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Einstein's constant or Einstein's gravitational constant, denoted κ (kappa), is the coupling constant appearing in the Einstein field equation which can be written: where ''Gαγ'' is the Einstein tensor and ''Tαγ'' is the stress–energy tensor. This equation relates to the curvature of space and time, telling that stress-energy is what causes the disturbance of spacetime, thus gravitation. Einstein used Newton's law of universal gravitation in his field equations, and the constant of κ is found to have a value of:〔 (see Chapter 10 "The Gravitational Field Equations or Nonempty Space", section 10.5 " Classical Limit of the Gravitational Equations" p. 345)〕 N.B.: Writing Einstein's constant depends on how the stress–energy tensor is defined, so the Einstein field equations are always invariant (see details in the section ''"About the two possible writings"'' further). == Calculation == In the following, the value of Einstein's constant will be calculated. To do so, at the beginning a field equation where the cosmological constant Λ is equal to zero is taken, with a steady state hypothesis. Then we use the Newtonian approximation with hypothesis of a weak field and low velocities with respect to the speed of light. The Newton law will arise and its corollary Poisson's equation. In this approximation, Poisson's equation appears as the approached form of the field equation (or the field equation appears as a generalization of Poisson's equation). The identification gives the expression of Einstein's constant related to quantities ''G'' and ''c''. 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「Einstein's constant」の詳細全文を読む スポンサード リンク
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