The Dark Forest

by Cixin Liu

  Fortunately, there weren’t many people like him.

  * * *

  Temperatures were cooling rapidly these days, and it had started to snow, causing the green to gradually disappear from the surrounding area and a thin layer of ice to freeze on the surface of the lake. Nature lost its bright coloring, like a color photograph turned black-and-white. Warm weather here had always been short-lived, but to Luo Ji, the Garden of Eden felt like it had lost its aura since the departure of his wife and child.

  Winter was a season for thinking.

  When Luo Ji began to think, he was surprised to find that his thoughts were already in progress. He remembered back to middle school and a lesson a teacher had taught him for language arts exams: First, take a look at the final essay question, then start the exam from the top, so that as you work on the exam, your subconscious will be thinking over the essay question, like a background process in a computer. Now he knew that from the moment he became a Wallfacer, his thinking had started up and had never stopped. The entire process was subconscious and he had never been aware of it.

  He quickly retraced the steps his thoughts had already completed.

  He was now certain that everything about his current situation stemmed from his chance encounter with Ye Wenjie nine years ago. Afterward, he had never spoken of the meeting with anyone for fear of causing unnecessary trouble for himself, but with Ye Wenjie gone, the meeting was a secret known only to him and Trisolaris. In those days, only two sophons had reached Earth, but he could be certain that on that evening, they had been there by Yang Dong’s grave, listening to their every word. And the fluctuation in their quantum formation that instantly crossed the space of four light-years meant that Trisolaris had also been listening.

  But what had Ye Wenjie said?

  Secretary General Say had been wrong about one thing. Luo Ji’s never-begun research into cosmic sociology was quite likely the immediate reason why Trisolaris wanted to kill him. Of course, Say didn’t know that the project had been Ye Wenjie’s suggestion, and although it had just seemed to Luo Ji like an excellent opportunity to make scholarship entertaining, he had been looking for just such an opportunity. Prior to the Trisolar Crisis, the study of alien civilization was indeed a sensational project that would have garnered easy media attention.

  The aborted research project wasn’t important in and of itself. What mattered was the instruction that Ye Wenjie had given him, so that’s where Luo Ji’s mind was stuck.

  Over and over again he recalled her words: Suppose a vast number of civilizations are distributed throughout the universe, on the order of the number of detectable stars. Lots and lots of them. The mathematical structure of cosmic sociology is far clearer than that of human sociology.

  The factors of chaos and randomness in the complex makeups of every civilized society in the universe get filtered out by the immense distance, so those civilizations can act as reference points that are relatively easy to manipulate mathematically.

  First: Survival is the primary need of civilization. Second: Civilization continuously grows and expands, but the total matter in the universe remains constant.

  One more thing: To derive a basic picture of cosmic sociology from these two axioms, you need two other important concepts: chains of suspicion and the technological explosion. I’m afraid there won’t be that opportunity.… Well, you might as well just forget I said anything. Either way, I’ve fulfilled my duty.

  He had returned countless times to these words, analyzing each sentence from every angle and chewing over every word. The component words had been strung into a set of prayer beads, and like a pious monk he stroked them time and again; and unstrung them, scattered them, and restrung them in different orders until a layer of each had been worn away.

  Try as he might, he couldn’t extract the clue from those words, the clue that made him the only person that Trisolaris wanted to destroy.

  During his lengthy contemplation he strolled aimlessly. He walked along the desolate lakeside, walked through the wind as it grew ever colder, oftentimes completing a circuit of the lake unawares. Twice he even walked to the foot of the snow peak, where the patch of exposed rock that looked like a moonscape was blanketed with snow, becoming one with the snowcap ahead of him. Only then did his mood leave the track of his thoughts, Zhang Yan’s eyes appearing before his own in the boundless blank white of the natural painting. But he was now able to keep his mood in check and continue turning himself into a thinking machine.

  A month went by without him knowing it, and then winter came in full force. But he still conducted his lengthy thought process outside, sharpening his mind on the cold.

  By this time, most of the prayer beads had been worn faint, except for twenty-one of them. These ones seemed only to get newer the more he polished them, and now emitted a faint light:

  Survival is the primary need of civilization.

  Civilization continuously grows and expands, but the total matter in the universe remains constant.

  He fixated on these two sentences, the axioms Ye Wenjie had proposed for cosmic civilization. Although he did not know their ultimate secret, his long meditation told him that the answer lay within them.

  But it was too simple a clue. What could he and the human race gain from two self-evident rules?

  Don’t dismiss simplicity. Simple means solid. The entire mansion of mathematics was erected on a foundation of this kind of irreducibly simple, yet logically rock-solid, axiom.

  With this in mind, he looked around him. All that surrounded him was huddled up against the icy cold of winter, but most of the world still teemed with life. It was a living world brimming with a complex profusion of oceans, land, and sky as vast as the foggy sea, but all of it ran according to a rule even simpler than the axioms of cosmic civilization: survival of the fittest.

  Luo Ji now saw his problem: Where Darwin had taken the boundless living world and made a rule to sum it up, Luo Ji had to use the rules he knew to uncover a picture of cosmic civilization. It was the opposite road to Darwin’s, but a more difficult one.

  So he began sleeping in the daytime and thinking at night. Whenever the perils of his mental roadway terrified him, he found comfort in the stars overhead. Like Ye Wenjie had said, the distance hid the complex structure of each star, making them just a collection of points in space with a clear mathematical configuration. It was a thinker’s paradise, his paradise. To Luo Ji, at least, it felt like the world in front of him was far clearer and more concise than Darwin’s.

  But this simple world held a perplexing riddle: The entire galaxy was a vast empty desert, but a highly intelligent civilization had appeared on the star nearest to us. In this mystery, his thoughts found an entry point.

  Gradually, the two concepts Ye Wenjie had left unexplained came into focus: chains of suspicion and the technology explosion.

  The weather that day was colder than usual, and from Luo Ji’s vantage point on the lakeshore, the cold seemed to make the stars into an even purer silver lattice against the black sky, solemnly displaying for him their clear mathematical configuration. All of a sudden, he found himself in a state that was entirely new. In his perception, the entire universe froze, all motion stopped, and everything from stars down to atoms entered a state of rest, with the stars just countless cold, dimensionless points reflecting the cold light of an outside world.… Everything was at rest, waiting for his final awakening.

  The distant bark of a dog brought him back to reality. Probably a service canine belonging to the security forces.

  Luo Ji was beside himself with excitement. Although he hadn’t actually glimpsed that final mystery, he had clearly felt its presence just now.

  He collected his thoughts and tried to reenter that state, but was unsuccessful. Though the stars remained the same, the world around him interfered with his thinking. All was shrouded in darkness, but he could make out the distant snowcap, the lakeside forest and grassland, and the house behind him, and through the hou
se’s half-open door he could see the dark glow of the fire.… Next to the simple clarity of the stars, everything in the vicinity represented a complexity and chaos that mathematics would be forever unable to grasp, so he attempted to remove them from his perception.

  He walked out onto the frozen lake—cautiously, at first, but when he found that the icy surface seemed solid, he walked and slid ahead more quickly, until he reached a point where he could no longer make out the lakeshore through the night around him. Now he was surrounded on all sides by smooth ice. This distanced him somewhat from earthly complexity and chaos, and by imagining that the icy plane extended infinitely in every direction, he obtained a simple, flat world; a cold, planar mental platform. Cares vanished, and soon his perception reentered that state of rest, where the stars were waiting for him.…

  Then, with a crunch, the ice beneath Luo Ji’s feet broke and his body plunged straight into the water.

  At the precise instant the icy water covered Luo Ji’s head, he saw the stillness of the stars shatter. The starfield curled up into a vortex and scattered into turbulent, chaotic waves of silver. The biting cold, like crystal lightning, shot into the fog of his consciousness, illuminating everything. He continued to sink. The turbulent stars overhead shrank into a fuzzy halo at the break in the ice above his head, leaving nothing but cold and inky blackness surrounding him, as if he wasn’t sinking into ice water, but had jumped into the blackness of space.

  In the dead, lonely, cold blackness, he saw the truth of the universe.

  He surfaced quickly. His head surged out of the water and he spat out a mouthful. He tried crawling onto the ice at the edge of the hole but could only bring his body up halfway before the ice collapsed again. He crawled and collapsed, forging a path through the ice, but progress was slow and his stamina began to give out from the cold. He didn’t know whether the security team would notice anything unusual on the lake before he drowned or froze to death. Stripping off his soaked down jacket to lessen the burden on his movement, he had the idea that if he spread out the jacket on the ice, it might distribute the pressure and allow him to crawl onto it. He did so, and then, with just enough energy left for one last attempt, he used every last ounce of strength to crawl onto the down jacket at the edge of the ice. This time the ice didn’t collapse, and at last his entire body was lying on top of it. He crept carefully ahead, daring to stand up only after putting a fair distance between him and the hole. Then he saw flashlights waving on the shore and heard shouts.

  He stood on the ice, his teeth chattering in the cold, a cold that seemed to come not from the lake water or icy wind, but from a direct transmission from outer space. He kept his head down, knowing that from this moment on, the stars were not like they once were. He didn’t dare look up. As Rey Diaz feared the sun, Luo Ji had acquired a severe phobia of the stars. He bowed his head, and through chattering teeth, said to himself:

  “Wallfacer Luo Ji, I am your Wallbreaker.”

  * * *

  “Your hair’s turned white over the years,” Luo Ji said to Kent.

  “For many years to come, at least, it’s not going to get any whiter,” Kent said, laughing. In Luo Ji’s presence, he had always worn a courteous, studied face. This was the first time Luo Ji had seen him with such a sincere smile. In his eyes, he saw the words that remained unspoken: You’ve finally begun to work.

  “I need someplace safer,” he said.

  “Not a problem, Dr. Luo. Any particular requests?”

  “Nothing apart from safety. It must be absolutely secure.”

  “Doctor, an absolutely safe place does not exist, but we can come very close. I’ll have to warn you, though, these places are always underground. And as for comfort…”

  “Disregard comfort. However, it’d be best if it’s in China.”

  “Not a problem. I’ll take care of it immediately.”

  When Kent was about to leave, Luo Ji stopped him. Pointing out the window at the Garden of Eden, which was now completely blanketed in snow, he said, “Can you tell me the name of this place? I’m going to miss it.”

  * * *

  Luo Ji traveled more than ten hours under tight security before reaching his destination. When he exited the car, he knew immediately where he was: It was here, in the broad, squat hall that looked like an underground parking garage, that he had embarked on his fantastic new life five years before. Now, after five years of dreams alternating with nightmares, he had returned to the starting point.

  Greeting him was a man named Zhang Xiang, the same young man who—along with Shi Qiang—had sent him off five years ago, and who now was in charge of security. He had aged considerably in five years and now looked like a middle-aged man.

  The elevator was still operated by an armed soldier—not the one from back then, of course, but Luo Ji still felt a certain warmth in his heart. The old-style elevator had been swapped for one that was completely automated and did not require an operator, so the soldier merely pressed the “-10” button and the elevator started its descent.

  The underground structure had clearly undergone a recent renovation: The ventilation ducts in the hallways had been hidden, the walls coated with moisture-proof tile, and all traces of the civil air defense slogans had disappeared.

  Luo Ji’s living quarters took up the whole of the tenth basement floor. While it was no match in comfort for the house he had just left, it was equipped with comprehensive communications and computer equipment, along with a conference room set up with a remote video conferencing system, giving the place the feel of a command center.

  The administrator made a particular point of showing Luo Ji a set of light switches in the room, each of which bore a small picture of the sun. The administrator called them “sun lamps” and said they needed to be turned on for no fewer than five hours a day. Originally intended as labor-safety products for mine workers, they could simulate sunlight, including UV rays, as supplementary daylight for people spending long periods underground.

  The next day, as Luo Ji had requested, the astronomer Albert Ringier visited the tenth basement.

  When he saw him, Luo Ji said, “You were the first to observe the flight path of the Trisolaran Fleet?”

  Ringier looked a little unhappy to hear this. “I’ve repeatedly issued statements to reporters, but they insist on forcing this honor on my head. It should be credited to General Fitzroy. He was the one who demanded that Hubble II observe Trisolaris during testing. Otherwise we might have missed the chance, since the wake in the interstellar dust would have faded.”

  “What I’d like to talk to you about isn’t connected to that. I did a bit of astronomy once, but not in much depth, and I’m no longer familiar with the subject. My first question is this: If, in the universe, there exists another observer apart from Trisolaris, has Earth’s position been revealed to them?”

  “No.”

  “You’re sure of that?”

  “Yes.”

  “But Earth has exchanged communication with Trisolaris.”

  “That low-frequency communication would reveal only the general direction of Earth and Trisolaris in the Milky Way Galaxy, and the distance between the two worlds. That is, if there’s a third-party recipient, the communication would make it possible for them to know of the existence of two civilized worlds 4.22 light-years apart in the Orion Arm of the Milky Way, but they would still be ignorant of the precise position of those two worlds. In fact, determining each other’s position through this kind of exchange is only feasible for stars in close proximity, like the sun and the stars of Trisolaris. For a slightly more distant third-party observer, however, even if we communicate directly with them, we wouldn’t be able to determine each other’s position.”

  “Why is that?”

  “Marking the position of a star for another observer in the universe is hardly as easy as people imagine. Here’s an analogy: You’re taking a plane through the Sahara Desert and a grain of sand below you shouts ‘Here I am!’ You hear the sho
ut, but can you fix a location for that grain of sand from the plane? There are nearly two hundred billion stars in the Milky Way. It’s practically a desert of stars.”

  Luo Ji nodded in apparent relief. “I understand. So that’s it, then.”

  “What is?” Ringier asked in confusion.

  Luo Ji didn’t answer, but asked instead, “Using our present level of technology, is there a way to indicate the position of a star in the universe?”

  “Yes, by using directed very high frequency electromagnetic waves, equal to or higher in frequency than visible light, and then harnessing stellar power to transmit information. In simple terms, you’d make the star flash, like a cosmic lighthouse.”

  “This far exceeds our present technical capabilities.”

  “Oh, I’m sorry. I overlooked your precondition. At our present technical capabilities, it would be fairly difficult to show a star’s position to the far reaches of the universe. There’s still a way, but interpreting the positional information requires a level of technology far beyond that of humanity, and even, I believe, beyond that of Trisolaris.”

  “Tell me about that approach.”

  “The key information is the relative position of stars. If you specify a region of space in the Milky Way that contains a sufficient number of stars—perhaps a few dozen would be sufficient—their relative arrangement in three-dimensional space would be totally unique, like a fingerprint.”

  “I’m starting to understand. We send out a message containing the position of the star we wish to point out, relative to the surrounding stars, and the recipient compares the data to its star map to determine the star’s location.”

  “Right. But things aren’t that simple. The recipient must possess a three-dimensional model of the entire galaxy that precisely indicates the relative position of every one of a hundred billion stars. Then, after receiving our message, they would have to search through that enormous database to find an area of space that matches the pattern of positions we sent out.”