The elevator took almost twenty minutes to reach its terminus. Cheng Xin stepped out of the elevator and saw a black steel door. White text on the door gave the formal name for the Deterrence Center: Gravitational Wave Universal Broadcast System Control Station Zero. The insignias of the UN and the Solar System Fleet were embossed on the door.

Half a year ago, a joint session of the UN and the Solar System Fleet had elected Cheng Xin to succeed Luo Ji as the Swordholder and given her authority to control the gravitational wave deterrence system. She had received almost twice as many votes as the next candidate. She was now proceeding to the Deterrence Center in the Gobi Desert, where the deterrence authority handover ceremony was to take place.

The Deterrence Center was the deepest man-made structure ever, about forty-five kilometers beneath the surface. This location was already below the crust, past the Mohorovičić discontinuity, in the mantle of the Earth. The pressure and temperature here were both far higher than in the crust, and the stratum around her was made up mostly of solid, hard peridotite.

The high-speed elevator continued to descend, and the increasing layers of earth above seemed to put all their weight on Cheng Xin's heart.

The handover ceremony was a solemn occasion, but the bulk of it had been held on the surface forty-five kilometers above. There, all the leaders of Earth International and Fleet International, representing all of humanity, had gathered, and they watched as Cheng Xin entered the elevator. Only two people would oversee the final handover: the PDC chair and the chief of staff for the Solar System Fleet, representing the two institutions directly operating the deterrence system.

This ultra-deep structure was quite complex. It possessed its own independent air circulation system and was not directly connected with the atmosphere above the surface -- otherwise, the high air pressure generated by a depth of forty-five kilometers would cause great discomfort to the occupant. It was also equipped with a powerful cooling system to withstand the high temperature of the mantle, nearly five hundred degrees Celsius.

All Cheng Xin could see, however, was emptiness. The lobby's walls could all apparently act as electronic displays, but they showed nothing but whiteness, as though the building wasn't in use yet. Half a century ago, when the Deterrence Center was designed, Luo Ji had been consulted, but he had only provided one piece of input: As simple as a tomb.

The first dark forest deterrence system consisted of more than three thousand nuclear bombs wrapped in an oil film substance deployed in orbit around the sun. After detonation, the film would cause the sun to flicker and broadcast the location of Trisolaris to the universe. Although the system was grand, it was extremely unstable. After the droplets stopped blockading electromagnetic radiation from the sun, a transmission system based on using the sun as a superantenna was immediately put in place to supplement the nuclear bomb deterrence system.

"We don't want you to live like him," said the chief of staff. Perhaps because of his military uniform, Cheng Xin saw in him traces of men of the past, and his words warmed her slightly. But the heavy weight on her heart, as heavy as the forty-five kilometers of earth above her, did not lessen.

[Excerpt from A Past Outside of Time, The Choice of the Swordholder: Ten Minutes Between Existence and Annihilation]

The PDC chair pointed at the empty lobby and explained to Cheng Xin that they would redecorate the place based on her ideas. If she wanted, she could have a lawn, plants, a fountain, and so forth. She could also choose to have a holographic simulation of scenes from the surface.

At the time of the founding of deterrence, humankind already had a basic grasp of the technology for detecting gravitational waves and neutrinos, but they lacked the ability to modulate and transmit. These were the very first technologies humans demanded from Trisolaris. Compared to quantum communications, these technologies were still primitive, since both gravitational waves and neutrinos were limited by the speed of light, but they were a whole level above electromagnetic waves.

Both of these systems relied on electromagnetic radiation, including visible light, as the broadcast medium. We now know that this is the most primitive technique for interstellar communication, equivalent to smoke signals in space. Since electromagnetic waves decay and become distorted rapidly, the broadcast range is limited.

Both of these means of transmission decayed relatively slowly and had very long broadcast ranges. Neutrinos, in particular, interacted with almost nothing else. Theoretically, a modulated beam of neutrinos could transmit information to the other end of the universe, and the accompanying decay and distortion would not affect the decoding of the information. But while neutrinos must be focused in a particular direction, gravitational waves were omnidirectional, thus gravitational waves became the main method of establishing dark forest deterrence.

The degenerate matter forming the vibrating string was naturally found in white dwarves and neutron stars. Under typical conditions, this substance naturally decayed and turned into regular matter over time. Man-made vibrating strings typically had a half-life of around fifty years, beyond which the antennas lost their effectiveness. Thus, every half century, the antennas needed to be refreshed with new ones.

The fundamental principle of gravitational wave transmission relied on the vibration of a long string of extremely dense matter. The ideal transmission antenna would involve a large number of black holes connected together to form a chain that generated gravitational waves as it vibrated. But even Trisolaris didn't possess such a level of technology, and humankind had to resort to constructing the vibrating string out of degenerate matter. The extremely dense degenerate matter packed an enormous mass into strings mere nanometers in diameter. A single string took up only a minuscule portion of the giant antenna, the bulk of which consisted of support and protection for the ultra-dense string. Thus, the total mass of the antenna wasn't extraordinarily large.

During the Deterrence Era, the ETO gradually disappeared, but another kind of extremist organization sprang up. They believed in the cause of human supremacy, and advocated for the complete annihilation of Trisolaris. The "Sons of the Earth" was one of the largest of these organizations. In Year 6 of the Deterrence Era, more than three hundred "Sons of the Earth" attacked a gravitational wave broadcasting station located on Antarctica with the aim of seizing the transmitter. Equipped with advanced weapons such as mini-infrasonic nuclear bombs, and aided by members who had infiltrated the broadcasting station ahead of time, the attackers nearly succeeded. If the defending troops stationed at the site hadn't destroyed the antenna in time, the consequences would have been disastrous.

During the earliest stage of gravitational wave deterrence, the main strategic concern was with ensuring deterrence power. Plans were made to build a hundred broadcasting stations scattered around the continents. But gravitational wave communication suffered from a flaw: The transmission equipment could not be miniaturized. The complex, gigantic antennas were extremely costly to manufacture, and in the end only twenty-three gravitational transmitters were built. But the focus on ensuring deterrence finally faded, due to another event.

Initially, the gigantic gravitational wave antennas had to be built on the surface. As technology advanced, in Year 12 of the Deterrence Era, the three terrestrial antennas and their support systems moved deep underground. Everyone understood, however, that burying the transmitters and the control center beneath the Earth's surface primarily guarded against a threat originating from humankind itself, but was meaningless against an attack by Trisolaris. For droplets constructed from strong-interaction material, tens of kilometers of rock were not much different from mere liquid, barely able to impede their progress.

This incident terrified both worlds. People began to realize the great danger posed by gravitational wave transmitters. Simultaneously, Trisolaris pressured Earth until gravitational wave transmission technology was strictly controlled, and the twenty-three broadcasting stations were cut down to four. Three of the stations were terrestrial, located in Asia, North America, and Europe, and the last one was the spaceship Gravity.

All the transmitters relied on an active trigger, because the dead hand trigger technique used in the circumsolar nuclear bomb system was no longer necessary. Luo Ji had established deterrence by himself, but now, if the Swordholder were killed, others would be able to take over.

After Earth established deterrence, the Trisolar invasion fleet veered away, as verified through observation. With that threat diminished, most people turned their focus to the whereabouts of the ten droplets that had already reached the Solar System. Trisolaris insisted that four of the droplets remain in the Solar System, justifying the decision by arguing that the gravitational wave transmitters could be seized by extremist factions within humankind, and Trisolaris should have the power to take steps to protect both worlds in the event of such an occurrence. Reluctantly, the Earth agreed, but required the four droplets to stay beyond the Kuiper Belt. Moreover, each droplet had to be accompanied by a human probe, so that the droplets' locations and orbits were known at all times. Thus, in the event of a droplet attack, the Earth would have about fifty hours of advance warning. Of these four droplets, two eventually followed Gravity to hunt Blue Space, and only two remained in the vicinity of the Kuiper Belt.

No one knew where the other six droplets had gone.

Most people were convinced that the six droplets were hidden somewhere in the Solar System. But because the droplets were tiny, fast, and invisible to radar, they were extremely difficult to locate and track. Even by spreading oil films or using other advanced detection techniques, humans could only reliably detect droplets if they approached within 1/10 AU of the Earth, or fifteen million kilometers. Outside this sphere, the droplets were free to roam undetected.

Trisolaris claimed that the six droplets had left the Solar System to rejoin the Trisolaran Fleet, but no one on Earth believed this.

At maximum speed, a droplet could cross fifteen million kilometers in ten minutes.

Trisolarans were no longer creatures of transparent thought. During the past two centuries, they had learned a great deal about strategic thinking -- lies, ruses, and tricks. This was perhaps the greatest benefit they gained from studying human culture.

This was all the time the Swordholder would have to make a decision if dark forest deterrence broke down.

Luo Ji sat cross-legged on the ground in the middle of the white hall, facing the curved wall. His long hair and beard, combed neatly, were also white, almost merging with the white wall. The whiteness everywhere contrasted strongly with his black Zhongshan suit.5 Sitting there, he appeared as a stable upside-down T, a lonely anchor on a beach, immobile under the winds of time howling overhead and before the roaring waves of the ages, steadfastly waiting for a departed ship that would never return. In his right hand, he held a red ribbon, the hilt of his sword: the switch for the gravitational wave broadcast. His presence gave the empty eye of this room an iris. Though he was but a black dot, the desolate sense of loss was relieved, giving the eye a soul. Luo Ji sat facing the wall so that his own eyes were invisible, and he did not react to his visitors.

More emptiness and openness greeted Cheng Xin. This was a semicircular hall, with the curved wall facing her. The surface was translucent, resembling ice. The floor and ceiling were pure white. Cheng Xin's first thought was that she stood in front of an empty, iris-less eye, exuding a desolate sense of loss.

[Deterrence Era, Year 62, November 28, 4:00 P. M. to 4:17 P. M.: Deterrence Center]

With a deep rumble, the meter-thick heavy steel door opened and Cheng Xin and the others walked into the heart of the dark forest deterrence system.

Then she saw Luo Ji.

It was said that Master Batuo, the founder of Shaolin Monastery, had meditated in front of a wall for ten years until his shadow was carved into the stone. If so, Luo Ji could have inscribed his own shadow into this wall five times.

The PDC chair stopped Cheng Xin and the fleet chief of staff. "Still ten minutes until the handover," he whispered.

At the beginning of the Deterrence Era, Luo Ji had enjoyed a brief period of happiness. He had been reunited with his wife, Zhuang Yan, and daughter, Xia Xia, and relived the joy of two centuries ago. But within two years, Zhuang Yan took the child and left Luo Ji. There were many stories told about her reasons. A popular version went like this: While Luo Ji remained a savior in the eyes of the public, his image had already transformed in the minds of those he loved the most. Gradually, Zhuang Yan had come to realize that she was living with a man who had already annihilated one world and held the fate of two more in his hand. He was a strange monster who terrified her, and so she left with their child. Another popular story said that Luo Ji left them, instead, so that they could live a normal life. No one knew where Zhuang Yan and their child had gone -- they were probably still alive, living tranquil, ordinary lives somewhere.

In the last ten minutes of his fifty-four-year career as the Swordholder, Luo Ji remained steadfast.

In this cosmic arena, Luo Ji faced not the fancy moves of Chinese sword fighting, resembling dance more than war; nor the flourishes of Western sword fighting, designed to show off the wielder's skill; but the fatal blows of Japanese kenjutsu. Real Japanese sword fights often ended after a very brief struggle lasting no more than half a second to two seconds. By the time the swords had clashed but once, one side had already fallen in a pool of blood. But before this moment, the opponents stared at each other like statues, sometimes for as long as ten minutes. During this contest, the swordsman's weapon wasn't held by the hands, but by his heart. The heart-sword, transformed through the eyes into the gaze, stabbed into the depths of the enemy's soul. The real winner was determined during this process: In the silence suspended between the two swordsmen, the blades of their spirits parried and stabbed as soundless claps of thunder. Before a single blow was struck, victory, defeat, life, and death had already been decided.

His family had left him at the time when gravitational wave transmitters took over the task of deterrence from the circumsolar ring of nuclear bombs. Thereafter, Luo Ji embarked on his long career as the Swordholder.

But it could also happen in the next second.

Luo Ji stared at the white wall with just such an intense glare, aimed at a world four light-years away. He knew that the sophons could show his gaze to the enemy, and his gaze was endowed with the chill of the underworld and the heaviness of the rocks above him, endowed with the determination to sacrifice everything. The gaze made the enemy's heart palpitate and forced them to give up any ill-considered impulse.

In this manner, Luo Ji and Trisolaris stared at each other for fifty-four years. Luo Ji had changed from a carefree, irresponsible man into a true Wallfacer, who faced his wall for more than half a century; the protector of Earth civilization who, for five decades, was ready to deal the fatal blow at a moment's notice.

Throughout this time, Luo Ji had remained silent, not uttering a single word. As a matter of fact, after a person ceased to speak for ten or fifteen years, he lost his powers of speech. He might still be able to understand language, but he would not be able to speak. Luo Ji certainly could no longer speak; everything he had to say, he put into his gaze against the wall. He had turned himself into a deterrence machine, a mine ready to explode on contact at each and every moment during the long years of the past half century, maintaining the precarious balance of terror between two worlds.

There was always an end to the gaze of the swordsmen, a final moment of truth in the contest. For Luo Ji, one participant in this universal contest, the moment when the sword was swung for the first and last time might never arrive.

"Mr. Luo, this is Cheng Xin, your successor. Please pass the switch to her."

"It is time to hand over the final authority for the gravitational wave universal broadcast system." The PDC chair broke the silence solemnly.

Luo Ji did not move from his pose. The fleet chief of staff walked over, intending to help him get up, but Luo lifted a hand to stop him. Cheng Xin noticed that the motion of his arm was strong, energetic, without a hint of the hesitation one might expect in a centenarian. Then, Luo Ji stood up by himself, his posture steady. Cheng Xin was surprised to see that Luo Ji did not push against the ground with his hands as he uncrossed his legs and stood up. Even most young men couldn't perform such a motion effortlessly.

Luo Ji stood tall and straight. He looked at the white wall, which he had stared at for more than half a century, for a few more seconds. Then he bowed slightly.

He was paying his respects to his enemy. To have stared at each other across an abyss of four light-years for half a century had bonded them by a link of destiny.

The switch retained the warmth from Luo Ji's hand. It really did resemble the hilt of a sword. It had four buttons, three on the side and one at the end. To prevent accidental activation, the buttons required some strength to press, and they had to be pressed in a certain order.

With both hands, Luo Ji handed over the switch. With both hands, Cheng Xin accepted this heaviest object in the history of the Earth. And so, the fulcrum upon which two worlds rested moved from a 101-year-old man to a 29-year-old woman.

Then he turned to face Cheng Xin. The old and new Swordholders stood apart, silently. Their eyes met for only a moment, but in that moment, Cheng Xin felt a sharp ray of light sweeping across the dark night of her soul. In that gaze, she felt as light and thin as a sheet of paper, even transparent. She could not imagine what kind of enlightenment the old man in front of her had achieved after fifty-four years of facing the wall. She imagined his thoughts precipitating, becoming as dense and heavy as the crust above them or as ethereal as the blue sky above that. She had no way to know, not until and unless she herself had walked the same path. Other than a bottomless profundity, she could not read his gaze.

Luo Ji backed up two steps and nodded at the three people in front of him. With steady, strong strides, he walked toward the door.

Cheng Xin noticed that, throughout the entire process, no one offered a word of thanks to Luo Ji for his fifty-four years of service. She didn't know if the PDC chair or the fleet chief of staff meant to say something, but she could not recall any of the rehearsals for the ceremony including plans for thanking the old Swordholder.

Humankind did not feel grateful to Luo Ji.

In the lobby, a few black-suited men stopped Luo Ji. One of them said, "Mr. Luo, on behalf of the Prosecution for the International Tribunal, we inform you that you have been accused of suspected mundicide. You are under arrest and will be investigated."

Luo Ji did not even spare them a glance as he continued to walk toward the elevator. The prosecutors stepped aside instinctively. Perhaps Luo Ji did not even notice them. The sharp light in his eyes had been extinguished, and in its place was a tranquility like the glow of a sunset. His three-century-long mission was finally over, and the heavy load of responsibility was off his shoulders. From now on, even if the feminized humankind saw him as a devil and a monster, they all had to admit that his victory was unsurpassed in the entire history of civilization.

The PDC chair and the fleet chief of staff left as well, saying nothing.

The steel door had remained open, and Cheng Xin heard the words spoken in the lobby. She felt an impulse to rush over and thank Luo Ji but stopped herself. Dejectedly, she watched him disappear into the elevator.

With a deep rumble, the steel door closed. Cheng Xin felt her previous life seep out of the narrowing crack in the door like water escaping from a funnel. When the door shut completely, a new Cheng Xin was born.

The white, semicircular hall was deathly silent, as though time was sealed in here and no longer flowed. It really did resemble a tomb. But this would be her entire world from now on. She decided that she had to give life to this place. She didn't want to be like Luo Ji. She wasn't a warrior, a duelist; she was a woman, and she needed to live here for a long time -- perhaps a decade, perhaps half a century. Indeed, she had been preparing for this mission her whole life. Now that she stood at the starting point of her long journey, she felt calm.

She looked at the red switch in her hand. It was already a part of her. She and it would be inseparable from now on. Even when she slept, she had to keep it by her pillow.

But fate had other ideas. Her career as the Swordholder, a career she had been preparing for since her birth, lasted only fifteen minutes from the moment she accepted the red switch.