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.