Despite the efforts of the church, by about 1640 the work of Brahe, Kepler, and Galileo had been largely accepted by the scientific community. The old Aristotelian astronomy and physics were in ruins, and several fundamental breakthroughs had been made. 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 was born into the lower English gentry in 1642, and he enrolled at Cambridge University in 1661. A genius who spectacularly united the experimental and theoretical-mathematical sides of modern science, Newton was an intensely devout, albeit non-orthodox Christian, who privately rejected the doctrine of the Trinity. Newton was also fascinated by alchemy. He left behind thirty years’ worth of encoded journals recording experiments to discover the elixir of life and a way to change base metals into gold and silver. He viewed alchemy as one path, alongside mathematics and astronomy, to the truth of God’s creation. Like Kepler and other practitioners of the Scientific Revolution, he studied the natural world not for its own sake, but to understand the divine plan.

Newton arrived at some of his most basic ideas about physics between 1664 and 1666, during a break from studies at Cambridge caused by an outbreak of plague. As he later claimed, during this period he discovered his law of universal gravitation as well as the concepts of centripetal force and acceleration. Not realizing the significance of his findings, the young Newton did not publish them, and upon his return to Cambridge he took up the study of optics. It was in reference to his experiments in optics that Newton outlined his method of scientific inquiry most clearly, explaining the need for scientists “first to enquire diligently into the properties of things, and to establish these properties by experiment, and then to proceed more slowly to hypotheses for the explanation of them.”4

In 1684 Newton returned to physics and the preparation of his ideas for publication. The result appeared three years later in Philosophicae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Newton’s towering accomplishment was a single explanatory system that could integrate the astronomy of Copernicus, as corrected by Kepler’s laws, with the physics of Galileo and his predecessors. Principia Mathematica laid down Newton’s three laws of motion, using a set of mathematical laws that explain motion and mechanics. These laws of dynamics are complex, and it took scientists and engineers two hundred years to work out all their implications.

The key feature of the Newtonian synthesis was the law of universal gravitation. According to this law, every body in the universe attracts every other body in the universe 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 — from Kepler’s elliptical orbits to Galileo’s rolling balls — was unified in one coherent system. The German mathematician and philosopher Gottfried von Leibniz, with whom Newton contested the invention of calculus, was outraged by Newton’s claim that the “occult” force of gravity could allow bodies to affect one another at great distances. Newton’s religious faith, as well as his alchemical belief in the innate powers of certain objects, allowed him to dismiss such criticism.

Newton’s synthesis of mathematics with physics and astronomy prevailed until the twentieth century and established him as one of the most important figures in the history of science. Yet, near the end of his life, this acclaimed figure declared: “I do not know what I may appear to the world; but to myself I seem to have been only like a boy, playing on the seashore, and diverting myself, in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”5