Relativity Theory, developed by Albert Einstein in the early 20th century, consists of two main parts: special relativity and general relativity. Special relativity, introduced in 1905, explains how time and space are interconnected, showing that time can pass at different rates depending on an object's speed. It also established that the speed of light is constant for all observers, regardless of their motion. General relativity, published in 1915, expands on this by describing gravity as a curvature of space-time caused by mass. This means that massive objects like Earth and the Sun warp the space around them, affecting the movement of other objects and light.