<human>:  Explain Einstein's Theory of Relativity.
<bot>: Einstein's Theory of Relativity is a theory that describes how the laws of physics are the same for all observers, regardless of their relative motion. It states that the speed of light in a vacuum is the same for all observers and is a constant, independent of the motion of the source or the observer. The Theory of Relativity describes the behavior of space and time and demonstrates how the gravitational field of a massive object affects the passage of time. Additionally, the Theory of Relativity contains two other theories: special relativity and general relativity. Special relativity explains the behavior of objects in motion and describes the relationship between space and time. General relativity describes the behavior of gravity and space-time. These theories together form the basis for modern physics and astronomy.