Isaac Newton was a well-known scientist and mathematician from England who lived long ago. Newton wrote a well-known book about how things move, called the Principia, which was published in 1687. A mathematician at the Open University wrote that the Principia made Newton famous even though few people read it and even fewer understood it. In it, Newton applied his laws to orbiting bodies, projectiles, pendulums and free-fall near the Earth. It explained the eccentric orbits of comets, the tides and their variations, the wobble of the Earth's axis, and the Moon's motion as pulled by the Sun's gravity. Before Newton, thinkers assigned different causes to different types of motion, according to physicist Stephen Hawking, so by unifying all motion Newton shifted science toward a search for large, unifying patterns in nature.

His law of universal gravitation says all matter attracts all other matter, and the pull is proportional to the product of the masses and inversely proportional to the square of the distance between them. Newton showed that if gravity gets weaker with the square of the distance, then gravity on Earth's surface correctly predicts how long the Moon takes to orbit. Scientists on the European continent did not accept Newton's idea of action at a distance. They kept to Descartes's vortex theory, in which forces work through contact. Newton worked out a version of calculus in the 1660s but did not publish it. Leibniz formulated his own version in the 1670s and published a decade later. As of November 2026, the calculus used in classrooms follows Leibniz's system rather than Newton's. Newton's method of fluxions rested on one insight: integrating a function is the inverse of differentiating it.

His simple methods unified many techniques that had been used on separate problems, such as finding areas, tangents, the lengths of curves, and maxima and minima. Yet the proof Newton published for planetary orbits did not use calculus. It used the properties of ellipses and other conic sections. Every scientist since Aristotle had believed white light was a single basic thing, and the color fringes in a telescope lens convinced Newton otherwise. He shone sunlight through a glass prism and saw a band of colors, split white light into colors with one prism, and then used a second prism to join the colors back into white light. In a key experiment, Newton passed one color from the spectrum through a hole and a second prism, and the second prism bent it by the same amount without changing its color, showing that each color is a pure part of white light.

Newton's first scientific paper, 'New Theory About Light and Colours,' appeared in the Philosophical Transactions of the Royal Society in March 1672, after the Royal Society asked for a written account of his telescope. Robert Hooke and Christiaan Huygens objected to Newton trying to prove by experiment alone that light is made of small particles rather than waves. After critics challenged his light theory, Newton became impatient with hypothetical arguments. He insisted that science should be mainly mathematical and experimental. Newton's particle theory of light was so influential that it delayed acceptance of the wave theory for nearly a century. In the 1800s, scientists measured the wavelengths of visible light and showed light slows in denser media, as the wave theory predicted, while modern quantum theory gives light both particle and wave properties. Newton reasoned that lens telescopes would always blur colors, and so built a reflecting telescope, though MacTutor calls that conclusion erroneous.

Others, such as James Gregory in 1663, had described ideas for a reflecting telescope. Newton was the first to build one. As of November 2026, reflecting telescopes, which use mirrors as Newton's did, are mainstays of astronomy, including the Hubble Space Telescope. Newton became Warden of the Royal Mint in 1696 and Master of the Mint in 1699, a post he kept until his death in 1727. At the Royal Mint, Newton helped take old coins out of use and replace them with more reliable ones. In September 1717 Newton, as Master of the Mint, sent the Treasury a report setting a new ratio between silver and gold, which had the effect of moving Britain onto the gold standard. He lived to be 84 years old. He is buried in Westminster Abbey in London. Newton's laws of motion and universal gravitation stood unchallenged for nearly 220 years, until Albert Einstein presented special relativity in 1905.

Newton's theory depended on the assumption that mass, time and distance are constant wherever you measure them. As of November 2026, at slow speeds and large scales the differences predicted by relativity are small enough that Newton's laws still work. As of November 2026, Newton's laws still define the orbits of large, slow-moving satellites. Newton's laws are still used to reach the Moon, Mars and other places beyond Earth, and they became the base of classical mechanics, the study of how large things move. Newton once said that if he saw farther than others, it was because he stood on the shoulders of giants. Near the end of his life Newton said he felt like a boy on the seashore, finding a smoother pebble or prettier shell while the great ocean of truth lay undiscovered.

Words to know

• calculus: math of change
• fluxions: Newton's calculus
• relativity: Einstein's theory
• erroneous: mistaken
• spectrum: band of colors