Although math is not its main focus, there is enough mathematics lurking in the background to justify its inclusion in this database. Perhaps it is good, therefore, that the translation for the 2014 English edition was done by Ken Liu, himself an award winning author who has works listed in this database.

As the title implies, one major mathematical theme is the 3-body problem, which is a classical dynamical system considering the motion of three massive objects interacting under the influence of gravity. This mathematical problem has a notable history in that when Henri Poincaré worked on it he discovered the idea of sensitive dependence on initial conditions, one of the hallmarks of a chaotic dynamical system. In particular, it was because of this property, which means that even very close initial conditions have very different orbits, that he concluded we would not be able to accurately predict the future behavior of such a system.

One minor character in this novel is a (brilliant but very lazy) mathematician who develops an evolutionary algorithm which can be used to accurately predict 3-body problem dynamics. Considering the sensitive dependence, I find this a bit hard to believe, but as science fiction goes I suppose it is not beyond the realm of possibility. The novel not only explains quite a bit about the mathematical problem and this fictional solution, but also informs the reader about some of the real research results in this are, such as the stable periodic solutions found by Richard Montgomery and Alain Chenciner.

Prediction algorithms for the 3-body problem become important to the plot because of the existence of an unusual video game which, in the novel, is becoming popular with a small but elite group of individuals. in this game, which is rendered in stunningly accurate virtual reality, one is placed at some point in Earth's history, but on a planet which has three suns. Because of the chaotic dynamics of the 3-body problem, these suns do not rise and set with any regularity. And, because of the sensitive dependence on initial conditions, it is not possible to accurately predict when they will. And, the unpredictability is not the most serious problem with trying to live in this chaotic tri-solar system, because when two or more of the suns appear in the sky simultaneously the planet surface becomes unlivable and creatures can only survive if they "dehydrate" themselves.

Players of the game can talk to each other and also to simulations that exist within the virtual reality. These virtual people are historical figures from history, including mathematicians such as Isaac Newton and John von Neumann. In this sense, this novel reminded me of Quaternia, another book I read recently in which players of a video game encounter virtual reproductions of historical mathematicians.

And, there is also a computer in the game itself. Like in Souls in the Great Machine, the components of this computer are living beings rather than electronic circuits. An excerpt of the novel concerning this computer comprised of humans and its attempt to compute the digits of π was published separately as a short story entitled The Circle in the anthology Invisible Planets: Contemporary Chinese Science Fiction in Translation. (Note that a reader of the excerpt might be confused of the anachronism of characters in 227 B.C. talking about decimal representations and irrational numbers at all, but in the novel it is clear that this is all just happening within a modern computer game.)

Two other mathematical references in the novel include a mathematical model of the dynamics of the sun which allow a character to use the sun to amplify an electromagnetic signal and lots of (mostly meaningless?) discussion of the concept of "dimension" involving the manipulation of the dimensionality of an elementary particle to produce anything from a point-like black hole to a giant two-dimensional surface or even an object with dimensionality greater than four.