be hiding, or it might not last very long. If they're bizarre Starfish Aliens, we may simply not recognize what we're looking at. If they're Sufficiently Advanced Aliens, we may not even have discovered the technologies required to detect them. And if they're more than sufficiently advanced, their intelligence might have led to some sort of transcendence that we can't detect, even in theory. Alternatively, they may be perfectly visible already, but The Men in Black are making sure the general public doesn't realize it.
Related to the paradox is the Drake equation
, one attempt to quantify the elements required to actually discover other intelligent life forms out there — unfortunately, most of its terms are unknown, and can never be
known for sure until after we resolve the Fermi Paradox one way or the other: either by finally contacting an alien civilization, or by exploring enough of the universe to say convincingly that they don't exist.
The Other Wiki
has more details
Works that mention or discuss the paradox: