# What will happen if we use a speed greater than light speed and find a body'motion and energy relative to it?

In Einstein's papers, he used light speed as a reference speed. What if we use a greater finite speed and do the same calculations. Won't this greater speed then be the limit.

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OP's suggestion seems equivalent to giving the photon a (rest) mass, cf. physics.stackexchange.com/q/4700/2451 –  Qmechanic Dec 30 '11 at 14:28

The speed of light isn't the reference speed because Einstein picked it---which would imply that you could pick something else---but because the laws of physics seem to be invariant on Lorentz boosts with $c=\text{the speed of light in a vacuum}$.

When Einstein was doing the work the clearest experimental evidence came from the form of Maxwell's Equations and results of Michelson and Morley's interferometry experiments. These days we have other evidence, including direct evidence such as the behavior of very energetic particles in accelerators.

That is, the special place of the speed of light is an experimental fact.

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