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In theoretical physics, the issue of route dependence deals with whether a selected differential between two points is taken as absolute, or as being partly a function of the route along which comparative measurements are taken. It usually applies in discussions of gravitational potential or related effects such as gravitational redshift. * In simpler exercises in gravitational physics, it is common to invoke gravitational potential as an absolute difference between two positions that does not depend on the route, and to invoke energy conservation as a reason why the energy gained or lost when an object moves between two defined states is fixed, independent of the route taken. * In more advanced gravitational theory, things are not so straightforward: the nominal gravitational potential between two positions often has to be supplemented with route-dependent effects, or defined in a route-dependent manner. ==Spatial route dependence== If we place two observers (A and B) on opposite sides of a rotating black hole, both on the rotation plane, with the hole directly between them, and with both observers being the same height above the hole, then the effective gravitational differential between the A and B measured across the plane depends on the direction around the hole in which measurements are taken. If light signals are exchanged around one side of the hole, in the equatorial plane, where the adjacent section of event horizon is moving roughly in the direction A→B, then frame-dragging effects should make it easier for light to move with the horizon's motion than against it, and the measurements should show B to be ''downhill'' of A. If we repeat the exercise with light signals sent around the other side of the hole, the resulting anisotropy in the speed of light will now act in the opposite direction, and B will appear to be ''uphill'' of A. 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「Route dependence」の詳細全文を読む スポンサード リンク
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