by Liu Cixin
His hand felt warm and strong to Cheng Xin, and his broad body shielded her from the chill wind. She had the impulse to jump into this man’s arms, the first man she had met after traveling more than two hundred light-years from the Solar System.
“Did you come from the Solar System?” the man asked.
“Yes.” She leaned against the man and descended the stairs. She felt her trust for him grow, and put more of her weight on him.
“There’s no more Solar System,” AA said as she sat down at the top of the stairs.
“I know. Did anyone else escape?”
Cheng Xin was now on the ground. She sank her feet into the soft grass and sat down on the bottom step. “Probably not.”
“Oh…” The man nodded and climbed up again to help AA. “My name is Guan Yifan. I’ve been waiting for you here.”
“How did you know we would come?” AA asked, allowing Yifan to hold her hand.
“We received your gravitational wave transmission.”
“You’re from Blue Space?”
“Ha! If you’d asked those who had just left that question, they’d think you very strange. Blue Space and Gravity are ancient history from more than four centuries ago. But I really am an ancient. I was a civilian astronomer aboard Gravity. I’ve been hibernating for four centuries, and only awakened five years ago.”
“Where are Blue Space and Gravity now?” Cheng Xin struggled to stand, pulling herself up by the railing of the stairs. Yifan continued down with AA.
“In museums.”
“Where are the museums?” AA asked. She put her arm around Yifan’s shoulder so that Yifan was practically carrying her down.
“On World I and World IV.”
“How many worlds are there?”
“Four. And two more are being opened up for settlement.”
“Where are all these worlds?”
Guan Yifan gently deposited AA on the ground and laughed. “A word of advice: In the future, no matter who you meet—human or otherwise—don’t ask for the location of their worlds. That’s a basic bit of manners in the cosmos—like how it’s impolite to ask a lady’s age.… Nonetheless, let me ask you, how old are you now?”
“We’re as old as we look,” AA said, and sat down on the grass. “She’s seven hundred and I’m five hundred.”
“Dr. Cheng looks about the same as she did four centuries ago.”
“You know her?” AA looked up at Guan Yifan.
“I had seen pictures in transmissions from Earth. Four centuries ago.”
“How many people are on this planet?” Cheng Xin asked.
“Just the three of us.”
“That must mean that your worlds are all better than this one,” AA said.
“You mean the natural environment? Not at all. In some places, the air is barely breathable, even after a century of terraforming. This is one of the best planets we’ve seen for settlement. Although we welcome you here, Dr. Cheng Xin, we do not recognize your claim of title.”
“I’d given that up a long time ago,” Cheng Xin said. “So why haven’t people settled here?”
“It’s too dangerous. Outsiders come here often.”
“Outsiders? Extraterrestrials?” AA asked.
“Yes. This is close to the center of the Orion Arm. Two busy shipping lanes flow through here.”
“Then what are you doing here? Just waiting for us?”
“No. I came with an exploratory expedition. They’ve already left, but I stayed to wait for you.”
* * *
About a dozen hours later, the three welcomed night on Planet Blue. There was no moon, but compared to the Earth, the stars here were far brighter. The Milky Way was like a sea of silver fire that cast their shadows on the ground. This place wasn’t much closer to the center of the galaxy than the Solar System. However, the space between here and the Sun was filled with interstellar dust, making the Milky Way appear much dimmer from the Solar System.
In the bright starlight, they could see the grass around them moving. At first, Cheng Xin and AA thought it was an illusion produced by the wind, but then they realized that the grass underfoot was writhing as well, and making a rustling noise. Yifan told them that the blue grass really did move. The roots of the grass were also feet, and as the seasons changed, the grass migrated across the latitudes, mainly at night. As soon as AA heard that, she tossed away the stalks of grass she was playing with in her hands. Yifan explained that the blades of grass really were plants, and relied on photosynthesis, possessing only a basic sense of touch. The other plants in this world were also capable of moving. He pointed to the mountains and they saw the forests moving in the starlight. The trees moved far faster than the grass, and resembled armies marching at night.
Yifan pointed at a spot in the sky where the stars were slightly less dense. “A few days ago we could see the Sun in that direction, much more clearly than you could see this star from the Earth. Of course, what we saw was the Sun of two hundred eighty-seven years ago. The Sun went out on the day the expedition left me here.”
“The Sun is no longer emitting light, but its area is huge. Perhaps you can still see it through telescopes,” AA said.
“No, you won’t be able to see anything.” Yifan shook his head and pointed at that patch of sky again. “Even if you go back there now, you wouldn’t be able to see anything. That part of space is empty. The two-dimensional Sun and planets you saw were actually just the result of the release of energy when three-dimensional material collapsed into two dimensions. What you saw wasn’t two-dimensional material, only the refraction of electromagnetic radiation at the interface between two-dimensional and three-dimensional space. After the energy was released, nothing would be visible. The two-dimensional Solar Space has no contact with three-dimensional space.”
“How can that be?” Cheng Xin asked. “It’s possible to see the three-dimensional world from four-dimensional space.”
“True. I personally got to see three-dimensional space from four-dimensional space, but it’s not possible to see the two-dimensional world from three dimensions. This is because three-dimensional space has thickness, meaning that there is a dimension that could stop and scatter the light from four-dimensional space, making it visible from four dimensions. But two-dimensional space has no thickness, so light from three-dimensional space passes through it without hindrance. The two-dimensional world is completely transparent and cannot be seen.”
“There’s no way at all?” AA asked.
“No. In theory, nothing allows it.”
Cheng Xin and AA were silent for a while. The Solar System had disappeared completely. The only hope they had held out for the mother world was gone. But Guan Yifan did bring them a bit of comfort.
“There’s only one way to detect the presence of the two-dimensional Solar System from three-dimensional space: gravity. The gravity of the Solar System still has an effect, so, in that empty space ought to be detectable as an invisible source of gravity.”
Cheng Xin and AA looked at each other thoughtfully.
“Sounds like dark matter, doesn’t it?” Yifan laughed. Then he changed the subject. “Why don’t we talk about the date you came for?”
“You know Yun Tianming?” AA asked.
“No.”
“What about the Trisolaran Fleet?” Cheng Xin asked.
“We don’t know much. The First and Second Trisolaran Fleets never joined together. More than sixty years ago, there was a large-scale space battle near Taurus. It was brutal, and the resulting wreckage formed a new interstellar dust cloud. We know that one of the sides in the battle was the Second Trisolaran Fleet, but we don’t know who they were fighting against. We also don’t know how the battle ended.”
“What happened to the First Trisolaran Fleet?” Cheng Xin asked. Her eyes flickered in the starlight.
“We haven’t received any information about them.… In any event, you shouldn’t stay here too long. This is not a safe place. Why don’t you com
e with me to our world? The terraforming there is over, and life is getting better.”
“I agree!” AA said. Then she held Cheng Xin by the arm. “Let’s go with him. Even if you wait here for the rest of your life, you most likely won’t hear anything. Life shouldn’t be a lifetime of waiting.”
Cheng Xin nodded silently. She knew that she was chasing a dream.
* * *
They decided to wait one more day on Planet Blue before departing.
Guan Yifan had a small spaceship waiting in synchronous orbit. The ship was tiny and didn’t have a name, only a number. But Yifan called it Hunter, and explained that the name was to honor the memory of a friend who’d lived on Gravity more than four hundred years ago. Hunter was not equipped with an ecological cycling system, and for long voyages passengers had to enter hibernation. Although Hunter was only a few percent of Halo’s volume, it was also a lightspeed ship equipped with a curvature engine. They decided to have Yifan ride on Halo as well and control Hunter as a drone. Cheng Xin and AA didn’t ask about the course they would take, and Yifan even refused to answer questions about the duration of the anticipated voyage. He was extremely cautious when it came to information about the location of human worlds.
For the day, the three took short hikes in the vicinity of Halo. This was a day of many firsts for Cheng Xin, AA, and all the Solar System humans who had disappeared along with the home world: the first trip to an extrasolar planetary system; the first steps on the surface of an exoplanet; the first voyage to a world with life outside the Solar System.
Compared with the Earth, the ecology of Planet Blue was relatively simple. Other than the mobile blue vegetation, there was not much life to be found, except for a few species of fish in the ocean. There were no complex animals on land, only simple insects. The world resembled a simplified Earth. It was possible for Earth plants to survive here, so humans could live here even without advanced technology.
Guan Yifan was filled with admiration for Halo’s design. He said that for Galactic humans, people who had made their home in the Milky Way, there was one quality about Solar System humans that they did not inherit and could not learn: enjoyment of life. He spent much time in the lovely courtyards, and indulged himself with holographic projections of grand sights from ancient Earth. He still looked as thoughtful as ever, but his eyes were moist.
During this time, 艾 AA cast Yifan frequent amorous glances. The relationship between them gradually changed as the day went on. AA thought up all kinds of excuses to be close to Yifan, and listened intently while he spoke, nodding from time to time and smiling. She had never behaved like this in front of any other man. During the centuries Cheng Xin had known her, AA had countless lovers, often dating two or more at the same time, but Cheng Xin knew that AA had never really been in love. However, she was clearly smitten with this cosmologist from the Deterrence Era. Cheng Xin was happy to see this. AA deserved a happy new life in this new world.
As for Cheng Xin, she knew that she was spiritually dead. The only hope that had sustained her was finding Tianming, and now this hope seemed like an impossible dream. Truthfully, she had always known that a date made for four centuries later and 286 light-years away was an impossible dream. She would continue to keep her body alive, but it was just a matter of fulfilling her duty of preventing the death of half of the population to survive the destruction of Earth civilization.
Night fell again. They decided to sleep aboard Halo and leave in the morning.
At midnight, Guan Yifan was awakened by his wrist communicator. It was a call from Hunter in synchronous orbit. Hunter passed on the information gathered by the three small monitoring satellites left by the expedition—two of which orbited around Planet Blue and the last around Planet Gray. The alert had come from the one around Planet Gray.
Thirty-five minutes ago, five unidentified spacecraft had landed on Planet Gray. Twelve minutes later, the spacecraft had lifted off and disappeared without even entering planetary orbit. There was strong interference with the satellite, and the images it transmitted were blurry.
Yifan’s expedition was responsible for seeking out and studying traces left in this planetary system by other civilizations. After receiving the alert from the satellite, he immediately decided to take the shuttle up to Hunter to investigate. Cheng Xin insisted on coming with him. Yifan initially refused, but agreed after AA spoke to him.
“Let her come with you. She wants to know whether this has anything to do with Yun Tianming.”
Before departure, Yifan reminded AA to not communicate with Hunter unless it was an emergency. No one knew what other extraterrestrial monitoring equipment might be lurking in this system, and any communication could expose them to danger.
In this lonely world of only three people, even a brief separation was an occasion for anxiety. AA hugged Cheng Xin and Guan Yifan and wished them a safe journey. Before stepping onto the shuttle, Cheng Xin looked back and saw AA waving at them, lit by the watery starlight. Blue grass surged around her, and the cold wind lifted her short hair and made ripples in the grass.
The shuttle took off. In the view from the monitoring system, Cheng Xin saw the grass lit up by the flame from the thruster, and the blue grass scattering in every direction. As the shuttle rose up, the bright patch on the ground quickly dimmed, and soon, the ground sank back into starlight.
An hour later, the shuttle docked with Hunter in synchronous orbit. Hunter was tetrahedral in shape, like a tiny pyramid. The inside was very cramped and bare, and most of the space was taken up by the hibernation chamber, which had a maximum capacity for four.
Like Halo, Hunter was equipped with both a curvature engine and a fusion engine. When traveling between planets within the same system, only the fusion engine was used, because the curvature engine would have caused the ship to overshoot the target with no time for deceleration. Hunter left orbit and headed for Planet Gray, which appeared as a small spot of light. Out of consideration for Cheng Xin, Guan Yifan initially limited the acceleration to 1.5G, but Cheng Xin told him not to worry about her and just make the trip faster. He increased the acceleration, the blue flame emitted by the nozzles doubled in length, and the hypergravity increased to 3G. At this point, all they could do was to sit in the embrace of the acceleration seats. They were not able to move much, so Yifan switched the ship to surround-holographic display mode, and the ship’s hull disappeared. Suspended in space, they watched Planet Blue recede. Cheng Xin imagined the 3G gravity as coming from Planet Blue so that space separated into up and down, and they were flying up toward the galaxy.
It was possible to speak under 3G without too much trouble, so they began to converse. Cheng Xin asked Yifan why he had hibernated for so long. He told her that he had no duties during the long voyage searching for habitable worlds. After the two ships discovered the habitable World I, much of life consisted of opening up the world for settlement and constructing the basics. The first settlement resembled a small town from agrarian times, and the rough conditions did not permit any kind of scientific research. The new world’s government passed a resolution to let all scientists enter or remain in hibernation, to be awakened only when conditions permitted basic research. He was the only basic scientist aboard Gravity, although Blue Space had seven more. He was the last to be awakened of all the hibernators. Two centuries had passed since the day the two ships arrived at World I.
Cheng Xin was mesmerized by Yifan’s account of the new human worlds. But she noticed that while he discussed Worlds I, II, and IV, nothing was said about III.
“I’ve never been there. No one else has, either. Well, it’s more accurate to say that anyone who goes there cannot return. That world is sealed inside a light tomb.”
“A light tomb?”
“It’s a reduced-lightspeed black hole produced by the trails of lightspeed ships. Something happened on World III that caused them to think that their coordinates had been exposed. They had no choice but to turn their world into such a black hol
e.”
“We call such a place a black domain.”
“Ah, good name. As a matter of fact, the people of World III initially called it a light curtain, but outsiders referred to it as a light tomb.”
“Like a shroud?”10
“That’s right. Different people see things differently. The inhabitants of World III said it was a happy paradise—though I don’t know if they still think that way. After the light tomb was completed, it was impossible for any message from that world to reach the outside. But I think people there are pretty happy. For some people, safety is the sine qua non for happiness.”
Cheng Xin asked Yifan when the new world first produced lightspeed ships, and was told it was a century ago. Judging by this, her interpretation of Tianming’s secret message had allowed Solar System humans to achieve this stage about two centuries ahead of Galactic humans. Even taking into account the time it took to open up the worlds for settlement, Tianming had accelerated progress by at least a century.
“He’s a great man,” Yifan said after hearing Cheng Xin’s account.
But the civilization of the Solar System hadn’t been able to seize this opportunity. Thirty-five precious years had been lost, probably due to her. Her heart no longer felt pain as she thought of this; all she felt was the numbness that indicated a dead heart.
Yifan said, “Lightspeed spaceflight was a tremendous milestone for humankind. It was like another Enlightenment, another Renaissance. Lightspeed flight fundamentally transformed human thinking and changed civilization and culture.”
“I can see that. The moment I entered lightspeed, I felt myself change. I realized that I could, in my lifetime, leap across space-time and reach the edge of the cosmos and the end of the universe. Things that used to seem only philosophical suddenly became concrete and practical.”
“Yes. Things like the fate and goal of the universe used to be only ethereal concerns of philosophers, but now every ordinary person must consider them.”