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#37813, your hibernation is at an end. You have been in hibernation for 62 years, 8 months, 21 days, and 13 hours. Your remaining hibernation allotment is 238 years, 3 months, 9 days. This is Asia Hibernation Center #1, Bunker Era, Year 11, May 9, 2:17 P. M.

The small information window hovered in front of the just-awakened Cheng Xin for no more than a minute before disappearing. She looked at the smooth metallic ceiling. Out of habit, she stared at a certain spot in the ceiling. During the age she last entered hibernation, doing so would have caused the ceiling to recognize her gaze and bring up an information window. But the ceiling didn't respond. Although she still didn't have the strength to turn her head, she was able to see part of the room: All the walls were made of metal and there were no information windows. The air remained empty as well, with no holographic displays. The metal in the wall looked familiar: stainless steel or aluminum alloy, no decorations.

A nurse appeared in her field of view. She was very young and didn't look at Cheng Xin. Instead, the nurse busied herself around her bed, probably disconnecting the medical equipment attached to her body. Cheng Xin's body couldn't sense what the nurse was doing, but something about the nurse seemed familiar to her -- her uniform. During the last age Cheng Xin was awake, people wore self-cleaning clothes that always looked brand new, but this nurse's white uniform showed signs of wear. Although it was still clean, she could see signs of it being old, signs of the passage of time.

There were many pedestrians in the hallway, and no one paid attention to Cheng Xin. She concentrated on the clothes people wore. A few were medical personnel in white uniforms, and the rest wore simple, plain clothing that resembled work overalls. Cheng Xin had the impression that many people here seemed to be from the Common Era, but soon realized that she was wrong. The Common Era was a long time ago, and the human race had changed eras four times already. It was impossible for so many Common Era people to be around.

The hallway was made of empty metallic walls as well. Other than some ceiling lights, there were no other decorations. The lights looked ordinary enough, and Cheng Xin saw that the frame around one of the lights was loose and dangled from the ceiling. Between the frame and the ceiling she saw… wires.

The ceiling began to move. Cheng Xin's bed was being pushed out of the awakening room. She was astonished to find that the nurse was pushing the bed -- the bed actually needed someone to push it to move.

Cheng Xin struggled to recall the information window she had seen upon first awakening, but she couldn't be certain it had really been there. It now seemed a hallucination.

Cheng Xin's bed was pushed into a small room. "Number 37813 awakened without irregularities," the nurse called out. "She's in recovery room twenty-eight." Then the nurse left and closed the door. Cheng Xin noticed that she had to pull the door shut.

The men who had disappeared during the Deterrence Era had returned. This was another age capable of producing men.

Everyone seemed to be in a hurry. This seemed to be another swing of the pendulum: the leisure and comfort of the last age had disappeared, and it was once again a harried society. In this age, most people no longer belonged to the leisure class, but had to work for a living.

Her impression was due to the fact that she saw some men who looked like the men she was used to.

She was left alone in the room. For a long time, no one came to check on her, a situation in total contrast to the previous two awakenings she had experienced, when she had received a great deal of attention and care. She was certain of two things: First, in this age, hibernation and awakening were common events. Second, not many people knew that she had awakened.

She suddenly wondered if she had just awakened from a long dream. The Deterrence Era, the Broadcast Era -- they were all dreams. Although the memories were clear, they seemed too surreal, fantastic. Perhaps she had never leapt across time on three occasions, but had been in the Common Era all along?

After Cheng Xin recovered some motor control, she moved her head and saw the window. She remembered the world before she had gone into hibernation: The hibernation center had been a giant tree at the edge of the city, and she had been in one of the leaves near the top, from where she could see the grand city-forest. But now, outside this window, she could only see a few ordinary buildings erected on the ground, all of them the same shape and design. Based on the sunlight glinting off them, they were constructed of metal as well. The buildings gave her the feeling of having returned to the Common Era.

A holographic display window appeared next to her bed, removing her doubts. The window contained only a few simple buttons that could be used to call for the doctor and the nurse. The place seemed very familiar with the hibernation recovery process: The window had appeared just as Cheng Xin recovered the ability to lift her hand. But it was only a small window; the hyperinformation society where information windows filled every surface was gone.

Unlike the previous two awakenings, Cheng Xin recovered very quickly. By the time it was dark out, she was already able to get out of bed and walk about a bit. She found that the center provided only the simplest services. A doctor came in once to give her a cursory examination and then left; she had to do everything else by herself. She had to bathe herself while she still felt weak all over. As for meals, if she hadn't asked for them through that tiny holographic display, she might never have gotten to eat. Cheng Xin wasn't annoyed by this lack of solicitousness, as she had never completely adjusted to that excessively generous era where every person's every need was taken care of. She was still a Common Era woman at heart, and she felt at home here.

The next morning, a visitor came to see her. She recognized Cao Bin right away. This physicist had once been the youngest Swordholder candidate, but now he was much older, and a few strands of white appeared in his hair. Cheng Xin was certain, though, that he had not aged by sixty-two years.

"Mr. Thomas Wade asked me to come and get you."

"We'll talk about it after we get there." Cao Bin paused, and then added, "I'll take you around this new world before then so that you can make the right decision based on facts."

"What happened to you? You weren't awake these last sixty years," Cheng Xin asked.

"There have been some developments… We'll talk about it later." Cao Bin clearly didn't relish the topic.

Cheng Xin glanced at the undistinguished buildings outside the window; she didn't feel the world was new.

"What happened?" Cheng Xin's heart sank as she recalled the conditions for her awakening.

"How's the curvature propulsion project going?"

"I went into hibernation at about the same time you did. Seventeen years later, the circumsolar particle accelerator was operational, and I was awakened to research basic theory. That took fifteen years. Later, the research work turned to technical applications, and I was no longer needed, so I went back into hibernation until two years ago."

Cheng Xin looked outside again. A breeze passed by, and a small tree in front of the window rustled. A cloud seemed to pass overhead, and the glint given off by the metallic buildings dimmed. How could such a commonplace world have anything to do with lightspeed spaceships?

Half an hour later, Cheng Xin, dressed in a white outfit appropriate for this era, came onto a balcony of the hibernation center with Cao Bin. The city spread out before her, and Cheng Xin was again struck by the feeling that time had flowed backwards. After she had awakened for the first time during the Deterrence Era, the impact of seeing the giant forest-city for the first time was indescribable. After that, she never thought she would again see a cityscape so familiar: The plan for the city was very regular, as though all the buildings had been erected at once. The buildings themselves were monotonous and uniform, as though designed solely for utility with no consideration for architectural aesthetics. All of them were rectangular with no surface decorations, and all sported the same metallic gray exterior -- reminding her strangely of the aluminum lunch boxes of her youth. The buildings were neatly and densely arranged as far as she could see. At the horizon, the ground rose up like the side of a mountain, and the city extended onto the mountainside.

Cao Bin followed Cheng Xin's gaze and laughed. "You must feel the same as when I first awakened -- rather disappointed in this era, aren't you?… If you are up to it, let's go outside and take a look."

The clouds began to dissipate, revealing a large opening. Through the opening, Cheng Xin did not see a blue sky; instead, she saw… more ground.

The sun was below the clouds.

"Where is this?" Cheng Xin asked.

"Hmm, why is it overcast again? We can't see the other side." Cao Bin didn't answer her question, but shook his head at the sky in disappointment, as though the weather had something to do with Cheng Xin's understanding of this new world. But soon, she saw how strange the sky was.

The ground in the sky was studded with the buildings of a city very similar to the city around her, except she was now looking "down"-- or "up"-- at it. This must have been the "other side" Cao Bin referred to. Cheng Xin realized that the rising "mountainside" in the distance wasn't a mountain at all, but continued to rise until it connected with the "sky." The world was a giant cylinder, and she was standing on the inside of it.

The new world that had seemed so common a moment ago now stunned her. Cheng Xin felt that she had finally, truly awakened.

"This is Space City Asia I, in the shadow of Jupiter," Cao Bin said.

By custom, the central axis of the space city was treated as oriented north-south. They got on a bus outside the hibernation center -- this was a real bus that moved along the ground; probably running on electricity, but it looked indistinguishable from an ancient city bus. The bus was crowded, and Cheng Xin and Cao Bin took the last two seats at the back so that additional passengers had to stand. Cheng Xin thought back to the last time she had taken a bus -- even during the Common Era, she had long ceased riding crowded public transportation.

In the afternoon, Cao Bin brought Cheng Xin on a trip to the gateway terminal at the northern end of the city.

The bus moved slowly, so she could take in the view leisurely. Everything now held a new meaning for her. She saw swaths of buildings sweep past the window, interspersed with green parks and pools; she saw two schools with exercise yards painted in blue; she saw brown soil covering the ground on the sides of the road, looking no different from soil on Earth. Broad-leafed trees resembling Chinese parasol trees lined the road, and advertising billboards appeared from time to time -- Cheng Xin didn't recognize most of the products or brands, but the style of the ads was familiar.

The main difference from a Common Era city was that the entire world seemed to be constructed out of metal. The buildings were metallic, and the inside of the bus seemed to be mostly metal as well. She saw no plastic, and no composites either.

Cheng Xin paid the most attention to the other passengers on the bus. Across the aisle sat two men, one of whom dozed with a black briefcase on his lap, while the other wore yellow work overalls with black oil stains. Next to the man's feet was a tool bag, and some instrument Cheng Xin did not recognize poked out of it: It resembled an ancient power drill, but was translucent. The man's face showed the exhaustion and numbness of someone who performed physical labor. The last time Cheng Xin had seen such an expression was on the faces of migrant laborers in Common Era cities. In front of her sat a young couple. The man whispered something in the woman's ear, and the woman giggled from time to time while spooning something pink out of a paper cup -- ice cream, since Cheng Xin picked up the sweet fragrance of cream, no different from her memory of more than three centuries ago. Two middle-aged women stood in the aisle -- they were of a type familiar to Cheng Xin: The drudgery of everyday life had ground away their glamour, and they no longer took care with their appearance or were fashionable. Women like that had disappeared during the Deterrence Era or the Broadcast Era. Back then, women always had smooth, delicate skin, and no matter how old they were, they looked beautiful and refined, appropriate for their age. Cheng Xin eavesdropped on their conversation:

"You got it wrong. The morning market and the evening market have similar prices. Don't be lazy. Go to the wholesale market on the west side."

"They don't have enough, and they won't sell at wholesale prices anyway."

"You have to go later, after seven or so. The vegetable vendors will be gone, and they'll sell at wholesale prices."

"It's not right to charge separately for the heat; that should have been included in the electric bill."

"If they had subbed for that fool earlier they wouldn't have lost so badly."

She overheard snippets of other conversations in the bus as well.

"The city government is different from the atmospheric system, much more complicated. When you get there, pay attention to the office politics. Don't get too close to anyone at first, but don't hold yourself apart either."

"The other day, when they had to make an orbital adjustment, Park Four's water spilled again and flooded a large area."

"Don't be so disappointed. I've been here since the city was built, and how much do you think I make every year?"

"That fish is no longer fresh. Don't even think about steaming it."

Cheng Xin's heart felt warm and content. Ever since she had awakened for the first time during the Deterrence Era, she had been searching for this feeling. She had thought she'd never find it. She absorbed the conversations around her as though slaking a thirst, and didn't pay much attention to Cao Bin's narration of the city.

"If she doesn't like him, he should just give up. All that effort is just going to be wasted."

"That can't be authentic. I don't even think it's a high-quality imitation. Are you kidding me? At that price?"…

Space City Asia I was one of the earliest to be built as part of the Bunker Project. It was a regular cylinder that simulated gravity with the centrifugal force generated by spinning. With a length of thirty kilometers and a diameter of seven kilometers, its usable interior surface area was 659 square kilometers, about half the size of ancient Beijing. Once, about twenty million inhabitants had lived here, but after the completion of newer cities, the population had decreased to about nine million, so that it was no longer so crowded…

"The space city was adjusting its position," said Cao Bin.

Cheng Xin saw another sun appear in the sky before her. Cao Bin explained that there were a total of three artificial suns in the space city, all of them floating along the central axis, each separated by about ten kilometers. These produced energy by nuclear fusion, and brightened and dimmed on a twenty-four-hour cycle.

Cheng Xin felt a series of jolts. The bus was already at a stop, and the tremors seemed to originate from deep within the ground. She felt a force pushing against her back, but the bus remained unmoving. Outside the window, she could see the shadows cast by the trees and buildings suddenly shift to a new angle as the artificial suns abruptly shifted positions. But soon, the suns moved back into place. Cheng Xin saw that none of the passengers seemed surprised by this.

The bus arrived at the last stop after about thirty minutes. After getting off the bus, she saw that the everyday scenes that had so intoxicated her disappeared. In front of her was an enormous wall whose immense size made her gasp. It was as though she was standing at the end of the world -- and indeed, she was. This was the "northernmost" point in the city, a large circular disk eight kilometers in diameter. She couldn't see the entire disk from where she stood, but she could tell that the ground rose up on both sides of her. The top of the disk -- the other side of the city -- was about as high as the peak of Mount Everest. Many radial spokes converged from the rim of the disk to the center, four kilometers above. Each spoke was an elevator shaft, and the center was the space city's gateway.

Before entering the elevator, Cheng Xin cast a lingering glance back at this city that already seemed so familiar. From here, all three suns were visible in a row toward the other end of the city. It was dusk, and the suns dimmed, turning from a blinding orange-white to a gentle red, bathing the city in a warm golden glow. Cheng Xin saw a few girls in white school uniforms chatting and laughing on a lawn not too far away, their hair wafting in the breeze and drenched in the golden glow of the evening sun.

The interior of the elevator car was very spacious, like a large hall. The side facing the city was transparent, turning the car into an observation deck. Every seat was equipped with seat belts because, as the elevator rose, gravity quickly diminished. As they looked outside, the ground sank lower, while the "sky," another ground, grew clearer. By the time the elevator reached the center of the circle, gravity had completely disappeared, as well as the sensation of "up" and "down" when looking outside. Since this was the axis around which the city spun, the ground surrounded them in every direction. Here, the view of the city was at its most magnificent.

The three suns had dimmed to the level of moonlight, and their colors shifted to silver. Viewed from here, the three suns -- or moons -- were stacked on top of each other. All the clouds were concentrated in the gravity-free zone, forming an axis of white mist extending through the center of the city to the other end. The "southern" end, forty-five kilometers away, could be seen clearly. Cao Bin told Cheng Xin that that was where the city's thrusters were located. The lights of the city had just come on. In Cheng Xin's eyes, a sea of lights surrounded her and extended into the distance. She seemed to be looking down a giant well whose wall was covered with a brilliant carpet.

Cheng Xin casually locked her gaze on a certain spot in the city, and found the arrangement of buildings there very similar to the residential district of her home back in the Common Era. She imagined a certain ordinary apartment building in that area and a certain window on the second floor: Through blue curtains, a gentle light seeped, and behind the curtain, her mom and dad waited for her… She could not hold back her tears.

Ever since awakening for the first time during the Deterrence Era, Cheng Xin had never been able to integrate into the new eras, always feeling like a stranger from another time. But she could never have imagined that she would once again feel at home more than half a century later, here behind Jupiter, more than eight hundred million kilometers from the Earth. It was as if everything that she had been familiar with from more than three centuries ago had been picked up by a pair of invisible hands, rolled up like a giant painting, and then placed here as a new world slowly spinning around her.

Cheng Xin and Cao Bin entered a weightless corridor. This was a tube in which people moved by pulling themselves along handholds on cables. The passengers riding up from all the elevators along the rim gathered here to exit the city, and the corridor was filled with streaming crowds. A row of information windows appeared around the circular wall of the corridor, and the animated images in the windows were mostly news and ads. But the windows were few in number and neatly arranged, unlike the chaotic profusion of information windows in the previous era.

Cheng Xin had long since noticed that the overwhelming hyperinformation age had apparently ended. Information appeared in this world in a restrained, directed manner. Was this the result of changes in the Bunker World's political and economic systems?

Emerging from the corridor, Cheng Xin first noticed the stars spinning overhead. The spin was very rapid and made her dizzy. The view around her opened up dramatically. They were standing on a circular plaza with a diameter of eight kilometers "atop" the space city. This was the city's spaceport, and many spacecraft were parked here. Most of the vessels were shaped not too differently from those Cheng Xin had seen over sixty years ago, though these were generally smaller. Many were about the size of ancient automobiles. Cheng Xin noticed that the flames at the nozzles of the spaceships as they took off were far dimmer than what she remembered from more than half a century ago. The glow was a dark blue and no longer so blinding. This probably meant that the miniature fusion engines were much more efficient.

It was very cold here. Only when a nearby vessel took off did the engine's heat bring a brief feeling of warmth. Cheng Xin shuddered -- not just from the cold, but because she realized that she was completely exposed to space! But the air around her and the air pressure were real, and she could feel cold breezes. It appeared that the technology to contain an atmosphere in a nonenclosed area had advanced even further, to the point where an atmosphere could be maintained in completely open space.

Cheng Xin saw an eye-catching red-glowing circle all around the exit, with a radius of about a hundred meters. She quickly understood its meaning: The space city was spinning, and, outside the circle, the centrifugal force became very strong. Moving outside the warning circle meant a dramatic increase in centrifugal force, and vessels parked out there had to be anchored, while pedestrians needed to wear magnetic shoes lest they be thrown out.

Cao Bin saw her shock and said, "Oh, right now we can only maintain an atmosphere about ten meters thick above 'ground.'" He hadn't been in this world for too long, either, but he was already jaded by the technology that seemed like magic to Cheng Xin. He wanted to show her far more impressive sights.

Against the background of the spinning stars, Cheng Xin saw the Bunker World.

From here, most of the space cities behind Jupiter could be seen. She saw twenty-two cities (including the one she stood on), and there were four more blocked by the city they stood on. All twenty-six cities (six more than planned) were hiding in the shadow of Jupiter. They were loosely lined up in four rows, and reminded Cheng Xin of the spaceships lined up behind the giant rock in space more than sixty years ago. To one side of Asia I was North America I and Oceania I, and to the other side was Asia III. Only about fifty kilometers separated Asia I from its neighbors on either side, and Cheng Xin could feel their immensity, like two planets. The next row of four cities was 150 kilometers away, and it was difficult to tell their size visually. The most distant space cities were about one thousand kilometers away, and looked like delicate toys from here.

Cheng Xin thought of the space cities as a school of tiny fish hovering in place behind a giant rock to avoid the torrents in the river.

One of the space cities in front suddenly emitted a blue light. It was as though a small blue sun appeared in space, casting long shadows of the people and spaceships on the plaza. Cao Bin told Cheng Xin that this was because the space city's thrusters had been activated to adjust its position. The space cities revolved around the Sun in parallel with Jupiter, just outside its orbit. Jupiter's gravity gradually pulled the cities closer, and the cities had to constantly adjust their positions with thrusters. This operation required a great deal of energy. Once, the suggestion had been floated to turn the cities into Jupiter's satellites that would only shift into new orbits around the Sun after the issuance of a dark forest strike warning. But until the advance warning system had been further refined and proven to be reliable, no space city wanted to take the risk.

Behind the other three gas giants were three more space city clusters, consisting of a total of thirty-eight space cities. Twenty-six were behind Saturn, four behind Uranus, and eight more behind Neptune. Those space cities were in safer locations, though the environs were even more desolate.

North America I, closest to Asia I, was a pure sphere. It and the cylindrical Asia I represented the two extremes of space city design. Most of the other space cities were football-shaped, though the ratios of major to minor axes were different in each. A few other space cities took on unusual shapes: a wheel with spokes, a spindle, etc.

"Lucky you! Now you get to see a sight that happens only once every three days." Cao Bin pointed into space. Cheng Xin saw a tiny white dot in the distance, gradually growing bigger. Soon, it was a white sphere as big as a Ping-Pong ball.

"That's right. We're very close to its orbit right now. Watch your footing and don't be scared."

Cheng Xin tried to figure out what Cao meant. She had always thought of celestial bodies as moving slowly, almost imperceptibly -- as they did in most Earth-based observations. But then she remembered that the space city was not a Jovian satellite but remained stationary relative to it. Europa, on the other hand, was a satellite that moved very fast. She remembered its speed was about fourteen kilometers per second. If the space city was very close to Europa's orbit, then…

"Europa?"

The white sphere expanded rapidly -- so fast that it seemed unreal. Europa soon took up most of the sky, and turned from a Ping-Pong ball into a giant planet. The sensation of "up" and "down" switched in an instant, and Cheng Xin felt as if Asia I were falling toward that white world. Next, the three-thousand-kilometer-diameter moon swept overhead so that for an instant, it took up the entire sky. The space city was skimming over the icy oceans of Europa, and Cheng Xin could clearly see the crisscrossing lines in that frozen landscape, like lines in a giant palm print. The air, disturbed by the passage of Europa, whipped around her, and Cheng Xin felt an invisible force dragging her from left to right -- if she weren't wearing magnetic shoes, she was sure she'd be pulled off the ground. Whatever was nearby that hadn't been secured to the ground flew up, and a few cables attached to spaceships also drifted into the air. A terrifying rumbling came from below her -- it was the immense frame of the space city reacting to the rapidly shifting gravity field of Europa. It took only about three minutes for Europa to hurtle past Asia I, and then it was on the other side of the city and began to shrink rapidly. The eight space cities in the two front-most rows all activated their thrusters to adjust their positions after the disturbance caused by Europa. Eight fireballs lit up the sky.

Cao Bin found the dinghy he had taken to come here. It was tiny, shaped and sized like an ancient automobile, capable of seating only two. Cheng Xin instinctively felt unsafe going into space in such a tiny vehicle, even though she knew her fear wasn't reasonable. Cao Bin told the AI to go to North America I, and the dinghy took off.

"The closest approach, like you experienced just now, was a hundred and fifty kilometers, basically brushing right by us. We don't really have a choice. Jupiter has thirteen moons, and it's impossible for the space cities to avoid them all. Europa's orbit is inclined only slightly from the equator, and so it's very close to these cities here. It's the main source of water for the Jovian cities, and we've built a lot of industry on it. But when the dark forest strike comes, all of it will have to be sacrificed. After the solar explosion, all of the Jovian moons' orbits will shift dramatically. Maneuvering the space cities to avoid them at that time will be a very complicated operation."

"How… how close was that?" Cheng Xin asked in an unsteady voice.

Cheng Xin saw the ground receding quickly, and the dinghy flew along at a tangent to the spinning city. Soon, the eight-kilometer-diameter plaza came into view, followed by the entirety of Asia I. Behind the cylinder was a vast expanse of dark yellow. Only when the edge of this yellow expanse appeared did Cheng Xin realize that she was looking at Jupiter. Here, in the shadow of the gas giant, everything was cold and dark, and the Sun seemed to not exist at all. Only the phosphorescence of the planet's liquid helium and hydrogen, diffused through the thick atmosphere, formed patches of hazy light roving about like eyeballs behind the closed eyelids of a dreamer. The immensity of Jupiter astonished Cheng Xin. From here, she could only see a small portion of its rim, and the rim's curvature was minuscule. The planet was a dark barrier that blocked out everything, and once again gave Cheng Xin the feeling of standing at a giant wall at the end of the world.

In the following three days, Cao Bin took Cheng Xin to visit four more space cities.

Unlike Asia I, small spacecraft could enter the city directly from the gateway at the north pole. Once the dinghy was inside, the entire world spun around it, and the dinghy had to match the city's spin before landing.

Cheng Xin and Cao Bin rode a high-speed rail to go to low-latitude regions, and the train moved far faster than the bus in Asia I. Cheng Xin saw that the buildings here were denser and taller, looking like a metropolis. At the high-latitude, low-gravity regions especially, the buildings' heights were limited only by the volume of the sphere. Near the polar regions, some buildings were as tall as ten kilometers, looking like long thorns extending up from the ground toward the sun.

The first was North America I, the closest city to Asia I. The main advantage of its spherical construction was that a single artificial sun at the center was sufficient to illuminate the entire city, but the disadvantage of such a design was obvious as well: The gravity changed depending on one's latitude. The equator had the most gravity, which decreased as you went up in latitude. The polar regions were weightless. Inhabitants in the different regions had to adjust to life under various gravity conditions.

Here, Cheng Xin got to see a splendid sight that was absent from Asia I: the equatorial ring-ocean. As a matter of fact, most space cities had ring-oceans of various widths, and Asia I was rather unique in lacking one. In spherical or football-shaped cities, the equator was the lowest point in the city's simulated gravity, and all the city's water naturally collected there, forming a sparkling, undulating belt for the city. Standing on the shore, one could see the ocean rising on both sides and dividing the "sky" behind the sun. Cheng Xin and Cao Bin took a fast boat and navigated around the sea -- a journey of some sixty kilometers. The water in the sea came from Europa, clear, cold, and reflecting rippling light onto the skyscrapers on both sides. The dikes along the edge of the sea closest to Jupiter were higher, to avoid the water spilling out when the city accelerated during position adjustments. Even so, when the city had to engage in unexpected maneuvers, small-scale flooding would occur from time to time.

North America I had been completed early on. With a radius of twenty kilometers and twenty million inhabitants, it was the largest city by population. It acted as the prosperous commercial center for all the Jovian cities.

Next, Cao Bin took Cheng Xin to Europe IV, which sported a typical football-shaped design. Its distinguishing characteristic was the lack of a common artificial sun. Every district had its own miniature fusion sun, and the tiny suns hovered about two hundred to three hundred meters high to provide illumination. The advantage of this approach was that the weightless axis could be more efficiently utilized. The axis of Europe IV was taken up by the longest -- or tallest -- building among all the space cities. It was forty kilometers long and connected the north and south poles of the football. Since the interior of the building was weightless, it was mainly used as a spaceport and commercial entertainment district.

Europe IV had the smallest population of all the cities, only 4.5 million. It was the wealthiest city of the Bunker World. The exquisite houses illuminated by miniature suns amazed Cheng Xin. Each house came with its own swimming pool, and a few had wide lawns. Tiny white sails dotted the serene equatorial sea, and people sat on the shore, fishing leisurely. She saw a yacht sail by slowly, and it looked as luxurious as any yacht on ancient Earth. There was a cocktail party being held aboard the yacht with live musicians… She was astonished that such life could be transplanted into the shadow of Jupiter, eight hundred million kilometers from the Earth.

Pacific I, on the other hand, was the antithesis of Europe IV. This was the very first city completed by the Bunker Project, and like North America I, it was a sphere. Unlike all the other Jovian cities, it did orbit Jupiter as a satellite.

Millions of construction workers had lived in Pacific I during the early years of the Bunker Project. As the project progressed, it was used to warehouse construction materials. Later, as the numerous flaws of this early-phase experimental space city became apparent, it was abandoned. But, after the resettlement to the Bunker World had been completed, people began to live here again, and finally formed a city of their own, with a city government and police force. However, the authorities only maintained the most basic public infrastructure, and society was left basically to run on its own. Pacific I was the only city to which people were free to immigrate without a residential permit. Most of the population consisted of unemployed and homeless wanderers, poor people who had lost social security for various reasons, and bohemian artists. Later, it became the base for extremist political organizations.

Pacific I had no city thrusters, and there was no artificial sun inside. It also didn't spin, so the interior was completely weightless.

There was no notion of land ownership in Pacific I because all the buildings drifted around with no permanent location. In principle, each resident had the right to use any space in the city. The city had a large number of homeless individuals who didn't even possess a shack. All of their possessions were kept in a large net sling to prevent them from scattering everywhere, and the owners drifted along with the net slings. Transportation within the city was simple: There were no cars or weightless cables or personal thrusters. The residents moved around by pushing and kicking off buildings and drifting. Since the buildings were densely packed inside the city, one could navigate anywhere that way, but this method of locomotion required great skill. As Cheng Xin observed the residents flitting around the dense clusters of floating buildings, she was reminded of gibbons swinging easily from branch to branch.

After entering the city, Cheng Xin saw a fairy-tale world. It was as if a broken-down but once prosperous city had lost gravity abruptly, so that everything floated in the air. Pacific I was a city in permanent night, and each building maintained illumination with a nuclear battery. Thus, the interior was filled with glowing, floating lights. Most of the buildings in the city were simple shacks built from abandoned construction materials. Since there was no "up" or "down," most of the shacks were cube-shaped, with windows (which also acted as doors) on all six sides. Some were shaped as spheres, which had the advantage of being more resilient, as the drifting buildings inevitably collided against each other.

Cheng Xin and Cao Bin drifted close to a group of homeless men gathered around an open fire. Such a fire would have been prohibited in any other city. The fuel seemed to be some kind of flammable construction material. Due to the weightlessness, the flames did not rise up, but formed a ball of fire floating in place. The way they drank was also special. They tossed alcohol out of bottles, forming liquid spheres in the air. Then the men, dressed in rags and with unshaven faces, drifted along with them, capturing the spheres with their mouths and swallowing. One of the drunken men vomited, and the vomit rushing out of his mouth propelled him back, sending him tumbling in midair…

Cheng Xin and Cao Bin came to a market. All the goods floated in the air, forming a heterogeneous mess illuminated by a few drifting lights, with customers and vendors drifting among the hovering objects. In this chaos, it seemed hard to tell what belonged to whom, but if a customer examined something closely, a vendor would drift over to haggle. The goods offered for sale included clothing, electronics, food and liquor, nuclear batteries of various capacities, small arms, and so on. There were also exotic antiques on sale. In one place, a few metallic fragments were offered at very high prices. The vendor claimed that it was debris gathered from the outer Solar System from warships destroyed during the Doomsday Battle -- it was impossible to tell if he was telling the truth.

Cao Bin took Cheng Xin to the edge of the city -- the inside face of the spherical hull. There were no buildings attached to the hull, and there was no soil -- everything was left as bare as the day the city was constructed. It was impossible to tell the curvature in a small area, and they seemed to be standing on a large, flat plaza. Above them, the dense buildings of the city floated, and flickering lights projected onto the "plaza." Cheng Xin saw that the hull was marked with all kinds of graffiti, stretching as far as she could see. These pictures were vibrant, wild, unrestrained, wanton and full of energy. In the shifting, uncertain light, they seemed to come alive, as though they were dreams deposited from the city above.

Cheng Xin was surprised to find a vendor who sold antique books. She flipped through a few -- these books were not ancient for her. All the books drifted in a cloud, and many had their pages spread open like a flock of white-winged birds in the light… Cheng Xin saw a small wooden box drift in front of her, marked as cigars. She caught it, and immediately a young boy kicked his way over and swore up and down that these were authentic ancient Havana cigars that had been preserved for close to two hundred years. Since they had dried out a bit, he was willing to let them go at a low price that she would not be able to find anywhere else in the Solar System. He even opened the box to let Cheng Xin see what she was getting. She agreed and bought them.

Cao Bin also told Cheng Xin that the Federation Government had devoted enormous resources to build a social welfare system here in Pacific I. The six million or so inhabitants here were mostly unemployed, but at least they could get the basic necessities for life.

Cao Bin didn't bring Cheng Xin deeper into the city. According to him, the center of the city was chaotic and rather violent. Gangs fought each other, and a few years ago, one of the gang fights had managed to rupture the hull, causing a massive decompression incident. Later, the gangs seemed to come to some kind of unspoken agreement, and settled their disputes in the center of the city, away from the hull.

"What will happen here in the event of a dark forest strike?"

"Only annihilation. This city has no thrusters, and even if it did have them, it would be impossible to move it into the shadow of Jupiter and keep it there. Look --" He pointed to the drifting buildings. "If the city accelerated, everything would smash through the hull. Then the city would be like a bag with a hole in the bottom. If we receive a dark forest strike alert, the only thing that can be done is to evacuate the population to the other cities."

As they left the floating city in eternal night, Cheng Xin gazed at it through the porthole of the dinghy. This was a city of poverty and homelessness, but it also possessed its own rich life, like a weightless version of the famous Song Dynasty painting, Along the River During the Qingming Festival.

She understood that compared to the last era, the Bunker World was not at all an ideal society. The migration to the rim of the Solar System had caused some toxic social conditions, long eliminated by progress, to reemerge. This wasn't exactly regression, but a kind of spiraling ascent, a necessary condition for the exploration and settlement of new frontiers.

After they left Pacific I, Cao Bin brought Cheng Xin to see a few more space cities with unusual designs. One of them, fairly close to Pacific I, was a wheel with spokes, not unlike a larger version of the space elevator terminal station that Cheng Xin had visited more than sixty years ago.

Cheng Xin was a bit puzzled by the designs of the cities. As a matter of engineering, the wheel seemed ideal. It was far easier to construct than the large, hollow shells used by the other cities, and when completed, a wheel was stronger and better able to survive disasters, as well as being easier to expand.

"What?"

There were some other cities with even stranger designs. Most of these were industrial or agricultural centers with no permanent residents. For instance, there was a city called Resource I. Its length was 120 kilometers, but the diameter was only three kilometers, like a thin stick. It did not spin around the long axis, but rather, tumbled about its center, end over end. The city's interior was divided into levels, and the gravity at each level differed dramatically. Only a few levels were suitable for living, while the rest were devoted to various industries adapted to the different gravities. According to Cao Bin, near Saturn and Uranus, there were cities formed by combining two or more stick-shaped cities into crosses or stars.

Cao Bin's succinct reply to Cheng Xin's query was "world-sense."

"The sensation of being inside a world. A space city has to have ample interior volume and wide-open views so that the residents can feel they are living inside a world. Although the usable interior surface area isn't too different from a hollow-shell design, in a wheel design, people always know that they are living inside a narrow tube or a series of such tubes."

Currently, most cities docked along their axis of spin. This way, after docking, the cities could continue to spin as before without changing the distribution of gravity. There were proposals for parallel or perpendicular docking as well, which would allow the combined cities to expand in multiple directions, as opposed to only along the axis of spin. But the spin of such combinations would dramatically change the interior distribution of gravity, and these proposals had not been tested so far.

The earliest city clusters of the Bunker Project were built near Jupiter and Saturn. Later, as cities were built near Uranus and Neptune, some new city-design concepts emerged. The most important idea was city docking. In those two clusters at the edge of the Solar System, every city was equipped with one or more standardized docks so that cities could be interconnected. Docking multiplied the space available for inhabitants and created even better world-sense, greatly encouraging economic development. In addition, after docking, the atmospheres and ecological systems of the various cities merged, and that helped to stabilize their operation and maintenance.

The biggest combined city so far was located at Neptune, where four of the eight cities were docked together along their axis of spin, forming a two-hundred-kilometer-long combined city. When necessary -- such as when a dark forest strike alert was issued -- the combined city could be quickly taken apart to increase the mobility of each city. People hoped that, one day, all the cities in each cluster could be combined into one, so that humanity would live in four complete worlds.

In total, behind Jupiter, Saturn, Uranus, and Neptune, there were sixty-four large space cities and nearly a hundred medium and small cities, plus numerous space stations. Nine hundred million people lived in the Bunker World.

This was almost the entirety of the human race. Even before the arrival of the dark forest strike, Earth civilization had battened down the hatches.

Every space city was politically equivalent to a state. The four city clusters together formed the Solar System Federation, and the original UN had evolved into the Federation Government. Most of the Earth's major ancient civilizations had passed through a city-state stage -- and now, city-states had reemerged at the rim of the Solar System.

The Earth was now barely inhabited. Only about five million people remained there. These were individuals who did not wish to leave their home and who had no fear of the prospect of Death at any moment. Many brave men and women living in the Bunker World also traveled to Earth as tourists, though each journey meant gambling with their lives. As time passed, the anticipated dark forest strike loomed larger, and people gradually adapted to life in the Bunker World. Their yearning for their homeland lessened as they busied themselves in their new homes, and fewer and fewer now visited the Earth. The public no longer cared much about news from the home world, and were only vaguely aware that Nature was enjoying a resurgence. Forests and grasslands covered every continent, and those who stayed behind had to carry guns to defend against wild beasts when they went out, but it was rumored that they lived like kings, each with a vast estate and personal forests and lakes. The entire Earth was now only a single city in the Solar System Federation.

The sun has set.

Cheng Xin and Cao Bin's small dinghy was now at the outer edge of the Jovian cities. Before the immense, dark Jupiter, these cities appeared so small, so alone, like a few shacks at the foot of a gigantic cliff. From a distance, faint candlelight spilled out of them. Though tiny, they were the only hints of warmth, of home, in this endless frigidity and desolation, the goal of all weary travelers. Cheng Xin's mind churned up a short poem she had read in middle school, a composition by a long-forgotten Chinese poet of the Republican era:

Delighting in all they can see,

Mountain, tree, rock, river,

People light their lamps with great interest,

All the grand buildings are buried in shadows.

Hoping to find what they wish.