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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 Newtonian gauge ： ウィキペディア英語版 Newtonian gauge :''For context, see also scalar-vector-tensor decomposition and cosmological perturbation theory.'' In general relativity, Newtonian gauge is a perturbed form of the Friedmann–Lemaître–Robertson–Walker line element. The gauge freedom of general relativity is used to eliminate two scalar degrees of freedom of the metric, so that it can be written as :$ds^2\; =-(1+2\backslash Psi)dt^2+a^2(t)(1-2\backslash Phi)\backslash delta\_dx^adx^b,$ where the Latin indices ''a'' and ''b'' are summed over the ''spatial'' directions and $\backslash delta\_$ is the Kronecker delta. Conformal Newtonian gauge is the closely related gauge in which :$ds^2\; =a^2(t)()$ which is related by the simple transformation $dt=a(t)d\backslash tau$. These metrics are perturbed forms of the Friedmann–Lemaître–Robertson–Walker metric. They are called Newtonian gauge because $\backslash Psi$ is the Newtonian gravitational potential of classical Newtonian gravity, which satisfies the Poisson equation $\backslash nabla^2\backslash Psi=4\backslash pi\; G\backslash rho$ for non-relativistic matter and on scales where the expansion of the universe may be neglected. It includes only scalar perturbations of the metric: by the scalar-vector-tensor decomposition these evolve independently of the vector and tensor perturbations and are the predominant ones affecting the growth of structure in the universe in cosmological perturbation theory. The vector perturbations vanish in cosmic inflation and the tensor perturbations are gravitational waves, which have a negligible effect on physics except for the so-called B-modes of the cosmic microwave background polarization. The tensor perturbation is truly gauge independent, since it is the same in all gauges. In a universe without anisotropic stress (that is, where the stress–energy tensor is invariant under spatial rotations, or the three principal pressures are identical) the Einstein equation sets $\backslash Phi=\backslash Psi$. ==References== * * 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「Newtonian gauge」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.