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Theory of relativity is two theories of relativity by the German born physicist Albert Einstein.
Theory of relativity, or simply relativity, refers specifically to two theories: Albert Einstein's special relativity and General relativity.
The term "relativity" was coined by Max Planck in 1908 to emphasize how special relativity (and later, general relativity) uses the Principle of Relativity.
Special theory of relativity.
Special relativity is a theory of the structure of spacetime. It was introduced in Albert Einstein's 1905 paper "On the Electrodynamics of Moving Bodies". Special relativity is based on two postulates which are contradictory in classical mechanics:
The resultant theory has many surprising consequences. Some of these are:
The defining feature of special relativity is the replacement of the Galilean transformations of classical mechanics by the Lorentz transformations. (See Maxwell's equations of electromagnetism and introduction to special relativity).
General theory of relativity.
General relativity is a theory of gravitation developed by Einstein in the years 1907 - 1915.
The development of general relativity began with the Equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field are physically identical. The upshot of this is that free fall is inertial motion. This is incompatible with classical mechanics and special relativity because in those theories intertially moving objects cannot accelerate with respect to each other, but objects in free fall do so. To resolve this difficulty Einstein first proposed the spacetime is curved, and in 1915 devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and momentum within it.
Technically, general relativity is a Metric theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors which define the topology of the spacetime and how objects move intertially.
Some of the consequences of general relativity are:
References and links to the theory of relativity.
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