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🌌 The Universe is a dark forest.

Written on January 17, 2023
8 minutes to read.

I recently finished The Dark Forest by Liu Cixin (translated by Joel Martinsen), and found the use of the Dark Forest theory to be an excellent use of real life game theory in science fiction.

Life in the Universe

Consider the following axioms: 1. life on our planet arose due to natural coincidences (atmosphere + climate producing water, siesmic activity releasing necessary chemicals, etc.), and 2. these conditions, whilst rare, are not unique. Accepting both of these as being true, then life can be assumed to naturally arise as an inevitable outcome, at least within the vastness of the universe, or even within relatively local space such as our galaxy.

We have strong evidence that microbial life is not necessarily unique to Earth, with evidence from Mars suggesting life existed there some 3.9 billion years ago, before the planet lost it’s atmosphere and water [1]. What this is not evidence of, however, is intelligent life evolving from this microbial state.

Where are all the aliens?

The Fermi Paradox asks the simple question; “but where is everybody?”. Given the age of the universe, it can seem unreasonable that we are yet to encounter any signs of intelligent life. Despite optimism from numerous institutions, such as SETI and other Government-backed projects, decades of research are yet to provide evidence that to solve the paradox.

The dark forest

Numerous solutions exist to resolve Fermi’s question, considering inevitablity of natural disaster disrupting civilisations, vast distances between instances of life, isolationism, and the idea Earth might be deliberately ignored due to our civilisations immaturity. Whilst each of these concepts have merit, the most convincing, and perhaps most dramatic, is the Dark Forest hypothesis.

Sharing a brief excerpt from his novel, Liu Cixin illustrates this idea of interstellar civilisaitions:

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 another life — another hunter, angel, or a demon, a delicate infant to tottering old man, a fairy or demigod — there’s only one thing he can do: open fire and eliminate them.

The logic behind the theory is based on two axioms:

  1. Resources in the universe are finite, civilisations will compete for resources.
  2. You can’t determine if another civilisation is good or bad before making contact.

Following these principles, a civilisation encountering another must make one of three choices, however following the dark forest hypothesis, only one choice is optimal.

  1. Make contact with the civilisation - diplomacy.
  2. Ignore the encounter (if the civilisations existance hasn’t been revealed already) - isolationism.
  3. Seek to destroy the other civilisation.

Technological explosion

The risk behind revealing oneself to a lesser civilisation, one determined to not be an immediate threat, is the potential for technological explosion. Upon encountering advanced technology, a lesser civilisation may quickly emulate or acquire these advancements, becoming equally powerful. This changes the threat assessment of the civilisation, and can occur so rapidly that counter-measures are not possible. Reviewing the advances in 200 years of Human civilisation, and associated changes in society, a newly contacted civilisation might change it’s nature inbetween first contact and whenever physical contact is made, potentially becoming hostile.


Assuming, even with technological advancements, it remains difficult to review planets for signs of intelligent life, the path of isolationism could be a safer route for a civilisation. However, this relies on other civilisations encountered to be technologically inferior, and that the chance discovery of our own civilisation is considered an acceptable risk.

The Hunter

Should we encounter another civilisation, the risks of remaining passive or friendly when the current or future nature of this new threat means all alien civilisations should be treated according to their potential, providing motivation to intervene early to remove this threat, and further lay claim to valuable resources that can now be used to directly benefit our civilisation’s goals.

Diplomacy delivered down the barrel of a gun

Does this game theory mean all diplomacy is ultimately fruitless? If we consider humanity and separate countries / alliances as a microcosm of intergalatic civilisation, we can consider how major powers interact with other nations and react to their advances in technology.

The development of nuclear weapons by middle-east states has been met with widespread concern and criticism by western nations, who obtained this technology first and used their technological superiority to negotiate favourable peace with other nations who lacked this power. The development of nuclear weaponry is both an existential threat to the western nations, through it’s descructive capability, but further represents a destabilisation of the status quo and global power balance.

Reapplying this to an intergalatic setting, a civilisation finding itself in a disadvantageous conflict will seek to rapidly advance it’s abilities as a direct result of this interaction (technological explosion), and a civilisation faced with a less-technologically-developed group will seek to maintain this imbalance, as a defensive measure against the hidden agenda of this new threat.

But really, where are all the aliens?

The dark forest hypothesis is, at its root, a solution to the Fermi Paradox, but critiques find it requires some assumptions about alien civilisations that might be unrealistic. To clarify, the point of the dark forest hypothesis is that we haven’t heard from any other civilisations because the wisest course of action is to disguise your presence in the universe, instead of broadcasting information as a sign of intelligent life.

Whilst we have only been listening for a very short time (compared to the eons that have already passed) and how slowly information travels (compared to the vast distances between solar systems and galaxies), the unoptimistic view is that we will continue to hear nothing over any length of time.

Further, the theory treats alien civilisations as cohesive and undivided entities, with no factions choosing to break radio silence due to their own goals. Using humanity as a template for how other civilisations may develop, this concept seems unlikely, although is admittedly not impossible. What is much more unlikely, however, is every other civilisation forming their own version of the dark forest hypothesis without exception, which is also unlikely given the multiple Earth projects which have sent information about the human race into the local cosmos - humanity being the sole exception seems unlikely.


Is the universe more densly populated than we could ever guess? Probably not. Although our observations of other planets are hundreds of years outdated, the lack of recognisably intelligent signals being detected by listening stations indicate we are likely alone within our local space. However, the universe is vast, and the likelihood of Earth being the sole inhabited planet becomes dramatically less likely the further you look. Alien civilisation may well exist, but at present it is simply too far away for either us or them to ever know.