# A question based on the paper 'ON THE ELECTRODYNAMICS OF MOVING BODIES' [duplicate]

Light is emitting from a source. Velocity of photon is always constant 'C' w.r.t stationary system. Say the source is moving at velocity 'V'. Then what is the velocity of photon at the instant of time before starting the emission?

Actually my problem is about "An analogous consideration—applied to the axes of Y and Z—it being borne in mind that light is always propagated along these axes, when viewed from the stationary system, with the velocity $\sqrt{c^2-v^2}$gives us" this line

• There is no photon "before emission". Having said that, the notion that the velocity of light is a constant is an observed physical fact that clashed with the Galilean invariance of classical mechanics. The only question that needed to be answered was how one could modify the transformation laws to reflect the facts. This had to be done to make Maxwell's equations invariant under the new coordinate system changes and to have a new version of classical mechanics that was consistent with the laws of electromagnetism. – CuriousOne Dec 29 '14 at 18:56
• actually my problem is about 'An analogous consideration—applied to the axes of Y and Z—it being borne in mind that light is always propagated along these axes, when viewed from the stationary system, with the velocity $\sqrt{c^2-v^2}$gives us' this line @CuriousOne – Saprativ Saha Dec 29 '14 at 18:58
• I see, if you go back to his definition of "stationary system", it's the one for which he assumes that Newtonian physics holds, and in that system he will calculate the naive (and wrong) Newtonian velocity for light. I looked at the German version of the paper and the translation is about as correct as one can make it, there is nothing lost in translation. His "ruhender Raum" or "ruhendes System" is the one where all calculations are done based on Galilean rules, in which case I believe the factor to be correct. – CuriousOne Dec 29 '14 at 19:20