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  • Print publication year: 2013
  • Online publication date: May 2018

12 - The Special Theory of Relativity



In the centuries following publication of the Principia, Newtonian dynamics was accepted whole-heartedly not only because of its enormous success in explaining planetary motion but also in accounting for all motions commonly encountered on the Earth. Physicists and mathematicians (often the same people) created elegant reformulations of Newtonian physics and introduced more powerful analytical and calculational techniques, but the foundations of Newtonian physics were assumed to be unassailable. Then, on June 30 1905, Albert Einstein presented his special theory of relativity in his publication The Electrodynamics of Moving Bodies. The English translation, available on the web, is reprinted from Relativity: The Special and General Theory, Albert Einstein, Methuen, London (1920). The original publication is Zur Elektrodynamik bewegter Körper, Annalen der Physik 17 (1905). Einstein's paper transformed our fundamental view of space, time, and measurement.

The reason that Newtonian dynamics went unchallenged for over two centuries is that although we now realize that it is only an approximation to the laws of motion, the approximation is superb for motion with speed much less than the speed of light, c ≈ 3 × 108 m/s. Relativistic modifications to observations of a body moving with speed v typically involve a factor of v2/c2 . Most familiar phenomena involve speeds vc. Even for the high speed of an Earth-orbiting satellite, v2/c2 ≈ 10−10. There is one obvious exception to this generalization about speed: light itself.