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Section 52.4 Postulates of Special Relativity

Special relativity refers to relativity of frames that are in uniform relative motion with respect to each other. It was dicovered by Albert Einstein when he introduced an empirical procedure for measuring time on assumption that light traveled at the same speed in all frames. The assumptions made by Einstein are called postulated of special relativity.

The Postulates of Special Relativity

The two postulates of Special Relativity are the Principle of Relativity and the Principle of the Constancy of Speed of Light. We will quote them from Einstein's paper, “On the Electrodynamics of Moving Bodies,” published in Annalen de Physik, vol. 17, p 891, 1905.

  1. Principle of Relativity. The laws by which the states of physical systems change are not affected, whether these change of state be referred to the one or the other of the two systems of coordinates in uniform translatory motion.
  2. Principle of the Constancy of Speed of Light. Any ray of light moves in the “stationary” system of coordinates with the determined velocity \(c\text{,}\) whether the ray be emitted by a stationary or by a moving body.