Cixin Liu: Death's End

Yifan shook his head slowly. “I study a grand universe whose diameter is sixteen billion light-years. I don’t want to spend the rest of my life in this universe that’s only a kilometer in each direction. Let’s go back.”

“I must advise against that,” said Sophon. “We can’t precisely determine how fast time is passing in the great universe, but I can be certain that at least ten billion years have passed there since the time you came here. Planet Blue has long since vanished, and the star Mr. Yun gave you was extinguished a long time ago. We know nothing of the conditions in the great universe, and it’s possible that it’s not even three-dimensional anymore.”

“I thought you could move the exit of the mini-universe at lightspeed,” Yifan said. “Can’t you move it around to find a habitable location?”

“If you insist, I will try. But I still think staying here is the best choice. There are two possible futures if you remain: If the Returners succeed in their mission, the great universe will collapse into a singularity and lead to a new big bang so that we can go to the new universe. But if the Returners fail and the great universe dies, you can live out the rest of your lives in this mini-universe. This isn’t too bad.”

“If everyone in every mini-universe thinks that way,” said Cheng Xin, “then they will have doomed the great universe.”

Sophon gazed at Cheng Xin wordlessly. Given the speed of Sophon’s thought, perhaps this period of time felt as long as several centuries to her. It was hard to imagine that software and algorithms could produce such a complex expression. Perhaps Sophon’s AI software had brought up all the memories accumulated across almost twenty million years since she had met Cheng Xin. All these memories seemed to precipitate in her gaze: sorrow, admiration, surprise, reproach, regret… so many complicated feelings mixed together.

“You’re still living for your responsibility,” Sophon said.

All my life has been spent climbing up a flight of stairs made of responsibility.

When I was little, my only duty was to study hard and obey my parents.

Later, in high school and college, the responsibility to study hard continued, but there was also the added obligation to make myself useful rather than a drain on society.

By the time I started to work toward my doctorate, my responsibilities became more concrete. I needed to contribute to the development of chemical rockets, to build more powerful, more reliable rockets so that more materials and a few men and women could be sent into Earth orbit.

Later, I joined the PIA, and my responsibility was to send a probe into space a light-year away to meet the invading Trisolaran Fleet. This was a distance about ten billion times greater than the distance I had worked with as a rocket engineer.

And then, I received a star. During the new era, it brought me previously unimaginable responsibilities. I became the Swordholder, whose duty was to maintain dark forest deterrence. Looking back on it now, perhaps it was a bit of an exaggeration to claim that I held the fate of humankind; but I really did control the direction of development for two civilizations.

Later, my responsibilities became more complicated: I wanted to endow humans with lightspeed wings, but I also had to thwart that goal to prevent a war.

I don’t know how much those catastrophes and the final destruction of the Solar System had to do with me. Those are questions that could never be answered definitively. But I’m certain they had something to do with me, with my responsibilities.

And now, I’ve climbed to the apex of responsibility: I am responsible for the fate of the universe. Of course this responsibility doesn’t belong only to me and Guan Yifan, but we own a share of the responsibility, a share of something that I never could have imagined.

I want to tell all those who believe in God that I am not the Chosen One. I also want to tell all the atheists that I am not a history-maker. I am but an ordinary person. Unfortunately, I have not been able to walk the ordinary person’s path. My path is, in reality, the journey of a civilization.

And now we know that this is the journey that must be made by every civilization: awakening inside a cramped cradle, toddling out of it, taking flight, flying faster and farther, and, finally, merging with the fate of the universe as one.

The ultimate fate of all intelligent beings has always been to become as grand as their thoughts.

Through Universe 647’s control system, Sophon managed to move the mini-universe’s exit inside the great universe. The door moved quickly through the great universe, searching for a habitable world. The amount of information that the door could transmit to the mini-universe was very limited, and no images or videos were possible. All that could be sent back was a rough analysis of the environment. This was a number between negative ten and ten, indicating the habitability of the environment. Humans could survive only if the number were greater than zero.

The door jumped tens of thousands of times in the great universe. After three months, only once did they discover a habitable planet, with a rating of three. Sophon had to concede that this was probably the best result they could get.

“A rating of three indicates a dangerous and inhospitable world,” Sophon warned.

“We’re not afraid,” said a resolute Cheng Xin. Yifan nodded. “Let’s go there.”

The door appeared in Universe 647. Like the door Cheng Xin and Guan Yifan had seen on Planet Blue, it was also a rectangle limned by glowing lines. But this door was much bigger, perhaps to make it easier to transport material through it. Initially, the door was not connected to the great universe, and anything could pass through it without leaving the mini-universe. Sophon adjusted its parameters so that anything moving through it would disappear and reappear in the great universe.

Next, it was time to return matter from the mini-universe to the great universe.

Sophon had explained that the mini-universe had no matter of its own. All of its mass had come from material brought out of the great universe. Of the several hundred mini-universes constructed by the Trisolarans, Universe 647 was one of the smallest. In total, it required about five hundred thousand metric tons of matter from the great universe, which was about the carrying capacity of a large oil tanker. It was practically nothing at the scale of the universe.

They began with the soil. After the last harvest, the field had been left fallow. The robots used a wheelbarrow to cart the moist earth; at the door, two of the robots lifted the wheelbarrow to dump the soil through the door; and the soil disappeared. It happened very quickly. Three days later, all the soil in the mini-universe was gone. Even the trees around the house had been returned through the door.

With all the soil removed, they saw the metallic floor of the mini-universe. The floor was pieced together with smooth metal tiles that reflected the sun like a mirror. The robots took off the metal tiles one by one and sent them through the door as well.

Underneath the floor was a small spaceship. Although the ship was less than twenty meters long, it contained the most advanced technologies of the Trisolarans. Designed with human occupants in mind, it could seat three, and was equipped with both a nuclear fusion drive and a curvature drive. There was a miniature ecological cycling system aboard suitable for human needs as well as equipment for hibernation. Like Halo, it was capable of landing and taking off from planetary surfaces. It had a slender, streamlined profile, perhaps to make it easier to go through the mini-universe’s door. It had been intended for the inhabitants of Universe 647 to enter the new great universe after the next big bang. It could serve as a living base for a considerable amount of time, until they found a suitable location in the new universe. But now, they would use it to return to the old great universe.