Question

What is theory of relatively

Answer 1

Special relativity is a theory of the structure of spacetime. ... The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity). The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the light source.

Answer 2

The Theory of relativity is a theory published by Sir Albert Einstein in 1905 and 1915.Actually it is two theories that solve biggest blunder of the entire universe. One is the Special theory of relativity (1905)and other is General theory of relativity (1915) is the second pillar of modern physics, other is quantum mechanics.

SPECIAL THEORY OF RELATIVITY

The Theory of relativity is valid for two frame of reference. One is interia frame of reference ( travel at constant speed or in rest) and other is non - interia frame of reference ( travel in acceralation) . The Special relativity is valid for interia frame of reference. These two create two principle as follow :
1) The scientific observation is same for all interia frame of reference.
2) The speed of light is constant for all observer.
All changes in space is based on these principles by frame of reference traveller
GENERAL THEORY OF RELATIVITY

All non interia frame of reference is come in general relativity such as gravity.
Einstein said apace and time is one dimension and space is not empty as made 4 dimension called spacetime. It can bend, manipulate and stretch etc. The massive body curve this space time create gravity. Actually motion is done by two things, One is a body move space, turn or other done body and other is space change according to body, here mass curve spacetime and spacetime curve small mass direction to come to large mass body.