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.

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.

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

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.

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.

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.

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.

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 Bai 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.

Ten days after the two ships left port, General Vasilenko and Bai Ice, 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 Bai Ice was in charge of technical matters.

Bai Ice's original name was Bai Aisi. 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.

"Look familiar?" Vasilenko gestured at everything around them.

"Indeed. But the self-confidence and arrogance of humanity are all gone," said Bai Ice.

Bai 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.

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.

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."

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.

"Check this out."

"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. Bai 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. Bai 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.

"It's from the Doomsday Battle?" asked an awed Bai Ice.

"The target of our exploration might be more dangerous than even the droplets this time," Bai 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 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.

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.

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.

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.

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.

This was another scene that seemed familiar.

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.

Maybe it really was a letter?

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.

The scoop closed around the slip and the arm pulled back. But the slip remained where it was.

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.

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.

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

Bai 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.

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

"Don't worry. This time, we can trust our intuition." Vasilenko patted Bai Ice on the shoulder, but Bai Ice did not feel much comfort.

Bai 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.

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

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 Bai Ice caught him.

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.

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.

"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 Bai Ice's hand.

Bai 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."

Bai 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.

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.

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.

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.

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.

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.

Bai 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.

Bai 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.

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

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.

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."

"Professor Ding, why not wait until you're back to tell me?"

"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?"

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."

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.

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

"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?"

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."

"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 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."

"Perhaps I would have gone with her."

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."

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.

"If she had talked with you more back then, perhaps she wouldn't have chosen to go."

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."

"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."

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.

"That's true, especially those tobacco pipes… But I don't think I'll get them."

"Maybe it's not nonsense."

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.

Bai 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.

"Hahahahaha… There's no table untouched at the dinner party, and there's no virgin untouched in the universe… waheeheeheehee… wahahahaha…"

"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."

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.

"What?"

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

Bai 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?"

Bai 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.

Bai Ice grabbed Vasilenko by the shoulders and gazed into his eyes. "Don't be arrogant!"

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.

On Revelation, Bai 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, Bai Ice was anxious and irritable, like a trapped animal.

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.

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

"Has it evaporated?" Vasilenko asked.

"I don't think so. But we can't see it anymore." Bai Ice shook his head wearily and closed the information windows around him one by one.

"It's rising!"

"Look out below! What's going on?"

"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.

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

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

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

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.

Bai 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.

"There, of course."

"Channel open."

"Open a channel to Command," Bai Ice said. "There's no time, so we'll treat this as our formal report."

"The space is flowing? Where to?"

"Hadn't it evaporated?"

"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."

"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?"

"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."

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

"Can we escape it?"

"What is the escape velocity?"

"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."

"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.

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.

Bai 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.

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

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

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

"You know what I'm thinking of? Needle-Eye's pictures from Yun Tianming's fairy tales," Bai Ice said.

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

"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." Bai Ice now looked calm and stoic.

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.

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.

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.

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.

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

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.

"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 Bai 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.

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