The Dark Forest Theory - A Possible Solution To The Fermi Paradox
The universe is incredibly big and seems full of potential life, with billions of habitable planets. If an advanced civilization had the ability to travel between stars, at just 0.1% of the speed of light, it could colonise our galaxy in roughly 100 million years. Which is not that long, given the billions of years the Milky Way has existed - so, in principle, any spacefaring civilization should be able to spread rapidly over huge sectors of the galaxy. And yet, we see nothing, hear nothing. The universe seems empty; devoid of others. This is the Fermi Paradox.
Confronted with the seemingly empty universe, humanity faces a dilemma. We desperately want to know if we are alone in the Milky Way. We want to call out and reveal ourselves to anyone who might be watching, but that might be the last thing we do. Because maybe the universe is not empty. Maybe it’s full of civilizations, but they’re hiding from one another. Maybe the civilizations that attracted attention in the past were wiped out by invisible arrows. This is the Dark Forest solution to the Fermi Paradox.
The Way of Life
The hunter awakes in his hiding place and listens for suspicious noises before he gets up. Another night has passed without incident. The forest is dark and full of fog. He considers calling out to others to end his loneliness, but stops himself at the last moment. What if they are like him?
All living things seek to survive, secure resources and multiply. Their greatest obstacle is other living things that share the same objective. Competition between species favoured the survival of beings with advantageous traits. Our ancestors were inventive, competitive and greedy for resources. This led them to winning the competition for our planet. Today, most animals are so utterly at our mercy that we wipe out a dozen species a day, just as an unintentional byproduct of how we like to run things. But humans are more than individuals. From us, cultures emerge that also compete with each other. Competitive and expansionary cultures spread faster and further and merge with, subdue or destroy others. If we look at our history, it becomes clear: we are dangerous. Not just to others, but also to ourselves.
Our human nature has driven us to take over every corner of our planet, and soon we will look to the stars, both to expand our domain and to ensure access to ever more resources. And then, we might stumble upon others trying to do the same thing. It’s likely that the competition of life also takes place on far away planets, so it’s logical to assume an alien civilization that came to dominate their planet would be, in some regards, similar to us. But if they’re similar to us, they may be dangerous, too.
The hunter sneaks through the dark forest all alone. He knows there might be others like him. He can’t know their intentions, if they’re aggressive or not. The hunter knows he would kill to ensure his own survival, so he has to assume the others will do the same. And it might be that if he stumbles upon another hunter, the one that shoots first survives.
None of this means that conflict is unavoidable. So far, the progress of the modern world seems to have made us more peaceful, not more violent. Maybe this is true for other civilizations too, that eventually progress means less conflict, not more. Different alien civilizations should also vary from the mild and peaceful, to the malevolent and militaristic. The existential problem we’re facing is that when we meet others between the stars, we have no way of telling who is peaceful and aggressive and what their true intentions are. Similarly, they may not understand or trust our intentions, even if we tell them we’re peaceful. On top of that, if we did discover another civilization, and they discovered us, the light years between us would mean years of communication delay. Both sides would be in a state of uncertainty, wondering if the wisest move is to just attack, because there is another serious issue: technological explosions and first strike advantage.
We do not know where the limits of technology are, but we do know how much technological progress matters in war. A few hundred or thousand years can turn conflict with uncertain results into a one sided massacre. Caesar's legion would stand no chance against Napoleon’s army with their cannons and muskets. Napoleon’s army would be eradicated by artillery from the first World War. Which would not stand a chance against today’s drones and guided missiles. So the power level of civilizations may vary massively and even if not, between the time it takes us to detect another civilization and us saying ‘hi’, we might already be hopelessly behind on the tech tree. Which is bad enough, but the nature of interstellar conflicts makes it worse.
If your opponent is light years away, sending an invasion fleet takes so long that, by the time it arrives, it might be hopelessly obsolete. So, war between civilizations might just be about eliminating the other to remove an existential threat to yourself. Someone else might be so scared of you that they attack the first chance they get. In this environment, the only way to guarantee a win is to strike with such force and speed that the target has no chance of survival, no time to counter-attack and no time to escape to seek revenge later. The stakes are at the highest possible with no room for error.
If we assume that the majority of civilizations live on planets, that leaves them pretty vulnerable - all you need to do is throw something massive at a planet to make it uninhabitable. So the ultimate inter-planetary annihilation weapon is probably something like a Relativistic Kill Vehicle - a missile shot at a planet at a significant fraction of the speed of light. For example, a missile the size of a person, going 95% the speed of light, has as much energy as all the nuclear bombs on Earth. If you shot a few dozen at the civilization you wanted to wipe out, success would be fairly simple - even a single hit would suffice. This is not that absurd of an idea - a civilization only slightly above us on the Kardashev Scale would have enough energy to send strikes against every planet it suspects of harbouring life.
What makes these weapons so sinister is how much they favour a first strike, since they would be so fast that it might be impossible to protect yourself effectively against them once they’re launched. Conflict between planets might not be lengthy affairs but rapid winner takes all situations where the first one to shoot wins. This makes any civilization an existential threat to any other. And if every civilization is a threat to any other, there may be only two kinds of civilizations thriving out there: quiet ones and dead ones.
So What Should We Do?
So, should we worry? It’s unlikely that anyone has noticed humanity yet. The radio signals we’ve transmitted in the last 100 years travelled a relatively tiny distance and have long decayed into unreadable noise. At our technological stage, if we don’t actively try to get noticed and if nobody specifically looks at our pretty unremarkable solar system, we’ll stay hidden. But one day we will venture into space in a serious way and need to consider these kinds of questions again. We don’t know if there are others or if we’re going through the forest alone. And we have no way of knowing for sure. For the time being, it seems the best we can do is to carefully listen. And even if we see others step into a clearing and make themselves known, we should not reply right away, but carefully watch them from the undergrowth.
Perhaps we’re also thinking about this all wrong by allowing our primitive brain, that evolved in the context of the gruesome competition of life, to conjure fears of predatory aliens all around us. Maybe the fact that we’re looking at the universe like this is a sign that we’re not grown up yet as a species. There could be a friendly, welcoming community of alien civilizations waiting to hear from us when we’re ready. As for now, there’s little we need to do. We just need to be thoughtful about the signals we send out into the galaxy, we need to watch the sky and learn more about our galaxy, our forest. Because, whatever the nature of our forest may be, full of dangers or friends, or nobody at all, only careful observation can tell. So let’s do just that.
At last, the hunter reaches a clearing and finds a comfortable position. The sun melts the last of the fog away. Lost in thought he admires the vegetation until suddenly he is eye to eye with another hunter, frozen in terror just like himself. His mind is racing, considering all the different options. The hunter takes a deep breath and makes a decision. Maybe the only way out of the dark forest is to step into the clearing together.