by Cixin Liu
As they approached, the door on the bottom of the ship slid open noiselessly. They carried the artifacts up the airstair and into the cabin, took off their helmets, and took a deep breath in their cozy little world. Relief filled their hearts—without consciously being aware of it, they already thought of the yacht as home.
Cheng Xin asked the ship’s AI whether it had received any transmissions from Neptune and Saturn. As soon as she made the request, information windows flooded forth like a colorful avalanche that threatened to bury them. The scene reminded them of the first false alarm of 118 years ago. Back then, most of the information had come from media reports, but now, the news media seemed to have disappeared. Most of the information windows contained no discernible images at all—some were blurred, others shook, and most showed meaningless close-ups. But a few of the windows were filled with patches of gorgeous color which, as they flowed and shifted, revealed complex, detailed structures. They probably showed the two-dimensional universe.
AA asked the AI to filter the images. The AI asked them what kind of information they wanted. Cheng Xin asked for information about the space cities. The flood of windows cleared and was replaced by about a dozen others arranged in order. One of the windows enlarged and moved before the others. The AI explained that this had been taken twelve hours ago at Europe VI in the Neptune cluster. The city had once been part of a combined city that had separated after the strike alert.
The image was stable, and the field of view wide. The camera was probably at one end of the city, and almost the entire city could be seen.
Electricity had gone out in Europe VI, and only a few searchlight beams projected unsteady circles of light onto the city’s far side. The three artificial fusion suns along the city’s axis had all turned into silvery moons, giving out only illumination, but no heat. This was a standard football-shaped city, but the buildings inside the city were very different from what Cheng Xin had seen half a century ago. The Bunker World had prospered, and the buildings inside the city were no longer monotonous and uniform. They were much taller, and each had a unique design. The tips of some of the skyscrapers almost touched the axis of the city. Buildings in the shapes of trees reappeared as well, and they looked about as large as the ones that had been built on Earth, though the leaves hung more densely. It was possible to imagine the city’s beauty and magnificence when lit up at night. But now, only cold moonlight illuminated it, and the tree-buildings cast wide shadows so that the rest of the city appeared as ruins nestled in the shade of a giant forest.
The city had stopped spinning and everything was weightless. Countless objects floated through the air—vehicles, miscellaneous goods, and even entire buildings.
A black belt of clouds appeared along the city’s axis, connecting the two poles. The ship’s AI outlined a rectangular region in the image and zoomed in, creating a new information window. Cheng Xin and AA were shocked to see that the black cloud was formed from people drifting in the middle of the city! Some of the weightless individuals had pulled together into a cluster; some had linked hands and formed a line; but most floated alone. Everyone wore helmets and clothes that covered all parts of their body—most likely space suits. Even during Cheng Xin’s last time out of hibernation, it was hard to tell everyday clothes apart from space suits. Everyone seemed to have a pack for life-support systems—some wore it on their back, while others held it in their hands. But most people had their visors open, and it was possible to see a light breeze blowing through the city, indicating that the city still retained a breathable atmosphere. Many had congregated around the suns, perhaps hoping for more light as well as a bit of warmth, but the light emitted by the fusion suns was cold light. The silvery light shone through cracks in the people-cloud and turned into dappled shadows in the surrounding city.
According to the ship’s AI, of the six million inhabitants of Europe VI, half had already left the city on space vehicles. Of the remaining three million, some had no way to get off the city, but most understood that any attempt at escape was hopeless. Even if some ships miraculously managed to escape the collapsing zone and reached outer space, most ships had no ecological cycling system to maintain life for long. Access to stellar ships that could survive indefinitely in outer space was still a privilege of the very few. These people chose to wait for the end in a place they were familiar with.
The transmission wasn’t muted, but Cheng Xin couldn’t hear anything. The people-cloud and the city were both eerily quiet. Everyone looked in one direction. That part of the city looked no different from any other, filled with crisscrossing streets and row upon row of buildings. Everyone waited. In the watery, cold moonlight, people’s faces appeared as white as ghosts. The sight reminded Cheng Xin of the bloody dawn in Australia 126 years ago. Like then, Cheng Xin felt as though she were looking down upon an ant colony, and the black people-cloud looked just like a drifting swarm of ants.
Someone in the people-cloud screamed. A glowing dot appeared at a spot on the city’s equator, the same spot where everyone had been gazing. It was like a small opening in the roof of a dark house letting in the sunlight.
That was where Europe VI first came into contact with two-dimensional space.
The light grew rapidly and turned into a glowing oval. The light it emitted was sliced into many shafts by the tall buildings all around, and illuminated the people-cloud on the city’s axis. The space city now resembled a giant ship whose bottom had been breached, sinking in a flat sea. The plane of the two-dimensional space rose like water, and everything that came into contact with the surface instantaneously turned into two dimensions. Clusters of buildings were cut, and their two-dimensional images spread out on the plane. Since the city’s cross section was but a small portion of the entire flattened city, most of the two-dimensionalized buildings had expanded beyond the oval marked by the city’s hull. On the rising, expanding plane, gorgeous colors and complicated structures flashed by and zoomed away in every direction, as though the plane was a lens through which one could see colorful beasts running. Because the city still possessed air, they could hear the sound of the three-dimensional world falling into two dimensions: a crisp, piercing series of crunches, as though the buildings and the city itself were made of exquisitely carved glass and a giant roller was crushing everything.
As the plane continued to rise, the people-cloud began to spread out in the opposite direction, like a curtain being lifted by an invisible hand. The scene reminded Cheng Xin of a massive flock of millions of birds that she had seen once. The flock had seemed like a unified organism changing shape in the dusk sky.
Soon, the plane had swallowed one-third of the city, and it continued to flicker frantically as it rose irresistibly toward the axis. Some people had begun to fall into the plane by now. They either fell behind due to malfunctions in their space suit thrusters or they had given up on running. Like drops of colorful ink, they spread open on the plane in an instant, and each appeared as a unique figure in two dimensions. On one of the zoomed-in images shown by the AI, they saw a pair of lovers leaping into the plane while in an embrace. Even after the two had been flattened, it was possible to see the figures in an embrace lying side by side—their postures appeared odd, as though drawn by a clumsy child who did not understand the principles of perspective. Nearby there was a mother who lifted her baby overhead as she fell into the plane, all so that the baby would survive for an extra tenth of a second. The mother and child were also vividly portrayed in this giant painting. As the plane kept on rising, the rain of people falling on it became denser. Two-dimensional human figures flooded forth on the plane, most moving outside the boundary of the space city.
By the time the two-dimensional space approached the axis, most of the surviving population had landed against the city’s far side. Half of the city was now gone, and as people looked “up” they could no longer see the familiar city on the other side, but only a chaotic, two-dimensional sky pressing down on the parts of Europe VI that remaine
d in three dimensions. It was now no longer possible to escape from the main gateway at the north pole, so people congregated around the equator, where there were three emergency exits. The weightless crowd piled into mountains around the exits.
The two-dimensional space passed through the axis and swallowed up the three suns, but the light emitted by the two-dimensionalizing process made the world even brighter.
A low whistling sound began: The city was losing its air to space. The three emergency exits along the equator were wide open, each as large as a football field; outside them was the still-three-dimensional space.
The ship’s AI pushed another information window to the front. This was a feed from space looking down at Europe VI. The two-dimensionalized portion of the space city spread across the invisible plane, making the rapidly sinking, still-three-dimensional portion look minuscule by comparison, like the back of a whale peering out of the vast ocean. Three clumps of black smoke rose out of the city and dissipated in space; the “smoke” was formed from the people blown out by the fierce winds of the decompressing space city. The lonely, three-dimensional island continued to sink and melt into the two-dimensional sea. In less than ten minutes, all of Europe VI had turned into a painting.
The painting of Europe VI was so vast that it was hard to estimate its exact area. It was a dead city, but perhaps it was more accurate to call it a 1:1 drawing of the city. The drawing reflected every detail of the city, down to every screw, every fiber, every mite, and even every bacterium. The precision of the drawing was at the level of the individual atom. Every atom in the original three-dimensional space was projected onto its corresponding place in two-dimensional space according to ironclad laws. The basic principles governing this drawing were that there could be no overlap and no hidden parts, and every single detail had to be laid out on the plane. Here, complexity was a substitute for grandeur. The drawing wasn’t easy to interpret—it was possible to see the overall plan of the city and recognize some big structures, such as the giant trees, which still looked like trees even in two dimensions. But buildings looked very different after being flattened: it was almost impossible to deduce the original three-dimensional structure from the two-dimensional drawing by imagination alone. However, it was certain that image-processing software equipped with the right mathematical model would be able to.
In the information window, it was also possible to see two other flattened space cities in the distance. The cities appeared as perfectly flat continents drifting in dark space, gazing at each other across the plane. But the camera—perhaps located on a drone—was also falling toward the plane, and soon the two-dimensional Europe VI filled the screen.
Close to a million people had escaped Europe VI via the emergency exits; now, caught by the three-dimensional space around them collapsing into two dimensions, they fell toward the plane like a swarm of ants caught in a waterfall. A majestic rain of people fell onto the plane, and the two-dimensional human figures in the city multiplied. Flattened persons took up a lot of area—though still minuscule compared to the vast two-dimensional buildings—and resembled tiny, barely man-shaped marks in the immense picture.
More objects appeared in three-dimensional space in the information window: the skiffs and dinghies that had left Europe VI earlier. Their fusion reactors were operating at maximum capacity, but they still fell inexorably toward the plane. For a moment, Cheng Xin thought the blue flame of the fusion drives penetrated that depthless plane, but the plasma had simply been two-dimensionalized. In those areas, the two-dimensional buildings were distorted and twisted by the two-dimensional flames. Next, the skiffs and dinghies became part of the giant drawing. Obeying the no-overlapping principle, the two-dimensionalized city expanded to give these new objects space, and the whole image resembled spreading ripples on the surface of a pond.
The camera continued to fall toward the plane. Cheng Xin stared at the approaching two-dimensional city, hoping to find signs of movement in the city. But no, other than the distortion caused by the plasma flames earlier, everything in the flat city was still. Similarly, the two-dimensional bodies did not move at all, and gave no signs of being alive.
This was a dead world. A dead picture.
The camera moved still closer to the plane, falling toward a two-dimensional body. The body’s limbs soon filled the whole image, and then came the complicated patterns of muscle fibers and blood vessels. Perhaps it was just an illusion, but Cheng Xin seemed to see red, two-dimensional blood flowing through two-dimensional blood vessels. In a flash, the picture was gone.
* * *
Cheng Xin and AA began their second trip to retrieve more artifacts. They both felt the mission was likely to be meaningless. After observing the two-dimensionalized cities, they understood that the process preserved most of the information from the three-dimensional world. Any information loss would be at the atomic level. Due to the nonoverlapping principle used in projection, the flattened Pluto’s crust wouldn’t be commingled with the artifacts in the museum, and so the information in the artifacts should be preserved. But since they had accepted this mission, they would finish it. Like Cao Bin said, doing something was better than doing nothing.
They exited Halo and saw the two flattened planets still suspended overhead, but now they were much dimmer. This made the new long, glowing belt that appeared below the planets even more noticeable. The light belt went from one end of the sky to the other, like a necklace formed from numerous individual glowing spots.
“Is that the asteroid belt?” Cheng Xin asked.
“Yes. Mars will be next,” said AA.
“Mars is on this side of the Sun right now.”
The two fell silent. Without looking at the flattened asteroid belt, they walked toward the black monolith.
The Earth was next.
In the great hall of the museum, they saw that Luo Ji had already prepped a bunch of additional artifacts for them. Many of them were Chinese-brush-painting scrolls. AA unrolled one of them: Along the River During the Qingming Festival.
Cheng Xin and AA no longer had the initial awe and delight of seeing such precious works of art—compared to the grandeur of the destruction in process outside, this was nothing more than an old painting. When future explorers arrived at the great painting that was the flattened Solar System, they would have trouble imagining that this twenty-four-centimeter-by-five-meter rectangle was once very special.
Cheng Xin and AA asked Luo Ji to come onto Halo. Luo Ji said he would like to see it, and went to look for a space suit.
As the three of them carried the artifacts out of the monolith, the sight of a flattening Earth greeted them.
The Earth was the first solid planet to collapse into two dimensions. Compared to Neptune and Saturn, the “tree rings” in the two-dimensionalized Earth were even more replete with fine details—the yellow mantle gradually shifted over to the deep red nickel-iron core—but the overall area was much smaller than the gas giants.
Unlike in their imagination, they couldn’t see any hint of blue.
“What happened to our oceans?” Luo Ji asked.
“They should be near the outside … But two-dimensionalized water is transparent, so we can’t see it,” AA said.
The three carried the artifacts to Halo in silence. They couldn’t feel the grief yet, like one didn’t immediately feel the pain of a fresh wound cut by a sharp knife.
But the flattened Earth did show her own wonders. At her outermost rim, a white ring gradually appeared. At first it was barely visible, but soon it stood out sharply against the black backdrop of space. The white ring was pure, flawless, but seemed uneven in its makeup, like it was formed from countless small white grains.
“That’s our ocean!” Cheng Xin said.
“The water froze in two-dimensional space,” said AA. “It’s cold there.”
“Oh—” Luo Ji wanted to stroke his beard, but the visor got in the way of his hand.
The three carried the boxes of artifa
cts onto Halo. Luo Ji seemed familiar with the ship’s layout, heading for the ship’s hold without instruction from Cheng Xin or AA. The ship’s AI also recognized him, and accepted his orders. After they secured the artifacts, the three returned to the yacht’s living quarters. Luo Ji asked the AI for a cup of hot tea, and soon, a little robot that Cheng Xin and AA had never seen before brought it to him. Clearly, Luo Ji had some history with this ship that the two women did not know about. They were curious about the story, though more urgent matters had to be taken care of first.
Cheng Xin asked the AI to play some news from the Earth, but the AI said that it had received only a few transmissions from the planet, and the visual and audio content was essentially impossible to make sense of. They looked at the few open information windows and saw only blurred images taken by unmanned cameras. The AI added that it could provide the video taken by the spacecraft monitoring system near the Earth. A new, large window popped up and the flatted Earth filled the screen.
The three immediately thought the image looked unreal, even suspecting that the AI had synthesized the image to fool them.
“What in the world is this?” AA cried out.
“It’s the Earth about seven hours ago. The camera is fifty astronomical units away, and angular magnification is four hundred and fifty times.”
They looked more closely at the holographic video taken by the telescopic lens. The body of the flattened Earth appeared very clearly, and the “tree rings” were even denser than when observed with the naked eye. The collapse had probably already been completed, and the two-dimensional Earth was dimming. But what really shocked them was the frozen two-dimensional ocean—the white ring around the rim of the Earth. They could clearly make out the grains forming the ring: snowflakes! These were unimaginably large snowflakes, hexagonal in plan, but each with unique crystal branches—exquisite, lovely beyond words. To see snowflakes from fifty AU away was already extremely surreal, and these immense snowflakes were arranged side by side on the plane with no overlap, which further enhanced the feeling of unreality. They seemed to be purely artistic portrayals of snowflakes, powerfully decorative, turning the frozen two-dimensional sea into a piece of stage art.
