c. 420 BCE 2022
Physics wasn't discovered by one genius or one culture. Follow 2,500 years of ideas, experiments and arguments, and meet the people who made them.
c. 420 BCE
Democritus argued that if you keep cutting matter in half, you must reach tiny pieces that can't be cut: atomos, "uncuttable". It was pure reasoning; proof that atoms are real only came in the 1900s.
c. 400 BCE
The Mohist Canon describes the upside-down image formed through a pinhole and explains it with light rays crossing at the hole. It also studies flat, concave and convex mirrors.
c. 350 BCE
Aristotle taught that heavy things fall faster than light ones and that every motion needs a mover. Wrong on both counts, yet so convincing that it was taught for nearly 2,000 years.
c. 250 BCE
Archimedes proved the law of the lever and found that an object in a fluid is pushed up by the weight of the fluid it displaces. Physics written in real mathematics starts here.
c. 240 BCE
At noon on midsummer's day, the Sun shone straight down a well in Syene (Aswan) but cast a shadow of about 7° in Alexandria. From that angle and the distance between the two cities, Eratosthenes worked out the Earth's circumference.
c. 830
In Abbasid Baghdad, especially under Caliph al-Ma'mun, scholars translated Greek, Persian and Indian science into Arabic, then went further: they checked it against new observations and corrected it.
984
In On Burning Mirrors and Lenses, Ibn Sahl gave the correct law for how light bends when it enters glass, and used it to design lenses that focus light to a point. Europe rediscovered the same law in 1621.
c. 1011–1021
Ibn al-Haytham showed that we see because light from objects enters our eyes, explained the camera obscura, and insisted that every theory must be tested by careful, repeatable experiments.
c. 1020
Ibn Sina argued that a thrown stone carries an inner inclination (mayl) given by the thrower, which only air resistance wears away. In empty space nothing would wear it away, so the motion would go on forever: a big step towards inertia.
c. 1020s
Al-Biruni measured the height of a hill, then how far the horizon dipped below the horizontal as seen from its top. With trigonometry he found the Earth's radius to within about 1% of today's value.
1121
Al-Khazini built a precision balance that weighed objects in air and in water to find their densities, and wrote that heavy bodies are pulled towards the centre of the Earth.
c. 1350
Ibn al-Shatir, timekeeper of the Umayyad Mosque, built planetary models without Ptolemy's awkward fixes. His models of the Moon and Mercury are mathematically identical to those Copernicus published 200 years later.
1543
Copernicus put the Sun at the centre and set the Earth moving around it, ending 1,400 years of Ptolemy's Earth-centred universe. It took another century of arguments and observations to convince everyone.
1609
Using Tycho Brahe's precise observations of Mars, Kepler found that planets move on ellipses and sweep out equal areas in equal times. His third law, linking orbit size and period, followed in 1619.
1610
Galileo saw mountains on the Moon, countless stars in the Milky Way, the phases of Venus and four moons orbiting Jupiter: clear proof that not everything circles the Earth.
1638
Under house arrest, Galileo finished his book on motion: falling objects speed up steadily, and a thrown ball follows a parabola. It was printed in Leiden, out of the Inquisition's reach.
1676
Ole Rømer noticed that eclipses of Jupiter's moon Io came late when Jupiter was far from the Earth. The delay was the time light needed to cross the extra distance: light is fast, but not infinitely fast.
1687
Newton's three laws of motion and his law of universal gravitation explained falling apples, the tides, the Moon and the planets with the same few equations. Heaven and Earth obeyed one physics.
1740
Émilie du Châtelet argued that a moving body's "living force" grows with , backed by experiments in which balls dropped into clay sank deeper with the square of their speed. It is the seed of kinetic energy, .
1798
With lead balls hung from a delicate torsion balance in a sealed room, Henry Cavendish measured the tiny gravitational pull between ordinary objects, and worked out that the Earth is about 5.5 times as dense as water.
1800
Alessandro Volta stacked discs of zinc and copper separated by brine-soaked cardboard and got the first steady electric current. The unit of voltage, the volt, is named after him.
1801–1803
Thomas Young split a beam of sunlight in two and saw bright and dark stripes where the beams overlapped. Only waves can cancel each other out, so light had to be a wave. Young also helped decipher the Rosetta Stone.
1824
Sadi Carnot, a young French engineer, proved that no engine can turn all of its heat into work: some must always flow to somewhere colder. It was the first glimpse of the second law of thermodynamics.
1831
In 1820 Ørsted had shown that an electric current deflects a compass. Michael Faraday asked the reverse question and found that a changing magnetic field drives a current. Almost every power station still relies on it.
1840s
James Joule used falling weights to spin a paddle wheel in water and measured the water warming up. The same amount of work always made the same amount of heat: energy changes form but is never lost.
1865
James Clerk Maxwell united electricity and magnetism in one set of equations (today written as four). They predicted waves moving at about 300,000 km/s, the speed of light. Light, radio and X-rays are all the same thing.
1877
Ludwig Boltzmann explained why heat flows from hot to cold: there are vastly more disordered arrangements of molecules than ordered ones. His formula ties the world of atoms to the arrow of time.
1887
Albert Michelson and Edward Morley expected light's speed to change with the Earth's motion through the "ether" that supposedly carried it. They found no change at all. Einstein would explain why in 1905.
1898
After Becquerel found mysterious rays coming from uranium (1896), Marie and Pierre Curie discovered two new, far more radioactive elements: polonium and radium. Atoms were not unchangeable after all.
1900
To explain the glow of hot objects, Max Planck assumed energy is emitted in tiny chunks, . He called it "an act of desperation". It was the birth of quantum physics.
1905
While working as a patent clerk, Einstein published papers on light quanta (photons), the reality of atoms, special relativity and . Space and time would never be the same.
1912
Studying thousands of photographic plates, Henrietta Leavitt found that brighter Cepheid stars pulse more slowly. Time the pulse and you know the star's true brightness, and so its distance. Hubble used her law to measure the universe.
1913
Rutherford had found in 1911 that atoms have a tiny, dense nucleus. Niels Bohr proposed that electrons can only occupy certain energy levels, and jump between them by absorbing or emitting light of exact colours. Spectral lines were explained.
1915
In general relativity, mass bends space and time, and objects simply follow the curves. In 1919, Eddington's eclipse expedition saw starlight bend around the Sun by the predicted amount, and Einstein became world-famous overnight.
1918
Emmy Noether proved that every symmetry of nature comes with a conserved quantity. Physics is the same tomorrow as today, so energy is conserved; the same here as over there, so momentum is conserved.
1924
Satyendra Nath Bose found a new way to count photons, treating them as truly identical. Einstein translated his paper and extended it, predicting a strange new state of matter, the Bose–Einstein condensate, first made in a lab in 1995.
1925–1927
Heisenberg, Schrödinger, Born and Dirac built a new mechanics in which particles behave like waves of probability. Heisenberg's uncertainty principle (1927) showed that position and momentum can never both be known exactly.
1928
C. V. Raman discovered that a tiny fraction of the light scattered by molecules comes out with a slightly different colour, carrying a fingerprint of the molecule. India celebrates National Science Day every 28 February, the day it was announced.
1929
Edwin Hubble found that distant galaxies are rushing away from us, faster the farther they are. Georges Lemaître had predicted it in 1927 from Einstein's equations: the universe had a beginning.
1930
On a ship from India to England, 19-year-old Subrahmanyan Chandrasekhar calculated that a white dwarf heavier than about 1.4 Suns cannot hold itself up. It must collapse further, into a neutron star or a black hole.
1938
On a walk in the snow at Christmas, Lise Meitner and her nephew Otto Frisch worked out that uranium nuclei hit by neutrons split in two, releasing huge energy as predicted by . The Nobel Prize went to her colleague Otto Hahn alone.
1956
Chien-Shiung Wu cooled radioactive cobalt close to absolute zero and showed that its electrons fly out preferentially in one direction. The weak force breaks mirror symmetry, something almost everyone had thought impossible.
1961–1963
Rerunning a weather simulation, Edward Lorenz typed 0.506 instead of 0.506127. After a couple of simulated months the forecast was completely different: tiny differences can grow without limit. Chaos theory was born.
1965
Arno Penzias and Robert Wilson couldn't get rid of a faint hiss in their radio antenna, even after clearing out pigeon droppings. It came from every direction in the sky: light left over from the Big Bang, now cooled to 2.7 K.
1967–1968
Abdus Salam, Steven Weinberg and Sheldon Glashow showed that electromagnetism and the weak nuclear force are two faces of a single electroweak force. Experiments at CERN confirmed their predictions in 1973 and 1983.
1974
Stephen Hawking combined quantum physics with general relativity and found that black holes are not completely black: they slowly give off radiation and can eventually evaporate.
1970s
Vera Rubin measured how fast stars orbit in spiral galaxies. By Kepler's laws the outer stars should move slower, but they don't. Galaxies must be wrapped in invisible "dark matter"; across the universe there is about five times more of it than ordinary matter.
1998
Two teams measuring distant exploding stars found that the expansion of the universe is accelerating. Whatever drives it, now called dark energy, makes up about 70% of the universe, and nobody yet knows what it is.
2012
48 years after it was predicted, the Large Hadron Collider found the Higgs boson, a ripple in the field that gives elementary particles their mass. It was the last missing piece of the Standard Model.
2015
LIGO's 4-km laser arms stretched by less than a thousandth of a proton's width as a gravitational wave passed through, sent by two black holes that merged 1.3 billion years ago. Einstein had predicted such waves a century earlier.
2019
Radio observatories across the planet worked together as one Earth-sized telescope to photograph the shadow of the black hole in galaxy M87: 6.5 billion times the mass of the Sun, 55 million light-years away.
2022
Alain Aspect, John Clauser and Anton Zeilinger won the Nobel Prize for experiments showing that entangled particles share one quantum state, however far apart they are. Einstein called it "spooky action at a distance"; today it powers quantum cryptography.
c. 470–391 BCE
Ancient China
Known for
Founded the Mohist school, whose Canon holds some of the oldest known studies of light, mirrors, levers and forces.
Fun fact
China's first quantum-communication satellite, launched in 2016, is named Micius in his honour.
c. 460–370 BCE
Abdera, Greece
Known for
Proposed that all matter is made of tiny, uncuttable atoms moving through empty space.
Fun fact
He was nicknamed "the laughing philosopher" because he found human foolishness so amusing.
384–322 BCE
Stagira and Athens, Greece
Known for
Wrote the first book called Physics. His ideas about motion were wrong, but his way of observing and classifying nature shaped science for 2,000 years.
Fun fact
He was the private tutor of the young Alexander the Great.
c. 287–212 BCE
Syracuse, Sicily
Known for
The law of the lever, the principle of buoyancy, and a remarkably accurate estimate of π.
Fun fact
"Give me a place to stand and I will move the Earth," he is said to have boasted about his levers.
c. 276–194 BCE
Cyrene and Alexandria
Known for
Measured the circumference of the Earth with shadows, and invented a famous method (the "sieve") for finding prime numbers.
Fun fact
Rivals nicknamed him "Beta", second-best at everything, though he ran the greatest library of the ancient world.
c. 940–1000
Baghdad
Known for
Discovered the law of refraction and used it to design lenses and burning mirrors that focus light (984).
Fun fact
His priority was only recognised in 1990, when historian Roshdi Rashed pieced his book together from scattered manuscripts.
c. 965–1040
Basra and Cairo
Known for
The Book of Optics: how vision works, the camera obscura, reflection and refraction, and testing every idea by experiment.
Fun fact
UNESCO's International Year of Light in 2015 celebrated 1,000 years since his work on optics.
973–c. 1050
Khwarazm (today Uzbekistan) and Ghazni
Known for
Measured the Earth's radius and the densities of metals and gems, and discussed whether the Earth rotates, centuries before Copernicus.
Fun fact
As a young man he argued by letter with Ibn Sina about Aristotle's physics. Their debate still survives.
980–1037
Bukhara and Hamadan
Known for
His theory of mayl (inclination): a thrown object keeps moving until something resists it, an early step towards inertia.
Fun fact
His Canon of Medicine remained a standard textbook in European universities until the 1600s.
active c. 1115–1130
Merv (today Turkmenistan)
Known for
The Book of the Balance of Wisdom (1121): precision balances, densities, buoyancy, and gravity directed towards the centre of the Earth.
Fun fact
Born a Byzantine Greek, he was enslaved as a boy; his master in Merv gave him the finest education in mathematics and philosophy.
1473–1543
Toruń and Frombork, Poland
Known for
Put the Sun at the centre of the solar system, with the Earth as one planet among others.
Fun fact
He was also a church canon, a doctor and an economist. Legend says he received the first printed copy of his book on his deathbed.
1564–1642
Pisa, Padua and Florence, Italy
Known for
Falling bodies, projectiles, pendulums, inertia and the first telescope discoveries. He made experiments and mathematics work together.
Fun fact
His middle finger is on display in a glass egg at the Museo Galileo in Florence.
1571–1630
Prague and Linz
Known for
His three laws of planetary motion: elliptical orbits, equal areas in equal times, and the link between orbit size and period.
Fun fact
He wrote Somnium, one of the first science-fiction stories, about a journey to the Moon, and defended his own mother in a witchcraft trial.
1643–1727
Cambridge and London, England
Known for
The three laws of motion, universal gravitation, calculus, and the discovery that white light is a mix of all colours.
Fun fact
As Warden and then Master of the Royal Mint, he personally hunted down counterfeiters.
1706–1749
Paris and Cirey, France
Known for
Argued that the energy of motion grows with , and made the French translation of Newton's Principia that is still used today.
Fun fact
Barred from the Paris café where scientists met, she is said to have come back dressed as a man.
1791–1867
London, England
Known for
Electromagnetic induction, the electric motor and generator, and the idea of invisible field lines filling space.
Fun fact
He left school at 13 to work for a bookbinder, and started the Royal Institution's Christmas Lectures for young people, still held every year.
1831–1879
Edinburgh and Cambridge, UK
Known for
The equations of electromagnetism, the discovery that light is an electromagnetic wave, and the statistics of moving gas molecules.
Fun fact
He made the world's first colour photograph in 1861: a tartan ribbon.
1844–1906
Vienna and Graz, Austria
Known for
Statistical mechanics: explaining heat, pressure and entropy by counting the ways atoms can be arranged.
Fun fact
His formula is carved on his tombstone in Vienna.
1858–1947
Kiel and Berlin, Germany
Known for
Founded quantum theory in 1900 by proposing that energy is emitted in packets, . Nobel Prize 1918.
Fun fact
As a student he was advised not to study physics because almost everything had already been discovered.
1867–1934
Warsaw and Paris
Known for
Pioneered the study of radioactivity, discovered polonium and radium, and coined the word "radioactivity".
Fun fact
The only person to win Nobel Prizes in two different sciences. Her notebooks are still radioactive and are kept in lead-lined boxes.
1868–1921
Harvard College Observatory, USA
Known for
Discovered the period–luminosity law of Cepheid stars, the first reliable way to measure distances to other galaxies.
Fun fact
She was paid about 30 cents an hour as a human "computer". In 1925 a mathematician tried to nominate her for a Nobel Prize, only to learn she had died four years earlier.
1878–1968
Vienna, Berlin and Stockholm
Known for
With Otto Frisch, explained nuclear fission and calculated the enormous energy it releases (1938).
Fun fact
Element 109, meitnerium, is named after her. She refused to work on the atomic bomb.
1879–1955
Bern, Berlin and Princeton
Known for
Special and general relativity, , light quanta (photons) and the proof that atoms are real.
Fun fact
His Nobel Prize (1921) was for the photoelectric effect, not for relativity.
1882–1935
Erlangen and Göttingen, Germany
Known for
Noether's theorem: every symmetry of nature comes with a conserved quantity, like energy or momentum. Also a founder of modern algebra.
Fun fact
For years she taught at Göttingen without pay, with her courses advertised under David Hilbert's name.
1885–1962
Copenhagen, Denmark
Known for
The quantum model of the atom, with electrons on fixed energy levels, and leadership of the Copenhagen school of quantum physics. Nobel Prize 1922.
Fun fact
He was a keen football goalkeeper; his brother Harald won an Olympic silver medal with Denmark in 1908.
1888–1970
Calcutta and Bangalore, India
Known for
The Raman effect: light scattered by molecules changes colour slightly, revealing which molecules are there. Nobel Prize 1930, the first for an Asian scientist.
Fun fact
His research began with a simple question on a ship in 1921: why is the sea blue?
1894–1974
Calcutta and Dhaka
Known for
Bose statistics, the rules for counting identical particles like photons. Particles of this kind are called bosons in his honour.
Fun fact
After a journal rejected his paper, he sent it to Einstein, who translated it into German himself and had it published.
1907–1981
Osaka and Kyoto, Japan
Known for
Predicted the meson in 1935 to explain the strong force that holds the nucleus together. Japan's first Nobel laureate (1949).
Fun fact
A committed pacifist, he signed the 1955 Russell–Einstein Manifesto against nuclear weapons.
1910–1995
Lahore, Cambridge and Chicago
Known for
The Chandrasekhar limit: a dead star heavier than about 1.4 Suns must collapse. Nobel Prize 1983.
Fun fact
He was C. V. Raman's nephew, and NASA's Chandra X-ray Observatory is named after him.
1912–1997
Liuhe (China) and New York
Known for
The 1956 experiment showing that the weak force breaks mirror symmetry, and some of the most precise studies of beta decay ever made.
Fun fact
The 1957 Nobel Prize went to the two theorists who proposed the idea, not to Wu, who proved it. She became known as "the First Lady of Physics".
1918–1988
New York and Pasadena, USA
Known for
Quantum electrodynamics, Feynman diagrams, and the idea that a particle explores every possible path at once. Nobel Prize 1965.
Fun fact
He played the bongo drums, cracked safes for fun at Los Alamos, and explained the Challenger shuttle disaster with a glass of ice water.
1926–1996
Jhang (today Pakistan), London and Trieste
Known for
Unified electromagnetism and the weak force into the electroweak theory. Nobel Prize 1979, the first for a Pakistani scientist.
Fun fact
He founded the International Centre for Theoretical Physics in Trieste (1964) so that scientists from developing countries could do world-class research without having to leave home for good.
1928–2016
Washington, D.C., USA
Known for
Showed that stars in the outskirts of galaxies orbit far too fast, the strongest early evidence for dark matter.
Fun fact
In 1965 she became the first woman officially allowed to observe at Palomar Observatory. There was no women's toilet, so she cut out a paper skirt and stuck it on the door sign.
1942–2018
Oxford and Cambridge, England
Known for
Hawking radiation, and theorems with Roger Penrose showing that general relativity predicts singularities, as at the Big Bang.
Fun fact
He was born on 8 January 1942, exactly 300 years after Galileo died.
born 1943
Lurgan (Northern Ireland) and Cambridge
Known for
As a PhD student in 1967, discovered pulsars: spinning neutron stars that flash like cosmic lighthouses.
Fun fact
The first pulsar was jokingly labelled LGM-1, for "little green men". In 2018 she gave away her entire Breakthrough Prize, 3 million dollars, to help under-represented students become physicists.