Resolving the Fermi Paradox - Island of Sanity

Island of Sanity


Resolving the Fermi Paradox

The Fermi Paradox is a problem that comes up when we consider finding other intelligent life in the universe. The name comes from Enrico Fermi, the nuclear physicist who formulated it back in the 1940s. For those not familiar with the paradox, Let me explain.

The Theory

The theory behind the Fermi Paradox goes like this:

There are billions of stars in our galaxy alone, many billions of billions in the universe as a whole. We don't know exactly how many stars have planets, or how many of those planets are suitable for life, or on how many such planets life actually evolved, or how many of them achieved intelligence and technology. But plugging in plausible guesses for all these percentages, there are probably about 20,000 intelligent civilizations in our galaxy.

The universe is 14 billion years old, and human beings have only been capable of space travel for a few decades, so almost all of these civilizations must be older than ours. Many must have mastered interstellar travel millions of years ago. Even if we assume that it is impossible to travel faster than light, they have had plenty of time to explore and colonize the galaxy.

Maybe some of those 20,000 decided that exploring the galaxy at sub-light speeds wasn't worth the trouble. But if even a fraction of 1% did it, they could have colonized the entire galaxy by now. The galaxy is about 100,000 light years across, so travelling at just 1/10 of the speed of light they could cross the galaxy in a "mere" million years. The "entire galaxy" includes the Earth.

So ... where are they? Why aren't we in regular contact with aliens? Why don't we see their spaceships flitting about our solar system every day?


A number of solutions to the Fermi Paradox have been proposed.

The Great Filter

Maybe most civilizations destroy themselves. Back in the 1950s, many suggested that when civilizations discover nuclear power they ultimately destroy themselves in a nuclear war. In more recent decades the idea has shifted to suggesting that they destroy themselves in an environmental catastrophe, pollution or global warming. Others suggest that the Great Filter may come much earlier in history, like a civilization might destroy itself by trying to convert from hunter/gatherer to agriculture too quickly, and they are wiped out by the first bad harvest. Etc.

The problem with this theory is that you have to assume that the Great Filter is over 99.9% effective at destroying civilizations. If even 100 of that 20,000 survived, that would still be plenty for Fermi's Paradox to be a problem. If even 10 survived, we should still be seeing them all the time.

When nuclear weapons were first invented, many people feared that this would lead to the destruction of all human life in a terrible nuclear war. Perhaps that's a reasonable fear and perhaps not. But even if we had destroyed ourselves, or do sometime in the future, is it reasonable to assume that EVERY alien race would do the same? That out of 20,000 alien races, not one was peaceful? Not one found a way to defend themselves from nuclear attack? Indeed, not one had even a small number of beings survive a nuclear war and rebuild their civilization? That's quite an assumption.

The Dark Forest

Perhaps there are thousands of civilizations out there, but they are all deliberately hiding from each other and therefore from us. Perhaps they fear that if another civilization knew of their existence, it would wipe them out. If another civilization was a million years ahead of them technologically, they could attack them with weapons that these creatures couldn't even understand, let alone defend against. So maybe there are 20,000 civilizations out there, but they are all deliberately hiding.

There are two problems with this theory. One is that it assumes they could successfully 100% hide. When human beings invented radio, we started transmitting signals that were broadcast in all directoins. Not just to the intended receiver, but also out into space. Even though we had no intention of announcing our presence to aliens, any alien race with a radio receiver could pick up our signals. (Subject to the signal having had time to reach them, and their equipment being sensitive enough to detect it given the distances.) Would these paranoid aliens all think of this problem before broadcasting their first radio message?

Two, like for the Great Filter, you have to assume that 99.9% of intelligent aliens came to this same conclusion. Not even ONE civilizatin either never thought of the possibility of being destroyed by a hostile alien race, or decided to take the risk. Not one of these civilizations was peaceful enough that the thought of alien invasion didn't occur to them, or optimistic enough to think that the potential benefits of contact with another civilization would outweigh the risks. Indeed, this case is more problematic than the Great Filter, because you have to assume that not only every civilization as a whole thinks this way, but also that their are no subgroups within the civilization that disagree. Like if they have multiple nations like we do, that every nation thinks the same way.

There are humans who worry that if we did meet aliens, they might destroy us. But there are also humans who are eager to meet aliens. Which will win out in the end? It's hard to say.

The Nature Preserve

If the aliens are millions of years ahead of us, maybe they see us as a primitive culture that must be carefully protected. Just like advanced nations on Earth sometimes believe that primitive native societies should be protected. Indeed maybe they see us as little better than clever animals who must be protected from poachers. Just like humans create nature preserves to protect endangered species.

So maybe the aliens have "quarantined" the Earth, and hide themselves from us. The fact that we have not seen any evidence of their existence proves how effective this quarantine is.

Statements of this theory always start out with "just like humans protect endangered species", but then end up with "and so they hide themselves from us". But when people create a nature preserve, we don't hide our existence from the animals in it. We build fences around it that the animals can clearly see, game wardens patrol the grounds, etc. So the theory says, "maybe aliens are acting toward us just like we act toward endangered species", and then ends up concluding that the aliens would act totally differently for no stated reason.

I deliberately included the statement about "the fact that we can't see them proves how good they are at hiding". This is often a part of the argument. It's an attempt to create an argument that cannot be refuted by any conceivable evidence. You see evidence of aliens? Than that proves that aliens exist. You see no evidence of aliens? Than that proves that aliens exist and are hiding from us. It's like a conspiracy theory: The fact that there is no evidence to prove that there is this vast secret conspiracy proves that there must be a vast secret conspiracy.


Trying to nibble around the edges of the problem with ad hoc theories gets us nowhere. The only solution to the Fermi Paradox is to attack the fundamental premises of the theory.

Definitive Evidence

I've read many articles and seen many videos on the idea of intelligent alien life that include a statement like, "So far there is no definitive evidence for the existence of intelligent aliens." This greatly understates the problem. The issue isn't that there is no DEFINITIVE evidence. The issue is that there is no evidence at all. There is not one scrap of evidence for the existence of aliens. No one has ever detected a signal from an alien civilization. No alien spaceships have ever landed on Earth or been detected by any instruments we have.

Well, at this point someone may say, Wait, what about all those UFO sightings? To which one can only reply, Interesting, but not very convincing. If UFOs really are alien spaceships, why have they never landed some place where they were photographed by hundreds of people so that their existence was unquestionable? Why are photos of UFOs always blurry or otherwise ambiguous? Maybe aliens are visiting the Earth and don't want to be found so they are deliberately concealing themselves. Or they just have no desire to "make contact" so they come, do what they want, and leave. But the evidence is too slim to be convincing.

One could say a lot more about UFO sightings, but that's another subject.


Note that the theory starts by admitting that we don't know how many planets are habitable, how many habitable planets evolve life, etc. Some will say "we don't know EXACTLY how many", but the reality is that we have no idea at all. There is no experimental evidence one way or the other. So what people are saying is that we have this string of variable, W, X, Y, and Z, we have absolutely no idea what the value of any of those variables is, but we are absolutely sure that if you multiply them all together the result is 20,000. How in the world could you know that? (Curiously, I see that same 20,000 number over and over. It frankly surprises me that some don't say 5,000, others 100,000 etc. But it always seems to be 20,000 for some reason. I'm guessing some famous writer came up with that number and others blindly copied it, but that's just a guess. Anyway ...)

Sometimes people will say this without giving a specific number. Like they'll say, "The universe is so big, there are so many stars and planets out there, that there just MUST be others with intelligent life." But who says? Maybe the probabiilty of a given planet having intelligent life is so small that it is amazing that there is even one example -- us, that is.

I saw a documentary on TV once that talked about the hope of finding life on Mars. The speaker was talking about finding microbes, not an intelligent civilization, but whatever. At one point he said that a positive result would be much more significant than a negative result. Because, he said, if we found life on Mars, that would mean that we looked at two planets, Earth and Mars, and both had life. A negative result would mean that we looked at two planets, Earth and Mars, and one had life and the other didn't. Well of course that's silly, because it's not like we picked the Earth at random as a place to look. We look at Earth because we live here, i.e. we only looked for intelligent life on Earth first because it has intelligent life -- us. If Earth didn't have intelligent life, we wouldn't be looking here.

Would you accept this "so big" argument if it was used for something you find doubtful? Like suppose someone said, "The Earth is so big, there just MUST be a Bigfoot somewhere!" Or, "There are so many people in the world, some of them just MUST have psychic powers."

The catch, of course, is that if the probability of something is zero, trying it a billion times still gives zero hits. If the probability of something is 1 in a trillion, trying it a billion times still gives very little likelihood of even one hit.


Another key component of the theory is that it assumes that the universe is billions of years old. What if Creationists are right and the universe is only thousands of years old? In that case, if there are 20,000 other intelligent civilizations out there, some might be hundreds of years ahead of us. Maybe a few are even thousands of years ahead of us. But none could be millions of years ahead of us. So it would be quite possible that none would yet have achieved interstellar travel. Even if they had, if they're limited by the speed of light, they could only have travelled at most a few thousand light years from their home planet. There could be thousands of space-faring civilizations out therer and It would not be at all surprising that none of them had yet reached us.

Of course if evolution is false and creation is true, then all the cards are thrown up in the air anyway. The question ceases to be "what is the probability of live evoloving" and becomes "would a creator God have created other intelligent civilizations".

A young Earth creatist has much better grounds to be optimistic about their being intelligent alien life than an evolutionist. The Fermi Paradox just wouldn't be relevant. We wouldn't expect aliens to be millions of years ahead of us, but at most thousands. And that wouldn't be enough time for them to colonize the galaxy.


I doubt that any ad hoc explanation is going to resolve the Fermi Paradox. The only way to resolve it is to attack the fundamental assumptions. Either the probability of intelligent life evolving on another planet is orders of magnitude smaller than we are guessing, or the universe is nowhere near as old as current evolutionary theories require.

© 2023 by Jay Johansen


Lishan Sep 13, 2023

I haven't looked at this website for... decades? but I'm honestly glad you're still writing and want to catch up with it sometime. And also, to thank you! I grew up in a very liberal area of the country and didn't have that much regular contact with thoughtfully articulated conservative points of view. I feel like somehow coming across this site as a teenager in the early days of the internet was really valuable to me, and I'm curious to see how it's changed over the years, given our era of increased political and ideological polarization.

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