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special relativity
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relativity of simultaneity
Understand Albert Einstein's theory of relativity, about what is absolute and not relative
Know about the common misconceptions in physics like how gravity affects light, the shape of the earth, and measuring velocity in special relativity
Understand the concept of Albert Einstein's special theory of relativity
Understand the proof of Albert Einstein's special relativity equation
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special relativity

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Also known as: special theory
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special relativity, part of the wide-ranging physical theory of relativity formed by the German-born physicist Albert Einstein. It was conceived by Einstein in 1905. Along with quantum mechanics, relativity is central to modern physics.

relativity of simultaneity
relativity of simultaneityBrian Greene derives the time discrepancy between two people who are moving relative to one another but who disagree on what happens at the same time. This video is an episode in his Daily Equation series.
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Special relativity is limited to objects that are moving with respect to inertial frames of reference—i.e., in a state of uniform motion with respect to one another such that one cannot, by purely mechanical experiments, distinguish one from the other. Beginning with the behaviour of light (and all other electromagnetic radiation), the theory of special relativity draws conclusions that are contrary to everyday experience but fully confirmed by experiments that examine subatomic particles at high speeds or measure small changes between clocks traveling at different speeds. Special relativity revealed that the speed of light is a limit that can be approached but not reached by any material object. It is the origin of the most famous equation in science, E = mc2, which expresses the fact that mass and energy are the same physical entity and can be changed into each other. (For a more-detailed treatment of special relativity, see relativity: Special relativity.)

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Barbara A. Schreiber.