Establishing the laws of universal gravity and the fundamental laws of motion, Newton's momentous 1687 essay stands as one of the most important works in physics, and it revolutionized the way scientists investigate and prove their theories. In Principia, Newton used mathematical terms to present the principles of time, force, and motion, which have been instrumental in the development of modern physics. In his introduction, the famed physicist and bestselling author Stephen Hawking shows how his work built on that of his predecessors, Nicolaus Copernicus and Johannes Kepler.