by Cixin Liu
“I don’t have a home,” Cheng Xin said. The word “home” stabbed into her heart like a knife, and her heart, numbed by extreme pain, nevertheless convulsed one more time. She thought of that winter night three centuries ago when she left her home, thought of the dawn that had greeted her outside her window.… Both of her parents had died before the Great Ravine. They could never have imagined where their daughter had ended up, tempest-tossed by time and fate.
“No. Everyone’s getting ready to go home. We’re all leaving Australia and going back to where we came from.”
Cheng Xin whipped her head up. She still couldn’t get used to this stubborn darkness before her wide-open eyes. She tried to make out something, anything. “What?”
“Gravity initiated the universal broadcast.”
How is that possible?
“The location of Trisolaris has been exposed—which of course means the Solar System is exposed as well. The Trisolarans are running away. The Second Fleet has changed direction to head away from the Solar System. All the droplets are gone. Sophon was explaining that there’s no more need to worry about them invading the Solar System. Like the Trisolaran system, this is now a place of death that everyone will want to escape from.”
How!?
“We’re going home. Sophon has ordered the Earth Security Force to make every effort to assist with the evacuation of Australia. The process will get faster over time, but moving all the refugees out of Australia will take three to six months. You can leave first. The mayor wants me to take you to the provincial government.”
“Was it Blue Space?”
“No one knows the details, not even Sophon. But Trisolaris received the universal broadcast, and it was initiated a year ago, when deterrence failed.”
“Can you let me be by myself for a while?”
“All right, Dr. Cheng. But you should be happy. They did what you needed to do.”
The man stopped talking, but Cheng Xin could still feel his presence. The commotion around her gradually died down, and was followed by a rainstorm of footsteps. The footsteps grew sparse—everyone must be leaving the city government tent to take care of their own business. Cheng Xin felt the sea retreat around her, revealing solid land beneath. She stood in the middle of an empty continent, the sole survivor after the Flood. Her face felt a trace of warmth: The sun was rising.
Post-Deterrence Era, Day 1–Day 5
Gravity and Blue Space, Deep Space Beyond the Oort Cloud
“It’s possible to detect the warped points using the naked eye,” Chu Yan said. “But the best way is to monitor the electromagnetic radiation. The emission from these points is very faint, but it has a distinct spectral signature. The regular sensors on our ships can detect and locate them. Typically, a volume of space as large as a ship in this region contains one to two warped points, but we once found twelve at once. Look, right now there are three.”
Chu Yan, Morovich, and Guan Yifan were floating through a long corridor on Blue Space. In front of them drifted an information window showing a map of the interior of the ship. Three red dots flashed on the map, and the three of them were approaching one of these dots now.
“Right there!” Guan pointed straight ahead.
In the bulkhead in front of them was a circular hole about a meter in diameter. The edge was smooth, mirrorlike. Through the hole they could see tubes of various thicknesses. Several tubes had entire sections missing in the middle. In two of the thicker tubes, they could see liquid flowing. The liquid seemed to flow from one section, disappear, and then reappear in the corresponding section of the tube on the other side. The missing sections were of different lengths, but overall seemed to describe a spherical space. Based on the shape of the missing sections, part of the invisible bubble protruded into the corridor. Morovich and Guan carefully avoided it.
Chu Yan carelessly extended a hand into the invisible bubble, and half of his arm disappeared. Standing to the side, Guan Yifan saw a clear cross section of his cut-off arm, like the cross sections of Vera’s legs that had been seen by Sublieutenant Ike aboard the Gravity. Chu Yan pulled his arm back and showed the astonished Morovich and Guan that it was unharmed. Then he encouraged them to try it. The two carefully reached into the invisible bubble. They watched their hands, and then arms, vanish, but they felt nothing.
“Let’s go in,” said Chu Yan. Then he jumped into the bubble, as though diving into a pool. Morovich and Guan watched in consternation as Captain Chu disappeared from head to toe. The cross section of his body on the surface of the invisible bubble rapidly changed shape, and the mirrorlike edge of the hole threw reflections onto the surrounding bulkheads like ripples.
As Morovich and Guan stared at each other, two hands and forearms emerged from the bubble and remained suspended in midair. Each hand grabbed hold of one of theirs, and they were pulled into fourth-dimensional space.
All who had experienced it agree that the sensation of being in four-dimensional space was indescribable. They would even say that it was the only thing encountered by humanity thus far that absolutely could not be captured by language.
People usually resorted to this analogy: Imagine a race of flat beings living inside a two-dimensional picture. No matter how rich or colorful the picture was, the flat people could only see the profile of the world around them. In their eyes, everything consisted of line segments of various lengths. Only when such a two-dimensional being was taken up out of the picture into three-dimensional space and looking down on the world could he see the entirety of the image.
This analogy simply expressed in some more detail the indescribability of experiencing four-dimensional space.
A person looking back upon the three-dimensional world from four-dimensional space for the first time realized this right away: He had never seen the world while he was in it. If the three-dimensional world were likened to a picture, all he had seen before was just a narrow view from the side: a line. Only from four-dimensional space could he see the picture as a whole. He would describe it this way: Nothing blocked whatever was placed behind it. Even the interiors of sealed spaces were laid open. This seemed a simple change, but when the world was displayed this way, the visual effect was utterly stunning. When all barriers and concealments were stripped away, and everything was exposed, the amount of information entering the viewer’s eyes was hundreds of millions times greater than when he was in three-dimensional space. The brain could not even process so much information right away.
In Morovich and Guan’s eyes, Blue Space was a magnificent, immense painting that had just been unrolled. They could see all the way to the stern, and all the way to the bow; they could see the inside of every cabin and every sealed container in the ship; they could see the liquid flowing through the maze of tubes, and the fiery ball of fusion in the reactor at the stern.… Of course, the rules of perspective remained in operation, and objects far away appeared indistinct, but everything was visible.
Given this description, those who had never experienced four-dimensional space might get the wrong impression that they were seeing everything “through” the hull. But no, they were not seeing “through” anything. Everything was laid out in the open, just like when we look at a circle drawn on a piece of paper, we can see the inside of the circle without looking “through” anything. This kind of openness extended to every level, and the hardest part was describing how it applied to solid objects. One could see the interior of solids, such as the bulkheads or a piece of metal or a rock—one could see all the cross sections at once! Morovich and Guan were drowning in a sea of information—all the details of the universe were gathered around them and fighting for their attention in vivid colors.
Morovich and Guan had to learn to deal with an entirely novel visual phenomenon: unlimited details. In three-dimensional space, the human visual system dealt with limited details. No matter how complicated the environment or the object, the visible elements were limited. Given enough time, it was always possible to take in most
of the details one by one. But when one viewed the three-dimensional world from four-dimensional space, all concealed and hidden details were revealed simultaneously, since three-dimensional objects were laid open at every level. Take a sealed container as an example: One could see not only what was inside, but also the interiors of the objects inside. This boundless disclosure and exposure led to the unlimited details on display.
Everything in the ship lay exposed before Morovich and Guan, but even when observing some specific object, such as a cup or a pen, they saw infinite details, and the information received by their visual systems was incalculable. Even a lifetime would not be enough to take in the shape of any one of these objects in four-dimensional space. When an object was revealed at all levels in four-dimensional space, it created in the viewer a vertigo-inducing sensation of depth, like a set of Russian nesting dolls that went on without end. Bounded in a nutshell but counting oneself a king of infinite space was no longer merely a metaphor.
Morovich and Guan looked at each other, then looked at Chu Yan to the side. They saw bodies revealed at every level with the details displayed in parallel: They could see bones, organs, the marrow inside the bones, the blood flowing through the ventricles and atria of the heart, the openings and closings of the mitral and tricuspid valves. When gazing at each other, they could see clearly the interior structure of the lenses of the eyes.…
The phrase “in parallel” might also lead to misunderstanding. The physical locations of the parts of the body had not been shifted around: The skin still enclosed the organs and the bones, and the familiar shape of each person in three-dimensional space persisted—but it was now merely one detail among an infinity of details, visible at the same time, in parallel.
“Be careful of where you move your hands,” Chu Yan said. “You might poke an internal organ—yours or someone else’s—by mistake. But as long as you don’t use too much force, even contact won’t be a big deal. You’ll feel a bit of pain or nausea, and of course there’s the risk of infections. Also, don’t touch or move things unless you know exactly what they are. Everything on the ship is now naked: You might be touching a live wire or heated steam, or even integrated circuits, and cause system malfunctions. Overall, you’re like gods in the three-dimensional world, but you have to get used to being in four-dimensional space before you can use your powers effectively.”
Morovich and Guan quickly learned how to avoid touching inner organs. By moving in a certain direction, they could grasp someone’s hand instead of the bones inside the hand. To touch the bones or organs required exertion in another direction—a direction that didn’t exist in three-dimensional space.
Next, Morovich and Guan discovered something else that excited them: They could see the stars in every direction. They could see the bright glow of the Milky Way extending through the universal eternal night. They knew that they were still inside the ship—none of them wore space suits, and all breathed the air on the ship—but in the fourth dimension, they were exposed to space. All three veteran spacers had performed countless spacewalks, but they had never felt so utterly intimate with space. During spacewalks, they were at least enclosed by space suits, but now, nothing stood between space and them. The ship that revealed infinite details did not shield them from space. In the fourth dimension, the ship lay in parallel with all of space.
The brain that had been adapted from birth to sense and feel three-dimensional space could not handle the infinite information generated by countless details, and initially, information overload threatened to shut down processing. But the brain soon grew used to the four-dimensional environment, and without conscious thought it learned to ignore most details, leaving only the frames around objects.
After the initial vertigo, Morovich and Guan experienced another, even greater shock. Once their attention was no longer completely absorbed by the inexhaustible details of the environment around them, they sensed space itself, or sensed the fourth dimension. Later, people would call this feeling “high-dimensional spatial sense.” For those who had experienced it, high-dimensional spatial sense was hard to convey in words. They often tried to explain it this way: Concepts like “vastness” or “boundlessness” in three-dimensional space were replicated an infinite number of times in four-dimensional space in a direction that did not exist in three-dimensional space. They often resorted to the analogy of two mirrors facing each other: In either mirror one could see a boundless multitude of replicated mirrors, a hall of mirrors that extended into infinity. In this analogy, each mirror in the hall was a three-dimensional space. In other words, the vastness that one experienced in three-dimensional space was but a cross-section of the vastness of four-dimensional space. The difficulty of describing high-dimensional spatial sense lay in the fact that for observers situated in four-dimensional space, the space they could see was empty and uniform, but there was a depth to it that could not be captured by language. This depth was not a matter of distance: It was bound up in every point in space. Guan Yifan’s exclamation later became a classic quote:
“A bottomless abyss exists in every inch.”
The experience of high-dimensional spatial sense was a spiritual baptism. In one moment, concepts like freedom, openness, profundity, and infinity all gained brand-new meanings.
Chu Yan said, “We should return. The warped points remain stable for only a brief period of time before drifting away or disappearing. To find a new warped point requires moving in four-dimensional space. That’s a dangerous undertaking for novices like you.”
“How does one find a warped point in four-dimensional space?” Morovich asked.
“Simple. A warped point is usually spherical. Light is refracted inside the sphere, and objects inside are distorted, causing a visual break in the image of the objects. Of course, this is just an optical effect in four-dimensional space, not a real change in the shapes of the objects. Look over there—”
Chu Yan pointed in the direction they had come from. Morovich and Guan saw those tubes again, which now also lay open so that all the liquids flowing through them could be seen clearly. Inside the spherical region, the tubes were curved and distorted, and the sphere appeared like a drop of dew hanging on a spiderweb. This was different from how the region had appeared in three-dimensional space. There, the warped point didn’t refract light, and so appeared completely invisible. Its presence could only be made known via the disappearance of objects that had entered four-dimensional space inside the bubble.
“If you come here again, you must wear space suits. Novices can’t always tell locations accurately, and finding a new warped point for the return trip might result in landing outside the ship in three-dimensional space.”
Chu Yan indicated that the other two should follow, and entered the dewdrop-like bubble. In an instant they were back inside the three-dimensional world, back in the corridor inside the ship, in exactly the place where, ten minutes ago, they had entered four-dimensional space. In fact, they had never left—the space they were in had just gained an extra dimension. The round opening in the bulkhead was still there, and they could still see the “broken” tubes inside.
But to Morovich and Guan, the world no longer seemed familiar. They now experienced the three-dimensional world as narrow and smothering. Guan dealt with it slightly better—he had at least experienced four-dimensional space once before, in a semiconscious state. But Morovich was feeling claustrophobic, as though he was being suffocated.
“This is normal. You’ll get used to it after a few times.” Chu Yan laughed. “The two of you now know what real vastness means. Even if you put on space suits and go take a walk in space now, you’ll feel confined.”
“How did all this happen?” Morovich tore open his collar and gasped.
“We entered a region of space where space has four dimensions. That’s it. We call this region a four-dimensional fragment.”
“But we’re in three-dimensional space now!”
“Four-dimensional space contains th
ree-dimensional space, just as three-dimensional space contains two-dimensional space. To make another analogy: We’re located inside a three-dimensional sheet of paper in four-dimensional space.”
“Let me propose a model,” said Guan excitedly. “The entirety of our three-dimensional space is a large, thin sheet of paper, sixteen billion light-years across. Somewhere on this sheet of paper is a tiny, four-dimensional soap bubble.”
“Perfect, Dr. Guan!” Chu Yan clapped Guan’s shoulder, making him tumble in weightlessness. “I’ve been trying to come up with a good analogy, and you hit it in one try. This is why we need a cosmologist! You’re exactly right. We were on this three-dimensional sheet of paper, crawling over the surface. Then we came into the soap bubble. From a warped point, we can manage to leave the surface of the paper and entered the space inside the bubble.”
“Though we were in four-dimensional space just now, our bodies remained three-dimensional,” Morovich said.
“That’s right. We were flat, three-dimensional people drifting in four-dimensional space. It’s not clear how our bodies are able to survive in four-dimensional space, given that the physical laws are likely different. There are many such mysteries.”
“What exactly are warped points?”
“The three-dimensional sheet of paper is not completely flat everywhere. Some places are warped, reaching into the fourth dimension. That’s what a warped point is: a tunnel from lower dimensions into higher dimensions. We can get into four-dimensional space by jumping into them.”
“Are there many warped points?”
“Oh yes. They’re everywhere. Blue Space was able to discover their secret earlier because we have more people aboard, and so there were many more opportunities to encounter warped points. Gravity, besides having fewer people, also had a much stricter psychological monitoring regime—even those who encountered warped points dared not discuss them.”
