The theory of relativity, 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 slow down or speed up depending on an object's speed relative to another. This leads to the famous equation E=mc², which describes the relationship between energy and mass. General relativity, published in 1915, expands on this by describing gravity as the curvature of space-time caused by mass. This means that massive objects like planets and stars bend the fabric of space-time, affecting the motion of other objects. This theory has been confirmed through various experiments and observations, including the bending of light around massive bodies.