Death's End

by Cixin Liu

  “Are all warped points this small?”

  “No. Some are much bigger. There’s one mystery we’ve never been able to solve: We once observed that the rear third of Gravity had warped into four-dimensional space, and stayed there for several minutes. How could you have not noticed anything odd?”

  “Well, the last third of the ship usually had no crew. Oh, wait, he was there.” Morovich turned to Guan Yifan. “You must have experienced that. I think I heard about it from Dr. West.”

  “I was only half awake. Later, that idiot convinced me that I was only hallucinating.”

  “It’s not possible to look into the fourth dimension from three-dimensional space. But it is possible to be in four-dimensional space and see everything happening in three-dimensional space and to affect things in it. We were able to lay an ambush against the droplets from four-dimensional space. No matter how powerful the strong-interaction probes were, they were still three-dimensional objects. In a sense, three-dimensionality is synonymous with fragility. Viewed from four-dimensional space, it was an unrolled painting, defenseless. We approached it from the fourth dimension, and, without understanding its principles of operation, sabotaged its internal mechanisms—completely exposed—at random.

  “Is Trisolaris aware of the existence of the four-dimensional fragment?”

  “We think not.”

  “The soap bubble—uh, four-dimensional fragment—how big is it?”

  “Talking about the size of four-dimensional space from three-dimensional space is kind of meaningless. We can only discuss how big the projection of the fragment is in three dimensions. Based on preliminary investigation, we think the three-dimensional projection is spherical. If that’s true, based on the data collected so far, its radius is between forty to fifty AU.”

  “About the size of the Solar System.”

  The round opening in the bulkhead next to the three of them began to move slowly and to shrink. When it was just over ten meters from them, the opening disappeared completely. But the information window floating near them indicated that two more warped points had appeared aboard Blue Space.

  “How could a four-dimensional fragment appear in three-dimensional space?” Guan Yifan muttered to himself.

  “No one knows. Doctor, this is your puzzle to solve.”

  After the discovery of the four-dimensional fragment, Blue Space had explored and studied the space inside extensively. The addition of Gravity brought more advanced equipment and techniques, so the crews could conduct more comprehensive and in-depth exploration.

  In three-dimensional space, this region appeared very empty and showed no irregularities. Much of the exploration had to be conducted in four-dimensional space. Since releasing probes into four-dimensional space was no trivial matter, most of the research was conducted by inserting a telescope into the fragment through a warped point. Manipulating a three-dimensional instrument in four dimensions required some practice, and a period of adjustment, but once the scientists got the hang of it, they immediately made shocking discoveries.

  Through the telescope, they discovered a ring-shaped object. Since it was impossible to determine its distance from the ship, it was also impossible to estimate its size. The best guess was that its three-dimensional diameter was between eighty to one hundred kilometers, and the band of the ring was about twenty kilometers thick. The whole thing resembled a giant wedding band spinning in space. Complex patterns resembling circuitry could be discerned on the surface of the band. Based on the evidence, it seemed reasonable to conclude that the ring had been constructed by intelligent beings.

  This was the first time humanity had observed another civilization outside of the Earth and Trisolaris.

  But the most shocking thing was that the “Ring” was sealed. It existed in four-dimensional space, but didn’t reveal its interior as a three-dimensional object would have. Since its inside was concealed, that meant it was a true four-dimensional object. This was also the first true four-dimensional object detected by humanity since entering four-dimensional space.

  People initially feared an attack, but the surface of the Ring showed no signs of any activity. They also detected no emission of any electromagnetic, neutrino, or gravitational wave signals. Other than a slow, stately revolving motion, the Ring showed no acceleration. The working theory was that this was a ruin, perhaps a long-abandoned space city or spaceship.

  Further observations revealed more unknown objects in the depths of four-dimensional space. They were all sealed four-dimensional objects of different sizes and shapes, and many seemed to be artifacts fashioned by intelligence: pyramids, crosses, polyhedral frames, and so on. Other objects were irregular forms composed from simpler shapes, also clearly not natural. More than a dozen of these objects had shapes that could be discerned by telescope, though farther away were many more objects that appeared only as point sources. In total, about a hundred such objects were found. Like the Ring, none of them showed signs of activity, and they emitted no detectable signals.

  Guan Yifan proposed to Captain Chu the plan of piloting a pinnace to the Ring and studying it up close. If possible, he wanted to enter the Ring. The captain denied this proposal unequivocally. Navigating through four-dimensional space was fraught with risks. To precisely fix one’s location required four coordinates, but equipment brought from three-dimensional space could only determine three coordinates. This meant three-dimensional explorers could not determine the location of any object in four-dimensional space with precision. An explorer could not ascertain the location or distance of the Ring using instrumentation or visual observation, so it would be possible to collide with the Ring at any moment.

  Similarly, locating a warped point to return to three-dimensional space would be very difficult. Since the coordinate in one of the four directions could not be determined, when a warped point was found, all that was known was its direction, not its distance from the observer. The crew of the pinnace could use a warped point to return to three-dimensional space and, to their surprise, find themselves far away from Blue Space.

  Finally, most of the radio waves linking Blue Space and the pinnace would spill into the fourth dimension, leading to far faster decay of signal strength and causing communication difficulties.

  After that, Blue Space and Gravity suffered six micrometeoroid strikes in one day. A 140-nanometer micrometeoroid struck and completely destroyed the magnetic levitation controller of Blue Space’s fusion reactor core. This was a key system aboard the ship. The fusion reactor core could reach temperatures as high as a million degrees, which would vaporize any material it came in contact with. A magnetic field kept it centered within the reaction chamber. If the controller failed, the superheated reactor core could escape from the magnetic field and instantly destroy the ship. Fortunately, the backup unit kicked in immediately and shut off the reactor—which was operating at minimal power—and averted catastrophe.

  As the two ships sailed deeper into the four-dimensional fragment, the density of micrometeoroid strikes increased, and even larger meteoroids, visible to the naked eye, passed near the ships. Their velocity relative to the ships was several times the third cosmic velocity. In three-dimensional space, the critical parts of the ships were wrapped in layers of protection, but here, they lay exposed to the fourth dimension, completely defenseless.

  Chu Yan decided that the two ships should retreat from the four-dimensional fragment. The fragment as a whole was moving away from the Solar System, heading in the same direction as the ships’ course; thus, although Blue Space and Gravity were sailing away from the Solar System at a high speed, their velocity relative to the fragment was small, and they had only slowly caught up to the fragment. They weren’t deep within the fragment and should be able to decelerate and leave it easily.

  Guan Yifan raged against this decision. “The greatest mystery in the universe is right in front of us. The answers to all our cosmological questions may be found here. How can we leave?”

 
“Are you talking about the three and three hundred thousand syndrome? The fragment did remind me of it.”

  “Even if you focus only on the practical, we can probably recover unimaginable knowledge and artifacts from that ring-shaped ruin.”

  “Such gains are only meaningful if we survive this ordeal. Right now, both of our ships could be annihilated any moment.”

  Guan sighed and shook his head. “Fine. But before you leave, let me ride a pinnace to explore the Ring. Give me a chance. You spoke of survival, but perhaps our future survival depends on what I can discover here!”

  “We can consider sending a drone.”

  “In a four-dimensional world, only a live observer can understand what is seen. You know this better than I.”

  * * *

  After a brief discussion, the senior staff of both ships approved Guan’s proposal. Guan Yifan, Lieutenant Zhuo Wen, and Dr. West made up the exploratory team. Lieutenant Zhuo was the science officer aboard Blue Space and had comparatively extensive experience navigating in four dimensions. Dr. West, on the other hand, simply insisted that he come; the request was ultimately approved because he had studied Trisolaran language before the voyage.

  Prior to this, the longest voyage in four-dimensional space had been the attack on the droplets and Gravity. During the attack, a pinnace had sailed through four-dimensional space to approach Gravity, and then three people, including Lieutenant Commander Park Ui-gun, had entered Gravity via a warped point to reconnoiter. Thereafter, more than sixty marines had boarded Gravity in three separate waves. The attack on the droplets had relied on smaller shuttles. But this voyage of discovery to the Ring would be far longer.

  The pinnace entered four-dimensional space from a warped point between the two ships. At the tail of the pinnace, the small fusion reactor’s core turned from dim red to a faint blue as its power level increased. This flame, together with the balls of fire in the reactors of the two larger ships, illuminated this world of infinity times infinity. Blue Space and Gravity quickly receded, and as the pinnace sailed deeper into four-dimensional space, the high-dimensional spatial sensation intensified. Although Dr. West had already been to four-dimensional space twice, he exclaimed, “How grand is the spirit that can grasp such a world!”

  Lieutenant Zhuo piloted the pinnace using voice commands or by moving the cursor with his gaze—it was a good idea to avoid using hands and risking contact with some sensitive piece of equipment that now lay exposed in four dimensions. To the naked eye, the Ring was still but a barely visible dot, but Zhuo cautiously kept the pinnace flying at a very low speed. Due to the extra unmeasurable dimension, visual judgments of distance were completely unreliable. The Ring might be as far away as an astronomical unit or as close as the pinnace’s bow.

  After three hours, the pinnace had already exceeded the previous record of distance sailed from the ships in four-dimensional space. The Ring remained but a dot. Lieutenant Zhuo grew even more cautious and was prepared to decelerate at full power and to change the heading at a moment’s notice. Guan Yifan grew impatient and asked Zhuo to fly faster. Just then, West cried out in surprise.

  The Ring turned into a real ring—it just happened. One moment, it was still a dot; the next moment, it was a ring the size of a coin. There was no gradual process of change at all.

  “You’ve got to remember that we’re basically blind in the fourth dimension,” Lieutenant Zhuo said. He decreased their speed again.

  Two more hours passed. If they were still in three-dimensional space, they would have sailed about two hundred thousand kilometers.

  All of a sudden, the coin-sized Ring turned into a gigantic structure. Lieutenant Zhuo banked sharply and barely managed to avoid collision. The pinnace passed through the Ring like an arch in space. The pinnace decelerated, turned around, and came to a stop a short distance from the Ring.

  This was the first time humans had come close to a four-dimensional object. Similar to high-dimensional spatial sense, they felt the magnificence of high-dimensional materiality. The Ring was completely sealed, and they could not look inside the band, but they could feel an immense sense of depth and of containment. What they were seeing wasn’t just a Ring, but an infinity of Rings all stacked together in concealment. This sensation of four-dimensionality impressed itself upon the soul, and gave the observers the experience of seeing the mountain contained in a mustard seed described in Buddhist parables.

  From up close, the surface of the Ring appeared very different from images taken by the telescope. Instead of a golden yellow light, it gave off a dark copper glow. Those faint etched lines that had looked like circuitry were really lines left by micrometeoroids striking its surface. There was still no evidence of any activity, and it didn’t emit light or other radiation. Looking at the ancient surface of the Ring, all three felt a sense of familiarity. They recalled the destroyed droplets, and then tried to imagine the immense four-dimensional Ring with a mirrorlike smooth surface—it would have been a breathtaking sight.

  Following the preestablished plan, Lieutenant Zhuo transmitted a message to the Ring via medium-frequency radio waves. This was a simple bitmap, a bit array that could be interpreted as six lines of dots that formed a sequence of prime numbers: 2, 3, 5, 7, 11, 13.

  They weren’t expecting any answers, but an answer arrived immediately, so fast that they couldn’t believe their eyes. The information window hovering in the middle of the pinnace cabin displayed a simple bitmap similar to the one they had sent. It also consisted of six lines portraying the next six prime numbers: 17, 19, 23, 29, 31, 37.

  The original plan had intended the hailing message as an experiment; there was no preparation for how to develop further communications. While the three in the pinnace debated what to do, the Ring sent a second bitmap to the pinnace: 1, 3, 5, 7, 11, 13, 1, 4, 2, 1, 5, 9.

  Then a third bitmap: 1, 3, 5, 7, 11, 13, 16, 6, 10, 10, 4, 7.

  A fourth: 1, 3, 5, 7, 11, 13, 19, 5, 1, 15, 4, 8.

  A fifth: 1, 3, 5, 7, 11, 13, 7, 2, 16, 4, 1, 14.

  The bitmaps came one after another. The first six numbers in each consisted of the six prime numbers sent by the pinnace as a greeting. As for the next six numbers in each series, both Lieutenant Zhuo and Dr. West turned to Guan Yifan, the scientist. The cosmologist stared at the scrolling numbers in the floating window and shrugged.

  “I can’t see any pattern.”

  “Then let’s suppose that there is no pattern.” West pointed at the window. “The first six numbers were sent by us, so it’s possible that they mean ‘you.’ The next six numbers in the transmissions show no recognizable pattern, so maybe they mean ‘all’—‘everything about you.’”

  “They—or it—want to know everything about us?”

  “Or at least a linguistic sample. It wants to decode it, study it, and then communicate with us further.”

  “Then we should send it the Rosetta System.”

  “We have to ask for authorization.”

  The Rosetta System was a database developed to teach Earth languages to Trisolarans. The database included about two million characters’ worth of documents concerning the natural and human histories of Earth with numerous videos and images. There was also software to draw connections between the linguistic symbols and the images so that an alien civilization could decode and study Earth languages.

  The mother ship authorized the request from the exploration team. But the pinnace didn’t have the Rosetta System in its onboard computer memory, and due to the extremely tenuous communication link between the pinnace and the mother ship, it was impossible to transmit such a large volume of data. The only solution was to have the mother ship beam the information directly at the Ring. This couldn’t be done via radio, but luckily, Gravity was equipped with a neutrino communication system. They weren’t sure if the Ring could receive neutrino signals, however.

  Three minutes after Gravity transmitted the Rosetta System via a neutrino beam to the Ring, the pinnace received a new series of
bitmaps from the Ring. The first one was a perfect square of sixty-four dots arranged eight by eight; the second bitmap was missing one dot in a corner, leaving sixty-three; the third bitmap was missing two, leaving sixty-two.…

  “It’s a countdown, or a progress bar,” said West. “I think this is to show that it has received the Rosetta System and is in the process of decoding it. We should wait.”

  “Why sixty-four dots?”

  “It’s a reasonably big number if you’re in base two. It’s like how we use one hundred for lots of things in base ten.”

  Lieutenant Zhuo and Guan were both glad to have West with them. The psychologist did seem to have some skills when it came to establishing communications with unknown intelligences.

  When the countdown reached fifty-seven, something exciting happened: The next number didn’t come in the form of a bitmap of dots. The Ring transmitted the Arabic number 56.

  “Wow, fast learner,” Guan said.

  The number kept on decreasing by one every ten seconds or so. A few minutes later, the number reached 0. The last message consisted of four Chinese characters:

  I am a tomb.

  The Rosetta System was written in a language that mixed English with Chinese. It would make sense that the Ring would use the same language to communicate with them. It just happened that this message consisted entirely of Chinese characters. Guan Yifan typed a question into the floating window, and began the conversation between humanity and the Ring.

  Whose tomb is this?

  The tomb of those who created it.

  Is this a spaceship?

  It used to be a spaceship. But now it’s dead, and so it’s a tomb.

  Who are you? Who is conversing with us?

  I am the tomb. It is the tomb speaking to you. I’m dead.

  You mean you’re a ship whose crew died? In other words, you’re the control system for the ship?

  (There was no reply to this.)