Death's End

Eras

The story line is divided into seven eras:

• Common Era: The period before humans learned of the existence of Trisolaran civilization. The book starts during the Fall of Constantinople with the story of a prostitute seemingly able to retrieve objects and even human organs without penetrating their enclosures. Offering her services to Constantine XI, she is thus tasked with killing Mehmed II, but mysteriously loses her powers the day before Constantinople falls.
• The Crisis Era (present era – 2208 AD) is the time period after Trisolaris and the Trisolarans become widely known and Sophons begin to block all scientific progress. The story of this era starts with Yang Dong, the daughter of Ye Wenjie, having uncovered her mother's conspiracy with Trisolaris and losing hope in life; she has a conversation with a colleague that suggests to her that just as civilization is shaped by nature and the environment, so too can civilization change the structure of the Universe. The plot then moves to Yun Tianming, who suffers from terminal cancer. Receiving an unexpected sum of money, Yun Tianming secretly buys a star, DX3906, for scientist Cheng Xin, whom he has loved since college. Cheng Xin is working on a project called the Staircase Program, using nuclear pulse propulsion to send a spacecraft containing a human to the Trisolaran Fleet to potentially gather information. After being forced to lower the maximum weight multiple times, they realize that they will only be able to send a brain, and will not be able to preserve it - the host will have to be dead. They must hope that a Trisolaran ship intercepting the brain will be able to restore the brain to life. The government sends out applications to be the host of the brain. Yun Tianming, about to be euthanized, is told about the program and terminates the euthanasia. He eventually becomes the final choice, and, on death, his brain is sent on an intercepting course towards the Trisolaran fleet, but a mistake in bomb detonation sends Yun's brain off in an unknown direction, potentially lost forever. Cheng Xin's superior, Thomas Wade, reveals that Yun Tianming was the one who gave her DX3906, causing her to feel overwhelming guilt over her role in getting him accepted to the Staircase Program. Cheng Xin enters hibernation to be the Staircase Program's liaison to people of the future.
• The Deterrence Era describes the age after Luo Ji deters the Trisolarans with the threat of mutually assured destruction by threatening to broadcast the location of their home world, which would indirectly expose the Solar System's location as well. Luo Ji becomes the first Swordholder, the individual endowed with the sole responsibility for initiating broadcast. Earth Federation recalls the two human ships that survived the Doomsday Battle, Bronze Age and Blue Space. Upon their return, the crew of Bronze Age is charged with crimes against humanity for destroying other ships in the fleet, but the captain manages to warn Blue Space not to return to Earth. Earth Federation and Trisolaris together send the ship Gravity to pursue Blue Space. Two Droplets are also sent as assurance to Trisolaris because Gravity has the ability to broadcast the location of Trisolaris. Earth and Trisolaris mysteriously lose contact with Gravity as the pursuit reaches the Oort cloud; the crew of Gravity begin seeing patches of space disappear or see the crew of Blue Space on their own ship, which they rationalize as hallucinations. Cheng Xin awakens from hibernation and meets Ai AA, an astronomer who has discovered valuable planets around DX3906. They sell the planets to Earth but retain ownership of the star; with the money from this transaction, Cheng Xin starts the Halo company, managed by AA. They meet Sophon, a Trisolaran android whose body is directly controlled by Trisolaran sophons, who provides a diplomatic and communicative link between Earth and Trisolaris. Cheng Xin is elected the next Swordholder, as humanity find her unintimidating image reassuring, beating out her old project supervisor Wade, who has also been brought to the future through hibernation. Wade loses an arm in a failed assassination attempt against Cheng Xin soon after. The Trisolarans, having correctly predicted Cheng Xin's unwillingness to broadcast their location and thus doom both civilizations, begin an invasion immediately after the Swordholder title is transferred from Luo Ji to Cheng Xin, destroying all broadcasting stations in the Solar System. Simultaneously, the Droplets attack Gravity and Blue Space.
• The Post-Deterrence Era describes the age when Trisolarans prepare Earth for Trisolaran settlement. Within a year, nearly all of humanity is forced to Australia under the threat of Droplet attacks, where the Trisolarans plan to reduce their numbers drastically through starvation. Cheng Xin and Ai AA live under the protection of Fraisse, an Australian aboriginal leader, and Sophon, who still respects them, and thus do not suffer the material shortages of other human refugees. Meanwhile, the Droplets suddenly become incapacitated and miss Blue Space and Gravity, careening harmlessly into space. Blue Space crew members explain that they have found patches of 4-dimensional space that 3-dimensional beings can enter, through which they manipulated the Droplets, by breaking the strong-interaction forces that held them together. They find a large patch of 4-dimensional space and are able to communicate with an AI aboard an abandoned 4-dimensional ship in this space. The ship states that it was left as a "tomb" by a now-extinct fourth-dimensional race, and suggests that this "puddle" of 4-D space is drying up due to the actions of other civilizations. The patch of 4-dimensional space eventually shrinks and decays to normal 3-D space, destroying the alien ship. The two human ships congregate and vote to broadcast the location of Trisolaris in retaliation for the attack on Earth, knowing the Solar System will likely be located and destroyed as well.
• The Broadcast Era begins after humanity broadcasts the location of Trisolaris from the Oort cloud. One of the three suns of Trisolaris is destroyed by a photoid, a small piece of matter moving so close to lightspeed that it causes the star to go supernova on impact. The planet Trisolaris is completely incinerated as a result, and Trisolarans cease their planned colonization of Earth on the assumption that Earth will soon be destroyed as well. Humans, including Cheng Xin, return to the other continents. Before leaving Earth, Sophon tells Cheng Xin that she can speak to Yun Tianming, who has indeed been located by the Trisolarans and cloned. Their conversation is meant to be personal and is closely monitored for intelligence that Trisolarans do not want divulged; however, Yun Tianming tells Cheng Xin three interconnected fairy tales. She and Yun promise to meet at DX3906 one day. Cheng Xin understands that the fairy tales are coded messages, and humanity is able to decode most of the content. Yun's clues lead scientists to conceive of "curvature propulsion," which could in theory allow lightspeed travel, as well as the concept of a "black domain," a region of spacetime in which the speed of light is lowered artificially to completely seal it off (and protect it) from the rest of the Universe. In anticipation of a similar photoid attack on Earth, humans choose between building space cities shielded by the outer planets, permanently isolating the Solar System in a black domain with reduced light speed, and developing lightspeed ships using curvature propulsion to escape. The "bunker project" is chosen as the most feasible, since the black domain project is too far beyond humanity's scientific ability, and research into lightspeed ships is strictly banned to discourage escapism. During a test of these space cities, Cheng Xin meets Wade again. He demands that she turn over her company's vast resources to him, stating that only he has the ruthlessness needed to research illegal lightspeed propulsion technology. Cheng Xin reluctantly agrees and enters hibernation after turning ownership of her company to Wade, but makes Wade promise to reawaken her if his research threatens human lives in any way.
• In the Bunker Era, most humans living on Earth move to space cities in the shadow of Jupiter and other gas giants, having chosen to use them as shields. Research on lightspeed ships remains illegal, but Wade has been making progress by conducting research on his own independent space station. Cheng Xin is woken as Wade has threatened armed resistance with antimatter bullets should the government prevent them from researching lightspeed travel. Cheng Xin reminds Wade of his promise and demands that he disarm and surrender; he honors their agreement and does so. He is found guilty of illegal research and executed as a result. Cheng Xin reenters hibernation and is woken upon a dark forest attack warning. However, instead of the expected photoid strike, the attack takes the form of a paper-like projectile that begins to collapse space into two dimensions. Since the escape velocity is the speed of light, no human ships can escape, and the entire Solar System faces destruction in a matter of days. Cheng Xin and Ai AA are given a mission to fling selected human artifacts into space so as to safely preserve them in two dimensions, in hopes that later civilizations will be able to reconstruct or at least appreciate the artifacts. As the Solar System is inexorably collapsed into two dimensions, they take a ship provided by Wade's company to Pluto, where Luo Ji, who is now over 200 years old, maintains a museum of priceless human artifacts. Luo Ji reveals that the ship is in fact the only human ship capable of lightspeed travel, built in secret with his assistance. Cheng Xin and Ai AA depart at lightspeed towards DX3906; Luo Ji chooses to remain behind, and is destroyed along with the rest of the Solar System and every human living there.
• The Galaxy Era focuses on Cheng Xin and Ai AA, the only survivors of the dark forest strike, and civilization founded by the surviving crews of Blue Space and Gravity and their descendants, referred to as "Galactic Humans". Cheng Xin and Ai AA travel to Planet Blue, which orbits star DX3906, and meet Guan Yifan, a crew member from Gravity who has been kept in hibernation for over 400 years. He reveals that dimensional attacks like the one that destroyed the Solar System are being used throughout the Universe, progressively reducing the number of dimensions and damaging the fabric of spacetime. Even more advanced civilizations are waging war by changing the laws of physics themselves, threatening the long-term existence of the Universe. Cheng Xin and Guan Yifan leave for an expedition aboard the latter's ship to investigate alien activity detected nearby when they receive a call from Ai AA that Yun Tianming has arrived at Planet Blue. However, when attempting to return, Cheng Xin and Guan Yifan's ship is caught in a black domain, accidentally formed by the curvature drives of the nearby alien ships. They are forced to orbit Planet Blue at light speed for 16 days before they can repair their ship and slow down to normal speed. By this time, due to time dilation, over 18 million years have passed on Planet Blue, and Ai AA and Yun Tianming are long dead. Cheng Xin and Guan Yifan discover they have carved a message into the bedrock itself: instructions to enter into a miniature universe, constructed by surviving offshoots of Trisolaran civilization, and wait for the big crunch and subsequent big bang so the corrupted laws of physics can finally be reset. They enter the pocket universe, discovering an idyllic small farm administered by Sophon. Their plans to wait out the destruction of the universe are interrupted by a message sent by an unknown civilization to all pocket universes at great expense: the innumerable pocket dimensions created by various civilizations have reduced the mass of the Universe too much, preventing a big crunch. If the mass is not returned to the main Universe, a big rip will occur instead, the Universe will never reset, and there will be no life possible anywhere in the cosmos. To save the main Universe from this fate, Cheng Xin and Guan Yifan return all the mass in the pocket universe to the main universe, and leave the pocket universe in a spaceship to explore. They leave behind only a small self-contained habitat for some small fish, and a computer drive with the contained knowledge of Trisolaris and humanity, to serve as a "message in a bottle" to any far-future explorers after the Universe has finally been reborn.