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This article proves that speed of light in all uniformly moving inertial reference frames is absolute as postulated by Einstein. This is first done by considering light propagating with a speed c in all directions in an inertial frame of reference. If that frame is moving uniformly with a speed v relative to a second stationary inertial frame, we assume that light in the second frame is propagating in all directions with a different speed cp=pc. Consequently, modified transformation Equations are formed. The established Poincaré ellipsoidal light waves are then used to find the Equation that governs the relation of p at any speed v. The analytical solution and numerical calculations to this equation yield a value p =1. This proves that speed of light propagates through empty space with speed c independent of the speed of the light source or the observer.

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