Threebody

The three-body problem refers to the problem in celestial mechanics of predicting the motion of three bodies interacting through gravity. The general problem has no closed-form solution; the evolution depends strongly on initial conditions and exhibits chaotic behavior. Special cases include the restricted three-body problem, where one body's mass is negligible, leading to configurations such as the Lagrange points. The problem has played a central role in the development of dynamical systems theory and has applications in astrodynamics and the study of triple-star systems. Numerical methods and qualitative analysis remain essential tools in exploring possible trajectories.

The Three-Body Problem is a science fiction novel by Liu Cixin, originally published in Chinese as Sān Tǐ; the English-language edition translated by Ken Liu appeared in 2014. It is the first volume of the Remembrance of Earth's Past trilogy, followed by The Dark Forest and Death's End. The novel centers on contact between humanity and an alien civilization from Alpha Centauri and engages with physics, cosmology, and the societal impact of scientific discovery. It won the Hugo Award for Best Novel in 2015 and has influenced global interest in Chinese science fiction.

The two senses share an emphasis on complex gravitational and cosmic questions, though one is a mathematical problem and the other a fictional narrative. The term three-body thus spans both scientific theory and speculative fiction, illustrating how foundational physics can intersect with culture and storytelling.

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