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One of the most important developments of twentieth-century physics was the formulation of the special theory of relativity. This theory was an outgrowth of the failure of all attempts to show that the motion of the source of light relative to the observer had any effect on the speed of light. It is impossible to account for these experimental findings of Michelson and Morley, and others, on the basis of classical mechanics and electromagnetic theory. In 1905, Albert Einstein put forth the suggestion that all experimental findings would be clarified if it were assumed that the speed of light is a constant and is independent of the relative motion of the source and the observer. This statement forms the first postulate of the special, or restricted, theory of relativity. The second postulate of the theory is that all systems which are in uniform motion relative to one another are equally valid frames of reference, and all fundamental physical laws must have the same mathematical forms in each of these reference frames. Einstein expressed the viewpoint that all motion was relative motion, that there was no absolute coordinate frame, and that it was impossible to distinguish between a state of rest and a state of uniform translational motion by any physical experiment whatever. Thus, if the statement that the velocity of light was 3 X 1010 cm/sec was a fundamental physical law, every observer in uniform translational motion who measures the velocity of light must obtain this value, regardless of the motion of the source of light.