What is the Great Filter? The Great Filter is one of the possible explanations for why we might not find other intelligent life in the universe. It is a point at which no intelligent life can pass.
You may have heard of the Fermi Paradox. I wrote an article about it before. Enrico Fermi was an scientist who posed a question. There are billions of stars similar to our sun in the Milky Way and there are billions of these galaxies that we can observe. Many of these stars will have habitable planets and many of them are much older than our sun. If intelligent life is common, then it must have formed someone on these worlds. So, why haven’t we found any evidence of intelligent life? There are many reasons why this could be. The sheer vastness of the universe is one. There may be billions of intelligent lifeforms out there, but they might just be too far away from each other to find any signs. There is also the problem of time. The chances of these billions of intelligent lifeforms all appearing at exactly the same time is remote. They may have come and gone, or not arrived yet. Or maybe they are keeping quiet so no one can see them. One of the most interesting reasons is called the Great Filter.
The idea behind the Great Filter is that there is a point beyond which no intelligent life can pass. There are potentially three things that could create this filter. These intelligent civilizations either destroy themselves, get destroyed by another civilization, or get destroyed by natural causes. It might be impossible for an intelligent species to exist for long enough to find other civilizations or to leave any trace. What could cause that?
We can obviously see how an intelligent species would destroy themselves. As a species, we are inherently drawn to war and we are constantly finding new and inventive ways to destroy everyone on our planet. If we don’t blow ourselves up with nuclear weapons, or whatever we invent to replace them, then climate change could theoretically destroy life on the planet. There is also a high probability that the AI we are currently creating will wipe us out one day a well. Perhaps all intelligent life is like this and it can never progress past a certain point because it kills itself. That would be rather sad, but you can certainly see how it would be possible. There is no way of knowing if all intelligent species think and act the same way that we do because we have never found any other intelligent species. We can only base our ideas on observations of the only intelligent species we know, which is us.
The second thought is a little chilling, but it is that every intelligent species gets wiped out by another species at some point. Perhaps there is one form of intelligent life travelling around the universe, wiping out all of the other intelligent life it finds. Although, if that were the case, it would mean that one form of intelligent life had managed to get past the Great Filter. Perhaps it isn’t intelligent life, but artificial intelligence. Or maybe there is something out there, like a universe wide disease, that tracks down intelligent life and kills it. Whatever is out there hunting intelligent life, it may pay to keep quiet.
The third reason could be planet wide destruction from an external source. Every day we are struck by tiny meteors. We get hit by approximately 100 tons of dust and small rock sized pieces every day. They all burn up in our atmosphere. Occasionally, we get hit by larger ones. There is an inverse relationship between the size of the meteors that hit us and the frequency with which they hit. We get hit by an awful lot of small meteors and very few large ones. That is because there are a lot more small meteors floating in space, so there is a higher probability that they will hit us. Earth gets hit by a car sized meteor about once a year. This is large enough to be visible as it comes through the atmosphere, but it will burn up and not reach the ground. Every 2,000 years, Earth gets hit by a meteor the size of a football field. That will reach the ground and cause significant damage to that area. Meteors about 1 km across hit Earth every 500,000 years. That would do significant damage. Every 20 million years, Earth gets hit by a meteor that is 5 km or larger. That can be a life ending event and the last one hit Earth 66 million years ago and wiped out the dinosaurs. If it takes a species twenty million years to evolve and become intelligent enough to travel the universe and find other intelligent life, then the chance of them being wiped out by a meteor is high. Perhaps the Great Filter is just the fact that the probability of being wiped out by a large meteor is almost 100% if given enough time. I guess we’ll only know in the future. And this is what I learned today.
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Sources
https://en.wikipedia.org/wiki/Impact_event
https://en.wikipedia.org/wiki/Great_Filter