The Fermi Paradox is a complex term for a simple question: why have no alien civilizations contacted humanity? The paradox states that there are millions of Earth-like planets in the Milky Way, and many are older than Earth. Assuming life exists in other places, some of those planets should have intelligent life more advanced than humans. Enrico Fermi, one of the most brilliant physicists of all time and creator of the first nuclear reactor, came up with the paradox. Once he realized that aliens within our own galaxy should have made contact with humanity, he exclaimed, “Where is everybody?”
Thousands of scholars have come up with solutions to the Fermi Paradox. Roughly in order of optimistic to pessimistic, here are a few of the most common answers:
Advanced civilizations let less advanced societies—like humans—develop without interference
Our solar system is younger than most in the galaxy, so humanity is the most developed civilization
Human communications aren’t strong enough to reach other civilizations (and vice versa)
Humanity’s communication technology is incompatible with alien technology
Aliens have made contact, but the public is unaware
Life is exceedingly rare, so there are not many other intelligent civilizations
The galaxy is too big for any civilization to traverse or communicate across quickly
We live in a simulation someone programmed to exclude alien civilizations
Civilizations always wipe themselves out before they are capable of contacting others
However, there is another answer that is as sublime as it is compelling. The Dark Forest (2008), the second science fiction novel in Cixin Liu’s critically-acclaimed Three-Body Trilogy, explores perhaps the most pessimistic solution to the paradox: other life is out there, but they have camouflaged themselves because they are hunting us.
The cornerstone of the dark forest interpretation is that civilizations of different species do not develop technology at the same rate. The protagonist explains:
"Human civilization has five thousand years of history, and life on Earth might be as much as a few billion years old. But modern technology was developed over the course of three hundred years. . . [T]here’s no reason why humanity should be the fastest of all cosmic civilizations. . . . On the scale of the universe, several hundred years is the snap of a finger. And it might be that my knowledge of your existence and the information I received from our communication was the perfect spark to set off that explosion. That means that even though I’m just a newborn or growing civilization, I’m still a big danger to you."
The main plot of The Dark Forest is also basic: a super-advanced alien civilization is coming to exterminate humanity. However, Liu incorporates realistic space travel, which means that traveling at light speed or through wormholes is impossible. Therefore, the alien fleet is only four light years away, but it will take 400 years to traverse that distance, which gives the human race time to prepare. During that time, the book shows human technology advance so far that Earth’s civilizations are almost unrecognizable. In only two centuries, the human army becomes twice as large as the invading fleet. While humans at the beginning of the book felt that victory was impossible, the characters later in the story feel the opposite. The power of tech explosions made humanity optimistic instead of pessimistic.
However, Liu does not let humanity stay optimistic for long. A single alien probe arrives and—with technology beyond human comprehension—demolishes the advanced human fleet. The probe appears to be made of raw neutrons, making it denser than any material humans can create. It is so resilient that it smashes through two thousand titanium ships without a scratch or dent. This battle shows that technology explosions do not occur at equal rates, and optimistic races like humans will lose wars.
Liu has another, better example of sublime power—strength so great and horrible that it inspires awe. After the probe destroys humanity’s best hope of survival, the protagonist sends a message into space that reveals the coordinates of an uninhabited solar system. A third, unnamed civilization receives the message and, assuming that the message came from a new alien race announcing its presence in the galaxy, destroys the star of the solar system. Once again, Liu shows that there may always a superior predator.
One civilization might go through periods of development that put the Industrial Revolution to shame, but another civilization might reach one breakthrough that renders everyone else obsolete. Everyone in the galaxy—even the strongest—must preemptively defend themselves or risk being exterminated by someone faster and less compassionate.
Liu imagines the universe as a dark forest full of an unknown number of hunters. Each hunter keeps themself hidden while pursuing others. Therefore, Liu’s answer to the Fermi Paradox is that no alien civilizations have contacted us because they cannot risk telling anyone that they exist. Perhaps the most striking part of the dark forest solution is that, if it is true, then humanity’s best hope at survival is that no civilization ever finds us. Any other solution—except the answer where every civilization destroys itself—is preferable.
The irony of the dark forest’s pessimism, however, is that it turns humanity’s current situation into an unequivocal positive. No aliens have found us? Great! That means no one with an unimaginable superweapon is coming to destroy our sun. As far as we know, that is.