I think I know what the Great Filter is now

Sep 3, JDN 2458000

One of the most plausible solutions to the Fermi Paradox of why we have not found any other intelligent life in the universe is called the Great Filter: Somewhere in the process of evolving from unicellular prokaryotes to becoming an interstellar civilization, there is some highly-probable event that breaks the process, a “filter” that screens out all but the luckiest species—or perhaps literally all of them.

I previously thought that this filter was the invention of nuclear weapons; I now realize that this theory is incomplete. Nuclear weapons by themselves are only an existential threat because they co-exist with widespread irrationality and bigotry. The Great Filter is the combination of the two.

Yet there is a deep reason why we would expect that this is precisely the combination that would emerge in most species (as it has certainly emerged in our own): The rationality of a species is not uniform. Some individuals in a species will always be more rational than others, so as a species increases its level of rationality, it does not do so all at once.

Indeed, the processes of economic development and scientific advancement that make a species more rational are unlikely to be spread evenly; some cultures will develop faster than others, and some individuals within a given culture will be further along than others. While the mean level of rationality increases, the variance will also tend to increase.

On some arbitrary and oversimplified scale where 1 is the level of rationality needed to maintain a hunter-gatherer tribe, and 20 is the level of rationality needed to invent nuclear weapons, the distribution of rationality in a population starts something like this:


Most of the population is between levels 1 and 3, which we might think of as lying between the bare minimum for a tribe to survive and the level at which one can start to make advances in knowledge and culture.

Then, as the society advances, it goes through a phase like this:


This is about where we were in Periclean Athens. Most of the population is between levels 2 and 8. Level 2 used to be the average level of rationality back when we were hunter-gatherers. Level 8 is the level of philosophers like Archimedes and Pythagoras.

Today, our society looks like this:

Most of the society is between levels 4 and 20. As I said, level 20 is the point at which it becomes feasible to develop nuclear weapons. Some of the world’s people are extremely intelligent and rational, and almost everyone is more rational than even the smartest people in hunter-gatherer times, but now there is enormous variation.

Where on this chart are racism and nationalism? Importantly, I think they are above the level of rationality that most people had in ancient times. Even Greek philosophers had attitudes toward slaves and other cultures that the modern KKK would find repulsive. I think on this scale racism is about a 10 and nationalism is about a 12.

If we had managed to uniformly increase the rationality of our society, with everyone gaining at the same rate, our distribution would instead look like this:

If that were the case, we’d be fine. The lowest level of rationality widespread in the population would be 14, which is already beyond racism and nationalism. (Maybe it’s about the level of humanities professors today? That makes them substantially below quantum physicists who are 20 by construction… but hey, still almost twice as good as the Greek philosophers they revere.) We would have our nuclear technology, but it would not endanger our future—we wouldn’t even use it for weapons, we’d use it for power generation and space travel. Indeed, this lower-variance high-rationality state seems to be about what they have the Star Trek universe.

But since we didn’t, a large chunk of our population is between 10 and 12—that is, still racist or nationalist. We have the nuclear weapons, and we have people who might actually be willing to use them.


I think this is what happens to most advanced civilizations around the galaxy. By the time they invent space travel, they have also invented nuclear weapons—but they still have their equivalent of racism and nationalism. And most of the time, the two combine into a volatile mix that results in the destruction or regression of their entire civilization.

If this is right, then we may be living at the most important moment in human history. It may be right here, right now, that we have the only chance we’ll ever get to turn the tide. We have to find a way to reduce the variance, to raise the rest of the world’s population past nationalism to a cosmopolitan morality. And we may have very little time.

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