01
Physics · Entry 001
Why Ice Floats
Most solids sink in their own liquid. Ice is weird.
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TOPICS
Every entry in the field guide. Short, true, sourced.
02
Space · Entry 002
Is Our Universe Inside a Black Hole?
What if everything you know - every star, every planet, every YOU - is sitting inside what we usually call the end of everything?
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Human Body · Entry 003
Why We Get Goosebumps
Hundreds of tiny muscles in your skin are still trying to fluff up fur you don't have.
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Animals · Entry 004
The Bird That Bent a Hook
A crow named Betty looked at a piece of straight garden wire and bent it into a hook to fish food out of a tube. She had never seen a hook before. Her brain does not have a cortex.
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Space · Entry 005
Why the Night Sky Is Dark
Look up at the night sky. Most of it is black. That single fact, by itself, tells you the universe is finite, that it had a beginning, and that it is expanding. It took us two hundred years to realize…
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Animals · Entry 006
The Water Bear That Knows When to Die
A tardigrade is a microscopic eight-legged animal smaller than a comma. It can survive boiling, freezing close to absolute zero, gamma rays a thousand times the dose that would kill a person, and ten days in the open vacuum of…
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Earth · Entry 007
The Woman Who Discovered the Greenhouse Effect
August 1856. In a small front yard in Seneca Falls, New York, a 37-year-old amateur scientist named Eunice Newton Foote sets two brass cylinders side by side in the sun. One holds ordinary air. The other holds carbon dioxide. After…
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Human Body · Entry 008
The Destitute Graduate Student Who Discovered Dreaming
December 1952. In a basement room at the University of Chicago, a 30-year-old graduate student with no money for rent has been studying the slow rolling eye movements of his eight-year-old son as the boy sleeps. For months the recording…
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Space · Entry 009
The Day the Sun Tried to Burn the Telegraph Down
September 1, 1859. In a private observatory south of London, a 33-year-old amateur astronomer is sketching the morning's sunspots on a sheet of paper when, between two of the largest spots, a sudden white-light flash erupts. Eighteen hours later, the…
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Entry 010
The Helix He Folded in Bed With the Flu
At Easter weekend in 1948, in Oxford, England, the 47-year-old chemist Linus Pauling was stuck in bed with a bad cold. He had spent years trying to explain how proteins could fold, using the rules of quantum chemistry and the…
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Entry 011
The Postdoc, the Pottery, and the Levitating Magnet
In April 1986, at IBM's research lab in Rüschlikon, Switzerland, two physicists working on a neglected line of ceramic chemistry made a result that overturned a long-standing limit in superconductivity. J. Georg Bednorz, a 36-year-old postdoctoral researcher, and his supervisor…
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Entry 012
Both Numbers Were True
In the autumn of 1973, the University of California, Berkeley faced a charge of discrimination in graduate admissions. Across the whole university, 44% of male applicants were admitted, compared with 35% of women, a difference large enough to seem real,…
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Entry 013
You Are Invited to See the Earth Turn
On 3 February 1851, in the Meridian Hall of the Paris Observatory, Léon Foucault set a long pendulum swinging and showed something no one had managed to demonstrate directly on the ground before: the Earth turns beneath us. Foucault was…
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Entry 014
The Place on Earth Where No Wind Blows
On the surface of Earth, there is always at least one place where the horizontal wind is zero. It might be the eye of a hurricane, a calm spot in a larger weather system, or a brief stagnation point where…
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Entry 015
Lightning in a Jar
In May 1953, at the University of Chicago, graduate student Stanley Lloyd Miller used a sealed glass apparatus, boiling water, methane, ammonia, hydrogen, and a spark to test an idea about the early Earth. Working under Nobel chemist Harold Clayton…
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Entry 016
The Weight of Light
In 1959, in the basement and tower of Harvard University's Jefferson Physical Laboratory in Cambridge, Massachusetts, physicist Robert Pound and graduate student Glen Rebka tested a prediction from Einstein's 1907 equivalence principle: light should change frequency when it moves in…
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Entry 017
The Needle That Almost No One Saw Move
On the evening of 21 April 1820, in a lecture room at the University of Copenhagen, Danish physicist Hans Christian Ørsted set up a test he had been seeking for years. He had been convinced that electricity and magnetism might…
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Entry 018
why gold is yellow
Gold is not the color most metals would be expected to be. In pure metal form, it has a yellow shine instead of the white-grey look of silver, aluminium, or iron. That difference comes from the way light interacts with…
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Entry 019
The Night Quantum Mechanics Beat Einstein
On December 20, 1982, a three-person physics team at the Institut d'Optique in Orsay, south of Paris, published a four-page paper that changed a long argument about how nature works. The lead scientist was Alain Aspect, working with Jean Dalibard…
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Entry 020
how we know the earth has a solid inner core
On 17 June 1929, a magnitude-7.3 earthquake struck the Buller district of New Zealand's South Island. Seismic stations in Denmark, Greenland, the Faroe Islands, Britain, and Siberia recorded the quake's waves as they travelled through the planet. Most of the…
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Entry 021
how we measure the distance to other galaxies
In 1912 at the Harvard College Observatory in Cambridge, Massachusetts, a deaf woman named Henrietta Swan Leavitt published a small graph that changed astronomy. Working as one of the Harvard Computers, she studied variable stars in the Small Magellanic Cloud,…
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Entry 022
why any map needs only four colors
In October 1852, Francis Guthrie, a 21-year-old recent graduate at University College London, was colouring a map of English counties when he noticed a pattern: four colours seemed to be enough to keep neighbouring regions apart. He told his brother…
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Entry 023
how we know dark energy might be changing
For most of the last 25 years, cosmologists have used a simple rule for dark energy: its strength stays the same everywhere and everywhen. In March 2025, researchers working with the Dark Energy Spectroscopic Instrument, or DESI, at Kitt Peak…
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Entry 024
how bats see in the dark
In 1793, in Pavia, Italy, the naturalist and priest Lazzaro Spallanzani tested how bats move in darkness by covering their eyes, then later by removing them. The bats still flew around his study and into a dark passageway without trouble.…
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Chemistry · Entry 025
how a 100-year-old chemistry rule was broken
In July 2025, a chemistry team at the Okinawa Institute of Science and Technology Graduate University in Japan reported a new ferrocene derivative that behaves in a way textbooks had not allowed for 100 years. Ferrocene, the orange iron compound…
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Technology · Entry 026
How the Transistor Was Invented
On the afternoon of 16 December 1947, two physicists at Bell Labs in New Jersey pressed two strips of gold foil against a sliver of high-purity germanium with a plastic wedge - and amplified an electrical signal a hundredfold. Their…
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Earth · Entry 027
How a Lake Killed 1,746 People in One Night
On the night of 21 August 1986, a crater lake in a remote valley in northwest Cameroon belched a cloud of pure carbon dioxide into the air. The cloud was heavier than the air around it. It hugged the ground.…
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Entry 028
how black holes were first calculated
In November 1915, during the First World War, German astronomer Karl Schwarzschild was serving on the Russian Front when he read Albert Einstein's newly published equations of general relativity. From a field hospital, using a simple notebook, he worked out…
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Entry 029
why Einstein was wrong about quantum mechanics
In 1964, during a sabbatical from CERN, the Irish physicist John Stewart Bell worked on a question raised by Albert Einstein, Boris Podolsky, and Nathan Rosen almost 30 years earlier. Einstein had hoped that quantum mechanics must hide deeper, unseen…
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Entry 030
how the noble gases turned out not to be inert
On 23 March 1962, in a small inorganic-chemistry laboratory in the chemistry building at the University of British Columbia in Vancouver, Canada, chemistry lecturer Neil Bartlett tested a long-held rule about the periodic table. For decades, textbooks had said the…
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Entry 031
how Pluto was discovered
On 18 February 1930, at Lowell Observatory in Flagstaff, Arizona, astronomer Clyde Tombaugh made a discovery that changed how people thought about the outer solar system. Tombaugh was 24 years old and working in a small, cold room upstairs in…
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Entry 032
how we first measured a galaxy's speed
In September 1912, at Lowell Observatory on a mesa outside Flagstaff, Arizona, astronomer Vesto Melvin Slipher pointed a 24-inch telescope at the Andromeda nebula and did something no one had done before. He left a photographic plate in a spectrograph…
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Entry 033
why galaxies spin wrong
Between 1968 and 1970, astronomer Vera Rubin and instrument builder W. Kent Ford Jr. used telescopes at Kitt Peak and Mount Wilson to measure how stars and glowing gas move in the Andromeda Galaxy, the nearest large spiral galaxy to…
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Entry 034
how we counted human chromosomes
For more than 30 years, biology textbooks repeated the same number for human chromosomes: 48. That figure came from work by the American zoologist Theophilus Painter, whose 1921 and 1923 studies were treated as settled fact even though the chromosomes…
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Entry 035
how we discovered the sun went quiet for 70 years
In June 1976, astronomer John A. Eddy published a paper in Science that changed how scientists read the Sun's past. Working at the High Altitude Observatory in Boulder, Colorado, he checked old telescopic notebooks, historical sky reports, and tree-ring records…
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Entry 036
how argon was discovered
In 1892, at the Cavendish Laboratory in Cambridge, the physicist John William Strutt, Lord Rayleigh, noticed that nitrogen from the air was slightly heavier than nitrogen made in the lab. The difference was tiny, about half of one percent, but…
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Entry 037
how a beam of atoms first split in two
In February 1922, at the Physikalisches Institut at the University of Frankfurt, two young physicists, Otto Stern and Walther Gerlach, tested what would happen when a beam of silver atoms passed through a carefully shaped magnetic field. Classical physics said…
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Entry 038
how we proved DNA carries genes
In May 1952, at Cold Spring Harbor Laboratory on Long Island, bacteriophage geneticist Alfred Hershey and his assistant Martha Chase tested a big question in biology with an ordinary kitchen blender. They were studying T2 bacteriophages, viruses that infect E.…
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Entry 039
how we know dark matter is real
On 21 August 2006, astronomer Douglas Clowe and his collaborators at the University of Arizona published a new image of the Bullet Cluster, a pair of galaxy clusters in the constellation Carina about 3.7 billion light-years away. The picture combined…
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Entry 040
how clouds got their names
In December 1802, in east London, a 30-year-old Quaker pharmacist named Luke Howard read a paper to the Askesian Society, a small private club for dissenting scientists. His topic was clouds, which most people had long treated as too changeable…
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Entry 041
how the first woman won the Fields Medal
On 13 August 2014, at the International Congress of Mathematicians in Seoul, the mathematical world gave its highest award, the Fields Medal, to Maryam Mirzakhani. She was 37 years old, a professor at Stanford University, and the first woman and…
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Entry 042
how a 12-year-old proved extinction was real
In the autumn of 1811, on the Dorset coast of England, two children from Lyme Regis helped uncover a fossil that changed what many people thought about life on Earth. Fifteen-year-old Joseph Anning first noticed part of a huge skull…
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Entry 043
how a soccer-ball-shaped molecule was discovered
In early September 1985, a team at Rice University in Houston was trying to imitate carbon chemistry from the atmospheres of red-giant stars. Harold Kroto, Robert Curl, Richard Smalley, graduate students James Heath and Sean O'Brien, and postdoctoral researcher Yuan…
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Entry 044
how the ozone hole was discovered
In May 1985, three scientists working at Halley Bay, a British Antarctic Survey station on the edge of the Brunt Ice Shelf, reported a startling drop in the ozone above Antarctica. Joseph Farman, Brian Gardiner, and Jonathan Shanklin had spent…
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Entry 045
how antimatter was first photographed
On 2 August 1932, on the roof of the Guggenheim Aeronautical Laboratory at the California Institute of Technology in Pasadena, California, an American physics graduate student named Carl David Anderson captured a cloud-chamber photograph that changed particle physics. The track…
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Entry 046
how cosmic rays were discovered on a balloon ride
In August 1912, Austrian physicist Victor Franz Hess climbed into a hydrogen balloon with three gold-leaf electroscopes and drifted over Bohemia to test where the air's mysterious ionisation came from. For years, European scientists had argued that the radiation must…
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Entry 047
how we discovered a third domain of life
For most of the history of biology, scientists sorted life into two great groups: bacteria and everything else. That changed in November 1977, when a short paper from the University of Illinois at Urbana-Champaign argued that the living world actually…
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Entry 048
how we first photographed light turning into matter
They wired two Geiger counters above and below a cloud chamber so it would only photograph when a cosmic ray went through. In one of those photographs, a single gamma ray became matter.
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Entry 049
how the 1572 supernova was discovered
On the evening of 11 November 1572, Tyge Ottesen Brahe - better known as Tycho Brahe - was walking home from supper at Herrevad Abbey in Scania, then a Danish province. Looking up at Cassiopeia, the five-star pattern shaped like…
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Entry 050
how a dream discovered how nerves talk
On the night before Easter in 1921, in Graz, Austria, pharmacologist Otto Loewi woke from a dream with a way to test a question that had bothered him for years: do nerves speak to organs by electricity alone, or by…
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Entry 051
how we discovered the Earth is a magnet
In 1600, in London, English physician William Gilbert published a Latin book called De Magnete after nearly two decades of experiments. At the time, many people thought a compass pointed north because of the Pole Star or a magnetic mountain…
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Entry 052
how matter can be both solid and superfluid
In November 2024, a team at the Institute for Quantum Optics and Quantum Information in Innsbruck reported a long-sought test of a 55-year-old prediction about matter. Using a cloud of erbium atoms chilled to the nanokelvin range, Francesca Ferlaino's group,…
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Entry 053
how a 28-year-old measured Einstein's gravity in a basement
In the winter of 1957-58, Rudolf Ludwig Mößbauer was a 28-year-old physics graduate student working in the basement of the Max Planck Institute for Medical Research in Heidelberg. He was trying to measure the natural width of a gamma-ray line…
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Entry 054
how we discovered electrons spin
Two Dutch graduate students, aged twenty-four and twenty-three, worked out over one afternoon in Leiden that the electron must be spinning. Their advisor mailed the paper to a journal before Hendrik Lorentz could stop them.
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Entry 055
how we first measured the speed of light
In 1676, at the Paris Academy of Sciences, a young Danish astronomer made a bold prediction about a moon of Jupiter named Io. He had been watching Io vanish into Jupiter's shadow like a clockwork signal, and he noticed that…
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Entry 056
how we know galaxies evolve
In 1963, Beatrice Tinsley was a 22-year-old astronomer in Dallas who was told she could not work at the university where her husband had a faculty job. Instead of stopping, she began a long commute to Austin and, over the…
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Entry 057
the curve that is all corners
In 1872, the German mathematician Karl Weierstrass presented a function to the Prussian Academy of Sciences that changed how mathematicians thought about curves. It could be drawn in one unbroken stroke, so it was continuous everywhere, but no matter where…
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Entry 058
how the first metal was pulled out of a salt by electricity
In October 1807, at the Royal Institution in London, a 28-year-old chemist named Humphry Davy used the largest battery in the world to test a stubborn kind of salt called potash. For years, chemists had suspected that potash, soda, lime,…
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Entry 059
how Ramanujan got to Cambridge
In January 1913, a 25-year-old accounts clerk in Madras sent a letter to G. H. Hardy at Cambridge. Srinivasa Ramanujan had no university degree and had spent years teaching himself from a theorem handbook full of results and almost no…
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Entry 060
how the neutron was discovered
In late 1931, in Paris, the chemists Irène Joliot-Curie and Frédéric Joliot found that if they bombarded beryllium with alpha particles, the result was a radiation that could knock protons out of paraffin wax. They thought they had found a…
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Entry 061
why some chemical reactions change color back and forth
In 1950-51, Soviet chemist and biophysicist Boris Pavlovich Belousov was trying to mimic part of the Krebs cycle in a flask. When he mixed citric acid, bromate, and cerium ions in water, the liquid changed color again and again instead…
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Entry 062
why some people become convinced they are dead
A woman came to a Paris clinic in 1880 to explain, calmly, that she had already died.
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Entry 063
how a doctor proved bacteria cause ulcers by drinking them
In July 1984 at Fremantle Hospital in Western Australia, internal-medicine registrar Barry Marshall did something that shocked his field: he drank a broth containing bacteria grown from a patient with chronic gastritis. Marshall and his colleague J. Robin Warren had…
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Entry 064
how we figured out big stars can't die as white dwarfs
In July 1930, 19-year-old Subrahmanyan Chandrasekhar left Bombay on the steamship SS Pilsna, bound for Cambridge by way of Venice. During the 18-day voyage, seated in a deck chair with three books and the equations of stellar structure, he worked…
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Entry 065
how warm superconductors were discovered
In late 1985 and early 1986, at IBM's Zurich Research Laboratory in Rueschlikon, on the south shore of Lake Zurich, two physicists working on a quiet side project found something the field had not expected to see. Johannes Georg Bednorz,…
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Entry 066
how we first saw living things too small to see
In 1676 in Delft, a cloth merchant and city official named Antonie van Leeuwenhoek wrote to the Royal Society in London with a claim that sounded impossible: a drop of water could be crowded with living things too small for…
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Entry 067
how a deep-sea microbe rewrote the tree of life
In 2008, an expedition from the University of Bergen was exploring the Arctic Mid-Ocean Ridge between Greenland and Norway when it found a new hydrothermal vent field 2,300 meters below the surface. The team, led by Rolf Birger Pedersen aboard…
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Entry 068
why resistance comes in exact steps
In February 1980 at the Grenoble high-field laboratory in France, a physicist studying a thin sheet of electrons in a silicon MOSFET found something that should not have happened. He was measuring Hall resistance at about 1 kelvin in a…
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Entry 069
how we know an asteroid killed the dinosaurs
In 1977, geologist Walter Alvarez was studying a thin red clay layer in the Gola del Bottaccione gorge near Gubbio, Italy, where limestone records the change from the Cretaceous to the Paleogene. He and his father, physicist Luis Alvarez, asked…
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Entry 070
how one woman discovered eight comets
On 1 August 1786, in Slough, England, Caroline Lucretia Herschel climbed onto a garden roof with a small telescope and noticed a fuzzy object that did not appear on any star chart. Herschel was 36 years old, working alone while…
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Entry 071
how we figured out why the sun shines
In March 1938, Hans Bethe, a Cornell physicist, was traveling to Washington, D.C., for a conference about the stars when colleagues pressed him to solve a long-standing puzzle: what gives the Sun its energy. At the meeting, held from 17…
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Entry 072
how fluorine was finally isolated
For seventy years, the element blinded and killed the chemists who tried to pull it out of its salt. Then a Frenchman, half-poisoned himself, finally cornered it in a tube cooled to fifty below.
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Entry 073
why some atoms are unusually stable
In the summer of 1948, at the University of Chicago, theoretical physicist Maria Goeppert Mayer sat at her desk studying a puzzling list of numbers. They were 2, 8, 20, 28, 50, 82, and 126 - proton or neutron counts…
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Entry 074
how we found the first planet around another sun
In November 1994, a Swiss astronomy professor in his early fifties and his PhD student began pointing a *193-centimetre telescope* at the *Observatoire de Haute-Provence* in southern France at *142 nearby Sun-like stars*, one per night, to look for tiny…
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Entry 075
how photosynthesis was discovered
In August 1771, in a back-garden laboratory in Leeds, the English minister and chemist Joseph Priestley began with a simple problem: a candle and a mouse both used up the same air in sealed glass jars. The candle went out,…
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Entry 076
a sheet of gold one atom thick
In April 2024, a team at Linköping University in Sweden reported a result that had never been achieved before: a free-standing sheet of gold only one atom thick. The path to it began with a layered ceramic called a MAX…
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Entry 077
how the cosmic microwave background was discovered
In June 1964, at Bell Telephone Laboratories' Crawford Hill site outside Holmdel, New Jersey, two young radio astronomers - Arno Penzias and Robert Wilson - were testing a 20-foot horn-reflector antenna built for microwave studies. They expected to measure radio…
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Math · Entry 078
how Neptune was discovered by math
On 23 September 1846, a letter arrived at the Berlin Observatory with a very unusual instruction: point the telescope at a specific place in Aquarius, and a new planet should appear. The message came from French mathematician Urbain Jean Joseph…
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Entry 079
how a jellyfish grows young again
In the 1990s, marine biologists studying a tiny jellyfish called Turritopsis dohrnii found something unusual in the Mediterranean Sea: when the adult animal was starved, injured, or getting old, it did not simply die. Instead, it sank to the seafloor,…
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Entry 080
how X-rays were discovered
On Friday, 8 November 1895, in a physics laboratory at the Royal University of Würzburg in Bavaria, professor Wilhelm Conrad Röntgen was testing a cathode-ray tube wrapped in black card. He was trying to block visible light, but a screen…
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Entry 081
why galaxies are disappearing forever
On the scale of the universe, disappearance can be slow enough to miss. Because space itself is expanding faster and faster, galaxies outside our local neighborhood are slipping beyond a boundary called the cosmic event horizon. Once they cross it,…
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Entry 082
the shape that always stands back up
Set it down upside down or on its side, and this odd shape will wobble, roll, and right itself without a hidden weight at the bottom. That is what happened with the Gömböc, a solid object built in 2006 by…
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Entry 083
why a diamond is just carbon
In 1772, a French chemist aimed sunlight through a giant double-lens burning glass at a diamond sealed in oxygen and watched the stone disappear. There was no ash, no glittering fragment, only a gas we now call carbon dioxide. Then,…
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Entry 084
how we found out ice once covered europe
On 24 July 1837 in Neuchâtel, Switzerland, the president of the Swiss Society of Natural Sciences surprised his audience by setting aside the fossil fish they expected to hear about and arguing that ice, not floodwater, had reshaped Europe. He…
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Entry 085
why woodpeckers don't get concussions
For decades we thought a woodpecker's skull was a built-in crash helmet. It isn't — and the real reason it survives is stranger.
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Entry 086
why some people see objects change size
In 1955, British psychiatrist John Todd gave a name to a strange neurological problem that can make ordinary things seem to swell, shrink, or drift far away. He called it Alice in Wonderland Syndrome, after the way Lewis Carroll's heroine…
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Entry 087
how little space you need to turn a needle around
In 1917, the Japanese mathematician Sōichi Kakeya asked a simple-sounding question about a needle laid flat on a table: how little space is needed to turn it through every direction, including a full half-turn, without lifting it up? At first…
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Entry 088
how we discovered light we can't see
In 1800, astronomer William Herschel was testing sunlight in England by splitting it with a glass prism and measuring heat at different colors. He placed thermometers across the visible spectrum, from violet to red, and used others outside the light…
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Entry 089
why the number 1 shows up more than any other
If you collect numbers from the real world - river lengths, town populations, stock prices, physical constants - the first digit is not spread evenly. The digit 1 appears first in about a third of cases, while 9 shows up…
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Math · Entry 090
why math can never prove everything
In September 1930, at a mathematics conference in Königsberg, a 24-year-old logician named Kurt Gödel stood before a room of experts and overturned a long-held dream. For decades, leading mathematicians had hoped that arithmetic and all of mathematics could be…
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Entry 091
how a chemist hid two Nobel medals in a jar of acid
In April 1940, German troops occupied Copenhagen and began searching Niels Bohr's Institute. Hidden there were two solid-gold Nobel medals that had been smuggled out of Nazi Germany in the 1930s by two German physicists, because exporting gold from the…
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Entry 092
why old paper turns yellow
An old book page, a newspaper, or a poster from decades ago can change from white to yellow without anyone spilling anything on it. The change is part of the paper itself. Most paper is made from cellulose, which holds…
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Entry 093
how you can drill a square hole
A drill bit normally cuts by spinning in a circle, so it seems built for round holes. In 1917, English-American engineer Harry James Watts patented a different kind of bit shaped from a Reuleaux triangle, a curved form made from…
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Entry 094
why everyone thought Betelgeuse was about to explode
Betelgeuse is the orange-red shoulder star of Orion, one of the brightest stars in the night sky and a known future supernova candidate. From December 2019 to February 2020, it dimmed so much that anyone with good eyes could notice…
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Entry 095
how radioactivity was discovered
He was trying to prove uranium glowed after sunlight. The sun didn't come out, so he put the plate in a drawer. Days later, it was completely exposed.
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Entry 096
how a 2,000-year-old computer was found in a shipwreck
In 1900 and 1901, Greek sponge divers sheltering from a storm near the island of Antikythera came across a Roman-era shipwreck and hauled up statues, amphorae, and a lump of corroded bronze that looked ordinary at first. One diver died…
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Entry 097
why most stomach ulcers are an infection
On a Tuesday morning in 1984 at Fremantle Hospital in Perth, Australia, young physician Barry Marshall did something that shocked his colleagues: after a baseline endoscopy showed his stomach was healthy, he drank a broth full of live bacteria. He…
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