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In physics, the exchange interaction (with an exchange energy, and exchange term) is a quantum mechanical effect that only occurs between identical particles. Despite sometimes being called an exchange force in analogy to classical force, it is not a true force, as it lacks a force carrier. The effect is due to the wave function of indistinguishable particles being subject to exchange symmetry, that is, either remaining unchanged (symmetric) or changing its sign (antisymmetric) when two particles are exchanged. Both bosons and fermions can experience the exchange interaction. For fermions, it is sometimes called Pauli repulsion and related to the Pauli exclusion principle. For bosons, the exchange interaction takes the form of an effective attraction that causes identical particles to be found closer together, as in Bose–Einstein condensation. The exchange interaction alters the expectation value of the distance when the wave functions of two or more indistinguishable particles overlap. It increases (for fermions) or decreases (for bosons) the expectation value of the distance between identical particles (as compared to distinguishable particles).〔David J. Griffiths: ''Introduction to Quantum Mechanics'', Second Edition, pp. 207–210〕 Among other consequences, the exchange interaction is responsible for ferromagnetism and for the volume of matter. It has no classical analogue. Exchange interaction effects were discovered independently by physicists Werner Heisenberg〔''Mehrkörperproblem und Resonanz in der Quantenmechanik'', W. Heisenberg, ''Zeitschrift für Physik'' 38, #6–7 (June 1926), pp. 411–426. DOI (10.1007/BF01397160 ).〕 and Paul Dirac〔(''On the Theory of Quantum Mechanics'' ), P. A. M. Dirac, ''Proceedings of the Royal Society of London, Series A'' 112, #762 (October 1, 1926), pp. 661—677.〕 in 1926. =="Force" description== The exchange interaction is sometimes called the ''exchange force''. However, it is not a true force and should not be confused with the exchange forces produced by the exchange of force carriers, such as the electromagnetic force produced between two electrons by the exchange of a photon, or the strong force between two quarks produced by the exchange of a gluon.〔(''Exchange Forces'' ), HyperPhysics, Georgia State University, accessed June 2, 2007.〕 Although sometimes erroneously described as a force, the exchange interaction is a purely quantum mechanical ''effect'' unlike other forces. 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「Exchange interaction」の詳細全文を読む スポンサード リンク
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