by Cixin Liu
Tiny snowflakes—three-dimensional ones—now fell from the light purple Plutonian sky. These were the nitrogen and ammonia that had sublimated in the burst of energy during the Sun’s flattening, and which were now freezing into snow as the temperature plummeted following the Sun’s extinguishment. The snow fell more heavily, and soon accumulated a thick layer over the monolith and Halo. Although there were no clouds, the heavy snow blurred Pluto’s sky, and the two-dimensional Sun and the planets turned hazy behind a curtain of snow. The world looked smaller.
“Don’t you feel at home?” AA lifted both hands and spun in the snow.
“I was just thinking the same thing,” Cheng Xin said, and nodded. She had also thought of snow as something unique to the Earth, and the giant snowflakes around the flattened Earth had confirmed this feeling. The snow falling on this cold, dark world on the edge of the Solar System surprisingly provided her a trace of the warmth of home.
Luo Ji watched as AA and Cheng Xin tried to catch the snow. “Hey, you two! Don’t even think about taking off your gloves!”
Cheng Xin did feel an impulse to take off her gloves and catch the snow with her bare hands. She wanted to feel the slight chill, and watch the crystalline snowflakes melt with her own body heat.... but of course she had enough presence of mind to not indulge the impulse. The nitrogen-ammonia snowflakes were at a temperature of minus-210-degrees Celsius. If she really took off her gloves, her hand would turn as fragile and hard as glass and the feeling of being on Earth would disappear instantaneously.
“There’s no more home,” Luo Ji said, shaking his head and leaning against his cane. “Home is now just a picture.”
The nitrogen-ammonia snow didn’t last long. The snowflakes thinned out and the purple haze from the nitrogen-ammonia atmosphere faded. The sky was once again perfectly transparent and dark. They saw that the Sun and the planets had grown even bigger, indicating that Pluto had moved even closer to that two-dimensional abyss.
When the snow stopped, a bright glowing light appeared near the horizon. The intensity of the light grew rapidly, and soon overwhelmed the fading two-dimensional Sun. Although they couldn’t see the details, they knew that it was Jupiter, the Solar System’s largest planet, falling into the plane. Pluto spun slowly, and part of the flattened Solar System had fallen below the horizon, so they thought they wouldn’t get to witness Jupiter’s collapse, but it appeared that the rate of fall into two dimensions was accelerating.
They asked Halo’s AI to look for transmissions from Jupiter. Very few images and videos were being transmitted now, and most were indecipherable. Almost all of the messages they got were audio only. Every communication channel was filled with noise, mostly human voices, as though all the remaining space in the Solar System had been filled with a frenzied sea of people. The voices cried, screamed, sobbed, laughed hysterically... and some even sang. The chaotic background noise made it impossible to tell what they were singing, only that it was many voices singing in harmony. The music was solemn, slow, like a hymn. Cheng Xin asked the AI whether it was possible to receive any official broadcasts from the Federation Government. The AI said that all official communications from the government had terminated when the Earth was flattened. The Federation Government couldn’t fulfill the promise to carry out its duties until the end of the Solar System after all.
Ships trying to escape continued to stream by the vicinity of Pluto.
“Children, it’s time to go,” said Luo Ji.
“Let’s go together,” said Cheng Xin.
“What’s the point?” Luo Ji shook his head and smiled. He pointed at the monolith with his cane. “I’m more comfortable over there.”
“All right. We’ll wait until Uranus is flattened so that we get to spend more time with you,” AA said. There really didn’t seem to be any point in insisting. Even if Luo Ji got on Halo, it would only delay the inevitable by another hour. He didn’t need that bit of time. Indeed, if Cheng Xin and AA didn’t have a mission to carry out, they wouldn’t care for that bit of time either.
“No. You must go now!” Luo Ji said. He struck the ground with his cane forcefully, which made him float up under the low gravity. “No one knows how much faster the collapse is happening now. Carry out your mission! We can stay in contact, and that’s no different from being together.”
Cheng Xin hesitated for a moment, then nodded. “All right. We’ll leave. Stay in contact!”
“Of course.” Luo Ji lifted his cane in farewell and turned to walk toward the monolith. With the light gravity, he almost floated over the snow on the ground and had to use the cane to slow himself. Cheng Xin and AA watched until the aged figure of this Wallfacer, Swordholder, and humanity’s final grave keeper disappeared behind the door of the monolith.
Cheng Xin and AA went back inside Halo. The yacht took off right away, its thrusters tossing up snow everywhere. Soon, the ship achieved Pluto’s escape velocity—just a hair above one kilometer per second—and reached orbit. From the porthole and the monitor they could see that swaths of white now joined the blue and black patches of the Plutonian surface. The giant words “Earth Civilization,” written in multiple scripts and languages, had been covered by the snow and were almost illegible. Halo passed through the gap between Pluto and Charon as though flying through a canyon, the two celestial bodies were so close.
In this “canyon” there were now many other moving stars—the escaping spaceships. They all moved far faster than Halo. One ship swept past Halo at a distance of no more than a hundred kilometers, and the glow from its nozzles lit up Charon’s smooth surface. They could clearly see its triangular hull and the nearly ten-kilometer-long blue flame shooting out of its nozzles.
The AI explained, “That’s Mycenae, a midsized planetary ship without an ecological cycling system. After leaving the Solar System, a passenger would not last five years, even if all the ship’s supplies were used to sustain only them.”
The AI didn’t know that Mycenae would not be able to leave the Solar System. Like all the other escaping ships, it would continue to exist for no more than three hours in three-dimensional space.
Halo flew out of the Pluto-Charon canyon and left the two dark worlds for open space. They saw the entirety of the two-dimensionalized Sun and Jupiter, whose flattening process was almost over. Now, except for Uranus, the vast majority of the Solar System had fallen into the plane.
“Oh, heavens! Starry sky!” AA cried out.
Cheng Xin knew that she was referring to Van Gogh’s painting. True, the universe really did look like the painting. The painting in her memory was almost a perfect copy of the two-dimensional Solar System before her eyes. Giant planets filled space, the areas of the planets seeming to exceed even the gaps between them. But the immensity of the planets did not give them any sense of substantiality. Rather, they looked like whirlpools in space-time. In the universe, every part of space flowed, churned, trembled between madness and horror like fiery flames that emitted only frost. The Sun and the planets and all substance and existence seemed to be only hallucinations produced by the turbulence of space-time.
Cheng Xin now recalled the strange feeling she had experienced each time she had looked at Van Gogh’s painting. Everything else in the painting—the trees that seemed to be on fire, and the village and mountains at night—showed perspective and depth, but the starry sky above had no three-dimensionality at all, like a painting hanging in space.
Because the starry night was two-dimensional.
How could Van Gogh have painted such a thing in 1889? Did he, having suffered a second breakdown, truly leap across five centuries and see the sight before them using only his spirit and delirious consciousness? Or, maybe it was the opposite: He had seen the future, and the sight of this Last Judgment had caused his breakdown and eventual suicide.
“Children, is everything all right? What are you going to do next?” Luo Ji appeared in a pop-up window. He had taken off his space suit, and his white hair and beard floated
in the low gravity like in water. Behind him was the tunnel that had been intended to last a hundred million years.
“Hello! We’re going to toss the artifacts into space,” AA said. “But we want to keep Starry Night.”
“I think you should hold on to them all. Don’t toss any. Take them and leave.”
Cheng Xin and AA looked at each other. “Go where?” AA asked.
“Anywhere you like. You can go to any place in the Milky Way. In your lifetimes, you could probably get to the Andromeda Galaxy. Halo is capable of lightspeed flight. It is equipped with the world’s only curvature propulsion drive.”
Utter shock. AA and Cheng Xin couldn’t speak.
“I was a part of the group of scientists who worked on curvature propulsion in secret,” said Luo Ji. “After Wade died, those who had worked at Halo City didn’t give up. After those who had been imprisoned were released, they built another secret research base, and your Halo Group was revived and developed enough to keep it going. Do you know where the base was? Mercury, another place in the Solar System where few set foot. Four centuries ago, another Wallfacer, Manuel Rey Diaz, used giant hydrogen bombs to blast a crater there. The base was built in that crater, and its construction took over thirty years. The whole base was covered with a dome. They claimed that it was a research institute to study solar activity.”
A bright shaft of light pierced the porthole. AA and Cheng Xin ignored it, but the ship’s AI explained that Uranus had also undergone “state change,” meaning that it had also collapsed into two dimensions. By now, nothing stood between them and Pluto.
“Thirty-five years after Wade’s death, the research into curvature propulsion picked up at the Mercury base. They continued from the point where they were able to move a two-millimeter segment of your hair two centimeters. The research continued for half a century—though they were interrupted a few times for various reasons—and they gradually moved from theoretical research to technological development. During the last stages of the development process, they had to perform experiments on large-scale curvature propulsion. This was a problem for the Mercury base because the base’s resources were limited, and an experiment would produce massive trails, which would expose the Mercury base’s true goals. In reality, based on the comings and goings at the base for more than fifty years, it was inconceivable that the Federation Government had no clue what the Mercury base was really up to, but due to the small scale of the experiments and the fact that all the research was done under cover of other projects, the government had tolerated the base’s activities. Large-scale experiments, however, required the government’s cooperation. We sought it out, and the collaboration went very well.”
“Did they repeal the laws proscribing lightspeed ships?” Cheng Xin asked.
“No, not at all. The government collaborated with us because...” Luo Ji tapped his cane against the ground and hesitated. “Let’s not get into that for now. A few years ago, we completed three curvature engines and conducted three unmanned tests. Engine Number One entered lightspeed about one hundred and fifty astronomical units from the Sun, and returned here after flying at lightspeed for a while. For the engine itself, the experiment lasted only ten minutes or so, but for us, it was three years before the engine returned. The second test involved Engines Number Two and Number Three simultaneously. Right now, both of them are outside the Oort Cloud, and should return to the Solar System in six years.
“Engine Number One, which has already been tested, is installed in Halo.”
“But how could they have sent Cheng Xin and I alone?” AA shouted. “There should at least be two men with us.”
Luo Ji shook his head. “There was no time. The collaboration between the Halo Group and the Federation Government occurred in secret. Very few people knew of the existence of the curvature engines, and even fewer knew where the only engine left in the Solar System was installed. And it was too dangerous. Who knows what people are capable of when the end is nigh? Everyone would fight over Halo, and maybe nothing would be left afterward. And so we had to get Halo away from the Bunker World before releasing news of the dark forest strike to the public. There really wasn’t any time left. Cao Bin sent Halo to Pluto because he wanted you to take me with you. He should have just had Halo enter lightspeed at Jupiter.”
“Why didn’t you come with us?” AA shouted.
“I’ve lived long enough. Even if I get onto the ship, I won’t live much longer. I’d rather stay here as a grave keeper.”
“We can come back for you!” Cheng Xin said.
“Don’t you dare! There’s no time!”
The three-dimensional space they were in accelerated toward the two-dimensional plane. The two-dimensional Sun, which had now completely extinguished and appeared as a vast, dark red, dead sea, took up most of the view from Halo. Cheng Xin and AA noticed that the plane was not completely flat, but undulating! A long wave slowly rolled across the plane. It was a similar wave in three-dimensional space that had allowed Blue Space and Gravity to find warp points to enter four-dimensional space. Even in places where there were no two-dimensional objects in the plane, the rippling wave was apparent. The waves were a visualization of two-dimensional space in three dimensions that occurred only when the two-dimensional space was large enough.
On Halo itself, the space-time distortion produced by the accelerated fall had started to become apparent as space was stretched in the direction of the fall. Cheng Xin noticed that the circular portholes now appeared as ovals, and the slender AA now looked short and squat. But Cheng Xin and AA felt no discomfort, and the ship’s systems were operating normally.
“Return to Pluto!” Cheng Xin ordered the AI. Then she turned to Luo Ji’s window. “We’re going to come back. There’s time—Uranus is still being flattened.”
The AI replied stiffly, “Among all authorized users in communication range, Luo Ji has the highest authorization level. Only he can order Halo to return to Pluto.”
Luo Ji smiled before the tunnel. “If I wanted to go, I would have gotten on the ship with you earlier. I’m too old for voyages far from home. Do not worry about me, children. Like I said, I don’t think I’ve missed anything. Prepare for curvature propulsion!”
Luo Ji’s last words were directed at the ship’s AI.
“Course parameters?” asked the AI.
“Continue along the current heading. I don’t know where you want to go, and I don’t think you know, either. If you do think of a destination, just point it out on the star map. The ship is capable of automatic navigation to most stars within fifty thousand light-years.”
“Affirmative,” said the AI. “Initiating curvature propulsion in thirty seconds.”
“Do we need to be immersed in deep-sea fluid?” AA asked—though rationally, she knew that under conventional propulsion, such acceleration would compress her into a pancake no matter what kind of fluid she was immersed in.
“You don’t need any kind of preparation. This propulsion method relies on manipulating space, so there’s no hypergravity. Curvature propulsion drive online. System is operating within normal parameters. Local space curvature: twenty-three point eight. Forward curvature ratio: three point forty-one to one. Halo will enter lightspeed in sixty-four minutes, eighteen seconds.”
For Cheng Xin and AA, the AI’s announcement was like a Full Stop order, because everything suddenly quieted down. They understood that the silence was due to the nuclear fusion engine being shut off, but the humming produced by the fusion reactor and the thrusters disappeared without being replaced by any other noise. It was hard to believe that some other engine had been started.
But signs of curvature propulsion did appear. The distortion in space gradually disappeared: The portholes returned to being circles, and AA looked slender again. Looking through the portholes, they could still see other escaping ships passing by Halo, but they now passed far more slowly.
The ship’s AI began to play some of the messages passing between the escap
ing ships—perhaps because the messages concerned Halo.
“Look at that ship! How is it able to accelerate so fast?” a woman screamed.
“Oh! The people inside must have been crushed into meat pies,” a man said.
Another man spoke up. “You idiots. The ship itself would be crushed under that kind of acceleration. But look at it: It’s perfectly fine. That’s not a fusion drive, but something entirely different.”
“Curvature propulsion? A lightspeed ship? That’s a lightspeed ship!”
“The rumors were true, then. They were building secret lightspeed ships so that they could escape....”
“Aaahhhhh...”
“Hey, any ships ahead? Stop that ship! Crash into it. No one should live if we all have to die!”
“They can reach escape velocity! They can run away and live! Ahhhh! I want the lightspeed ship! Stop them; stop them and kill everyone inside!”
Another scream—this one from AA inside the ship. “How can there be two Plutos?”
Cheng Xin turned to the information window AA was looking at. The window showed a view of Pluto taken by the ship’s monitoring system. Although Pluto was some distance away, it was clear that both Pluto and Charon had been duplicated, and the twins were lined up side by side. Cheng Xin noticed that some of the flattened objects in the two-dimensional space had also been duplicated. The effect was like selecting a portion of a picture using image-processing software, cloning it, and then moving the clone a bit to the side.
“That’s due to the fact that light slows down inside the trail left by Halo,” Luo Ji said. His image was growing distorted, but his voice still came through clearly. “Pluto is still moving. One of the Plutos you are seeing is the result of slow light. Once Pluto has moved outside of Halo’s trail, light traveling at standard speed provides you with a second image. That’s why you’re seeing double.”