Death's End

Cao Bin and Cheng Xin visit Lightspeed II, an abandoned ghost city that was a Black Domain Plan research facility that created a microscopic, stable black hole and injected it into Leda, a moon of Jupiter. However, the head scientist, Gao Way, was obsessed with the black hole; six years after research commenced, he breached safety barriers, floated too close to the black hole, and fell in. Though he is dead, the black hole’s low speed of light makes it seem as though he is still falling—Cheng Xin can see his outline.

Cheng Xin and Cao Bin arrive at Halo City, Wade’s research center, to find it blockaded by the Federation Fleet. After Wade revealed his plans to test light-speed ships, the Federation threatened to take over Halo City, so Wade declared independence, leading to the current standoff.

Bunker World’s government allows Cheng Xin to cross the blockade to speak with Wade. In Halo City, Wade demonstrates their findings, transporting a strand of Cheng Xin’s hair from one side of the room to another at the speed of light. When Cheng Xin insists that they cannot withstand the Federation, but Wade has a small army of soldiers equipped with rifles and anti-matter bullets that can obliterate entire cities; some of these troops are already embedded in other cities. Wade intends to threaten war in hopes that the Federation backs down. Horrified, Cheng Xin orders him to stand down. Wade, begrudgingly, keeps his promise to do so if she ever asked.

He is arrested, sentenced to death, and vaporized by a laser. Cheng Xin and AA return to hibernation.

Singer, an intelligent being from another planet, works in a “seed”—a formation of ships that discern and eliminate star systems that house other aliens. Singer believes in the principle of “Hide yourself well; cleanse well” (468) and sees survival as the highest value. Singer is skilled at finding “sincere coordinates”—star systems that are or could become real threats. As Singer’s seed sails through space, he notices sincere coordinates nearby and decides to cleanse the system—only to discover that another civilization has beaten him to it, since one of the three stars in the system has already been destroyed. Singer realizes that all of this happened so fast because the world—Trisolaris—was clearly dangerous: It was using “slow fog” as a defense, which means it was technologically advanced enough to want to hide. Singer also analyzes the destroyed world’s communications with a nearby still extant world—Earth—which is not hiding. A civilization that won’t hide itself could still become dangerous by expanding, so Singer decides to cleanse the civilization’s system. However, rather than using a photoid launched into the star wouldn’t destroy every piece of the system, Singer gets the Elder’s permission to use a “dual-vector foil” (an as-yet unfamiliar weapon to readers) instead. After launching the foil, Singer asks the Elder if war with “fringe world” has collapsed their home world into two dimensions. The Elder’s silence confirms this.

Cheng Xin and AA wake from hibernation to learn that a dark forest strike is coming. They look around but do not see panic. Instead they see despondence and sadness. When they ask Cao Bin why the city is not moving behind Jupiter in preparation for the photoid strike, he tells them the attack is not from a photoid, but from a slip of paper.

A year earlier, Bunker World detects a spaceship a lightyear away from the Sun. As the ship passes, it launches something at the Sun. The object does not appear to be a photoid and even slows down as it nears the Solar System. The ships Revelation and Alaska pursue the object, which appears to be a piece of paper. However, nothing can touch it—the object passes through anything solid. Revelation places itself over the object, which now hovers in the ship’s lab.

On Revelation, Bai Ice remembers the hopeless days of the Doomsday Battle. He has a nightmare in which he and his old professor drive into the desert, which begins to collapse inward. In the dream, Bai Ice and his professor cannot drive fast enough to escape the collapsing sand. He wakes and immediately advises that the ship move away from the paper-like object. Fifty hours later, the object disappears. An hour after that, a small ship they left behind and its two crew members collapse into two-dimensions, trapped in the gravity of a plane created by the object. As they fall into the plane, the two people flatten and die. Revelation tries to flee at full speed, but finds cannot move.

As Revelation falls into the two-dimensional plane, its crew sends out a message: The escape velocity to flee the gravity of the plane is the speed of light—this kind of attack is what Needle-Eye’s paintings from Yun Tianming’s stories represented. However, the decision not to pursue light-speed research has now doomed humanity. The entire Solar System will collapse into two dimensions, and no one will survive.

With news that no one can escape, Cheng Xin wishes to return to Earth and wait for certain death, but Cao Bin directs her and AA to take the ship Halo to the Earth Civilization Museum on Pluto, where they can join Luo Ji in preserving as many human artifacts as possible by throwing them out into space where they will be flattened in plain view for any future observers to see.

On Pluto, a gigantic, black monolith resembling a gravestone marks the site of the museum. Luo Ji is happy, finally unburdened from protecting humanity. Much of the museum is just information carved into stone—the best method to preserve information over long periods of time. Cheng Xin sees that this is less a museum and more a tomb meant to be a remembrance of humanity. She, AA, and Luo Ji collect paintings into the ship to be thrown into space.

AA and Cheng Xin fly into space to deposit the first batch of artifacts. Neptune and Saturn are already flattened. They watch recordings of Bunker World cities falling into the plane—humanity’s final hours—and then the Earth flattening. As Earth collapses into two dimensions, the planet’s water freezes into gigantic snowflakes. Cheng Xin finds its beauty striking.

Spaceships fly past Pluto, carrying desperate people despite the impossibility of escape. Soon the Sun enters the two-dimensional plane, releasing great light and a burst of energy. As the Sun dies, it becomes apparent that nothing will survive the collapse. As more planets fall into the plane, Cheng Xin and AA no longer see a point to their mission. However, Luo Ji forces them onto the ship to deposit more artifacts. After Cheng Xin and AA are in space, Luo Ji hails them from the ground on Pluto, tells them to flee, and reveals that Halo has the only curvature propulsion engine in the entire Solar System: Research into light-speed ships continued secretly after Wade’s death.

Cheng Xin and AA want to come back for Luo Ji, but he refuses and commands Halo’s AI to prepare to enter light-speed. Luo Ji explains that scientists discovered that light travels slower in the trail of a light-speed ship; launching many light-speed ships out of the Solar System could thus unintentionally create a black domain. Cheng Xin realizes that demanding Wade’s surrender led to humanity’s downfall. Luo Ji suggests they find Blue Space and Gravity, but Cheng Xin and AA instead decide to go to the star Yun Tianming gave Cheng Xin.

Only eight days pass for Cheng Xin and AA on their light-speed voyage but when they reach the star, 286 years since the collapse of the Solar System have passed—the result of special relativity.

In this new system, they find two planets, which they name Planet Blue and Planet Gray. The ship’s AI picks up an intelligent radio signal from the surface of Planet Blue with instructions to land. When they land, Cheng Xin is disappointed that Yun Tianming is not waiting for them. Instead, they find Guan Yifan, the scientist from Gravity, who is there to fill them in on what’s happened. Humans have colonized many different planets, though he refuses to tell them where. Planet Blue is unsettled because it is near shipping lanes and therefore dangerous.

Cheng Xin now has little hope of meeting Yun Tianming, so she and AA decide to leave with Guan Yifan the next day for one of the human planets. That night though, Guan Yifan’s satellites record five spacecraft landing on Planet Gray and almost immediately leaving again. He and Cheng Xin decide to explore. As they travel, Guan Yifan explains that the universe is much darker than humanity believed. Dark forest strikes are nothing compared to the massive interstellar wars that have destroyed not only civilizations but the universe, collapsing its dimensions from ten to two.

On Planet Gray, they find five black lines streaming from the surface into the sky. These are death lines: Inside each, the speed of light is zero. Guan Yifan warns that if the lines rupture, a black domain will spread across the planetary system. As they return to Planet Blue, AA hails them: Yun Tianming is there with another gift for Cheng Xin. Suddenly, the death lines rupture and a black domain spreads, trapping Cheng Xin and Guan Yifan in orbit. Guan Yifan manages to reboot the ship and keep it operational, but this will take days. In the meantime, Cheng Xin and Guan Yifan must hibernate because of the ship’s limited capabilities. Before they do, Guan Yifan tells Cheng Xin that he does not blame her for her failure as Swordholder—humanity chose her because they wanted to restore love. 

Cheng Xin and Guan Yifan wake 16 days later; however, when they descend to Planet Blue, it now looks unrecognizable. The ship calculates that 18,903,729 years have passed on the ground. Cheng Xin realizes that she missed Yun Tianming and that he and AA are now surely dead. She feels like a piece of dust in the universe. Nevertheless, she asks the ship to scan for anything written in stone and finds an incomplete message, worn and destroyed by time, which references Yun Tianming’s gift. After they read the message, the faint outline of a doorway appears before them. Cheng Xin and Guan Yifan decide to walk through it together, not wanting to risk being separated in time again.

Cheng Xin and Guan Yifan find themselves in an enclosed space of one square kilometer. There are fields surrounding a house. Sophon comes out of the house and explains that Yun Tianming has left Cheng Xin this place—a mini-universe of Trisolaran creation. In this mini-universe, they can wait for the main universe to collapse, restart, and reach its full potential, since time passes much quicker outside. Cheng Xin and Guan Yifan decide to stay in the mini-universe, planting crops and studying Trisolaran language and science.

As their studies deepen, they encounter a theory that only a precise amount of mass that allowed the Big Bang to occur. This would mean that the mini-universes created by Trisolarans and other civilizations, which necessarily have some of that original mass, will impact the impending Big Bounce—the universe collapsing and reforming. One day, they receive a broadcast in over a million languages from the Returners, who argue that the mini-universes must return their mass for the main universe to collapse. If they don’t, the universe will continue to expand until everything dies. Feeling responsible for the fate of the universe, Cheng Xin and Guan Yifan direct Sophon to look for a habitable planet so that they can return the mass of their mini-universe.

Cheng Xin reveals herself to be the author of A Past Outside of Time. Her sense of duty has guided her entire life. Now, as she prepares to return to the main universe, she asserts that every civilization must eventually merge with the universe as a whole.

Sophon finds a habitable planet and begins depositing all of the mass from the mini-universe onto it. Sophon and robots throw out soil, plants, equipment, and the house from of the mini-universe, eventually revealing a spaceship. As air is sucked out of the mini-universe, Guan Yifan, Cheng Xin, and Sophon prepare to depart in their spaceship, ready for whatever awaits them. Sophon promises to keep them safe.

In the mini-universe, they leave two things. The first is a miniature computer, containing the entire histories and memories of Earth and Trisolaris, meant to be thrown into the new universe to be found after the next Big Bang. The second is a small transparent sphere containing a small sun, algae, water, and tiny fish. In the dark, abandoned mini-universe, it is the only light.