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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Decoupling (cosmology) ： ウィキペディア英語版 Decoupling (cosmology) In cosmology, decoupling refers to a period in the development of the universe when different types of particles fall out of thermal equilibrium with each other. This occurs as a result of the expansion of the universe, as their interaction rates decrease (and mean free paths increase) up to this critical point. The two verified instances of decoupling since the Big Bang which are most often discussed are photon decoupling and neutrino decoupling, as these led to the cosmic microwave background and cosmic neutrino background, respectively. ==Photon decoupling== (詳細はepoch known as the recombination. During this time, electrons combined with protons to form hydrogen atoms, resulting in a sudden drop in free electron density. Decoupling occurred abruptly when the rate of Compton scattering of photons $\backslash Gamma$ was approximately equal to the rate of expansion of the universe $H$, or alternatively when the mean free path of the photons $\backslash lambda$ was approximately equal to the horizon size of the universe $H^$. After this photons were able to stream freely, producing the cosmic microwave background as we know it, and the universe became transparent. The interaction rate of the photons is given by :$\backslash Gamma\; =\; \backslash frac\; =\; n\_e\; \backslash sigma\_e\; c$ where $n\_e$ is the electron number density, $\backslash sigma\_e$ is the electron cross sectional area, and $c$ is the speed of light. In the matter-dominated era (when recombination takes place), :$H\; \backslash varpropto\; a^\{-\{3/2\}\}$ where $a$ is the cosmic scale factor. $\backslash Gamma$ also decreases as a more complicated function of $a$, at a faster rate than $H$. By working out the precise dependence of $H$ and $\backslash Gamma$ on the scale factor and equating $\backslash Gamma=H$, it is possible to show that photon decoupling occurred approximately 380,000 years after the Big Bang, at a redshift of $z\; =\; 1100$ when the universe was at a temperature around 3000 K. 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「Decoupling (cosmology)」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.