

Albert Einstein
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Relativity  The Special and General Theory



General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics. General relativity generalises special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the fourmomentum (massenergy and linear momentum) of whatever matter and radiation are present.




Sidelights on Relativity


How does it come about that alongside of the idea of ponderable
matter, which is derived by abstraction from everyday
life, the physicists set the idea of the existence of another kind of
matter, the ether? The explanation is probably to be sought in those phenomena which have given rise to the theory of action at a
distance, and in the properties of light which have led to the undulatory
theory. Let us devote a little while to the consideration of these two
subjects.





