The Annus Mirabilis: One Year That Changed Everything
In 1665–1666, the Great Plague forced Cambridge University to close. Newton, then 23, retreated to his family home at Woolsthorpe in Lincolnshire. In roughly 18 months of isolation, he accomplished more than most scientists achieve in a lifetime:
- Invented differential and integral calculus (independently of Leibniz)
- Discovered that white light is composed of all the colors of the spectrum
- Formulated the law of universal gravitation
- Developed the foundations of his three laws of motion
His Three Laws of Motion
Published in his 1687 masterwork "Philosophiae Naturalis Principia Mathematica" (the "Principia"), Newton's three laws of motion remained the unchallenged foundation of physics for over 200 years:
First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same speed and direction, unless acted upon by an external force.
Second Law (F = ma): The force on an object equals its mass times its acceleration. This simple equation underlies all of classical mechanics.
Third Law (Action and Reaction): For every action, there is an equal and opposite reaction.
These laws, combined with his law of universal gravitation (F = Gm₁m₂/r²), gave humanity its first complete mathematical description of the physical world — from falling apples to the orbits of planets.
Calculus, Optics, and Beyond
Newton's invention of calculus — which he called "the method of fluxions" — was arguably his greatest mathematical achievement. Calculus is the mathematics of change and accumulation, and it became the language of all subsequent physics, engineering, and quantitative science.
In optics, Newton used prisms to demonstrate that white light is not pure but rather composed of all the visible wavelengths. He built the first reflecting telescope in 1668, a design still in use today. His "Opticks" (1704) remained the foundational text on light for a century.
Late in life, Newton turned to alchemy and biblical chronology — pursuits that have puzzled historians. He reportedly spent more hours on these esoteric subjects than on physics. Some scholars argue this reveals a holistic search for a single unified theory of everything; others simply note that even the greatest mind of his era was a product of his superstitious times.
Newton's Personality and Character
By most accounts, Newton was not a pleasant man. He was solitary, paranoid, and capable of vindictive feuds — his decades-long battle with Leibniz over credit for calculus being the most famous example. He never married, had few close friends, and suffered at least one serious mental breakdown.
Yet these traits may have been inseparable from his genius. His extraordinary ability to concentrate on a single problem for weeks without interruption — he reportedly once forgot to eat for days while working through a mathematical problem — is widely credited as the mechanism behind his unprecedented discoveries.
When asked how he had discovered so much, Newton replied: "By always thinking about it." Visit Newton's full profile and compare him with other great scientists in our explorer.