by Cixin Liu
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.
“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.
“Europa?”
“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...
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.
“How... how close was that?” Cheng Xin asked in an unsteady voice.
“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.”
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.
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.
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.
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.
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.
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.
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 illuminate
d 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.
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.
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.
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.
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 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.
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.
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.
“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 engineerin
g, 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.
Cao Bin’s succinct reply to Cheng Xin’s query was “world-sense.”
“What?”
“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.”
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.
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.
