Special Theory of Relativity:
Relativity is just a method for two people to agree on what they see if one of them is moving. There is no such thing as absolute motion since objects move relative to each other. The earth, sun and galaxy are constantly in motion therefore nothing is at absolute motion. If you were travelling in a car on a smooth straight stretch of highway, there would be no sensation of motion, because relative to the car you are not moving. But this happens only if it does not change direction or speed.
An example to understand the above theory:
Imagine A and B are travelling in a train at a certain uniform speed. The train relative to the outside environment is in motion. A and B sitting inside observe each other as stationary as both A and B and the train are moving at the same speed. Hence, relative to the train, A and B are stationary. Let’s consider that now A has gotten off the train, and he observes the train moving across front of him. Now A is stationary and relative to A, B is moving with he same speed as the train.
General Theory of Relativity:
Einstein prefers to think of space and time as one entity. He called it spacetime.
-Time slows down for objects travelling close to the speed of light.
-Time becomes faster for objects travelling much slower than the speed of light and
-Time stops all together for the objects traveling at the speed of light
Einstein realised that the special theory of relativity only worked for circumstances when things moved at constant speeds through the universe. He theorised that objects warped space time around it, causing it become curved and as a result objects experienced gravitational attraction to each other. This warping of spacetime explains how objects behave as they move through space