by Cixin Liu
Cheng Xin said, “I also want to go to the new universe. The singularity and the new big bang will erase all memories of our universe. I want to bring some memory of humanity there.”
Sophon nodded solemnly at Cheng Xin. “That is a great task you’ve set yourself. There are others doing similar work, but you’re the first human from the Solar System to do this.”
“You’ve always had higher goals in life than I,” Yifan whispered to Cheng Xin. She couldn’t tell if he was joking or being serious.
Sophon stood up. “Welcome to your new life in Universe 647. Why don’t we go outside and take a look around?”
Outside, the spring planting was in full swing. The columnar robots were all working the fields. Some used the rakes to level and smooth out the field—the soil was so loose already that it did not need to be plowed; some were planting seeds in the parts that had already been smoothed. The farming techniques they employed were primitive: There were no drag harrows, so the robots had to use small rakes to level the field a bit at a time; there were no planters, so the robots each carried a bag of seeds and buried the seeds in the field one at a time. The entire scene invoked a sense of ancient simplicity. Here, robots seemed somehow more natural than real farmers.
Sophon explained, “We have only enough food stored here to last two years. After that, you’ll need to rely on the food you grow. These seeds are descended from the seeds Cheng Xin sent along with Mr. Yun. Of course, they’ve all been genetically improved.”
Yifan looked somewhat puzzled by the black soil. “I feel that soilless cultivation tanks would be more suitable here.”
Cheng Xin said, “Anyone from the Earth has a kind of nostalgia for soil. Remember what Scarlett’s father told her in Gone With the Wind? ‘Why, land is the only thing in the world worth workin’ for, worth fightin’ for, worth dyin’ for, because it’s the only thing that lasts.’”
Yifan said, “The Solar System humans spilled their last drop of blood to stay with their land—well, save for two drops: you and AA. But what was the point? They didn’t last, and neither did their land. Hundreds of millions of years have passed in the great universe, and do you think anyone still remembers them? This obsession with home and land, this permanent adolescence where you’re no longer children but are afraid to leave home—this is the fundamental reason your race was annihilated. I am sorry if I’ve offended you, but it’s the truth.”
Cheng Xin smiled at the agitated Yifan. “You haven’t offended me. What you said is true. We knew that, but we couldn’t help it. You probably can’t help it, either. Don’t forget that you and all the crew of Gravity were prisoners before becoming Galactic humans.”
“That is true.” Guan Yifan lost some of his fire. “I’ve never thought of myself as a man qualified for space.”
By the standards of space, there were not too many “qualified” men—and it was doubtful Cheng Xin would like any of them. She did think of one person who was probably qualified. His voice still echoed in her ears: We’re going to advance! Advance! We’ll stop at nothing to advance!
“Don’t dwell on the past,” Sophon said in her sweet voice. “Everything starts anew here.”
* * *
A year passed in Universe 647.
The wheat had been harvested twice, and Cheng Xin and Guan Yifan had now watched twice as the green seedlings gradually turned into a sea of golden stalks. The vegetable fields next to the wheat had always remained green.
In this tiny world they were provided with all the other necessities of life. None of the objects had manufacturing marks or brand logos—Trisolarans made them—but they looked exactly like human products.
Cheng Xin and Guan Yifan sometimes went into the fields to work alongside the robots. Sometimes they strolled about the universe—as long as they were careful not to leave footprints, they could keep on walking indefinitely and experience the feeling of traversing countless worlds.
They spent most of their time in front of the computer, however. It was possible to invoke a terminal from anywhere in the small universe, but they didn’t know where the CPU for the computer was located. The computer had a massive databank of text, image, and video from the Earth, most of which dated from before the Broadcast Era. The Trisolarans had clearly gathered the info as they studied humanity, and the material covered every field in the sciences and the humanities.
But even more information existed in the databank written in the Trisolaran language. This massive ocean of data was what interested them the most. Since they couldn’t find any software on the computer for translating Trisolaran writing into human languages, they had to study the Trisolaran script itself. Sophon acted as their teacher, but they soon discovered that this was an extremely difficult endeavor because Trisolaran writing was purely ideographic; unlike human scripts, which were mostly phonetic, Trisolaran writing had no connection to their speech, but expressed ideas directly. In the distant past, humans had also used ideographic scripts—such as some hieroglyphs—but most of these later disappeared.11 Humans read by decoding speech made visible. However, the difficulty didn’t last long. The more they persisted, the easier the learning process became. After struggling for two months, they found themselves making rapid progress. Compared to phonetic scripts, the biggest advantage of an ideographic script was how fast one could read—Cheng Xin and Guan Yifan read at least ten times as fast in Trisolaran as they did with human scripts.
They began to read the Trisolaran material in the databank—at first haltingly, and then faster. They had two initial goals in mind: First, they wanted to know how the Trisolarans had recorded the period of history between their civilization and Earth civilization. Second, they wanted to know how this mini-universe was constructed. For the latter, they understood that they would likely not achieve a specialist’s level of understanding, but they wanted to at least understand it at the level of popular science. Sophon estimated that in order to achieve these two goals, they would need to spend one year to learn how to read Trisolaran better, then take another year to read in depth.
The fundamental principles underlying the small artificial universe seemed unimaginable to them; even the most basic mysteries puzzled them for the longest time. For instance, how could a complete ecological cycle function in a sealed space of only one cubit kilometer? What was the sun? What was its energy source? And most confounding: As a completely sealed system, where did the heat of the mini-universe go?
They asked Sophon these questions. Some she could answer; for others, she referred them to materials in the computer.
They also cared about the answer to one question in particular: Could the mini-universe communicate with the great universe? Sophon told them that there was no way for the mini-universe to transmit any information to the greater universe, but it was possible for the mini-universe to receive broadcasts from the great universe. She explained that all the universes were bubbles above a supermembrane—this was a fundamental conceptual image from Trisolaran physics and cosmology, and she could explain it no further. The great universe had enough energy to propagate information across the supermembrane. However, this was difficult and required a great expenditure of energy—the great universe would have to convert a Milky Way’s worth of matter into pure energy. As a matter of fact, the monitoring systems in Universe 647 often received messages from other great universes on the supermembrane. Some were natural phenomena; some were messages from intelligent beings that could not be decoded—but they had never received any message from the particular great universe they had come from.
Time flowed by day after day like the smooth, placid water in that little brook.
Cheng Xin began to write her memoir so that she could record the history she knew. She named the book A Past Outside of Time.
Sometimes, they also tried to imagine life in the new universe. Sophon told them that according to cosmological theories, the new universe was certain to possess more than four macro dimensions, perhaps even more than ten macr
o dimensions. After the birth of the new universe, Universe 647 could automatically construct an entrance to it and examine the interior conditions. If the new universe possessed more than four dimensions, the mini-universe’s exit could be moved around until a suitable habitable location was found in the great universe. Simultaneously, their mini-universe could establish communications with the refugees of other Trisolaran mini-universes, or even with Galactic human migrants. In the new universe, all the migrants coming from the old universe would practically be one race, and should be able to work together to construct a new world. Sophon emphasized that one characteristic greatly increased the probability of survival in a high-dimensional universe: Out of the many macro dimensions, it was likely that more than one dimension would belong to time.
“Multi-dimensional time?” Cheng Xin couldn’t understand the concept at first.
“Even if time were only two-dimensional, it would be a plane instead of a line,” Yifan explained. “There would be an infinite number of directions, and we could simultaneously make countless choices.”
“And at least one of those choices would turn out to be right,” added Sophon.
* * *
One night, after the second harvest, Cheng Xin woke up to find Yifan not beside her. She got up, went outside, and saw that the sun had already turned to the moon, and the little world was immersed in the watery, cool light. She saw Yifan sitting by the brook, his posture morose.
In this world of two, each of them had grown especially sensitive to the moods of the other. Cheng Xin had already known that something was troubling Yifan. Earlier, he had been sunny and upbeat. Until a few days ago, he had regularly shared his dream that, if they could find a peaceful life in the new great universe, perhaps their children could re-create the human race. But then he had abruptly changed, frequently going off by himself to ponder something, or to calculate something at a computer terminal.
Cheng Xin sat down next to Yifan, and he pulled her into his arms. The moonlit world was very quiet, and all they heard was the babbling brook. The moon revealed a field of ripe wheat; they’d have to start the harvest tomorrow.
“Loss of mass,” Yifan said.
Cheng Xin said nothing. She watched the moonlight dancing in the brook, knowing that Yifan was going to explain.
“I’ve been reading Trisolaran cosmology, and came across a proof for the elegance of the mathematics behind the great universe we all came from. The design of the total mass in the universe was precise and perfect. The Trisolarans had proved that the total mass of the universe was just enough to allow the big crunch. If the total mass were reduced even slightly, the universe would turn from being closed to open, and expand indefinitely.”
“But mass has been lost,” Cheng Xin said. She understood right away what he was getting at.
“Yes. The Trisolarans have already constructed several hundred mini-universes. How many more have been constructed by other civilizations in the universe to escape the big crunch, or for some other purpose? Each of these mini-universes took away some matter from the great universe.”
“We need to ask Sophon.”
“I have. She told me that at the time of Universe 647’s completion, the Trisolarans had not observed any influence from the loss of mass in the great universe. That universe was closed and was certain to eventually collapse.”
“What about after Universe 647 was constructed?”
“She had no idea, of course. She also mentioned that there was a group of intelligent beings in the universe that resembled the Zero-Homers, but they called themselves the Returners. They advocated against the construction of mini-universes, and called for the mass in completed mini-universes to be returned to the great universe.… But she didn’t know much else about them. All right, let’s forget all this. We’re not God.”
“But we’ve long been called on to think about matters that belonged to the province of God.”
They sat by the brook until the moon turned into the sun again.
Three days after the harvest, once all the wheat had been threshed and winnowed and stored away, Cheng Xin and Guan Yifan stood at the edge of the field and watched as the robots plowed the field to prepare for the next planting. The granary was now full, so there was no room for more wheat. Before, they would have debated what to plant for the next season. But now, both of them were troubled and had no interest in the topic. Throughout the entire harvest and threshing process, they had stayed in the house and discussed possible futures. They realized that even their individual life choices affected the fate of the universe, or even the fates of multiple universes. They really felt like God. The weight of responsibility made it hard to breathe, and so they left the house.
They saw Sophon walking toward them along one of the field ridges. Sophon rarely disturbed them and only appeared when they needed her. This time, her walk was different—she was in a hurry and did not exhibit her typical grace and dignity. Her anxious expression was also something they had not seen before.
“We’ve received a supermembrane broadcast from the great universe!” Sophon brought up a window and enlarged it. To make the window easier to see, she also dimmed the sun.
A torrent of symbols scrolled up the screen—the bitmap from the supermembrane broadcast. The symbols were strange and indecipherable. Cheng Xin and Guan Yifan noticed that each row of symbols was different: They rolled past like the surface of a chaotic river.
“The broadcast has been going on for five minutes and is still continuing.” Sophon pointed at the window. “In actuality, the message in the broadcast is very simple and brief, but it has lasted this long because it’s in many languages. We’ve seen a hundred thousand languages already!”
“Is the broadcast aimed at all the mini-universes?” Cheng Xin asked.
“Absolutely. Who else would receive it? They expended so much energy that the message must be important.”
“Have you seen Trisolaran or Earth languages?”
“No.”
Cheng Xin and Guan Yifan realized that this message was a record of which species had survived in the great universe.
By now, tens of billions of years had passed in the great universe. Regardless of the content of the broadcast, if a civilization’s language was listed in the broadcast, it meant that the civilization still existed or had existed once and lasted so long that it had left an indelible mark in the great universe.
The river of symbols continued to flow up the screen: two hundred thousand languages, three hundred thousand, four hundred thousand … a million. The number continued to go up.
There were no Trisolaran and no Earth languages.
“It doesn’t matter,” Cheng Xin said. “We know that we existed; we lived.” She and Guan Yifan leaned against each other.
“Trisolaran!” Sophon cried out and pointed at the screen. By now, over 1.3 million languages had been broadcast, and one row, written in Trisolaran, flashed by. Cheng Xin and Guan Yifan couldn’t catch it, but Sophon did.
“Earth!” Sophon cried out again a few seconds later.
After 1.57 million languages, the broadcast finished.
The window now showed only the message written in Trisolaran and Earth languages. Cheng Xin and Guan Yifan couldn’t even read the message because tears blurred their eyes.
On the day of the universe’s Last Judgment, two humans and a robot belonging to the Earth and Trisolaran civilizations embraced each other in ecstasy.
They knew that languages and scripts evolved very quickly. If the two civilizations had survived for a long time or even continued to exist now, their scripts were surely very different from what was being shown on the screen. But to allow those hiding in mini-universes to understand, they had to write in ancient scripts. Compared to the total number of civilizations that had lived in the great universe, 1.57 million was a tiny number.
In the eternal night of the Orion Arm of the Milky Way Galaxy, two civilizations had swept through like two shooting stars, and the u
niverse had remembered their light.
After Cheng Xin and Guan Yifan calmed down, they read the message. The content of the message in both scripts was the same, and very simple:
A notice from the Returners: The total mass of our universe has decreased to below the critical threshold. The universe will turn from being closed to open, and die a slow death in perpetual expansion. All lives and all memories will also die. Please return the mass you have taken away and send only memories to the new universe.
Cheng Xin and Guan Yifan locked gazes. In each other’s eyes, they saw the dark future for the great universe. In perpetual expansion, all the galaxies would move farther away from each other until none were visible from any other. By then, standing at any point in the universe, all one would see was darkness in every direction. The stars would go out one by one, and all celestial bodies would turn into thin dust clouds. Coldness and darkness would reign over all, and the universe would become a vast, empty tomb. All civilizations and all memories would be buried in that endless tomb for eternity. Death would be eternal.
The only way to prevent this future was to return the matter locked up in all the mini-universes constructed by all the civilizations. But such a decision meant that the mini-universes would not survive, and all the refugees in the mini-universes had to return to the great universe. That was the meaning of the name of the Returners’ movement.
The two said everything they needed to say to each other with their eyes and made their decision wordlessly. But Cheng Xin still spoke aloud. “I want to go back. But if you want to stay here, I’ll stay with you.”
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.”
