Cixin Liu - Death's End

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 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.