Death's End

by Liu Cixin

  Guan Yifan clutched Cheng Xin’s arm. “I was just getting to that. We’ve got to get out of here. Leave not just Planet Gray, but the entire system. This is a very dangerous place. Death lines are not like regular trails. Without disturbance, they’ll stay like this, with a diameter equal to the effective surface of the curvature engine. But if they’re disturbed, they’ll spread very rapidly. A death line of this size can expand to cover a region the size of a solar system. Scientists call this phenomenon a death line rupture.”

  “Does a rupture make the speed of light zero in the entire region?”

  “No, no. After rupture, it turns into a regular trail. The speed of light inside goes up as the trail dissipates over a wider region, but it will never be much more than a dozen meters per second. After these death lines expand, this entire system might turn into a reduced-lightspeed black hole, or a black domain.… Let’s go.”

  Cheng Xin and Guan Yifan turned toward the shuttle and began to run and leap.

  “What kind of disturbance makes them spread?” Cheng Xin asked. She turned to give the death lines another glance. Behind them, the five death lines cast long shadows that stretched across the plain to the horizon.

  “We’re not sure. Some theories suggest that the appearance of other curvature trails nearby would cause disturbance. We’ve confirmed that curvature trails within a short distance can influence each other.”

  “So, if Halo accelerates—”

  “That’s why we must get farther away using only the fusion engine before engaging the curvature engine. We’ve got to move … using your units of measurement … at least forty astronomical units away.”

  After the shuttle took off, Cheng Xin continued to stare at the receding death lines. She said, “The Zero-Homers give me a bit of hope.”

  Yifan said, “The universe contains multitudes. You can find any kind of ‘people’ and world. There are idealists like the Zero-Homers, pacifists, philanthropists, and even civilizations dedicated only to art and beauty. But they’re not the mainstream; they cannot change the direction of the universe.”

  “It’s just like the world of humans.”

  “At least the Zero-Homers’ task will ultimately be completed by the cosmos itself.”

  “You mean the end of the universe?”

  “That’s right.”

  “But based on what I know, the universe will continue to expand, and become sparser and colder forever.”

  “That’s the old cosmology you know, but we’ve disproved it. The amount of dark matter had been underestimated. The universe will stop expanding and then collapse under gravity, finally forming a singularity and initiating another big bang. Everything will return to zero, or home. And so Nature remains the final victor.”

  “Will the new universe have ten dimensions?”

  “Who knows? There are infinite possibilities. That’s a brand-new universe, and a brand-new life.”

  * * *

  The trip back to Planet Blue was as uneventful as the trip to Planet Gray. Most of the time, Cheng Xin and Guan Yifan remained asleep under the sleep-aid machines. By the time they were awakened, Hunter was in orbit around Planet Blue. Looking down at the blue-and-white world, Cheng Xin almost thought she was home.

  AA hailed them, and Yifan replied. “Hunter here. What’s wrong?”

  AA’s voice was agitated. “I’ve called you multiple times, and the ship’s AI refused to wake you!”

  “I told you we have to maintain radio silence. What happened?”

  “Yun Tianming is here!”

  Cheng Xin was thunderstruck. The last traces of sleep left her, and even Yifan’s jaw hung open.

  “What?” Cheng Xin said softly.

  “Yun Tianming is here! His ship landed three hours ago.”

  “Oh,” Cheng Xin answered mechanically.

  “He’s still young, as young as you!”

  “Really?” Cheng Xin’s voice seemed to come from far away, even to herself.

  “He brought a gift for you.”

  “He already gave me a gift. We’re inside his gift now.”

  “That’s nothing. Let me tell you, this is an awesome gift, and much bigger.… He’s outside right now. Let me get him.”

  Yifan interrupted. “No. We’re coming down right now. So much radio transmission is dangerous. I’m cutting it off.”

  Yifan and Cheng Xin stared at each other, and then laughed. “Are we really awake?” Cheng Xin asked.

  Even if it was just a dream, Cheng Xin wanted to be dreaming for longer. She turned on the holographic display, and the starry sky no longer seemed so dark and cold—in fact, it seemed filled with a clear beauty like the sky after a fresh rain. Even the starlight seemed to exude the fragrance of spring buds. It was the feeling of being reborn.

  “Let’s get into the shuttle and land,” Yifan said.

  Hunter initiated the shuttle separation sequence. Inside the cramped cabin, Yifan used an interface window to perform the final check prior to atmospheric reentry.

  “How did he get here so fast?” Cheng Xin muttered, as if still dreaming.

  Yifan was now completely calm. “This confirms our guess. The First Trisolaran Fleet founded a colony nearby, within a hundred light-years of here. They must have received the gravitational wave signal from Halo.”

  The shuttle separated from Hunter. They could see the tiny pyramid of Hunter recede on the monitoring system.

  “What kind of gift is bigger than a sun and its planetary system?” Yifan asked, smiling.

  An excited Cheng Xin shook her head.

  The shuttle’s fusion reactor activated, and the cooling ring outside began to glow red. The thrusters were preheating, and the control interface window showed that deceleration would begin in thirty seconds. The shuttle was about to descend rapidly as it entered Planet Blue’s atmosphere.

  Cheng Xin heard an abrupt noise, as though something had sliced across the shuttle from bow to stern. Sharp jolts followed. And then, she experienced an eerie moment—eerie, because she couldn’t be sure it was just a moment. The moment seemed to be infinitely short but also infinitely long. She had a strange feeling of stepping across time but being situated outside of time.

  Later, Yifan would explain to her that she had experienced a “time vacuum.” The length of that moment could not be measured in time because, during that moment, time did not exist.

  At the same time, she felt herself collapse, as though she was going to turn into a singularity. Meanwhile, the mass of her, Guan Yifan, and the shuttle approached infinity.

  And then everything plunged into darkness. At first, Cheng Xin thought something was wrong with her eyes. She couldn’t believe the inside of the shuttle could be so dark, so dark that she couldn’t see her fingers waving before her eyes. Cheng Xin called for Guan Yifan, but there was only silence in the space suit’s earpiece.

  Yifan felt around in the darkness until he grabbed Cheng Xin’s head. She felt her own face touching his. She did not resist; she only felt comfort. Then she understood that Yifan was only trying to talk to her. The communications system inside the space suits had shut down, and the only way they could talk to each other was to press the visors of their helmets together so that their voices could be transmitted across.

  “Don’t be scared. Don’t panic. Listen to me and don’t move!” Cheng Xin heard Yifan’s voice from the visor. She could tell from the vibrations that he was shouting, but what she heard was very faint, like a whisper. She felt his hand moving around in the dark until the inside of the cabin lit up. The light came from something held in his hand, a strip about the size of a cigarette. Cheng Xin knew it was some kind of chemical light source. Halo was equipped with similar emergency supplies. Bending it caused it to emit a cold light.

  “Don’t move. The space suits are no longer providing oxygen. Slow down your breathing. I’ll repressurize the cabin now. It won’t take long!” Yifan handed the glow stick to Cheng Xin, pulled open a storage unit next to his seat
, and took out a metal bottle that resembled a small fire extinguisher. He twisted the bottle’s opening, and a white gas rushed out of the bottle in raging torrents.

  Cheng Xin’s breath quickened. All she had left was the air remaining in her helmet, and the harder she inhaled, the more suffocated she felt. Her hand reached instinctively for the visor of her helmet, but Yifan stopped her in time. He embraced her again, this time to calm her down. She imagined that he was trying to rescue her from drowning. In the cold light, she saw his eyes, which seemed to be telling her that they were almost at the surface. Cheng Xin could feel the air pressure in the cabin rising, and just when she was about to pass out from lack of air, Yifan snapped her visor open, as well as his own. The two gulped air.

  After she caught her breath, Cheng Xin examined the metal bottle. She noticed the pressure gauge near the neck of the bottle, an ancient analog dial with a swinging needle that was now pointing into the green zone.

  Yifan said, “The oxygen from that won’t last long, and the cabin is going to get very cold very fast. We need to change space suits.” He pushed off from his seat and dragged out two metal boxes from the back of the cabin. He opened one and showed Cheng Xin the space suit inside.

  Modern space suits—in the Solar System and here—were very lightweight. If one kept the suit unpressurized, left off the small life-support pack, and took off the helmet, a modern space suit was virtually indistinguishable from ordinary clothes. However, the space suits in the boxes were heavy and clumsy, resembling Common Era space suits.

  They could now see their breaths. Cheng Xin took off her original space suit and felt the bone-chilling cold inside the cabin. The heavy space suit was difficult to put on, and Yifan had to help her. She felt like a child dependent on this man, a feeling that she had not experienced in a long time. Before Cheng Xin put on the helmet, Yifan explained the suit’s features to her in detail—the oxygen dial, the pressurization toggle, the knob for temperature adjustment, the switches for communications and illumination, and so on. The space suit had no automatic systems, and everything required manual operation.

  “There are no computer chips inside this suit at all. Right now, none of our computers—electronic or quantum—work anymore.”

  “Why?”

  “The speed of light right now is less than twenty kilometers per second.”

  Yifan helped Cheng Xin put on her helmet. Her body was almost frozen. He turned on the oxygen and the heater in her suit, and she felt herself thawing out. Yifan now turned to put on his own suit. He worked fast, but it took some work between when he put on his helmet and the two suits could be connected for communications. Neither was able to speak until their chilled bodies had recovered.

  The suits were so heavy and clumsy that Cheng Xin could imagine how difficult it would be to move around in them under 1G. Her suit wasn’t so much a suit as a house, the only place where she could find refuge. The light-emitting strip drifting in the cabin was dimming, so Yifan turned on the lamp on his own suit. Inside the cramped space, Cheng Xin thought they were like ancient miners trapped underground.

  “What happened?” Cheng Xin asked.

  Yifan floated up from his seat and struggled until he managed to open the screen over one of the portholes—the automatic controls for the porthole screens were also nonfunctional. He drifted to the other side of the cabin and repeated the operation with another porthole.

  Cheng Xin looked at the transformed universe outside.

  She saw two star clusters at the two ends of space: The cluster in front glowed blue and the cluster behind glowed red. Cheng Xin had seen a similar sight earlier when Halo was flying at lightspeed, but the two star clusters she saw now were not stable. Their shapes shifted abruptly like two balls of flame in fierce wind. Instead of stars leaping from the blue cluster into the red cluster from time to time, two light belts connected the two ends of the universe, only one of which was visible on each side of the ship.

  The wider belt took up half the space on one side. Its two ends were not connected to the blue and red star clusters; instead, the belt ended in two round tips. Cheng Xin could tell that this “belt” was actually an extremely flattened oval—or perhaps a circle that had been stretched out. Colored patches of various sizes flitted across the wide belt: blue, white, and light yellow. Instinctively, Cheng Xin understood that she was looking at Planet Blue.

  The light belt on the other side of the ship was thinner but brighter, and its surface showed no details. Unlike Planet Blue, this belt’s length cycled rapidly between a bright line that connected the red and blue clusters, and a bright circle. The belt’s periodic circular state told Cheng Xin that she was looking at the star DX3906.

  “We’re orbiting Planet Blue at lightspeed,” said Guan Yifan. “Except the speed of light is now very slow.”

  The shuttle had been moving far faster, but as the speed of light was an absolute speed limit, the shuttle’s velocity had been cut down to that.

  “The death lines ruptured?”

  “Yes. They spread out to cover the entire solar system. We’re trapped here.”

  “Was it due to the disturbance from Tianming’s ship?”

  “Perhaps. He didn’t know the death lines were here.”

  Cheng Xin didn’t want to ask what their next step was, knowing that nothing more could be done. No computer could operate when the speed of light was below twenty kilometers per second. The shuttle’s AI and control systems were all dead. Under such conditions, not even a light inside the spacecraft could be turned on—it was just a metal can with no electricity or power. Hunter was the same, also dead. Before falling into reduced lightspeed, the shuttle had not yet began decelerating, and so the small spaceship should be nearby—but it might as well be on the other side of the planet. Without the control systems, neither the shuttle nor Hunter could open their doors.

  Cheng Xin thought about Yun Tianming and 艾 AA. They were both on the ground, and should be safe. But now there was no way for the two sides to communicate. She never even got to say hello to him.

  Something light gently struck the visor of her helmet: the metal bottle. Cheng Xin looked at the ancient pressure gauge on it again, and touched her own space suit. Hope, once extinguished, lit up again like a firefly.

  “You’ve been preparing for situations like this?” she asked.

  “Yes.” Yifan’s voice sounded distorted in Cheng Xin’s earpiece due to the use of ancient analog signals. “Not for ruptured death lines, of course, but we were prepared for accidentally drifting into the trails of lightspeed ships. The situations are similar: The reduced lightspeed stops everything.… Next, we need to start the neurons.”

  “What?”

  “Neural computers. Computers that can operate under reduced lightspeed. The shuttle and Hunter both have two control systems, one of which is based on neural computers.”

  Cheng Xin was amazed that such machines existed.

  “The key isn’t the speed of light, but the system design. The transmission of chemical signals in the brain is even slower, only two or three meters per second—not much faster than us walking. Neural computers can still work because they imitate the highly parallel processing found in the brains of higher animals. All the chips are designed specifically to function under reduced-lightspeed conditions.”

  Yifan opened a metal bulkhead decorated with many dots connected in a complex web like the tentacles of an octopus. Inside was a small control panel with a flat display, as well as several switches and indicator lights. The whole assembly was built from components deemed obsolete by the end of the Crisis Era. He toggled a red switch and the screen lit up: text scrolling by. Cheng Xin could tell it was the boot sequence of some operating system.

  “The parallel neural mode hasn’t been started yet, so we have to load the operating system serially. You’ll probably have a hard time believing how slow serial data transmission is under reduced lightspeed: look, the data rate is a few hundred bytes per second. N
ot even a kilobyte.”

  “Then the boot sequence will take a long time.”

  “That’s right. But as the parallel mode gradually builds up, the loading will speed up. Still, it really will take a long time to complete the sequence.” Yifan pointed to the progress indicator, a line of text on the bottom of the screen.

  Remaining load time for boot module: 68 hours 43 minutes [flickering] seconds. Total remaining system load time: 297 hours 52 minutes [flickering] seconds.

  “Twelve days!” Cheng Xin exclaimed. “What about Hunter?”

  “Its systems will detect the reduced-lightspeed condition and automatically boot the neural computer. But it will take about as long to complete.”

  Twelve days. They could only get to the survival resources in the shuttle and on Hunter after twelve days. Until then, they had to rely on their primitive space suits. If the space suits were powered by nuclear batteries, the electricity should last long enough, but they didn’t have enough oxygen.

  “We have to hibernate,” said Yifan.

  “Do we have the equipment for hibernation on the shuttle?” As soon as she asked the question, Cheng Xin realized her error. Even if the shuttle had such equipment, it would be controlled by the computer, which was out of commission right now.

  Yifan opened the storage unit from which he had taken the oxygen bottle earlier and took out a small box. He opened it to show Cheng Xin a few capsules. “These are drugs for short-term hibernation. Unlike regular hibernation, you won’t need an external life-support system. Once you are in hibernation, your respiration will slow down to the point where you consume very little oxygen. One capsule is enough for fifteen days of hibernation.”

  Cheng Xin opened her visor and swallowed one of the pills. She watched as Yifan also took one. Then she looked outside the portholes.

  Patches of color now moved so fast over Planet Blue—the broad belt that connected the blue and red ends of the lightspeed universe on one side of the ship—that they turned into a blur.

  “Can you see the patterns on the belt repeating periodically?” Yifan wasn’t looking outside at all. His eyes were half-closed as he strapped himself into the hypergravity seat.