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The many-body problem is a general name for a vast category of physical problems pertaining to the properties of microscopic systems made of a large number of interacting particles. ''Microscopic'' here implies that quantum mechanics has to be used to provide an accurate description of the system. A ''large number'' can be anywhere from 3 to infinity (in the case of a practically infinite, homogeneous or periodic system, such as a crystal), although three- and four-body systems can be treated by specific means (respectively the Faddeev and Faddeev-Yakubovsky equations) and are thus sometimes separately classified as few-body systems. In such a quantum system, the repeated ''interactions'' between particles create quantum correlations, or entanglement. As a consequence, the wave function of the system is a complicated object holding a large amount of information, which usually makes exact or analytical calculations impractical or even impossible. Thus, many-body theoretical physics most often relies on a set of approximations specific to the problem at hand, and ranks among the most computationally intensive fields of science. == Examples == * Condensed matter physics (solid-state physics, nanoscience, superconductivity) * Bose–Einstein condensation and Superfluids * Quantum chemistry (computational chemistry, molecular physics) * Atomic physics * Molecular physics * Nuclear physics (Nuclear structure, nuclear reactions, nuclear matter) * Quantum chromodynamics (Lattice QCD, hadron spectroscopy, QCD matter, quark–gluon plasma) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Many-body problem」の詳細全文を読む スポンサード リンク
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