Isaac Newton

Chapter 1 · The Fatherless Boy at Woolsthorpe

An abandoned childhood and a mind left alone

1642 – 1665 · Woolsthorpe · Grantham · Cambridge

Isaac Newton was born at Woolsthorpe Manor in Lincolnshire on Christmas Day 1642 by the calendar then used in England — 4 January 1643 by the modern one. His father, an illiterate farmer, had died three months earlier. He was born premature and, family tradition holds, small enough to fit in a quart pot.

When he was three his mother Hannah remarried and moved to her new husband's parish, leaving Isaac with his grandmother. The resentment lasted. In a list of sins he wrote out privately in 1662, aged nineteen, he recorded threatening to burn the house down over his mother and stepfather with them in it.

At the King's School in Grantham he lodged with an apothecary, where he first encountered chemicals and instruments, and filled his room with sundials and mechanical models. His mother took him out of school at sixteen to farm; he was hopeless at it, and the schoolmaster persuaded her to send him back.

He entered Trinity College, Cambridge, in 1661 as a subsizar — a student who paid reduced fees by performing menial services for wealthier undergraduates. The official curriculum was still Aristotelian. Newton read it, then quietly turned to Descartes, Galileo, Kepler and Boyle, keeping a notebook headed with a line meaning that Plato and Aristotle are friends, but truth is a greater friend.

Why this matters

Newton's solitary, self-directed reading at Cambridge — outside the official syllabus — is where his physics actually began, and it set the working habits of a lifetime.

You have met the isolated boy. What would you ask him?

Ask Newton

• “What did it mean to be left behind when your mother remarried?”
• “What did you build in your room at Grantham?”
• “Why did you read outside the Cambridge curriculum?”
• “What was it like being a subsizar among wealthier students?”
• “Which of the earlier natural philosophers taught you most?”

Chapter 2 · The Plague Years

Eighteen months at home that changed physics

1665 – 1667 · Woolsthorpe

When plague closed Cambridge in 1665, Newton went home to Woolsthorpe and stayed for most of two years. He was twenty-two. In that time he laid the foundations of three separate fields.

He developed what he called the method of fluxions — differential and integral calculus — which gave him a mathematics capable of handling continuously changing quantities. He did not publish it for decades.

He worked on light. Sending a beam through a prism, he showed that white light is not modified by the glass but separated into component colours, and proved it with a second prism that recombined them. It overturned the accepted view that colour was something added to pure white light.

And he began on gravity. The apple story is real in the sense that Newton told it himself in old age, and William Stukeley recorded it in 1752 from a conversation in a garden. The apple did not hit his head. The point of the story is the question it prompted: why does an apple fall straight down toward the centre of the Earth, and does the same pull extend as far as the Moon? He compared the Moon's orbit against a force falling off with the square of distance and found the figures roughly agreed — 'pretty nearly', in his words.

He then put the whole thing aside for nearly twenty years. He later said that in those days he was in the prime of his age for invention, and minded mathematics and philosophy more than at any time since.

Why this matters

Newton's plague years are the single most productive period in the history of the physical sciences — and a demonstration of what sustained, undirected thinking time can produce.

You have the eighteen months. What would you ask him?

Ask Newton

• “How much of the apple story is true?”
• “What did the prism experiment actually prove?”
• “Why did you invent a new mathematics?”
• “Why did you put gravity aside for twenty years?”
• “What made those two years so productive?”

Chapter 3 · The Principia

Eighteen months of writing, and a new universe

1684 – 1687 · Cambridge · London

In August 1684 Edmond Halley travelled to Cambridge with a question that had defeated London's best minds: what curve would a planet follow if attracted by a force diminishing as the square of the distance? Newton replied immediately that it would be an ellipse. Asked how he knew, he said he had calculated it — and could not find the papers.

Halley pressed him to reconstruct the proof, and Newton kept going for eighteen months. The result, published in 1687 at Halley's personal expense, was *Philosophiæ Naturalis Principia Mathematica*.

It sets out three laws of motion — that a body continues in its state unless acted on by a force; that force equals the rate of change of momentum; and that every action has an equal and opposite reaction — and then the law of universal gravitation: every mass attracts every other with a force proportional to the product of the masses and inversely proportional to the square of the distance between them.

The word that matters is universal. The same law governs a falling stone, a cannonball, the tides, the orbits of the planets and the path of a comet. Aristotle's division between the corrupt earthly realm and the perfect heavens simply ceased to exist.

It was mathematically brutal — Newton admitted he had made it difficult on purpose to avoid being pestered by people who did not understand mathematics — and it worked. Halley used it to predict the return of the comet that now bears his name; nineteenth-century astronomers used it to predict Neptune's position before anyone saw it.

“If I have seen further it is by standing on the shoulders of Giants.”

— Letter from Newton to Robert Hooke, 5 February 1676

Why this matters

The Principia established that the physical universe follows mathematical laws that can be discovered — the founding assumption of modern physical science.

You have the book that reorganised the universe. What would you ask him?

Ask Newton

• “What did Halley's visit in 1684 actually set off?”
• “Why does it matter that gravity is universal?”
• “Did you deliberately make the Principia hard to read?”
• “You never explained what gravity is — does that trouble you?”
• “Was the compliment to Hooke about giants sincere?”

Chapter 4 · The Alchemist and the Heretic

A million words on things he could never publish

1670 – 1700 · Cambridge

Newton left behind roughly a million words on alchemy and a comparable quantity on theology and biblical chronology. For two centuries these were suppressed as an embarrassment. When the economist John Maynard Keynes bought a tranche of the papers at auction in 1936 and read them, he wrote that Newton was not the first of the age of reason but the last of the magicians.

The alchemy was serious work by his standards: decades of furnace experiments, coded notebooks, a search for the principle by which matter is transformed and for what he called the vegetable spirit animating substances. Some historians argue that his willingness to accept action at a distance in gravity — which orthodox mechanical philosophers rejected as occult — came from this side of his thinking.

The theology was more dangerous. Newton concluded from close study of scripture and church history that the doctrine of the Trinity was a fourth-century corruption, and that Christ was not co-equal with God. This was heresy, and it was illegal. As a Trinity College fellow he was required to take holy orders; he obtained a special royal dispensation in 1675 rather than swear to doctrines he did not believe. He never published a word of it in his lifetime.

He also worked on the chronology of ancient kingdoms and on decoding prophecy in Daniel and Revelation, treating them as a puzzle set by God for those willing to work.

He was, in his own understanding, doing one project with several parts: reading the book of nature and the book of scripture in search of the same divine plan.

Why this matters

Newton's hidden work is a corrective to the idea that scientific revolutions are made by purely modern minds: the man who mathematised the cosmos also spent decades on alchemy and prophecy.

You have the secret Newton. What would you ask him?

Ask Newton

• “What were you actually looking for in alchemy?”
• “Why did you keep your religious views secret?”
• “Did your alchemy help you accept gravity acting at a distance?”
• “Did you see your science and theology as one project?”
• “Why were these papers hidden for two hundred years?”

Chapter 5 · The Mint, the Feuds and the Legacy

Hunting counterfeiters and destroying rivals

1696 – 1727 and after · London · Tower of London

In 1696 Newton left Cambridge to become Warden, and later Master, of the Royal Mint. It was supposed to be a sinecure. He treated it as a job. England's silver coinage had been clipped and debased to the point of crisis, and Newton drove the Great Recoinage through, working long hours and improving assay standards.

He also went after counterfeiters personally, going in disguise to taverns, running informers and preparing cases himself. The most notorious, William Chaloner, who had publicly accused the Mint of incompetence, was convicted and hanged in 1699.

His feuds were relentless. He fought Robert Hooke for decades over optics and over credit for the inverse-square idea, and after Hooke's death, as president of the Royal Society, he ensured his rival's reputation faded — no authenticated portrait of Hooke survives. Against Leibniz he fought over the invention of calculus; as president of the Royal Society he appointed the committee to adjudicate, and then drafted its supposedly impartial report himself. Modern historians conclude both men invented calculus independently, and Leibniz's notation is the one still used.

He was knighted in 1705, served as president of the Royal Society until his death, and died on 20 March 1727. He never married; hair samples analysed in the twentieth century showed high mercury levels, consistent with decades of alchemical work.

His physics stood essentially unchallenged for two hundred years, until Einstein showed it to be an approximation that breaks down at great speeds and in strong gravity — an approximation still accurate enough to fly spacecraft.

Why this matters

Newton's mechanics remained the framework for physics for over two centuries and still governs almost all everyday engineering — an unmatched record for any single scientific theory.

You have the lawgiver of physics and the hunter of counterfeiters. What would you ask him?

Ask Newton

• “Why did you take the Mint job so seriously?”
• “Was hunting counterfeiters personal?”
• “Was the calculus dispute with Leibniz fairly conducted?”
• “Why did you pursue Hooke's reputation even after his death?”
• “How do you feel about Einstein showing your laws were approximate?”

What Newton changed

Newton's laws of motion and universal gravitation created the framework of classical physics, which held for over two centuries and still underpins engineering, ballistics and spaceflight. His calculus is the mathematical language of the physical sciences, and his optics established the modern understanding of light and colour.

A debate that continues

Scholars debate how far Newton's alchemical and theological work informed his physics rather than sitting alongside it, and continue to assess his conduct in the calculus priority dispute with Leibniz.

Keep exploring — ask Newton

• “How did you decide when an idea was ready to publish?”
• “What did you believe gravity actually was?”
• “Which problem defeated you?”

Related lives

• Albert Einstein — Nobel Laureate · Author of Relativity
• Galileo Galilei — Father of Modern Science
• Johannes Kepler — Discoverer of Planetary Motion
• Stephen Hawking — Explorer of Black Holes

Related themes

Forces and motion · Gravity and orbits · The Scientific Revolution