The concept of relativity, specifically referring to Albert Einstein's theory of relativity, revolutionized our understanding of space, time, and the nature of gravity. There are two main theories of relativity: special relativity and general relativity.
Special Relativity: Special relativity, published by Einstein in 1905, introduces two fundamental principles: the principle of relativity and the constancy of the speed of light. The theory states that the laws of physics are the same for all observers in uniform motion relative to each other. It also asserts that the speed of light in a vacuum is constant and independent of the motion of the source or observer.
Special relativity leads to some counterintuitive phenomena. For example, time dilation occurs when an object moving at a high speed relative to another observer experiences time passing slower. Similarly, length contraction occurs when an object moving at high speed appears shorter in the direction of motion from the perspective of a stationary observer. These effects become significant at speeds approaching the speed of light.