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In general relativity the light is assumed to propagate in the vacuum along null geodesic in a pseudo-Riemannian manifold. Besides the geodesics principle in a classical field theory there exists the Fermat's principle for stationary gravity fields. Belayev has proposed variational method without the violation of isotropy of the path of the lightlike particle, giving equations identical to those that follow from Fermat's principle. In this method the action principle leads to condition of zero variational derivative of the integral of energy, and it is applied also to non-stationary gravity fields. == Fermat's principle == In more general case for conformally stationary spacetime with coordinates a Fermat metric takes form , where conformal factor depending on time and space coordinates does not affect the lightlike geodesics apart from their parametrization. Fermat's principle for a pseudo-Riemannian manifold states that the light ray path between points and corresponds to zero variation of action , where is any parameter ranging over an interval and varying along curve with fixed endpoints and . 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「Fermat’s and energy variation principles in field theory」の詳細全文を読む スポンサード リンク
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