In classical physics, it was assumed that all observers anywhere in universe would obtain identical measurements of space and time intervals. But, according to relativity theory, this is not so; all measurements depend upon the relative motions of the observer and the object observed.
There are two theories based on relativity, both proposed by ALBERT EINSTEIN. They are:
- Special Theory of Relativity (1905)
- General Theory of Relativity (1916)
It is a physical theory of relativity based on the assumption that the speed of light in a vacuum is a constant in all reference frames, irrespective of their relative motion.
Einstein expanded the special theory of relativity into a general theory which was developed to deal with gravitation and involves accelerating reference frames.
Both these theories are major milestone in history of modern physics.
