by Cixin Liu
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 tur
ned 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 escaping 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.”
“The light slows down?” Cheng Xin sensed a great secret was being revealed.
Luo Ji continued, “I understand that you figured out curvature propulsion from a small boat propelled by soap. Let me ask you: After the ship reached the other side of the bathtub, did you pull it back and try again?”
They hadn’t. Due to the fear of sophons, Cheng Xin had tossed the paper boat aside. But it was easy to figure out what would have happened.
“The ship would not move, or at least it would only move slowly,” Cheng Xin said. “After the first trip, the surface tension of the water in the tub had already been reduced.”
“That’s right. It’s the same principle with lightspeed ships. The very structure of space itself is changed by the trail of a curvature-propelled ship. If a second curvature-propelled ship were placed inside the trail of the first, it would hardly move. Within the trails of lightspeed ships, one must use a more powerful curvature propulsion drive. It would still be possible to use curvature propulsion to achieve the highest speed possible within such a space, but the maximum velocity is much lower than the maximum velocity of the first ship. In other words, the speed of light through vacuum is lowered within the trail of lightspeed ships.”
“How much lower?”
“Theoretically, it could be reduced to zero, but that’s not achievable in reality. But if you adjust the curvature ratio of Halo’s engine to the maximum, you can lower the speed of light in its trail down to exactly what we’ve been looking for: sixteen point seven kilometers per second.”
“Then you’d have…” AA said, staring at Luo Ji.
The black domain, Cheng Xin thought.
“The black domain,” Luo Ji said. “Of course, a single ship is insufficient to produce a black domain containing an entire star and its planetary system. We calculated that it would take more than a thousand curvature propulsion ships to accomplish such a thing. If all these ships started near the Sun and spread out in every direction at lightspeed, the trails they produced would expand and connect to each other, forming a sphere that contained the entire Solar System. The speed of light within this sphere would be sixteen point seven kilometers per second—a reduced-lightspeed black hole, or a black domain.”
“So the black domain can be a product of lightspeed ships.…”
In the cosmos, the trail of a curvature propulsion drive could be a sign of danger, as well as a safety announcement. A trail far away from a world was the former; a trail that shrouded a world the latter. It was like a noose, indicating danger and aggression when held in the hand, but safety when wrapped around the holder’s own neck.
“Correct, but we found out about it too late. While studying curvature propulsion, the experimenters plowed ahead of the theoreticians. You should know that was Wade’s style. Many experimental discoveries could not be explained by theory, but without a theoretical framework, some phenomena were simply ignored. During the earliest years of research—when their biggest achievement was moving your hair—the trails produced by curvature propulsion were thin and small, and hardly anyone paid any attention, even though there were plenty of signs of something strange going on: For instance, after the trail expanded, the low speed of light caused quantum integrated circuits in nearby computers to malfunction, but no one sought to investigate. Later, after the experiments grew in scale, people finally discovered the secret of lightspeed trails. It was because of this discovery that the Federation Government agreed to collaborate with us. They did, in fact, pour all the resources they could command into the development of lightspeed spaceships, but there just wasn’t enough time.” Luo Ji shook his head and sighed.
Cheng Xin said what he couldn’t bring himself to say. “There were thirty-five years between the Halo City Incident and the completion of the Mercury base. Thirty-five precio
us years were lost.”
Luo Ji nodded. Cheng Xin thought the way he looked at her was no longer kind, but rather resembled the fires of the Last Judgment. His gaze seemed to say, Child, look at what you’ve done.
Cheng Xin now understood that of the three paths of survival presented to humanity—the Bunker Project, the Black Domain Plan, and lightspeed ships—only lightspeed ships were the right choice.
Yun Tianming had pointed this out, but she had blocked it.
If she hadn’t stopped Wade, Halo City might have achieved independence. Even if the independence was short-lived, they could have discovered the effects of lightspeed trails and changed the government’s attitude toward lightspeed ships. Humanity might have had time to construct a thousand lightspeed ships and build the black domain, to avoid this dimensional strike.
Humanity could have divided into two parts: those who wanted to fly to the stars, and those who wanted to stay within the black domain and live in tranquility. Each would have gotten what they wanted.
In the end, she had committed another grave error.
Twice, she had been placed in a position of authority second only to God, and both times she had pushed the world into the abyss in the name of love. This time, no one could fix her mistake for her.
She began to hate someone: Wade. She hated that he had kept his promise. Why? Out of his masculine pride, or for her? Cheng Xin understood that Wade did not know the effects of curvature propulsion trails. His goal in researching lightspeed ships was stated eloquently by that anonymous Halo City soldier: a fight for freedom, for a chance to live as free men in the cosmos, for the billions and billions of new worlds out there. She believed that if he had known that lightspeed spaceflight was the only path to life for humanity, he would not have kept his promise.
She could not shirk her responsibility. It didn’t matter whether she really was second only to God—if she was in that position, she had to carry out her duty.
