Special relativity

The special theory of relativity was proposed in 1905 by Albert Einstein in his article "On the Electrodynamics of Moving Bodies". Some three centuries earlier, Galileo's principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest; a person on the deck of a ship may be at rest in his opinion, but someone observing from the shore would say that he was moving. Einstein's theory generalized Galilean relativity from only mechanics to all laws of physics including electrodynamics. To stress this point, Einstein not only widened the postulate of relativity, but added the second postulate - that all observers will always measure the speed of light to be the same no matter what their state of uniform linear motion is.
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Noun
1. a physical theory of relativity based on the assumption that the speed of light in a vacuum is a constant and the assumption that the laws of physics are invariant in all inertial systems
(synonym) special theory of relativity, special relativity theory, Einstein's special theory of relativity
(hypernym) relativity, theory of relativity, relativity theory, Einstein's theory of relativity

A theory, developed by Albert Einstein and published in 1905, which describes the universe, as seen by observers in unaccelerated frames of reference . The theory states that everything is measured relative to something else and that the speed of light is always measured as having the same value, whatever the motion of the observer performing the measurement. The effects predicted by special relativity are time dilation , mass dilation and length contraction . Another consequence is the equivalence of mass and energy as described by the equation E=mc2. The accelerating frame of reference is dealt with by general relativity