by Cixin Liu
“Only a massive object can emit gravitational waves, so I guess that object must be large both in mass and volume, perhaps even a spaceship.… Well, in this business, the unexpected is to be expected.”
* * *
The two ships of the expedition continued on their course for another week until the distance between them and the gravitational wave source was only about a million kilometers. The expedition decelerated until their velocity was zero, and began to accelerate toward the Sun. This way, by the time the projectile caught up to the expedition, they would fly in parallel. Most of the close-range exploration would be conducted by Revelation; Alaska would observe from a distance of about a hundred thousand kilometers.
The distance continued to shrink; the projectile was now only about ten thousand kilometers from Revelation. The gravitational wave emissions were very clear and could be used for precise positioning. But even from this distance, radar returned no echo and nothing could be seen in the visible light range. By the time the distance shrank to one thousand kilometers, they still couldn’t see anything at the location of the gravitational wave source.
The crew of Revelation was close to panicking. Before departure, they had imagined all kinds of scenarios, but the idea of not being able to see their target when they were practically on top of it had never occurred to them. Vasilenko radioed the base at Neptune for instructions, and forty minutes later, received the order to approach the target until they were only 150 kilometers away.
Finally, the visible light detection systems noticed something: a small white dot at the gravitational wave source, visible even with a common telescope from the ship. Revelation sent out a drone to investigate. The drone flew at the target, the distance between them shrinking rapidly: five hundred kilometers, fifty kilometers, five hundred meters … Finally, the drone stopped five meters from the target. The clear holographic video it transmitted allowed the crew of both ships to see this extraterrestrial object that had been shot at the Sun.
A slip of paper.
There was really no better description. Formally, the object was called a rectangular membrane-like object: length: 8.5 cm; width: 5.2 cm; slightly bigger than a credit card. It was so thin that its thickness could not be measured. The surface was pure white, looking exactly like a slip of paper.
The members of the exploratory team were among the best officers and professionals in the world, and all had cool, rational minds. But instinct was more powerful. They had been prepared for giant, invasive objects. Some had guessed they would find a spaceship the size of Europa—a not unlikely possibility, given the strength of its gravitational wave emissions.
Faced with this paper slip—that was what they all called it—everyone heaved a sigh of relief. Rationally, they were still guarded. The object could certainly be a weapon that possessed enough power to destroy both spaceships. But it was impossible to believe that it could threaten the entire Solar System. By appearance, it was delicate, harmless, like a white feather floating in night air. People had long ceased to write letters on paper, but they were familiar with the concept from period films about the ancient world, and so the paper slip seemed almost romantic in their eyes.
Further investigation showed that the paper slip did not reflect electromagnetic radiation at any wavelength. The slip’s white color wasn’t reflected light, but light emitted by the object itself. All electromagnetic radiation, including visible light, simply passed through the slip, which was thus completely transparent. Images taken at close range showed the stars behind the slip, but due to interference from the white light it emitted and the dark background of space, it appeared as an opaque white from a distance. At least superficially, the object seemed harmless.
Maybe it really was a letter?
Since the drone had no appropriate collection tools, another drone with a mechanical arm and a sealable scoop had to be dispatched to capture the slip. As the open scoop extended toward the slip at the end of the mechanical arm, the hearts of everyone on the two ships hung in their throats.
This was another scene that seemed familiar.
The scoop closed around the slip and the arm pulled back.
But the slip remained where it was.
The attempt was repeated several more times with the same result. The drone operators aboard Revelation tried to maneuver the mechanical arm to touch the slip. The arm passed right through the slip, and neither appeared damaged. The arm felt no resistance, and the slip didn’t change its position. Finally, the operator directed the drone to approach the paper slowly, in an attempt to push it. As the hull of the drone came into contact with the slip, the slip disappeared inside the drone, and as the drone continued to move forward, the slip emerged from the stern, unchanged. During the process when the slip was inside the drone, its internal systems detected no anomalies.
By now, the expedition members understood that the paper slip was no ordinary object. It was like an illusion that did not interact with anything in the physical world. It was also like a tiny cosmic reference plane that maintained its position, unmovable. No contact was capable of shifting its position—or, more accurately, its set trajectory.
白 Ice decided to go investigate in person. Vasilenko insisted on coming with him. Having both leaders of the first exploratory team go together was a controversial proposition, and they had to wait forty minutes to receive approval from the base at Neptune. Their request was reluctantly granted, as Vasilenko would not back down, and there was also a backup team.
The two headed for the paper slip in a pinnace. As Revelation and its immense gravitational wave antenna shrank in the distance, 白 Ice thought he was leaving the only support in the universe, and his heart became fearful.
“Your advisor, Dr. Ding, must have felt the same way years ago,” Vasilenko said. He appeared perfectly calm.
白 Ice agreed with the sentiment in silence. He did feel spiritually connected to the Ding Yi of two centuries ago. Both of them headed for a great unknown, toward equally unknown fates.
“Don’t worry. This time, we can trust our intuition.” Vasilenko patted 白 Ice on the shoulder, but 白 Ice did not feel much comfort.
The pinnace was now next to the paper slip. After checking their space suits, they opened the pinnace’s hatch so that they were exposed to space. They fine-tuned the pinnace’s position until the paper slip hung half a meter above their heads. The tiny white plane was perfectly smooth, and through it they saw the stars behind, confirming that it really was a glowing, transparent object. The white light it emitted made the stars behind it appear a bit blurred.
They lifted themselves up in the pinnace until their eyes were lined up with the edge of the plane. Just like the camera had shown, the paper had no thickness. From the side, it completely disappeared. Vasilenko extended a hand toward the paper, but 白 Ice caught him.
“What are you doing?” 白 Ice asked severely. His eyes said the rest. Think about what happened to my teacher.
“If it really is a letter, perhaps the message won’t be released until an intelligent body makes direct contact with it.” Vasilenko brushed off 白 Ice’s hand.
Vasilenko touched the paper with his gloved hand. His hand passed through the paper and was not damaged. Vasilenko received no mental message, either. He again moved his hand through the paper and stopped, allowing the small white plane to divide his hand into two parts. Still, he felt nothing. The paper showed an outline of the cross section of the hand where the hand penetrated it: clearly, the sheet hadn’t been broken, but passed through the hand unharmed. Vasilenko pulled his hand back, and the slip hung still as before—or, more accurately, continued to move toward the Solar System at the rate of two hundred kilometers per second.
白 Ice also tried to touch the slip, then pulled his hand back. “It’s like a projection from another universe that has nothing to do with ours.”
Vasilenko had more practical concerns. “If nothing can affect it, then we have no way to bring it to the ship f
or further analysis.”
白 Ice laughed. “That’s a simple problem to solve. Have you forgotten the story told by Francis Bacon? ‘If the mountain will not come to Muhammad, then Muhammad must go to the mountain.’”
And so, Revelation slowly sailed toward the paper slip, made contact, and then allowed it to enter the ship. Even more slowly, it adjusted its position until the slip hung in the middle of the laboratory cabin. The only way to move the slip during study was to move the ship itself. This odd way to manipulate the research subject posed some challenges near the beginning, but luckily, Revelation was originally designed to investigate small space objects in the Kuiper Belt and possessed excellent maneuverability. The gravitational wave antenna was equipped with twelve high-precision thrusters. After the ship’s AI grew used to the necessary adjustments, the manipulation became quick and precise. If the world could not affect the slip in any way, the only solution was to let the world surround the slip and move about it.
Thus, an odd sight came to be: The slip was located in the center of Revelation, but the ship had no dynamical connection to the slip. The two simply happened to occupy the same space as both moved toward the Solar System at the same velocity.
Inside the spaceship, due to the stronger background light, the transparency of the slip became more obvious. It now no longer resembled a slip of paper, but some transparent film that only indicated its presence by the faint light it emitted. People continued to refer to it as a paper slip, however. When the ambient light was very strong, it was sometimes possible to lose sight of it, so the researchers had to dim the lights in the laboratory to see the slip better.
The first thing the researchers tried to do was to ascertain the slip’s mass. The only applicable method was to measure the gravity it generated. However, even at the highest precision level, the gravity meter showed nothing, suggesting that the slip’s mass was extremely small, perhaps even zero. Based on the latter possibility, some guessed that the object might be a photon or neutrino in macro form, but its geometric shape suggested that it was artificial.
No progress could be made on analysis of the slip because electromagnetic waves of all wavelengths passed through it without diffraction. Magnetic fields, no matter how strong, seemed to have no effect on it. The object appeared to have no internal structure.
Twenty hours later, the exploratory team still knew next to nothing about the slip. They were able to observe one thing, however: The intensity of the light and gravitational waves emitted by the slip was decreasing. This suggested that the light and gravitational waves it emitted were probably a form of evaporation. Since these two were the only indication of the existence of the slip, their disappearance would be the same as the disappearance of the slip itself.
The base informed the exploratory team that Tomorrow, a large science vessel, had left the Neptune city cluster and would meet the expedition in seven days’ time. Tomorrow possessed more advanced investigative instruments, and could study the slip in more depth.
As they became more used to the slip, the crew on Revelation became less guarded and were no longer so careful about keeping a respectful distance from it. They knew that the object did not interact with the real world and emitted no harmful radiation. They touched it casually, allowing it to pass through their bodies. Someone even let the plane pass through his eyes and brain, asking a friend to take a picture of the sight.
白 Ice was enraged when he saw this. “Stop it! This is not some joke,” he screamed. Having worked nonstop in the lab for more than twenty hours, he left the laboratory and returned to his own cabin.
白 Ice turned off the light in his cabin and tried to go to sleep. But in the darkness he felt uneasy; he imagined the paper slip would float into his cabin, glowing white, at any moment. So he turned on the light and drifted in the gentle light and memories.
* * *
One hundred and ninety-two years had passed since he said good-bye to his teacher for the last time.
It was dusk, and he and Ding Yi and he had come to the surface from the underground city and taken a car into the desert. Ding Yi liked to stroll and think in the desert, and even to hold his lectures there sometimes. His students hated the experience, but he explained his eccentric habit this way: “I like desolate places. Life is a distraction for physics.”
The weather that day was good. There was no wind and no sandstorms, and the early spring air smelled fresh. The two of them, teacher and student, lay against a dune. The desert of Northern China was bathed in the light of the setting sun. Normally, Bai Aisi thought of these rolling dunes as a woman’s body—possibly a comparison that had originated with Ding Yi himself—but now he thought of them as an exposed brain. In the golden dusk, the brain revealed its profusion of grooves and folds. He looked up at the sky. Today, the dusty air managed to let through a bit of long-missed blue, like a mind about to be enlightened.
Ding Yi said, “Aisi, I want to tell you a few things that you should not repeat to others. Even if I don’t return, don’t tell others. There’s no special reason. I just don’t want to be laughed at.”
“Professor Ding, why not wait until you’re back to tell me?”
Bai Aisi wasn’t trying to comfort Ding Yi. He was sincere. He was still drunk with the ecstasy and vision of humanity’s imminent great victory over the Trisolaran fleet, and he did not think Ding Yi’s trip to the droplet would involve much danger.
“Answer a question first, please.” Ding Yi ignored Bai Aisi’s question and pointed at the desert lit by the westering sun. “Forget about the uncertainty principle for a minute and suppose everything is determinable. If you know the initial conditions, you can calculate and derive the conditions at any later point in time. Suppose an extraterrestrial scientist were given all data about the Earth several billion years ago. Do you think it could predict the existence of this desert solely through calculation?”
Bai Aisi pondered this. “No. This desert wasn’t the result of the Earth’s natural evolution, but the result of man-made forces. The behavior of civilizations can’t be grasped through the laws of physics.”
“Very good. Then why do we and our colleagues all want to try to explain the conditions of today’s cosmos, and to predict its future, solely through deductions based on the laws of physics?”
Ding Yi’s words surprised Bai Aisi. The man had never revealed such thoughts in the past.
Bai Aisi said, “I think that’s beyond physics. The goal of physics is to discover the fundamental laws of nature. Although the man-made desertification of the Earth could not be calculated directly from physics, it still follows laws. Universal laws are constant.”
“Heh heh heh heh.” Ding Yi’s laugh was not joyous at all. As he recalled it later, Bai Aisi thought it was the most sinister laughter he had ever heard. There was a hint of masochistic pleasure, an excitement at seeing everything falling into the abyss, an attempt to use joy as a cover for terror, until terror itself became an indulgence. “Your last sentence! I’ve often comforted myself this way. I’ve always forced myself to believe that there’s at least one table at this banquet filled with dishes that remain fucking untouched.… I tell myself that again and again. And I’m going to say it one more time before I die.”
Bai Aisi thought Ding Yi’s mind was elsewhere and that he talked as if he were dreaming. He didn’t know what to say.
Ding Yi continued, “At the beginning of the crisis, when the sophons were interfering with the particle accelerators, a few people committed suicide. At the time, I thought what they did made no sense. Theoreticians should be excited by such experimental data! But now I understand. Those people knew more than I did. Take Yang Dong, for instance. She knew much more than I did, and thought further. She probably knew things we don’t even know now. Do you think only sophons create illusions? Do you think the only illusions exist in the particle accelerator terminals? Do you think the rest of the universe is as pure as a virgin, waiting for us to explore? Too bad that she lef
t with everything she knew.”
“If she had talked with you more back then, perhaps she wouldn’t have chosen to go.”
“Perhaps I would have gone with her.”
Ding Yi dug a pit in the sand and watched as the sand on the rim flowed back in like a waterfall. “If I don’t come back, everything in my room is yours. I know that you’ve always liked those Common Era things I brought.”
“That’s true, especially those tobacco pipes.… But I don’t think I’ll get them.”
“I hope you’re right. I also have some money—”
“Please, Professor!”
“I want you to use it to pay for hibernation. The longer the better—of course, that’s assuming you want to. I have two goals in mind: One, I want you to go look at the endgame for me—the endgame for physics. Two … how do I say this? I don’t want you to waste your life. After others have decided that physics actually exists, there will still be plenty of time for you to go do physics.”
“That … seems like something Yang Dong would say.”
“Maybe it’s not nonsense.”
Bai Aisi noticed that the pit Ding Yi had dug in the desert was rapidly expanding. They stood up and backed away as the pit continued to grow, getting deeper as well as wider. Soon, the bottom disappeared in shadows. Sand flooded into the pit in torrents, and soon, the diameter of the pit was close to a hundred meters, and a nearby dune was swallowed up. Bai Aisi ran toward the car and got into the driver’s seat; Ding Yi followed into the passenger seat. Bai Aisi noticed that the car was moving slowly toward the pit, dragged along by the sand underneath. He turned on the engine and the wheels began to turn, but the car continued to slide backwards.
Ding Yi laughed that sinister laugh again. “Heh heh heh heh…”
Bai Aisi turned the electric motor to the highest setting and the wheels spun madly, throwing up sand everywhere. But the car still moved toward the pit like a plate pulled along on a tablecloth.