Question

what is the theory of relativity

Answer 1

Albert Einstein, in his theory of specialrelativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels.

Answer 2

Hello Friend,
Theory is based on two postulates:-
1)the speed of light is constant for all observers.
2)observers moving at constant speed should be subject to the same physical laws.
hope it helps