Science & Technology

The Great Filter Might Be What's Preventing Aliens from Reaching Us

Where are all the dang aliens?! Since at least the 1950s, this pervasive question has inspired a never-ending menu of creative solutions. One answer proposes something called the Great Filter. But which side are we on?

What's the Interstellar Password?

Robin Hanson, a research associate at Oxford University and professor at George Mason University, attempted to answer the Fermi paradox in 1998 with his Great Filter hypothesis. (Side note: The Fermi paradox wonders why we haven't seen a shred of evidence for aliens despite the overwhelming probability that alien life exists.) According to Hanson, there could be something standing in the way of life forms that prevents them from becoming interstellar. If a civilization could achieve interstellar communication, that would mean we could've made contact with civilizations from outside our solar system by now. But, you know, we haven't, and this theoretical roadblock may be to blame.

The Great Filter hypothesis suggests that without something getting in the way, planets within a hospitable star system should give rise to life, which eventually leads to tool-using animals with big brains, which eventually leads to colonization beyond the homeworld. But considering we haven't bumped into alien life yet, either we're the only species to make it past the filter or (gulp) the filter is going to weed us out before we get there.

Related Video: Will We Ever Find Alien Life?


Now, the big question is: Where does the filter sit in the evolutionary chain?

If we've already passed the filter, maybe other life hasn't because the step from zero life to simple life is very difficult and rare. Or maybe it's insanely difficult for simple life forms to become multicellular; that, too, could be the filter. Either would satisfy the Fermi paradox. Think of it all like a universe-wide survival of the fittest. Only the best, biggest, and brightest civilizations make it past the filter and into an exclusive club, waiting for the aliens to walk in and take a seat.

Whenever we discover life beyond Earth, we'll get a better idea of where the filter might be. If we found simple life in our own solar system, we'd know that life isn't that rare elsewhere, so the filter must be further up the ladder.

If we found multicellular organisms in our solar system, or even, holy crap, vertebrates, that would mean the filter doesn't make forming complex life very difficult either. This would be a mind-blowing discovery, but also a terrifying one, assuming the Great Filter really is a thing.

Finding complex life in our own solar system would mean humanity has yet to ... get ... past ... the ... filter. If the Great Filter isn't in humanity's past, then we have yet to face it. If it even exists. Whatever it may be. Mass destruction via asteroid? Climate change? Nuclear annihilation? But enough of that fear-mongering. Assuming we already passed the filter, there's only one question to ask: What nearly impossible obstacle did humanity miraculously overcome?

Get stories like this one in your inbox or your headphones: sign up for our daily email and subscribe to the Curiosity Daily podcast.

Demystify the Fermi Paradox in "The Great Silence: Science and Philosophy of Fermi's Paradox" by Milan M. Ćirković. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Joanie Faletto August 22, 2017

Curiosity uses cookies to improve site performance, for analytics and for advertising. By continuing to use our site, you accept our use of cookies, our Privacy Policy and Terms of Use.