The dark forest theory.

Can aliens exist? Is it possible that aliens see us, but they don’t make contact? And why don't they want to contact us? The answer can be that, as we don’t know anything about aliens, they will not know anything about us. There is a possibility that the call signal in the universe is a trap. Just like if we walk in a dark forest and hear somebody calling. We cannot be sure if that call was just meant to make contact. Or, if it is a trap. If alien culture exists, that would not be the same as our culture. Even if we see a signal. We might not have the chance to break the message. Making contact with alien civilization is not like calling using cell phones. 

When we see a message come to our cell phones. We know immediately. That humans sent that message. And we know that it's the message. But if we see an alien message, the situation is more complicated. First, we must be sure that there is a message. First, the message is the radio signal that arrives at some radio telescope. That message will be one of the thousands or even millions. 

Or billions of radio signals that the telescope receives during that day. The system must separate those synthetic signals from the natural radio sources like pulsars, quasars, or fast radio bursts. Then we must try to find the code that opens the message. And then we must realize that we might not like that message. But when we think about detection and the separation process, their system filters messages from natural radio signals; there is a possibility that this system removes the synthetic signal. Because it thinks that it's from Earth. Or it thinks that the signal is the receiver's error. 

The base of the dark forest theory or hypothesis is that all civilizations are hostile. And they just wait for the right moment to attack. 

"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." (Big Think, Dark Forest theory: A terrifying explanation of why we haven’t heard from aliens yet)

Then we must realize that if we make that thing, it certainly is the military action against those aliens. And if they are powerful and advanced, they might take revenge. Just this thing would be similar to things that started colonialism. Natives attacked Europeans because they established their irrigation on native lands. Because Europeans were hurt, they sent troops to take revenge. The military superiority gave Europeans the ability to conquer their colonies. In the same way. If we attack aliens, they might try to avenge us. 

Dark forest theory is one of the darkest theories that tries to explain why we aren't able to make contact with other civilizations. The model is taken from the dark forest where we travel alone. We can yell and call other people, but even if somebody answers, that doesn’t mean that the person who answers means good. The forests are full of animals and humans, but they are not always good-willed. 

We can think that there are cities full of kind people, but those people are kind because they are under observation. In the same way, we must realize that some people who live in forests are probably not as well under surveillance as we might think. The thing that makes people commit crimes is that they believe nobody sees their crimes. 

The thing in the dark forest model is that the space is the forest. The civilization that lives on a certain planet is the community that lives in cities. And those members of the hypothetical alien civilizations who live in their research centers and other outposts like colonies are members who live in dark forests. They might not have the ability to communicate with their home planets very often. And that means those colonies might start to live their own life. 

When we think about that hypothetical civilization and compare it with things like conquistadors and great voyages, we must realize that the first colonists returned home. But then those colonies turned more and more independent. The first voyagers returned home. Then they left for colonies forever. Those people never return. And that path made the colonies turn independent. 

And in space, the scale is far bigger than on the great sails and voyages. And then some of those colonies rise more powerful than the nation that created them. So, if we think that the alien colonies or colonies that the human race will someday establish are separating from the home planet. That means those colonies become alien to their establishments. They might turn more powerful than the planet that created them. 

The thing is that. As in a dark forest, in the universe. There are actors who wait for the right moment to find a helpless civilization or some other colony. Those creatures can attack and conquer the helpless planet anytime they see something that cannot resist. If we yell and try to make contact, we actually don’t know what we face. In the worst case, friendly discussion with aliens is meant as a trap. 

And we must not forget that. We don’t know if aliens will try to contact us in our lifetime. But we must realize that there is always the possibility that another species tries to conquer our planet. One of the reasons for that can be that those hypothetical aliens can think of us as competitors. Or maybe they are cosmic outlaws who want to set up an accident. The dark forest hypothesis means that aliens exist, but they don’t want to contact us. 

https://bigthink.com/surprising-science/the-dark-forest-theory-a-terrifying-explanation-of-why-we-havent-heard-from-aliens-yet/

https://en.wikipedia.org/wiki/Dark_forest_hypothesis