Iv just been reading a physics text book and i feel iv completely missed something. It may help to draw a diagram and to read the thread slowly. Sorry if it is a little thick. My understanding of Special Relativity is that it allows two seemingly conflicting principles to co-exist, these being the principle of relativity and the principle of invariant light speed. If one considers the hypothetical where there exists two points, point A and point B, an observer that is stationary relative to these points and an observer that moves from point A to point B at 0.5 C. If a ray of light is emitted from point A to point B then according to classical relativity the relative speed between that ray and the moving observer is 0.5 C. As this is relative speed is not permitted by the principle of invariant light speed. Special relativity states that Lorentz trasformations affect any moving body to ensure that the speed of light is perceived to be C relative to the observer themselves. Lorentz transformations affect the moving observer so that instead of observing 0.5 C as the light ray speed, it is perceived as C. Lorentz trasformations speed up the perceived speed of the light ray by slowing the rate of time relative the the stationary observer and contracting length. Now here is my problem. If one considers the same situation but adds in a light ray that moves in the opposing direction, that being from point B to point A, the relative speed between this ray and the moving observer is 1.5 C; to maintain that this light ray as C, Lorentz transformations would have to increase the rate of time and increase length of the moving observer, so the light ray is slowed. As these rays require different Lorentz transformations, one of these rays is not going to be perceived to be C; i can not see how it would be possible to apply two different Lorentz transformations. The outcome seems paradoxical. thank you for your help in advance.