"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.

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.

"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?"

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.

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.

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.

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.

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

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

"Yes, if you are using their frame of reference."

It was best to not think about it too much.

Would the collapse never stop?

"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.

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.

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.

"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."

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

"Do you think it's him?" AA asked.

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

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 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.

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

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.

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.

"Is that him?" AA asked.

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.

"He's good-looking," said AA.

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.

Cheng Xin and AA exited the ship. They hadn't adjusted to the gravity yet, and stumbled a bit as they walked.

"Standard human being," the AI replied.

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.

"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.

"I know. Did anyone else escape?"

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.

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."

"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.

"There's no more Solar System," AA said as she sat down at the top of the stairs.

"In museums."

"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 the museums?" AA asked. She put her arm around Yifan's shoulder so that Yifan was practically carrying her down.

"How many worlds are there?"

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

"We received your gravitational wave transmission."

"On World I and World IV."

"Four. And two more are being opened up for settlement."

"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.

"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?"

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

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

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

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

"You know her?" AA looked up at Guan Yifan.

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

"Then what are you doing here? Just waiting for us?"

"It's too dangerous. Outsiders come here often."

"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?"

"Just the three of us."

"Outsiders? Extraterrestrials?" AA asked.

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

"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."

"There's no way at all?" AA asked.

"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."

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

"No. In theory, nothing allows it."

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 were silent for a while. The Solar System had disappeared completely. The only hope they had held out for the mother world was gone.

Cheng Xin and AA looked at each other thoughtfully.

"You know Yun Tianming?" AA asked.

"No."

"What about the Trisolaran Fleet?" Cheng Xin asked.

"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?"

"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.

"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."

"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."

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.

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

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

"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."

"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?"

"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?"

"We call such a place a black domain."

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.

"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."

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.

"He's a great man," Yifan said after hearing Cheng Xin's account.

"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."

"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."

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."

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

"Ultimate spaceships?"

"Of course. Five ultimate spaceships have already been launched."

"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."

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

"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."

"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."

"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."

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.

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."

"You mean the dark forest state?"

"My heart is already completely dark. I want to know."

Cheng Xin pondered for a while and then struggled to shake her head. "I don't know."

"The universal laws of physics," Cheng Xin said.

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."

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?

"Your experiences should give you a hint."

"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."

"It will never cease."

"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?"

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

Cheng Xin shuddered.

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."

"You're too… kind-hearted," Guan Yifan said softly. "I don't understand --"

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

"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."

Did you build this four-dimensional fragment?

Are you saying that for you, or at least for your creators, this four-dimensional space is like the sea for us?

Cheng Xin was silent again.

You told me that you came from the sea. Did you build the sea?

"Are you reminded of anything?" Yifan asked.

The fish responsible for drying the sea are not here.

We're sorry. What you said is really hard to understand.

More like a puddle. The sea has gone dry.

Why are so many ships, or tombs, gathered in such a small space?

When the sea is drying, the fish have to gather into a puddle. The puddle is also drying, and all the fish are going to disappear.

Are all the fish here?

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

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.

"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.

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."

"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.

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

"It's better than death," said Yifan.

"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."

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?"

"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.

"What were you going to say?"

"The foundation of mathematics."

"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. "Did you build this four-dimensional fragment? You told me that you came from the sea. Did you build the sea?"

"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 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."

"I shouldn't have told you all that," Yifan said. His sorrow was sincere.

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.

"Yes, it is enough, thank you." Cheng Xin held Yifan's hand.

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 is that?" Cheng Xin cried out.

"Death lines." Yifan recognized them right away. "Don't get too close," he said to the AI.

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 are they?"

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.

"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.

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.

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

"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."

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

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

"Far from it."

"So you've seen these before, then?"

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."

"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?

"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."

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

"Are these the most advanced lightspeed ships?"

"Zero-Homers?"

"Zero dimensions! Have you seen such a thing done?"

"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."

"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?"

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

"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."

"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."

"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?"

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."

"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."

"That's right."

"Yun Tianming is here!"

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's voice was agitated. "I've called you multiple times, and the ship's AI refused to wake you!"

"He's still young, as young as you!"

"What?" Cheng Xin said softly.

"Will the new universe have ten dimensions?"

"Oh," Cheng Xin answered mechanically.

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

"Who knows? There are infinite possibilities. That's a brand-new universe, and a brand-new life."

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

AA hailed them, and Yifan replied. "Hunter here. What's wrong?"

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

"Really?" Cheng Xin's voice seemed to come from far away, even to herself.

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.

"He brought a gift for you."

Yifan and Cheng Xin stared at each other, and then laughed.

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

"He already gave me a gift. We're inside his gift now."

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

"Are we really awake?" Cheng Xin asked.

"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.

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

An excited Cheng Xin shook her head.

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.

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.

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.

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.

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.

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.

"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.

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.

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.

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.

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.

"What happened?" Cheng Xin asked.

"Why?"

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 speed of light right now is less than twenty kilometers per second."

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.

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

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 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.

"Was it due to the disturbance from Tianming's ship?"

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

"Yes. They spread out to cover the entire solar system. We're trapped here."

"Perhaps. He didn't know the death lines were here."

"The death lines ruptured?"

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.

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.

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.

"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."

"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?"

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."

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

"Then the boot sequence will take a long time."

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?"

"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.

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.

"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.

"We have to hibernate," said Yifan.

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

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."

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.

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.

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.

A moment here; eons there.

"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.

"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."

"Thank you," Cheng Xin said.

"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. Her eyes felt hot and wet.

"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."

"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.