Question

what is relativity theory??

Answer 1

The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity. 

Answer 2

In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.