Isaac Newton — The Physicist Who Unified Heaven and Earth
Newton's three laws of motion, law of universal gravitation, and contributions to calculus and optics form the bedrock of modern physics. His Principia Mathematica remains the most influential scientific work ever published.
Quick Facts
- Full Name
- Sir Isaac Newton
- Born
- 25 Dec 1642 (OS) / 4 Jan 1643 (NS), Woolsthorpe, Lincolnshire, England
- Died
- 20 Mar 1727 (OS) / 31 Mar 1727 (NS), Kensington, London
- Lived
- 84 years
- Nationality
- English
- Fields
- Physics, Mathematics, Astronomy, Optics
- Institutions
- Trinity College Cambridge, Royal Society, Royal Mint
- Known For
- Laws of Motion, Universal Gravitation, Calculus, Optics, Reflecting Telescope
- Key Work
- Philosophiae Naturalis Principia Mathematica (1687)
- Honours
- Lucasian Professor (1669–1702), FRS (1672), President of the Royal Society (1703–1727), Knighted 1705, Buried in Westminster Abbey
Sir Isaac Newton was an English physicist, mathematician, and astronomer who transformed humanity's understanding of the natural world. During 1665–1666, while Cambridge University was closed by plague, he laid the foundations for calculus, the theory of light and colour, and universal gravitation. His masterwork, Philosophiae Naturalis Principia Mathematica (1687), unified terrestrial and celestial mechanics under a single mathematical framework for the first time in history. He served as Lucasian Professor of Mathematics for 33 years, President of the Royal Society for 24 years, and Master of the Royal Mint for 28 years. He was knighted in 1705 and buried in Westminster Abbey in 1727.
Early Life and Education
Isaac Newton was born on Christmas Day 1642 in Woolsthorpe, a small village in Lincolnshire, England. His father, a farmer also named Isaac, had died three months before his birth. Newton arrived premature and was reportedly so small he could fit inside a quart mug, and was not expected to survive his first day.
When Newton was three, his mother Hannah married a wealthy clergyman named Barnabas Smith and moved to a neighbouring village, leaving young Isaac in the care of his maternal grandmother. This separation lasted nine years until Smith's death in 1653. Historians, including Newton's biographer Richard Westfall, have suggested this early abandonment shaped his lifelong tendency toward isolation and distrust.
Newton attended The King's School in Grantham, where he showed more interest in building mechanical models — working clocks, sundials, and a miniature windmill — than in farming. His uncle and the school's headmaster persuaded his mother to send him to university rather than keep him on the farm.
In 1661, at age 18, Newton entered Trinity College, Cambridge — somewhat older than most of his classmates. He initially studied the standard Aristotelian curriculum but soon discovered the works of René Descartes, Pierre Gassendi, and Robert Boyle on his own. By early 1664 he had taught himself advanced mathematics from the works of Oughtred, Viète, Wallis, and Descartes's Géométrie. He completed his Bachelor of Arts degree in 1665.
The Plague Years and the Annus Mirabilis
In the summer of 1665, an outbreak of bubonic plague forced Cambridge University to close. Newton retreated to his family home at Woolsthorpe Manor, where he spent approximately 18 months in near-total isolation. He later wrote that these years were his most productive:
"For in those days I was in the prime of my age for invention, and minded mathematics and philosophy more than at any time since."
— Isaac Newton
During this period, Newton laid the foundations for three separate revolutionary breakthroughs.
Calculus
Newton developed what he called the "method of fluxions" — the mathematical framework we now know as calculus. By late 1666, he had worked out both the direct method (differentiation) and the inverse method (integration). His October 1666 tract summarising these results effectively made him the leading mathematician in Europe, though these findings would not be published for decades. The German mathematician Gottfried Wilhelm Leibniz independently developed his own version of calculus in 1675, sparking a bitter priority dispute that lasted decades and was not resolved during either man's lifetime.
Optics and the Nature of Light
Newton conducted his famous prism experiments, passing a beam of sunlight through a small hole in darkened window shutters and through a glass prism. He observed the beam spread into an elongated spectrum of colours — red, orange, yellow, green, blue, and violet — rather than the circular spot predicted by existing theories. In his decisive "experimentum crucis" (crucial experiment), he isolated a single colour from the spectrum using a second aperture and passed it through another prism. The colour remained unchanged. Red light stayed red. This proved that white light is not a pure substance but a composite of all visible colours, and that the prism does not create colours but separates them based on their different degrees of "refrangibility" (refractive index). This discovery overturned theories that had stood since Aristotle.
Gravitation
Newton began thinking about how gravity might extend beyond the Earth's surface to hold the Moon in its orbit. Using Kepler's third law — that the square of a planet's orbital period is proportional to the cube of its mean distance from the Sun — he deduced that the gravitational force keeping the planets in orbit must decrease with the inverse square of the distance. He later tested this idea by comparing the acceleration of the Moon toward the Earth with the acceleration of objects falling at Earth's surface, confirming a rough agreement. However, this was far from a complete theory. The full formulation of universal gravitation would take another 20 years.
Modern historians have cautioned that the "miracle year" is somewhat mythologised. Newton's biographer Richard Westfall noted that by the end of 1666, "nothing was complete, and most were not even close to complete." The plague years laid foundations, but the finished theories came later through years of further work.
Cambridge Career
Newton returned to Cambridge in 1667 and was elected a Fellow of Trinity College. In 1669, at age 26, he succeeded Isaac Barrow as the Lucasian Professor of Mathematics — a position he held for 33 years, until 1702. The Lucasian Chair is today considered among the most prestigious academic positions in the world, later held by figures such as Charles Babbage and Stephen Hawking.
The Reflecting Telescope (1668–1671)
Newton's optical research led him to conclude that the colour fringing (chromatic aberration) afflicting all refracting telescopes was inherent to lenses themselves, not a flaw that could be corrected through better lens shapes. His solution was radical: replace the lens with a mirror.
In late 1668, Newton built his first reflecting telescope prototype. It was only about 6 inches long with a primary mirror approximately 1.3 inches in diameter, made from speculum metal (an alloy of copper, tin, and arsenic that he ground and polished himself). Despite its tiny size, it achieved a magnification of roughly 38 to 40 times — sufficient to resolve Jupiter's moons.
In 1671, he built a second, improved version with a 2-inch mirror and presented it to the Royal Society through his mentor Isaac Barrow. The demonstration was a sensation. Newton was elected a Fellow of the Royal Society in 1672, and the Newtonian telescope design remains widely used today — the Hubble Space Telescope and most amateur telescopes use variants of the reflecting principle Newton pioneered.
Published Work on Optics
Newton published his optical discoveries in the Philosophical Transactions of the Royal Society in 1672 and 1675. These papers triggered fierce debates, most notably with Robert Hooke, who advocated a wave theory of light, and with Christiaan Huygens. Newton found the criticism so distressing that he withdrew from public scientific discourse for years. His full treatment of optics, the book Opticks, was finally published in 1704 — only after Hooke's death in 1703 removed his most persistent critic.
The Principia — The Most Important Scientific Book Ever Written
How It Came to Be Written
In August 1684, the astronomer Edmond Halley visited Newton at Cambridge to discuss a problem that had stumped London's leading scientists: what mathematical law of force would produce the elliptical planetary orbits described by Kepler? Newton immediately replied that it was an inverse-square law, and that he had already calculated it. Halley was astonished and urged Newton to publish.
What began as a short tract called De Motu ("On Motion") in November 1684 expanded over the next two and a half years into the three-volume Philosophiae Naturalis Principia Mathematica ("Mathematical Principles of Natural Philosophy"). Halley personally financed the publication after the Royal Society's funds were exhausted from an earlier project. The Principia was published on 5 July 1687.
What the Principia Contains
The first edition ran to 510 pages of Latin text, with extensive geometric proofs and diagrams. It is divided into three books.
Book I opens with the famous Definitiones (definitions of mass, momentum, and force) followed by the Axiomata sive Leges Motus — the three laws of motion:
A body at rest stays at rest, and a body in motion stays in uniform straight-line motion, unless acted upon by an external force.
The rate of change of momentum of a body is proportional to the applied force and occurs in the direction of that force.
For every action, there is an equal and opposite reaction.
Book I then derives the mathematics of motion under central forces. Book II addresses motion through resisting media (fluids). Book III, titled "The System of the World," applies the mathematical framework to real astronomical data, demonstrating that a single law — universal gravitation — governs falling apples, ocean tides, lunar orbit, planetary motion, and the paths of comets.
The Law of Universal Gravitation
Every particle of matter attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centres. The gravitational constant G = 6.674 × 10⁻¹¹ N·m²/kg² was not measured in Newton's lifetime — it was first determined experimentally by Henry Cavendish in 1798, over 70 years after Newton's death, and Cavendish's result was within 1% of the modern accepted value.
Editions and Impact
The Principia appeared in three editions during Newton's lifetime: the first in 1687 with a print run of approximately 300–400 copies, the second revised edition in 1713, and the third in 1726. A 2020 census by scholars Mordechai Feingold and Andrej Svorenčik confirmed the location of 387 surviving first-edition copies, suggesting the original print run was at least 500. The first English translation by Andrew Motte appeared in 1729, two years after Newton's death.
The Principia unified terrestrial and celestial mechanics for the first time in human history. Before Newton, the motion of falling objects on Earth and the orbits of planets were considered entirely separate phenomena governed by different principles. After the Principia, they were understood as manifestations of a single universal law.
The Calculus Priority Dispute with Leibniz
Newton developed calculus (his "method of fluxions") in the mid-1660s, but did not publish it. The German mathematician Gottfried Wilhelm Leibniz independently developed his own version and published it first in 1684. Newton only published his calculus formally in 1704, appended to the Opticks.
What began as mild suggestions of priority escalated into open accusations of plagiarism on both sides. As President of the Royal Society, Newton appointed a committee to investigate the dispute, secretly wrote the committee's report himself, then anonymously reviewed it in the Philosophical Transactions. He also ghostwrote papers published under the names of younger supporters. Even Leibniz's death in 1716 did not end Newton's fury — he continued attacking his rival's reputation for the rest of his life.
"Considering mathematics from the beginning of the world to Newton's time, what Newton had done was much the better half."
— Gottfried Wilhelm Leibniz, to Queen Sophia Charlotte of Prussia, 1701
Despite the bitter rivalry, Leibniz himself acknowledged Newton's supremacy in mathematics.
Today, both men are credited as independent co-inventors of calculus. Leibniz's notation (dy/dx) became the standard used worldwide, while Newton's fundamental theorems provided the rigorous mathematical foundation.
Later Career — The Royal Mint and Royal Society
In 1696, Newton left Cambridge for London after being appointed Warden of the Royal Mint. Though the position was traditionally a sinecure, Newton took it seriously, overseeing a massive recoinage of English currency and personally pursuing counterfeiters — counterfeiting was then a capital offence classified as high treason. He was promoted to Master of the Mint in 1699, a position he held until his death and from which he drew a substantial income.
In 1701, Newton resigned his Lucasian professorship and his Trinity College fellowship. He was elected to Parliament twice as a representative of Cambridge University (1689–1690 and 1701–1702).
In 1703, following the death of Robert Hooke, Newton became President of the Royal Society. He was re-elected annually for the remaining 24 years of his life, presiding over the Society until his death. He was knighted by Queen Anne on 16 April 1705 during a royal visit to Trinity College — making him only the second scientist in English history to receive a knighthood, after Francis Bacon. Historians note the honour was likely motivated by political considerations related to a parliamentary election rather than recognition of his scientific work.
In 1717, Newton authored a report to the Lords Commissioners of the Treasury that led to a royal proclamation fixing the exchange rate of gold guineas to 21 silver shillings. This inadvertently initiated Britain's transition from the silver standard to the gold standard — a shift with profound economic consequences.
Newton Beyond Physics — Alchemy, Theology, and the Hidden Writings
Newton's scientific publications represent only a fraction of his intellectual output. Of an estimated 10 million words in his surviving papers, approximately 1 million deal with alchemy and over half of his total writing concerned theology and alchemy rather than physics or mathematics.
The Alchemist
Newton immersed himself in alchemical research for over 30 years, copying treatises by hand, annotating them, and conducting chemical experiments. He kept this work largely hidden from contemporaries. The economist John Maynard Keynes, who purchased a large portion of Newton's alchemical papers at a 1936 Sotheby's auction (the collection sold for approximately £9,000 total), later wrote:
"Newton was not the first of the age of reason. He was the last of the magicians."
— John Maynard Keynes
Keynes reassembled roughly half of Newton's alchemical papers and donated them to Cambridge University in 1946. Indiana University's "Chymistry of Isaac Newton" project is digitising all known alchemical writings.
The Secret Heretic
Newton held deeply unorthodox religious beliefs that he kept private throughout his life. He rejected the doctrine of the Trinity, viewing it as a corruption of original Christianity, and considered the worship of Christ as God to be idolatry. In Newton's view, Christ was divine but subordinate to God the Father — a position aligned with the ancient heresy of Arianism.
He nearly lost his Cambridge fellowship over his refusal to take holy orders, saved only by a special royal dispensation in 1675 exempting the Lucasian Chair from the ordination requirement. His encrypted theological manuscripts, purchased by Keynes and others in 1936, were only deciphered in the twentieth century, finally confirming what scholars had long suspected. The historian Stephen Snobelen concluded that Newton was "at least a Socinian sympathiser, possibly an Arian and almost certainly an anti-trinitarian."
"You know more divinity than all of us put together."
— Archbishop of Canterbury Thomas Tenison, to Newton
Despite his unorthodox private beliefs, Newton was respected as a theologian by contemporaries.
Death, Burial, and Legacy
Newton died on 20 March 1727 (Old Style) at his home in Kensington, London, at the age of 84. He had never married. Before the funeral, his body lay in state in the Jerusalem Chamber at Westminster. On 28 March 1727, he was buried in the nave of Westminster Abbey. His pall-bearers included the Lord Chancellor and two dukes, and most Fellows of the Royal Society attended — an extraordinary honour for a man of science in the 18th century.
Newton's grave in Westminster Abbey lies in an area now known as Scientists' Corner. Stephen Hawking's ashes were interred nearby in 2018, and Charles Darwin's grave is also in the nave.
The Apple Tree
The story of Newton being inspired by a falling apple is not mere legend. William Stukeley recorded a conversation with Newton on 15 April 1726 in which Newton himself described sitting in "a contemplative mood" when the fall of an apple set him wondering why it always descended perpendicularly toward the Earth's centre rather than sideways or upwards — and whether the same drawing power might extend as far as the Moon.
The apple tree at Woolsthorpe Manor has been identified through dendrochronology and DNA analysis. It was blown over in a storm around 1816, regrew from its roots, and survives today under National Trust care. A descendant tree grows outside the main gate of Trinity College, Cambridge, beneath the room Newton occupied as a student.
Honours and Cultural Recognition
Newton's image appeared on Bank of England £1 banknotes from 1978 to 1988, the last £1 notes the Bank ever issued. In 1999, Time magazine named him Person of the Century for the 17th century. A 1999 poll of 100 leading physicists voted Einstein the greatest physicist ever, with Newton the runner-up — but a parallel survey of rank-and-file physicists ranked Newton first. In 2002, he placed 6th in the BBC's 100 Greatest Britons poll, and in 2003 was voted the greatest Briton in a BBC World poll, ahead of Winston Churchill.
The physicist Lev Landau ranked physicists on a logarithmic scale from 0 to 5, with 0 being the highest. Newton alone received a 0. Einstein was ranked 0.5. The founders of quantum mechanics — Heisenberg, Dirac — received 1.
His monument in Westminster Abbey, executed by sculptor Michael Rysbrack in 1731 with design by architect William Kent, features Newton reclining on a sarcophagus with a celestial globe showing the path of the comet of 1680. A bronze statue by Eduardo Paolozzi, inspired by William Blake's etching, stands in the piazza of the British Library in London.
Newton's Contributions That Shape Physics Today
Newton's work remains embedded in modern science, engineering, and daily technology in specific, quantifiable ways.
Space Exploration and Orbital Mechanics
NASA's trajectory calculations for every space mission — from the Apollo programme to the Mars rovers — use Newtonian mechanics for initial mission planning. The gravitational assist manoeuvres (slingshot trajectories) that sent Voyager 1 and 2 to the outer solar system are computed directly from Newton's law of universal gravitation. Only when extreme precision is needed near massive bodies does Einstein's general relativity provide corrections.
Engineering and Structural Design
The three laws of motion are foundational to structural engineering, automotive crash safety analysis, bridge design, and aerospace engineering. Every force diagram taught in engineering programmes worldwide uses Newton's framework.
The Unit of Force
The SI unit of force — the newton (N) — is named in his honour. One newton is the force required to accelerate a 1 kg mass at 1 m/s². It remains the standard unit used across all branches of physics and engineering.
Key Publications
Published in His Lifetime
- De Analysi per Aequationes Numero Terminorum Infinitas (1669, published 1711)
- De Motu Corporum in Gyrum (1684)
- Philosophiae Naturalis Principia Mathematica (1687, 2nd ed. 1713, 3rd ed. 1726)
- Opticks (1704, Latin ed. 1706, 2nd English ed. 1717–18)
- Arithmetica Universalis (1707)
- Reports as Master of the Mint (1701–1725)
Published Posthumously
- De Mundi Systemate (The System of the World, 1728)
- The Chronology of Ancient Kingdoms Amended (1728)
- Observations on Daniel and The Apocalypse of St. John (1733)
- Method of Fluxions (written 1671, published 1736)
- An Historical Account of Two Notable Corruptions of Scripture (1754)
Life Timeline
Frequently Asked Questions About Isaac Newton
What did Isaac Newton discover?
Newton made foundational discoveries across three major fields. In mechanics, he formulated the three laws of motion and the law of universal gravitation, showing that the same force governing a falling apple also holds the Moon in orbit. In optics, he proved that white light is a mixture of all visible colours by splitting sunlight through a prism in 1666. In mathematics, he developed calculus (his "method of fluxions") independently of Leibniz. He also built the first working reflecting telescope in 1668 and discovered Newton's rings — periodic colour patterns in thin films that demonstrated the first known periodic optical phenomenon.
When was Isaac Newton born and when did he die?
Newton was born on 25 December 1642 under the Old Style Julian calendar (4 January 1643 under the Gregorian calendar we use today) at Woolsthorpe Manor, Lincolnshire, England. He died on 20 March 1727 (Old Style) / 31 March 1727 (New Style) at his home in Kensington, London, at the age of 84. He was buried in Westminster Abbey on 28 March 1727, with the Lord Chancellor and two dukes serving as pallbearers.
What are Newton's three laws of motion?
The first law (law of inertia) states that a body remains at rest or in uniform straight-line motion unless acted upon by an external force. The second law states that force equals mass times acceleration (F = ma) — the rate of change of momentum is proportional to the applied force. The third law states that for every action there is an equal and opposite reaction. All three were published in his Principia in 1687 and remain the foundation of classical mechanics used in engineering and physics today.
Did an apple really fall on Newton's head?
The apple story is partly true but commonly exaggerated. Newton himself told the story to William Stukeley in 1726, describing how watching an apple fall in his garden at Woolsthorpe set him wondering why objects always fall perpendicularly toward the Earth's centre — and whether that same force might reach as far as the Moon. However, there is no credible historical evidence that the apple hit him on the head. That detail is an embellishment added later in popular retellings. The actual apple tree at Woolsthorpe Manor has been identified through DNA analysis, was blown over in a storm around 1816, regrew from its roots, and survives today under National Trust care.
What is Newton's law of universal gravitation?
Newton's law of universal gravitation states that every particle of matter attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centres. Expressed mathematically: F = G × (m₁ × m₂) / r². The gravitational constant G = 6.674 × 10⁻¹¹ N·m²/kg² was not measured during Newton's lifetime — Henry Cavendish first determined it experimentally in 1798, more than 70 years after Newton's death.
What is Newton's most important book?
The Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), published on 5 July 1687. It contains the three laws of motion, the law of universal gravitation, and their application to planetary orbits, comets, tides, and the shape of the Earth. The physicist Stephen Hawking called it "probably the most important single work ever published in the physical sciences." It was published in three editions during Newton's lifetime (1687, 1713, 1726), with a first edition print run of approximately 300–400 copies. A 2020 census confirmed 387 surviving first-edition copies.
Did Newton invent calculus?
Newton developed the core ideas of calculus — which he called the "method of fluxions" — during 1665–1666 at his family home during the plague years. However, the German mathematician Gottfried Wilhelm Leibniz independently developed his own version of calculus around 1675 and published it first in 1684. Newton did not formally publish his calculus until 1704. Today, both men are credited as independent co-discoverers. Leibniz's notation (dy/dx, the integral sign ∫) became the worldwide standard, while Newton's theoretical results provided the rigorous mathematical foundation.
What was Newton's "Annus Mirabilis"?
The Annus Mirabilis (Latin for "year of wonders") refers to the period of 1665–1666 when the bubonic plague forced Cambridge University to close and Newton retreated to his family home at Woolsthorpe Manor. During these roughly 18 months, he laid the groundwork for calculus, conducted his prism experiments on the nature of light, and began formulating ideas about gravitational attraction. Newton later wrote that he was "in the prime of my age for invention" during this period. Historians note that while the foundations were laid during these years, none of his major theories were complete until much later.
Where is Isaac Newton buried?
Newton is buried in the nave of Westminster Abbey, London, in an area now known as Scientists' Corner. His funeral on 28 March 1727 was attended by most Fellows of the Royal Society. His monument, designed by architect William Kent and sculpted by Michael Rysbrack in 1731, features Newton reclining on a sarcophagus with a celestial globe above showing the path of the comet of 1680. Stephen Hawking's ashes were interred near Newton's grave in 2018, and Charles Darwin is also buried in the nave.
Was Newton religious?
Newton was deeply religious but privately held unorthodox beliefs. He rejected the doctrine of the Trinity, considering it a corruption of original Christianity, and viewed the worship of Christ as God to be idolatry. These views aligned with the ancient heresy of Arianism. He kept his beliefs hidden because they would have been considered heretical. Encrypted manuscripts purchased by the economist John Maynard Keynes in 1936 confirmed Newton's anti-Trinitarian stance. Despite this, contemporaries respected him as a theologian — the Archbishop of Canterbury told Newton "You know more divinity than all of us put together." Over half of Newton's total writing concerned theology and alchemy rather than science.