Death's End

Galaxy Era, Year 409 Our Star

Halo shut off the curvature engine and coasted at lightspeed.

During the voyage, AA tried to comfort Cheng Xin, even though she knew this was a hopeless task.

“It’s ridiculous for you to blame yourself for the destruction of the Solar System. Who do you think you are? Do you think if you stand on your hands, you’ve lifted the Earth? Even if you hadn’t stopped Wade, the outcome of that war would have been hard to predict.

“Could Halo City really have achieved independence? Even Wade couldn’t be certain of that. Could the Federation Government and Fleet really have been scared of a few antimatter bullets? Maybe Halo City could have destroyed a few warships, or even a space city, but ultimately, Halo City would have been exterminated by the Federation Fleet. And in that version of history, there would be no Mercury base, no second chance.

“Even if Halo City had managed to achieve independence, continued to research curvature propulsion, discovered the slowing effects of the trails, and finally collaborated with the Federation Government to build more than a thousand lightspeed ships in time, do you think people would have agreed to build the black domain? Remember how confident people were that the Bunker World would survive a dark forest strike—why would they have agreed to isolate themselves in the black domain?”

AA’s words slid across Cheng Xin’s thoughts like drops of water across a lily pad, leaving no trace. Cheng Xin’s only thought was to find Yun Tianming and tell him everything. In her mind, a journey of 287 light-years would take a long time, but the ship’s AI informed her that the trip would only take fifty-two hours in the ship’s frame of reference. Everything felt unreal to Cheng Xin, as though she had already died and gone to another world.

Cheng Xin spent a long time gazing out of the portholes at space. She understood that each time a star leapt out of the blue cluster in front, swept past the ship, and joined the red cluster behind the ship, it meant that Halo had passed it. She counted the stars and watched as they turned from blue to red—the sight was hypnotic. Eventually, she fell asleep.

By the time Cheng Xin awakened, Halo was close to its destination. It turned 180 degrees and activated the curvature engine for deceleration—in fact, the ship was pushing against its own trail. As the ship decelerated, the blue and red clusters began to spread out like two clusters of exploding fireworks, and soon evolved into a sea of stars distributed evenly around the ship. The slowing down of the ship also gradually erased the red and blue shifts. Cheng Xin and AA saw that the Milky Way ahead of them still looked about the same, but behind them, none of the stars looked familiar. The Solar System was long gone.

“We’re now two hundred eighty-six point five light-years from the Solar System,” said the ship’s AI.

“So two hundred eighty-six years has already passed back there?” AA asked. She looked as if she had just awakened from a dream.

“Yes, if you are using their frame of reference.”

Cheng Xin sighed. For the Solar System in its current condition, was there a difference between 286 years and 2.86 million years? But she thought of something.

“When did the collapse into two dimensions stop?”

The question made AA speechless, as well. Right: When—if ever—did it stop? Was there an instruction within that small, packaged two-dimensional foil that would eventually stop it? Cheng Xin and AA had no theoretical understanding of how three-dimensional space collapsed into two dimensions, but they instinctively thought the idea of an instruction embedded into two-dimensional space to halt its infinite expansion was too magical, the kind of magic that seemed impossible.

Would the collapse never stop?

It was best to not think about it too much.

The star called DX3906 was about the Sun’s size. As Halo began decelerating, it still looked like an ordinary star, but by the time the curvature engine shut off, the star appeared as a disk whose light seemed redder than the Sun’s.

Halo engaged the fusion reactor, and the silence on the ship was broken. The humming of the engine filled the ship, and every surface vibrated slightly. The ship’s AI analyzed the data obtained by the monitoring system and confirmed the basic facts about this solar system: DX3906 had two planets, both of them solid. The one farther from the star was about the size of Mars, but it had no atmosphere and appeared gray in color—so Cheng Xin and AA decided to call it Planet Gray. The other planet, closer to the star, was about the size of the Earth, and its surface resembled the Earth’s: an atmosphere containing oxygen and many signs of life, but without evidence of agriculture or industry. Since it was blue, like the Earth, they decided to call it Planet Blue.

AA was very happy that her research had been confirmed. More than four hundred years ago, she had discovered the star’s planetary system. Before then, people had thought it was a bare star without any planets. Through that work, AA had gotten to know Cheng Xin. Without that coincidence, her life would have turned out completely differently. Fate was such an odd thing: Four centuries ago, when she had gazed at this distant world through the telescope, she could never have imagined that she’d come here one day.

“Were you able to see these two planets back then?” Cheng Xin asked.

“No. They were impossible to see in the visible light range. Maybe those telescopes from the Solar System advance warning system could have seen them, but all I could do was deduce their existence through the data obtained via the solar gravitational lens…. I did theorize about the appearance of these two planets, and it looks like I was basically right.”

Halo had taken only fifty-two hours (by the ship’s frame of reference) to traverse the 286 light-years between the Solar System and the planetary system around DX3906, but it took eight full days to cross the sixty AU between the rim of the planetary system and Planet Blue at sub-light speeds. As Halo approached Planet Blue, Cheng Xin and AA discovered that its resemblance to the Earth was only superficial. The blue hue of this planet wasn’t the result of an ocean, but the color of the vegetation covering the continents. Planet Blue’s oceans were light yellow and took up only about a fifth of the planet’s surface. Planet Blue was a cold world; about a third of its continental surface was covered by blue vegetation, with the rest shrouded in snow. Most of the ocean was frozen, and only small patches near the equator were in liquid form.

Halo entered orbit around Planet Blue and began its descent. But the ship’s AI announced a new discovery. “An intelligent radio signal has been detected from the surface. It’s a landing beacon using communication formats dating from the start of the Crisis Era. Would you like me to follow its instructions?”

Cheng Xin and AA looked at each other excitedly. “Yes!” Cheng Xin said. “Follow its instructions to land.”

“Hypergravity will approach 4G. Please enter into secured landing positions. Landing sequence will be initiated once you’re secure.”

“Do you think it’s him?” AA asked.

Cheng Xin shook her head. In her life, moments of happiness were only gaps between mass catastrophes. She was now afraid of happiness.

Cheng Xin and AA sat in hypergravity seats, and the seats closed around them like giant palms squeezing them tight. Halo decelerated and descended, entering Planet Blue’s atmosphere after a series of powerful jolts. They could see the blue-and-white continents swinging into view in the images captured by the ship’s monitoring system.

Twenty minutes later, Halo landed near the equator. The ship’s AI suggested that Cheng Xin and AA wait ten minutes before getting out of their seats, to give their bodies a chance to adjust to Planet Blue’s gravity, which was similar to the Earth’s. Out of the porthole and on the monitoring system terminals, they could see that the yacht had landed in the middle of a blue grassland. Not too far away, they could see rolling mountains covered by snow—the landing site was near the foot of the mountain range. The sky was a light yellow, like the ocean when viewed from space. A light red sun shone in the sky. It was noon on Planet Blue, but the sky and the sun’s colors made it resemble dusk on the Earth.

Cheng Xin and AA didn’t examine the environment around them too carefully. Their attention was taken up by another small vehicle parked near Halo. It was a tiny craft, about four to five meters tall, with a dark gray surface. The profile was streamlined, but the tail fins were tiny. It didn’t seem to be an aircraft, but rather a ground-to-space shuttle.

A man stood next to the shuttle, dressed in a white jacket and dark-colored pants. The turbulence of Halo’s landing disturbed his hair.

“Is that him?” AA asked.

Cheng Xin shook her head. She knew right away that this wasn’t Yun Tianming.

The man waded through the blue sea of grass toward Halo. He moved slowly, and his posture and movements showed some exhaustion. He didn’t show any signs of surprise or excitement, as if the appearance of Halo was a perfectly normal occurrence. He stopped a few tens of meters away from the yacht and waited patiently in the grass.

“He’s good-looking,” said AA.

The man looked to be in his forties. He was East Asian in appearance, and he was indeed more handsome than Yun Tianming, with a broad forehead and wise but gentle eyes. His gaze made you believe he was always thinking, as if nothing in the universe, including Halo, could surprise him, but only cause him to think more. He lifted his hands and moved them around his head, indicating a helmet. Then he shook his head and waved one hand, indicating that they didn’t need space suits out there.

The ship’s AI agreed. “Atmospheric composition: thirty-five percent oxygen, sixty-three percent nitrogen, two percent carbon dioxide, with trace amounts of inert gasses. Breathable. But the atmospheric pressure is only point five three of Earth standard. Do not engage in strenuous exercise.”

“What is that biological entity standing next to the ship?” asked AA.

“Standard human being,” the AI replied.

Cheng Xin and AA exited the ship. They hadn’t adjusted to the gravity yet, and stumbled a bit as they walked. Outside, they breathed easily, not feeling the thinness of the air. A chill breeze blew at them and brought the fragrance of grass, refreshing them. The wide-open view showed the blue-and-white mountains and earth, the light yellow sky and red sun. The whole thing resembled a false-color photograph of the Earth. Other than the strange colors, everything looked familiar. Even the blades of grass looked just like the grass on the Earth, except for their blue hue. The man came to the foot of the stairs.

“Wait a minute. The stairs are too steep. I’ll help you down.” He climbed up the stairs easily and helped Cheng Xin down. “You should have rested longer before coming out. There’s no urgency.” Cheng Xin could hear an obvious Deterrence Era accent.

His hand felt warm and strong to Cheng Xin, and his broad body shielded her from the chill wind. She had the impulse to jump into this man’s arms, the first man she had met after traveling more than two hundred light-years from the Solar System.

“Did you come from the Solar System?” the man asked.

“Yes.” She leaned against the man and descended the stairs. She felt her trust for him grow, and put more of her weight on him.

“There’s no more Solar System,” AA said as she sat down at the top of the stairs.

“I know. Did anyone else escape?”

Cheng Xin was now on the ground. She sank her feet into the soft grass and sat down on the bottom step. “Probably not.”

“Oh…” The man nodded and climbed up again to help AA. “My name is Guan Yifan. I’ve been waiting for you here.”

“How did you know we would come?” AA asked, allowing Yifan to hold her hand.

“We received your gravitational wave transmission.”

“You’re from Blue Space?”

“Ha! If you’d asked those who had just left that question, they’d think you very strange. Blue Space and Gravity are ancient history from more than four centuries ago. But I really am an ancient. I was a civilian astronomer aboard Gravity. I’ve been hibernating for four centuries, and only awakened five years ago.”

“Where are Blue Space and Gravity now?” Cheng Xin struggled to stand, pulling herself up by the railing of the stairs. Yifan continued down with AA.

“In museums.”

“Where are the museums?” AA asked. She put her arm around Yifan’s shoulder so that Yifan was practically carrying her down.

“On World I and World IV.”

“How many worlds are there?”

“Four. And two more are being opened up for settlement.”

“Where are all these worlds?”

Guan Yifan gently deposited AA on the ground and laughed. “A word of advice: In the future, no matter who you meet—human or otherwise—don’t ask for the location of their worlds. That’s a basic bit of manners in the cosmos—like how it’s impolite to ask a lady’s age…. Nonetheless, let me ask you, how old are you now?”

“We’re as old as we look,” AA said, and sat down on the grass. “She’s seven hundred and I’m five hundred.”

“Dr. Cheng looks about the same as she did four centuries ago.”

“You know her?” AA looked up at Guan Yifan.

“I had seen pictures in transmissions from Earth. Four centuries ago.”

“How many people are on this planet?” Cheng Xin asked.

“Just the three of us.”

“That must mean that your worlds are all better than this one,” AA said.

“You mean the natural environment? Not at all. In some places, the air is barely breathable, even after a century of terraforming. This is one of the best planets we’ve seen for settlement. Although we welcome you here, Dr. Cheng Xin, we do not recognize your claim of title.”

“I’d given that up a long time ago,” Cheng Xin said. “So why haven’t people settled here?”

“It’s too dangerous. Outsiders come here often.”

“Outsiders? Extraterrestrials?” AA asked.

“Yes. This is close to the center of the Orion Arm. Two busy shipping lanes flow through here.”

“Then what are you doing here? Just waiting for us?”

“No. I came with an exploratory expedition. They’ve already left, but I stayed to wait for you.”

About a dozen hours later, the three welcomed night on Planet Blue. There was no moon, but compared to the Earth, the stars here were far brighter. The Milky Way was like a sea of silver fire that cast their shadows on the ground. This place wasn’t much closer to the center of the galaxy than the Solar System. However, the space between here and the Sun was filled with interstellar dust, making the Milky Way appear much dimmer from the Solar System.

In the bright starlight, they could see the grass around them moving. At first, Cheng Xin and AA thought it was an illusion produced by the wind, but then they realized that the grass underfoot was writhing as well, and making a rustling noise. Yifan told them that the blue grass really did move. The roots of the grass were also feet, and as the seasons changed, the grass migrated across the latitudes, mainly at night. As soon as AA heard that, she tossed away the stalks of grass she was playing with in her hands. Yifan explained that the blades of grass really were plants, and relied on photosynthesis, possessing only a basic sense of touch. The other plants in this world were also capable of moving. He pointed to the mountains and they saw the forests moving in the starlight. The trees moved far faster than the grass, and resembled armies marching at night.

Yifan pointed at a spot in the sky where the stars were slightly less dense. “A few days ago we could see the Sun in that direction, much more clearly than you could see this star from the Earth. Of course, what we saw was the Sun of two hundred eighty-seven years ago. The Sun went out on the day the expedition left me here.”

“The Sun is no longer emitting light, but its area is huge. Perhaps you can still see it through telescopes,” AA said.

“No, you won’t be able to see anything.” Yifan shook his head and pointed at that patch of sky again. “Even if you go back there now, you wouldn’t be able to see anything. That part of space is empty. The two-dimensional Sun and planets you saw were actually just the result of the release of energy when three-dimensional material collapsed into two dimensions. What you saw wasn’t two-dimensional material, only the refraction of electromagnetic radiation at the interface between two-dimensional and three-dimensional space. After the energy was released, nothing would be visible. The two-dimensional Solar Space has no contact with three-dimensional space.”

“How can that be?” Cheng Xin asked. “It’s possible to see the three-dimensional world from four-dimensional space.”

“True. I personally got to see three-dimensional space from four-dimensional space, but it’s not possible to see the two-dimensional world from three dimensions. This is because three-dimensional space has thickness, meaning that there is a dimension that could stop and scatter the light from four-dimensional space, making it visible from four dimensions. But two-dimensional space has no thickness, so light from three-dimensional space passes through it without hindrance. The two-dimensional world is completely transparent and cannot be seen.”

“There’s no way at all?” AA asked.

“No. In theory, nothing allows it.”

Cheng Xin and AA were silent for a while. The Solar System had disappeared completely. The only hope they had held out for the mother world was gone. But Guan Yifan did bring them a bit of comfort.

“There’s only one way to detect the presence of the two-dimensional Solar System from three-dimensional space: gravity. The gravity of the Solar System still has an effect, so, in that empty space ought to be detectable as an invisible source of gravity.”

Cheng Xin and AA looked at each other thoughtfully.

“Sounds like dark matter, doesn’t it?” Yifan laughed. Then he changed the subject. “Why don’t we talk about the date you came for?”

“You know Yun Tianming?” AA asked.

“No.”

“What about the Trisolaran Fleet?” Cheng Xin asked.

“We don’t know much. The First and Second Trisolaran Fleets never joined together. More than sixty years ago, there was a large-scale space battle near Taurus. It was brutal, and the resulting wreckage formed a new interstellar dust cloud. We know that one of the sides in the battle was the Second Trisolaran Fleet, but we don’t know who they were fighting against. We also don’t know how the battle ended.”

“What happened to the First Trisolaran Fleet?” Cheng Xin asked. Her eyes flickered in the starlight.

“We haven’t received any information about them…. In any event, you shouldn’t stay here too long. This is not a safe place. Why don’t you come with me to our world? The terraforming there is over, and life is getting better.”

“I agree!” AA said. Then she held Cheng Xin by the arm. “Let’s go with him. Even if you wait here for the rest of your life, you most likely won’t hear anything. Life shouldn’t be a lifetime of waiting.”

Cheng Xin nodded silently. She knew that she was chasing a dream.

They decided to wait one more day on Planet Blue before departing.

Guan Yifan had a small spaceship waiting in synchronous orbit. The ship was tiny and didn’t have a name, only a number. But Yifan called it Hunter, and explained that the name was to honor the memory of a friend who’d lived on Gravity more than four hundred years ago. Hunter was not equipped with an ecological cycling system, and for long voyages passengers had to enter hibernation. Although Hunter was only a few percent of Halo’s volume, it was also a lightspeed ship equipped with a curvature engine. They decided to have Yifan ride on Halo as well and control Hunter as a drone. Cheng Xin and AA didn’t ask about the course they would take, and Yifan even refused to answer questions about the duration of the anticipated voyage. He was extremely cautious when it came to information about the location of human worlds.

For the day, the three took short hikes in the vicinity of Halo. This was a day of many firsts for Cheng Xin, AA, and all the Solar System humans who had disappeared along with the home world: the first trip to an extrasolar planetary system; the first steps on the surface of an exoplanet; the first voyage to a world with life outside the Solar System.

Compared with the Earth, the ecology of Planet Blue was relatively simple. Other than the mobile blue vegetation, there was not much life to be found, except for a few species of fish in the ocean. There were no complex animals on land, only simple insects. The world resembled a simplified Earth. It was possible for Earth plants to survive here, so humans could live here even without advanced technology.

Guan Yifan was filled with admiration for Halo’s design. He said that for Galactic humans, people who had made their home in the Milky Way, there was one quality about Solar System humans that they did not inherit and could not learn: enjoyment of life. He spent much time in the lovely courtyards, and indulged himself with holographic projections of grand sights from ancient Earth. He still looked as thoughtful as ever, but his eyes were moist.

During this time, 艾 AA cast Yifan frequent amorous glances. The relationship between them gradually changed as the day went on. AA thought up all kinds of excuses to be close to Yifan, and listened intently while he spoke, nodding from time to time and smiling. She had never behaved like this in front of any other man. During the centuries Cheng Xin had known her, AA had countless lovers, often dating two or more at the same time, but Cheng Xin knew that AA had never really been in love. However, she was clearly smitten with this cosmologist from the Deterrence Era. Cheng Xin was happy to see this. AA deserved a happy new life in this new world.

As for Cheng Xin, she knew that she was spiritually dead. The only hope that had sustained her was finding Tianming, and now this hope seemed like an impossible dream. Truthfully, she had always known that a date made for four centuries later and 286 light-years away was an impossible dream. She would continue to keep her body alive, but it was just a matter of fulfilling her duty of preventing the death of half of the population to survive the destruction of Earth civilization.

Night fell again. They decided to sleep aboard Halo and leave in the morning.

At midnight, Guan Yifan was awakened by his wrist communicator. It was a call from Hunter in synchronous orbit. Hunter passed on the information gathered by the three small monitoring satellites left by the expedition—two of which orbited around Planet Blue and the last around Planet Gray. The alert had come from the one around Planet Gray.

Thirty-five minutes ago, five unidentified spacecraft had landed on Planet Gray. Twelve minutes later, the spacecraft had lifted off and disappeared without even entering planetary orbit. There was strong interference with the satellite, and the images it transmitted were blurry.

Yifan’s expedition was responsible for seeking out and studying traces left in this planetary system by other civilizations. After receiving the alert from the satellite, he immediately decided to take the shuttle up to Hunter to investigate. Cheng Xin insisted on coming with him. Yifan initially refused, but agreed after AA spoke to him.

“Let her come with you. She wants to know whether this has anything to do with Yun Tianming.”

Before departure, Yifan reminded AA to not communicate with Hunter unless it was an emergency. No one knew what other extraterrestrial monitoring equipment might be lurking in this system, and any communication could expose them to danger.

In this lonely world of only three people, even a brief separation was an occasion for anxiety. AA hugged Cheng Xin and Guan Yifan and wished them a safe journey. Before stepping onto the shuttle, Cheng Xin looked back and saw AA waving at them, lit by the watery starlight. Blue grass surged around her, and the cold wind lifted her short hair and made ripples in the grass.

The shuttle took off. In the view from the monitoring system, Cheng Xin saw the grass lit up by the flame from the thruster, and the blue grass scattering in every direction. As the shuttle rose up, the bright patch on the ground quickly dimmed, and soon, the ground sank back into starlight.

An hour later, the shuttle docked with Hunter in synchronous orbit. Hunter was tetrahedral in shape, like a tiny pyramid. The inside was very cramped and bare, and most of the space was taken up by the hibernation chamber, which had a maximum capacity for four.

Like Halo, Hunter was equipped with both a curvature engine and a fusion engine. When traveling between planets within the same system, only the fusion engine was used, because the curvature engine would have caused the ship to overshoot the target with no time for deceleration. Hunter left orbit and headed for Planet Gray, which appeared as a small spot of light. Out of consideration for Cheng Xin, Guan Yifan initially limited the acceleration to 1.5G, but Cheng Xin told him not to worry about her and just make the trip faster. He increased the acceleration, the blue flame emitted by the nozzles doubled in length, and the hypergravity increased to 3G. At this point, all they could do was to sit in the embrace of the acceleration seats. They were not able to move much, so Yifan switched the ship to surround-holographic display mode, and the ship’s hull disappeared. Suspended in space, they watched Planet Blue recede. Cheng Xin imagined the 3G gravity as coming from Planet Blue so that space separated into up and down, and they were flying up toward the galaxy.

It was possible to speak under 3G without too much trouble, so they began to converse. Cheng Xin asked Yifan why he had hibernated for so long. He told her that he had no duties during the long voyage searching for habitable worlds. After the two ships discovered the habitable World I, much of life consisted of opening up the world for settlement and constructing the basics. The first settlement resembled a small town from agrarian times, and the rough conditions did not permit any kind of scientific research. The new world’s government passed a resolution to let all scientists enter or remain in hibernation, to be awakened only when conditions permitted basic research. He was the only basic scientist aboard Gravity, although Blue Space had seven more. He was the last to be awakened of all the hibernators. Two centuries had passed since the day the two ships arrived at World I.

Cheng Xin was mesmerized by Yifan’s account of the new human worlds. But she noticed that while he discussed Worlds I, II, and IV, nothing was said about III.

“I’ve never been there. No one else has, either. Well, it’s more accurate to say that anyone who goes there cannot return. That world is sealed inside a light tomb.”

“A light tomb?”

“It’s a reduced-lightspeed black hole produced by the trails of lightspeed ships. Something happened on World III that caused them to think that their coordinates had been exposed. They had no choice but to turn their world into such a black hole.”

“We call such a place a black domain.”

“Ah, good name. As a matter of fact, the people of World III initially called it a light curtain, but outsiders referred to it as a light tomb.”

“Like a shroud?”[10]

“That’s right. Different people see things differently. The inhabitants of World III said it was a happy paradise—though I don’t know if they still think that way. After the light tomb was completed, it was impossible for any message from that world to reach the outside. But I think people there are pretty happy. For some people, safety is the sine qua non for happiness.”

Cheng Xin asked Yifan when the new world first produced lightspeed ships, and was told it was a century ago. Judging by this, her interpretation of Tianming’s secret message had allowed Solar System humans to achieve this stage about two centuries ahead of Galactic humans. Even taking into account the time it took to open up the worlds for settlement, Tianming had accelerated progress by at least a century.

“He’s a great man,” Yifan said after hearing Cheng Xin’s account.

But the civilization of the Solar System hadn’t been able to seize this opportunity. Thirty-five precious years had been lost, probably due to her. Her heart no longer felt pain as she thought of this; all she felt was the numbness that indicated a dead heart.

Yifan said, “Lightspeed spaceflight was a tremendous milestone for humankind. It was like another Enlightenment, another Renaissance. Lightspeed flight fundamentally transformed human thinking and changed civilization and culture.”

“I can see that. The moment I entered lightspeed, I felt myself change. I realized that I could, in my lifetime, leap across space-time and reach the edge of the cosmos and the end of the universe. Things that used to seem only philosophical suddenly became concrete and practical.”

“Yes. Things like the fate and goal of the universe used to be only ethereal concerns of philosophers, but now every ordinary person must consider them.”

“Has anyone in the new world thought of going to the end of the universe?”

“Of course. Five ultimate spaceships have already been launched.”

“Ultimate spaceships?”

“Some call them doomsday ships. These lightspeed ships have no destination at all. They turn their curvature engines to maximum and accelerate like crazy, infinitely approaching the speed of light. Their goal is to leap across time using relativity until they reach the heat death of the universe. By their calculations, ten years within their frame of reference would equal fifty billion years in ours. As a matter of fact, you don’t even need to plan for it. If some malfunction occurs after a ship has accelerated to lightspeed, preventing the ship from decelerating, then you’d also reach the end of the universe within your lifetime.”

“I pity Solar System humans,” said Cheng Xin. “Even at the very end, most of them lived lives confined to a tiny portion of space-time, like those old men and women who never left their home villages during the Common Era. The universe remained a mystery to them until the end.”

Yifan lifted his head to gaze at Cheng Xin. Under 3G, this was a very strenuous exercise. But he persisted for some time.

“You don’t need to pity them. Really, let me tell you: don’t. The reality of the universe is not something to envy.”

“Why?”

Yifan lifted a hand and pointed at the stars of the galaxy. Then he let the 3G force pull his arm back to this chest.

“Darkness. Only darkness.”

“You mean the dark forest state?”

Guan Yifan shook his head, a gesture that appeared to be a struggle in hypergravity. “For us, the dark forest state is all-important, but it’s just a detail of the cosmos. If you think of the cosmos as a great battlefield, dark forest strikes are nothing more than snipers shooting at the careless—messengers, mess men, etc. In the grand scheme of the battle, they are nothing. You have not seen what a true interstellar war is like.”

“Have you?”

“We’ve caught a few glimpses. But most things we know are just guesses…. Do you really want to know? The more you possess of this kind of knowledge, the less light remains in your heart.”

“My heart is already completely dark. I want to know.”

And so, more than six centuries after Luo Ji had fallen through ice into that lake, another dark veil hiding the truth about the universe was lifted before the gaze of one of the only survivors of Earth civilization.

Yifan asked, “Why don’t you tell me what the most powerful weapon for a civilization possessing almost infinite technological prowess is? Don’t think of this as a technical question. Think philosophy.”

Cheng Xin pondered for a while and then struggled to shake her head. “I don’t know.”

“Your experiences should give you a hint.”

What had she experienced? She had seen how a cruel attacker could lower the dimensions of space by one and destroy a solar system. What are dimensions?

“The universal laws of physics,” Cheng Xin said.

“That’s right. The universal laws of physics are the most terrifying weapons, and also the most effective defenses. Whether it’s by the Milky Way or the Andromeda Galaxy, at the scale of the local galactic group or the Virgo Supercluster, those warring civilizations possessing godlike technology will not hesitate to use the universal laws of physics as weapons. There are many laws that can be manipulated into weapons, but most commonly, the focus is on spatial dimensions and the speed of light. Typically, lowering spatial dimensions is a technique for attack, and lowering the speed of light is a technique for defense. Thus, the dimensional strike on the Solar System was an advanced attack method. A dimensional strike is a sign of respect. In this universe, respect is not easy to earn. I guess you could consider it an honor for Earth civilization.”

“I thought of something I wanted to ask you. When will the collapse of space in the vicinity of the Solar System into two dimensions cease?”

“It will never cease.”

Cheng Xin shuddered.

“You are scared? Do you think that in this galaxy, in this universe, only the Solar System is collapsing into two dimensions? Haha…”

Guan Yifan’s bitter laughter caused Cheng Xin’s heart to seize up. She said, “What you’re saying makes no sense. At least, it doesn’t make sense to lower spatial dimensions as a weapon. In the long run, that’s the sort of attack that would kill the attacker as well as the target. Eventually, the side that initiated attack would also see their own space fall into the two-dimensional abyss they created.”

Nothing but silence. After a long while, Cheng Xin called out, “Dr. Guan?”

“You’re too… kind-hearted,” Guan Yifan said softly.

“I don’t understand—”

“There’s a way for the attacker to avoid death. Think about it.”

Cheng Xin pondered and then said, “I can’t figure it out.”

“I know you can’t. Because you’re too kind. It’s very simple. The attacker must first transform themselves into life forms that can survive in a low-dimensional universe. For instance, a four-dimensional species can transform itself into three-dimensional creatures, or a three-dimensional species can transform itself into two-dimensional life. After the entire civilization has entered a lower dimension, they can initiate a dimensional strike against the enemy without concern for the consequences.”

Cheng Xin was silent again.

“Are you reminded of anything?” Yifan asked.

Cheng Xin was thinking of more than four hundred years ago, when Blue Space and Gravity had stumbled into the four-dimensional fragment. Yifan had been a member of the small expedition that conversed with the Ring.

The fish that dried out the sea went onto land before they did this. They moved from one dark forest to another dark forest.

“Is it worth it to pay such a price for victory in war?” Cheng Xin asked. She could not imagine how it was possible to live in a world of one fewer dimension. In two-dimensional space, the visible world consisted of a few line segments of different lengths. Could anyone who was born in three-dimensional space willingly live in a thin sheet of paper with no thickness? Living in three dimensions must be equally confining and unimaginable for those born to a four-dimensional world.

“It’s better than death,” said Yifan.

While Cheng Xin was still recovering from the shock, Yifan continued, “The speed of light is also frequently used as a weapon. I’m not talking about building light tombs—or, as you call them, black domains. Those are just defensive mechanisms employed by weak worms like us. The gods do not stoop so low. In war, it’s possible to make reduced-lightspeed black holes to seal the enemy inside. But more commonly, the technique is used to construct the equivalents of pits and city walls. Some reduced-lightspeed belts are large enough to traverse an entire arm of a galaxy. In places where the stars are dense, many reduced-lightspeed black holes can be connected together into chains that stretch for tens of millions of light-years. That’s a Great Wall at the scale of the universe. Even the most powerful fleets, once trapped, would not be able to escape. Those barriers are very difficult to cross.”

“What is the ultimate result of all this manipulation of space-time?”

“Dimensional strikes will eventually cause more and more of the universe to become two-dimensional, until one day the entire universe is two-dimensional. Similarly, the construction of fortifications will eventually cause all the reduced-lightspeed areas to connect, until the different lowered lightspeeds all average out: This new average will be the new c for the universe.

“At that time, any scientist from a baby civilization—like us—would think that the speed of light through vacuum is barely a dozen kilometers per second, and this is an ironclad universal constant, just like we now think the same of three hundred thousand kilometers per second.

“Of course, I’ve only brought up two examples. Other universal laws of physics have been used as weapons as well, though we don’t know all of them. It’s very possible that every law of physics has been weaponized. It’s possible that in some parts of the universe, even… Forget it, I don’t even believe that.”

“What were you going to say?”

“The foundation of mathematics.”

Cheng Xin tried to imagine it, but it was simply impossible. “That’s… madness.” Then she asked, “Will the universe turn into a war ruin? Or, maybe it’s more accurate to ask: Will the laws of physics turn into war ruins?”

“Maybe they already are…. The physicists and cosmologists of the new world are focused on trying to recover the original appearance of the universe before the wars more than ten billion years ago. They’ve already constructed a fairly clear theoretical model describing the pre-war universe. That was a really lovely time, when the universe itself was a Garden of Eden. Of course, the beauty could only be described mathematically. We can’t picture it: Our brains don’t have enough dimensions.”

Cheng Xin thought back to the conversation with the Ring again.

“You are saying that the universe of the Edenic Age was four-dimensional, and that the speed of light was much higher?”

“No, not at all. The universe of the Edenic Age was ten-dimensional. The speed of light back then wasn’t only much higher—rather, it was close to infinity. Light back then was capable of action at a distance, and could go from one end of the cosmos to the other within a Planck time…. If you had been to four-dimensional space, you would have some vague hint of how beautiful that ten-dimensional Garden must have been.”

“You’re saying—”

“I’m not saying anything.” Yifan seemed to have awakened from a dream. “We’ve only seen small hints; everything else is just guessing. You should treat it as a guess, just a dark myth we’ve made up.”

But Cheng Xin continued to follow the course of the discussion taken so far. “—that during the wars after the Edenic Age, one dimension after another was imprisoned from the macroscopic into the microscopic, and the speed of light was reduced again and again…. ”

“As I said, I’m not saying anything, just guessing.” Yifan’s voice grew softer. “But no one knows if the truth is even darker than our guesses…. We are certain of only one thing: The universe is dying.”

The ship stopped accelerating, and weightlessness returned. Before Cheng Xin’s eyes, space and the stars appeared more and more hallucinatory, more and more like a nightmare. Only the 3G hypergravity had brought some sense of solidity. She had welcomed the powerful embrace of those arms, an embrace that had provided some protection against the terror and frigidity of the dark myths of the universe. But now the hypergravity was gone, and only nightmare remained. The Milky Way appeared as a patch of ice hiding bloody remains, and DX3906 nearby appeared as a cremator burning over an abyss.

“Can you turn off the holographic display?” Cheng Xin asked.

Yifan turned it off, and Cheng Xin returned from the vastness of space to the cramped eggshell interior of the cabin. Here, she recovered a trace of the security she craved.

“I shouldn’t have told you all that,” Yifan said. His sorrow was sincere.

“I would have found out sooner or later,” Cheng Xin said.

“Let me repeat: They are just guesses. There’s no real scientific proof. Don’t think about it too much. Focus on what’s before your eyes; focus on the life you must live.” Yifan put a hand over hers. “Even if what I told you is true, those events are measured at the scale of hundreds of millions of years. Come with me to our world, which is now also your world. Live out your life and stop skipping across the surface of time. As long as you live your life within a hundred thousand years and a thousand light-years, none of those things need concern you. That ought to be enough for anyone.”

“Yes, it is enough, thank you.” Cheng Xin held Yifan’s hand.

Cheng Xin and Guan Yifan spent the rest of the journey in the forced slumber of the sleep-aid machine. The trip lasted four days. By the time they awakened in the hypergravity of deceleration, Planet Gray took up most of their field of view.

Planet Gray was a small planet. It visually resembled the moon, a barren rock, but instead of craters, much of Planet Gray’s surface was taken up by desolate plains. Hunter entered orbit around Planet Gray. Due to the lack of an atmosphere, the orbit was very low. The ship approached the coordinates provided by the monitoring satellite, where the five unidentified spacecraft had landed and then taken off. Yifan had planned to land the shuttle there and investigate the traces left by the spacecraft, but he and Cheng Xin had not anticipated that the mysterious visitors would leave behind such large signs that they were visible from space.

“What is that?” Cheng Xin cried out.

“Death lines.” Yifan recognized them right away. “Don’t get too close,” he said to the AI.

He was referring to five black lines. One end of each line was connected to the surface of the planet, and the other end extended into space, like five black hairs growing out of Planet Gray. Each line stretched higher than Hunter’s orbit.

“What are they?”

“Trails left by curvature propulsion. Those lines are the result of extreme curvature manipulation. The speed of light within the trails is zero.”

On the next orbit, Guan Yifan and Cheng Xin entered the shuttle and descended toward the surface. Due to the low orbit and the lack of an atmosphere, the descent was smooth and fast. The shuttle landed about three kilometers from the death lines.

They leapt across the surface under 0.2G. A thin layer of dust covered the surface of Planet Gray, along with gravel of various sizes. Due to the lack of atmospheric scattering of sunlight, shadows and lit areas were sharply delineated. When they were about a hundred meters from the death lines, Yifan waved Cheng Xin to a stop. Each death line was about twenty or thirty meters in diameter, and from here, they resembled death columns.

“These are probably the darkest things in the universe,” Cheng Xin said. The death lines showed no details except an exceptional blackness showing the boundaries of the zero-lightspeed region, with no real surface. Looking up, the lines showed up clearly even against the dark backdrop of space.

“These are the deadest things in the universe as well,” said Guan Yifan. “Zero-lightspeed means absolute, one hundred percent death. Inside it, every fundamental particle, every quark is dead. There is no vibration. Even without a source of gravity inside, each death line is a black hole. A zero-gravity black hole. Anything that falls in cannot reemerge.”

Yifan picked up a rock and tossed it toward one of the death lines. The rock disappeared inside the absolute darkness.

“Can your lightspeed ships produce death lines?” Cheng Xin asked.

“Far from it.”

“So you’ve seen these before, then?”

“Yes, but only rarely.”

Cheng Xin gazed up at the giant black columns reaching into space. They lifted up the domed sky and seemed to turn the universe into a Palace of Death. Is this the ultimate end for everything?

In the sky, Cheng Xin could see the end of the columns. She pointed in that direction. “So the ships entered lightspeed at the end?”

“That’s right. These are only about a hundred kilometers high. We’ve seen columns even shorter than these, presumably left by ships that entered lightspeed almost instantaneously.”

“Are these the most advanced lightspeed ships?”

“Maybe. But this is a rarely seen technique. Death lines are usually the products of Zero-Homers.”

“Zero-Homers?”

“They’re also called Resetters. Maybe they’re a group of intelligent individuals, or a civilization, or a group of civilizations. We don’t know exactly who they are, but we’ve confirmed their existence. The Zero-Homers want to reset the universe and return it to the Garden of Eden.”

“How?”

“By moving the hour hand of the clock past twelve. Take spatial dimensions as an example. It’s practically impossible to drag a universe in lower dimensions back into higher dimensions, so maybe it’s better to work forward in the other direction. If the universe can be lowered into zero dimensions and then beyond, the clock might be reset and everything returned to the beginning. The universe might possess ten macroscopic dimensions again.”

“Zero dimensions! Have you seen such a thing done?”

“No. We’ve only witnessed two-dimensionalization. We’ve never even seen one-dimensionalization. But somewhere, some Zero-Homers must be trying. No one knows if they’ve ever succeeded. Comparatively, it’s easier to lower the speed of light to zero, so we’ve seen more evidence of such attempts to lower the speed of light past zero and return it to infinity.”

“Is that even theoretically possible?”

“We don’t know. Maybe the Zero-Homers have theories that say yes, but I don’t think so. Zero-lightspeed is an impassable wall. Zero-lightspeed is absolute death for all existence, the cessation of all motion. Under such conditions, the subjective cannot influence the objective in any way, so how can the ‘hour hand’ be shifted past it? I think the Zero-Homers are practicing a kind of religion, a kind of performance art.”

Cheng Xin stared at the death lines, her terror mixed with awe. “If these are trails, why don’t they spread?”

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. Not 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.

“They’re moving too fast.”

“Try to follow the motion with your eyes.”

Cheng Xin tried to match her moving gaze with the patterns flowing across the belt. For a moment, she could see the blue, white, and yellow patches, but they blurred almost immediately. “I can’t,” she said.

“That’s all right. They’re moving too fast. The pattern could be repeating several hundred times per second.” Yifan sighed. Cheng Xin noticed his sorrow, despite his effort to hide it. And she knew why.

She understood that every time the pattern repeated on the broad belt, it meant that the shuttle had completed another orbit around Planet Blue at lightspeed. Even at reduced lightspeed, the demonic rules of the theory of special relativity still held. In the planet’s frame of reference, time was passing tens of millions of times faster than in here, like blood seeping out of her heart.

A moment here; eons there.

Cheng Xin turned away from the porthole and strapped herself into the seat as well. Light flickered through the porthole on the other side. Outside, the sun of this world was alternately a bright line that connected the two ends of the universe, and a ball of light. It was dancing the mad dance of death.

“Cheng Xin.” Yifan called for her softly. “It’s possible that when we wake up, we’ll find the screen telling us that an error has occurred.”

Cheng Xin turned and smiled at him through the visor. “I’m not afraid.”

“I know you’re not afraid. I just want to tell you something in case we don’t… I know about your experience as the Swordholder. I want to let you know that you didn’t do anything wrong. Humanity chose you, which meant they chose to treat life and everything else with love, even if they had to pay a great price. You fulfilled the wish of the world, carried out their values, and executed their choice. You really didn’t do anything wrong.”

“Thank you,” Cheng Xin said.

“I don’t know what happened to you after that, but you still didn’t do anything wrong. Love isn’t wrong. A single individual cannot destroy a world. If that world was doomed, then it was the result of the efforts of everyone, including those living and those who had already died.”

“Thank you,” Cheng Xin said. Her eyes felt hot and wet.

“As for what will happen next, I’m not afraid either. When I was on Gravity, all those stars in the emptiness made me afraid and tired, and I wanted to stop thinking about the universe. But it was like a drug, and I couldn’t stop. Well, now I can stop.”

“That’s good. You know something? The only thing I’m scared of is that you’ll be afraid.”

“I’m the same.”

They held hands, and as the sun continued its mad dance, they gradually lost consciousness and stopped breathing.

About Seventeen Billion Years After the Beginning of Time Our Star

It took a long time to wake up.

Cheng Xin recovered her awareness gradually. After her memory and sight came back, she knew right away that the neural computer had booted successfully. A soft light illuminated the inside of the cabin, and she could hear the machines humming reassuringly. The air was warm. The shuttle had been revived.

But Cheng Xin soon realized that the lights inside the cabin came from different fixtures than before—perhaps these were backups designed specifically for reduced-lightspeed use. There were no information windows in the air. It was possible that the reduced lightspeed meant such holographic displays were no longer operable. The interface of the neural computer was limited to that flat screen, which now resembled a color bitmap display from the Common Era.

Guan Yifan was drifting in front of the display, tapping on it with the fingers of a gloveless hand. He turned and smiled at Cheng Xin, made a hand gesture indicating that it was okay to drink, and then handed her a bottle of water.

“It’s been sixteen days,” he said.

The bottle felt warm. Cheng Xin saw that she wasn’t wearing gloves, either. She realized that although she was still wearing the primitive space suit, her helmet had been removed. The temperature and pressure inside the cabin were comfortable.

Since she had recovered enough to move her hands, Cheng Xin unstrapped herself and drifted next to Yifan to look at the screen with him, their space suits squeezed tightly side by side. Several windows were up on the screen, each showing rapidly scrolling numbers: diagnostics on the shuttle’s various systems. Yifan told Cheng Xin that he had established contact with Hunter, whose neural computer had also apparently booted successfully.

Cheng Xin looked up and saw that the two portholes were still open. She drifted over. Guan Yifan dimmed the cabin lights so she could see through them without glare. They anticipated each other’s needs now as though they were a single person.

At first, the universe didn’t appear to have changed from what she had seen before: The ship continued to orbit around Planet Blue at reduced lightspeed; the two star clusters, blue and red, continued to change their shapes erratically at the two ends of the universe; the sun continued to dance madly between being a line and a circle; and color patches continued to whip across Planet Blue’s surface. When Cheng Xin tried to match her gaze to the rapidly flowing surface of Planet Blue, she finally noticed something different: the blue and white patches had been replaced by purple ones.

Yifan pointed to the screen. “The propulsion system self-diagnosis is complete. Everything’s basically working. We can decelerate out of lightspeed anytime.”

“The fusion drive still works?” Cheng Xin asked. Before they entered hibernation, this question had weighed on her mind. She had not asked because she knew that she was likely to receive a disappointing answer, and she didn’t want to give Yifan more to worry about.

“Of course not. With such a reduced lightspeed, nuclear fusion puts out too little power. We have to use the backup antimatter drive.”

“Antimatter? But wouldn’t the containment field be affected by the reduced lightspeed?”

“No problems there. The antimatter engine was designed specifically for reduced-lightspeed conditions. When we’re on long expeditions like this, we equip all our spacecraft with reduced-lightspeed propulsion systems…. Our world puts a lot of effort into developing such technologies. The goal isn’t to solve the problem of accidentally entering trails left by curvature propulsion; rather, it’s because we have to plan for the possibility of having to conceal ourselves inside a light tomb, or a black domain.”

Half an hour later, the shuttle and Hunter both activated their antimatter engines and began decelerating. Cheng Xin and Guan Yifan were pressed against their seats by the hypergravity, and the porthole screens rose to block out the outside. Violent jolts seized the shuttle, but gradually subsided. The deceleration process took less than twenty minutes. Then the engines shut off, and they were again weightless.

“We’re out of lightspeed,” Guan Yifan said. He pressed a button, and the screens over the two portholes retracted.

Through the portholes, Cheng Xin saw that the blue and red star clusters were gone, and the sun was now a normal sun. But the sight of Planet Blue in the porthole on the other side surprised her: Planet Blue was now “Planet Purple.” Other than the ocean, which was still a light yellow, the rest of the planet was covered by purple—even the snow was gone. She was, however, most shocked by the appearance of space itself.

“What are those lines?” Cheng Xin cried out.

“I think they are… stars.” Yifan was as amazed as she.

All the stars in space had turned into thin lines of light. Cheng Xin was actually familiar with such a sight: She had seen plenty of long-exposure photographs taken of the starry sky from Earth. Due to the Earth’s rotation, the stars in the pictures all became concentric arcs of approximately the same length. But now, the stars she saw were segments of different lengths and aligned every which way. The longest few lines, in fact, took up almost a third of the sky. These lines crossed each other at different angles and made space appear far more confusing and chaotic than before.

“I think they’re stars,” repeated Yifan. “A star’s light must pass through two interfaces before getting to us: First, it must go through the interface between regular lightspeed and reduced lightspeed, and then through the event horizon of the black hole. That’s why the stars look so strange to us now.”

“We’re inside the black domain?”

“That’s right. We’re inside the light tomb.”

The DX3906 solar system was now a reduced-lightspeed black hole completely sealed off from the rest of the universe. The starry sky woven by the multitude of crisscrossing silver threads was a dream that could be seen but would never be achieved.

“Let’s go down to the surface,” Yifan said after a long silence.

The shuttle decelerated further and lowered its orbit. With a series of powerful jolts, it entered the atmosphere of the planet and descended toward the surface of this world in which the two of them were doomed to spend the rest of their lives.

The purple continents took up most of the view from the monitoring system. They were able to confirm that the purple was due to the color of the vegetation. The change in the sun’s radiation had probably caused the plants on Planet Blue to change from blue to purple as they evolved to adapt to the new light.

As a matter of fact, the very existence of the sun puzzled Cheng Xin and Guan Yifan. Since E = mc2, reduced-lightspeed nuclear fusion could produce only small amounts of energy. Perhaps the interior of the sun maintained normal lightspeed?

The shuttle’s landing coordinates were set to the same spot from which it had taken off and left Halo. As they approached the surface, they saw a dense purple forest at the landing spot. Just when the shuttle was about to lift off again in search of a more open spot, the trees dashed away to escape the flames from the shuttle’s thrusters. The shuttle then gently set itself down in the open space vacated by the fleeing trees.

The screen showed that the outside air was breathable. Compared to the last time they had been here, the oxygen content in the atmosphere was substantially higher. Moreover, the atmosphere was denser, and the atmospheric pressure was one and a half times higher than at the last landing.

Cheng Xin and Guan Yifan exited the shuttle and once again stepped onto the surface of Planet Blue. Warm, moist air welcomed them, and a layer of soft, bouncy humus covered the ground. The soil around them was filled with numerous holes left by the roots of the trees that had gotten out of the way. Those trees now huddled around the clearing, their broad leaves rustling in the breeze, like a crowd of whispering giants gathered around them. The clearing was completely covered by their shade. Such dense vegetation made Planet Blue a completely different world than the one they had seen before.

Cheng Xin didn’t like purple. She’d always thought of it as a sick, depressing color that reminded her of the lips of invalids whose hearts did not supply them with sufficient oxygen. Yet now she was surrounded by purple everywhere she looked, and she would have to spend the rest of her life in this purple world.

There was no sign of Halo, no sign of Yun Tianming’s ship, no sign of any human presence.

Guan Yifan and Cheng Xin surveyed the landscape around them and realized that the geographical features were completely different from the last time. They clearly remembered that there had been rolling mountains nearby, but now the forest was growing over a plain. They went back to the shuttle to confirm that the coordinates were really correct—they were. Then they looked even more carefully all around them, but still found no trace of any prior human visit. The site resembled virgin land—it was as though their last visit had occurred on another planet in another space-time that had nothing to do with here.

Yifan returned to the shuttle and established a link with Hunter, which was still in near-ground orbit. Hunter’s neural computer was very powerful, and its AI was capable of direct natural language communications. Under reduced-lightspeed conditions, the conversation from ground to space suffered a transmission delay of over ten seconds. After dropping out of lightspeed along with the shuttle, Hunter had been scanning the surface of the planet from low orbit. By now, it had completed a survey of most of the land on Planet Blue, and it had discovered no trace of humans or signs of any other intelligent life.

Next, Cheng Xin and Guan Yifan had to turn to a task that terrified them but was absolutely necessary: determining how much time had elapsed in this frame of reference. There was a special technique for radiometric dating under reduced-lightspeed conditions: Some elements that did not decay under normal lightspeed decayed at different rates under reduced lightspeed, which could be used to precisely tell the passage of time. Given its scientific mission, the shuttle was equipped with a device for measuring atomic decay, but the instrument required a computer for processing. Yifan had to go to some trouble to connect the instrument to the neural computer on the shuttle. They directed the instrument to test the ten rock samples taken from different parts of the planet one after another so that the results could be compared. The assay required half an hour.

While waiting for the test results, Cheng Xin and Guan Yifan left the shuttle and waited in the clearing. Sunlight illuminated the clearing through gaps in the canopy. Many strange, small creatures flitted through: Some were insects with spinning rotors on top like helicopters; others were like tiny, transparent balloons that drifted through the air, giving off a rainbow sheen as they passed through shafts of sunlight; but none of them had wings.

“Maybe several tens of thousands of years have passed,” Cheng Xin muttered.

“Or even longer,” said Guan Yifan, looking deep into the woods. “In our current state, tens of thousands of years aren’t very different from hundreds of thousands of years.”

Then they said no more, but sat on the stairs outside the shuttle, leaning against each other and taking comfort in their heartbeats.

Half an hour later, they climbed back into the shuttle to face facts. The screen on the control panel showed the test results from the ten samples. Many elements had been tested and the charts were complicated. All the samples yielded similar results. Underneath, the average of the results was listed simply:

Average atomic decay dating results (error range: 0.4%): Stellar time periods lapsed: 6,177,906; Earth years lapsed: 18,903,729.

Cheng Xin counted the digits in the last number three times, turned around, and quietly exited the shuttle. She descended the stairs and returned to this purple world. Tall purple trees surrounded her, a beam of sunlight cast a tiny circle of brightness next to her feet, moist wind lifted her hair, living balloons drifted overhead, and almost nineteen million years followed her.

Yifan came to her. They locked gazes, and their souls embraced.

“Cheng Xin, we missed them.”

More than eighteen million years after the DX3906 system turned into a reduced-lightspeed black hole, seventeen billion years after the birth of the universe, a man and a woman held each other tightly.

Cheng Xin sobbed her heart out over Yifan’s shoulder. In her memories, she had cried like this only once before, when Tianming’s brain had been taken out of his body. That was… 18,903,729 years plus six centuries ago, and those six centuries were but a rounding error at such geologic timescales. This time, she cried not only for Tianming. She cried out of a sense of surrender. She finally understood how she was but a mote of dust in a grand wind, a small leaf drifting over a broad river. She surrendered completely and allowed the wind to pass through her, allowed the sunlight to pierce her soul.

Letting the past go, she allowed her growing esteem for Guan Yifan to take over her heart.

They sat on the yielding humus and continued to hold each other, letting time flow by. The dappled sunlight gently shifted around them as the planet continued to rotate. Sometimes Cheng Xin asked herself, Has another ten million years passed by? A small, rational part of her mind strangely whispered to her that such a thing was possible: There really were worlds where one could step through a thousand years at will. Consider the death lines: If they ruptured and expanded just a bit, the speed of light within would rise from zero to an extremely small number, like the rate at which continents drifted over the ocean: a centimeter for every ten thousand years. In such a world, if you got up from your lover and walked a few steps away, you would be separated from him by ten million years.

They’d missed each other.

After they knew not how long, Yifan asked her softly, “What should we do?”

“I want to look more. There must be some sign.”

“There really won’t be anything. Eighteen million years will erase everything: Time is the cruelest force of all.”

“Carving words into stone.”

Yifan looked at Cheng Xin, confused.

“艾 AA would know to carve words into stone,” Cheng Xin muttered.

“I don’t understand….”

Cheng Xin didn’t explain; instead, she grabbed Yifan by the shoulders: “Can you have Hunter do a deep scan of this area and see if there’s anything under the surface?”

“What are you looking for?”

“Words. I want to see if there are words.”

Yifan shook his head. “I understand your desire, but—”

“To better last through the eons, the words ought to be large.”

Yifan nodded, but obviously only to appease her. They returned to the shuttle. Although this was a walk of only a few steps, they leaned against each other as if afraid time would divide them if they were physically separated. Yifan contacted Hunter and directed it to do a deep scan of the area within a circle centered on this coordinate with a radius of three kilometers. The depth of the scan was set to be between five and ten meters, focusing on human writing or other significant markings.

Hunter passed overhead fifteen minutes later and sent back the results about ten minutes after that: nothing.

Guan Yifan ordered the ship to do another scan at a depth range between ten and twenty meters. This took another hour, the bulk of which was spent waiting for the ship to pass overhead. Still nothing. At that depth there was no more soil, only bedrock.

Guan Yifan adjusted the scanning range to between twenty and thirty meters. “This is the last time,” he said to Cheng Xin. “The sensors can’t go deeper than that.”

They waited for the ship to orbit Planet Blue another time. The sun was setting and the sky was full of lovely, fiery clouds, while the purple woods were limned with a golden glow.

This time, the shuttle’s screen showed the images transmitted back by the ship. After processing by enhancement software, they could see a few fragments of white words embedded in the dark rock: “e,” “liv,” “a,” “life,” “you,” “little,” “side,” “Go.” The white color was to indicate that the words were carved into the bedrock; each character was about a meter square, and they were arranged into four rows. The words were twenty-three to twenty-eight meters below them, carved into a forty-degree incline.

Hunter’s AI invoked the geological expert system to interpret the results. They found out that the giant characters had initially been carved into the surface of a large sedimentary rock formation on the side of a mountain. The original surface was about 130 square meters. Over the eons, the mountain on which the rock had been located sank, and that was how the carved rock ended up below them. More than four lines of text had been carved into it, but the lower portion of the rock had been broken up during the geological transformations and all the text there lost. The surviving text was incomplete as well—the last three lines all had missing characters at the end.

Cheng Xin and Guan Yifan embraced again. They cried tears of joy at the news concerning 艾 AA and Yun Tianming, and shared the happiness that they had enjoyed more than one hundred eighty thousand centuries ago. Their despairing hearts grew peaceful.

“I wonder what their life here was like?” Cheng Xin asked, tears glistening in her eyes.

“Anything was possible,” said Yifan.

“Did they have children?”

“Anything was possible. They could have even founded a civilization here.”

Cheng Xin knew that was indeed possible. But even if that civilization had lasted ten million years, the eight million-plus years that had come after would have erased all traces of it.

Time really was the cruelest force of all.

Something strange interrupted their meditation: a rectangle limned by faint lines of light, about a man’s height, hovered over the clearing like the dashed selection lines marked out by dragging a mouse. It moved through the air, but did not go far before returning to its original position. It was possible that it had been there all along, but the outline was so faint and thin that it was invisible during daytime. Whether it was made by a force field or actual substance, there was no doubt it was the creation of intelligence. The lines making up the rectangle seemed to evoke the line-shaped stars in the sky.

“Do you think this is the… gift they left for us?” Cheng Xin asked.

“Seems hard to believe. How could it have survived more than eighteen million years?”

But he was wrong. The object had indeed survived eighteen million years. And, if necessary, it could survive until the end of the universe, because it existed outside of time.

The door remembered that, initially, it had been placed next to the rock carved with text, and it had a real metal frame. But the metal had eroded away after only five hundred thousand years, though the object had always remained brand new. It had no fear of time because its own time had not yet started. It had been thirty meters underground, next to the carved rock, but it had detected the presence of humans and risen to the surface. During the process, it did not interact with the crust, moving like a ghost. It now confirmed that these two were indeed the ones it had been expecting.

“I think it looks like a door,” Cheng Xin said.

Yifan picked up a small branch and tossed it at the rectangle. The branch passed through it and landed on the other side. They saw a luminescent flock of little balloon creatures drift over. A few passed through the rectangle and one even crossed the glowing outline.

Yifan reached out and touched the frame. The light and his finger passed through each other, and he felt nothing. Without even thinking, he extended his hand into the space outlined by the rectangle. Cheng Xin screamed. Yifan pulled his hand back, and everything looked unharmed.

“Your hand…. It didn’t go through.” Cheng Xin pointed to the other side of the rectangle.

Yifan tried again. His hand and forearm disappeared as they entered the plane of the rectangle and did not go through. From the other side, Cheng Xin saw the cross section of his forearm, like the surface of a window. All his bones, muscles, and blood vessels were clearly visible. He pulled his hand back and tried again with a branch. It went through the frame without problems. Right after, two insects with spinning rotors passed through the rectangle as well.

“It really is a door—a smart door that recognizes what’s going through it,” Yifan said.

“It allowed you in.”

“Probably you, as well.”

Cheng Xin gingerly tried, and her arm also disappeared in the “door.” Yifan observed the cross section of her arm from the other side, and had a moment of déjà vu.

“Wait for me here,” Yifan said. “I’ll go investigate.”

“We should go together,” Cheng Xin said resolutely.

“No, you wait here.”

Cheng Xin grabbed him by both shoulders and turned him to face her. She looked into his eyes. “Do you really want us to also be separated by eighteen million years?”

Yifan stared back into her eyes for a long moment, and finally nodded. “Perhaps we should bring some things with us.”

Ten minutes later, they passed through the door, hand in hand.

Outside of Time Our Universe

Primordial darkness.

Cheng Xin and Guan Yifan were once again immersed in a time vacuum. The sensation was similar to when they had entered reduced lightspeed back in the shuttle. Time did not flow here, or maybe it was more accurate to say that time did not exist. They lost all sense of time, and experienced again that feeling of stepping across time, but existing outside of it.

Darkness disappeared; time began.

There is no appropriate expression in human language to express the moment at the start of time. To say that time began after they entered the door would be wrong because “after” required time. There was no time here, and thus no before or after. The time “after” they entered could have been shorter than a billion-billionth of a second, or longer than a billion billion years.

The sun brightened. It did so very gradually: At first it was just a disk, and then the light began to unveil the world. It was like a song that began as barely audible notes, then grew and grew into a mighty chorus. A circle of blue appeared around the sun, expanded, and turned into a blue sky. Under the blue sky, a pastoral scene slowly took shape. There was an unplanted field with black soil; next to it was an exquisite white house. There were also a few trees that brought a hint of the exotic with their broad, strangely shaped leaves. As the sun continued to brighten, the peaceful scene appeared like a welcoming embrace.

“There are people here!” Guan Yifan pointed at the distance.

They could see the backs of two figures standing on the horizon: a man and a woman. The man had just put down his uplifted arm.

“That’s us,” said Cheng Xin.

In front of those two figures, they could see a distant white house and trees, exact duplicates of the ones nearby. They couldn’t see what was at the feet of those figures due to the distance, but they could guess that it was another black field. At the end of the world was a duplicate of it, or maybe a projection.

Duplicates or projections of the world existed all around them. They looked to their sides and saw the same scene repeated. The two of them also existed in those worlds, but all they could see were the backs of those figures, who turned their heads away as Cheng Xin and Yifan turned to look at them. They looked behind them and saw the same thing—except now they were looking at the world from the other direction.

The entrance to the world had disappeared.

They followed a path of stepping-stones, and around them, the copies of themselves in the copies of their world walked along with them. The path was broken by a brook with no bridge over it, but the brook was so small that they could step over it. Only now did they realize that gravity was a standard 1G. They passed the copse of trees and came to the white house. The door was shut and the windows covered by blue curtains. Everything looked brand new, dustless—as a matter of fact, they were brand new, also, as time had just begun to flow.

In front of the house was a pile of simple, primitive farming tools: shovels, rakes, baskets, water pails, and so on. Although some of them were shaped a bit oddly, it was easy to tell their function by appearance. What most drew their attention, though, was a row of metal columns erected next to the farming tools. They were about the height of a person, and the smooth surfaces glinted in the sunlight. Each column had four metal attachments that seemed to be folded limbs. The columns were probably robots in a resting state.

They decided to familiarize themselves with the environment before entering the house, and so they continued to walk past it. After a bit less than a kilometer, they reached the edge of the small world and faced the duplicate world before them. At first, they thought it was just a reflected image of their own world, though it was not mirrored. But after they were halfway there they decided that it couldn’t be a reflection: Everything looked so real. They took a step forward and entered the duplicate world without any resistance. Looking around, Cheng Xin was struck with a hint of terror.

Everything looked the same as when they had first entered the world. They were in the same pastoral scene, with duplicates of the scene before them and to the sides, and in those copies, copies of them also existed. They turned around to look back, and they saw copies of themselves at the far end of the world they had just left, looking behind them.

Yifan let out a long sigh. “I don’t think we need to go any farther. We’ll never reach the end.” He pointed up and then down. “I bet that without these barriers, we’d see the same scene above and below us as well.”

“Do you know what this is?”

“Are you familiar with the work of Charles Misner?”

“Who was he?”

“A physicist of the Common Era. He was the one who first came up with this concept. The world we’re in is actually very simple. It’s a regular cube about a kilometer on each side. You can imagine it as a room with four walls and a ceiling as well as a floor. But the room is constructed such that the ceiling is also the floor, and each wall is the same as the opposite wall. In reality, it has only two walls. If you walk through one of the walls, you’ll immediately reappear at the opposite wall, and the same is true of the floor and ceiling. Thus, this is a completely enclosed world in which the end is also the beginning. The images we see all around us are the result of light returning to the starting point after crossing the world. We’re still in the same world we started from, because this is the only world that exists. Every copy we see around us is just an image of this world.”

“So this is…”

“Yes!” Yifan swept his arm around to indicate everything. “Yun Tianming once gave you a star, and now he’s given you a universe. Cheng Xin, this is an entire universe. It might be small, but it’s a complete universe.”

Cheng Xin looked around, at a loss for words. Yifan sat down quietly on a ridge in the field and picked up a fistful of black earth, letting the soil slip from between his fingers. He sounded depressed. “He’s quite a man to be able to give the woman he loved a star and a universe. But I can’t give you anything.”

Cheng Xin sat down as well and leaned on his shoulder. She laughed as she said, “You’re the only man in this universe. I don’t think you need to give me anything.”

The feeling of being alone in the universe was soon shattered by the sound of a door opening. A figure in white came out of the house and walked toward them. The world was so small that it was possible to clearly see anyone at any distance. They saw that the newcomer was a woman dressed in a kimono. The kimono, decorated with tiny red flowers, was like a walking flower bush that brought the feeling of spring to the universe.

“Sophon!” Cheng Xin cried out.

“I know her,” Yifan said. “She’s the robot controlled by sophons.”

They walked over to meet the woman under one of the trees. Cheng Xin saw that it really was Sophon: That unparalleled beauty remained unchanged.

Sophon bowed deeply to Cheng Xin and Guan Yifan. When she straightened, she smiled at Cheng Xin. “I said that the universe is grand, but life is grander. Fate has indeed directed us to meet again.”

“I couldn’t have imagined,” Cheng Xin said. “I’m really glad to see you. Really.” Sophon brought her to the past—more than eighteen million years ago. But that wasn’t really accurate, because they were now in another time stream altogether.

Sophon bowed again. “Welcome to Universe 647. I am its manager.”

“The manager of the universe?” Yifan looked at Sophon, astounded. “What a grand title! For a cosmologist like me, that sounds like—”

“Oh no!” Sophon laughed and waved his remark away. “You are the true masters of Universe 647 and have full authority over everything here. I’m just here to serve you.”

Sophon made a gesture indicating that they should follow her. They followed her to a refined parlor inside the house. The parlor was decorated in an Eastern style with a few calming brush paintings and calligraphy scrolls hung on the walls. Cheng Xin looked for artifacts taken from Pluto by Halo but didn’t find any. After they sat down at an antique wooden desk, Sophon poured tea for them—without going through the complicated steps of the Way of Tea. The tea leaves seemed to be Longjing, and they stood up at the bottom of the cups like a tiny green forest, giving off a fresh fragrance.

To Cheng Xin and Guan Yifan, everything seemed to be a dream.

Sophon spoke. “This universe is a gift. Mr. Yun Tianming gave it to the both of you.”

“I think it’s meant for Cheng Xin,” said Yifan.

“No. You’re also one of the intended recipients. Your authorization was added to the recognition system later; otherwise you wouldn’t have been allowed in. Mr. Yun hoped that you could hide in this tiny universe and avoid the collapse of the great universe—or the big crunch—and, after the next big bang, enter the new universe and see its Edenic Age. Right now, we exist in an independent timeline. Time is passing rapidly in the great universe, and you will certainly be able to see its end within your lifetimes. More specifically, I estimate that the great universe will collapse into a singularity after about ten years here.”

“If a new big bang occurs, how will we know?” asked Yifan.

“We’ll know. We can sense the conditions in the great universe through the supermembrane.”

Sophon’s words reminded Cheng Xin of what Yun Tianming and 艾 AA had carved into the rock. But Guan Yifan was reminded of something else. He noticed that Sophon spoke of the “Edenic Age” of the new universe. This was a term invented by the Galactic humans. Two possibilities presented themselves. One was that coincidentally, the Trisolarans had also picked this term. The second possibility was far more terrifying: the Trisolarans had already discovered the Galactic humans. Given how quickly Yun Tianming had arrived on Planet Blue, it was apparent that the First Trisolaran Fleet was very close to the worlds of humankind. And now, the Trisolaran civilization had developed to the point where they were capable of constructing small universes: This was a great threat to humanity.

Then he laughed.

“What are you laughing at?” Cheng Xin asked.

“Myself.”

He found himself ridiculous. More than eighteen million years had passed since the day he’d departed World II to come to Planet Blue, and that was before they entered this small universe with its own time. By now, hundreds of millions of years must have passed in the great universe. He was worried about truly ancient history.

“Have you seen Yun Tianming?” Cheng Xin asked.

Sophon shook her head. “No. I’ve never met him.”

“What about 艾 AA?”

“The last time I saw her was on Earth.”

“Then how did you come to be here?”

“Universe 647 was a custom order. I’ve been here since its completion. Remember that I am fundamentally just a collection of digital bits, and many copies of me can be made.”

“Did you know that Tianming brought this universe to Planet Blue?”

“I don’t know what Planet Blue is. If it’s a planet, then Mr. Yun couldn’t have brought Universe 647 to it, because this is an independent universe that does not exist within the great universe. He could only bring the entrance to the universe there.”

“Why aren’t Tianming and AA here?” Yifan asked. This was also the question Cheng Xin most wanted answered. She hadn’t asked earlier because she was afraid of hearing an answer she didn’t want to know.

Sophon shook her head again. “I don’t know. The recognition system has always had Mr. Yun’s authorization.”

“Is anyone else’s authorization in the system?”

“No. Only the three of you.”

After a while, Cheng Xin said to Yifan, “AA always cared more than me about the world around her. I don’t think she would have been interested in a new universe tens of billions of years later.”

“I’m interested,” said Yifan. “I really want to see what a new universe is like before it’s distorted and tampered with by life and civilization. I think it must exhibit the highest degree of harmony and beauty.”

Cheng Xin said, “I also want to go to the new universe. The singularity and the new big bang will erase all memories of our universe. I want to bring some memory of humanity there.”

Sophon nodded solemnly at Cheng Xin. “That is a great task you’ve set yourself. There are others doing similar work, but you’re the first human from the Solar System to do this.”

“You’ve always had higher goals in life than I,” Yifan whispered to Cheng Xin. She couldn’t tell if he was joking or being serious.

Sophon stood up. “Welcome to your new life in Universe 647. Why don’t we go outside and take a look around?”

Outside, the spring planting was in full swing. The columnar robots were all working the fields. Some used the rakes to level and smooth out the field—the soil was so loose already that it did not need to be plowed; some were planting seeds in the parts that had already been smoothed. The farming techniques they employed were primitive: There were no drag harrows, so the robots had to use small rakes to level the field a bit at a time; there were no planters, so the robots each carried a bag of seeds and buried the seeds in the field one at a time. The entire scene invoked a sense of ancient simplicity. Here, robots seemed somehow more natural than real farmers.

Sophon explained, “We have only enough food stored here to last two years. After that, you’ll need to rely on the food you grow. These seeds are descended from the seeds Cheng Xin sent along with Mr. Yun. Of course, they’ve all been genetically improved.”

Yifan looked somewhat puzzled by the black soil. “I feel that soilless cultivation tanks would be more suitable here.”

Cheng Xin said, “Anyone from the Earth has a kind of nostalgia for soil. Remember what Scarlett’s father told her in Gone With the Wind? ‘Why, land is the only thing in the world worth workin’ for, worth fightin’ for, worth dyin’ for, because it’s the only thing that lasts.’”

Yifan said, “The Solar System humans spilled their last drop of blood to stay with their land—well, save for two drops: you and AA. But what was the point? They didn’t last, and neither did their land. Hundreds of millions of years have passed in the great universe, and do you think anyone still remembers them? This obsession with home and land, this permanent adolescence where you’re no longer children but are afraid to leave home—this is the fundamental reason your race was annihilated. I am sorry if I’ve offended you, but it’s the truth.”

Cheng Xin smiled at the agitated Yifan. “You haven’t offended me. What you said is true. We knew that, but we couldn’t help it. You probably can’t help it, either. Don’t forget that you and all the crew of Gravity were prisoners before becoming Galactic humans.”

“That is true.” Guan Yifan lost some of his fire. “I’ve never thought of myself as a man qualified for space.”

By the standards of space, there were not too many “qualified” men—and it was doubtful Cheng Xin would like any of them. She did think of one person who was probably qualified. His voice still echoed in her ears: We’re going to advance! Advance! We’ll stop at nothing to advance!

“Don’t dwell on the past,” Sophon said in her sweet voice. “Everything starts anew here.”

A year passed in Universe 647.

The wheat had been harvested twice, and Cheng Xin and Guan Yifan had now watched twice as the green seedlings gradually turned into a sea of golden stalks. The vegetable fields next to the wheat had always remained green.

In this tiny world they were provided with all the other necessities of life. None of the objects had manufacturing marks or brand logos—Trisolarans made them—but they looked exactly like human products.

Cheng Xin and Guan Yifan sometimes went into the fields to work alongside the robots. Sometimes they strolled about the universe—as long as they were careful not to leave footprints, they could keep on walking indefinitely and experience the feeling of traversing countless worlds.

They spent most of their time in front of the computer, however. It was possible to invoke a terminal from anywhere in the small universe, but they didn’t know where the CPU for the computer was located. The computer had a massive databank of text, image, and video from the Earth, most of which dated from before the Broadcast Era. The Trisolarans had clearly gathered the info as they studied humanity, and the material covered every field in the sciences and the humanities.

But even more information existed in the databank written in the Trisolaran language. This massive ocean of data was what interested them the most. Since they couldn’t find any software on the computer for translating Trisolaran writing into human languages, they had to study the Trisolaran script itself. Sophon acted as their teacher, but they soon discovered that this was an extremely difficult endeavor because Trisolaran writing was purely ideographic; unlike human scripts, which were mostly phonetic, Trisolaran writing had no connection to their speech, but expressed ideas directly. In the distant past, humans had also used ideographic scripts—such as some hieroglyphs—but most of these later disappeared.[11] Humans read by decoding speech made visible. However, the difficulty didn’t last long. The more they persisted, the easier the learning process became. After struggling for two months, they found themselves making rapid progress. Compared to phonetic scripts, the biggest advantage of an ideographic script was how fast one could read—Cheng Xin and Guan Yifan read at least ten times as fast in Trisolaran as they did with human scripts.

They began to read the Trisolaran material in the databank—at first haltingly, and then faster. They had two initial goals in mind: First, they wanted to know how the Trisolarans had recorded the period of history between their civilization and Earth civilization. Second, they wanted to know how this mini-universe was constructed. For the latter, they understood that they would likely not achieve a specialist’s level of understanding, but they wanted to at least understand it at the level of popular science. Sophon estimated that in order to achieve these two goals, they would need to spend one year to learn how to read Trisolaran better, then take another year to read in depth.

The fundamental principles underlying the small artificial universe seemed unimaginable to them; even the most basic mysteries puzzled them for the longest time. For instance, how could a complete ecological cycle function in a sealed space of only one cubit kilometer? What was the sun? What was its energy source? And most confounding: As a completely sealed system, where did the heat of the mini-universe go?

They asked Sophon these questions. Some she could answer; for others, she referred them to materials in the computer.

They also cared about the answer to one question in particular: Could the mini-universe communicate with the great universe? Sophon told them that there was no way for the mini-universe to transmit any information to the greater universe, but it was possible for the mini-universe to receive broadcasts from the great universe. She explained that all the universes were bubbles above a supermembrane—this was a fundamental conceptual image from Trisolaran physics and cosmology, and she could explain it no further. The great universe had enough energy to propagate information across the supermembrane. However, this was difficult and required a great expenditure of energy—the great universe would have to convert a Milky Way’s worth of matter into pure energy. As a matter of fact, the monitoring systems in Universe 647 often received messages from other great universes on the supermembrane. Some were natural phenomena; some were messages from intelligent beings that could not be decoded—but they had never received any message from the particular great universe they had come from.

Time flowed by day after day like the smooth, placid water in that little brook.

Cheng Xin began to write her memoir so that she could record the history she knew. She named the book A Past Outside of Time.

Sometimes, they also tried to imagine life in the new universe. Sophon told them that according to cosmological theories, the new universe was certain to possess more than four macro dimensions, perhaps even more than ten macro dimensions. After the birth of the new universe, Universe 647 could automatically construct an entrance to it and examine the interior conditions. If the new universe possessed more than four dimensions, the mini-universe’s exit could be moved around until a suitable habitable location was found in the great universe. Simultaneously, their mini-universe could establish communications with the refugees of other Trisolaran mini-universes, or even with Galactic human migrants. In the new universe, all the migrants coming from the old universe would practically be one race, and should be able to work together to construct a new world. Sophon emphasized that one characteristic greatly increased the probability of survival in a high-dimensional universe: Out of the many macro dimensions, it was likely that more than one dimension would belong to time.

“Multi-dimensional time?” Cheng Xin couldn’t understand the concept at first.

“Even if time were only two-dimensional, it would be a plane instead of a line,” Yifan explained. “There would be an infinite number of directions, and we could simultaneously make countless choices.”

“And at least one of those choices would turn out to be right,” added Sophon.

One night, after the second harvest, Cheng Xin woke up to find Yifan not beside her. She got up, went outside, and saw that the sun had already turned to the moon, and the little world was immersed in the watery, cool light. She saw Yifan sitting by the brook, his posture morose.

In this world of two, each of them had grown especially sensitive to the moods of the other. Cheng Xin had already known that something was troubling Yifan. Earlier, he had been sunny and upbeat. Until a few days ago, he had regularly shared his dream that, if they could find a peaceful life in the new great universe, perhaps their children could re-create the human race. But then he had abruptly changed, frequently going off by himself to ponder something, or to calculate something at a computer terminal.

Cheng Xin sat down next to Yifan, and he pulled her into his arms. The moonlit world was very quiet, and all they heard was the babbling brook. The moon revealed a field of ripe wheat; they’d have to start the harvest tomorrow.

“Loss of mass,” Yifan said.

Cheng Xin said nothing. She watched the moonlight dancing in the brook, knowing that Yifan was going to explain.

“I’ve been reading Trisolaran cosmology, and came across a proof for the elegance of the mathematics behind the great universe we all came from. The design of the total mass in the universe was precise and perfect. The Trisolarans had proved that the total mass of the universe was just enough to allow the big crunch. If the total mass were reduced even slightly, the universe would turn from being closed to open, and expand indefinitely.”

“But mass has been lost,” Cheng Xin said. She understood right away what he was getting at.

“Yes. The Trisolarans have already constructed several hundred mini-universes. How many more have been constructed by other civilizations in the universe to escape the big crunch, or for some other purpose? Each of these mini-universes took away some matter from the great universe.”

“We need to ask Sophon.”

“I have. She told me that at the time of Universe 647’s completion, the Trisolarans had not observed any influence from the loss of mass in the great universe. That universe was closed and was certain to eventually collapse.”

“What about after Universe 647 was constructed?”

“She had no idea, of course. She also mentioned that there was a group of intelligent beings in the universe that resembled the Zero-Homers, but they called themselves the Returners. They advocated against the construction of mini-universes, and called for the mass in completed mini-universes to be returned to the great universe…. But she didn’t know much else about them. All right, let’s forget all this. We’re not God.”

“But we’ve long been called on to think about matters that belonged to the province of God.”

They sat by the brook until the moon turned into the sun again.

Three days after the harvest, once all the wheat had been threshed and winnowed and stored away, Cheng Xin and Guan Yifan stood at the edge of the field and watched as the robots plowed the field to prepare for the next planting. The granary was now full, so there was no room for more wheat. Before, they would have debated what to plant for the next season. But now, both of them were troubled and had no interest in the topic. Throughout the entire harvest and threshing process, they had stayed in the house and discussed possible futures. They realized that even their individual life choices affected the fate of the universe, or even the fates of multiple universes. They really felt like God. The weight of responsibility made it hard to breathe, and so they left the house.

They saw Sophon walking toward them along one of the field ridges. Sophon rarely disturbed them and only appeared when they needed her. This time, her walk was different—she was in a hurry and did not exhibit her typical grace and dignity. Her anxious expression was also something they had not seen before.

“We’ve received a supermembrane broadcast from the great universe!” Sophon brought up a window and enlarged it. To make the window easier to see, she also dimmed the sun.

A torrent of symbols scrolled up the screen—the bitmap from the supermembrane broadcast. The symbols were strange and indecipherable. Cheng Xin and Guan Yifan noticed that each row of symbols was different: They rolled past like the surface of a chaotic river.

“The broadcast has been going on for five minutes and is still continuing.” Sophon pointed at the window. “In actuality, the message in the broadcast is very simple and brief, but it has lasted this long because it’s in many languages. We’ve seen a hundred thousand languages already!”

“Is the broadcast aimed at all the mini-universes?” Cheng Xin asked.

“Absolutely. Who else would receive it? They expended so much energy that the message must be important.”

“Have you seen Trisolaran or Earth languages?”

“No.”

Cheng Xin and Guan Yifan realized that this message was a record of which species had survived in the great universe.

By now, tens of billions of years had passed in the great universe. Regardless of the content of the broadcast, if a civilization’s language was listed in the broadcast, it meant that the civilization still existed or had existed once and lasted so long that it had left an indelible mark in the great universe.

The river of symbols continued to flow up the screen: two hundred thousand languages, three hundred thousand, four hundred thousand… a million. The number continued to go up.

There were no Trisolaran and no Earth languages.

“It doesn’t matter,” Cheng Xin said. “We know that we existed; we lived.” She and Guan Yifan leaned against each other.

“Trisolaran!” Sophon cried out and pointed at the screen. By now, over 1.3 million languages had been broadcast, and one row, written in Trisolaran, flashed by. Cheng Xin and Guan Yifan couldn’t catch it, but Sophon did.

“Earth!” Sophon cried out again a few seconds later.

After 1.57 million languages, the broadcast finished.

The window now showed only the message written in Trisolaran and Earth languages. Cheng Xin and Guan Yifan couldn’t even read the message because tears blurred their eyes.

On the day of the universe’s Last Judgment, two humans and a robot belonging to the Earth and Trisolaran civilizations embraced each other in ecstasy.

They knew that languages and scripts evolved very quickly. If the two civilizations had survived for a long time or even continued to exist now, their scripts were surely very different from what was being shown on the screen. But to allow those hiding in mini-universes to understand, they had to write in ancient scripts. Compared to the total number of civilizations that had lived in the great universe, 1.57 million was a tiny number.

In the eternal night of the Orion Arm of the Milky Way Galaxy, two civilizations had swept through like two shooting stars, and the universe had remembered their light.

After Cheng Xin and Guan Yifan calmed down, they read the message. The content of the message in both scripts was the same, and very simple:

A notice from the Returners: The total mass of our universe has decreased to below the critical threshold. The universe will turn from being closed to open, and die a slow death in perpetual expansion. All lives and all memories will also die. Please return the mass you have taken away and send only memories to the new universe.

Cheng Xin and Guan Yifan locked gazes. In each other’s eyes, they saw the dark future for the great universe. In perpetual expansion, all the galaxies would move farther away from each other until none were visible from any other. By then, standing at any point in the universe, all one would see was darkness in every direction. The stars would go out one by one, and all celestial bodies would turn into thin dust clouds. Coldness and darkness would reign over all, and the universe would become a vast, empty tomb. All civilizations and all memories would be buried in that endless tomb for eternity. Death would be eternal.

The only way to prevent this future was to return the matter locked up in all the mini-universes constructed by all the civilizations. But such a decision meant that the mini-universes would not survive, and all the refugees in the mini-universes had to return to the great universe. That was the meaning of the name of the Returners’ movement.

The two said everything they needed to say to each other with their eyes and made their decision wordlessly. But Cheng Xin still spoke aloud. “I want to go back. But if you want to stay here, I’ll stay with you.”

Yifan shook his head slowly. “I study a grand universe whose diameter is sixteen billion light-years. I don’t want to spend the rest of my life in this universe that’s only a kilometer in each direction. Let’s go back.”

“I must advise against that,” said Sophon. “We can’t precisely determine how fast time is passing in the great universe, but I can be certain that at least ten billion years have passed there since the time you came here. Planet Blue has long since vanished, and the star Mr. Yun gave you was extinguished a long time ago. We know nothing of the conditions in the great universe, and it’s possible that it’s not even three-dimensional anymore.”

“I thought you could move the exit of the mini-universe at lightspeed,” Yifan said. “Can’t you move it around to find a habitable location?”

“If you insist, I will try. But I still think staying here is the best choice. There are two possible futures if you remain: If the Returners succeed in their mission, the great universe will collapse into a singularity and lead to a new big bang so that we can go to the new universe. But if the Returners fail and the great universe dies, you can live out the rest of your lives in this mini-universe. This isn’t too bad.”

“If everyone in every mini-universe thinks that way,” said Cheng Xin, “then they will have doomed the great universe.”

Sophon gazed at Cheng Xin wordlessly. Given the speed of Sophon’s thought, perhaps this period of time felt as long as several centuries to her. It was hard to imagine that software and algorithms could produce such a complex expression. Perhaps Sophon’s AI software had brought up all the memories accumulated across almost twenty million years since she had met Cheng Xin. All these memories seemed to precipitate in her gaze: sorrow, admiration, surprise, reproach, regret… so many complicated feelings mixed together.

“You’re still living for your responsibility,” Sophon said.

Excerpt from A Past Outside of Time The Stairs of Responsibility

All my life has been spent climbing up a flight of stairs made of responsibility.

When I was little, my only duty was to study hard and obey my parents.

Later, in high school and college, the responsibility to study hard continued, but there was also the added obligation to make myself useful rather than a drain on society.

By the time I started to work toward my doctorate, my responsibilities became more concrete. I needed to contribute to the development of chemical rockets, to build more powerful, more reliable rockets so that more materials and a few men and women could be sent into Earth orbit.

Later, I joined the PIA, and my responsibility was to send a probe into space a light-year away to meet the invading Trisolaran Fleet. This was a distance about ten billion times greater than the distance I had worked with as a rocket engineer.

And then, I received a star. During the new era, it brought me previously unimaginable responsibilities. I became the Swordholder, whose duty was to maintain dark forest deterrence. Looking back on it now, perhaps it was a bit of an exaggeration to claim that I held the fate of humankind; but I really did control the direction of development for two civilizations.

Later, my responsibilities became more complicated: I wanted to endow humans with lightspeed wings, but I also had to thwart that goal to prevent a war.

I don’t know how much those catastrophes and the final destruction of the Solar System had to do with me. Those are questions that could never be answered definitively. But I’m certain they had something to do with me, with my responsibilities.

And now, I’ve climbed to the apex of responsibility: I am responsible for the fate of the universe. Of course this responsibility doesn’t belong only to me and Guan Yifan, but we own a share of the responsibility, a share of something that I never could have imagined.

I want to tell all those who believe in God that I am not the Chosen One. I also want to tell all the atheists that I am not a history-maker. I am but an ordinary person. Unfortunately, I have not been able to walk the ordinary person’s path. My path is, in reality, the journey of a civilization.

And now we know that this is the journey that must be made by every civilization: awakening inside a cramped cradle, toddling out of it, taking flight, flying faster and farther, and, finally, merging with the fate of the universe as one.

The ultimate fate of all intelligent beings has always been to become as grand as their thoughts.

Outside of Time Our Universe

Through Universe 647’s control system, Sophon managed to move the mini-universe’s exit inside the great universe. The door moved quickly through the great universe, searching for a habitable world. The amount of information that the door could transmit to the mini-universe was very limited, and no images or videos were possible. All that could be sent back was a rough analysis of the environment. This was a number between negative ten and ten, indicating the habitability of the environment. Humans could survive only if the number were greater than zero.

The door jumped tens of thousands of times in the great universe. After three months, only once did they discover a habitable planet, with a rating of three. Sophon had to concede that this was probably the best result they could get.

“A rating of three indicates a dangerous and inhospitable world,” Sophon warned.

“We’re not afraid,” said a resolute Cheng Xin. Yifan nodded. “Let’s go there.”

The door appeared in Universe 647. Like the door Cheng Xin and Guan Yifan had seen on Planet Blue, it was also a rectangle limned by glowing lines. But this door was much bigger, perhaps to make it easier to transport material through it. Initially, the door was not connected to the great universe, and anything could pass through it without leaving the mini-universe. Sophon adjusted its parameters so that anything moving through it would disappear and reappear in the great universe.

Next, it was time to return matter from the mini-universe to the great universe.

Sophon had explained that the mini-universe had no matter of its own. All of its mass had come from material brought out of the great universe. Of the several hundred mini-universes constructed by the Trisolarans, Universe 647 was one of the smallest. In total, it required about five hundred thousand metric tons of matter from the great universe, which was about the carrying capacity of a large oil tanker. It was practically nothing at the scale of the universe.

They began with the soil. After the last harvest, the field had been left fallow. The robots used a wheelbarrow to cart the moist earth; at the door, two of the robots lifted the wheelbarrow to dump the soil through the door; and the soil disappeared. It happened very quickly. Three days later, all the soil in the mini-universe was gone. Even the trees around the house had been returned through the door.

With all the soil removed, they saw the metallic floor of the mini-universe. The floor was pieced together with smooth metal tiles that reflected the sun like a mirror. The robots took off the metal tiles one by one and sent them through the door as well.

Underneath the floor was a small spaceship. Although the ship was less than twenty meters long, it contained the most advanced technologies of the Trisolarans. Designed with human occupants in mind, it could seat three, and was equipped with both a nuclear fusion drive and a curvature drive. There was a miniature ecological cycling system aboard suitable for human needs as well as equipment for hibernation. Like Halo, it was capable of landing and taking off from planetary surfaces. It had a slender, streamlined profile, perhaps to make it easier to go through the mini-universe’s door. It had been intended for the inhabitants of Universe 647 to enter the new great universe after the next big bang. It could serve as a living base for a considerable amount of time, until they found a suitable location in the new universe. But now, they would use it to return to the old great universe.

As the rest of the metal floor tiles were removed, they also revealed more machinery beneath. These were the first objects Cheng Xin and Guan Yifan had seen in the mini-universe that bore obvious signs of being of Trisolaran origin. Like Cheng Xin had suspected, the design of these machines evinced an aesthetic completely different from human ideals. Cheng Xin and Guan Yifan couldn’t even tell at first that they were looking at machinery; rather, the objects resembled strange sculptures or natural geologic formations. The robots began to disassemble the machinery and send the pieces through the door.

Cheng Xin and Sophon busied themselves in a room and wouldn’t let Yifan in. They said that they were working on a “women’s project” and would surprise him later.

After some machine under the floor was shut off, gravity disappeared from the mini-universe. The white house began to float in air.

The weightless robots disassembled the sky, which was a thin membrane capable of displaying a blue sky and white clouds. Finally, the remnants of the floor below the machinery were also disassembled and sent away.

The water in the mini-universe had evaporated and fog was everywhere. The sun shone from behind a veil of clouds and a spectacular rainbow appeared that crossed from one end of the universe to the other. Whatever liquid water was left in the mini-universe formed spheres of various sizes and drifted around the rainbow, reflecting and refracting sunlight.

Disassembling the machines also meant turning off the ecological cycling system. Cheng Xin and Yifan had to put on space suits.

Sophon adjusted the parameters in the door again to allow gas through. A low rumble shook the mini-universe, caused by air escaping through the door. Below the rainbow, the white fog cloud formed a great maelstrom around the door, like a view of a typhoon from space. And then, the whirling fog turned into a tornado, and let out a high-pitched howl. The drifting balls of water were sucked into the twister, torn apart, and disappeared through the door. Countless small objects drifting in the air were also swallowed up by the cyclone. The sun, the house, the spaceship, and other large objects also drifted in the direction of the door, but robots equipped with thrusters quickly secured them back in place.

As the air thinned, the rainbow disappeared, and the fog dissipated. The air became more transparent, and gradually, the mini-universe’s space appeared. Like space in the great universe, it was also dark and deep, but there were no stars. Only three objects floated in space: the sun, the house, and the spaceship, along with about a dozen weightless robots. In Cheng Xin’s eyes, this simplified world resembled the naïve, clumsy pictures she had drawn in her childhood.

Cheng Xin and Guan Yifan activated the thrusters on their space suits and flew toward the depths of space. After a kilometer, they reached the end of the universe and, in a flash, found themselves back where they had started. They could see the projected images of every floating object repeated endlessly in every direction. Like two mirrors placed against each other, the images extended in rows into infinity.

The house was disassembled. The last room to be taken apart was the parlor decorated in an Eastern style in which Sophon had welcomed them. All the scrolls, the tea table, and the pieces of the house were sent out the door by the robots.

The sun finally went out. It was a metal sphere where one hemisphere, the part that had emitted light, was transparent. Three robots pushed it through the door. Only lamps now illuminated the mini-universe, and the vacuum that was space soon cooled. What was left of the water and air soon turned into ice fragments that sparkled in the lamplight.

Sophon directed the robots to line up and go through the door, one after the other.

Finally, only the slender ship was left in the mini-universe, along with three figures drifting near it.

Sophon held a metal box. This box would be left behind in the mini-universe, a message in a bottle for the new universe that would be born after the next big bang. The box contained a miniature computer whose quantum memory held all the information in the mini-universe’s computer—this was practically the entire memory of the Trisolaran and Earth civilizations. After the birth of the new universe, the metal box would receive a signal from the door, and it would go through the door using its own tiny thrusters and enter the new universe. It would drift through the high-dimensional space of the new universe until the day it was picked up and read. At the same time, it would continuously broadcast its message using neutrinos—assuming the new universe also had neutrinos.

Cheng Xin and Guan Yifan believed that in the other mini-universes, at least those mini-universes that heeded that call of the Returners, the same things were being done. If the new universe were really born, it would contain many bottles containing messages drifting through it. It was believable that a considerable number of bottles contained storage mechanisms that held the memories and thoughts of every individual of that civilization, as well as their complete biological details—maybe the records would be sufficient for a new civilization in the new universe to revive that old civilization.

“Can we keep another five kilograms here?” Cheng Xin asked. She was on the other side of the ship and dressed in her space suit. In her hand, she held a glowing, transparent sphere. The sphere was about half a meter in diameter, and a few balls of water drifted inside it. Inside some of the water spheres were tiny fish, along with green algae. There were also two miniature drifting continents covered with green grass. The light came from the top of the transparent sphere, where there was a tiny glowing emitter, the sun of this miniature world. This was a completely sealed ecological sphere, the result of more than ten days of work by Cheng Xin and Sophon. As long as the tiny sun inside the sphere continued to give off light, this miniature ecological system would persist. As long as it remained here, Universe 647 would not be a lifeless, dark world.

“Of course,” said Guan Yifan. “The great universe isn’t going to fail to collapse because it misses five kilograms.” He had another thought that he did not voice: Perhaps the great universe really would fail to collapse because it lacked a single atom’s mass. The precision of Nature can sometimes exceed the imagination. For instance, life itself required the precise collaboration of various universal constants within a billion-billionth of a certain range. But Cheng Xin could still leave behind her ecological sphere. Out of all the countless mini-universes created by the countless civilizations, it was certain that some number of them would not heed the call of the Returners. Ultimately, the great universe was certain to lose at least a few hundred million tons of matter, or perhaps even a million billion billion tons.

Hopefully, the great universe could ignore such a loss.

Cheng Xin and Guan Yifan entered the spaceship, and Sophon came in last. She had long ceased wearing her magnificent kimono and turned once again into that lean and nimble warrior dressed in camouflage. She had all sorts of weapons and survival gear strapped to her body, the most prominent being the katana on her back.

“Don’t worry,” she said to her two human friends. “As long as I’m alive, no harm will come to you.”

The fusion drive activated and the thrusters emitted a dim blue light. The spaceship slowly went through the door of the universe.

The message in a bottle and the ecological sphere were the only things left in the mini-universe. The bottle faded into the darkness so, in this one-cubic-kilometer universe, only the little sun inside the ecological sphere gave off any light. In this minuscule world of life, a few clear watery spheres drifted serenely in weightlessness. One tiny fish leapt out of a watery sphere and entered another, where it effortlessly swam between the green algae. On a blade of grass on one of the miniature continents, a drop of dew took off from the tip of the grass blade, rose spiraling into the air, and refracted a clear ray of sunlight into space.