Who Discovered Gravity? The Legacy of Isaac Newton
From Aristotle’s ancient misconceptions to Galileo’s inclined planes, and from a falling apple in plague-ravaged England to the publication that changed science forever — the complete history of how humanity came to understand gravity.
📋 What You’ll Learn on This Page
Who Discovered Gravity? The Short Answer
Isaac Newton
Discovered the Law of Universal Gravitation in 1665–1666. First to mathematically unify falling objects on Earth with the orbital motion of planets into a single universal law.
Galileo Galilei
Laid the crucial experimental groundwork 60 years earlier. First to show all objects fall with the same acceleration regardless of mass, and to describe free-fall with mathematics.
Albert Einstein
Didn’t “discover” gravity but redefined what gravity is in 1915 — not a force, but the curvature of spacetime. Einstein’s framework supersedes Newton’s for extreme conditions.
Important note: Gravity itself was not “invented” or “discovered” in the sense of being found for the first time — it has always existed and people have always experienced it. What Newton discovered was the mathematical law governing how gravity works. The question “who invented gravity?” is therefore a common misconception; Newton described gravity, he did not create it.
How Was Gravity Understood Before Newton?
For nearly two thousand years before Newton, the dominant explanation for why things fall came from the ancient Greek philosopher Aristotle (384–322 BC). His ideas, though entirely wrong, were so authoritative that they went largely unchallenged until the 16th century.
Understanding what Aristotle got wrong — and how Galileo corrected him — makes Newton’s achievement all the more remarkable.
Aristotle’s 2,000-Year-Old Mistake
❌ What Aristotle Believed (Incorrect)
- Objects fall because they are trying to reach their “natural place” — heavy objects seek the centre of the Earth.
- Heavier objects fall faster than lighter ones. A 10 kg stone should fall ten times faster than a 1 kg stone.
- The four elements (earth, water, air, fire) each have a natural upward or downward tendency.
- The heavens (stars and planets) follow completely different, perfect circular rules governed by a fifth element — the “aether.”
✅ Why It Lasted So Long
- Aristotle’s authority was almost theological in medieval Europe — questioning him was close to heresy.
- In everyday experience, a heavy rock does fall faster than a feather — because of air resistance, which Aristotle didn’t account for.
- No one performed properly controlled experiments to test his claims for nearly 2,000 years.
- The Church incorporated Aristotelian philosophy into Christian doctrine, making alternatives dangerous to propose.
Galileo Galilei: The Man Who Broke Aristotle
Galileo Galilei was the first scientist to systematically challenge Aristotle’s theory of falling bodies with actual experiments — and the first to describe the motion of falling objects with precise mathematics. Without Galileo, Newton would have had far less to build on.
The Leaning Tower Experiment (c. 1589–1592)
According to his biographer Vincenzo Viviani, Galileo dropped objects of different weights from the Leaning Tower of Pisa, demonstrating they fell at virtually the same rate — directly contradicting Aristotle. Most historians now believe this specific experiment may have been more of a thought experiment or demonstration rather than a controlled test, but Galileo did perform the underlying measurements using inclined planes.
What he actually proved through meticulous ramp experiments: all objects, regardless of mass, fall with the same constant acceleration — assuming no air resistance. Drop a cannonball and a musket ball together: they hit the ground at the same time. This was genuinely revolutionary.
The Inclined Plane Experiments
Galileo’s masterstroke was using inclined planes to “dilute” the effect of gravity and slow the motion down enough to measure it accurately. By rolling balls down ramps at different angles, he discovered that:
- ✅ The distance a ball travels is proportional to the square of the time (d ∝ t²)
- ✅ Falling bodies undergo constant acceleration — they speed up by the same amount each second
- ✅ This acceleration is the same for all objects, regardless of their mass or composition
- ✅ Horizontal and vertical motions are completely independent of each other
What Galileo Gave Newton
Galileo gave Newton two indispensable gifts. The first was the concept of inertia — that objects in motion continue moving in a straight line unless a force acts on them. This became Newton’s First Law of Motion.
The second was the experimental proof that gravitational acceleration is the same for all objects. This was critical for Newton’s universal law: it implied that the gravitational “pull” on an object is exactly proportional to its inertial resistance — a profound coincidence (called the equivalence principle) that Einstein later made the cornerstone of General Relativity.
Galileo described the kinematics of gravity — the “how” of how objects fall. Newton provided the dynamics — the “why,” the underlying force responsible.
Isaac Newton: Life, Mind & Discovery
Isaac Newton was born prematurely on Christmas Day 1642 (Julian calendar) — so small at birth that his mother Hannah said he could have fit inside a quart mug. His father, also named Isaac, had died three months before he was born. He was not expected to survive infancy. That this fragile baby would go on to become arguably the most influential scientist in history remains one of the great ironies of the story of science.
Birth at Woolsthorpe Manor
Born to a widowed mother in a hamlet in Lincolnshire, England. Father died before he was born. When he was 3, his mother remarried and left him in the care of his grandmother, an abandonment that left lasting psychological scars and, arguably, drove his ferocious intellectual ambition.
Enters Trinity College, Cambridge
Admitted to Trinity College, Cambridge as a “sizar” — performing menial work-study duties to fund his education. The curriculum was still largely based on Aristotle, but Newton secretly immersed himself in the modern works of Descartes, Galileo, and Kepler. He was not considered a standout student.
The Plague Years — Annus Mirabilis
The Great Plague of London forced Cambridge to close. Newton returned to Woolsthorpe, where over approximately 18 months he produced what may be the most concentrated burst of scientific genius in history. He developed the foundations of calculus, made key discoveries in optics and light, and began formulating the law of universal gravitation. He later recalled: “For in those days I was in the prime of my age for invention.”
Return to Cambridge — Refinement in Secret
Newton returned to Cambridge as a Fellow of Trinity in 1667 and was appointed Lucasian Professor of Mathematics at only 26 — one of the most prestigious academic chairs in the world. But he kept most of his discoveries to himself, famously reluctant to publish. He continued refining his gravitational theory for nearly two decades before the world would see it.
Publication of the Principia
Finally, with the encouragement and financial help of astronomer Edmond Halley, Newton published Philosophiæ Naturalis Principia Mathematica on 5 July 1687. The book changed science — and humanity’s understanding of the universe — forever.
London, the Mint & Knighthood
Newton spent his final decades in London as Warden and then Master of the Royal Mint, where he cracked down aggressively on coin counterfeiting. He was knighted by Queen Anne in 1705 — the first scientist to receive the honour primarily for scientific achievement. He died in 1727 at age 84 and was buried in Westminster Abbey.
The “Year of Wonders”: What Newton Achieved in 18 Months
Between 1665 and 1666, while most of England cowered from plague, a 23-year-old at a Lincolnshire farm quietly produced more foundational science than most people produce in a lifetime.
Calculus
Independently invented the mathematics of calculus (what he called “the method of fluxions”), giving science the tool needed to describe continuously changing quantities — including motion under gravity.
Optics & Light
Discovered that white light is composed of all colours of the spectrum by passing sunlight through a prism — founding the science of spectroscopy.
Universal Gravitation
Began developing his law of universal gravitation — the insight that the same force pulling an apple down also holds the Moon in orbit around Earth.
Laws of Motion
Began formulating his three laws of motion — the foundation of classical mechanics that engineers still use today to design everything from bridges to spacecraft.
“Nature and Nature’s laws lay hid in night; God said, ‘Let Newton be!’ and all was light.” — Alexander Pope’s famous epitaph for Newton
The Apple Story: Separating Myth from Historical Fact
The tale of Newton being hit on the head by a falling apple is one of the most famous stories in science. But how much of it is true? The real story is both more mundane and more interesting than the legend.
❌ The Popular Myth
- Newton was struck on the head by a falling apple.
- This single moment instantly gave him the idea for gravity.
- The event happened at Trinity College, Cambridge.
- He immediately understood the complete theory.
- One apple = one eureka moment = one discovery.
✅ What Historical Evidence Actually Shows
- Newton did observe an apple fall — at Woolsthorpe Manor, his family home, not at Cambridge.
- He told the story himself to biographer William Stukeley and others, so there is genuine historical basis for it.
- He was NOT struck on the head — he simply observed the apple falling and began to wonder whether the force pulling it down extended to the Moon.
- The apple prompted a question, not an instant answer. The full theory took years of mathematics to develop.
- The apple tree at Woolsthorpe Manor still stands today and is a protected historical monument. Grafted descendants of it grow at institutions worldwide, including NIST in the US.
The Question the Apple Triggered
According to biographer William Stukeley’s account of Newton’s own words, seeing the apple fall made Newton wonder: why does the apple always fall perpendicularly toward the ground? Why not sideways, or upward? There must be a drawing power in the Earth. The crucial leap was then asking: does this drawing power extend to the Moon — some 384,000 km away? If so, could it explain why the Moon orbits Earth rather than flying off in a straight line?
This was the idea that gravity might be a universal force — reaching not just to the top of a tree, but to the Moon and beyond. That insight, not any specific mathematical formula, was Newton’s founding moment. The maths came later, over years of painstaking work.
Philosophiæ Naturalis Principia Mathematica (1687)
Published on 5 July 1687, Newton’s Principia is widely considered the most important and influential book in the history of physics — possibly in the history of science. Here is what made it so revolutionary.
What the Principia Contained
- ✅ Three Laws of Motion — the foundation of classical mechanics, still used in every engineering discipline today
- ✅ Law of Universal Gravitation — F = Gm₁m₂/r² — quantifying the attractive force between any two masses
- ✅ Proof of Kepler’s Laws — mathematically deriving from gravity why planets follow elliptical orbits
- ✅ Explanation of tides — the Moon’s gravitational pull on Earth’s oceans
- ✅ Precession of the equinoxes — how Earth’s axis slowly wobbles over ~26,000 years
- ✅ Motion of comets — Halley used it to correctly predict the return of the comet that now bears his name
Why It Took So Long to Publish
Newton developed most of the ideas in the Principia during his annus mirabilis of 1665–1666 — but the book was not published until 1687, over 20 years later. Newton was notoriously secretive about his work, deeply reluctant to expose his ideas to public criticism and priority disputes.
The catalyst was astronomer Edmond Halley, who visited Newton in 1684 to ask about the orbital paths of planets. Newton said he had already solved it but could not find his papers. He rederived the result on the spot. Halley — recognising its importance — personally encouraged Newton to write up his full theory, and financially underwrote the cost of publication.
Newton spent two intense years writing the Principia. It took him that long to write — it represented 20+ years of thinking.
The Law Published in the Principia
Newton’s Law of Universal Gravitation, as stated in the Principia: “Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.” This was the first time the universe had been described with such mathematical precision.
After Newton: The Story Continues
Newton’s law stood unchallenged for over 200 years — but the story of gravity’s discovery did not end in 1687.
Henry Cavendish (1798)
Newton could not measure the value of G (the gravitational constant) — he only knew its mathematical form. Over a century later, Henry Cavendish used a torsion balance apparatus to measure the tiny gravitational force between lead spheres in his laboratory, determining G for the first time. His result was within 1% of today’s accepted value.
Albert Einstein (1915)
Einstein’s General Theory of Relativity replaced Newton’s “force at a distance” with the geometry of curved spacetime. His theory correctly predicted the precise precession of Mercury’s orbit (which Newton’s couldn’t), the bending of light around the Sun (confirmed 1919), and gravitational waves (confirmed 2015). For most everyday purposes, Newton’s simpler equations remain perfectly adequate.
LIGO (2015)
The LIGO collaboration detected gravitational waves for the first time — ripples in spacetime produced by two black holes merging 1.3 billion light-years away. This confirmed the last major unverified prediction of General Relativity and opened a new era of gravitational astronomy. Einstein himself had doubted this would ever be experimentally possible.
The Complete History of Gravity: Discovery Timeline
| Date | Who | What They Contributed | Significance |
|---|---|---|---|
| ~330 BC | Aristotle | Objects fall to their “natural place”; heavier objects fall faster | Influential but entirely wrong; dominated thinking for 2,000 years |
| ~1590 | Galileo Galilei | All objects fall with the same constant acceleration; d ∝ t² | Disproved Aristotle with experiment; gave Newton the equivalence principle |
| 1609–1619 | Johannes Kepler | Three empirical laws of planetary motion (elliptical orbits, etc.) | Described planetary motion precisely without explaining the cause — Newton provided that explanation |
| 1665–1666 | Isaac Newton | Conceived universal gravitation; apple observation at Woolsthorpe | The central insight: gravity is universal, reaches the Moon, follows inverse-square law |
| 1687 | Isaac Newton | Published Principia Mathematica: F = Gm₁m₂/r² + 3 Laws of Motion | Most important physics book ever written; unified celestial and terrestrial mechanics |
| 1798 | Henry Cavendish | First laboratory measurement of G (gravitational constant) | Made Newton’s formula fully quantitative; calculated Earth’s mass |
| 1915 | Albert Einstein | General Relativity: gravity = curvature of spacetime | Supersedes Newton in extreme conditions; explains black holes, gravitational waves, GPS corrections |
| 1919 | Arthur Eddington | Measured bending of starlight around the Sun during a solar eclipse | First experimental confirmation of General Relativity; made Einstein world-famous |
| 2015 | LIGO Collaboration | First direct detection of gravitational waves | Confirmed last major unverified prediction of GR; opened gravitational wave astronomy |
Common Misconceptions About Gravity’s Discovery
- ❌“Newton invented gravity” — Gravity is a natural force that has existed since the formation of the universe. Newton discovered the mathematical law that describes it. You cannot invent a force of nature.
- ❌“Newton was the first person to know about gravity” — Humans have always experienced gravity and wondered about falling objects. Aristotle wrote about it in 330 BC. Gravity was well known — Newton was the first to quantify it correctly.
- ❌“The apple hit Newton on the head” — Newton himself never claimed this. He said he observed an apple fall and began to wonder about the force acting on it. The “hit on the head” embellishment appeared in later retellings.
- ❌“Einstein proved Newton wrong” — Newton’s law is still correct within its domain. Einstein’s General Relativity is more complete and works across a wider range of conditions, but Newton’s equations remain the standard for everyday gravitational calculations.
Frequently Asked Questions
Who discovered gravity — Newton or Galileo? ▼
Both made essential contributions, but in different ways. Galileo (1564–1642) was first to show experimentally that all objects fall with the same acceleration regardless of mass, and described that motion mathematically. Newton (1643–1727) built directly on Galileo’s work to formulate the universal law of gravitation — the mathematical formula that describes the gravitational force between any two masses anywhere in the universe. If forced to choose one, Newton is credited with “discovering gravity” in the scientific sense of providing the governing law.
When was gravity discovered? ▼
Newton conceived the key ideas during 1665–1666 during the plague years at Woolsthorpe, but the full mathematical theory was not published until 1687 in the Principia. So the date of “discovery” depends on what you mean — the original insight (1665–1666) or the published, proven theory (1687). Galileo’s foundational experimental work on falling bodies preceded this by about 80 years, in the 1580s and 1590s.
Is the Newton apple story true? ▼
Largely, yes — with important caveats. Newton did observe a falling apple at Woolsthorpe Manor during the plague years, and he told this story himself to biographers. The apple prompted his key question: does the force pulling this apple down also extend to the Moon? What is myth is the “hit on the head” embellishment and the idea that one apple equalled one instant discovery. The real theory took years of mathematical development. The original apple tree at Woolsthorpe Manor still stands and is a protected monument.
What did Newton discover about gravity exactly? ▼
Newton’s key discovery was that gravity is universal — the same force that pulls an apple to the ground also holds the Moon in its orbit and governs the motion of every planet around the Sun. He quantified this with his Law of Universal Gravitation: F = Gm₁m₂/r², showing that gravitational force is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them. Before Newton, celestial motion and terrestrial falling were considered completely separate phenomena. Newton unified them into one law.
Did Newton work alone? ▼
Newton famously said “If I have seen further, it is by standing on the shoulders of giants.” He built on Galileo’s experimental foundations, Kepler’s empirical orbital laws, Descartes’ mathematical framework, and the work of many others. The Principia itself was only published because Edmond Halley recognised its importance and personally financed it. Great scientific breakthroughs are rarely solitary — even Newton’s extraordinary genius was built on a community of prior knowledge.
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