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Gravity had been pursuing Blue Space for half a century. It finally approached its target. Only three AU separated the hunter and the hunted. Compared to the 1.5 light-years that the two ships had traversed, this was mere inches.

Once Gravity left the Oort Cloud behind, the ship entered true outer space. From here, the sun appeared as just another star behind the ship. It lost its reality and became like an illusion. In every direction, all one could see was a bottomless abyss, and the only objects whose existence could be ascertained by the senses were the droplets flying in formation with Gravity. The droplets flanked the ship at a distance of about five kilometers, just visible to the naked eye. Those aboard Gravity liked to gaze at the droplets with telescopes as a source of comfort in the endless emptiness. Observing the droplets was, in a sense, just looking at themselves. The mirrorlike surface of the droplets reflected an image of Gravity. The dimensions were a bit distorted, but due to the perfect smoothness of the surface, the image was particularly clear. With sufficient magnification on their telescopes, the observers could even pick out the porthole, and themselves in it, in the reflection.

A decade ago, Gravity had passed through the Oort Cloud. This region, about one light-year from the sun at the edge of the Solar System, was the birthplace of comets. Blue Space and Gravity were the first human spaceships to cross this border. The region didn't feel anything like a cloud, though. Once in a while, a frozen ball of dirt and ice -- a tailless comet -- passed tens of thousands or hundreds of thousands of kilometers away, invisible to the naked eye.

Most of the one hundred-plus officers and crew aboard Gravity didn't experience this solitude because they had spent the majority of the past fifty years in hibernation. During routine cruising, only about five to ten crew members needed to be on duty. As the crew rotated through hibernation, each person was usually on duty for three to five years.

The entire pursuit was a complex game of acceleration between Gravity and Blue Space. First of all, Blue Space couldn't just accelerate continuously, as doing so would cost it precious fuel and ultimately deprive it of mobility. Even if it managed to escape Gravity, it would be committing suicide in the endless empty desert of outer space if it exhausted its fuel. Although Gravity had more fuel onboard than Blue Space, it had constraints of its own. Since it needed to be prepared for a return voyage, its fuel reserves had to be divided into four equal parts: the acceleration away from the Solar System; the deceleration before its destination; the acceleration toward the Solar System; and the deceleration before arriving at the Earth. Thus, the portion available for acceleration during the pursuit amounted to only one-quarter of the fuel. Based on calculations of Blue Space's previous maneuvers and intelligence gathered by the sophons, Gravity had an accurate idea of Blue Space's fuel reserves, but the latter had no information about the former's stores. Thus, in this game, Gravity knew all the cards held by Blue Space, while Blue Space struggled in ignorance. During pursuit, Gravity consistently maintained a speed higher than Blue Space, but neither ship approached their maximum velocities. Moreover, twenty-five years after the start of the chase, Blue Space stopped accelerating, perhaps because it had used up all the fuel it dared.

A year previously, when Gravity and Blue Space were thirty AU apart, something not entirely unexpected occurred: Gravity and the two accompanying droplets entered a region of space where the sophons lost their quantum ties to home, terminating real-time communications with Earth. Gravity had to communicate with Earth through only neutrinos and radio. Transmissions from Gravity now took a year and three months to reach the Earth, and the ship had to wait an equally long time to receive a reply.

During the half century of the hunt, Gravity repeatedly hailed Blue Space, explaining that running was meaningless. Even if the crew of Blue Space somehow escaped the hunters from Earth, the droplets would catch up and destroy them. But if they returned to Earth, they would receive a fair trial. They had the option to greatly shorten the pursuit by surrendering. But Blue Space ignored these entreaties.

Near the beginning of the Crisis Era, as Trisolaris sent sophons toward the Earth, it also launched six sophons at near-lightspeed to explore other regions of the galaxy.

[Excerpt from A Past Outside of Time, More Indirect Evidence for the Dark Forest: Sophon-Blind Regions]

All of these sophons soon entered blind regions and lost contact with home. The longest-lasting one managed to get seven light-years away. Additional sophons launched later met with the same fate. The closest blind region, only about 1.3 light-years from Earth, was the one encountered by the sophons that accompanied Gravity.

Trisolaris remained mystified by the kind of interference the sophons received: Perhaps it was a natural phenomenon, or perhaps it was "man"-made. Scientists from both Trisolaris and Earth leaned toward the latter explanation.

Before being blinded, the sophons were able to explore only two nearby stars with planets. Neither system exhibited signs of life or civilization. But Earth and Trisolaris both came to the conclusion that their desolation was precisely why the sophons were allowed to approach.

Once the quantum entanglement between sophons was broken, it could not be restored. Any sophon entering a blind region was lost forever.

Thus, even deep into the Deterrence Era, the universe at large remained hidden from the two worlds by a mysterious veil. The existence of these blind regions seemed to provide indirect proof for the dark forest nature of the universe: Something was preventing the cosmos from becoming transparent.

The captain of Gravity decided that he could no longer afford to wait. He ordered Gravity to accelerate further.

[Deterrence Era, Year 62, Gravity, in the Vicinity of the Oort Cloud]

As Gravity approached, Blue Space hailed the hunters for the first time, proposing a plan: Blue Space would load two-thirds of the crew -- including the main suspects -- onto pinnaces and send the pinnaces to Gravity if the remainder of the crew was allowed to continue their voyage into deep space aboard Blue Space. This way, a vanguard and seed for the human race would be preserved in space, keeping alive the hope for further exploration.

Losing the sophons was not fatal to Gravity's mission, though it did make the job much harder. Before, the sophons could enter Blue Space at will and report on everything that was going on; now Blue Space appeared to Gravity as a sealed box. Moreover, the droplets lost real-time communications with Trisolaris and had to rely on the onboard AI. This led to unpredictable results.

Gravity vehemently denied this request. The entire crew of Blue Space was suspected of murder, and all had to be tried. Space had transformed them until they were no longer members of the human race. Under no circumstances could they be allowed to "represent" humanity in space exploration.

Gravity's crew emerged from hibernation and readied the ship for combat. The vessel, once silent and deserted, was once again filled with people.

Those who had been awakened faced the prospect of both a target nearly at hand and the loss of real-time communications with Earth. This loss did not pull them spiritually closer to the crew of Blue Space. To the contrary, like a child who was separated from her parents, the crew distrusted the parentless wild children even more. Everyone wished to capture Blue Space as quickly as possible and return home. Even though both crews were in the cold vastness of space, voyaging in the same direction at approximately the same speed, the natures of their voyages were completely different. Gravity had a spiritual anchor, while Blue Space was adrift.

Blue Space apparently realized the futility of running and of resisting. If only a human spaceship pursued them, then they at least stood a chance if they fought. But the two droplets changed the strategic calculus. Before them, Blue Space was nothing but a paper target, and there was no chance of escape. When the two ships were only fifteen AU apart, Blue Space announced its surrender and began to decelerate at maximum power. The distance between the two ships shrank rapidly, and it seemed that the long hunt was at last coming to an end.

"Commander, in my professional capacity, I wouldn't laugh at anyone."

In the ninety-eighth hour after the crew's emergence from hibernation, Dr. West, Gravity's psychiatrist, received his first patient. This visit from Commander Devon surprised the doctor. According to his records, Devon had the highest stability score of anyone aboard. Devon was in charge of the military police aboard Gravity, and it would be his responsibility to disarm Blue Space and arrest the crew once it was caught. Gravity's male crew members belonged to the last generation from Earth who still looked masculine, and Devon had the most masculine appearance among them. He was sometimes even mistaken for a Common Era man. He had often spoken out in favor of taking a hard line toward the suspects, suggesting that the death penalty ought to be revived.

"Doctor, I know that you'll keep my confidence," Devon said carefully. His tone was in marked contrast to his usual hard-edged style. "I know that what I'm about to say will sound funny."

"The man and I passed by each other. He saluted me, and I glanced at him…"

"What was wrong?"

Devon didn't answer the question. "Doctor, you know that as part of my duties, I've been monitoring the interior of Blue Space through the real-time images transmitted by the sophons. I know the crew of that ship better than I know the crew here. I know what Lieutenant Commander Park Ui-gun looks like."

"Yesterday, at approximately stellar time 436950, I left Conference Room Four and followed Passageway Seventeen back to my cabin. As I approached the Intelligence Center, a sublieutenant came toward me -- or, at least, a man dressed in the uniform of a Space Force sublieutenant. At that time, except for crew members on duty, everyone should have been asleep. But I didn't think it was so strange to meet someone in the passageway. Except…" Devon shook his head and his eyes lost focus, as though trying to recall a dream.

"He was… he was the commander of the marines from Blue Space, Lieutenant Commander Park Ui-gun."

Devon stopped again, and the doctor nodded for him to continue.

"You mean Blue Space, our prey?" West's tone was calm, betraying no hint of surprise.

"No, there's no one -- I know everyone onboard. Also… after the salute, he passed by me without any expression. I stood there, stunned. But by the time I turned around, the passageway was empty."

"Maybe it was someone from our ship who looks like him."

"When did you wake up from hibernation?"

"Three years ago. I needed to keep an eye on the activities onboard our target. Before that, I was also among those aboard who had stayed out of hibernation the longest."

"Before that, you spent so much of your time watching those aboard Blue Space that I think you probably felt as though you were on Blue Space rather than Gravity."

"Then you must have experienced the moment when we entered the sophons' blind region."

"And then, the surveillance images were cut off. You couldn't see anything over there anymore. And you were tired… Commander, it's simple. Trust me: This is normal. I suggest you get more rest. We have plenty of people now to do the work that needs to be done."

"Of course."

"Yes, Doctor. I did often feel that way."

"Doctor, I'm a survivor of the Doomsday Battle. After my ship exploded, I was curled up in a life pod the size of your desk, drifting in the vicinity of Neptune's orbit. By the time I was rescued, I was close to death, but my mind was still sound, and I never suffered any delusions… I believe what I saw." Devon got up and walked away. He turned around at the cabin door. "If I meet that bastard again -- doesn't matter where -- I'm going to kill him."

Some time after that, an accident happened in Ecological Area #3-- a nutrient tube ruptured. The tube was made of carbon fiber, and as it wasn't subject to pressure, the probability of a malfunction was very low. Ecological Engineer Ivantsov passed through the aeroponically grown plants, as dense as a rainforest, and saw that others had already shut off the valve leading to the ruptured tube and were cleaning up the yellow nutrient broth.

Ivantsov stopped dead when he saw the ruptured tube. "This… is caused by a micrometeoroid!"

Someone laughed. Ivantsov was an experienced and prudent engineer, and that made his outburst even funnier. All the ecological areas were buried in the center of the ship. Ecological Area #3 was tens of meters away from the nearest section of the exterior hull.

As one, they looked up.

"I worked more than a decade in external maintenance and I know what a micrometeoroid strike looks like! Look, you can see the typical signs of high-temperature ablation around the edges of the rupture."

The ceiling above the ruptured tube looked smooth and undamaged. Furthermore, above the ceiling, tens, maybe hundreds more bulkheads of various thicknesses separated this place from space. An impact-breach in any of these bulkheads would have triggered a high-level alert.

Ivantsov closely examined the inside of the tube; then he asked a technician to cut off a ring of material around the rupture and magnify it. The chatter died down as everyone stared at the 1000x image. There were tiny black particles, a few microns in diameter, embedded in the wall of the tube. The particles twinkled like unfriendly eyes in the magnified image. They all knew what they were looking at. The meteoroid must have been about one hundred microns in diameter. It had shattered as it went through the tube, its broken pieces winding up embedded in the wall opposite the breach.

"It's like a ghost," a sublieutenant named Ike muttered, and left. His choice of words was meaningful: About ten hours earlier, he had seen another, bigger ghost.

Ike had been trying to fall asleep in his cabin when he saw a round opening appear in the wall opposite his bed. It was about a meter across, and occupied the space where a Hawaiian landscape had hung. It was true that many of the bulkheads on the ship could shift and transform so that doors could appear anywhere, but a circular opening like this was impossible. Moreover, the cabin walls of mid-level officers were made of metal and could not deform this way. A closer examination by Ike revealed that the edge of the opening was perfectly smooth and reflective, like a mirror.

But the micrometeoroid had to have come from space. Based on the condition of the rupture, the micrometeoroid had struck the tube at a relative velocity of thirty thousand meters per second. It would have been impossible to accelerate the projectile to such speed from within the ship, much less from within the ecological area.

Although the hole was strange, Ike was rather pleased by it. Sublieutenant Vera lived next door.

Verenskaya was the AI system engineer aboard Gravity. Ike had been trying to get the Russian beauty to go out with him, but she hadn't shown any interest. Ike still remembered his latest attempt two days ago.

He and Verenskaya had just gotten off duty. As usual, they walked back to the officers' quarters together, and as they reached Verenskaya's cabin, Ike tried to invite himself in. Verenskaya blocked her door.

Verenskaya looked askance at Ike. "Any real men on this ship would be too worried about our mission to think about getting into the pants of every woman around them."

"Come on, sweetheart," Ike said. "Let me in for a visit. It's not very neighborly to never invite me over. They'll think I'm not a real man."

"What's there to worry? After we catch those murderers, there will be no more danger. Happy times will be here!"

"They're not murderers! Without deterrence, Blue Space would be humankind's only hope. Yet we're now hunting them down, allied with the enemies of the human race. Don't you feel ashamed?"

However, now Ike had a perfect excuse to enter Verenskaya's cabin. He unbuckled his weightlessness belt and sat up in his bed, but stopped when he saw that the bottom half of the round opening made the top of the cabinet against the wall disappear as well. The edge of what remained of the cabinet was also perfectly smooth and reflective, like the edge of the opening itself. It was as if some invisible knife had cut through the cabinet and everything inside, including the stacks of folded clothes. The mirrorlike surface of the cross-section ran up against the edge of the round opening, and the whole reflective surface looked like a portion of the inside of a sphere.

"Um… baby, if you feel this way… how did you…"

Ike pushed against the bed and lifted off in the weightlessness. Looking through the opening, he almost screamed in fright. This must be a nightmare!

"How did I get to join this mission? Is that what you want to say? Why don't you go to the psychiatrist and the captain to report me? They'll put me in forced hibernation and kick me out of the fleet after we return. That's just my wish!" Verenskaya slammed the door in his face.

Through the hole, he could see that a part of Verenskaya's bed, pushed up against the cabin wall, had also disappeared. Verenskaya's lower legs had been cut off. Although the cross section of the bed and the legs were also smooth and reflective, as though covered by a layer of mercury, he could see Verenskaya's muscles and bones through it. But Verenskaya seemed all right. She was still in deep sleep, and her firm breasts slowly moved up and down as she breathed. Normally, Ike would have admired such a sight, but right now he only felt a supernatural fright. When he calmed down and looked closer, he saw that the cross-section of Verenskaya's legs and bed also formed a spherical surface that matched the round opening.

He was looking at a bubble-shaped space about a meter in diameter, which erased everything within its path.

Ike picked up a violin bow from the nightstand, and, with a trembling hand, poked it into the bubble. The part of the bow extended inside the bubble disappeared, but the bow hair remained taut. He pulled the bow back and saw that it was undamaged. But he was still glad that he hadn't tried to go through the hole -- who knew if he would emerge from the other side unharmed?

So he set the sleep cap for an hour. When he woke up this time, the bubble and the hole in the wall were gone. The Hawaiian landscape was back on the wall and everything was as it was before the incident.

He woke up after half an hour, and the bubble was still there.

Ike forced himself to be calm and tried to think of the most rational explanation for the eerie sight. Then he made what he thought was a wise decision: He put on his sleep cap and lay back down on the bed. He buckled his weightlessness belt back on and set the sleep cap for half an hour.

It took a while before the door opened, and a not-completely-awake Verenskaya demanded to know what he wanted.

But Ike was worried about Verenskaya. He dashed out of his cabin and stopped in front of Verenskaya's door. Instead of ringing the doorbell, he pounded on the door. His mind was filled with the terrifying vision of Verenskaya, close to death, lying on the bed with her legs cut off.

"I came to see if you are… all right." Ike's gaze shifted down, and he saw that Verenskaya's beautiful legs were perfect below the hem of her nightgown.

After returning to his cabin, Ike put his sleep cap on and set it for eight hours. As for what he had seen, the only wise thing to do was to shut up and say nothing. Due to Gravity's special mission, the crew's psychological state -- especially that of the officers -- was subject to constant monitoring. There was a special psychological monitoring corps aboard, comprising more than a dozen crew members out of the full complement of just over a hundred. Some crew members had wondered whether Gravity was a stellar ship or a psychiatric hospital. And then there was also the annoying civilian psychiatrist West, who thought of everything in terms of mental disorders and illnesses and blockages, until one could come to the conclusion that he would subject a clogged toilet to psychiatric analysis. The mental screening process onboard Gravity was extremely strict, and even slight mental disorders would result in the sufferer being forced into hibernation.

"Idiot!" Verenskaya slammed the door shut.

Ike was terrified of missing the upcoming historical encounter between the two ships. If that happened, when the ship returned to Earth in half a century, the girls back home would not see him as a hero.

But Ike did feel a slight diminution in his dislike for the psych corps and Dr. West. He had always thought of them as making mountains out of molehills, but he had never imagined that people could suffer such realistic delusions.

Compared to Ike's minor delusion, Petty Officer Liu Xiaoming's supernatural encounter would be considered quite spectacular.

Liu was performing a routine exterior hull inspection. This involved piloting a small pinnace at a certain distance from Gravity and examining the hull for any abnormalities, such as evidence of meteor strikes. This was an ancient, outdated practice no longer strictly necessary and rarely performed. The ship was full of sensors that monitored the hull continuously; any problems would be detected right away. Also, the operation could only be done when Gravity was coasting instead of accelerating or decelerating. As the ship approached Blue Space, frequent acceleration and deceleration was necessary for adjustments. This was one of those rare windows when the ship was coasting again, and Petty Officer Liu was ordered to take advantage of the opportunity.

But Liu noticed something incredible: Gravity was shaped like a perfect cylinder, however, right now, its tail ended in an inclined plane! The ship was also much shorter than it should be -- about 20 percent shorter, to be exact. A giant, invisible knife had cut off Gravity's tail.

Liu piloted the pinnace out of the bay in the middle of the ship and smoothly glided away from Gravity until he was at a distance where he could see the whole ship. The giant hull was bathed in the light from the galaxy. Unlike when most of the crew was in hibernation, light spilled from all the portholes, making Gravity seem even more magnificent.

Liu shut his eyes, then opened them a few seconds later. The tail was still missing. He felt chilled to the bone. The giant ship before him was an organic whole. If the tail were suddenly gone, the power distribution systems would suffer a catastrophic failure, and the ship would shortly explode. But nothing of the sort was happening. The ship cruised along without trouble, as though suspended in space. No alerts of any kind came from his earpiece or were shown on his screens.

He pressed the switch for the intercom and got ready to give a report, but shut off the channel before saying anything. He recalled the words of an old spacer who had been at the Doomsday Battle: "Your intuition is unreliable in space. If you must act based on intuition, count from one to one hundred first. At least count from one to ten."

He closed his eyes and began to count. When he got to ten, he opened his eyes. The tail was still missing. He closed his eyes and continued to count, his breath coming faster now, but he struggled to remember his training, and forced himself to calm down. He opened his eyes when he reached thirty, and this time he saw the complete Gravity. He closed his eyes again, sighed, and waited until his heartbeat slowed down.

He piloted the pinnace to the stern of the ship, where he could see the three giant nozzles of the fusion drive. The engine wasn't on, and the fusion reactor was kept at minimal power so that the nozzles only showed a faint red glow, reminding him of the clouds back on Earth at dusk.

Petty Officer Liu was glad that he hadn't made a report. An officer might get therapy, but an NCO like himself would be forced into hibernation. Like Ike, Liu Xiaoming didn't want to return to Earth a useless man.

Dr. West went to find Guan Yifan, a civilian scholar who worked in the observatory at the stern. Guan had a midship cabin assigned to him as living quarters, but he rarely went there. Most of the time, he remained in the observatory and asked the service robots to bring his meals. The crew referred to him as "the hermit at the stern."

The observatory was a tiny spherical cabin where Guan lived and worked. His appearance was disheveled, with an unshaven face and long hair, but he still looked relatively youthful. When West saw Guan, he was floating in the middle of the cabin, looking restless: sweaty forehead, anxious eyes, his hand pulling at his collar as if he was unable to catch his breath.

"I already told you on the phone: I'm working and don't have time for a visit." Guan Yifan said. Obviously tired of the doctor's arrival.

"I'm not a member of the space force. As long as I'm no danger to the ship or the crew, you have no power over me."

"It's precisely because your call betrayed signs of mental disorder that I came to see you."

"Fine. I'll leave." West turned around. "I just don't believe that someone with claustrophobia can work in here without trouble."

"I'm not complaining. Gravity's mission is bringing fugitives to justice, not scientific exploration. I'm grateful to have this space at all… Look, my claustrophobia has nothing to do with this."

Guan called out for West to stop, but West ignored him. As he expected, Guan chased after him and stopped him. "How did you know that? I am indeed… claustrophobic. I feel like I'm being packed into a narrow tube, or sometimes squeezed between two iron plates until I'm flat as a sheet…"

"Not surprising. Look at where you are." The doctor indicated the cabin -- it resembled a tiny egg nestled in a nest of crisscrossing cables and pipes. "You research phenomena at the largest scale, but you stay in the smallest space. And how long have you been here? It's been four years since your last hibernation, hasn't it?"

The doctor pulled Guan Yifan along, and the two drifted toward the bow of the ship. If the ship were accelerating, going from the stern of the ship to the bow would be equivalent to climbing up a one-kilometer well, but in the weightlessness of coasting, the trip was a lot easier. Plaza #1 was located at the bow of the cylindrical ship, under a semispherical, transparent dome. Standing there was like standing in space itself. Compared to the holographic projections of the star field on the walls of spherical cabins, this place induced an even stronger sense of the "desubstantiation effect."

"Desubstantiation effect" was a concept from astronautic psychology. Humans on Earth were surrounded by objects, and the image of the world in their subconscious was thus material and substantial. But in deep space, away from the Solar System, the stars were only distant points of light and the galaxy was nothing more than a luminous mist. To the senses and the mind, the world lost its materiality, and empty space dominated. A space voyager's subconscious image of the world thus became desubstantiated. This mental model was the baseline in astronautic psychology. Mentally, the ship became the only material entity in the universe. At sub-light speeds, the motion of the ship was undetectable, and the universe turned into one boundless, empty exhibition hall. Here, the stars were illusions, and the ship was the only object on display. This mental model brought with it a profound sense of loneliness, and it could cause the voyager to have subconscious delusions of being a "superobserver" toward the lone "object on display." This feeling of being completely exposed could lead to passivity and anxiety.

"Why don't we take a walk on Plaza One? It will help."

Thus, many of the negative psychological effects of deep-space flight were due to the extreme openness of the external environment. In West's extensive professional experience, it was extremely rare to develop claustrophobia the way Guan Yifan did. Even stranger to West was the fact that Guan did not seem relieved by the vast, open sky of Plaza #1; the restlessness caused by claustrophobia seemed to abate not one whit. This tended to support Guan's assertion that his claustrophobia had nothing to do with the narrow confines of his observatory. West grew even more interested in his case.

"Don't you feel better?" The doctor asked.

Guan glanced at the starry sky and then focused his gaze in the direction Gravity was heading. The doctor knew he was looking for Blue Space. The two ships were now only one hundred thousand kilometers apart, and coasting at approximately the same speed. At the scale of deep space, the two ships were practically flying in close formation. The leadership of both ships was in the process of negotiating the technical details of their docking. But Blue Space was still too far away to be seen with the naked eye. The droplets were invisible as well. Based on the agreement made with Trisolaris half a century ago, the droplets had shifted to a position about three hundred thousand kilometers from both Gravity and Blue Space. The two ships and the droplets formed a narrow isosceles triangle.

"No, not at all. I feel trapped. Here, everything is so… enclosed."

"Tell me more about this place in your dream."

Guan Yifan turned his gaze back to West. "Last night, I had a dream. I went somewhere, somewhere really open, open in a way that you can't even imagine. After I woke up, reality felt very enclosed and narrow, and that was how I came to be claustrophobic. It's like… if, as soon as you were born, you were locked inside a small box, you wouldn't care because that was all you've known. But once you've been let out and they put you back in, it feels completely different."

"But you just told me it was a dream."

Guan shook his head, struggling to remember. "I don't know if it was a dream; I don't know if I was awake. Sometimes, you can think you're waking from a dream, only to find yourself still dreaming; other times, you're awake, but it seems like you're dreaming."

Guan gave the doctor a mysterious smile. "I will describe it to the other scientists on the ship, maybe even the scientists on Blue Space. But I won't tell you. I don't have anything against you, Doctor, but I can't stand the attitude shared by everyone in your profession: If you think someone has a mental disorder, you treat everything he says as merely the delusion of a diseased mind."

"The second situation is extremely rare. If you experienced that, then it was almost certainly a symptom of some mental disorder. Oh, sorry, now you're unhappy with me again."

"No, no. I think we're actually very similar. We both have our targets of observation. You observe the deranged, and I observe the universe. Like you, I also have some criteria for evaluating whether the observed objects are sound: harmony and beauty, in the mathematical sense."

"Why?"

"But you're wrong, Doctor." Guan pointed at the glowing Milky Way, but his gaze remained on West, as though showing him some monster that had suddenly appeared out of nowhere. "Out there is a patient who may be mentally sound, but whose body suffers from paraplegia!"

"Of course the objects you observe are sound."

Guan curled up and hugged his knees. The movement caused his body to slowly rotate in place. The magnificent Milky Way revolved around him, and he saw himself as the center of the universe.

"Because of the speed of light. The known universe is about sixteen billion light-years across, and it's still expanding. But the speed of light is only three hundred thousand kilometers per second, a snail's pace. This means that light can never go from one end of the universe to the other. Since nothing can move faster than the speed of light, it follows that no information and motive force can go from one end of the universe to the other. If the universe were a person, his neural signals couldn't cover his entire body; his brain would not know of the existence of his limbs, and his limbs would not know of the existence of the brain. Isn't that paraplegia? The image in my mind is even worse: The universe is but a corpse puffing up."

"What do you mean?"

"Other than the speed of light, three hundred thousand kilometers per second, there's another three-based symptom."

"Interesting, Dr. Guan, very interesting!"

"I think string theory provides an explanation."

"The three dimensions. In string theory, excepting time, the universe has ten dimensions. But only three are accessible at the macroscopic scale, and those three form our world. All the others are folded up in the quantum realm."

"Some think that it is only when two strings encounter each other and some qualities are canceled out that the dimensions are unfolded into the macroscopic, and dimensions above three will never have such chances for encountering each other… I don't think much of this explanation. It is not mathematically beautiful. Like I said, this is the universe's three and three hundred thousand syndrome."

Guan laughed uproariously and put his arm around the doctor's shoulders. "Great question! I don't think anyone has thought this far. I'm sure there's a root cause, and it might be the most horrifying truth that science is capable of revealing. But… Doctor, who do you think I am? I'm nothing more than a tiny observer curled up in the tail of a spaceship, and only an assistant researcher at that." He released West's shoulders, and, facing the galaxy, let out a long sigh. "I've been in hibernation the longest of anyone aboard. When we left Earth, I was only twenty-six, and even now I'm only thirty-one. But in my eyes, the universe has already transformed from a source of beauty and faith into a bloating corpse. I feel old. The stars no longer hold any attraction for me. I want to go home."

"What do you propose as the cause?"

As if in response to their conversation, the battle alert klaxons blared, sounding like the entire sky full of stars was screaming. Warning information scrolled on floating windows that appeared above the plaza. The overlapping windows sprang up one after another and quickly covered the Milky Way like colorful clouds.

"Droplet attack!" West said to the confused Guan Yifan. "They're both accelerating. One is headed for Blue Space, the other for us!"

Unlike Guan Yifan, West had been awake for much of the voyage. He always believed that to maintain the mental health of others, he needed to keep his own emotions under control. But something seemed to buffet his heart now, and as he reviewed his own half century of travels, his eyes moistened. "My friend, I'm old, too."

Guan looked around, instinctively searching for something to grab on to in case the ship accelerated. But there was nothing around. In the end, he held on to the doctor.

West held his hands. "There won't be enough time for any evasive maneuvers. We have only a few seconds left."

They both thought of the same thing, but Guan spoke it aloud first. "Looks like neither of us needs to worry about our patients anymore."

After a brief panic, both felt an unexpected sense of relief. They were glad that death would arrive so quickly that there wasn't even time to be terrified. Perhaps their discussion about the universe was the best preparation for death.