Our galaxy is full of stars exactly like our Sun. There are many other planets like Earth orbiting around these stars. The age of the universe is is almost 14 billion years. It stands to reason that with this infinite potential, some of these other planets could have actually developed life and over the last 14 billions years some of those alien lifeforms have evolved into civilizations capable of interplanetary travel and communication. So why haven’t we heard anything?
This contradiction (the seemingly infinite ability for alien life to exist, but the absence of our discovery of them) is called the Fermi paradox. There are a lot of creepy ideas about how to explain the Fermi paradox. For example, the “zoo hypothesis” suggests that aliens exist, but they have all agreed to leave Earth alone so that human life can develop organically. This hypothesis means that aliens could be using Earth as a laboratory to experiment on humans or just visiting and observing us, but they’re out there and they are close.
Another theory that explains the Fermi paradox is the dark forest theory. Imagine you are alone walking through a dark forest. You hear a noise. Is it your inclination to be friendly to anyone or anything you happen to stumble across while exploring the unknown?
This is the dark forest theory. It comes from the sci-fi book The Dark Forest, by Liu Cixin. Cixin says that any life that has sustained itself has a core desire for self-protection. Because of this, it is safer for any species who discovers another species to annihilate them rather than risk being annihilated by them. When you are moving in a dark forest, you strike before you can be struck. The alien species in the novel all hide in silence, knowing that communication is most dangerous for the people receiving the communication.
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.
While this makes sense to us, what scares me the most about the dark forest theory is that everyone has to treat each other as an enemy. This means that if even a peace-loving alien race discovers life on Earth, they have motivation to nuke us out of existence. It’s hard to even find fault here. Given our history of colonization, slavery, wars and treating people who are slightly different from us as undeserving of basic human dignity and rights, it’s pretty easy to understand why an alien species would treat us as a dangerous threat. To be honest? We don’t deserve the benefit of the doubt. I wouldn’t take that risk if my family’s lives were on the line.
We keep putting these signals out in space, but as we aren’t even currently capable of interstellar travel, I’m not sure what we think is going to happen if/when someone answers.
I think we assume that if aliens are so advanced they can come to Earth and visit us than they’ve shaken off any of the self-interest imbued in them by evolution. We think they’re going to come here and help us. There is nothing in the natural world that suggests this would be the case. It is much more likely that an alien species will view us as a threat to be contained, not as a planet of friendly strangers they want to be friends with.