The Dark Forest Theory of the Universe

A terrifying answer to “where are all the aliens?”

There may be a good reason for the Great Silence. Image by Troy Moon.

It’s a pleasant night in the city. There’s a cool wind and a luminous moon giving off a soft light that trickles down through the buildings and mixes with the hazy but weak street lights. You’re on your way back home through the empty roads, walking in the unsettling silence. It’s unsettling because it’s deep night — the time when dangerous people come out to look for victims. It’s the time for drug deals and murders, for kidnappings and theft. Seeing the familiar figure of another person standing just down the street from you is a heart-pounding affair. There’s no clear way to tell their intentions, no sign that they’re just enjoying the view of the stars or that they have a more insidious plan on their mind. The full moon overhead, you know from watching the news, has been witness to many a person becoming a victim in the surly, uncertain dark. Walking beneath the electric lights draws attention to yourself. The safest option is to keep hidden, avoiding people and assuming the worst of them until daylight arrives. But there’s a difference between the cityscape of Earth and the all-encompassing universe: in the universe daylight will never come to flood the streets, there’s no locked home to go to and no policemen to seek out for safety. There’s only the potential for danger and the inability to know the other civilization’s true intent.

The above thought experiment was written years before the Dark Forest theory, appearing first in the hard science fiction novel The Killing Star by Charles R. Pellegrino and George Zebrowski. It’s a very similar premise to the Dark Forest theory in which the authors ask the reader to agree to two things. The first is that a species’ own survival is more important than the survival of another species. That is, to us humans the survival of humanity will always come before the survival of an alien race if it comes down to choosing. The second is that a species which has come together to ascertain themselves on their own planet and become capable of spaceflight and technological innovations, will have some level of aggression and alertness. It’s certainly something which has proven true on Earth. In order to survive, humans have imposed upon other tribes, other animals, and upon the planet itself. If these two conditions are true and we assume them to be true of the other species, then they will assume it to be true of us as well. This can be a problematic manner of thinking. It leaves always on the horizon this potential for conflict.

But this scenario is a bit different in the Dark Forest theory which arises from Liu Cixin’s novel The Dark Forest, a sequel to the award-winning Three Body Problem. In the novel, the theory becomes an attempt to answer the question of the Fermi Paradox, a problem in science named after physicist Enrico Fermi. It is, in short, an exploration of why we’ve so far seen no signs of alien life when we should statistically be able to see at least 10,000 of them in the universe with 20 of those alien civilizations existing somewhere nearby (on a cosmic scale). These numbers come from the Drake equation, conceived by astronomer Frank Drake in 1961. The equation is an estimate of how many civilizations should exist in our galaxy by examining the many factors that might play a role in their development.

In the Drake equation, N is equal to the number of civilizations in our galaxy with which we should be able to communicate. R* is the galaxy’s average rate of star formation per year, fp is the number of stars with planets, ne is the number of those planets capable of developing an ecosystem, fl is planets where life develops, fi is the planets that develop intelligent life (a notable distinction), fc is the portion of those lifeforms which develop interstellar communication, and L is the average length of time civilizations survive and are able to send out communications.

In The Dark Forest, the assumptions of life are this: living organisms want to stay alive — they have a survival drive — and there is no way to know the true intentions of other lifeforms. Because there can be no certainties of a peaceful encounter, the safest course of action is to eradicate the other species before they have a chance to attack you instead. This also explains why an alien society might want to stay quiet, reducing the risk of discovering that humanity, for example, might be hostile after all. The novel also brings up the point of limited resources. A civilization that wishes to continue expanding across the universe will need to compete for the limited resources with any other intelligent life. With this assumption, one need not even consider that the species is hostile. We endanger animal populations on our planet all the time, not out of hatred but out of need for resources.

“The universe is a dark forest. Every civilization is an armed hunter stalking through the trees like a ghost, gently pushing aside branches that block the path and trying to tread without sound. Even breathing is done with care. The hunter has to be careful, because everywhere in the forest are stealthy hunters like him. If he finds other life — another hunter, an angel or a demon, a delicate infant or a tottering old man, a fairy or a demigod — there’s only one thing he can do: open fire and eliminate them. In this forest, hell is other people. An eternal threat that any life that exposes its own existence will be swiftly wiped out. This is the picture of cosmic civilization. It’s the explanation for the Fermi Paradox.” An excerpt from Liu’s novel.

This manner of thinking is supported by physicist and NASA consultant David Brin in explaining the utter silence of space. In fact, it would only take one civilization thinking this way to produce the lack of radio signals we’ve observed over the past century. As soon as other intelligent lifeforms discovered and began using radio, they would be eradicated by a more advanced civilization. But doesn’t this mean that humanity, too, is already doomed? Even beyond the purposeful signals we’ve sent into space in an attempt to communicate, we’ve also been giving off the signals daily over the past few decades as we watch TV, use our phones, and peruse the night beneath those flickering street lights. However, signals that are just a product of our everyday life tend to be faint and aimless, making them much less likely to give us away than a signal we consciously direct towards another planet.

In the film “Arrival” [spoilers ahead], aliens come to learn our language and give us the gift of seeing into the future. But films like this are optimistic about first contact. There’s no universal moral code by which any lifeforms must abide. In fact, Liu believes this optimistic way of thinking is a little naive. If we can’t abide by our own moral guidelines, what makes us think other beings will? Image from “Arrival”.

But therein lies one of the problems with this theory. Is it possible to have a civilization that’s always completely hidden and silent? And even if it is, can this silence be guaranteed for long periods of time? If there was an alien civilization stalking the galaxy for any signs of life, surely they would have already detected Earth and decided to attack. Unless they have detected Earth and exist camouflaged somewhere in the night sky, patient and observing. Another possible flaw in the Dark Forest theory is that these alien civilizations will not consider the value of alliances. As a species who had to come together to achieve interstellar travel, it is likely they’ll understand the rewards of cooperation and the possibility of trade — not just in resources but in knowledge. Historically, however, the possibility of alliances hasn’t stopped humans from warring with one another. Liu answers this critique of his theory by bringing up a chain of suspicion. Even if two societies were able to communicate, there would still be incredible distances to surmount, both physically and in terms of culture and language. If another civilization is younger than one’s own, they may seem to pose no threat at first but this wide distance and time span between the two worlds would mean an uncertainty of how fast the other civilization is evolving. Technology doesn’t follow a linear path. Instead it develops exponentially, turning a now harmless and young civilization into a threat as they advance in leaps.

When everything’s at stake, it’s easy to see why extraterrestrial lifeforms might view communication as too high-risk to entertain.

David Brin isn’t the only scientist to consider this a plausible scenario. Stephen Hawking and a roster of dozens of other scientists have also warned against searching so boldly for extraterrestrial life. A petition has been signed to prevent humans from actively sending signals into space, disclosing information about us and our location. This opens up the discussion to the broader question of who can make the decision that we should be attempting to communicate with other beings? Who can decide on behalf of the planet as a whole?

The Dark Forest theory is an examination of life on Earth: how we treat one another, our propensity both for violence and for cooperation, our ability both to consider and disregard life. The theory applies these characteristics to the great beyond — the voids of space which may harbor life that might follow a similar way of thinking and acting. One of the biggest consolations walking the streets of Earth at night is that even if one confronts another person, one can still appeal to their humanity. We can all understand desires and fears. But that’s not a guarantee when addressing civilizations in space. Would it be better if their nature was similar to ours, or should we hope to find a very different race under those warm yellow street lights? Perhaps we’ll find a society kinder than ours, and wiser. Perhaps not.