The Great Filter

One of the greatest mysteries of the universe is the Fermi paradox. At it's most basic level, the Fermi Paradox asks that if the universe is teeming with intelligent life, then why don't we see evidence of it? While one may be rightly skeptical when claims of finding aliens are advanced, the fact of the matter is that it may be more likely that our galaxy would be teeming with intelligent life than not.

The reason for this is simple. Fermi stated that there are billions of stars in our galaxy that are comparable to our sun. No small amount of these stars are older than our sun. Some of these stars are bound to have planets similar to Earth. Some of those will develop intelligent life like Earth has. If you take that premise, or the related Drake equation that can be used to predict how many intelligent species should be present in the galaxy, you come up with staggering numbers every time in favor of intelligent life being everywhere and easily detected. But it's not.

There is no shortage of solutions for the Fermi Paradox. These can range anywhere from an ocean planet where life is intelligent but can't develop technology because, well,  fins are bad for manufacturing things to the need for a presence of a Jupiter-sized planet to clean out enough asteroids to keep life from going extinct every few million years. But one potential solution stands out.

It's called the Great Filter and it suggests that the reason we don't see alien civilizations all over the place is because something, which could be one of several things, causes those civilizations to go extinct before they ever have a chance of branching out into the universe. More, the idea of a great filter comes along with a rather spooky conclusion. The easier it is for life to evolve to our stage, the worse our chances are for long-term survival.

Part of the reason that the Great Filter is such an attractive solution to the Fermi Paradox is that we know how earth-life behaves on a fundamental basis and we can assume that other life behaves much the same way. One thing we notice time and again about Earth life is that it's unbelievably tenacious. You can drill miles into the earth and take rock samples and still find bacteria living there. Conversely, you can do the same in the arctic. Bacteria have even survived being trapped inside a camera lens on the moon retrieved during an Apollo mission after being there for years.
Knowing that, we can reasonably expect that life will fill any void it can.

Some of that life will eventually evolve intelligence and move out to colonize literally any space it can find to live. That would include earth. But, we have seen no reliable evidence that alien races have ever visited earth at all and the life here all seems to be related. And when we look out into the cosmos, we don't see aliens, at least not yet.

Instead, we seem to be able to explain everything we've observed in the universe using natural physical processes rather than resorting to chalking anything up to the activities of aliens. While certain phenomena such as Boyajian's star or the Wow! Signal might be suggestive of alien activity, they aren't conclusive and as far as we have seen the universe appears dead other than life here. But it shouldn't be, suggesting the Great Filter.

Now one possibility is that the filter is biological. In other words, some aspect of evolution has to happen just so for an advanced civilization such as the human race to form. In other words, earth got lucky. Trouble is, there doesn't seem to be anything in the way for evolution to eventually create intelligent life on literally thousands of worlds in our galaxy alone. That may suggest something else.

That something else is extinction. Let's face it, since 1945 the human race has had the ability to destroy itself in a nuclear war. And while it's encouraging that we haven't yet done that, there is no guarantee that we won't either. We also seem to be able to alter the composition of our atmosphere through our activities, which could also potentially prove fatal. And there will be other dangers to our existence posed by future technologies such as artificial intelligence and nanotechnology.

While I have confidence that we'll survive our infancy, never underestimate the power of our human self-preservation instinct, with so much seemingly standing in our way, it's not a far stretch to envision that civilizations may more often than not destroy themselves.

So if the Great Filter exists then one of three things must be the case regarding our civilization.

1. We're already past the Great Filter, unlike most other civilizations in the universe which didn't make. This would make us incredibly rare, but with a very bright future.

2. We're early in the game meaning that in most places in the universe life has not had enough time to evolve intelligence. In this scenario, we'll be the great old ones to any new intelligences that crop up.

3. We haven't hit the filter yet. If we find life elsewhere in our solar system such as on Mars, this would not bode well for us. It would mean that life is not rare and that would imply that the filter lies ahead.

But it's also possible that there is no such thing as the Great Filter and that some civilizations may indeed destroy themselves, but it's not a hard rule. It may simply be too expensive for a civilization to colonize the galaxy, or they may simply hide their presence for security purposes, or advanced civilizations don't build huge megastructures and simply exist as a nanotechnological cloud that cannot be easily detected. They may even live in virtual reality and ignore the universe entirely.