Do We Live in a Dark Forest?

What Cultural Diversity Can Tell Us About Solving the Fermi Paradox

Let's do something a little different today. I’m honestly worn out, and if you are too, maybe you need to read something a little more fanciful and fun just as much as I need to write it.

I’ve been slowly working my way through the Three Body Problem trilogy by Cixin Liu. If I had to describe those books in one sentence it would be this: “What if the reason we haven’t found signs of extra-solar civilization is because they’re all trying to kill each other?” What Liu imagines in the trilogy is an answer to the Fermi Paradox.

“The Three Body Problem” is the first book in the interested sci-fi trilogy that coined the term for the “Dark Forest Hypothesis”

The Fermi Paradox is named after physicist Enrico Fermi, the creator of the first artificial nuclear reactor, Chicago Pile-1, and a key member of the Manhattan Project. Fermi was perplexed by the fact that humanity has yet seen no evidence of alien civilizations, despite the high probability that they exist. His logic goes as follows: There are billions of stars similar to the sun in the Milky Way. Many of those stars have planets in the habitable zone. So even if intelligent life is relatively rare, the opportunities for such life to arise are so numerous that the galaxy should be home to several alien civilizations. If it's a one in a million chance, but there are a billion chances, it should have happened a thousand times!

Furthermore, because many of those stars with planets that could support life are much older than the sun, potentially a billion or more years older, those civilizations could have arisen far earlier than our own. Even though the galaxy is very large, a civilization that is able to achieve a spaceflight speed of one tenth the speed of light would take about 2 million years to colonize across the entire Milky Way. Even if that analysis is way off, say it takes 20 million years, that's still a very small amount of time for a civilization that has a 1 billion year head start on us.

The Drake Equation illustrates how with large numbers of planets over long time scales, the galaxy could be home to vast numbers of alien civilizations. So where are they?

So, given that alien civilizations are likely, and given that many of those civilizations have likely had ample time to travel all throughout the galaxy, they should have had some sort of contact with Earth prior to now. But there is no evidence for such contact. What Fermi wondered is, why not?

There are probably as many solutions floating around to the Fermi Paradox as there are alien civilizations in the galaxy. But the one that Liu proposes is called the Dark Forest Hypothesis. The Dark Forest Hypothesis suggests that there is no evidence of alien civilizations because any civilization that does not actively hide itself gets destroyed by one of the many other civilizations hiding out there. The hypothesis imagines the galaxy like a dark forest, filled with hunters all stalking one another.

The whole universe could just be a Mexican standoff, but the first shooter is the one who wins.

The theory has two basic axioms. First, all civilizations that survive long enough to colonize the galaxy will prioritize the survival of their civilization over all other considerations. Second, that civilizations expand while resources stay constant. These two axioms combined make conflict inevitable. Eventually expanding civilizations will run into resource limits and will either have to stop expanding, die out, or destroy the others for their resources, and according to the two basic axioms, only one of those is an actual option.

Of course this doesn’t explain why civilizations would proactively destroy one another. In Liu’s universe, he explains this through what he calls a “chain of suspicion.” He uses game theory to describe how any two given space faring civilizations might interacti. He imagines, basically, a game in which there are three moves each civilization can make. They can try to communicate, destroy another civilization, or do nothing. However, the key is that both civilizations are playing, and neither knows what moves the other is going to make. They might not even know whether the other civilization knows about them.

So, if Earth discovers another civilization, but we have no evidence that they have discovered us, what do we do? We can try to communicate to them, but that will reveal our position, and they may try to destroy us. We can stay silent and wait and see, but if they eventually discover us, they may still try and destroy us.

But let's look at a more optimistic scenario: another civilization tries to communicate with us. We want to communicate with them too. After all, the complete annihilation of another intelligent species seems pretty reprehensible. Most reasonable people would want to avoid doing that unless left with no other choice. But interstellar communication has the challenge of taking years or decades to complete a single message. By the time we receive an alien message of peace, their leadership may have changed and they are now aggressive, or the general attitude of the population may have changed, or their technology may have advanced so much that they no longer see a need for peace. Just because we get a message offering peace, even if it is sincere, doesn’t mean we can expect peace. And even if those aliens continue to genuinely want peace by the time they receive our message, they will have the same suspicions of us. This leads all interactions back to the same basic problem: it is impossible to tell from communication whether a civilization is safe or not.

This game is similar to the prisoner’s dilemma: we are better off if we both choose to communicate and live peacefully, but that decision always carries with it the risk of total destruction. However, there is one key difference: the prisoner's dilemma is symmetric but Dark Forest is asymmetric. What that means is that, while two prisoners who both act rationally both have a worse outcome, in the Dark Forest, it is possible that a first strike will only destroy one civilization and the other will be totally spared. In other words, with no rational downside to destroying every civilization you come across (other than a moral one), the best way for a civilization to survive is to try to stay undetected, and destroy every civilization they detect immediately.

Liu’s trilogy throws Earth from one existential threat to another as seemingly the entire galaxy is trying to destroy us. The irony of the book is that humanity never threatens or poses any initial risks to other civilizations, and the destruction we cause in our defense is, in fact, the result of other civilizations behaving as if Dark Forest was true. It becomes a self fulfilling prophecy.

But the Dark Forest hypothesis is more than just a literary device. The theory predates the novel, and scholars trying to understand the Fermi Paradox take it seriously. But the main challenge of such studies is that, by the nature of the problem scholars are trying to solve, we have no alien civilizations from whom to gather data. Inevitably, then, most solutions to the Fermi Paradox are reflections of people’s beliefs about society and humanity.

Modern history is a history of expansion and colonialism. It can be hard to view society from outside of that lens. And from within it, it seems obvious that civilizations will expand into one another, clash, and annihilate, or nearly annihilate, one another. But is expansion a constant of civilization, like gravity is to physics? 

Not on Earth it's not. Most civilizations have, in fact, gone through periods of expansion. But just as common are periods or stability or contraction. After hundreds of years of conquest, Roman civilization spent several hundred years instead maintaining its borders. Here in New Mexico, the Ancestral Puebloans contracted and de-urbanized in response to resource pressures. Although they didn’t “disappear,” as the story often goes (I mean, their ancestors still live here for goodness sake!). And although Pacific Islanders rapidly spread across nearly the whole pacific ocean, they had reached Rapa Nui and the islands of New Zealand by around 1200 AD. From then until contact with Europeans, these civilizations thrived without continual expansion for hundreds more years. Even the colonial expansion of Europe couldn’t last forever. While the consequences will surely be far reaching, Europe and the people they colonized started decolonizing in the 20th century.

Like many others, the civilizations of the pacific islands expanded for thousands of years, but were just as capable at surviving when their expansion was done.

Even violence, as ubiquitous as it feels today, is not a universal trait of all civilizations. The Harappan civilization, also known as the Indus Valley civilization, shows limited archeological evidence for warfare. While war did almost certainly exist in that civilization, it was probably much less prevalent and smaller in scale. The same is true of the pre-agricultural Jomon people in Japan. Even more extreme in their pacifism, the Orang Asli peoples in Malaysia (who, though they are not a single ethnic group, share several cultural traits) all share a cultural aversion to interpersonal violence. While this does not mean they are incapable of violence, many of these people fought as soldiers for various factions during Malaysia’s tumultuous history of colonization, it does mean that many types of violence that you or I might find benign they might find immoral. Thus why such interpersonal violence is so rare.

Being more or less expansionist, or more or less violent are both neutral traits for a civilization. The cultures and civilizations I have just described aren’t somehow superior to others. But what is clear is that, within a single species on a single planet, there is a huge diversity of types of interactions and relationships between civilizations. The diversity between civilizations across the cosmos is likely to be unimaginable! But if the axioms of the Dark Forest Hypothesis don’t even hold true on Earth, how can we expect them to somehow otherwise be universal?

The answer, of course, is that we can’t. There may be violent and expansionist alien civilizations. But there may be civilizations that are willing to risk communication and cooperation. While it still may be true that the Dark Forest Hypothesis does, in fact, explain the Fermi Paradox, there isn’t any special reason to believe that is the case. What I think the diversity of civilizations on Earth implies is that there probably isn’t one single explanation for the Fermi Paradox, at least, not if the explanations are social and/or cultural. Yes, it may be that life, or intelligent life, is so rare that even in the vastness of the cosmos there are few, if any, other civilizations out there. But if that isn’t the case, it is probably also not true that everyone who doesn’t hide gets killed off before we have a chance to discover them.