By about 1640 the work of Brahe, Kepler, and Galileo had been largely accepted by the scientific community despite opposition from religious leaders (see “Science and Religion”). But the new findings failed to explain what forces controlled the movement of the planets and objects on earth. That challenge was taken up by English scientist Isaac Newton (1642–1727).

Newton arrived at some of his most basic ideas about physics in 1666 at age twenty-four but was unable to prove them mathematically. In 1684, after years of studying optics, Newton returned to physics for eighteen intensive months. The result was his towering accomplishment, a single explanatory system that integrated the astronomy of Copernicus, as corrected by Kepler’s laws, with the physics of Galileo and his predecessors. Newton did this through a set of mathematical laws that explain motion and mechanics. These laws were published in 1687 in Newton’s Mathematical Principles of Natural Philosophy (also known as the Principia).

The key feature of the Newtonian synthesis was the law of universal gravitation. According to this law, each body in the universe attracts every other body in a precise mathematical relationship, whereby the force of attraction is proportional to the quantity of matter of the objects and inversely proportional to the square of the distance between them. The whole universe was unified in one majestic system. Matter moved on earth and throughout the heavens according to the same laws, which could be understood and expressed in mathematical terms.