# Death's End

Death's End (Chinese: 死神永生) is a science fiction novel by the Chinese writer Liu Cixin. It is the third novel in the trilogy titled Remembrance of Earth's Past, following the Hugo Award-winning novel The Three-Body Problem and its sequel, The Dark Forest. The original Chinese version was published in 2010. Ken Liu translated the English edition in 2016. It was a finalist for the 2017 Hugo Award for Best Novel and winner of the 2017 Locus Award for Best Science Fiction Novel.

## Plot

During the Fall of Constantinople in AD 1453, the passage of a "four-dimensional fragment" through the Solar System imbues a prostitute with temporary powers to retrieve objects from enclosed spaces by exploiting the fourth dimension.
In the 2010s, the early years of the Trisolar Crisis, young aerospace engineer Cheng Xin is recruited by the Planetary Intelligence Agency (PIA) under its coldly rational chief Thomas Wade. They initiate the "Staircase Project", which attempts to send a human spy at relativistic speed to the approaching Trisolaran invasion fleet. Taking inspiration from Project Orion, they decide to use a series nuclear explosions to push a large sail with the payload attached to high speeds. The speed requirement means they are unable to send a live human and are instead limited to a human brain, which they hope the technologically advanced Trisolarans will revive.
Meanwhile, Cheng's college classmate and secret admirer Yun Tianming is being treated for terminal cancer. Hu Wen, one of his classmates, visits him and gives him 3 million yuan as thanks for giving him an idea for a startup which has earned him great wealth. Yun uses the money to buy the star DX3906 for Cheng and decides to undergo euthanasia. However, at the last moment, Cheng arrives and persuades him to donate his brain for the Staircase Project. Unfortunately, during the acceleration of the probe, one of the ropes holding the sail to the brain breaks. The probe deviates from its path and is flung deep into space. Cheng then enters hibernation to await the Staircase Project's outcome.
By the 2200s, Earth and Trisolaris have entered a truce due to the dark forest deterrence. The deterrence is enforced by the "Swordholder": an individual who, should Trisolaris violate the truce, is authorized to send a cosmic broadcast containing Trisolaris' location, which would invite the mutual destruction of both Trisolaris and Earth by third parties. Cheng wakes from hibernation, and is elected to succeed the aging Luo Ji, the inaugural Swordholder who established the dark forest deterrence. However, immediately after the Swordholder succession, Trisolaris launches an attack on Earth's cosmic broadcast abilities, gambling correctly that Cheng will refuse to activate the deterrence.
With Earth-based deterrence systems neutralized, Trisolaris announces a renewed invasion effort, and it is revealed that they have developed light speed travel thanks to incredibly technological advancement from cultural exchange with Earth. Sophon, a robot representative of Trisolaris on Earth, begins the forced migration of all humans to Australia to prepare for the Trisolarans' arrival in four years.
However, one remaining functional broadcast system remains onboard the starship Gravity, which was initially sent to deep space to capture the fugitive ship Blue Space. Trisolaris' attempt to attack Gravity is thwarted by Blue Space's crew, who exploit the fourth dimension to do so. Believing Earth to be lost, the two ships' combined crew activate Gravity's broadcast system as revenge against Trisolaris' treachery, resulting in Trisolaris' destruction by a third party. Understanding that Earth is also at risk of imminent destruction due to its relative proximity to Trisolaris, the surviving Trisolaran fleets abandon their invasion attempt.
Having intercepted Yun's brain and revived him, the Trisolarans permit Cheng to converse with him. He sends a coded message containing survival advice for humanity. Three survival tactics are decoded:
* the "Bunker Project": building of space cities in the gas giants' shadows to survive the Sun's destruction
* the development of lightspeed travel (which is later banned, as its use may attract unwanted alien attention)
* the development of a "black domain", a region of space with decreased lightspeed that can act as a shield.
During the next few decades, as Cheng hibernates, humanity builds several space cities according to the Bunker Project, but progress on the Black Domain Plan is stalled. Cheng is awoken as Wade has successfully but illegally developed the backbone technology for lightspeed travel, and requests Cheng's permission to proceed, which she denies. Wade is executed for his transgressions as Cheng re-enters hibernation.
Several decades later, an unknown hostile alien race launches the anticipated dark-forest attack, which progressively collapses the three-dimensional Solar System into two dimensions. As the escape velocity from the dimensional attack is lightspeed, the vast majority of humanity is killed.
Cheng and her aide AA are awoken amidst the attack. They visit Luo Ji on Pluto, who informs them their spaceship contains the only surviving lightspeed engine from Wade's experiments. Cheng and AA escape the attack, joining the crews of Gravity and Blue Space as the only humans remaining in the universe.
286 years later, Cheng and AA arrive at the distant star DX3906's "Planet Blue", though the voyage passes quickly for them due to time dilation from lightspeed travel. There they encounter Guan Yifan, a civilian cosmologist on Gravity, who explains that the two ships' crew have founded several interstellar societies.
Leaving AA on Planet Blue, Cheng and Guan fly to the nearby "Planet Gray", where they discover several unstable seed elements of a black domain. As they attempt to escape back to Planet Blue, the black domain grows to encompass the entire DX3906 system. The significantly decreased lightspeed within the black domain cause Cheng and Guan to experience severe time dilation; almost 19 million years have passed on Planet Blue's reference frame by the time Cheng and Guan manage to decelerate and return.
In their absence, Yun had visited Planet Blue to deliver "Universe 647": a Trisolaran-constructed self-contained micro-universe that exists outside of the conventional timeline. Cheng and Guan live in Universe 647's pastorally decorated interior, hoping to outlast the main universe and observe its rebirth in a Big Bounce. After a period of idyllic living, they receive a message from the main universe, stating that the presence of micro-universes deprives the main universe of mass, disrupting its cycle of expansion, collapse and rebirth. Cheng, feeling a moral responsibility to the universe, orders Universe 647's re-integration with the main universe.

## Key characters
### Cheng Xin (程心)

    Aerospace engineer from the early 21st century, the proposer of the Staircase Project, the second Swordholder, and the owner of the DX3906 star system

### Yun Tianming (云天明)

    Cheng Xin's university classmate who is romantically interested in her. His brain is sent into space and captured by the Trisolaran fleet, who clones his body and returns him to life

### Thomas Wade (托马斯·维德)

    The cold-hearted and ruthlessly rational PIA Chief who later leads an effort to create lightspeed propulsion

### Ai AA (艾AA)

    Astronomer from the Deterrence Era; Cheng Xin's aide, friend and travelling companion

### Luo Ji (罗辑)

    Cosmic sociologist, former Wallfacer, and the first Swordholder, returning from The Dark Forest

### Guan Yifan (关一帆)

    Civilian astronomer aboard the spaceship Gravity

## Awards

| Awards | |
| 2017 Hugo Award for Best Novel | Finalist |
| 2017 Locus Award for Best Science Fiction Novel | Won |
| 2017 Dragon Awards for Best Science Fiction Novel | Nominated |