Death's End

Bunker Era, Year 67 Orion Arm of the Milky Way

Examining the data was Singer’s job; judging the sincerity of the coordinates was Singer’s joy.

Singer understood that what he did wasn’t important—it just filled in the pieces. But it had to be done, and the task was enjoyable.

Speaking of enjoyment, when this seed had departed from the home world, that world was still a place full of joy. But later, as the home world began to war against the fringe world, joy diminished. By now, more than ten thousand grains of time had passed. There wasn’t much joy to speak of on the home world or in this seed. The happiness of the past was recorded in classical songs, and singing those songs was another of the few joys left.

Singer sang one of these classical songs as he reviewed the data.

Singer did not complain much. Survival required so much thought and mental energy.

Entropy increased in the universe, and order decreased. The process was like the boundless wings of the giant balance bird pressing down upon all of existence. But low-entropy entities were different. The low-entropy entities decreased their entropy and increased their order, like columns of phosphorescence rising over the inky-dark sea. This was meaning, the highest meaning, higher than enjoyment. To maintain this meaning, low-entropy entities had to continue to exist.

As for any meaning higher than that, it was pointless to think about. Thinking about the subject led nowhere and was dangerous. It was even more pointless to think about the apex of the tower of meaning—maybe there wasn’t an apex at all.

Back to the coordinates. Many sets of coordinates flitted across space, like the matrix insects flitting across the sky of the home world. Picking up coordinates was the job of the main core, which swallowed all the messages passing through space: medium membrane, long membrane, light membrane, and maybe one day even short membrane. The main core remembered the positions of all the stars. By matching the received data against various map projections and position schema, it could pick out the coordinates of the messages’ origin. It was said that the main core could match position schema from five hundred million time grains ago. Singer never tried anything like that—it would be meaningless. In that distant age, the low-entropy clusters in space were rare and far apart, and had not evolved the hiding gene and the cleansing gene. But now—

Hide yourself well; cleanse well.

Out of all the coordinates, only some were sincere. Believing in insincere coordinates meant cleansing empty worlds. This was wasteful. And there were other harms besides. These empty worlds might be useful in the future. It was incomprehensible why anyone would send out insincere coordinates—they would get what they deserved someday.

Sincere coordinates followed certain patterns. For instance, a mass cluster of coordinates was usually insincere. But these patterns were all only heuristics. Judging the sincerity of coordinates effectively required intuition. The main core on this seed was incapable of this task, and even the supercore back on the home world could not do it. This was one reason why low-entropy entities had no substitute.

Singer had this skill, this intuition, but it wasn’t a gift or instinct; rather, it was something honed by the accumulated experience of tens of thousands of time grains. A set of coordinates seemed nothing more than a simple matrix in the eyes of the uninitiated, but to Singer, it was alive. Its every detail was expressive. For instance, how many reference points were taken? What was the method for marking the target star? And many other subtle details besides. The main core was able to provide some information, such as the historical records associated with this set of coordinates, the direction of the coordinate broadcast source, the broadcast time, and so forth. Together, these formed an organic whole, and what emerged in Singer’s consciousness was a sense of the coordinate broadcaster himself. Singer’s spirit crossed the chasm of space and time, resonated with the spirit of the broadcaster, and felt its terror and anxiety, along with other feelings unfamiliar to the home world, such as hatred, envy, greed, and so on. But for the most part, it was terror. Terror was what endowed a set of coordinates with sincerity. For all low-entropy entities, terror guaranteed existence.

Just then, Singer noticed a sincere set of coordinates near the course of the seed. The set of coordinates was broadcast by long membrane, and even Singer himself couldn’t be sure what told him that the set of coordinates was sincere—intuition could not always be explained. He decided to cleanse it. He wasn’t busy, and the task wasn’t going to distract him from singing. Even if he got it wrong, it was not a big deal. Cleansing was not a precision task and didn’t require absolute accuracy. It also wasn’t urgent. He just had to get it done eventually. This was also why his position wasn’t prestigious.

Singer took a mass dot out of the seed’s magazine, then he turned to look for the star indicated by the set of coordinates. The main core guided his gaze, like a spear sweeping through the starry sky. Singer grasped the mass dot with a force field feeler and prepared to flick it. But then he saw the location indicated by the set of coordinates and the feeler relaxed.

Of the three stars, one was missing. There was a white cloud of dust in its place, like the feces of an abyss whale.

It’s already been cleansed. Nothing more to do.

Singer put the mass dot back into storage.

That was fast.

He activated a main core process to trace the source of the mass dot that had killed that star. This was a hopeless task with almost zero chance of success, but required by established procedure. The process soon terminated, and like every other time, yielded no results.

Singer soon understood why the cleansing had happened so fast. He saw a slow fog in the vicinity of that destroyed world. The slow fog was about half a structure length away from that world. Seen by itself, it wasn’t apparent where the fog had come from, but when connected with the broadcast coordinates, it was obvious that the fog belonged to that world. The slow fog showed that the world was dangerous, which was why the cleansing had come so quickly. It appeared that there were other low-entropy entities with even sharper intuition than he; but that wasn’t strange. It was as the Elder said: In the cosmos, no matter how fast you are, someone will be faster; no matter how slow you are, someone will be slower.

Every set of broadcast coordinates would eventually be cleansed; it was just a matter of sooner versus later. One low-entropy entity might think this set of coordinates insincere, but on the millions upon millions of low-entropy worlds there were billions upon billions tasked with cleansing—someone would think it sincere. All low-entropy entities possessed the cleansing gene, and cleansing was an instinct. Also, cleansing was a very simple thing. The cosmos was full of sources of potential power—one just had to trigger them to complete the task. It required so very little, and didn’t even delay singing.

If Singer were patient, all sincere coordinates would eventually be cleansed by other, unknown low-entropy entities. But this was not a good thing for either the home world or the seed. Since Singer had received the set of coordinates and even glanced at the world pointed to by the coordinates, Singer had a connection to that world. It would be naïve to think of this connection as unidirectional. Recall the great law of reversible discovery: If you could see a low-entropy world, then that low-entropy world could also see you—it was only a matter of time. Thus, waiting for others to complete cleansing was dangerous.

The next task was to put this now-useless set of coordinates into the data bank called the tomb. This was also required by established procedure. Of course, all other information having to do with the location needed to go into the data bank as well, just as personal effects were buried with the body, as was the custom on the home world.

Among the “personal effects” was something that piqued Singer’s interest. It was a record of the dead world’s three communications with another location using medium membrane. Medium membrane was the least efficient communication membrane, also called primitive membrane. Most communications preferred long membrane, though it was said that even short membrane could be used to convey messages. If true, that would make the communicators akin to gods. But Singer liked primitive membrane. He thought primitive membrane possessed a simple beauty, symbolizing an age full of joy. He often turned primitive membrane messages into songs. He thought they sounded pretty, even if he didn’t understand them. Understanding them wasn’t necessary, however; other than coordinates, primitive membrane messages didn’t have much useful information. It was enough to enjoy the music.

But this time, Singer was able to understand some of the message, because some parts carried a self-decoding system! Although Singer was only able to understand a little, grasp an outline, it was enough for him to see an incredible history.

First, the other location had broadcast a message via primitive membrane. The low-entropy entities of that world clumsily plucked their star—Singer decided to call them the Star-Pluckers—like ancient bards of the home world plucking the strings of the rough country zither, to send out the message. It was this message that contained the self-decoding system.

Although the self-decoding system was primitive and clumsy, it was sufficient to allow Singer to see that a subsequent message sent out by the dead three-star world followed the same encoding scheme—apparently an answer to the first message sent by the Star-Pluckers! This was already nearly inconceivable, but after that, the Star-Pluckers responded again!

Interesting. Very interesting!

Singer had indeed heard of low-entropy worlds that possessed neither the hiding gene nor the hiding instinct, but this was the first time he had seen one. Of course, the three communications between these two would not reveal their absolute coordinates, but they did expose the distance between the two worlds. If the distance were fairly large, it wouldn’t be a big deal either; but the distance was very short, only 416 structures—the two worlds were practically on top of each other. This meant that if one world’s coordinates were exposed, the other would also be exposed—it was just a matter of time.

This was how the Star-Pluckers’ coordinates were revealed.

Nine time grains after the first three communications, another record appeared: The Star-Pluckers plucked their star again to send out another broadcast… a set of coordinates! The main core was certain that it was a set of coordinates. Singer looked for the star indicated by the coordinates and saw that it had also been cleansed, about thirty-five time grains ago.

Singer thought that perhaps he had been wrong. The Star-Pluckers must have possessed the hiding gene. They obviously had the cleansing gene, so it was impossible that they didn’t also possess the hiding gene. But like most coordinate broadcasters, they didn’t have the ability to cleanse on their own.

Interesting. Very interesting.

Why did whoever cleansed the dead three-star world not also cleanse the world of the Star-Pluckers? Many possibilities. Perhaps they hadn’t noticed these three communications—primitive membrane messages often didn’t get much attention. But given the millions upon millions of worlds out there, someone would have noticed—Singer was just one who did. Even without Singer, some other low-entropy entity would have noticed them; it was just a matter of time. Or perhaps they had noticed them, but decided that a low-entropy group that didn’t possess the hiding gene wasn’t much of a threat, and cleansing them was more trouble than it was worth.

But that would be a mistake, a terrible mistake! Broadly speaking, if low-entropy entities like these Star-Pluckers really didn’t have the hiding gene, then they would not be afraid of exposing their own presence, and they would expand and attack without fear.

At least until they got killed.

However, as applied to this particular case, the situation was more complicated. The first three communications were followed nine time grains later by the coordinate broadcast. Then, sixty time grains after that, there was another long-membrane coordinate broadcast from somewhere else, pointing at the dead three-star world. The chain of events painted an uneasy picture, a picture that indicated danger. The cleansing against the dead three-star world had happened twelve time grains ago, so the Star-Pluckers must have realized that their own position had been revealed. Their only choice was to shroud themselves in slow fog so that they would appear perfectly safe and no one would bother them.

But they hadn’t. Maybe they didn’t have the ability? But more than sufficient time had passed from the time they could pluck their star to send out a primitive membrane message for them to possess this ability.

Perhaps they didn’t want to shroud themselves.

If that was so, that made the Star-Pluckers very dangerous; far more dangerous than the dead world.

Hide yourself well; cleanse well.

Singer gazed at the world of the Star-Pluckers. It was an ordinary star that had at least a billion more time grains of life left. It possessed eight planets: four giant liquid planets and four solid ones. Singer’s experience told him that the low-entropy entities who had sent out the primitive membrane broadcast lived on one of the solid planets.

Singer activated the process for the big eye—he rarely did this; he was exceeding his authority.

“What are you doing?” asked the seed’s Elder. “The big eye is busy.”

“I’d like to take a closer look at one of the low-entropy worlds.”

“Your job doesn’t require close-up examinations.”

“I’m just curious.”

“The big eye has to observe more important targets. There’s no time for your curiosity. Go back to doing your job.”

Singer didn’t persist in his request. The cleansing agent had the lowest position on the seed. Everyone thought of him contemptuously, thought of his work as easy and trivial. But they forgot that coordinates that had been broadcast often indicated far more danger than the vast majority who kept themselves well hidden.

The only thing left was cleansing. Singer took a mass dot out of the magazine again, then realized that he couldn’t use a mass dot to cleanse the Star-Pluckers. Their planetary system had a different structure than the dead world’s system: it possessed blind corners. Using a mass dot might leave something behind, thereby wasting effort. He needed to use a dual-vector foil. However, Singer didn’t have the authority to retrieve a dual-vector foil out of the magazine; he had to ask the Elder for approval.

“I need a dual-vector foil for cleansing.”

“Permission granted,” said the Elder.

The dual-vector foil drifted in front of Singer. It was sealed in its package, crystal clear. Although it was an ordinary object, Singer liked it a lot. He didn’t like the expensive tools too much; they were too violent. He liked the unyielding tenderness displayed by the dual-vector foil, a kind of aesthetic that could turn death into a song.

Yet Singer felt a bit uneasy. “Why did you give it to me without so much as asking a question?”

“It’s not like this is very costly.”

“But if we make too much use of this—”

“It’s being used everywhere in the cosmos.”

“Yes, that is true. But in the past, we’ve always been restrained. Now—”

“Have you heard something?” The Elder began to riffle through Singer’s thoughts, and Singer shuddered. Very quickly, the Elder found the rumor in Singer’s mind. It wasn’t a great sin—the rumor was an open secret on the seed.

It was a rumor about the war between the home world and the fringe world. Before, news about the war had been frequent, but then the reports stopped, indicating that the war wasn’t going well, perhaps even heading into a crisis. But the home world couldn’t coexist with the fringe world. The fringe world had to be destroyed, lest the home world be destroyed by it. If the war couldn’t be won, then…

“Has the home world decided to transform into two dimensions?” Singer asked. Of course, the Elder already knew the question.

The Elder did not answer, which was also an answer.

If the rumor was true, then it was a great sorrow. Singer couldn’t imagine such a life. On the tower of values, survival ranked above all. When survival was threatened, all low-entropy entities could only pick the lesser of two evils.

Singer removed these thoughts from his organ of cogitation. These were not thoughts he should have, and he was only going to be uselessly troubled by them. He tried to remember where he had stopped in his song. It took a while before he found his place. He continued to sing:

As he continued to sing, Singer picked up the dual-vector foil with a force field feeler and carelessly tossed it at the Star-Pluckers.

Bunker Era, Year 67 Halo

Cheng Xin awakened to find herself in weightlessness.

Hibernation wasn’t like regular sleep. A hibernator didn’t feel the passage of time. Throughout the entire process, one could only feel time during the hour spent entering hibernation and the hour emerging from it. No matter how much time passed during hibernation, subjectively, the hibernator only felt that he or she had slept no more than two hours. Thus, waking up always involved a sharp break, a feeling that the self had passed through a door in time and emerged into a new world.

Cheng Xin found herself in a white spherical space. She saw that 艾 AA was floating nearby, dressed in the same skintight hibernation suit. Her hair was wet and her limbs were spread out powerlessly; clearly, she had just been awakened as well. As their eyes met, Cheng Xin wanted to speak, but the numbness caused by the cold had still not left her, and she couldn’t make any noise. AA shook her head, meaning that she was in the same state and didn’t know anything.

Cheng Xin noticed that the space was filled with a golden light like the setting sun. The light came in through a circular window—a porthole. Outside the porthole, Cheng Xin could see only blurred streaks and swirling lines. The lines were arranged into parallel bands of blue and yellow, revealing a world covered by raging storms and torrents, clearly the surface of Jupiter. Cheng Xin saw that the surface of Jupiter looked much brighter than she remembered.

Strangely, the wide, raging cloud band in the middle reminded her of the Yellow River. She knew, of course, that an eddy in this “Yellow River” was big enough to contain the Earth. Against this background, Cheng Xin saw an object. The main body of the object was a long column whose sections were of different diameters. Three short cylinders were perpendicularly attached to the main column at different locations. The entire assembly slowly rotated around the axis of the column. Cheng Xin decided that she was looking at a combined space city formed from eight separate space cities docked together.

She discovered another amazing fact as well: The place they were in stayed at rest relative to the combined space city, but Jupiter was slowly moving in the background. Based on the brightness of Jupiter, they were now on the side facing the Sun, and she could see the shadow of the combined space city against the gaseous surface of Jupiter. After a while, the Jovian terminator appeared, dividing Jupiter’s day from night, and she saw the monstrous eye that was the Great Red Spot drifting into view. Everything confirmed the fact that both the place they were in and the combined space city were not in Jupiter’s shadow and did not orbit the Sun in parallel with Jupiter; instead, they were Jupiter’s satellites and revolved around the gas giant.

“Where are we?” Cheng Xin asked. She was finally able to speak in a hoarse voice, but she still couldn’t move her body.

AA shook her head again. “No idea. I think we’re on a spaceship.”

They continued to drift in the golden glow of Jupiter, like a dreamscape.

“You’re on Halo.”

The voice came from an information window that had just popped up next to them. In the window was an old man with a head full of white hair. Cheng Xin recognized him as Cao Bin. Based on his age, she realized that she had leapt across another long stretch of years. Cao Bin told her that it was now May 19 of Year 67 of the Bunker Era. She realized that fifty-six more years had passed since her last brief awakening.

She avoided life by staying outside of time, and she watched as others aged, seemingly in an instant. Her heart was filled with regret and guilt. She decided that no matter what happened from now on, this was her last hibernation.

Cao Bin told them that they were on the latest ship to bear the Halo name. It had been constructed only three years ago. After the Halo City Incident, more than half a century earlier, he and Bi Yunfeng had both been convicted, though both had served short sentences and then been released. Bi Yunfeng had died more than ten years earlier, and Cao Bin brought along his well wishes for her and AA. Cheng Xin’s eyes moistened.

Cao Bin also told them that there were now fifty-two large space cities in the Jupiter cluster, most of which had been combined into bigger cities. What they could see was Jupiter Combination II. Since the advance warning system had been refined twenty years ago, all cities had decided to become Jovian satellites. Only after an alert was issued would the cities change orbit and go into hiding.

“Life in the cities is once again like being in paradise. It’s too bad that you won’t get to see it, because there’s no time.” Cao Bin paused. Cheng Xin and AA exchanged uneasy glances. They realized that he had been so loquacious until now because he was trying to delay this moment.

“Was there an attack alert?”

Cao Bin nodded. “Yes, there’s been an alert. During the last half century, there were two false alarms, and each time, we almost awakened you. But this time it’s real. Children—I’m already one hundred and twelve years of age, so I think I can call you that—the dark forest strike is finally here.”

Cheng Xin’s heart tensed. It wasn’t because the attack had arrived—humanity had been preparing for this moment for more than a century. Rather, she sensed that something was wrong. She and AA had been awakened by contract. It would have taken at least four to five hours for them to recover to this stage, which meant that the alert had been issued some time ago. But outside the porthole, Jupiter Combination II had not disassembled nor changed its orbit, but continued to drift as a Jovian satellite, as though nothing had happened. They turned to Cao Bin: The centenarian’s expression was too placid, as though hiding utter despair.

“Where are you now?” AA asked.

“I’m at the advance warning center,” Cao Bin said, and pointed behind him.

Cheng Xin saw a hall behind him that looked like a control center. Information windows filled almost every bit of space. The windows drifted around the hall, but new windows kept on popping open before them, only to be covered in turn by still newer windows—like the flood after a burst dam. But the people in the hall seemed to be doing nothing. Half of them were in military uniforms, but they all either stood leaning against a desk or sat still. Everyone had dull eyes, and all had the same ominous calm expression that was on Cao Bin’s face.

It shouldn’t be like this.

This didn’t look like a world hunkered down inside a bunker, certain it could survive the attack. It looked more like three centuries ago—no, four centuries ago now—when the Trisolar Crisis had first developed. Back then, at the offices of the PIA and the PDC, Cheng Xin had seen this kind of atmosphere and expression everywhere: despair against some superpowerful force in the universe, a kind of numbness and indifference that said We give up.

Most of the people in the control center were quiet, but a few whispered to each other with somber faces. Cheng Xin saw a man sitting numbly. A cup had fallen over on the table in front of him, and a blue liquid spilled off the table onto his pants, but he ignored it. On the other side, in front of a large information window that seemed to show some complicated, evolving situation, a man in military uniform embraced a woman dressed as a civilian. The woman’s face seemed wet….

“Why aren’t we entering Jupiter’s shadow?” AA pointed at the combined city outside the porthole.

“There’s no point. The bunker is useless,” Cao Bin said, lowering his eyes.

“How far is the photoid from the Sun?” Cheng Xin asked.

“There’s no photoid.”

“Then what have you found?”

Cao Bin gave a wretched laugh. “A slip of paper.”

Bunker Era, Year 66 Outside the Solar System

A year before Cheng Xin’s awakening, the advance warning system discovered an unknown flying object sweeping past the edge of the Oort Cloud at a speed close to lightspeed. At its closest approach, the object was only 1.3 light-years from the Sun. The object’s volume was immense, and at its near-lightspeed velocity, the radiation generated by its impact with the scattered dust and atoms in space was intense. The advance warning system also observed the object making a small course change during flight to avoid a patch of interstellar dust, before resuming its previous course. It was most certainly an intelligent spaceship.

This was the first time that Solar System humans—as opposed to Galactic humans—had observed another extraterrestrial civilization besides the Trisolarans.

Due to lessons learned from the previous three false alarms, the Federation Government did not publicize this discovery. No more than a thousand people in the entire Bunker World knew about it. During the few days when the spaceship had been closest to the Solar System, these individuals lived in extreme anxiety and terror. In the few tens of space observation units comprising the advance warning system, in the advance warning center (a space city in the Jupiter cluster), in the battle center of Federation Fleet Command, and in the office of the president of the Solar System Federation, people held their breaths and watched the spaceship’s course like a trembling school of fish hiding at the bottom of a pond, waiting for the trawler to pass overhead. These individuals’ terror developed to absurd levels later: They refused to use radio communications, walked noiselessly, and spoke only in whispers…. In reality, everyone understood that these gestures were meaningless, not the least because what the advance warning system observed had happened a year and four months ago. By now, the spaceship was already gone.

After the extraterrestrial spaceship moved farther away, these individuals did not relax. The advance warning system discovered something else that was worrisome. The strange spaceship did not shoot a photoid at the Sun, but did launch something else. This object was also shot at the Sun at lightspeed, but it produced none of the emissions associated with photoids and was completely invisible electromagnetically. The advance warning system only managed to discover it through gravitational waves. The object continuously emitted weak gravitational waves whose strength and frequency remained constant. The waves clearly carried no message, and were probably the result of some physical characteristic of the projectile. When the advance warning system initially discovered these gravitational waves, the source was thought to be the extraterrestrial spaceship. But they soon found that the source was separate from the spaceship, and it was approaching the Solar System at lightspeed.

Further analysis of the observation data revealed that the projectile wasn’t aimed precisely at the Sun. According to its current trajectory, it would sweep past the Sun outside the orbit of Mars. If the intended target had been the Sun, this was a relatively gross error. This showed another way that the projectile was different from a photoid: The data gathered from the previous two photoid strikes all showed that after a photoid was launched, it followed a precise, straight trajectory to the target star (taking into account the motion of the star) and did not require any course correction. It could be surmised that a photoid was essentially a rock flying under inertia at lightspeed. Tracking the gravitational wave source showed that the projectile did not make any course corrections, apparently indicating that its target was not the Sun. This provided some comfort for everyone involved.

When the projectile was about 150 AU from the Sun, the gravitational waves it emitted began to rapidly decrease in frequency. The advance warning system discovered that this was due to its deceleration. Within a few days, the projectile’s velocity went from lightspeed to one-thousandth of lightspeed, and continued to decrease. Such low speed meant that it wasn’t enough to threaten the Sun, which provided further comfort. In addition, at this speed, human spacecraft could keep up with it. In other words, it was possible to send out ships to intercept it.

Revelation and Alaska departed the Neptune city cluster and flew in formation to investigate the unknown projectile.

Both ships were equipped with gravitational wave reception systems and could form a positioning network to determine the location of the transmission source with precision at close range. Since the Broadcast Era, more ships had been built that could transmit and receive gravitational waves. But the design concepts used in these ships were very different from earlier antenna ships. One of the main innovations was separating the gravitational wave antenna from the ship itself so that they formed two independent units. The antenna could then be combined with different ships, and could be replaced after it failed due to decay. Revelation and Alaska were only medium-sized ships, but they had about the same total volumes as large ships because the gravitational wave antennas made up a large portion of their structures. The two ships resembled helium-filled airships of the Common Era: They looked immense, but the effective payload was just the small gondola hanging below the gasbags.

Ten days after the two ships left port, General Vasilenko and 白 Ice,[8] dressed in lightweight space suits and magnetic shoes, took a stroll on the gravitational wave antenna of Revelation. They enjoyed doing this because there was much more space out here compared to the interior of the spaceship, and walking around the antenna made one feel like walking on solid earth. They were the leaders of the first exploratory team: Vasilenko was the commander while 白 Ice was in charge of technical matters.

Alexei Vasilenko had been an observer in the advance warning system during the Broadcast Era. Together with Widnall, he had discovered the trails of the Trisolaran lightspeed ships, which led to the first false alarm. After the incident, Sublieutenant Vasilenko was made one of the scapegoats and was dishonorably discharged. But he thought the punishment unjust and hoped that history would ultimately clear his name, and thus entered hibernation. As time passed, the discovery of the lightspeed trails grew in importance, and the damage from the first false alarm was gradually forgotten. Vasilenko awakened in Year 9 of the Bunker Era, was restored to his former rank, and by now had been promoted to vice admiral of the Solar Federation Space Force. However, he was close to eighty years of age. As he looked at 白 Ice strolling next to him, he thought how unfair life was: This man had been born eighty years before himself and came from the Crisis Era; yet, after hibernation, he was just over forty.

白 Ice’s original name was Bai Aisi.[9] After awakening, he wanted to appear more integrated and not so behind the times, and chose a more common modern name that mixed English and Chinese elements. He had been a doctoral student under Ding Yi and had gone into hibernation near the end of the Crisis Era, awakening only twenty-two years ago. Usually, such a long leap across the years meant the hibernator would have trouble catching up to the new age, but theoretical physics was a special case. The sophon lock meant that Common Era physicists could still be considered professionally relevant during the Deterrence Era, and the creation of the circumsolar particle accelerator upended all the assumptions of fundamental theoretical physics, as though a deck of cards had been reshuffled.

Back during the Common Era, superstring theory had been thought of as advanced theory, the physics of the twenty-second century. The creation of the circumsolar particle accelerator allowed superstring theory to be confirmed via experiments. The result, however, was disastrous. Concepts that had to be rejected far outnumbered predictions that were confirmed. Many results that the Trisolarans had passed on were falsified. Based on the high level of technology the Trisolarans were later able to achieve, it was inconceivable that they had made such mistakes in fundamental theory. The only conclusion was that they had lied to humans even in the areas of basic theory.

白 Ice had proposed some theoretical models that were among the few confirmed by the circumsolar particle accelerator. By the time he awakened, physics had essentially been called back to the starting line. He quickly distinguished himself and won great honors, and after ten or so years, he was once again at the vanguard of the field.

“Look familiar?” Vasilenko gestured at everything around them.

“Indeed. But the self-confidence and arrogance of humanity are all gone,” said 白 Ice.

This resonated with Vasilenko. He looked back along the ship’s course. Neptune was only a tiny blue dot and the Sun a faint spot of light, incapable of even casting their shadows against the antenna surface. Where were the two thousand stellar-class warships that had formed a magnificent phalanx all those years ago? Now, there were just these two lonely ships with a complement of no more than a hundred crew. Alaska was about a hundred thousand kilometers away but not visible to them. That ship wasn’t only acting as the other end of the positioning network, but also held another exploratory team organized the same as the team aboard Revelation. Fleet Command called the team aboard Alaska the backup, indicating that the brass had made ample preparations for the risk and danger inherent in this expedition. Here, at the cold, desolate frontier of the Solar System, the antenna under their feet seemed a lonesome island in the universe. Vasilenko wanted to sigh, but thought better of it. He took something out of the pocket of his spacesuit and let it float between the two of them, spinning slowly.

“Check this out.”

The object appeared to be a bone from some animal. In fact, it was a metallic machine component; the frigid light of the stars glinted against its smooth surface.

Vasilenko pointed at the spinning object. “About a hundred hours ago, we detected a patch of floating metallic debris next to the ship’s course. A drone retrieved a few items, and this is one of them: a piece of the cooling system for a nuclear fusion reactor aboard a stellar-class warship from the end of the Crisis Era.”

“It’s from the Doomsday Battle?” asked an awed 白 Ice.

“Yes. We also found the armrest from a chair and a bulkhead fragment.”

They had been passing through the vicinity of the ancient battlefield from nearly two centuries earlier. After the Bunker Project started, people often discovered remnants of ancient warships. Some were placed in museums while others were bought and sold through the black market. 白 Ice held the component and felt a chill pass through the glove of the space suit, straight into his marrow. He let it go, and the component continued to spin slowly, as though moved by some soul embedded within. 白 Ice moved his eyes away and gazed into the distance. All he could see was a bottomless, empty abyss. Two thousand warships and millions of dead bodies had been drifting in this patch of desolate space for nearly two centuries. The sacrificial blood of the dead had long ago sublimated from ice to gas and dissipated.

“The target of our exploration might be more dangerous than even the droplets this time,” 白 Ice said.

“True. Back then, we already had some familiarity with the Trisolarans. But we know nothing about the world that created and sent this…. Dr. Bai, do you have any guesses as to what we will encounter?”

“Only a massive object can emit gravitational waves, so I guess that object must be large both in mass and volume, perhaps even a spaceship…. Well, in this business, the unexpected is to be expected.”

The two ships of the expedition continued on their course for another week until the distance between them and the gravitational wave source was only about a million kilometers. The expedition decelerated until their velocity was zero, and began to accelerate toward the Sun. This way, by the time the projectile caught up to the expedition, they would fly in parallel. Most of the close-range exploration would be conducted by Revelation; Alaska would observe from a distance of about a hundred thousand kilometers.

The distance continued to shrink; the projectile was now only about ten thousand kilometers from Revelation. The gravitational wave emissions were very clear and could be used for precise positioning. But even from this distance, radar returned no echo and nothing could be seen in the visible light range. By the time the distance shrank to one thousand kilometers, they still couldn’t see anything at the location of the gravitational wave source.

The crew of Revelation was close to panicking. Before departure, they had imagined all kinds of scenarios, but the idea of not being able to see their target when they were practically on top of it had never occurred to them. Vasilenko radioed the base at Neptune for instructions, and forty minutes later, received the order to approach the target until they were only 150 kilometers away.

Finally, the visible light detection systems noticed something: a small white dot at the gravitational wave source, visible even with a common telescope from the ship. Revelation sent out a drone to investigate. The drone flew at the target, the distance between them shrinking rapidly: five hundred kilometers, fifty kilometers, five hundred meters… Finally, the drone stopped five meters from the target. The clear holographic video it transmitted allowed the crew of both ships to see this extraterrestrial object that had been shot at the Sun.

A slip of paper.

There was really no better description. Formally, the object was called a rectangular membrane-like object: length: 8.5 cm; width: 5.2 cm; slightly bigger than a credit card. It was so thin that its thickness could not be measured. The surface was pure white, looking exactly like a slip of paper.

The members of the exploratory team were among the best officers and professionals in the world, and all had cool, rational minds. But instinct was more powerful. They had been prepared for giant, invasive objects. Some had guessed they would find a spaceship the size of Europa—a not unlikely possibility, given the strength of its gravitational wave emissions.

Faced with this paper slip—that was what they all called it—everyone heaved a sigh of relief. Rationally, they were still guarded. The object could certainly be a weapon that possessed enough power to destroy both spaceships. But it was impossible to believe that it could threaten the entire Solar System. By appearance, it was delicate, harmless, like a white feather floating in night air. People had long ceased to write letters on paper, but they were familiar with the concept from period films about the ancient world, and so the paper slip seemed almost romantic in their eyes.

Further investigation showed that the paper slip did not reflect electromagnetic radiation at any wavelength. The slip’s white color wasn’t reflected light, but light emitted by the object itself. All electromagnetic radiation, including visible light, simply passed through the slip, which was thus completely transparent. Images taken at close range showed the stars behind the slip, but due to interference from the white light it emitted and the dark background of space, it appeared as an opaque white from a distance. At least superficially, the object seemed harmless.

Maybe it really was a letter?

Since the drone had no appropriate collection tools, another drone with a mechanical arm and a sealable scoop had to be dispatched to capture the slip. As the open scoop extended toward the slip at the end of the mechanical arm, the hearts of everyone on the two ships hung in their throats.

This was another scene that seemed familiar.

The scoop closed around the slip and the arm pulled back.

But the slip remained where it was.

The attempt was repeated several more times with the same result. The drone operators aboard Revelation tried to maneuver the mechanical arm to touch the slip. The arm passed right through the slip, and neither appeared damaged. The arm felt no resistance, and the slip didn’t change its position. Finally, the operator directed the drone to approach the paper slowly, in an attempt to push it. As the hull of the drone came into contact with the slip, the slip disappeared inside the drone, and as the drone continued to move forward, the slip emerged from the stern, unchanged. During the process when the slip was inside the drone, its internal systems detected no anomalies.

By now, the expedition members understood that the paper slip was no ordinary object. It was like an illusion that did not interact with anything in the physical world. It was also like a tiny cosmic reference plane that maintained its position, unmovable. No contact was capable of shifting its position—or, more accurately, its set trajectory.

白 Ice decided to go investigate in person. Vasilenko insisted on coming with him. Having both leaders of the first exploratory team go together was a controversial proposition, and they had to wait forty minutes to receive approval from the base at Neptune. Their request was reluctantly granted, as Vasilenko would not back down, and there was also a backup team.

The two headed for the paper slip in a pinnace. As Revelation and its immense gravitational wave antenna shrank in the distance, 白 Ice thought he was leaving the only support in the universe, and his heart became fearful.

“Your advisor, Dr. Ding, must have felt the same way years ago,” Vasilenko said. He appeared perfectly calm.

白 Ice agreed with the sentiment in silence. He did feel spiritually connected to the Ding Yi of two centuries ago. Both of them headed for a great unknown, toward equally unknown fates.

“Don’t worry. This time, we can trust our intuition.” Vasilenko patted 白 Ice on the shoulder, but 白 Ice did not feel much comfort.

The pinnace was now next to the paper slip. After checking their space suits, they opened the pinnace’s hatch so that they were exposed to space. They fine-tuned the pinnace’s position until the paper slip hung half a meter above their heads. The tiny white plane was perfectly smooth, and through it they saw the stars behind, confirming that it really was a glowing, transparent object. The white light it emitted made the stars behind it appear a bit blurred.

They lifted themselves up in the pinnace until their eyes were lined up with the edge of the plane. Just like the camera had shown, the paper had no thickness. From the side, it completely disappeared. Vasilenko extended a hand toward the paper, but 白 Ice caught him.

“What are you doing?” 白 Ice asked severely. His eyes said the rest. Think about what happened to my teacher.

“If it really is a letter, perhaps the message won’t be released until an intelligent body makes direct contact with it.” Vasilenko brushed off 白 Ice’s hand.

Vasilenko touched the paper with his gloved hand. His hand passed through the paper and was not damaged. Vasilenko received no mental message, either. He again moved his hand through the paper and stopped, allowing the small white plane to divide his hand into two parts. Still, he felt nothing. The paper showed an outline of the cross section of the hand where the hand penetrated it: clearly, the sheet hadn’t been broken, but passed through the hand unharmed. Vasilenko pulled his hand back, and the slip hung still as before—or, more accurately, continued to move toward the Solar System at the rate of two hundred kilometers per second.

白 Ice also tried to touch the slip, then pulled his hand back. “It’s like a projection from another universe that has nothing to do with ours.”

Vasilenko had more practical concerns. “If nothing can affect it, then we have no way to bring it to the ship for further analysis.”

白 Ice laughed. “That’s a simple problem to solve. Have you forgotten the story told by Francis Bacon? ‘If the mountain will not come to Muhammad, then Muhammad must go to the mountain.’”

And so, Revelation slowly sailed toward the paper slip, made contact, and then allowed it to enter the ship. Even more slowly, it adjusted its position until the slip hung in the middle of the laboratory cabin. The only way to move the slip during study was to move the ship itself. This odd way to manipulate the research subject posed some challenges near the beginning, but luckily, Revelation was originally designed to investigate small space objects in the Kuiper Belt and possessed excellent maneuverability. The gravitational wave antenna was equipped with twelve high-precision thrusters. After the ship’s AI grew used to the necessary adjustments, the manipulation became quick and precise. If the world could not affect the slip in any way, the only solution was to let the world surround the slip and move about it.

Thus, an odd sight came to be: The slip was located in the center of Revelation, but the ship had no dynamical connection to the slip. The two simply happened to occupy the same space as both moved toward the Solar System at the same velocity.

Inside the spaceship, due to the stronger background light, the transparency of the slip became more obvious. It now no longer resembled a slip of paper, but some transparent film that only indicated its presence by the faint light it emitted. People continued to refer to it as a paper slip, however. When the ambient light was very strong, it was sometimes possible to lose sight of it, so the researchers had to dim the lights in the laboratory to see the slip better.

The first thing the researchers tried to do was to ascertain the slip’s mass. The only applicable method was to measure the gravity it generated. However, even at the highest precision level, the gravity meter showed nothing, suggesting that the slip’s mass was extremely small, perhaps even zero. Based on the latter possibility, some guessed that the object might be a photon or neutrino in macro form, but its geometric shape suggested that it was artificial.

No progress could be made on analysis of the slip because electromagnetic waves of all wavelengths passed through it without diffraction. Magnetic fields, no matter how strong, seemed to have no effect on it. The object appeared to have no internal structure.

Twenty hours later, the exploratory team still knew next to nothing about the slip. They were able to observe one thing, however: The intensity of the light and gravitational waves emitted by the slip was decreasing. This suggested that the light and gravitational waves it emitted were probably a form of evaporation. Since these two were the only indication of the existence of the slip, their disappearance would be the same as the disappearance of the slip itself.

The base informed the exploratory team that Tomorrow, a large science vessel, had left the Neptune city cluster and would meet the expedition in seven days’ time. Tomorrow possessed more advanced investigative instruments, and could study the slip in more depth.

As they became more used to the slip, the crew on Revelation became less guarded and were no longer so careful about keeping a respectful distance from it. They knew that the object did not interact with the real world and emitted no harmful radiation. They touched it casually, allowing it to pass through their bodies. Someone even let the plane pass through his eyes and brain, asking a friend to take a picture of the sight.

白 Ice was enraged when he saw this. “Stop it! This is not some joke,” he screamed. Having worked nonstop in the lab for more than twenty hours, he left the laboratory and returned to his own cabin.

白 Ice turned off the light in his cabin and tried to go to sleep. But in the darkness he felt uneasy; he imagined the paper slip would float into his cabin, glowing white, at any moment. So he turned on the light and drifted in the gentle light and memories.

One hundred and ninety-two years had passed since he said good-bye to his teacher for the last time.

It was dusk, and he and Ding Yi and he had come to the surface from the underground city and taken a car into the desert. Ding Yi liked to stroll and think in the desert, and even to hold his lectures there sometimes. His students hated the experience, but he explained his eccentric habit this way: “I like desolate places. Life is a distraction for physics.”

The weather that day was good. There was no wind and no sandstorms, and the early spring air smelled fresh. The two of them, teacher and student, lay against a dune. The desert of Northern China was bathed in the light of the setting sun. Normally, Bai Aisi thought of these rolling dunes as a woman’s body—possibly a comparison that had originated with Ding Yi himself—but now he thought of them as an exposed brain. In the golden dusk, the brain revealed its profusion of grooves and folds. He looked up at the sky. Today, the dusty air managed to let through a bit of long-missed blue, like a mind about to be enlightened.

Ding Yi said, “Aisi, I want to tell you a few things that you should not repeat to others. Even if I don’t return, don’t tell others. There’s no special reason. I just don’t want to be laughed at.”

“Professor Ding, why not wait until you’re back to tell me?”

Bai Aisi wasn’t trying to comfort Ding Yi. He was sincere. He was still drunk with the ecstasy and vision of humanity’s imminent great victory over the Trisolaran fleet, and he did not think Ding Yi’s trip to the droplet would involve much danger.

“Answer a question first, please.” Ding Yi ignored Bai Aisi’s question and pointed at the desert lit by the westering sun. “Forget about the uncertainty principle for a minute and suppose everything is determinable. If you know the initial conditions, you can calculate and derive the conditions at any later point in time. Suppose an extraterrestrial scientist were given all data about the Earth several billion years ago. Do you think it could predict the existence of this desert solely through calculation?”

Bai Aisi pondered this. “No. This desert wasn’t the result of the Earth’s natural evolution, but the result of man-made forces. The behavior of civilizations can’t be grasped through the laws of physics.”

“Very good. Then why do we and our colleagues all want to try to explain the conditions of today’s cosmos, and to predict its future, solely through deductions based on the laws of physics?”

Ding Yi’s words surprised Bai Aisi. The man had never revealed such thoughts in the past.

Bai Aisi said, “I think that’s beyond physics. The goal of physics is to discover the fundamental laws of nature. Although the man-made desertification of the Earth could not be calculated directly from physics, it still follows laws. Universal laws are constant.”

“Heh heh heh heh.” Ding Yi’s laugh was not joyous at all. As he recalled it later, Bai Aisi thought it was the most sinister laughter he had ever heard. There was a hint of masochistic pleasure, an excitement at seeing everything falling into the abyss, an attempt to use joy as a cover for terror, until terror itself became an indulgence. “Your last sentence! I’ve often comforted myself this way. I’ve always forced myself to believe that there’s at least one table at this banquet filled with dishes that remain fucking untouched…. I tell myself that again and again. And I’m going to say it one more time before I die.”

Bai Aisi thought Ding Yi’s mind was elsewhere and that he talked as if he were dreaming. He didn’t know what to say.

Ding Yi continued, “At the beginning of the crisis, when the sophons were interfering with the particle accelerators, a few people committed suicide. At the time, I thought what they did made no sense. Theoreticians should be excited by such experimental data! But now I understand. Those people knew more than I did. Take Yang Dong, for instance. She knew much more than I did, and thought further. She probably knew things we don’t even know now. Do you think only sophons create illusions? Do you think the only illusions exist in the particle accelerator terminals? Do you think the rest of the universe is as pure as a virgin, waiting for us to explore? Too bad that she left with everything she knew.”

“If she had talked with you more back then, perhaps she wouldn’t have chosen to go.”

“Perhaps I would have gone with her.”

Ding Yi dug a pit in the sand and watched as the sand on the rim flowed back in like a waterfall. “If I don’t come back, everything in my room is yours. I know that you’ve always liked those Common Era things I brought.”

“That’s true, especially those tobacco pipes…. But I don’t think I’ll get them.”

“I hope you’re right. I also have some money—”

“Please, Professor!”

“I want you to use it to pay for hibernation. The longer the better—of course, that’s assuming you want to. I have two goals in mind: One, I want you to go look at the endgame for me—the endgame for physics. Two… how do I say this? I don’t want you to waste your life. After others have decided that physics actually exists, there will still be plenty of time for you to go do physics.”

“That… seems like something Yang Dong would say.”

“Maybe it’s not nonsense.”

Bai Aisi noticed that the pit Ding Yi had dug in the desert was rapidly expanding. They stood up and backed away as the pit continued to grow, getting deeper as well as wider. Soon, the bottom disappeared in shadows. Sand flooded into the pit in torrents, and soon, the diameter of the pit was close to a hundred meters, and a nearby dune was swallowed up. Bai Aisi ran toward the car and got into the driver’s seat; Ding Yi followed into the passenger seat. Bai Aisi noticed that the car was moving slowly toward the pit, dragged along by the sand underneath. He turned on the engine and the wheels began to turn, but the car continued to slide backwards.

Ding Yi laughed that sinister laugh again. “Heh heh heh heh… ”

Bai Aisi turned the electric motor to the highest setting and the wheels spun madly, throwing up sand everywhere. But the car still moved toward the pit like a plate pulled along on a tablecloth.

“Niagara Falls! Heh heh heh heh…”

Bai Aisi looked back and saw a sight that made his blood curdle: The pit now took up his entire field of vision. The whole desert was swallowed up by it, and the world was like a giant pit whose bottom was an abyss. At the rim, flowing sand poured in and formed a spectacular yellow sandfall. Ding Yi wasn’t exactly right in his description: The Niagara Falls were minuscule compared to this sandfall of terror. The sandfall extended from the near edge of the pit all the way to the far edge on the horizon, forming an immense sandfall ring. The sand torrents rumbled as if the world itself were coming apart. The car continued to slide toward the pit, faster and faster. Bai Aisi floored the accelerator and leaned his weight into it, but there was no effect.

“You fool. Do you really think we can escape?” Ding Yi said while still laughing sinisterly. “Escape velocity! Why don’t you calculate the escape velocity? Are you thinking with your butt? Heh heh heh heh…”

The car tumbled over the rim and dropped in the sandfall. The sand raining down around them seemed to stop as everything plunged into the abyss. Bai Aisi screamed with utter terror, but he couldn’t hear himself. All he heard was Ding Yi’s wild laughter.

“Hahahahaha… There’s no table untouched at the dinner party, and there’s no virgin untouched in the universe… waheeheeheehee… wahahahaha…”

白 Ice woke from his nightmare and found himself covered in cold sweat. Around him, more droplets of sweat hung suspended in air. He floated for a while, his body stiff, and then dashed out of his cabin and headed for Vasilenko’s cabin. It took a while before the door opened, as Vasilenko was also sleeping.

“General! Do not keep that thing, that thing they call a slip of paper, in the spaceship! No, I mean, don’t allow Revelation to hover around it. We should leave immediately, and get as far away as possible!”

“What have you discovered?”

“Nothing. It’s my intuition.”

“You don’t look so good. Exhaustion? I think you’re worrying too much. That thing… I don’t think it’s anything. There’s nothing inside. It should be harmless.”

白 Ice grabbed Vasilenko by the shoulders and gazed into his eyes. “Don’t be arrogant!”

“What?”

“Don’t be arrogant. Weakness and ignorance are not barriers to survival, but arrogance is. Remember the droplet!”

白 Ice’s last sentence had an effect. Vasilenko stared at him in silence for a few seconds, then nodded slowly. “All right, Dr. Bai, I’ll listen to you. Revelation will depart from the slip and back off one thousand kilometers. We’ll leave just a pinnace to monitor it…. Maybe two thousand kilometers?”

白 Ice let Vasilenko go and wiped his forehead. “You decide. I suggest, the farther the better. I will write a formal report as soon as possible and let Command know of my theories.” Stumbling, he drifted away.

Revelation left the slip. It passed through the ship’s hull and was reexposed to space. Since the background was dark again, it once again appeared to be an opaque white slip of paper. Revelation pulled away from the slip until the two were about two thousand kilometers apart, then continued to sail in parallel, waiting for the arrival of Tomorrow. A pinnace with a crew of two stayed about ten meters from the slip to monitor it continuously.

The gravitational waves emitted by the paper slip continued to diminish, and its light gradually dimmed.

On Revelation, 白 Ice shut himself in the laboratory. Around him, he set up more than a dozen information windows, all connected to the ship’s quantum computer, which was carrying out massive computations. The windows were packed with equations, curves, and matrices. Surrounded by the windows, 白 Ice was anxious and irritable, like a trapped animal.

Fifty hours after the separation from Revelation, the gravitational wave emitted from the paper slip disappeared completely. The white light from it blinked twice and also went out. The slip of paper was gone.

“Has it evaporated?” Vasilenko asked.

“I don’t think so. But we can’t see it anymore.” 白 Ice shook his head wearily and closed the information windows around him one by one.

After another hour during which no signs of the slip could be detected, Vasilenko ordered the pinnace to return to Revelation. But the two crew members on duty in the pinnace didn’t acknowledge the order; the radio only transmitted a hurried conversation between them.

“Look out below! What’s going on?”

“It’s rising!”

“Don’t touch it! Get out!!”

“My leg! Ahhh—”

After the scream, the monitoring terminal on Revelation showed one of the crew members leaving the pinnace and activating the thrusters on his space suit in an attempt to escape. They saw a bright light; the source was the bottom of the pinnace, which was melting! The pinnace looked like a scoop of ice cream dropped onto a scalding sheet of glass: The bottom was melting and spreading in every direction. The “glass” was invisible, and the plane’s existence was indicated only by the spreading pool of melted pinnace material. The pool spread into an extremely thin sheet and emitted bewitching, colorful lights, like fireworks scattered through a sheet of glass.

The escaped crewman flew some distance but seemed to be pulled by gravity toward that plane marked by the melted pinnace. His feet touched the plane and immediately melted into a shiny puddle. The rest of his body also began to spread out on the plane, and he had time only for a scream that was abruptly cut off.

“All hands to hypergravitation seats! Full Ahead!”

As soon as he saw the escaping crewman’s feet touch the invisible plane, Vasilenko gave the order. Revelation wasn’t a stellar ship, so when it engaged in Full Ahead acceleration, the crew did not need to enter into the protective deep-sea state. But the hypergravity was enough to sink everyone deep into their seats. Since the order was given in such a hurry, a few couldn’t get to their seats in time and fell to the stern of the ship with injuries. Revelation’s exhaust nozzles emitted a plasma stream several kilometers long that pierced the dark night of space. Far in the distance, where the pinnace was still melting, they could see the phosphorescent glow like will-o’-the-wisps in the wilderness.

From the zoomed-in view on the monitoring terminal, they could see that only the very top part of the pinnace was left, and that too soon disappeared into the brilliant plane. The body of the dead crewman was also diffused into the plane, showing up as a gigantic, man-shaped glow. His body had been transformed into a slice on the plane without thickness. Though large in area, it had no volume.

“We’re not moving,” the pilot of Revelation said. He had trouble talking through the hypergravity. “The ship isn’t accelerating.”

“What are you babbling about?” Vasilenko wanted to shout, but the hypergravity turned it into a whisper.

It really did seem as if the pilot should have been wrong. Everyone on the ship was pressed against their seat by hypergravity, which indicated that the ship was in the process of extreme acceleration. It was visually impossible for a passenger to tell whether the ship was moving in space because all celestial bodies that could act as reference points were too far away, so they couldn’t see parallax in a short time frame. However, the ship’s navigation system could detect even tiny amounts of motion and acceleration; it couldn’t be wrong.

Revelation was under hypergravity, but had no acceleration. Some force had nailed it to this point in space.

“There is acceleration,” said 白 Ice weakly. “But the space in this region is flowing in the opposite direction, thus canceling out our motion.”

“The space is flowing? Where to?”

“There, of course.”

白 Ice couldn’t lift his hand, which was now too heavy. But everyone knew where he meant. Revelation sank into a deathlike silence. Normally, hypergravity made people feel safe, as though they were escaping from danger under the embrace of some protective power. But now it seemed as oppressive and suffocating as a tomb.

“Open a channel to Command,” 白 Ice said. “There’s no time, so we’ll treat this as our formal report.”

“Channel open.”

“General, you once said, ‘I don’t think it’s anything. There’s nothing inside.’ You were right. That slip really wasn’t anything, and contained nothing. It’s only space, just like the space around us, which isn’t anything and contains nothing. But there’s a difference: It’s two-dimensional. It’s not a block, but a slice. A slice without thickness.”

“Hadn’t it evaporated?”

“The protective field around it evaporated. The force field acted like packaging that separated the two-dimensional space from the three-dimensional space. But now the two are in direct contact. Do you remember what Blue Space and Gravity saw?”

No one answered, but they all remembered: the four-dimensional space falling into three dimensions, like a waterfall off a cliff.

“Just as four-dimensional space collapses into three dimensions, three-dimensional space can collapse into two dimensions, with one dimension folding and curling into the quantum realm. The area of that slice of two-dimensional space—it only has area—will rapidly expand, causing more space to collapse…. We’re now in space that is falling toward two dimensions, and ultimately, the entire Solar System will follow. In other words, the Solar System will turn into a painting with no thickness.”

“Can we escape it?”

“Escaping this is like rowing a boat above a waterfall. Unless we exceed a certain escape velocity, we’ll tumble over the cliff. It’s like tossing a pebble up from the ground: No matter how high you throw the rock, it will eventually fall back down. The entire Solar System is within the zone of collapse, and anyone trying to escape must reach escape velocity.”

“What is the escape velocity?”

“I’ve computed it four separate times. Pretty sure I got it right.”

“What is it?!”

Everyone aboard Revelation and Alaska held their breaths and listened to this final calculation as representatives of humanity.

白 Ice calmly announced his judgment. “Lightspeed.”

The navigation system showed that Revelation was now moving in the opposite direction from its heading. It started by moving slowly toward the two-dimensional space, but gradually accelerated. The ship’s drive was still powering Full Ahead. This would at least slow down the rate of the ship’s fall and delay the inevitable.

On the plane two thousand kilometers away, the light emitted by the two-dimensionalized pinnace and crewmen had already gone out. Compared to collapsing from four dimensions to three, the fall from three dimensions to two gave off much less energy. Two two-dimensional structures were revealed clearly by the starlight. On the two-dimensionalized pinnace, it was possible to see the details of three-dimensional structures unfolded in two dimensions—the crew cabin, the fusion reactor, and so on—as well as the curled-up figure of the crewman in the cabin. In the figure of the other crewman, the bones and blood vessels could be clearly discerned, as well as all the body parts. During the process of falling into two dimensions, every point on a three-dimensional object was projected onto the plane in accordance with precise geometric principles, and so these two figures turned out to be the most complete and precise images of the original three-dimensional pinnace and people. All the internal structures were now laid out side by side in two dimensions with nothing hidden. The projection process, however, was very different from that used in engineering drawings, and so it was difficult to visually reimagine the shapes’ original three-dimensional structure. The greatest difference from engineering drawings lay in the fact that the two-dimensional unfolding occurred at every scale: All the original three-dimensional structures and details were laid out in parallel in two dimensions, and the result replicated, in some measure, the effect of viewing the three-dimensional world from four-dimensional space. This closely resembled drawings of fractals: No matter how much you zoomed in on a part of the image, it would get no less complex. However, fractals were theoretical concepts—actual representations were inevitably limited by the resolution, and after zooming in a number of times, the images lost their fractal nature. The complexity of the two-dimensionalized three-dimensional objects, on the other hand, was real: The resolution was at the level of fundamental particles. On the monitoring terminal of Revelation, the eye could only see a limited resolution, but the complexity and number of details already made the viewers dizzy. This was the universe’s most complicated image; staring at it for too long would drive one mad.

Of course, the pinnace and the crewmen no longer possessed any thickness.

It was unclear how large the plane had spread by now; only those two images indicated its presence.

Revelation slid faster toward the plane, toward that abyss whose thickness was zero.

“Everyone, don’t be sad. No one will be able to escape from the Solar System, not even a bacteria or virus. All of us will become a part of this grand picture.” 白 Ice now looked calm and stoic.

“Stop accelerating,” said Vasilenko. “What difference does a few minutes make? Let’s at least breathe easier at the end.”

Revelation’s engine shut off. The plasma column at the stern of the ship disappeared, and the ship drifted, powerless, in space. In reality, the ship was still accelerating toward the two-dimensional patch of space, but since the ship moved along with the surrounding space, those inside could not feel any gravity from acceleration. They enjoyed the weightlessness and took deep breaths.

“You know what I’m thinking of? Needle-Eye’s pictures from Yun Tianming’s fairy tales,” 白 Ice said.

Only a few people aboard Revelation knew about Yun Tianming’s secret message. Now, in a flash, they all understood the meaning of this detail in the stories. It was a simple metaphor, and there were no bearing coordinates because it was so direct. Yun must have thought he was taking a great risk to put such an obvious metaphor into his stories, yet he had to try because the message was so important.

He probably thought that with the knowledge of Blue Space and Gravity’s discoveries, humanity would understand the metaphor. Unfortunately, he had overestimated their ability to comprehend.

The inability to decipher this key piece of information led humanity to place all their hopes in the Bunker Project.

It was true that both dark forest strikes humans had witnessed involved photoids, but they ignored a salient fact: Those two target planetary systems were structured differently from the Solar System. The star known as 187J3X1 had three giant Jupiter-like planets, but they all orbited extremely close to their sun. Their average distance from the sun was but 3 percent of the distance from Jupiter to the Sun, even closer than Mercury’s orbit. Since they almost brushed up against their sun, the solar explosion destroyed them completely, and they could not have been used as barriers. The Trisolaran system, on the other hand, had only one planet, Trisolaris.

The structure of the planetary system around a star was a characteristic observable from a distance. For a sufficiently advanced civilization, a quick glance was sufficient.

If humans could figure out the plan to use the gas giants as barriers, couldn’t observers from such advanced civilizations do so, as well?

Weakness and ignorance are not barriers to survival, but arrogance is.

Revelation was now no more than a thousand kilometers from the plane; it fell faster and faster.

“Thank you, everyone, for doing your duty. Although we haven’t been together long, we worked together well,” Vasilenko said.

“I also thank every member of the human race,” said 白 Ice. “Once, we lived together in the Solar System.”

Revelation fell into the two-dimensional space. In a few seconds, it was flattened. Light akin to fireworks once again lit up the darkness of space. This was a vast two-dimensional image that could be clearly seen from Alaska, a hundred thousand kilometers away. It was possible to distinguish every individual on Revelation: They were laid out side by side, holding hands, every single cell in their body exposed to space in two dimensions.

They were the first to be painted into this grand painting of annihilation.

Bunker Era, Year 68 Pluto

“Let’s head back to the Earth,” Cheng Xin said softly. This was the first idea that floated up through the chaos and darkness of her jumbled thoughts.

“The Earth is not a bad place to wait for the end. A falling leaf seeks to return to the root. But we hope Halo will go to Pluto,” Cao Bin said.

“Pluto?”

“Pluto is at its apogee, rather far from the two-dimensional space. The Federation Government is about to issue a formal attack alert to the world, and many ships will be headed there. Although the final result will be the same, at least there will be more time left.”

“How much longer?”

“The entire Solar System within the Kuiper Belt will collapse into two dimensions in eight to ten days.”

“That’s not long enough to be worth worrying about. Let’s go back to Earth,” said AA.

“The Federation Government would like to ask you to do something.”

“What can we possibly do now?”

“Not anything important. There’s nothing important now. But someone came up with the idea that theoretically, there might exist image-processing software that could process a two-dimensionalized image of a three-dimensional object and re-create the three-dimensional object. We hope that in the distant future, some intelligent civilization might re-create a three-dimensional representation of our world from its two-dimensionalized image. Though it would be nothing more than a dead representation, at least human civilization would not be forgotten.

“The Earth Civilization Museum is on Pluto. A large portion of humanity’s precious artifacts are stored there. The museum is buried under the surface, however, and we are concerned that during the process of falling into the plane, these artifacts would be mixed together with the strata of the crust and their structures would be damaged. We’d like to ask you to carry some of the artifacts away from Pluto on Halo and scatter them in space so that they can fall into two dimensions separately. This way, their structures would be preserved without harm in two dimensions. I guess this counts as a kind of rescue mission…. Of course, I admit that the idea is nearly science fiction, but doing something now is better than doing nothing.

“Also, Luo Ji is on Pluto. He wants to see you.”

“Luo Ji? He’s alive?!” AA cried out.

“Yes. He’s almost two hundred.”

“All right. Let’s go to Pluto,” Cheng Xin said. In the past, this would have been an extraordinary journey. But now, nothing mattered.

A pleasant male voice spoke up. “Do you wish to go to Pluto?”

“Who are you?” asked AA.

“I’m Halo, or Halo’s AI. Do you wish to go to Pluto?”

“Yes. What do we do?”

“You just have to confirm the request. There’s no need to do anything. I will complete the voyage for you.”

“Yes, we want to go to Pluto.”

“Authorization confirmed. Processing. Halo will accelerate at 1G in three minutes. Please pay attention to the direction of gravity.”

Cao Bin said, “Good. Better leave early. After the attack alert is issued, there might be total mayhem. Hopefully we’ll get a chance to talk again.” He closed the window link before AA and Cheng Xin could say good-bye. At this moment, AA, Cheng Xin, and Halo were not his top priorities.

Outside the porthole, they could see a few blue reflections appearing on the shell of the combined city—reflections of Halo’s nozzle lights. Cheng Xin and AA fell to one side of the spherical hall and felt their bodies grow heavier. The acceleration soon reached 1G. After the two of them—still weak from hibernation—struggled up and looked outside the porthole again, they saw the entirety of Jupiter. It was still immense, and shrinking at too slow a rate to be perceived.

The ship’s AI led AA and Cheng Xin on a tour of the ship to familiarize them with it. Like its predecessor, this new Halo was still a small stellar yacht with a maximum capacity of four. Most of the space on the ship was taken up by the ecological cycling system. By conventional measures, the ecological cycling system was extremely redundant—a volume of space that would have supported forty was used to provide for only four. The system was divided into four identical subsystems, linked together and acting as each other’s backups. If any of the four failed accidentally, the other three could bring it back to life. Halo’s other distinguishing characteristic was the ability to land directly on a medium-sized solid planet. This was a rare design choice among stellar ships—similar ships typically used shuttles to carry landing parties onto planets. Directly descending into a planet’s deep gravity well required the ship to have a very strong hull, which greatly increased the cost. Moreover, the need for atmospheric flight required a streamlined profile, which was also very rare among stellar ships. All of these design features meant that if Halo could find another Earthlike planet in outer space, it could act as a habitable base for the crew on the surface of the planet for a considerable amount of time. Maybe it was these characteristics of Halo that led to it being chosen for the artifact-rescuing mission to Pluto.

There were numerous other unusual features on the yacht. For instance, it had six small courtyards, each about twenty to thirty square meters in size. Each courtyard automatically adjusted to the direction of gravity under acceleration, and, during coasting, spun independently within the ship to generate artificial gravity. Each courtyard displayed a different natural scene: a green lawn with a babbling brook running through the grass; a small copse with a spring in the middle; a beach with waves of clear water throwing up surf…. These scenes were small but exquisite, like a string of pearls made of the best parts of the Earth. On a small stellar spaceship, such a design was extremely luxurious.

Cheng Xin felt both distressed and sorry for Halo. Such a perfect little world was soon going to be turned into a slice without thickness. She tried to avoid thinking about those other grander things facing imminent destruction—annihilation covered the sky of her thoughts like a giant pair of black wings, and she dared not look directly up at it.

Two hours after departure, Halo received the formal dark forest attack alert issued by the Solar System Federation Government. The president, a beautiful woman who looked very young, made the announcement. She stood in front of the blue flag of the Federation and spoke without expression. Cheng Xin noticed that the blue flag resembled the ancient UN flag, though a diagram of the Sun replaced the diagram of the Earth. This most important document, marking the end of human history, was very short:

Five hours ago, the advance warning system confirmed that a dark forest strike has been initiated against our world.

The attack takes the form of a dimensional strike, which will collapse the space around the Solar System from three dimensions to two dimensions. The result will be the complete destruction of all life.

The process is estimated to take eight to ten days. At this moment, the collapse is ongoing and the rate and extent of collapse are rapidly growing.

We have confirmed that the escape velocity for the collapsing region is the speed of light.

An hour ago, the Federation Government and Parliament have passed a new resolution that repeals all laws regarding Escapism. However, the government wishes to remind all citizens that the escape velocity far exceeds the maximum velocity of all human space vehicles. The probability of a successful escape is zero.

The Federation Government, Parliament, the Supreme Court, and Federation Fleet will carry out their duties until the end.

AA and Cheng Xin didn’t bother to watch more news. It was possible that, just like Cao Bin said, the Bunker World had approached paradise. They wanted to see what paradise looked like, but they didn’t dare look. If everything was heading toward ruination, the more beautiful it all was, the more pain they would suffer. In any event, it was a paradise that was collapsing in the terror of death.

Halo stopped accelerating. Behind it, Jupiter became a small yellow dot. The next few days of the voyage were spent in the uninterrupted slumber produced by the sleep-aid machine. In this lonely voyage through the night before the end, just the unstoppable mad imaginings were enough to make anyone fall apart.

Halo’s AI awakened AA and Cheng Xin from their dreamless sleep as the ship reached Pluto.

Out of the porthole and on the monitor they could see the entirety of Pluto. Their initial impression of the dwarf planet was one of darkness, like an eye that remained perpetually shut. This far from the Sun, the light was extremely dim. Only when Halo entered low orbit could they see the colors on the surface of the planet: Pluto’s crust appeared to be made of patches of blue and black. The black was rocks—not necessarily black in color, but the light was too dim to tell otherwise. The blue was solidified nitrogen and methane. Two centuries ago, when Pluto had been near its perigee and inside Neptune’s orbit, the surface would have looked completely different. The ice cover would have partially melted and produced a thin atmosphere. From the distance, it would have appeared a deep yellow.

Halo continued to descend. On Earth, this would have involved a soul-stirring atmospheric reentry, but Halo continued to fly through the silent vacuum, decelerating by the power of its own thrusters. On the blue-black ground below, an attention-grabbing line of white text appeared:

EARTH CIVILIZATION

The text was written in the modern script that mixed Latin and Chinese elements. After it, there were a few more lines of smaller text repeating the same thing in different scripts. Cheng Xin noticed that none of them said “museum.” The yacht was still about one hundred kilometers above the surface, which meant that the text was gigantic. Cheng Xin couldn’t make an exact estimate of the size of the characters, but she was certain that these were the largest written characters ever produced by humankind, each big enough to contain a city. By the time Halo was only about ten thousand meters above the surface, one of the large characters took up the entire field of view. Finally, Halo touched down on the broad landing field, which was the topmost dot in the Chinese character qiu (球), a part of the word Earth.

With the guidance of the ship’s AI, Cheng Xin and AA put on light space suits and exited Halo onto the surface of Pluto. Given the frigid surroundings, the heating systems in their space suits were operating at maximum power. The landing field was empty, white, and seemed to phosphoresce in the starlight. The numerous burn marks left on the ground indicated that many spacecraft had once landed and taken off here, but Halo was the only ship here now.

During the Bunker Era, Pluto was akin to Antarctica on ancient Earth. No one lived here permanently, and few came to visit.

In the sky, a black sphere moved rapidly among the stars. It was large, but the surface was shrouded in darkness: Charon, Pluto’s moon. Its mass was a tenth of Pluto’s, and the two almost formed a double-planet system, revolving around a common center of mass.

Halo turned on its searchlights. Due to the lack of atmosphere, there wasn’t a visible beam of light. It cast a circle of light on a distant rectangular object. This black monolith was the only protrusion above the white ground. It gave off an eerie sense of simplicity, as though it was an abstraction of the real world.

“That looks a bit familiar,” Cheng Xin said.

“I don’t know what it is, but I don’t have a good feeling about it.”

Cheng Xin and AA headed for the monolith. Pluto’s gravity was only one-tenth of the Earth’s, and so they proceeded by leaping. Along the way, they noticed a row of arrows pointing toward the monolith on the ground. Only when they reached the monolith did its immensity impress itself on their minds. When they looked up, it was as though a chunk had been taken out of the starry sky. They looked around and saw that there were rows of arrows coming from other directions, all pointing toward the monolith. At the foot of the monolith was another prominent protuberance: a metal wheel about a meter in diameter. To their surprise, they found the wheel to be hand-operated. Above the wheel was a diagram formed from white lines against the black surface of the monolith. Two curved arrows indicated the directions in which the wheel could be turned. Next to one of the arrows was a drawing of a half-open door, while the other bore a drawing of a shut door. Cheng Xin turned to survey the arrows on the ground pointing to the monolith. All the simple, clear, wordless instructions gave her a strange feeling, which AA voiced.

“These things… I don’t think they’re intended for humans.”

They turned the wheel clockwise. The wheel was stiff, but eventually a door opened in the surface of the monolith. Some gas escaped, and the water vapor within quickly deposited into ice crystals that glinted in the searchlight. They entered the door and saw another door facing them, also operated by a wheel. This time, there were simple written instructions above the wheel, informing them that they were in an air lock and needed to close the first door before opening the second. This was unusual, since as early as the end of the Crisis Era, pressurized buildings could open their doors directly to vacuum without needing an air lock.

Cheng Xin and AA turned the wheel on the inside of the door they had entered to shut it. The searchlight was cut off. They were about to turn on the lights on their space suits to hold off the terror of darkness when they noticed a small lamp in the ceiling of the narrow air lock. This was the first sign they had seen of electricity. They began to turn the wheel to open the second door. Cheng Xin was certain that even if they hadn’t closed the first door, they would still have been able to open the second. The only thing that prevented air from leaking was following the instructions. In this low-technology environment, there was no automatic mechanism to prevent errors.

The rush of air almost toppled them, and the rapidly warming temperature fogged their visors. But the space suits told them that the external air pressure and composition was breathable; they could open their helmets.

They saw a tunnel lit by a series of dim lamps heading into the earth. The dark walls of the tunnel swallowed up the dim light they emitted so that, between the cones of light, all was darkness. The floor of the tunnel was a smooth incline. Although the angle was steep, close to forty-five degrees, there were no stairs. This design was probably motivated by two considerations: There was no need for stairs in low gravity, or the path wasn’t meant for humans.

“There’s no elevator?” AA asked. She was frightened by the steep way down.

“An elevator might break down over time. This building was intended to last through geologic eons.” The voice came from the other end of the tunnel, where an old man appeared. In the dim light, his long white hair and beard floated in the low gravity. They seemed to be giving off their own light.

“Are you Luo Ji?” AA shouted.

“Who else? Children, my legs don’t work so well anymore, so forgive me for not coming up to meet you. Come on down by yourselves.”

Cheng Xin and AA descended the incline in leaps. Due to the low gravity, this wasn’t a very dangerous maneuver. As they approached the old man, they saw that he was indeed Luo Ji. He wore a long white changshan, a Chinese-style robe, and leaned against a cane. His back was slightly bowed, but his voice was hale and loud.

At the bottom of the incline, Cheng Xin bowed deeply. “Honored Elder, hello.”

“Haha, there’s no need for that.” Luo Ji waved his hands. “We used to be… colleagues.” He looked at Cheng Xin and in his eyes was a surprised delight that almost seemed incongruent with his age. “You’re still so young. There was a time when I saw you only as the Swordholder, and then, gradually, you became a lovely young woman. Haha….”

In Cheng Xin’s and AA’s eyes, Luo Ji had also changed. The stately Swordholder was gone. They didn’t know that the cynical, playful Luo Ji in front of them now was a return to the Luo Ji from four centuries ago, before he had become a Wallfacer. That Luo Ji had returned, as if awakening from hibernation, but the passage of time had moderated him, and filled him with more transcendence.

“Do you know what has happened?” AA asked.

“Of course, child.” He pointed behind him with his cane. “Those idiots all left on spaceships. They knew that they ultimately couldn’t escape, but they still tried to run. Foolish.”

He meant the other workers in the Earth Civilization Museum.

“You and I have both busied ourselves for nothing,” said Luo Ji to Cheng Xin.

It took Cheng Xin a bit of time before she understood what he meant, but the flood of emotions and memories was interrupted by Luo Ji’s next words. “Forget it. Carpe diem has always been the right path. Of course there’s not much diem now for carpe, but we need not look for trouble. Let’s go. You don’t need to help support me. You haven’t even learned how to walk properly around here yet.”

Given Luo Ji’s advanced age of two hundred, the difficulty of locomotion under such low gravity wasn’t moving too slow, but too fast. The cane wasn’t so much a support as a decelerator.

After a while, space opened up before them. Cheng Xin and AA realized that they were now in a much wider and bigger tunnel—a cavern, really. The ceiling was high above, but the space was still only lit by a dim row of lights. The cavern looked very long, and the other end was not visible.

“This is the main body of the museum,” Luo Ji said.

“Where are the artifacts?”

“In the halls down at the other end. Those aren’t so important. How long can they keep? Ten thousand years? A hundred thousand years? A million, at the most. Practically all of them will have turned to dust by then. But these—” Luo Ji pointed around them. “—were intended to be preserved for hundreds of millions of years. Why, do you still think this is a museum? No, no one visits here. This is not a place for visitors. All of this is but a tombstone—humankind’s tombstone.”

Cheng Xin looked around the empty, dim cavern and thought back to all she had seen. Indeed, everything was filled with hints of death.

“How did such an idea come up?” AA looked all around.

“You ask that because you’re too young.” Luo Ji pointed to Cheng Xin and himself. “During our time, people often planned for their own gravesites while they were still alive. Finding a graveyard for humanity isn’t so easy, but erecting a tombstone is doable.” He turned to Cheng Xin. “Do you remember Secretary General Say?”

Cheng Xin nodded. “Of course.”

Four centuries ago, while she had worked for the PIA, Cheng Xin had met Say, the UN secretary general, a few times at various meetings. The last time was at a PIA briefing. Wade was there, too. On a big screen, Cheng Xin had given Say a PowerPoint presentation about the Staircase Project. Say had sat there quietly and listened to the whole thing without asking any questions. Afterwards, Say walked next to Cheng Xin, leaned in, and whispered, “We need more people to think like you.”

“She was a true visionary. I’ve thought of her often through the years. Could she really have died almost four hundred years ago?” Luo Ji leaned on the cane with both hands and sighed. “She was the one who thought of this first. She wanted to do something so that humanity would leave behind a legacy that could be preserved for a long time after our civilization was gone. She planned an unmanned ship filled with cultural artifacts and information about us, but it was deemed a form of Escapism, and the project halted with her death. Three centuries later, after the Bunker Project began, people remembered it. That was a time when people worried that the world was going to end any moment. The new Federation Government decided to build a tombstone at the same time that the Bunker Project was built, but it was officially referred to as the Earth Civilization Museum so as not to be seen as a sign of pessimism. I was named the chair of the tombstone committee.

“At first, we engaged in a large research project to study how to preserve information across geologic eons. The initial benchmark was a billion years. Ha! A billion. Those idiots thought that would be easy—after all, if we could build the Bunker World, how difficult could this be? But they soon realized that modern quantum storage devices, while capable of storing a whole library in a grain of rice, could only preserve the information without loss for about two thousand years. After that, decay would make it impossible to decode. As a matter of fact, that only applied to the highest-quality storage devices. Two-thirds of more common varieties failed within five hundred years. This suddenly transformed the project from a detached, contemplative matter into an interesting practical problem. Five hundred years was real—you and I came from only four hundred years ago, right? So the government stopped all work on the museum and directed us to study how to back up important data about the modern world so that it could be read in five hundred years, heh heh…. Eventually, a special institute had to be set up to tackle the problem so that the rest of us could focus on the museum, or tombstone.

“Scientists realized that in terms of data longevity, storage devices from our time were better. They found some USB flash drives and hard drives from the Common Era and some still had recoverable data! Experiments showed that if these devices were of high quality, information was safe on them for about five thousand years. The optical disks from our era were especially resilient. When made from special metal, they could reliably preserve data for a hundred thousand years. But none of these were a match for printed material. Special ink printed on composite paper could be read in two hundred thousand years. But that was the limit. Our conventional data storage techniques could preserve information for two hundred thousand years, but we needed to get to a billion!

“We informed the government that, given current technology, preserving ten gigabytes of images and one gigabyte of text—that was the basic information requirement for the museum—for one billion years was impossible. They wouldn’t believe us, and we had to show them the evidence. Finally, they agreed to lower the requirement to one hundred million years.

“But this was still an extremely difficult task. We looked for information that had survived for such a long time. Patterns drawn on prehistoric pottery survived about ten thousand years. Cave paintings in Europe were from about forty thousand years ago. If you count the markings made on stones back when our ancestors, the hominids, made the first tools as information, then the earliest instances occurred during the Pliocene, two point five million years ago. And we did indeed find information left one hundred million years ago, though it wasn’t left by humans: dinosaur footprints.

“The research continued, but there was no progress. The other specialists had obviously reached conclusions, but they didn’t want to speak up. I told them, ‘Don’t worry about it. Whatever conclusions you’ve reached, no matter how bizarre or outrageous, we must accept them if there are no alternatives.’ I promised them that there was nothing that could be more bizarre and outrageous than what I’d gone through, and I would not laugh at them. So they told me that, according to the most advanced theories and techniques in every field, based on extensive theoretical research and experimentation, through analysis and comparison of multiple proposals, they did find a way to preserve information for about one hundred million years. And they emphasized that this was the only method known to be practicable. Which is—” Luo Ji lifted the cane over his head, and as his white hair and beard danced in the air, he resembled Moses parting the Red Sea. Solemnly, he intoned, “—carving words into stone.”

AA giggled. But Cheng Xin wasn’t laughing. She was stunned.

“Carving words into stone.” Luo Ji pointed at the walls of the cavern.

Cheng Xin walked to one of the walls. In the dim light, she saw that it was covered with dense, carved text, as well as images in relief. The wall was not the original rock, but seemed to have been infused with metal, or perhaps the surface had been coated with some durable titanium alloy or gold. Fundamentally, however, it was no different from carving words into stone. The carved text wasn’t small: each character or letter was about a square centimeter. This was another feature intended to help with information longevity, as smaller text tended to be harder to preserve.

“Of course, this approach meant that the information storage capacity was greatly reduced, leaving us with less than one-ten-thousandth of the planned amount. But they had no choice but to accept this limitation,” Luo Ji said.

“These lamps are really strange,” said AA.

Cheng Xin looked at the lamp on the cave wall. First, she noticed its shape: an arm poking out of the wall holding a torch. She thought this was a familiar design, but clearly that wasn’t what AA meant. The torch-shaped lamp seemed very clumsy. The size and structure resembled an ancient searchlight, but the light it emitted was very weak, about the same as an ancient twenty-watt incandescent light bulb. After passing through the thick lampshade, the light was not much brighter than a candle.

Luo Ji said, “Back that way is the machinery dedicated to providing electricity to this complex, like a power plant. This lamp is an amazing accomplishment. There’s no filament or excitable gas inside, and I don’t know what the luminous element is, but it can continue to glow for a hundred thousand years. The doors you came through should continue to be operable under normal conditions for five hundred thousand years. After that, the doors will deform and whoever wants to come in will have to break them down. By then, these lamps will have gone out more than four hundred thousand years earlier, and darkness will reign here. But that will be but the start of the journey of a hundred million years.”

Cheng Xin took off a space suit glove and caressed the characters carved into the cold stone. Then she leaned against the cave wall and stared woodenly at the lamps. She realized where she had seen this design: the Panthéon in Paris. A hand holding a torch just like the one on Rousseau’s tomb. The faint yellow lights before her now didn’t seem to be electric, but like tiny flames about to go out.

“You are not very talkative,” Luo Ji said. His voice was suffused with a solicitousness that Cheng Xin had long missed.

“She’s always been like that,” said AA.

“Ah, I used to love to talk, and then I forgot how. But now I’ve learned again. I can’t stop chattering, like a kid. I hope I’m not bothering you?”

Cheng Xin struggled to smile. “Not at all. It’s just that… looking at all this, I don’t know what to say.”

True. What was there to say? Civilization was like a mad dash that lasted five thousand years. Progress begot more progress; countless miracles gave birth to more miracles; humankind seemed to possess the power of gods; but in the end, the real power was wielded by time. Leaving behind a mark was tougher than creating a world. At the end of civilization, all they could do was the same thing they had done in the distant past, when humanity was but a babe:

Carving words into stone.

Cheng Xin examined the carvings on the wall carefully. They began with the relief carving of a man and a woman, perhaps an attempt to show future discoverers what humans looked like. But unlike the stiff bearing of the drawings of the man and woman on the metal plaque carried by the Pioneer probes during the Common Era, the two cave carvings were done with lively expressions and postures, evoking Adam and Eve.

Cheng Xin walked along the wall. After the man and the woman came some hieroglyphs and cuneiforms, probably copied from ancient artifacts—it was possible that some of them were not even intelligible to modern men and women, and if so, how would future extraterrestrial discoverers understand them? Going further, Cheng Xin saw Chinese poetry—or, at least, she could tell the carvings were poetry based on the arrangement of the characters. But she didn’t recognize any of the characters; she could only tell they were in Great Seal Script.

“That’s the Classic of Poetry, from a millennium before the time of Christ,” Luo Ji said. “If you keep on walking, you’ll see fragments of Classical Greek philosophy. To see letters and characters that you can read, you’ll have to walk tens of meters.”

Under the Greek letters, Cheng Xin saw another relief, which seemed to portray ancient scholars in simple robes debating in an agora surrounded by stone columns.

Cheng Xin had a strange idea. She turned back and looked near the beginning of the cave carvings, but didn’t find what she was looking for.

“You are looking for a Rosetta Stone?” Luo Ji asked.

“Yes. Isn’t there some system to help with interpretation?”

“Child, we’re talking about carving in stone, not a computer. How can we possibly fit something like that here?”

AA looked at the cave wall and then stared at Luo Ji. “You’re saying that we’ve carved things here that we don’t even understand with the hope that someday, some extraterrestrial will be able to read them?”

True, to the extraterrestrial discoverers of the far future, the human classics left on the walls here would probably resemble Linear A, Cretan hieroglyphics, and other ancient scripts that no one could read. Perhaps there was no realistic hope that anyone would. By the time the builders of this monument truly understood the power of time, they no longer believed that a vanished civilization could really leave behind any marks that would last through geologic eons. As Luo Ji had said, this wasn’t a museum.

A museum was built for visitors; a tombstone was built for the builders.

The three continued onward, and Luo Ji’s cane tapped along the ground rhythmically.

“I often stroll around here thinking my own crazy thoughts.” Luo Ji paused and pointed at a relief carving of an ancient soldier in armor and wielding a spear. “This is about the conquests of Alexander the Great. If he had kept on going a bit farther east, he would have encountered the Qin at the end of the Warring States Period—what would have happened then? And how would history have changed?” They walked some more, and he pointed at the cave wall again. By now, the characters carved on the wall had turned from Small Seal Script to Clerical Script. “Ah, we’ve reached the Han Dynasty. From here to later, China completed two unifications. Are a unified territory and a unified system of thought good things for civilization as a whole? The Han Dynasty ended up endorsing Confucianism above all, but if the multiplicity of schools of thinking during the Spring and Autumn Period had continued, what would have happened later? How would the present be different?” He waved his cane around in a circle. “At every moment in history, you can find endless missed opportunities.”

“Like life,” said Cheng Xin softly.

“Oh, no no no.” Luo Ji shook his head vigorously. “At least not for me. I don’t think I’ve missed anything, haha.” He looked at Cheng Xin. “Child, do you think you’ve missed out? Then don’t let opportunities go by again in the future.”

“There’s no future now,” said AA coldly. She wondered if Luo Ji was suffering from dementia.

They reached the end of the cave. Turning around to survey this underground tombstone, Luo Ji sighed. “We had designed this place to last a hundred million years, but it won’t even survive a hundred.”

“Who knows? Perhaps a flat two-dimensional civilization will be able to see all this,” said AA.

“Interesting! I hope you’re right…. Look, this is where the artifacts are kept. We have a total of three halls.”

Cheng Xin and AA saw space open up before them once more. The room they were in didn’t resemble an exhibit hall so much as a warehouse. All the artifacts were placed in identical metal boxes, and each box was labeled in detail.

Luo Ji tapped one of the nearby boxes with his cane. “As I said, these are not so important. Most of these objects have longevities shorter than fifty thousand years, though some of the statues can survive up to a million years. But I suggest you not move the statues: Though the gravity makes them easy to move, they take up too much space…. All right, pick whatever you like.”

AA looked around excitedly. “I suggest we take paintings. We can forget about old classics and ancient manuscripts—no one will understand those.” She walked in front of one of the metal boxes and pushed what looked like a button on top, but the box didn’t open by itself, and there were no instructions. Cheng Xin walked over and struggled to lift the cover open. AA took out an oil painting.

“I guess paintings take up a lot of space, too,” said AA.

Luo Ji picked up a set of work overalls from on top of another box and retrieved a small knife and screwdriver from the pockets. “The frame takes up a lot of space. You can take it off.”

AA picked up the screwdriver, but before she could get started on the painting, Cheng Xin cried out. “No!” The painting was Van Gogh’s Starry Night.

Cheng Xin’s surprise wasn’t just because the painting was valuable. She had seen it once before. Four centuries ago, right after she had started working at the PIA, she had visited New York’s Museum of Modern Art on a weekend and saw a few of Van Gogh’s paintings. Van Gogh’s representation of space had left a deep impression on her. In his subconscious, space seemed to have structure. Cheng Xin wasn’t an expert in theoretical physics back then, but she knew that according to string theory, space, like material objects, was made up of many microscopic vibrating strings. Van Gogh had painted these strings: In his paintings, space—like mountains, wheat fields, houses, and trees—was filled with minute vibrations. Starry Night had left an indelible mark in her mind, and she was amazed to see it again four centuries later on Pluto.

“Get rid of the frame. That way, you can take more.” Luo Ji waved his cane carelessly. “Do you think these objects are still worth a city’s ransom? Now, even a city is worthless.”

And so they pried away the frame that was perhaps five centuries old, but they kept the hard backing to avoid damaging the painting by bending the canvas. They continued to do the same to other oil paintings, and soon, empty frames littered the floor. Luo Ji came over and put his hand on a small painting.

“Would you leave this one for me?”

Cheng Xin and AA moved the painting aside and set it on top of a box next to the wall. They were surprised to see that it was the Mona Lisa.

Cheng Xin and AA continued to work at disassembling frames. AA whispered, “Clever old man. He kept the most expensive piece for himself.”

“I don’t think that’s the reason.”

“Maybe he once loved a girl named Mona Lisa?”

Luo Ji sat next to the Mona Lisa and caressed the ancient frame with one hand. He muttered, “I didn’t know you were here. Otherwise I could have come to see you often.”

Cheng Xin saw that he wasn’t looking at the painting. His eyes stared ahead as if looking into the depths of time. Cheng Xin saw that his ancient eyes were filled with tears, and she wasn’t sure if she was mistaken.

Inside the grand tomb under the surface of Pluto, lit by the dim lamps that could shine for a hundred thousand years, Mona Lisa’s smile seemed to appear and disappear. The smile had puzzled humankind for nearly nine centuries, and it looked even more mysterious and eerie now, as though it meant everything and nothing, like the approaching Death.

Bunker Era, Year 68 The Two-Dimensional Solar System

Cheng Xin and AA carried the first batch of artifacts to the surface. Other than a dozen or so frameless paintings, they also carried two bronze ritual vessels from the Western Zhou Period and some ancient books. Under standard 1G gravity, they would not have been able to move all these, but with Pluto’s weak gravity, it didn’t require too much effort. Going through the air lock, they were careful to close the inner door first before opening the outer door, lest they and the artifacts be blown into the open by escaping air. As soon as they opened the outer door, the small amount of air inside the air lock turned into a flurry of ice crystals. Initially, they thought the ice crystals were illuminated by the searchlight on Halo, but after the flurry subsided, they realized that Halo’s searchlight had already shut off. Some source of light in space illuminated Pluto’s surface, and Halo and the black monolith cast long shadows on the white ground. They looked up, and backed up two steps with shock.

A pair of giant eyes stared down at them from space.

Two glowing ovals hung in space, looking exactly like eyes. The “whites” were white or light yellow, and the “irises” were dark.

“That’s Neptune, and the other one is Ura—oh, no, that’s Saturn!” AA said.

Both gas giants had been two-dimensionalized. Uranus’s orbit was outside Saturn’s, but since Uranus was currently on the other side of the Sun, Saturn had fallen into the two-dimensional plane first. The giant planets ought to look like circles after collapsing, but due to the angle of view from Pluto, they appeared as ovals. The two-dimensional planets showed up as clear, concentric rings. Neptune consisted mainly of three rings: the outermost was blue, bright and vivid, like lashes and eye shadow—that was the atmosphere of hydrogen and helium. The middle ring was white—that was the twenty-thousand-kilometer mantle, which astronomers thought of as a water-ammonia ocean. The dark center was the core, formed of rocks and ice, with a mass equal to the entire Earth. Saturn’s structure was similar, except it didn’t have the outer blue ring.

Each large ring was composed of many smaller rings, full of detailed structures. As they examined the planets further, the two giant eyes now more resembled the rings of a newly felled tree. Around each two-dimensional planet were a dozen or so small circles—moons that had also been flattened. Around Saturn was another faint large circle—its rings. They could still find the Sun in the sky, a small disk emitting faint yellow light. Since the two planets were still on the other side of the sun, their area after collapsing into two dimensions was breathtaking.

Both planets had no thickness anymore.

In the light emitted by these two-dimensional planets, Cheng Xin and AA carried the artifacts across the white landing field toward Halo. The ship’s smooth, streamlined body was like a funhouse mirror, and the reflections of the two-dimensional planets were stretched into long, flowing shapes. The yacht’s profile naturally made people think of droplets, and evinced a comforting strength and lightness. On the way to Pluto, AA had told Cheng Xin that she thought Halo’s hull was probably made up in large part of strong-interaction materials.

As they approached, the door on the bottom of the ship slid open noiselessly. They carried the artifacts up the airstair and into the cabin, took off their helmets, and took a deep breath in their cozy little world. Relief filled their hearts—without consciously being aware of it, they already thought of the yacht as home.

Cheng Xin asked the ship’s AI whether it had received any transmissions from Neptune and Saturn. As soon as she made the request, information windows flooded forth like a colorful avalanche that threatened to bury them. The scene reminded them of the first false alarm of 118 years ago. Back then, most of the information had come from media reports, but now, the news media seemed to have disappeared. Most of the information windows contained no discernible images at all—some were blurred, others shook, and most showed meaningless close-ups. But a few of the windows were filled with patches of gorgeous color which, as they flowed and shifted, revealed complex, detailed structures. They probably showed the two-dimensional universe.

AA asked the AI to filter the images. The AI asked them what kind of information they wanted. Cheng Xin asked for information about the space cities. The flood of windows cleared and was replaced by about a dozen others arranged in order. One of the windows enlarged and moved before the others. The AI explained that this had been taken twelve hours ago at Europe VI in the Neptune cluster. The city had once been part of a combined city that had separated after the strike alert.

The image was stable, and the field of view wide. The camera was probably at one end of the city, and almost the entire city could be seen.

Electricity had gone out in Europe VI, and only a few searchlight beams projected unsteady circles of light onto the city’s far side. The three artificial fusion suns along the city’s axis had all turned into silvery moons, giving out only illumination, but no heat. This was a standard football-shaped city, but the buildings inside the city were very different from what Cheng Xin had seen half a century ago. The Bunker World had prospered, and the buildings inside the city were no longer monotonous and uniform. They were much taller, and each had a unique design. The tips of some of the skyscrapers almost touched the axis of the city. Buildings in the shapes of trees reappeared as well, and they looked about as large as the ones that had been built on Earth, though the leaves hung more densely. It was possible to imagine the city’s beauty and magnificence when lit up at night. But now, only cold moonlight illuminated it, and the tree-buildings cast wide shadows so that the rest of the city appeared as ruins nestled in the shade of a giant forest.

The city had stopped spinning and everything was weightless. Countless objects floated through the air—vehicles, miscellaneous goods, and even entire buildings.

A black belt of clouds appeared along the city’s axis, connecting the two poles. The ship’s AI outlined a rectangular region in the image and zoomed in, creating a new information window. Cheng Xin and AA were shocked to see that the black cloud was formed from people drifting in the middle of the city! Some of the weightless individuals had pulled together into a cluster; some had linked hands and formed a line; but most floated alone. Everyone wore helmets and clothes that covered all parts of their body—most likely space suits. Even during Cheng Xin’s last time out of hibernation, it was hard to tell everyday clothes apart from space suits. Everyone seemed to have a pack for life-support systems—some wore it on their back, while others held it in their hands. But most people had their visors open, and it was possible to see a light breeze blowing through the city, indicating that the city still retained a breathable atmosphere. Many had congregated around the suns, perhaps hoping for more light as well as a bit of warmth, but the light emitted by the fusion suns was cold light. The silvery light shone through cracks in the people-cloud and turned into dappled shadows in the surrounding city.

According to the ship’s AI, of the six million inhabitants of Europe VI, half had already left the city on space vehicles. Of the remaining three million, some had no way to get off the city, but most understood that any attempt at escape was hopeless. Even if some ships miraculously managed to escape the collapsing zone and reached outer space, most ships had no ecological cycling system to maintain life for long. Access to stellar ships that could survive indefinitely in outer space was still a privilege of the very few. These people chose to wait for the end in a place they were familiar with.

The transmission wasn’t muted, but Cheng Xin couldn’t hear anything. The people-cloud and the city were both eerily quiet. Everyone looked in one direction. That part of the city looked no different from any other, filled with crisscrossing streets and row upon row of buildings. Everyone waited. In the watery, cold moonlight, people’s faces appeared as white as ghosts. The sight reminded Cheng Xin of the bloody dawn in Australia 126 years ago. Like then, Cheng Xin felt as though she were looking down upon an ant colony, and the black people-cloud looked just like a drifting swarm of ants.

Someone in the people-cloud screamed. A glowing dot appeared at a spot on the city’s equator, the same spot where everyone had been gazing. It was like a small opening in the roof of a dark house letting in the sunlight.

That was where Europe VI first came into contact with two-dimensional space.

The light grew rapidly and turned into a glowing oval. The light it emitted was sliced into many shafts by the tall buildings all around, and illuminated the people-cloud on the city’s axis. The space city now resembled a giant ship whose bottom had been breached, sinking in a flat sea. The plane of the two-dimensional space rose like water, and everything that came into contact with the surface instantaneously turned into two dimensions. Clusters of buildings were cut, and their two-dimensional images spread out on the plane. Since the city’s cross section was but a small portion of the entire flattened city, most of the two-dimensionalized buildings had expanded beyond the oval marked by the city’s hull. On the rising, expanding plane, gorgeous colors and complicated structures flashed by and zoomed away in every direction, as though the plane was a lens through which one could see colorful beasts running. Because the city still possessed air, they could hear the sound of the three-dimensional world falling into two dimensions: a crisp, piercing series of crunches, as though the buildings and the city itself were made of exquisitely carved glass and a giant roller was crushing everything.

As the plane continued to rise, the people-cloud began to spread out in the opposite direction, like a curtain being lifted by an invisible hand. The scene reminded Cheng Xin of a massive flock of millions of birds that she had seen once. The flock had seemed like a unified organism changing shape in the dusk sky.

Soon, the plane had swallowed one-third of the city, and it continued to flicker frantically as it rose irresistibly toward the axis. Some people had begun to fall into the plane by now. They either fell behind due to malfunctions in their space suit thrusters or they had given up on running. Like drops of colorful ink, they spread open on the plane in an instant, and each appeared as a unique figure in two dimensions. On one of the zoomed-in images shown by the AI, they saw a pair of lovers leaping into the plane while in an embrace. Even after the two had been flattened, it was possible to see the figures in an embrace lying side by side—their postures appeared odd, as though drawn by a clumsy child who did not understand the principles of perspective. Nearby there was a mother who lifted her baby overhead as she fell into the plane, all so that the baby would survive for an extra tenth of a second. The mother and child were also vividly portrayed in this giant painting. As the plane kept on rising, the rain of people falling on it became denser. Two-dimensional human figures flooded forth on the plane, most moving outside the boundary of the space city.

By the time the two-dimensional space approached the axis, most of the surviving population had landed against the city’s far side. Half of the city was now gone, and as people looked “up” they could no longer see the familiar city on the other side, but only a chaotic, two-dimensional sky pressing down on the parts of Europe VI that remained in three dimensions. It was now no longer possible to escape from the main gateway at the north pole, so people congregated around the equator, where there were three emergency exits. The weightless crowd piled into mountains around the exits.

The two-dimensional space passed through the axis and swallowed up the three suns, but the light emitted by the two-dimensionalizing process made the world even brighter.

A low whistling sound began: The city was losing its air to space. The three emergency exits along the equator were wide open, each as large as a football field; outside them was the still-three-dimensional space.

The ship’s AI pushed another information window to the front. This was a feed from space looking down at Europe VI. The two-dimensionalized portion of the space city spread across the invisible plane, making the rapidly sinking, still-three-dimensional portion look minuscule by comparison, like the back of a whale peering out of the vast ocean. Three clumps of black smoke rose out of the city and dissipated in space; the “smoke” was formed from the people blown out by the fierce winds of the decompressing space city. The lonely, three-dimensional island continued to sink and melt into the two-dimensional sea. In less than ten minutes, all of Europe VI had turned into a painting.

The painting of Europe VI was so vast that it was hard to estimate its exact area. It was a dead city, but perhaps it was more accurate to call it a 1:1 drawing of the city. The drawing reflected every detail of the city, down to every screw, every fiber, every mite, and even every bacterium. The precision of the drawing was at the level of the individual atom. Every atom in the original three-dimensional space was projected onto its corresponding place in two-dimensional space according to ironclad laws. The basic principles governing this drawing were that there could be no overlap and no hidden parts, and every single detail had to be laid out on the plane. Here, complexity was a substitute for grandeur. The drawing wasn’t easy to interpret—it was possible to see the overall plan of the city and recognize some big structures, such as the giant trees, which still looked like trees even in two dimensions. But buildings looked very different after being flattened: it was almost impossible to deduce the original three-dimensional structure from the two-dimensional drawing by imagination alone. However, it was certain that image-processing software equipped with the right mathematical model would be able to.

In the information window, it was also possible to see two other flattened space cities in the distance. The cities appeared as perfectly flat continents drifting in dark space, gazing at each other across the plane. But the camera—perhaps located on a drone—was also falling toward the plane, and soon the two-dimensional Europe VI filled the screen.

Close to a million people had escaped Europe VI via the emergency exits; now, caught by the three-dimensional space around them collapsing into two dimensions, they fell toward the plane like a swarm of ants caught in a waterfall. A majestic rain of people fell onto the plane, and the two-dimensional human figures in the city multiplied. Flattened persons took up a lot of area—though still minuscule compared to the vast two-dimensional buildings—and resembled tiny, barely man-shaped marks in the immense picture.

More objects appeared in three-dimensional space in the information window: the skiffs and dinghies that had left Europe VI earlier. Their fusion reactors were operating at maximum capacity, but they still fell inexorably toward the plane. For a moment, Cheng Xin thought the blue flame of the fusion drives penetrated that depthless plane, but the plasma had simply been two-dimensionalized. In those areas, the two-dimensional buildings were distorted and twisted by the two-dimensional flames. Next, the skiffs and dinghies became part of the giant drawing. Obeying the no-overlapping principle, the two-dimensionalized city expanded to give these new objects space, and the whole image resembled spreading ripples on the surface of a pond.

The camera continued to fall toward the plane. Cheng Xin stared at the approaching two-dimensional city, hoping to find signs of movement in the city. But no, other than the distortion caused by the plasma flames earlier, everything in the flat city was still. Similarly, the two-dimensional bodies did not move at all, and gave no signs of being alive.

This was a dead world. A dead picture.

The camera moved still closer to the plane, falling toward a two-dimensional body. The body’s limbs soon filled the whole image, and then came the complicated patterns of muscle fibers and blood vessels. Perhaps it was just an illusion, but Cheng Xin seemed to see red, two-dimensional blood flowing through two-dimensional blood vessels. In a flash, the picture was gone.

Cheng Xin and AA began their second trip to retrieve more artifacts. They both felt the mission was likely to be meaningless. After observing the two-dimensionalized cities, they understood that the process preserved most of the information from the three-dimensional world. Any information loss would be at the atomic level. Due to the nonoverlapping principle used in projection, the flattened Pluto’s crust wouldn’t be commingled with the artifacts in the museum, and so the information in the artifacts should be preserved. But since they had accepted this mission, they would finish it. Like Cao Bin said, doing something was better than doing nothing.

They exited Halo and saw the two flattened planets still suspended overhead, but now they were much dimmer. This made the new long, glowing belt that appeared below the planets even more noticeable. The light belt went from one end of the sky to the other, like a necklace formed from numerous individual glowing spots.

“Is that the asteroid belt?” Cheng Xin asked.

“Yes. Mars will be next,” said AA.

“Mars is on this side of the Sun right now.”

The two fell silent. Without looking at the flattened asteroid belt, they walked toward the black monolith.

The Earth was next.

In the great hall of the museum, they saw that Luo Ji had already prepped a bunch of additional artifacts for them. Many of them were Chinese-brush-painting scrolls. AA unrolled one of them: Along the River During the Qingming Festival.

Cheng Xin and AA no longer had the initial awe and delight of seeing such precious works of art—compared to the grandeur of the destruction in process outside, this was nothing more than an old painting. When future explorers arrived at the great painting that was the flattened Solar System, they would have trouble imagining that this twenty-four-centimeter-by-five-meter rectangle was once very special.

Cheng Xin and AA asked Luo Ji to come onto Halo. Luo Ji said he would like to see it, and went to look for a space suit.

As the three of them carried the artifacts out of the monolith, the sight of a flattening Earth greeted them.

The Earth was the first solid planet to collapse into two dimensions. Compared to Neptune and Saturn, the “tree rings” in the two-dimensionalized Earth were even more replete with fine details—the yellow mantle gradually shifted over to the deep red nickel-iron core—but the overall area was much smaller than the gas giants.

Unlike in their imagination, they couldn’t see any hint of blue.

“What happened to our oceans?” Luo Ji asked.

“They should be near the outside… But two-dimensionalized water is transparent, so we can’t see it,” AA said.

The three carried the artifacts to Halo in silence. They couldn’t feel the grief yet, like one didn’t immediately feel the pain of a fresh wound cut by a sharp knife.

But the flattened Earth did show her own wonders. At her outermost rim, a white ring gradually appeared. At first it was barely visible, but soon it stood out sharply against the black backdrop of space. The white ring was pure, flawless, but seemed uneven in its makeup, like it was formed from countless small white grains.

“That’s our ocean!” Cheng Xin said.

“The water froze in two-dimensional space,” said AA. “It’s cold there.”

“Oh—” Luo Ji wanted to stroke his beard, but the visor got in the way of his hand.

The three carried the boxes of artifacts onto Halo. Luo Ji seemed familiar with the ship’s layout, heading for the ship’s hold without instruction from Cheng Xin or AA. The ship’s AI also recognized him, and accepted his orders. After they secured the artifacts, the three returned to the yacht’s living quarters. Luo Ji asked the AI for a cup of hot tea, and soon, a little robot that Cheng Xin and AA had never seen before brought it to him. Clearly, Luo Ji had some history with this ship that the two women did not know about. They were curious about the story, though more urgent matters had to be taken care of first.

Cheng Xin asked the AI to play some news from the Earth, but the AI said that it had received only a few transmissions from the planet, and the visual and audio content was essentially impossible to make sense of. They looked at the few open information windows and saw only blurred images taken by unmanned cameras. The AI added that it could provide the video taken by the spacecraft monitoring system near the Earth. A new, large window popped up and the flatted Earth filled the screen.

The three immediately thought the image looked unreal, even suspecting that the AI had synthesized the image to fool them.

“What in the world is this?” AA cried out.

“It’s the Earth about seven hours ago. The camera is fifty astronomical units away, and angular magnification is four hundred and fifty times.”

They looked more closely at the holographic video taken by the telescopic lens. The body of the flattened Earth appeared very clearly, and the “tree rings” were even denser than when observed with the naked eye. The collapse had probably already been completed, and the two-dimensional Earth was dimming. But what really shocked them was the frozen two-dimensional ocean—the white ring around the rim of the Earth. They could clearly make out the grains forming the ring: snowflakes! These were unimaginably large snowflakes, hexagonal in plan, but each with unique crystal branches—exquisite, lovely beyond words. To see snowflakes from fifty AU away was already extremely surreal, and these immense snowflakes were arranged side by side on the plane with no overlap, which further enhanced the feeling of unreality. They seemed to be purely artistic portrayals of snowflakes, powerfully decorative, turning the frozen two-dimensional sea into a piece of stage art.

“How big are the snowflakes?” AA asked.

“Most have diameters between four thousand and five thousand kilometers.” The ship’s AI, incapable of wonder, continued to speak in a serene tone.

“Bigger than the moon!” Cheng Xin said.

The AI opened a few other windows, and each showed a zoomed-in snowflake. In these images, the sense of scale was lost, and they seemed to be tiny spirits under a magnifying lens, each snowflake ready to turn into a tiny droplet as soon as it touched down on a palm.

“Oh—” Luo Ji stroked his beard again, and this time, succeeded.

“How are they formed?” AA asked.

“I don’t know,” the AI said. “I can’t find any information about the crystallization of water at astronomical scales.”

In three-dimensional space, snowflakes formed in accordance with the laws of ice-crystal growth. Theoretically, these laws did not restrict the size of snowflakes. The largest snowflake previously on record was thirty-eight centimeters in diameter.

No one knew the laws of ice crystal growth in two-dimensional space. Whatever they were, they permitted ice crystals in two dimensions to grow to five thousand kilometers.

“There’s water on Neptune and Saturn, and ammonia can also form crystals. Why didn’t we see large snowflakes there?” Cheng Xin asked.

The AI said it didn’t know.

Luo Ji squinted his eyes and enjoyed the two-dimensional version of the Earth. “The ocean looks rather nice this way, don’t you think? Only the Earth is worthy of such a lovely wreath.”

“I really want to know what the forests look like, what the grasslands look like, what the ancient cities look like,” Cheng Xin said slowly.

Grief finally struck them, and AA began to sob. Cheng Xin turned her eyes away from the snowflake ocean and made no sound as her eyes filled with tears. Luo Ji shook his head, sighed, and continued to sip his tea. Their grief was moderated to some extent by the thought that the two-dimensional space would also be their home in the end.

They would attain their eternal rest alongside Mother Earth on that plane.

The three decided to begin their third cargo trip. They exited Halo, gazed up at the sky, and saw the three two-dimensional planets. Neptune, Saturn, and the Earth had grown even larger, and the asteroid belt was wider. This was no hallucination. They asked the AI about it.

“The navigation system has detected a split in the Solar System’s navigational frame of reference. Frame of reference one continues as before. The navigational markers within this system—the Sun, Mercury, Mars, Jupiter, Uranus, Pluto, and some asteroids and Kuiper Belt objects—still satisfy the recognition criteria. Frame of reference two, however, has transformed dramatically. Neptune, Saturn, the Earth, and some asteroids have lost their characteristics as navigational markers. Frame of reference one is moving toward frame of reference two, which leads to the phenomenon you’ve observed.”

In the sky in the other direction, many moving points of light appeared before the stars—the fleet of ships seeking to escape the Solar System. Some of the glowing blue lights dragged long tails behind them. Some of the ships swept by the three of them, fairly close. The bright lights of their engines operating at maximum capacity cast moving shadows of the three observers on the ground. None of the ships tried to land on Pluto.

But it was impossible to escape from the collapsing zone. Halo’s AI was trying to say this: The three-dimensional space of the Solar System was like a large carpet that was being pulled by invisible hands into a two-dimensional abyss. These ships were nothing more than worms on the carpet inching along—they couldn’t extend their already limited allotment of time by much.

“Go ahead by yourselves,” Luo Ji said. “Just take a few more objects. I want to wait here. I don’t want to miss it.” Cheng Xin and AA understood what he meant by “it,” but they had no desire to witness the scene.

After returning to the underground hall, Cheng Xin and AA, not in the mood to pick and choose, randomly gathered a collection of artifacts. Cheng Xin wanted to take along a Neanderthal skull, but AA tossed it aside.

“You’ll have plenty of skulls on this picture,” AA said.

Cheng Xin acknowledged that she was right. The earliest Neanderthals had lived no more than a few hundred thousand years ago. Optimistically, the flattened Solar System would not have visitors until a few hundred thousand years from now. In their eyes, Neanderthals and modern humans would appear to be the same species. Cheng Xin looked around at the other artifacts, and none excited her. For themselves in the present, and for those unimaginable observers in the far future, nothing here mattered as much as the world that was dying outside.

They took a last look at the dim hall and left with the artifacts. Mona Lisa watched them leave, smiling sinisterly and eerily.

On the surface, they saw that yet another two-dimensional planet had appeared in the sky: Mercury (Venus was on the other side of the Sun at this moment). It looked smaller than the two-dimensional Earth, but the light generated by its recent collapse into two dimensions made it very bright.

After they packed the artifacts in the hold, Cheng Xin and AA came out of Halo. Luo Ji, who was waiting outside, leaning on his cane, said, “All right. I think that’s enough. It’s meaningless to carry more, anyway.”

The women agreed. They stood together with Luo Ji on the Plutonian ground and waited for the most magnificent scene of the play: the flattening of the Sun.

At this moment, Pluto was forty-five AU from the Sun. Earlier, since both Pluto and the Sun were in the same region of three-dimensional space, the distance between them hadn’t changed. But when the Sun came into contact with the plane, it ceased to move, while Pluto continued to fall toward it, along with the space around it, causing the distance between them to shrink rapidly.

When the Sun began to two-dimensionalize, the naked eye could only see that its brightness and size appeared to increase suddenly. The latter was due to the rapid expansion of the flattened portion of the Sun on the plane, but from a distance it appeared as though the Sun itself was growing. Halo’s AI projected a large information window outside the ship to show a holographic feed from a telescopic lens, but as Pluto pulled closer to the Sun, even the naked eye could see the grand spectacle of a star collapsing into two dimensions.

As soon as the Sun began to two-dimensionalize, a circle expanded on the plane. Soon, the planar Sun’s diameter exceeded the diameter of the remaining part of the Sun. This process took only thirty seconds. Based on the mean solar radius of seven hundred thousand kilometers, the rim of the two-dimensional Sun grew at the rate of twenty thousand kilometers per second. The planar Sun continued to grow, forming a sea of fire on the plane, and the three-dimensional Sun sank slowly into this blood-red sea of fire.

Four centuries ago, Ye Wenjie had stood on the peak of Red Coast Base and watched such a sunset during the last moments of her life. Her heart had struggled to beat like a zither string about to break, and a black fog had begun to cloud her eyes. On the western horizon, the Sun that was falling into the sea of clouds seemed to melt, and the Sun’s blood seeped into the clouds and the sky, creating a large crimson swath. She had called it humanity’s sunset.

And now, the Sun really was melting, its blood seeping into the deadly plane. This was the last sunset.

In the distance, white fog rose from the ground outside the landing field. Pluto’s solid nitrogen and ammonia sublimated, and the fresh, thin atmosphere began to scatter the sunlight. The sky no longer appeared pure black, but showed hints of purple.

While the three-dimensional Sun was setting, the two-dimensional Sun was rising. A flat star could still radiate its light inside the plane, so the two-dimensional Solar System received its first sunlight. The sides of the four two-dimensional planets facing the sun—Neptune, Saturn, the Earth, and Mercury—all took on a golden glow, though the light only fell along a one-dimensional curved edge. The giant snowflakes that surrounded the Earth melted and turned into white vapor, which was blown by two-dimensional solar wind into two-dimensional space. Some of the vapor soaked up the golden sunlight and appeared as if the Earth had hair that drifted with the wind.

An hour later, the Sun had completely collapsed into two dimensions.

From Pluto, the Sun appeared as a giant oval. The two-dimensional planets were tiny fragments compared to it. Unlike the planets, the Sun did not display clear “tree rings” but was separated into three concentric sections around a core. The center was very bright, and no details could be seen—probably corresponding to the core of the original Sun. The wide ring outside the core probably corresponded to the original radiation zone—a boiling, two-dimensional, bright red ocean where countless cell-like structures rapidly formed, split, combined, and disappeared in a manner that seemed chaotic and agitated when viewed locally, but followed grand patterns and order when viewed as a whole. Outside that was the original Sun’s convection zone. Like in the original Sun, currents of solar material transferred heat into space. But unlike the chaotic radiation zone, the new convection zone revealed clear structure, as many ring-shaped convection loops, similar in shape and size, arranged themselves side by side in neat order. The outermost layer was the solar atmosphere. Golden currents leapt away from the circular rim and formed a large number of two-dimensional prominences, resembling graceful dancers cavorting wantonly around the Sun. Some of the “dancers” even escaped the Sun and drifted far into the two-dimensional universe.

“Is the Sun still alive in two dimensions?” asked AA. She spoke for the hope of all three. They all wished for the Sun to continue to give light and heat to the planar Solar System, even if there was no more life in it.

But her hope was soon dashed.

The flattened Sun began to dim. The light from the core diminished rapidly and soon it was possible to see fine annular structures within. The radiation zone was also quieting, and the boiling calmed down, turning into a viscous peristalsis. The loops in the convection zone distorted, broke apart, and soon disappeared. The golden dancers around the rim of the Sun wilted like dried leaves and lost their vivaciousness. Now it was possible to tell that at least gravity continued to function in the two-dimensional universe. The dancing solar prominences lost the support of solar radiation and began to be dragged back to the edge of the Sun by its gravity. Finally, the dancers yielded to gravity and fell lethargically, until the Sun’s atmosphere was no more than a thin, smooth ring wrapped around the Sun. As the Sun went out, the golden arcs at the edges of the planets also dimmed, and the Earth’s two-dimensional hair, formed from the sublimated ocean, lost its golden glow.

Everything in the three-dimensional world died after collapsing into two dimensions. Nothing survived in a painting with no thickness.

Perhaps a two-dimensional universe could possess its own sun, planets, and life, but they would have to be created and operate under completely different principles.

While the three were focused on the flattening Sun, Venus and Mars collapsed into the plane as well. Compared to the Sun, however, the two-dimensionalization of these two terrestrial planets was rather unremarkable. The flattened Mars and Venus were very similar to the Earth in terms of their “tree ring” structure. There were many hollow areas near the rim of Mars, places in the Martian crust that contained water, suggesting that Mars had possessed far more water than people thought. After a while, the water also turned an opaque white, but no giant snowflakes appeared. There were giant snowflakes around the flattened Venus, but they weren’t anywhere as numerous as the ones near the Earth, and the Venusian snowflakes were yellow in hue, indicating that they were not water crystals. A while later, the asteroids on that side of the Sun were also flattened, completing the other half of the Solar System necklace.

Tiny snowflakes—three-dimensional ones—now fell from the light purple Plutonian sky. These were the nitrogen and ammonia that had sublimated in the burst of energy during the Sun’s flattening, and which were now freezing into snow as the temperature plummeted following the Sun’s extinguishment. The snow fell more heavily, and soon accumulated a thick layer over the monolith and Halo. Although there were no clouds, the heavy snow blurred Pluto’s sky, and the two-dimensional Sun and the planets turned hazy behind a curtain of snow. The world looked smaller.

“Don’t you feel at home?” AA lifted both hands and spun in the snow.

“I was just thinking the same thing,” Cheng Xin said, and nodded. She had also thought of snow as something unique to the Earth, and the giant snowflakes around the flattened Earth had confirmed this feeling. The snow falling on this cold, dark world on the edge of the Solar System surprisingly provided her a trace of the warmth of home.

Luo Ji watched as AA and Cheng Xin tried to catch the snow. “Hey, you two! Don’t even think about taking off your gloves!”

Cheng Xin did feel an impulse to take off her gloves and catch the snow with her bare hands. She wanted to feel the slight chill, and watch the crystalline snowflakes melt with her own body heat…. but of course she had enough presence of mind to not indulge the impulse. The nitrogen-ammonia snowflakes were at a temperature of minus-210-degrees Celsius. If she really took off her gloves, her hand would turn as fragile and hard as glass and the feeling of being on Earth would disappear instantaneously.

“There’s no more home,” Luo Ji said, shaking his head and leaning against his cane. “Home is now just a picture.”

The nitrogen-ammonia snow didn’t last long. The snowflakes thinned out and the purple haze from the nitrogen-ammonia atmosphere faded. The sky was once again perfectly transparent and dark. They saw that the Sun and the planets had grown even bigger, indicating that Pluto had moved even closer to that two-dimensional abyss.

When the snow stopped, a bright glowing light appeared near the horizon. The intensity of the light grew rapidly, and soon overwhelmed the fading two-dimensional Sun. Although they couldn’t see the details, they knew that it was Jupiter, the Solar System’s largest planet, falling into the plane. Pluto spun slowly, and part of the flattened Solar System had fallen below the horizon, so they thought they wouldn’t get to witness Jupiter’s collapse, but it appeared that the rate of fall into two dimensions was accelerating.

They asked Halo’s AI to look for transmissions from Jupiter. Very few images and videos were being transmitted now, and most were indecipherable. Almost all of the messages they got were audio only. Every communication channel was filled with noise, mostly human voices, as though all the remaining space in the Solar System had been filled with a frenzied sea of people. The voices cried, screamed, sobbed, laughed hysterically… and some even sang. The chaotic background noise made it impossible to tell what they were singing, only that it was many voices singing in harmony. The music was solemn, slow, like a hymn. Cheng Xin asked the AI whether it was possible to receive any official broadcasts from the Federation Government. The AI said that all official communications from the government had terminated when the Earth was flattened. The Federation Government couldn’t fulfill the promise to carry out its duties until the end of the Solar System after all.

Ships trying to escape continued to stream by the vicinity of Pluto.

“Children, it’s time to go,” said Luo Ji.

“Let’s go together,” said Cheng Xin.

“What’s the point?” Luo Ji shook his head and smiled. He pointed at the monolith with his cane. “I’m more comfortable over there.”

“All right. We’ll wait until Uranus is flattened so that we get to spend more time with you,” AA said. There really didn’t seem to be any point in insisting. Even if Luo Ji got on Halo, it would only delay the inevitable by another hour. He didn’t need that bit of time. Indeed, if Cheng Xin and AA didn’t have a mission to carry out, they wouldn’t care for that bit of time either.

“No. You must go now!” Luo Ji said. He struck the ground with his cane forcefully, which made him float up under the low gravity. “No one knows how much faster the collapse is happening now. Carry out your mission! We can stay in contact, and that’s no different from being together.”

Cheng Xin hesitated for a moment, then nodded. “All right. We’ll leave. Stay in contact!”

“Of course.” Luo Ji lifted his cane in farewell and turned to walk toward the monolith. With the light gravity, he almost floated over the snow on the ground and had to use the cane to slow himself. Cheng Xin and AA watched until the aged figure of this Wallfacer, Swordholder, and humanity’s final grave keeper disappeared behind the door of the monolith.

Cheng Xin and AA went back inside Halo. The yacht took off right away, its thrusters tossing up snow everywhere. Soon, the ship achieved Pluto’s escape velocity—just a hair above one kilometer per second—and reached orbit. From the porthole and the monitor they could see that swaths of white now joined the blue and black patches of the Plutonian surface. The giant words “Earth Civilization,” written in multiple scripts and languages, had been covered by the snow and were almost illegible. Halo passed through the gap between Pluto and Charon as though flying through a canyon, the two celestial bodies were so close.

In this “canyon” there were now many other moving stars—the escaping spaceships. They all moved far faster than Halo. One ship swept past Halo at a distance of no more than a hundred kilometers, and the glow from its nozzles lit up Charon’s smooth surface. They could clearly see its triangular hull and the nearly ten-kilometer-long blue flame shooting out of its nozzles.

The AI explained, “That’s Mycenae, a midsized planetary ship without an ecological cycling system. After leaving the Solar System, a passenger would not last five years, even if all the ship’s supplies were used to sustain only them.”

The AI didn’t know that Mycenae would not be able to leave the Solar System. Like all the other escaping ships, it would continue to exist for no more than three hours in three-dimensional space.

Halo flew out of the Pluto-Charon canyon and left the two dark worlds for open space. They saw the entirety of the two-dimensionalized Sun and Jupiter, whose flattening process was almost over. Now, except for Uranus, the vast majority of the Solar System had fallen into the plane.

“Oh, heavens! Starry sky!” AA cried out.

Cheng Xin knew that she was referring to Van Gogh’s painting. True, the universe really did look like the painting. The painting in her memory was almost a perfect copy of the two-dimensional Solar System before her eyes. Giant planets filled space, the areas of the planets seeming to exceed even the gaps between them. But the immensity of the planets did not give them any sense of substantiality. Rather, they looked like whirlpools in space-time. In the universe, every part of space flowed, churned, trembled between madness and horror like fiery flames that emitted only frost. The Sun and the planets and all substance and existence seemed to be only hallucinations produced by the turbulence of space-time.

Cheng Xin now recalled the strange feeling she had experienced each time she had looked at Van Gogh’s painting. Everything else in the painting—the trees that seemed to be on fire, and the village and mountains at night—showed perspective and depth, but the starry sky above had no three-dimensionality at all, like a painting hanging in space.

Because the starry night was two-dimensional.

How could Van Gogh have painted such a thing in 1889? Did he, having suffered a second breakdown, truly leap across five centuries and see the sight before them using only his spirit and delirious consciousness? Or, maybe it was the opposite: He had seen the future, and the sight of this Last Judgment had caused his breakdown and eventual suicide.

“Children, is everything all right? What are you going to do next?” Luo Ji appeared in a pop-up window. He had taken off his space suit, and his white hair and beard floated in the low gravity like in water. Behind him was the tunnel that had been intended to last a hundred million years.

“Hello! We’re going to toss the artifacts into space,” AA said. “But we want to keep Starry Night.”

“I think you should hold on to them all. Don’t toss any. Take them and leave.”

Cheng Xin and AA looked at each other. “Go where?” AA asked.

“Anywhere you like. You can go to any place in the Milky Way. In your lifetimes, you could probably get to the Andromeda Galaxy. Halo is capable of lightspeed flight. It is equipped with the world’s only curvature propulsion drive.”

Utter shock. AA and Cheng Xin couldn’t speak.

“I was a part of the group of scientists who worked on curvature propulsion in secret,” said Luo Ji. “After Wade died, those who had worked at Halo City didn’t give up. After those who had been imprisoned were released, they built another secret research base, and your Halo Group was revived and developed enough to keep it going. Do you know where the base was? Mercury, another place in the Solar System where few set foot. Four centuries ago, another Wallfacer, Manuel Rey Diaz, used giant hydrogen bombs to blast a crater there. The base was built in that crater, and its construction took over thirty years. The whole base was covered with a dome. They claimed that it was a research institute to study solar activity.”

A bright shaft of light pierced the porthole. AA and Cheng Xin ignored it, but the ship’s AI explained that Uranus had also undergone “state change,” meaning that it had also collapsed into two dimensions. By now, nothing stood between them and Pluto.

“Thirty-five years after Wade’s death, the research into curvature propulsion picked up at the Mercury base. They continued from the point where they were able to move a two-millimeter segment of your hair two centimeters. The research continued for half a century—though they were interrupted a few times for various reasons—and they gradually moved from theoretical research to technological development. During the last stages of the development process, they had to perform experiments on large-scale curvature propulsion. This was a problem for the Mercury base because the base’s resources were limited, and an experiment would produce massive trails, which would expose the Mercury base’s true goals. In reality, based on the comings and goings at the base for more than fifty years, it was inconceivable that the Federation Government had no clue what the Mercury base was really up to, but due to the small scale of the experiments and the fact that all the research was done under cover of other projects, the government had tolerated the base’s activities. Large-scale experiments, however, required the government’s cooperation. We sought it out, and the collaboration went very well.”

“Did they repeal the laws proscribing lightspeed ships?” Cheng Xin asked.

“No, not at all. The government collaborated with us because…” Luo Ji tapped his cane against the ground and hesitated. “Let’s not get into that for now. A few years ago, we completed three curvature engines and conducted three unmanned tests. Engine Number One entered lightspeed about one hundred and fifty astronomical units from the Sun, and returned here after flying at lightspeed for a while. For the engine itself, the experiment lasted only ten minutes or so, but for us, it was three years before the engine returned. The second test involved Engines Number Two and Number Three simultaneously. Right now, both of them are outside the Oort Cloud, and should return to the Solar System in six years.

“Engine Number One, which has already been tested, is installed in Halo.”

“But how could they have sent Cheng Xin and I alone?” AA shouted. “There should at least be two men with us.”

Luo Ji shook his head. “There was no time. The collaboration between the Halo Group and the Federation Government occurred in secret. Very few people knew of the existence of the curvature engines, and even fewer knew where the only engine left in the Solar System was installed. And it was too dangerous. Who knows what people are capable of when the end is nigh? Everyone would fight over Halo, and maybe nothing would be left afterward. And so we had to get Halo away from the Bunker World before releasing news of the dark forest strike to the public. There really wasn’t any time left. Cao Bin sent Halo to Pluto because he wanted you to take me with you. He should have just had Halo enter lightspeed at Jupiter.”

“Why didn’t you come with us?” AA shouted.

“I’ve lived long enough. Even if I get onto the ship, I won’t live much longer. I’d rather stay here as a grave keeper.”

“We can come back for you!” Cheng Xin said.

“Don’t you dare! There’s no time!”

The three-dimensional space they were in accelerated toward the two-dimensional plane. The two-dimensional Sun, which had now completely extinguished and appeared as a vast, dark red, dead sea, took up most of the view from Halo. Cheng Xin and AA noticed that the plane was not completely flat, but undulating! A long wave slowly rolled across the plane. It was a similar wave in three-dimensional space that had allowed Blue Space and Gravity to find warp points to enter four-dimensional space. Even in places where there were no two-dimensional objects in the plane, the rippling wave was apparent. The waves were a visualization of two-dimensional space in three dimensions that occurred only when the two-dimensional space was large enough.

On Halo itself, the space-time distortion produced by the accelerated fall had started to become apparent as space was stretched in the direction of the fall. Cheng Xin noticed that the circular portholes now appeared as ovals, and the slender AA now looked short and squat. But Cheng Xin and AA felt no discomfort, and the ship’s systems were operating normally.

“Return to Pluto!” Cheng Xin ordered the AI. Then she turned to Luo Ji’s window. “We’re going to come back. There’s time—Uranus is still being flattened.”

The AI replied stiffly, “Among all authorized users in communication range, Luo Ji has the highest authorization level. Only he can order Halo to return to Pluto.”

Luo Ji smiled before the tunnel. “If I wanted to go, I would have gotten on the ship with you earlier. I’m too old for voyages far from home. Do not worry about me, children. Like I said, I don’t think I’ve missed anything. Prepare for curvature propulsion!”

Luo Ji’s last words were directed at the ship’s AI.

“Course parameters?” asked the AI.

“Continue along the current heading. I don’t know where you want to go, and I don’t think you know, either. If you do think of a destination, just point it out on the star map. The ship is capable of automatic navigation to most stars within fifty thousand light-years.”

“Affirmative,” said the AI. “Initiating curvature propulsion in thirty seconds.”

“Do we need to be immersed in deep-sea fluid?” AA asked—though rationally, she knew that under conventional propulsion, such acceleration would compress her into a pancake no matter what kind of fluid she was immersed in.

“You don’t need any kind of preparation. This propulsion method relies on manipulating space, so there’s no hypergravity. Curvature propulsion drive online. System is operating within normal parameters. Local space curvature: twenty-three point eight. Forward curvature ratio: three point forty-one to one. Halo will enter lightspeed in sixty-four minutes, eighteen seconds.”

For Cheng Xin and AA, the AI’s announcement was like a Full Stop order, because everything suddenly quieted down. They understood that the silence was due to the nuclear fusion engine being shut off, but the humming produced by the fusion reactor and the thrusters disappeared without being replaced by any other noise. It was hard to believe that some other engine had been started.

But signs of curvature propulsion did appear. The distortion in space gradually disappeared: The portholes returned to being circles, and AA looked slender again. Looking through the portholes, they could still see other escaping ships passing by Halo, but they now passed far more slowly.

The ship’s AI began to play some of the messages passing between the escaping ships—perhaps because the messages concerned Halo.

“Look at that ship! How is it able to accelerate so fast?” a woman screamed.

“Oh! The people inside must have been crushed into meat pies,” a man said.

Another man spoke up. “You idiots. The ship itself would be crushed under that kind of acceleration. But look at it: It’s perfectly fine. That’s not a fusion drive, but something entirely different.”

“Curvature propulsion? A lightspeed ship? That’s a lightspeed ship!”

“The rumors were true, then. They were building secret lightspeed ships so that they could escape….”

“Aaahhhhh…”

“Hey, any ships ahead? Stop that ship! Crash into it. No one should live if we all have to die!”

“They can reach escape velocity! They can run away and live! Ahhhh! I want the lightspeed ship! Stop them; stop them and kill everyone inside!”

Another scream—this one from AA inside the ship. “How can there be two Plutos?”

Cheng Xin turned to the information window AA was looking at. The window showed a view of Pluto taken by the ship’s monitoring system. Although Pluto was some distance away, it was clear that both Pluto and Charon had been duplicated, and the twins were lined up side by side. Cheng Xin noticed that some of the flattened objects in the two-dimensional space had also been duplicated. The effect was like selecting a portion of a picture using image-processing software, cloning it, and then moving the clone a bit to the side.

“That’s due to the fact that light slows down inside the trail left by Halo,” Luo Ji said. His image was growing distorted, but his voice still came through clearly. “Pluto is still moving. One of the Plutos you are seeing is the result of slow light. Once Pluto has moved outside of Halo’s trail, light traveling at standard speed provides you with a second image. That’s why you’re seeing double.”

“The light slows down?” Cheng Xin sensed a great secret was being revealed.

Luo Ji continued, “I understand that you figured out curvature propulsion from a small boat propelled by soap. Let me ask you: After the ship reached the other side of the bathtub, did you pull it back and try again?”

They hadn’t. Due to the fear of sophons, Cheng Xin had tossed the paper boat aside. But it was easy to figure out what would have happened.

“The ship would not move, or at least it would only move slowly,” Cheng Xin said. “After the first trip, the surface tension of the water in the tub had already been reduced.”

“That’s right. It’s the same principle with lightspeed ships. The very structure of space itself is changed by the trail of a curvature-propelled ship. If a second curvature-propelled ship were placed inside the trail of the first, it would hardly move. Within the trails of lightspeed ships, one must use a more powerful curvature propulsion drive. It would still be possible to use curvature propulsion to achieve the highest speed possible within such a space, but the maximum velocity is much lower than the maximum velocity of the first ship. In other words, the speed of light through vacuum is lowered within the trail of lightspeed ships.”

“How much lower?”

“Theoretically, it could be reduced to zero, but that’s not achievable in reality. But if you adjust the curvature ratio of Halo’s engine to the maximum, you can lower the speed of light in its trail down to exactly what we’ve been looking for: sixteen point seven kilometers per second.”

“Then you’d have…” AA said, staring at Luo Ji.

The black domain, Cheng Xin thought.

“The black domain,” Luo Ji said. “Of course, a single ship is insufficient to produce a black domain containing an entire star and its planetary system. We calculated that it would take more than a thousand curvature propulsion ships to accomplish such a thing. If all these ships started near the Sun and spread out in every direction at lightspeed, the trails they produced would expand and connect to each other, forming a sphere that contained the entire Solar System. The speed of light within this sphere would be sixteen point seven kilometers per second—a reduced-lightspeed black hole, or a black domain.”

“So the black domain can be a product of lightspeed ships….”

In the cosmos, the trail of a curvature propulsion drive could be a sign of danger, as well as a safety announcement. A trail far away from a world was the former; a trail that shrouded a world the latter. It was like a noose, indicating danger and aggression when held in the hand, but safety when wrapped around the holder’s own neck.

“Correct, but we found out about it too late. While studying curvature propulsion, the experimenters plowed ahead of the theoreticians. You should know that was Wade’s style. Many experimental discoveries could not be explained by theory, but without a theoretical framework, some phenomena were simply ignored. During the earliest years of research—when their biggest achievement was moving your hair—the trails produced by curvature propulsion were thin and small, and hardly anyone paid any attention, even though there were plenty of signs of something strange going on: For instance, after the trail expanded, the low speed of light caused quantum integrated circuits in nearby computers to malfunction, but no one sought to investigate. Later, after the experiments grew in scale, people finally discovered the secret of lightspeed trails. It was because of this discovery that the Federation Government agreed to collaborate with us. They did, in fact, pour all the resources they could command into the development of lightspeed spaceships, but there just wasn’t enough time.” Luo Ji shook his head and sighed.

Cheng Xin said what he couldn’t bring himself to say. “There were thirty-five years between the Halo City Incident and the completion of the Mercury base. Thirty-five precious years were lost.”

Luo Ji nodded. Cheng Xin thought the way he looked at her was no longer kind, but rather resembled the fires of the Last Judgment. His gaze seemed to say, Child, look at what you’ve done.

Cheng Xin now understood that of the three paths of survival presented to humanity—the Bunker Project, the Black Domain Plan, and lightspeed ships—only lightspeed ships were the right choice.

Yun Tianming had pointed this out, but she had blocked it.

If she hadn’t stopped Wade, Halo City might have achieved independence. Even if the independence was short-lived, they could have discovered the effects of lightspeed trails and changed the government’s attitude toward lightspeed ships. Humanity might have had time to construct a thousand lightspeed ships and build the black domain, to avoid this dimensional strike.

Humanity could have divided into two parts: those who wanted to fly to the stars, and those who wanted to stay within the black domain and live in tranquility. Each would have gotten what they wanted.

In the end, she had committed another grave error.

Twice, she had been placed in a position of authority second only to God, and both times she had pushed the world into the abyss in the name of love. This time, no one could fix her mistake for her.

She began to hate someone: Wade. She hated that he had kept his promise. Why? Out of his masculine pride, or for her? Cheng Xin understood that Wade did not know the effects of curvature propulsion trails. His goal in researching lightspeed ships was stated eloquently by that anonymous Halo City soldier: a fight for freedom, for a chance to live as free men in the cosmos, for the billions and billions of new worlds out there. She believed that if he had known that lightspeed spaceflight was the only path to life for humanity, he would not have kept his promise.

She could not shirk her responsibility. It didn’t matter whether she really was second only to God—if she was in that position, she had to carry out her duty.

Not long ago on Pluto, Cheng Xin had experienced one of the most relaxed moments of her life. Indeed, it was easy to face the end of the world: All responsibilities were gone, as were all worries and anxieties. Life was as simple and pure as the moment when one first emerged from the mother’s womb. Cheng Xin just had to wait in peace for her poetic, artistic end, for her moment to join the giant painting of the Solar System.

But now, everything had been turned upside down. Early cosmology had presented a paradox: If the universe was infinite, then every spot in the universe would feel the cumulative effects of the infinite gravity exerted by an infinity of celestial bodies. Cheng Xin really did feel an infinite gravity now. The power came from every corner of the universe, ruthlessly tearing at her soul. The horror of her last moments as the Swordholder 127 years ago resurfaced as four billion years of history pressed down on her and suffocated her. The sky was full of eyes staring at her: the eyes of dinosaurs, trilobites, ants, birds, butterflies, bacteria… just the number of men and women who had lived on the Earth possessed a hundred billion pairs of eyes.

Cheng Xin saw AA’s eyes, and understood the words in her gaze: You’ve finally experienced something worse than death.

Cheng Xin knew that she had no choice but to live on. She and AA were the last two survivors of human civilization. Her death would mean the death of half of all that was left of humanity. Living on was the appropriate punishment for her mistake.

But the course ahead was a blank. In her heart, space was no longer black, but colorless. What was the point of going anywhere?

“Where should we go?” Cheng Xin muttered.

“Go find them,” Luo Ji said. His image was even more blurred and now only black and white.

His words illuminated Cheng Xin’s dark thoughts like lightning. She and AA looked at each other and immediately understood who “them” meant.

Luo Ji continued, “They’re still alive. The Bunker World received a gravitational wave transmission from them five years ago. It was a short message, and didn’t explain where they were. Halo will periodically hail them with gravitational waves. Maybe you’ll find them; maybe they’ll find you.”

Luo Ji’s black-and-white image disappeared as well, but they could still hear his voice. He said one last thing, “Ah, it’s time for me to go into the picture. Safe travels, children.”

The transmission from Pluto was cut off.

On the monitor, they could see Pluto light up and expand in two dimensions. The part of Pluto containing the museum was the first to touch the plane.

The Doppler effect of Halo’s speed was now visible. The light from the stars ahead shifted to bluish, while the light from the stars behind shifted to reddish. The color shift was apparent in the two-dimensional Solar System.

Outside, no other fleeing spaceships could be seen; Halo had passed them all. All the fleeing spaceships were now falling onto the two-dimensional space like drops of rain against glass.

Very few transmissions could now be received from the direction of the Solar System. Due to the Doppler effect, the brief bursts of voices sounded strange, like singing.

“We’re very close! Are you behind us?”…“Don’t do this! No!”…“There’s no pain. I’m telling you, it’ll be over in a flash.”…“You still don’t believe me, after all this? Fine, don’t believe me.”…“Yes, sweetie, we’ll become very thin.”…“Come here! We should be together.”

Cheng Xin and AA listened. The voices became fewer and fewer, and separated by longer gaps. After thirty minutes, they heard the last voice coming out of the Solar System:

“Ahhhhhhhhh—”

The voice was cut off. The giant painting called the Solar System was complete.

Halo continued to fall toward the plane. The speed it had already achieved was slowing down its fall, but the ship still hadn’t achieved escape velocity. By now, Halo was the only man-made three-dimensional object in the Solar System, and Cheng Xin and AA were the only people not in the painting. Halo was very close to the plane, and from this angle, looking at the two-dimensional Sun was like looking at the sea from shore: the dim, dark red surface stretched into the distance without bounds. The freshly flattened Pluto was now very large, and still expanded at a rate that was visible to the naked eye. Cheng Xin examined the exquisite “tree rings” of Pluto and tried to find traces of the museum, but she couldn’t see anything—it was too small. The giant waterfall that was three-dimensional space tumbling into the flat plane seemed inexorable. Cheng Xin began to doubt whether the curvature propulsion engine really was capable of propelling the ship to lightspeed. She hoped for everything to be over.

But then, the ship’s AI spoke.

“Halo will enter lightspeed in one hundred and eighty seconds. Please select a destination.”

“We don’t know where to go,” said AA.

“You can select a destination after we’ve entered lightspeed. However, you won’t subjectively be spending much time in lightspeed, and it’s easy to overshoot your destination. It’s best if you select it now.”

“We don’t know where to find them,” Cheng Xin said. Their existence gave the future some light, but she still felt lost.

AA clutched Cheng Xin’s hands. “Have you forgotten? Other than them, he also exists in the universe.”

Yes, he still exists. Cheng Xin was overwhelmed by heartache. She had never yearned to see anyone as much as him.

“You have a date,” AA said.

“Yes, we have a date,” Cheng Xin repeated mechanically. The torrents of emotion left her numb.

“Then let’s go to your star.”

“Yes, let’s go to our star!” Cheng Xin turned to the ship’s AI. “Can you find DX3906? That was the assigned number back at the beginning of the Crisis Era.”

“Yes. The star is now numbered S74390E2. Please confirm.”

A large holographic star map appeared before them. It showed everything within five hundred light-years of the Solar System. One of the stars glowed bright red, and a white arrow pointed at it. Cheng Xin was very familiar with it.

“That’s the one. Let’s go there.”

“Course set and confirmed. Halo will enter lightspeed in fifty seconds.”

The holographic star map disappeared. In fact, the ship’s entire hull disappeared, and Cheng Xin and AA seemed to be floating in space itself. The AI had never employed this display mode before. In front of them was the starry sea that was the Milky Way, which was now pure blue, reminding them of the real sea. Behind them was the two-dimensional Solar System, suffused with a bloody red.

The universe shuddered and transformed. All the stars in front of them shot straight ahead, as though that half of the universe had transformed into a black bowl and all the stars were falling into the bottom. They clustered ahead of the ship and fused into a single glow, like a giant sapphire in which it was not possible to distinguish individual stars. From time to time, individual stars shot out of the sapphire and swept past the pure black space to fall behind the ship, changing color the whole way: from blue to green, then yellow, and turning red once they were behind the ship. Looking back from the ship, the two-dimensional Solar System and the stars fused into a red ball like a campfire at the end of the universe.

Halo flew at the speed of light toward the star that Yun Tianming had given Cheng Xin.