On most days, I’ll tell you I both hope and think we’ll find alien life before I die. Though when I say that, I’m thinking primarily of microbial life in a chemical soup somewhere, not much different from how life began on Earth. Sometimes I imagine intelligent aliens, largely because I consume so many stories about them. In many stories, aliens are paternalistic. In Arthur Clarke’s Childhood’s End aliens make Earth a utopia free of crime, war, and disease (at least, for a while). In Carl Sagan’s Contact, aliens concerned about humanity (they catch Hitler on TV) give Earth a paradigm-shifting understanding of the universe. Arrival broadly follows a similar trajectory, and the gift is more a new understanding of time. In these stories, humans develop complicated and meaningful relationships with aliens. Those relationships, like all relationships, are founded on common goals, peace, fairness, and decency often among them.
I both hope and think we’ll find alien life before I die.
On Babylon 5, representatives from different worlds gather to try and preserve peace in the universe. In Star Wars—well, you know how that goes, empires, alliances, and rebels. Even though the U.S.S. Enterprise can’t avoid drama, races from 150 planets in the Star Trek universe are part of a United Federation. They’re civilized. There’s some overlap of values.
I like those stories. Give me Cocoon, Close Encounters, E.T., or The Sparrow—I’ll take a story about the relationships humans and aliens forge over an alien attack narrative any day. Recently, though, a book has me thinking that maybe all our radar, broadcasts (besides radio and television, NASA transmitted the Beatles’ song “Across the Universe” toward Polaris), and even the Golden Record might not be such a great idea.
Credit: Max Pixel
Liu Cixin’s award-winning Three-Body Problem trilogy has complicated my thinking about alien races, the Fermi Paradox, and whether we ought to make contact. That in itself serves as an endorsement of this series, which is among the most satisfying trilogies I’ve ever read. The New Yorker calls Liu “China’s Arthur Clarke”—high praise indeed, and deserved. Unlike so many trilogies, the last installment is the strongest, epic in sweep and existentialism. There are no Ewoks.
The rest of this essay contains spoilers, so if you haven’t read the Three-Body Problem books, stop reading now (and get a copy of them) or be warned (and then go read the books anyway!)
The narrative kicks off when a disillusioned Chinese astronomer, Ye Wenjie, plummets into despair about humanity and the state of the planet after reading Silent Spring. Wenjie, who’s stationed on a remote coast listening for extraterrestrial signals, sends out one of her own—a cosmic SOS. To her surprise, she receives a response—a warning from a member of another civilization whose race is searching for a stable planet to call home. We’ll take you up on your offer and that won’t be so good for you, the being says. It can’t be worse than the way things are now, Wenjie responds.
Three-Body Problem book cover. Credit: Artur Coelho
Thus begins the Trisolarans’ journey toward Earth—one that takes them 400 years. Four centuries is enough for both technological and social circumstances on Earth to change dramatically, and it gives the human race plenty of time to think about what to do about the impending invasion. The hard part is that initially, the humans know nothing about the Trisolaran race. They can conclude that Trisolaran technology outstrips human technology, but in what ways? What insights do the aliens possess? What do the humans need to fight back? And what would fighting back actually look like? What kind of weapon does a civilization develop to combat unknown alien tech? What about hiding? Or escaping? Who calls the shots and how do we know they’re right?
The consideration of those questions comprises vast stretches of the trilogy and yields some surprising answers. I won’t provide all the details—it would be impossible given the length of the books—but someone comes up with a solution that relies on what Liu calls “Dark Forest Theory” (also the name of the second book).
Dark Forest Theory starts with a seemingly obvious axiom: that every civilization will do whatever it has to do to survive. Hard to argue with that. The second axiom is that civilizations want to expand—they want to increase population sizes and spread out among the stars, which aids in survival. But the universe doesn’t offer unlimited opportunities for survival or expansion. While the universe might seem infinite and inexhaustible, in terms of resources, it isn’t. Thus, civilizations are in competition.
Credit: Max Pixel
To make noise in a dark forest is to court death.
With those premises in mind, Liu’s theory posits that the universe is a dark forest. Its inhabitants, who traverse the forest in the hopes of finding food, building materials, and other useful items and knowledge, move through it quietly, carefully. They know others search for the same things, so they can never be sure who’s lurking in the darkness. They also know that if they encounter someone in the forest, that person is an enemy, and it behooves them to attack anyone or anything they see – if they can. Alliances would be virtually unheard of. Neither trust nor the genuine desire for coexistence exists in the forest, as no one knows if they’re the hunter or the hunted (or they know they’re both at all times). Survival in the dark forest is equal parts science, subterfuge, and aggression.
To make noise in a dark forest is to court death. The odds that someone hears you are perhaps slim, but the outcome would be disastrous, so you don’t play the odds. Because if someone or something did hear you, then it could find you, and you have no idea how powerful, intelligent, or malicious it is or what it might do to you. And that alien race is likely more advanced than yours. Even if it isn’t, it could become more advanced in the period of time it takes that race to locate and travel to your planet. Either way, you can never know for sure and given that your race’s existence depends on not being found in the dark forest, you keep the muzzle on—unless you’re taking out someone else, which might be noisy but secures survival and serves as a warning.
Credit: Max Pixel
While Liu’s theory is dark, it’s grounded in what we know about the universe. According to scientists’ best estimates, the Big Bang occurred approximately 13.7 billion years ago. What we know about our solar system suggests Earth formed roughly 4.54 billion years ago (the most basic forms of life developed on Earth between 3.5-3.9 billion years ago). That means there are roughly 9 billion years of pre-Earth cosmic history during which life could be flourishing on other worlds. Back in 2003, the Hubble telescope identified what astronomers believe is a 13-billion-year-old planet. How many of these planets exist? How many of them harbor intelligent life? Who knows, but suffice it to say that Earth is relatively young in the grand scheme of things. Not only is it likely that intelligent life exists elsewhere in the universe, but it’s also likely that such life is considerably older and more technologically advanced than ours. Perhaps much, much more advanced, like the Trisolarans, who among other things figure out how to travel at the speed of light. iPhones, 3D-printers, and space shuttles are kids’ toys.
Think about the technological leaps that would be made by a civilization that’s been around twice as long as any on Earth. Perhaps that’s the point—while we can imagine some leaps, such as the one from biological to digital life, there would be countless innovations and advances we can’t even conceive. Such knowledge increases Dark Forest Theory’s potency. Imagine a trip through the forest with the understanding that anyone or anything you might come into contact with possesses technology you’ve never imagined. Imagine how desperately you’d want to avoid such a confrontation. Imagine how much effort you’d put into cloaking, whether through stealth technology, misdirection, or hidden outposts.
Hidden civilizations comprise one possible answer to the Fermi Paradox, which raises the question of why we haven’t seen evidence of intelligent alien life if many such races exist out there. Rather than support Enrico Fermi’s theory that intelligent life is unique to Earth, the Fermi Paradox raises the possibility that alien life is too intelligent to be detected, either because it’s hiding and/or because it’s plotting another race’s destruction. Even if an alien race knows about Earth and humanity’s relatively young age, it might not think it worth the risk of testing us. Not only would aliens have to guess about Earth’s scientific prowess, but they’d have to rely on Earth not having a paradigm-shifting technological leap in the time it would take them to get here. They’d also have to worry about humans—or another race—spotting them as they sped Earthward.
Voyager 1. Credit: NASA/JPL
What could a race do if it spotted an incoming alien fleet? Liu poses this question as humans grapple with their options. The Trisolaran homeworld is 400 light-years from Earth—Earth doesn’t have any technology, no weapon or satellite, that can traverse such a distance, and by the time the Trisolarans are within firing distance of Earth, it would be too late (if they hadn’t enacted their plan long before then). What does a traveler in the dark forest do upon realizing it’s being followed?
The best option, at least the best one the Earthlings in Liu’s book can conceive, is to make noise. It’s risky, as it reveals Earth’s location, but if it also reveals another civilization’s location, then the other inhabitants of the dark forest have a choice to make. Which race do they attack? And how do they know their coordinates won’t also be revealed? Is it worth the risk? Such questions underscore the premise of Dark Forest Theory, which in Liu’s trilogy functions—sometimes effectively, sometimes not—as a deterrent.
Stephen Hawking continues to warn us against responding to alien signals—he likens a meeting between humanity and an extraterrestrial race to “Native Americans encountering Columbus,” a scenario that “didn’t turn out so well.” But others, such as astronomer and former SETI research director Seth Shostak, disagree. Shostak eludes to the underpinnings of Dark Forest Theory by agreeing with Hawking that we can’t know the intentions of aliens and that “in any Darwinian system, there’s always a benefit to aggression by some.” But ultimately, he argues, it’s simply too late. Our radio, television, and radar broadcasts are out there and any advanced society that could potentially harm us has—and has long possessed—the ability to pick up these emissions. So where does that leave us?
Credit: Jon Lomberg
In Shostak’s mind, it leaves us right where we are, where we’ve always been—on Earth, as members of a massive, intergalactic dark forest. The dark forest has been populated for billions and billions of years—that hasn’t changed. What has changed is our awareness of our relative smallness and fragility—the precarious of all civilizations, all life—in the universal grand scheme of things. But such awareness doesn’t change reality or the odds of an alien civilization attacking. “Yes, anything’s possible. But that doesn’t mean that everything’s plausible,” says Shostak. “Sure, Martians could mount an attack on Earth in the near future. But that’s one worry that won’t keep me awake at night. Nor should it trouble you.”
Generally, I agree with Shostak. The prospect of contact with an intelligent extraterrestrial race excites me beyond description. But at the same time, imagining a dark forest populated by countless races of various ages and technological abilities makes my heart pound. Underneath the exhilaration and adrenaline, there’s a kernel of fear. After all, we are babes in the woods.