Death's End

by Liu Cixin

  Guan Yifan turned his gaze back to West. “Last night, I had a dream. I went somewhere, somewhere really open, open in a way that you can’t even imagine. After I woke up, reality felt very enclosed and narrow, and that was how I came to be claustrophobic. It’s like … if, as soon as you were born, you were locked inside a small box, you wouldn’t care because that was all you’ve known. But once you’ve been let out and they put you back in, it feels completely different.”

  “Tell me more about this place in your dream.”

  Guan gave the doctor a mysterious smile. “I will describe it to the other scientists on the ship, maybe even the scientists on Blue Space. But I won’t tell you. I don’t have anything against you, Doctor, but I can’t stand the attitude shared by everyone in your profession: If you think someone has a mental disorder, you treat everything he says as merely the delusion of a diseased mind.”

  “But you just told me it was a dream.”

  Guan shook his head, struggling to remember. “I don’t know if it was a dream; I don’t know if I was awake. Sometimes, you can think you’re waking from a dream, only to find yourself still dreaming; other times, you’re awake, but it seems like you’re dreaming.”

  “The second situation is extremely rare. If you experienced that, then it was almost certainly a symptom of some mental disorder. Oh, sorry, now you’re unhappy with me again.”

  “No, no. I think we’re actually very similar. We both have our targets of observation. You observe the deranged, and I observe the universe. Like you, I also have some criteria for evaluating whether the observed objects are sound: harmony and beauty, in the mathematical sense.”

  “Of course the objects you observe are sound.”

  “But you’re wrong, Doctor.” Guan pointed at the glowing Milky Way, but his gaze remained on West, as though showing him some monster that had suddenly appeared out of nowhere. “Out there is a patient who may be mentally sound, but whose body suffers from paraplegia!”

  “Why?”

  Guan curled up and hugged his knees. The movement caused his body to slowly rotate in place. The magnificent Milky Way revolved around him, and he saw himself as the center of the universe.

  “Because of the speed of light. The known universe is about sixteen billion light-years across, and it’s still expanding. But the speed of light is only three hundred thousand kilometers per second, a snail’s pace. This means that light can never go from one end of the universe to the other. Since nothing can move faster than the speed of light, it follows that no information and motive force can go from one end of the universe to the other. If the universe were a person, his neural signals couldn’t cover his entire body; his brain would not know of the existence of his limbs, and his limbs would not know of the existence of the brain. Isn’t that paraplegia? The image in my mind is even worse: The universe is but a corpse puffing up.”

  “Interesting, Dr. Guan, very interesting!”

  “Other than the speed of light, three hundred thousand kilometers per second, there’s another three-based symptom.”

  “What do you mean?”

  “The three dimensions. In string theory, excepting time, the universe has ten dimensions. But only three are accessible at the macroscopic scale, and those three form our world. All the others are folded up in the quantum realm.”

  “I think string theory provides an explanation.”

  “Some think that it is only when two strings encounter each other and some qualities are canceled out that the dimensions are unfolded into the macroscopic, and dimensions above three will never have such chances for encountering each other.… I don’t think much of this explanation. It is not mathematically beautiful. Like I said, this is the universe’s three and three hundred thousand syndrome.”

  “What do you propose as the cause?”

  Guan laughed uproariously and put his arm around the doctor’s shoulders. “Great question! I don’t think anyone has thought this far. I’m sure there’s a root cause, and it might be the most horrifying truth that science is capable of revealing. But … Doctor, who do you think I am? I’m nothing more than a tiny observer curled up in the tail of a spaceship, and only an assistant researcher at that.” He released West’s shoulders, and, facing the galaxy, let out a long sigh. “I’ve been in hibernation the longest of anyone aboard. When we left Earth, I was only twenty-six, and even now I’m only thirty-one. But in my eyes, the universe has already transformed from a source of beauty and faith into a bloating corpse. I feel old. The stars no longer hold any attraction for me. I want to go home.”

  Unlike Guan Yifan, West had been awake for much of the voyage. He always believed that to maintain the mental health of others, he needed to keep his own emotions under control. But something seemed to buffet his heart now, and as he reviewed his own half century of travels, his eyes moistened. “My friend, I’m old, too.”

  As if in response to their conversation, the battle alert klaxons blared, sounding like the entire sky full of stars was screaming. Warning information scrolled on floating windows that appeared above the plaza. The overlapping windows sprang up one after another and quickly covered the Milky Way like colorful clouds.

  “Droplet attack!” West said to the confused Guan Yifan. “They’re both accelerating. One is headed for Blue Space, the other for us!”

  Guan looked around, instinctively searching for something to grab on to in case the ship accelerated. But there was nothing around. In the end, he held on to the doctor.

  West held his hands. “There won’t be enough time for any evasive maneuvers. We have only a few seconds left.”

  After a brief panic, both felt an unexpected sense of relief. They were glad that death would arrive so quickly that there wasn’t even time to be terrified. Perhaps their discussion about the universe was the best preparation for death.

  They both thought of the same thing, but Guan spoke it aloud first. “Looks like neither of us needs to worry about our patients anymore.”

  Deterrence Era, Year 62

  November 28, 4:00 P.M. to 4:17 P.M.: Deterrence Center

  The high-speed elevator continued to descend, and the increasing layers of earth above seemed to put all their weight on Cheng Xin’s heart.

  Half a year ago, a joint session of the UN and the Solar System Fleet had elected Cheng Xin to succeed Luo Ji as the Swordholder and given her authority to control the gravitational wave deterrence system. She had received almost twice as many votes as the next candidate. She was now proceeding to the Deterrence Center in the Gobi Desert, where the deterrence authority handover ceremony was to take place.

  The Deterrence Center was the deepest man-made structure ever, about forty-five kilometers beneath the surface. This location was already below the crust, past the Mohorovičić discontinuity, in the mantle of the Earth. The pressure and temperature here were both far higher than in the crust, and the stratum around her was made up mostly of solid, hard peridotite.

  The elevator took almost twenty minutes to reach its terminus. Cheng Xin stepped out of the elevator and saw a black steel door. White text on the door gave the formal name for the Deterrence Center: Gravitational Wave Universal Broadcast System Control Station Zero. The insignias of the UN and the Solar System Fleet were embossed on the door.

  This ultra-deep structure was quite complex. It possessed its own independent air circulation system and was not directly connected with the atmosphere above the surface—otherwise, the high air pressure generated by a depth of forty-five kilometers would cause great discomfort to the occupant. It was also equipped with a powerful cooling system to withstand the high temperature of the mantle, nearly five hundred degrees Celsius.

  All Cheng Xin could see, however, was emptiness. The lobby’s walls could all apparently act as electronic displays, but they showed nothing but whiteness, as though the building wasn’t in use yet. Half a century ago, when the Deterrence Center was designed, Luo Ji had been consulted, but he had only provided one piece of i
nput:

  As simple as a tomb.

  The handover ceremony was a solemn occasion, but the bulk of it had been held on the surface forty-five kilometers above. There, all the leaders of Earth International and Fleet International, representing all of humanity, had gathered, and they watched as Cheng Xin entered the elevator. Only two people would oversee the final handover: the PDC chair and the chief of staff for the Solar System Fleet, representing the two institutions directly operating the deterrence system.

  The PDC chair pointed at the empty lobby and explained to Cheng Xin that they would redecorate the place based on her ideas. If she wanted, she could have a lawn, plants, a fountain, and so forth. She could also choose to have a holographic simulation of scenes from the surface.

  “We don’t want you to live like him,” said the chief of staff. Perhaps because of his military uniform, Cheng Xin saw in him traces of men of the past, and his words warmed her slightly. But the heavy weight on her heart, as heavy as the forty-five kilometers of earth above her, did not lessen.

  Excerpt from A Past Outside of Time

  The Choice of the Swordholder: Ten Minutes Between Existence and Annihilation

  The first dark forest deterrence system consisted of more than three thousand nuclear bombs wrapped in an oil film substance deployed in orbit around the sun. After detonation, the film would cause the sun to flicker and broadcast the location of Trisolaris to the universe. Although the system was grand, it was extremely unstable. After the droplets stopped blockading electromagnetic radiation from the sun, a transmission system based on using the sun as a superantenna was immediately put in place to supplement the nuclear bomb deterrence system.

  Both of these systems relied on electromagnetic radiation, including visible light, as the broadcast medium. We now know that this is the most primitive technique for interstellar communication, equivalent to smoke signals in space. Since electromagnetic waves decay and become distorted rapidly, the broadcast range is limited.

  At the time of the founding of deterrence, humankind already had a basic grasp of the technology for detecting gravitational waves and neutrinos, but they lacked the ability to modulate and transmit. These were the very first technologies humans demanded from Trisolaris. Compared to quantum communications, these technologies were still primitive, since both gravitational waves and neutrinos were limited by the speed of light, but they were a whole level above electromagnetic waves.

  Both of these means of transmission decayed relatively slowly and had very long broadcast ranges. Neutrinos, in particular, interacted with almost nothing else. Theoretically, a modulated beam of neutrinos could transmit information to the other end of the universe, and the accompanying decay and distortion would not affect the decoding of the information. But while neutrinos must be focused in a particular direction, gravitational waves were omnidirectional, thus gravitational waves became the main method of establishing dark forest deterrence.

  The fundamental principle of gravitational wave transmission relied on the vibration of a long string of extremely dense matter. The ideal transmission antenna would involve a large number of black holes connected together to form a chain that generated gravitational waves as it vibrated. But even Trisolaris didn’t possess such a level of technology, and humankind had to resort to constructing the vibrating string out of degenerate matter. The extremely dense degenerate matter packed an enormous mass into strings mere nanometers in diameter. A single string took up only a minuscule portion of the giant antenna, the bulk of which consisted of support and protection for the ultra-dense string. Thus, the total mass of the antenna wasn’t extraordinarily large.

  The degenerate matter forming the vibrating string was naturally found in white dwarves and neutron stars. Under typical conditions, this substance naturally decayed and turned into regular matter over time. Man-made vibrating strings typically had a half-life of around fifty years, beyond which the antennas lost their effectiveness. Thus, every half century, the antennas needed to be refreshed with new ones.

  During the earliest stage of gravitational wave deterrence, the main strategic concern was with ensuring deterrence power. Plans were made to build a hundred broadcasting stations scattered around the continents. But gravitational wave communication suffered from a flaw: The transmission equipment could not be miniaturized. The complex, gigantic antennas were extremely costly to manufacture, and in the end only twenty-three gravitational transmitters were built. But the focus on ensuring deterrence finally faded, due to another event.

  During the Deterrence Era, the ETO gradually disappeared, but another kind of extremist organization sprang up. They believed in the cause of human supremacy, and advocated for the complete annihilation of Trisolaris. The “Sons of the Earth” was one of the largest of these organizations. In Year 6 of the Deterrence Era, more than three hundred “Sons of the Earth” attacked a gravitational wave broadcasting station located on Antarctica with the aim of seizing the transmitter. Equipped with advanced weapons such as mini-infrasonic nuclear bombs, and aided by members who had infiltrated the broadcasting station ahead of time, the attackers nearly succeeded. If the defending troops stationed at the site hadn’t destroyed the antenna in time, the consequences would have been disastrous.

  This incident terrified both worlds. People began to realize the great danger posed by gravitational wave transmitters. Simultaneously, Trisolaris pressured Earth until gravitational wave transmission technology was strictly controlled, and the twenty-three broadcasting stations were cut down to four. Three of the stations were terrestrial, located in Asia, North America, and Europe, and the last one was the spaceship Gravity.

  All the transmitters relied on an active trigger, because the dead hand trigger technique used in the circumsolar nuclear bomb system was no longer necessary. Luo Ji had established deterrence by himself, but now, if the Swordholder were killed, others would be able to take over.

  Initially, the gigantic gravitational wave antennas had to be built on the surface. As technology advanced, in Year 12 of the Deterrence Era, the three terrestrial antennas and their support systems moved deep underground. Everyone understood, however, that burying the transmitters and the control center beneath the Earth’s surface primarily guarded against a threat originating from humankind itself, but was meaningless against an attack by Trisolaris. For droplets constructed from strong-interaction material, tens of kilometers of rock were not much different from mere liquid, barely able to impede their progress.

  After Earth established deterrence, the Trisolar invasion fleet veered away, as verified through observation. With that threat diminished, most people turned their focus to the whereabouts of the ten droplets that had already reached the Solar System. Trisolaris insisted that four of the droplets remain in the Solar System, justifying the decision by arguing that the gravitational wave transmitters could be seized by extremist factions within humankind, and Trisolaris should have the power to take steps to protect both worlds in the event of such an occurrence. Reluctantly, the Earth agreed, but required the four droplets to stay beyond the Kuiper Belt. Moreover, each droplet had to be accompanied by a human probe, so that the droplets’ locations and orbits were known at all times. Thus, in the event of a droplet attack, the Earth would have about fifty hours of advance warning. Of these four droplets, two eventually followed Gravity to hunt Blue Space, and only two remained in the vicinity of the Kuiper Belt.

  No one knew where the other six droplets had gone.

  Trisolaris claimed that the six droplets had left the Solar System to rejoin the Trisolaran Fleet, but no one on Earth believed this.

  Trisolarans were no longer creatures of transparent thought. During the past two centuries, they had learned a great deal about strategic thinking—lies, ruses, and tricks. This was perhaps the greatest benefit they gained from studying human culture.

  Most people were convinced that the six droplets were hidden somewhere in the Solar System. But because the droplets were tiny,
fast, and invisible to radar, they were extremely difficult to locate and track. Even by spreading oil films or using other advanced detection techniques, humans could only reliably detect droplets if they approached within 1/10 AU of the Earth, or fifteen million kilometers. Outside this sphere, the droplets were free to roam undetected.

  At maximum speed, a droplet could cross fifteen million kilometers in ten minutes.

  This was all the time the Swordholder would have to make a decision if dark forest deterrence broke down.

  Deterrence Era, Year 62

  November 28, 4:00 P.M. to 4:17 P.M.: Deterrence Center

  With a deep rumble, the meter-thick heavy steel door opened and Cheng Xin and the others walked into the heart of the dark forest deterrence system.

  More emptiness and openness greeted Cheng Xin. This was a semicircular hall, with the curved wall facing her. The surface was translucent, resembling ice. The floor and ceiling were pure white. Cheng Xin’s first thought was that she stood in front of an empty, iris-less eye, exuding a desolate sense of loss.

  Then she saw Luo Ji.

  Luo Ji sat cross-legged on the ground in the middle of the white hall, facing the curved wall. His long hair and beard, combed neatly, were also white, almost merging with the white wall. The whiteness everywhere contrasted strongly with his black Zhongshan suit.5 Sitting there, he appeared as a stable upside-down T, a lonely anchor on a beach, immobile under the winds of time howling overhead and before the roaring waves of the ages, steadfastly waiting for a departed ship that would never return. In his right hand, he held a red ribbon, the hilt of his sword: the switch for the gravitational wave broadcast. His presence gave the empty eye of this room an iris. Though he was but a black dot, the desolate sense of loss was relieved, giving the eye a soul. Luo Ji sat facing the wall so that his own eyes were invisible, and he did not react to his visitors.