The father of modern physics, known for his theory of relativity, is Albert Einstein. His groundbreaking work reshaped the understanding of space, time, and gravity. The theory of relativity comprises two parts: the special theory and the general theory. Special relativity introduced the concept that the laws of physics are the same for all non-accelerating observers and that the speed of light is constant. General relativity expanded this idea, explaining gravity as the curvature of spacetime caused by mass.