Abstract

It has been claimed since at least 1910 that the Lorentz Transformation and Einstein's Theory of Relativity are derivable without using the constancy of the velocity of light as a postulate. The proof makes three (in some versions, more) very basic and natural assumptions, and derives the Lorentz transformation with a constant velocity of light as the only possible transformation between moving inertial frames that satisfies experimental observations. It is shown that the proof is flawed by illegitimately interpreting a constant that has the dimensions of a velocity as the velocity of light, and by claiming that this is the only choice confirmed by experiment.