There is are many scientific puzzles which have long attracted my attention. I am a nerdy guy, and that’s just the nature of nerds. One of the more interesting puzzles to me is the Fermi Paradox.

In 1950, a scientist named Enrico Fermi was in an informal discussion with other scientists about Extraterrestrial Intelligence (ETI). Suddenly, Fermi loudly asked, “Where are they?” Mind you, this is 1950, long before we had made any observations of extrasolar planets. Science had some hypotheses about how many planets might be orbiting other stars and recent observations have made the numbers they had available very conservative. Even with the lower estimates of 1950, however, it seemed a probable impossibility that humans would be the first civilization to rise in the galaxy. More to the point, there should be lots of more advanced civilizations out there. Even assuming sub-light speed space travel, probes could have been sent out and, by this time, found us.

The point of the paradox is that we should have found some evidence of an ETI by now. SETI has been running for half a century now, and so far no conclusive evidence of anybody here but us. Now some, myself included, are convinced aliens have visited and continue to visit Earth. This changes nothing. Even if this is true, there should still be mainstream evidence of an extraterrestrial presence. Not of visitation to Earth, necessarily, but out there.

The conspiracy theorist in me wants to scream the evidence is all suppressed. The evil government has kept us from seeing the signals SETI has picked up, or perhaps even fed SETI false data from the various radio telescopes the project has used. While this is in the realm of possibility (my conspiracy muse says it is, anyway), the task of keeping all evidence from everyone’s eyes would be nigh impossible. Somebody somewhere, with all of today’s technology and internet access, would find and convincingly present the evidence to the world.

So, where are they? There is the extremely limited possibility we are the only one. As time goes by and we learn more about the universe in general and our galaxy specifically, this option becomes increasingly small. Data from NASA’s Kepler mission suggested there may be as many as forty billion Earth-sized planets in what is considered to be the habitable zone, the best orbit around a sun-like star. Forty billion possible places for life to happen and for civilization to rise earlier than it did on Earth. The odds against this not happening are staggering.

There are a few theories as to why we haven’t found the evidence. I won’t enumerate them here; read the article in Wikipedia I linked at the start if you want to see the best ones. It’s mind-boggling to think about…and I have hope we find the answer, and other civilizations, in the next few decades.