Cixin Liu - Death's End

“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 come 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.