What people found out about the world, from ancient times to today: the firsts, the big questions answered, and the discoveries that changed how we see everything.
A clay tablet from ancient Iraq, now called Plimpton 322, lists sets of whole numbers that make the sides of right-angled triangles, such as 3, 4 and 5. The Babylonians knew this rule more than a thousand years before Pythagoras, whose name it carries today.
An Egyptian scroll, copied from even older texts, describes 48 injuries, from broken bones to head wounds, with how to examine each one and whether to treat it. It contains the first known written description of the brain. Unlike most medicine of its time, it relies on looking carefully, not on magic.
Greek doctors following Hippocrates taught that diseases come from natural causes such as food, water and way of life, not from angry gods. They wrote down what they saw at the bedside, case by case. Doctors still speak of the Hippocratic Oath, a promise to help and not to harm.
In Greece, Democritus taught that everything is made of tiny pieces that cannot be cut, which he called atoms. In India, the Vaisheshika school of Kanada had a similar idea. It was only a guess with no way to test it, but it turned out to be right more than 2,000 years later.
Aristotle gave evidence that the Earth is a ball: its shadow on the Moon during an eclipse is always round, and travelers going south see stars that cannot be seen further north. Educated people have known the Earth is round ever since.
Euclid, a teacher in Alexandria, Egypt, collected the geometry of his time into 13 books. Starting from a few simple statements, he proved hundreds of facts about shapes, each one following from the ones before. It was used to teach math for more than 2,000 years.
Aristarchus of Samos worked out that the Sun is much bigger than the Earth, and suggested that the Earth goes around the Sun, not the other way around. Almost no one agreed with him. The idea came back 1,800 years later with Copernicus.
Archimedes found that an object in water is pushed up by a force equal to the weight of the water it pushes aside. That is why a heavy steel ship floats and a small stone sinks. The story says he worked it out in his bath and ran into the street shouting “Eureka!” (“I have found it!”).
Eratosthenes knew that at noon on the longest day, the Sun shone straight down a well in Syene, Egypt, while in Alexandria, to the north, it cast a short shadow. From the angle of the shadow and the distance between the two cities, he worked out the distance around the Earth, and got close to the real 40,000 km.
In his book the Aryabhatiya, the Indian astronomer Aryabhata wrote that the stars seem to move across the sky because the Earth turns, like the riverbank seems to move to someone in a boat. He also explained eclipses as shadows of the Earth and Moon, not a demon swallowing the Sun, and gave π as 3.1416.
Indian mathematicians had been writing numbers with ten digits and a dot for an empty place. Brahmagupta was the first to treat zero as a number of its own, with rules such as “a number minus itself is zero.” These digits, now called Hindu-Arabic numerals, spread through Baghdad to the whole world.
In Baghdad, Muhammad ibn Musa al-Khwarizmi wrote a book on solving problems with an unknown amount, such as sharing an inheritance. Its title gave us the word “algebra,” and his name gave us “algorithm,” a set of steps for solving a problem, which is what every computer program is.
Many thinkers had said the eye sends out rays to see things. Ibn al-Haytham, working in Cairo, showed with careful experiments that light travels in straight lines from objects into the eye. His Book of Optics insisted that ideas be tested by experiment, the heart of science today.
Ibn Sina, known in Europe as Avicenna, gathered the medicine of Greece, Persia and India into one huge book. It explained that some diseases spread by contact and through water and soil, and set out how to test new medicines. Doctors in Europe and Asia learned from it for 600 years.
Chinese astronomers recorded a “guest star” so bright that it could be seen in daylight for 23 days. Today we know it was a supernova, a giant star blowing itself apart. Its remains, the Crab Nebula, are still spreading out, 6,500 light-years away.
The Chinese scholar Shen Kuo wrote the first known description of the magnetic compass needle, and noticed that it points a little away from true north. This difference, which changes from place to place and year to year, matters for anyone finding their way by compass.
In Kerala, in southern India, Madhava of Sangamagrama found that π can be worked out by adding up an endless series of fractions, getting closer with every step. Europeans found the same series about 250 years later. His school’s work was an early step towards calculus.
Nicolaus Copernicus published a book showing that the planets’ movements make more sense if the Sun is at the center and the Earth is one of the planets going around it. It was printed as he was dying. The idea took more than a century to be accepted.
Andreas Vesalius, a young professor in Italy, studied human bodies himself instead of trusting old books, and found more than 200 mistakes in what doctors had believed for 1,300 years. His book’s detailed drawings set a new standard for medicine.
Tycho Brahe saw a bright new star appear in the constellation Cassiopeia. By measuring carefully, he proved it was far beyond the Moon. People had believed the heavens never changed; this was a supernova, and it showed they were wrong.
William Gilbert made a small ball of magnetic rock and found that a compass needle behaves near it just as it does on Earth. He concluded that the whole Earth is a magnet, which is why compasses work. He also gave us the word “electricity.”
Using Tycho Brahe’s careful measurements of Mars, Johannes Kepler found that planets move around the Sun in ovals, called ellipses, not perfect circles, and go faster when closer to the Sun. His three laws describe the motion of every planet and moon.
Galileo Galilei turned one of the first telescopes to the sky and saw mountains on the Moon, countless stars in the Milky Way, and four moons going around Jupiter. Not everything went around the Earth. He later saw that Venus has phases like the Moon, strong evidence for Copernicus.
John Napier found a way to turn hard multiplications into simple additions using tables of numbers he called logarithms. Astronomers and sailors saved months of work. Slide rules based on them were used by engineers until pocket calculators arrived in the 1970s.
William Harvey worked out how much blood the heart pumps with each beat, and saw it was far more than the body could make from food. The same blood, he realized, must go around and around, pumped by the heart through arteries and back through veins.
René Descartes showed how to place every point on a grid with two numbers, so that lines and curves can be written as equations, and equations drawn as pictures. Every graph you have ever seen uses his idea.
Robert Boyle, with his assistant Robert Hooke, found that if you squeeze a gas into half the space, its pressure doubles. It was one of the first laws of nature found by careful experiment, and Boyle insisted that chemists publish exactly what they did so others could check it.
Looking at a thin slice of cork through his microscope, Robert Hooke saw tiny boxes and called them “cells,” like the small rooms of monks. His book Micrographia, full of huge drawings of fleas, flies and mold, showed people a world too small to see.
Isaac Newton split sunlight into a rainbow with a glass prism, then used a second prism to put the colors back together into white light. White light, he showed, is a mix of all the colors, and a prism only separates them. This is also why rainbows form.
Ole Rømer noticed that Jupiter’s moon Io appears from behind Jupiter a little later when the Earth is farther from Jupiter. The light, he realized, takes longer to reach us. Light is not instant: it travels about 300,000 km every second.
Antonie van Leeuwenhoek, a cloth seller in the Netherlands, made tiny but powerful lenses and looked at pond water. He saw it full of “little animals” swimming about. Later he saw bacteria in the plaque from his own teeth. A whole world of microbes had been there all along.
Gottfried Leibniz published calculus, a way to work out how things change from moment to moment, such as the speed of a falling stone. Isaac Newton had found it too, years before, and the two men argued bitterly about who was first. It is the math behind physics and engineering.
In his book the Principia, Isaac Newton set out three laws of motion and showed that the same force of gravity that makes an apple fall keeps the Moon going around the Earth and the planets around the Sun. For the first time, the heavens and the Earth followed the same rules.
Carl Linnaeus gave every plant and animal a two-part Latin name, such as Homo sapiens for humans and Panthera tigris for the tiger, and sorted them into groups. Scientists all over the world still use his system, so a name means the same thing everywhere.
People in the city of Königsberg wondered if they could walk across all seven of its bridges exactly once. Leonhard Euler proved it was impossible, and in doing so started a new kind of math about networks of points and lines. Maps apps use it to find your route.
Benjamin Franklin suggested that lightning is a giant electric spark. In France, Thomas-François Dalibard proved it by drawing sparks from a tall iron rod during a storm; Franklin is said to have done it with a kite. It led to the lightning rod, which still protects buildings. The experiment was very dangerous.
Edmond Halley used Newton’s laws to work out that comets seen in 1531, 1607 and 1682 were the same one, going around the Sun every 76 years, and predicted it would return in 1758. He died before he could see it, but it came back on Christmas Day, as he had said.
Joseph Priestley heated a red powder and collected a gas in which a candle burned brightly and a mouse lived longer. Carl Scheele in Sweden had found it a little earlier. Antoine Lavoisier named it oxygen and showed that it is what burning and breathing use up.
William Herschel, a musician who built his own telescopes, spotted a faint object that moved slowly against the stars. It was a planet beyond Saturn, the first found since ancient times. Overnight, the known Solar System doubled in size.
James Hutton saw layers of rock tilted upright with flat layers on top of them, and understood that this needed slow wearing away and building up over unimaginably long times. “No vestige of a beginning, no prospect of an end,” he wrote. We now know the Earth is about 4.5 billion years old.
Antoine Lavoisier, helped by Marie-Anne Paulze Lavoisier, weighed everything before and after chemical reactions in sealed containers, and found the total weight never changed. Matter is not created or destroyed, only rearranged. Their careful methods turned chemistry into a modern science.
Georges Cuvier compared the bones of mammoths with those of living elephants and showed they were different animals, no longer alive anywhere. Most people had thought no kind of animal could ever vanish. Extinction, he showed, is real.
Henry Cavendish measured the tiny pull of gravity between lead balls hanging in a shed, a force about as strong as the weight of a grain of sand. From it he worked out how heavy the whole Earth is: about 6 million billion billion kilograms.
William Herschel put thermometers in the colors of sunlight split by a prism. The one just past the red end, where there was no visible light, got the warmest. He had found infrared, invisible light that we feel as heat. TV remotes and night cameras use it.
John Dalton, a teacher in Manchester, showed that chemicals always combine in fixed amounts, and explained it with atoms: each element has its own kind, with its own weight. The ancient idea of atoms became a theory that could be tested.
During a lecture, Hans Christian Ørsted noticed that a compass needle moved when he switched on an electric current in a nearby wire. Electricity and magnetism, thought to be separate, were linked. Every electric motor works because of it.
William Buckland described a giant meat-eating reptile from bones found in England and called it Megalosaurus. In 1842 Richard Owen gave such animals a name of their own: dinosaurs, “terrible lizards.” Mary Anning had already found other giant reptiles of the sea.
Friedrich Wöhler made urea, a chemical found in urine, from simple chemicals in his laboratory. Many people believed that the chemicals of living things could only be made by living things. This was a first step to making medicines and plastics in factories.
Michael Faraday found that moving a magnet near a coil of wire makes an electric current flow. Almost all the electricity we use, including from Nepal’s hydropower plants, is made this way, with magnets spinning inside coils of wire.
Matthias Schleiden found that all plants are made of cells, and Theodor Schwann that animals are too. The cell, they proposed, is the basic unit of life. In 1855 Rudolf Virchow added that every cell comes from another cell.
Louis Agassiz showed that huge boulders scattered across Europe, and scratches on rocks, were left by glaciers far bigger than any today. Large parts of the Earth, he concluded, had once been covered by ice. We now know there have been many ice ages.
Uranus was not moving quite as Newton’s laws predicted. Urbain Le Verrier worked out that an unseen planet must be pulling on it, and where it should be. Johann Galle pointed a telescope there and found Neptune within an hour of starting to look.
In a hospital in Vienna, Ignaz Semmelweis noticed that many more mothers died after giving birth when doctors came straight from examining dead bodies. When he made doctors wash their hands with chlorinated lime, deaths dropped sharply. Many doctors refused to believe him.
James Joule measured how much heat a falling weight makes when it turns a paddle in water, and Hermann von Helmholtz set out the law: energy can change form, from movement to heat to electricity, but the total never changes. It is one of the most important rules in science.
Working for the Great Trigonometrical Survey of India, the mathematician Radhanath Sikdar calculated from measurements taken from far away in India that Peak XV, on the border of Nepal and Tibet, was the highest mountain on Earth. It was announced in 1856 and named after a former head of the survey, George Everest; in Nepal it is Sagarmatha. In 2020 Nepal and China measured its height together as 8,848.86 m.
When cholera killed hundreds of people in one part of London, John Snow marked each death on a map. They clustered around one water pump. He had its handle taken off, and showed that cholera spreads through dirty water, not bad air. Clean water still saves more lives than almost any medicine.
Eunice Foote filled glass jars with different gases and put them in the sun. The jar with carbon dioxide got hottest, and she wrote that more of it in the air would make the Earth warmer. Because she was a woman, a man read her paper for her, and she was forgotten until 2010. John Tyndall’s more detailed experiments followed in 1859.
Charles Darwin published On the Origin of Species, showing how all living things are related and change over many generations: those best suited to their surroundings survive and have more young. Alfred Russel Wallace had found the same idea on his own, and their papers were read together in 1858.
Gustav Kirchhoff and Robert Bunsen found that each element, when heated, gives off its own pattern of colored lines, like a fingerprint. Splitting sunlight with a prism, they found the fingerprints of sodium, iron and other elements in the Sun. We could learn what stars are made of without ever going there.
Quarry workers in Germany found the fossil of Archaeopteryx, an animal with feathers and wings like a bird, but teeth, claws and a long bony tail like a small dinosaur. Coming just after Darwin’s book, it showed one kind of animal changing into another. Birds, we now know, are living dinosaurs.
Louis Pasteur showed with flasks with long, curved necks that broth only goes bad when microbes from the air get into it; they don’t appear from nothing. He went on to argue that microbes cause many diseases. Doctors began to clean wounds and tools, and later to make vaccines.
James Clerk Maxwell wrote down four equations for how electricity and magnetism work together, and found they predict waves that travel at the speed of light. Light, he concluded, is one of these waves, and there must be others. They were found 22 years later: radio waves.
During a total eclipse seen from Guntur, India, Jules Janssen saw a yellow line in the light of the Sun’s edge that matched no known element. Norman Lockyer named it helium, after the Greek word for the Sun. It was found on Earth only 27 years later.
Dmitri Mendeleev arranged the 63 known elements by weight and found that their properties repeat in a pattern. He left gaps, and said they belonged to elements not yet found, even predicting what they would be like. Three were found within 17 years, just as he had said.
Friedrich Miescher found a new substance in the center of white blood cells, which he got from bandages full of pus. He called it nuclein; we call it DNA. No one knew what it was for until 75 years later, when it turned out to carry genes.
Georg Cantor proved that there are more points on a line than there are whole numbers, even though there are endlessly many of both. Some infinities are bigger than others. Many mathematicians attacked the idea, but it is now a basic part of mathematics.
Does a running horse ever have all four hooves off the ground? The eye is too slow to tell. In California, Eadweard Muybridge lined up 12 cameras whose shutters were tripped by threads as a horse galloped past, and the photos settled it: yes, for a moment, with its legs tucked under it, not stretched out as painters had shown. Pictures taken one after another like this led to the first films.
Robert Koch showed that tuberculosis, which then killed one in seven people in Europe, is caused by a bacterium, and set out rules for proving which germ causes which disease. TB can now be cured with medicines, but it is still common, including in Nepal.
Albert Michelson and Edward Morley tried to measure how the Earth’s motion through space changes the speed of light. Physicists expected it to, but it did not, in any direction. Einstein’s relativity later explained why: light’s speed is the same for everyone.
Heinrich Hertz made sparks jump across a gap in one circuit and saw tiny sparks appear in a loop of wire across the room. Invisible waves were carrying the energy, just as Maxwell had predicted. He thought they would be of no use. Within 15 years they carried messages across the Atlantic.
Wilhelm Röntgen saw a screen glowing across his lab when he switched on an electric tube covered in black paper. Invisible rays were passing through it. They also passed through flesh but not bone, and he took a picture of the bones in his wife’s hand. Within months, doctors were using X-rays.
Henri Becquerel left uranium salts on a wrapped photographic plate in a drawer, and found the plate fogged. The uranium was giving off rays all by itself, without any light. Marie Curie named this radioactivity and set out to find where it came from.
Svante Arrhenius spent a year doing calculations by hand and worked out that doubling the carbon dioxide in the air would warm the Earth by several degrees. He thought it would take thousands of years and might be welcome in cold Sweden. It is happening far faster.
J. J. Thomson showed that cathode rays, the glow inside an electric tube, are made of tiny particles with a negative charge, about 2,000 times lighter than the lightest atom. Atoms, believed to be the smallest things, had something smaller inside. Electrons carry the electricity in every wire.
In Secunderabad, India, Ronald Ross found the malaria parasite inside a mosquito that had bitten a sick person. Alphonse Laveran had found the parasite in blood in 1880, but no one knew how it spread. Bed nets and fighting mosquitoes have since cut malaria greatly, including in Nepal’s Terai.
Marie and Pierre Curie processed tonnes of pitchblende, a black ore, to find the source of its strong radioactivity, and found two new elements. They named one polonium, after Marie’s homeland, Poland, and the other radium, which glows in the dark. Marie Curie went on to win two Nobel Prizes.
Martinus Beijerinck squeezed the juice of sick tobacco plants through a filter that stops all bacteria, and it still made healthy plants sick. Something much smaller was causing the disease; Dmitri Ivanovsky had seen the same in 1892. Viruses could not be seen until the electron microscope, in the 1930s.
In the 1860s, a monk named Gregor Mendel crossed thousands of pea plants and found simple rules for how traits like flower color pass from parents to children. Hardly anyone noticed. In 1900 three scientists found the same rules on their own and then found his paper, and the science of genetics began.
To explain the colors of light given off by hot objects, Max Planck had to assume that energy comes in tiny fixed amounts, which he called quanta. He thought it was just a math trick. It turned out to be the first step towards quantum physics.
Karl Landsteiner found that human blood comes in different groups, now called A, B, AB and O, and that mixing the wrong ones makes the blood clump. Once doctors matched blood groups, blood transfusions became safe, and they now save millions of lives every year.
Albert Einstein, a 26-year-old clerk at a patent office, published four papers in one year. They showed that light comes in packets, gave strong evidence that atoms are real, and set out special relativity, including E = mc²: a little mass holds a huge amount of energy.
Richard Oldham studied how earthquake waves travel through the Earth and found that some of them are slowed and bent deep inside. He concluded that Earth has a core different from the rock above it. In 1936 Inge Lehmann showed that the core has a solid inner part.
Fritz Haber found a way to join nitrogen from the air with hydrogen to make ammonia, and Carl Bosch turned it into a factory process. Fertilizer made this way grows the food for about half the people on Earth today. Haber also led Germany’s poison-gas weapons in World War I.
Ernest Rutherford’s team fired tiny particles at a thin sheet of gold. Most went straight through, but a few bounced back, “as if you fired a shell at tissue paper and it came back and hit you.” Atoms, he realized, are mostly empty space, with almost all their mass in a tiny nucleus.
Alfred Wegener noticed that the coasts of Africa and South America fit together like puzzle pieces and have the same fossils and rocks. He proposed that the continents were once joined and have drifted apart. Most geologists rejected the idea for 50 years, until the seafloor discoveries of the 1960s proved him right.
Victor Hess carried instruments up in a balloon to more than 5 km and found that radiation got stronger the higher he went, not weaker. It was coming from space. These cosmic rays led to the discovery of many new particles, including antimatter.
Albert Einstein finished his theory of gravity: heavy things like the Sun bend space and time around them, and other things move along the curves. It explains black holes and the expanding universe, and GPS satellites have to correct for it every day.
During a total eclipse of the Sun, Arthur Eddington’s teams photographed stars near the darkened Sun from Africa and Brazil. The stars appeared slightly shifted, because the Sun’s gravity bent their light by the amount Einstein predicted. Einstein became world famous overnight.
Frederick Banting and Charles Best got insulin from the pancreas of dogs and then cattle. Leonard Thompson, a 14-year-old boy dying of diabetes in Toronto, became the first person to be treated with it, and he recovered. Before insulin, children with type 1 diabetes usually lived only months.
Raymond Dart found the skull of a young child, nearly 3 million years old, in a quarry in South Africa. It had a small, ape-sized brain but teeth and a skull that showed it walked upright. Dart said humans first evolved in Africa; most scientists disagreed for decades, but he was right.
Edwin Hubble measured special flickering stars in the Andromeda “nebula” and showed it is far outside our own Milky Way: a whole separate galaxy. Until then, many astronomers thought the Milky Way was the entire universe. Today we think there are hundreds of billions of galaxies.
In 1925 and 1926, Werner Heisenberg, Erwin Schrödinger and others worked out the math that describes atoms and electrons. In this tiny world, things don’t have exact positions until they are measured, and energy comes in fixed steps. It sounds strange, but every computer chip, laser and LED is built on it. In 1927 its makers met in Brussels for the Solvay Conference, where Einstein and Bohr argued over what it means; 17 of the 29 people in the famous photo of that meeting won Nobel Prizes.
Studying the light of stars, Cecilia Payne showed that they are made almost entirely of hydrogen and helium, the two lightest elements. Astronomers had thought stars were made of much the same things as the Earth, and a senior astronomer told her to call her result “almost certainly not real.” Four years later, he found the same.
In Kolkata, C. V. Raman and K. S. Krishnan found that when light bounces off molecules, a tiny part of it comes out with a slightly different color, which depends on the molecule. It works like a fingerprint for chemicals, and is used to check medicines and even rocks on Mars. India celebrates 28 February as National Science Day.
Alexander Fleming came back from holiday to find mold growing on one of his dishes of bacteria, and the bacteria around the mold had died. The mold made penicillin. It took until the 1940s for other scientists to make it in large amounts, and since then antibiotics have saved many millions of lives.
Edwin Hubble found that distant galaxies are moving away from us, and the farther away they are, the faster they go. Georges Lemaître had already worked out that this would happen if the whole universe were expanding. Run the movie backwards, and everything started very close together: the idea we now call the Big Bang.
Clyde Tombaugh, a 24-year-old farm boy turned astronomer, spotted a dot that moved between two photos of the night sky taken days apart. It was Pluto. The name was suggested by Venetia Burney, an 11-year-old girl in England.
Kurt Gödel proved that in any math system rich enough to do arithmetic, there are true statements that the system can never prove. Mathematicians had hoped to build one complete set of rules for all of math; Gödel showed it is impossible.
Carl Anderson photographed the track of a particle just like an electron but with a positive charge: the positron, the first antimatter ever found. Paul Dirac’s equations had predicted it four years earlier. Hospitals now use positrons in PET scans to look inside the body.
James Chadwick found the neutron, the particle with no electric charge that sits in the center of atoms next to the protons. It explained why atoms of the same element can have different weights, and it opened the way to nuclear power.
Alan Turing described an imaginary machine that reads and writes symbols on a long tape by following simple rules, and showed it could carry out any calculation that can be written as steps. Every computer and phone is a real version of his idea.
Otto Hahn and Fritz Strassmann found that uranium hit by neutrons breaks into lighter elements, and Lise Meitner and Otto Frisch explained why: the nucleus splits in two and releases a huge amount of energy. Only Hahn received the Nobel Prize, one of its best-known omissions.
Under the seats of a sports field in Chicago, Enrico Fermi’s team stacked blocks of graphite and uranium and started the first controlled chain reaction, where each splitting atom splits others. Nuclear power plants work the same way, and so, uncontrolled, do nuclear bombs.
Oswald Avery, Colin MacLeod and Maclyn McCarty showed that DNA taken from one kind of bacteria could pass its traits on to another. Most scientists had expected genes to be made of protein. Now the race was on to find out how DNA does it.
Claude Shannon showed that any message, whether text, sound or pictures, can be turned into 1s and 0s, and worked out how much a noisy wire or radio signal can carry without errors. The internet, mobile phones and video streaming all rest on his math.
Willard Libby found that living things take in a little radioactive carbon, and after they die it slowly disappears: half of it is gone after about 5,700 years. Measuring what is left tells the age of bones, wood and cloth up to about 50,000 years old.
Richard Doll and Austin Bradford Hill compared people with lung cancer to people without, and then followed thousands of British doctors for years. Smokers were many times more likely to get lung cancer. It was one of the first times careful statistics proved a cause of disease.
James Watson and Francis Crick worked out that DNA is two strands twisted around each other, held together by pairs of four “letters,” using X-ray pictures made by Rosalind Franklin. The pairs explain how DNA copies itself: each strand is a pattern for the other.
Stanley Miller filled glass flasks with water and gases thought to be in Earth’s early air, and passed electric sparks through them like lightning. After a week, he found amino acids, the building blocks of proteins. How life itself began is still an open question.
A huge trial with more than a million children showed that Jonas Salk’s vaccine protected against polio, a disease that paralyzed hundreds of thousands of children every year. Polio is now gone from most of the world, including Nepal, which was certified free of it in 2014 along with the rest of South-East Asia.
Clair Patterson measured the lead in a meteorite, left over from when the planets formed, and worked out that the Earth is about 4.55 billion years old, close to today’s figure. While doing it, he found that lead from car fuel was polluting the whole planet, and he fought for years until it was banned.
Neutrinos are so tiny and shy that trillions pass through your body every second without touching anything. Clyde Cowan and Frederick Reines put tanks of water next to a nuclear reactor and finally caught a few, 26 years after Wolfgang Pauli predicted them.
The Soviet Union launched a metal ball 58 cm wide with four long antennas. It circled Earth every 96 minutes, beeping a radio signal anyone could pick up. The Space Age had begun, and the race to the Moon soon followed.
Charles David Keeling began measuring carbon dioxide on top of Mauna Loa, a volcano in Hawai‘i, far from cities. It was about 315 parts per million. The measurements have continued ever since and now show over 420, mostly from burning coal, oil and gas: the clearest record of how people are changing the air.
Jacques Piccard and Don Walsh rode the submersible Trieste to the bottom of the Challenger Deep in the Pacific, nearly 11 km down: deeper than Mount Everest is tall. They spent 20 minutes on the bottom.
Yuri Gagarin flew once around Earth in the Soviet spacecraft Vostok 1, a trip of 108 minutes. Two years later, in 1963, Valentina Tereshkova became the first woman in space.
Fred Vine and Drummond Matthews explained the stripes of magnetism in the rocks of the ocean floor: new seafloor forms in the middle of the ocean and spreads outwards. Within a few years this grew into plate tectonics, the idea that Earth’s surface is made of moving plates. It explains earthquakes, and why the Himalaya keep rising as India pushes into Asia.
Arno Penzias and Robert Wilson could not get rid of a faint hiss in their radio antenna, even after cleaning out pigeon droppings. It came from every direction in the sky: the leftover heat of the Big Bang, cooled to about −270 °C.
Jocelyn Bell Burnell, a graduate student, noticed a radio signal that pulsed every 1.3 seconds. It turned out to be a spinning neutron star, the collapsed core of a dead star, sweeping a beam past Earth. The 1974 Nobel Prize for the discovery went to her supervisor, not to her.
In Cape Town, South Africa, Christiaan Barnard’s team gave Louis Washkansky the heart of a young woman who had died in a car accident. He lived for 18 days. Better medicines to stop the body rejecting a new organ came later, and today many heart transplant patients live for more than ten years.
Frank Borman, Jim Lovell and Bill Anders of Apollo 8 were the first people to leave the Earth’s orbit. They went around the Moon ten times and were the first to see its far side with their own eyes. On Christmas Eve, Anders photographed the Earth rising over the Moon’s horizon; the photo, Earthrise, showed how small and alone our planet is, and is often said to have helped start the movement to protect the environment.
Neil Armstrong and Buzz Aldrin landed on the Moon in Apollo 11 while Michael Collins circled above. They collected 21.5 kg of rock and dust. Twelve people walked on the Moon between 1969 and 1972, and none since.
Vera Rubin and Kent Ford measured how fast stars go around the center of the Andromeda galaxy, and found the outer stars move far too fast for the matter we can see to hold them. There must be much more mass that gives off no light. What this “dark matter” is made of is still one of the biggest unsolved questions in science.
Tu Youyou’s team in China searched old Chinese medicine books and found a 1,600-year-old recipe using sweet wormwood. Following it, cold instead of boiled, they got artemisinin, which kills the malaria parasite. Medicines based on it have saved millions of lives, especially in Africa.
Stanley Cohen and Herbert Boyer cut a gene out of one organism and put it into bacteria, which then copied it. Within a few years, bacteria were making human insulin for people with diabetes, which before came from the pancreas of pigs and cows.
In Ethiopia, Donald Johanson and Tom Gray found about 40% of the skeleton of a small female who lived 3.2 million years ago. She walked upright on two legs but had a brain the size of a chimpanzee’s, showing that walking came before big brains. She was named after a Beatles song playing at the camp.
People had guessed for over a hundred years that any map can be colored with just four colors so that no two neighbors match. Kenneth Appel and Wolfgang Haken proved it, but only by having a computer check almost 2,000 cases. It was the first major proof that no person could check by hand, and some mathematicians didn’t like that.
Scientists in the submersible Alvin went to hot springs on the dark Pacific seafloor, 2.5 km down, expecting bare rock. They found giant tube worms, clams and crabs, living on bacteria that get energy from chemicals in the hot water, not from the Sun. It changed where we look for life on other worlds.
Louise Brown was born in England after Robert Edwards and Patrick Steptoe joined an egg and a sperm in a dish and placed the embryo back in her mother. People called her a “test-tube baby.” More than ten million babies have since been born this way.
The World Health Organization declared that smallpox, which killed about 300 million people in the 20th century alone, was gone from the world, thanks to vaccination teams who tracked down every case. It is still the only human disease ever eradicated.
Luis and Walter Alvarez found a thin layer of clay, rich in the metal iridium, in rocks from the moment the dinosaurs disappeared 66 million years ago. Iridium is rare on Earth but common in asteroids. In 1991 the crater was found, 180 km wide, under Mexico’s Yucatán Peninsula.
Françoise Barré-Sinoussi and Luc Montagnier in Paris found the virus now called HIV. Knowing the cause led to blood tests, and later to medicines that let people with HIV live long, healthy lives, though there is still no cure or vaccine.
British scientists in Antarctica found that the ozone layer, which blocks harmful ultraviolet light from the Sun, was getting much thinner each spring. The cause was gases called CFCs, used in fridges and spray cans. Countries agreed to ban them in 1987, and the hole is slowly healing: a rare global problem that is being fixed.
Harold Kroto, Robert Curl and Richard Smalley found molecules of 60 carbon atoms joined in the shape of a football. Before, the only known pure forms of carbon were diamond and graphite. It started the study of carbon nanomaterials.
Above the blurring air, Hubble could see the universe more sharply than any telescope on the ground. At first its mirror was ground slightly wrong, and astronauts fixed it in 1993. It has since helped measure the age of the universe and photographed galaxies more than 13 billion light-years away.
In 1637 Pierre de Fermat wrote in a book margin that he had a proof too big to fit there. For 358 years no one could find one. Andrew Wiles, who had dreamed of it since he was 10, finally published a proof of more than 100 pages.
Michel Mayor and Didier Queloz found a giant planet circling the star 51 Pegasi every four days, much closer than Mercury is to our Sun. No one had expected planets like that. More than 6,000 planets around other stars have now been found.
Dolly the sheep was born in Scotland from a cell taken from an adult sheep’s udder, so she was a genetic copy of that sheep. Scientists had thought an adult cell could not be turned back into one that builds a whole animal. The discovery led to research on stem cells.
Two teams measuring exploding stars in distant galaxies expected to find the universe’s expansion slowing down. Instead, it is getting faster. Something called “dark energy” seems to make up about 70% of the universe, and no one yet knows what it is.
Three astronauts moved into the International Space Station, built by the USA, Russia, Europe, Japan and Canada. There have been people living in space every day since then.
After 13 years and the work of thousands of scientists, the Human Genome Project finished reading almost all of the 3 billion letters of human DNA. It cost about US$3 billion. Today reading one person’s genome takes about a day and costs a few hundred dollars.
Grigori Perelman, a Russian mathematician, solved a famous 100-year-old problem about the possible shapes of three-dimensional space and posted the proof online. He turned down both the Fields Medal, math’s top prize, and a US$1 million reward.
Andre Geim and Konstantin Novoselov peeled layers off a piece of graphite with sticky tape until they had a sheet of carbon just one atom thick. Graphene is very strong, bendy and carries electricity well. It showed that materials one atom thick can exist and opened a whole new field.
After astronomers found Eris, an icy world beyond Pluto about the same size, they had to decide what a planet is. The International Astronomical Union said a planet must clear its orbit of other objects, which Pluto doesn’t, so the Solar System now has eight planets.
Svante Pääbo’s team read the DNA from Neanderthal bones over 38,000 years old and compared it with people living today. People whose ancestors left Africa carry about 2% Neanderthal DNA, so our ancestors and Neanderthals had children together.
Jennifer Doudna and Emmanuelle Charpentier showed that a system bacteria use to fight viruses can be programmed to cut DNA at any chosen spot. Editing genes became fast and cheap, and labs everywhere began using it, for crops, research and medicine.
At CERN, the Large Hadron Collider, a 27 km ring of magnets under Switzerland and France, found the particle Peter Higgs and others predicted in 1964. It confirms the idea of an invisible field that gives particles their mass, the last missing piece of the Standard Model of particle physics.
Launched in 1977, Voyager 1 passed Jupiter and Saturn and kept going. In 2012 it crossed into interstellar space, outside the bubble of the solar wind, the first human-made object to do so. It is still sending faint signals home.
Europe’s Rosetta spacecraft dropped a washing-machine-sized lander called Philae onto comet 67P, the first landing on a comet. Its harpoons failed and it bounced twice before stopping in a shadow, but it still sent back measurements of the comet’s surface.
After a nine-year journey, NASA’s New Horizons flew past Pluto and found ice mountains and a smooth plain shaped like a heart. The plain is named Tombaugh Regio, after the man who found Pluto in 1930.
Chemists confirmed the discovery of elements 113, 115, 117 and 118, made by smashing atoms together and lasting only fractions of a second. Named nihonium, moscovium, tennessine and oganesson in 2016, they filled the table’s seventh row.
The LIGO detectors in the USA caught a tiny stretch and squeeze of space from two black holes crashing into each other over a billion light-years away. Albert Einstein predicted these ripples a hundred years earlier but thought they would be too small ever to measure.
The Event Horizon Telescope linked radio dishes around the world into one telescope the size of Earth. It photographed the glowing ring around the black hole at the center of the galaxy M87, 55 million light-years away, which is about 6.5 billion times as heavy as the Sun.
A protein’s shape decides what it does, and working it out used to take years per protein. DeepMind’s AlphaFold 2 could predict it from the protein’s recipe in DNA, nearly as accurately as lab experiments, solving a 50-year-old problem. Its predictions now cover over 200 million proteins.
Less than a year after the new coronavirus was found, the United Kingdom approved the first COVID-19 vaccine, which gives the body instructions (mRNA) to make one harmless piece of the virus and learn to fight it. It was the first approved mRNA vaccine, built on decades of work by Katalin Karikó and Drew Weissman.
Ingenuity, a small helicopter carried to Mars by the Perseverance rover, rose 3 meters into the thin Martian air and hovered for about 40 seconds. It was planned to fly 5 times; it flew 72.
The World Health Organization recommended the first vaccine against malaria, which kills about 600,000 people a year, most of them young children in Africa. It protects only partly, but together with bed nets and medicines it saves many lives. A second vaccine was recommended in 2023.
The biggest telescope ever sent to space, with a gold-coated mirror 6.5 meters wide, sees infrared light 1.5 million km from Earth. Its first pictures showed thousands of galaxies in a tiny patch of sky, some of them shining when the universe was young.
NASA crashed the DART spacecraft into Dimorphos, a small moon of an asteroid, on purpose. It shortened its 12-hour orbit by 32 minutes. It was the first test of a way to protect Earth if a dangerous asteroid were ever found coming our way.
At the National Ignition Facility in the USA, 192 lasers squeezed a tiny capsule of hydrogen until its atoms fused, like in the Sun, releasing more energy than the lasers delivered to it. A goal for 60 years, but the lasers themselves used far more energy from the grid, so fusion power plants are still a long way off.
India’s Vikram lander touched down closer to the Moon’s south pole than any spacecraft before it, making India the fourth country to land on the Moon. Its rover Pragyan measured sulfur and other elements in the soil.
The United Kingdom, and then the USA, approved Casgevy, which edits a patient’s own blood stem cells to treat sickle cell disease and beta thalassemia, inherited blood diseases. It was the first approved medicine made with CRISPR, just 11 years after the tool was invented. It still costs about US$2 million per patient.
China’s Chang’e 6 brought back almost 2 kg of rock and soil from the far side of the Moon, the side that always faces away from Earth. All earlier Moon samples came from the near side, which looks quite different.
Hundreds of scientists and volunteers, helped by AI, mapped every one of the roughly 140,000 nerve cells in a fruit fly’s brain and the more than 50 million connections between them. It is the first complete wiring map of an adult animal brain this complex.
2024 was the hottest year on record and the first full year more than 1.5 °C warmer than before factories began burning coal. The Paris climate goal is about the average over many years, so it isn’t broken yet, but a single year crossing the line is a warning.
A baby named KJ was born with a rare disease caused by one wrong letter in his DNA. Doctors in Philadelphia designed a CRISPR treatment to fix that one letter in his liver cells and made it in about six months. It was the first gene-editing treatment made for a single patient.
Reid Wiseman, Victor Glover, Christina Koch and Canada’s Jeremy Hansen flew around the Moon in NASA’s Artemis II, the first people to go there since 1972. They went 406,771 km from Earth, farther than anyone ever before, and splashed down after almost ten days.
An entry makes this timeline when it is a discovery: something seen, measured, or understood for the first time, or a long-standing question answered. Things people built are on the Inventions timeline, and the people themselves on Scientists.
Babylonian tables of right triangles: photo author unknown, Public domain · The oldest book of surgery: Jeff Dahl, Public domain · The Earth is round: JMA/NOAA, CC BY 4.0 · Euclid’s Elements: proving things step by step: Euclid, Public domain · The Canon of Medicine: Coffeetalkh, CC BY-SA 3.0 · A star explodes: NASA, ESA, J. Hester and A. Loll, Public domain · Copernicus: the Earth goes around the Sun: Nicolaus Copernicus, Public domain · The first accurate book of human anatomy: Wikimedia Commons, Public domain · A new star: the sky can change: NASA/CXC, Public domain · The Earth is a giant magnet: Unknown author Unknown author, Public domain · Galileo’s telescope: moons around Jupiter: Galileo Galilei, Public domain · Cells: Robert Hooke (1635–1707), Public domain · Living things too small to see: Photo by Eric Erbe, digital colorization by Christopher Pooley, both of USDA, ARS, EMU., Public domain · Gravity and the laws of motion: The original uploader was Zhaladshar at English Wikisource ., Public domain · A name for every living thing: Carl Linnaeus, Public domain · The seven bridges puzzle: Twotwos, CC BY-SA 4.0 · Halley’s comet comes back: NASA/W. Liller, Public domain · Oxygen: Staff Sgt. Nika Glover, U.S. Air Force, Public domain · A new planet, Uranus: NASA/JPL, CC0 · Weighing the Earth: Henry Cavendish, Public domain · Light we cannot see: Wikimedia Commons, CC BY-SA 3.0 · The first dinosaur is named: Ballista at English Wikipedia, CC BY-SA 3.0 · A map finds the cause of cholera: John Snow, Public domain · Evolution by natural selection: John Murray, Publisher, Public domain · A link between dinosaurs and birds: H. Raab, CC BY-SA 3.0 · The periodic table: The original uploader was Den fjättrade ankan at Swedish Wikipedia ., Public domain · A galloping horse leaves the ground: Eadweard Muybridge, Public domain · Light needs no “ether”: Case Western Reserve University, Public domain · X-rays: Wilhelm Röntgen, Public domain · Radium and polonium: grenadier, CC BY 3.0 · Viruses, smaller than bacteria: Unknown author Unknown author, Public domain · An eclipse proves Einstein right: F. W. Dyson, A. S. Eddington, C. Davidson, Public domain · Quantum mechanics: the rules of the very small: Benjamin Couprie, Public domain · Sputnik, the first artificial satellite: NASA, Public domain · Measuring the carbon dioxide in the air: Oeneis, CC BY-SA 4.0 · The afterglow of the Big Bang: NASA, Public domain · People fly around the Moon and see the Earth rise: NASA, Bill Anders, Public domain · People walk on the Moon: Neil Armstrong, Public domain · Lucy, an early human ancestor: 120, CC BY 2.5 · Life without sunlight: NOAA Okeanos Explorer Program, Galapagos Rift Expedition 2011, Public domain · The Hubble Space Telescope: NASA, crew of STS-125, Public domain · Dolly, the first cloned mammal: Toni Barros, CC BY-SA 2.0 · Landing on a comet: ESA/Rosetta/NAVCAM, CC BY-SA 3.0 igo · The first close look at Pluto: NASA/JHUAPL/SwRI, Public domain · The first picture of a black hole: Event Horizon Telescope, CC BY 4.0 · The first powered flight on another planet: NASA/JPL-Caltech, Public domain · The James Webb Space Telescope’s first pictures: NASA, ESA, CSA, and STScI, Public domain · Pushing an asteroid off course: NASA/Johns Hopkins APL, Public domain · Chandrayaan-3 lands near the Moon’s south pole: ISRO, GODL-India · People travel around the Moon again: NASA, Public domain
