Do you know that it’s almost impossible that aliens do not exist? The famous Drake equation had calculated that in the Milky Way Galaxy, there are about 100 million planets that contain communicative and active civilizations. However, the Earth seems to evolve independently; humans always look up to the sky with loneliness. The dead silence of space and the inevitable possibility of extraterrestrial civilizations made Enrico Fermi and many others question: where is everybody? Where are all the aliens? The question is known as the Fermi Paradox that remains unsolved today, but there are many hypotheses proposed for it. The dark forest theory is the scariest and most hopeless answer of all.
       The dark forest theory first appeared in Liu Cixin’s science fiction series called The Three-Body Problem, the representative of Chinese Sci-Fi with a Hugo award. In the series, the theory appears in an age (23rd century) when humans came into contact with an extraterrestrial civilization that is significantly more advanced than ours. To prevent the destruction of human civilization, one of the characters called Luoji discovers this “ultimate rule” of the universe and starts the Deterrence Era. The dark forest theory is set under four foundational cosmic laws that apply to all. First, survival is the priority of civilization. Second, civilization keeps growing and expanding, but the total amount of matter in the universe remains mostly the same; this assumption reveals that the universe is like a larger Earth where creatures have to compete for resources. The first two rules can be extended to additional two rules. The first is the chain of suspicion, meaning civilizations cannot tell whether other civilizations are good or evil and their purposes. The second is the possibility of an unexpected technical explosion. Civilizations fear that the outbreak could suddenly make a weak civilization advanced. Thus, it’s a rational choice for a civilization to attack before the other civilization has a chance to overcome a technical explosion and become a threat.
       These four rules draw out a border form of game theory in which every civilization faces a prisoner’s dilemma. Unfortunately, this situation causes an tragically eternal Nash equilibrium where every civilization must act hostile and destructive toward others for the best chance of its own survival. To depict this situation in a metaphorical way, imagine that the universe is a dark forest where all civilizations are hunters with guns. No one dares to make a sound because in this forest, “hell is other people.” Pulling the trigger is the only choice a civilization has if it finds the presence of another, and bullets are what a civilization gets if it exposes its existence. Thus, everyone hides in silence, surrounded by the pitch blackness of the hopeless forest where the secret butchery never ends. This is the true cosmic picture, and this is the solution to the Fermi paradox.
       If we assume that the dark forest theory is the ultimate rule of the universe, then what is the fate of humans— a civilization that had sent out messages to this forest? On November 16, 1974, the famous ‘Arecibo message’ was broadcasted, introducing Earth, its species’ DNA, and mathematics. The aimed location of this message is a star cluster near the edge of the Milky Way galaxy, about 21000 light-years away from us, which means that the Arecibo message has only traversed less than 0.2% of the entire distance. This might seem exciting at first sight, but anyone who has read the three-body series will understand that a destructive end is inevitable. According to the dark forest theory’, the moment our message is received is the moment when a hunter in the forest opens fire and shoots.
       If we put the theory aside and only look at the most realistic outcome of the messages, the possibility of an optimal future is equally tiny. When our scientists send our information to space, they are aiming for at least similar or much more advanced civilizations. Understanding human messages and daring to reply reveals extreme confidence an alien civilization holds in comparison to humans. If Earth had already made contacts with aliens, we could definitely conclude that these aliens have technologies humans cannot even imagine. While humans are still struggling to get on Mars, they would have already managed to travel and locate the entire solar system to get on Earth. No matter what situation, we humans have put ourselves in a very passive position that we can only pray for the aliens to be friendly. However, praying for friends doesn’t seem to work if we believe in the dark forest theory and its universe game theory, which dictates being hostile and attacking the exposed Earth civilization is the safest choice for any alien civilization. Moreover, if cosmic civilizations are friendly, why is the galaxy so quiet? What are they afraid of, and why are they hiding?
       Lastly, perhaps all of those worries are useless; perhaps Earth contains the only advanced civilizations, we are truly alone, or perhaps our existence was received by a far more intelligent civilization since early stages, and the apocalypse can come at any second after the 21000 light-years time lag which we can do nothing about.