Reasonable estimates make it seem that the odds that intelligent alien life exists are quite high.
Here’s a great, short video introduction to the subject. Feel free to skip it if you’re already an initiate.
If alien life does exist, it should not be hard to detect. Interstellar distances may be daunting for craft made of atoms, but at the least our galaxy should be suffused by a cacophony of structured broadcasts on all wavelengths.
Yet we have no such evidence that even a single civilization other than our own exists.
There are a number of explanations for why this might be, but let’s set those aside—here’s how I solved the Fermi Paradox to my own satisfaction.
We’ve not encountered alien life because there is no profit in civilizations contacting one another.
Call this the “every alien invasion movie you have ever seen makes no sense” hypothesis.
Resources—organic matter, minerals, sources of energy—are abundant in the universe. Life is a system for accelerating entropy, so an inhabited planet is in many ways less valuable than a system full of untouched resources. The enormous cost of interstellar travel therefore demands that ships sent in search of resources avoid inhabited planets.
An additional disincentive to contacting other civilizations is that they may decide you are a threat to their ultimate expansion. Yes, the galaxy is full of exploitable resources, but like any other ecosystem, it is finite, and civilizations will ultimately compete for them.
We’ve not encountered aliens because the smartest thing to do when you become an interplanetary species is to hide your existence.
If you’re smart enough not to blow yourself up (intelligent civilizations eventually committing suicide through nuclear war or some other means is a common solution to the Fermi Paradox) you’re probably smart enough to cloak your wireless communications.
Since you’re not visiting inhabited planets nor contacting them on any portion of the electromagnetic spectrum, you are effectively invisible to all but the the most sophisticated of your peers.
Maybe super-sophisticated galaxy-spanning civilizations know about each other. Maybe they contact one another, for some reason or another. But probably, they’re (rightly) afraid of one another, and of inspiring civilizations less sophisticated than themselves to reach their heights of technology.
I don’t think we’re alone in the universe. I just think no one is interested in us.
Note: I’m hardly the first to come up with this solution to the Fermi Paradox. In a way, I stole the whole idea from Douglas Adams.