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1 Universe and astronomy
The History of the Universe and the Big BangThe name “Big Bang” was first uttered on 28 March 1949, on British radio, by an astronomer who did not believe in the theory.
Galaxies and the Milky WayA little over a hundred years ago, nobody knew whether other galaxies existed.
The birth, life and death of starsIn 1925, a young student discovers what stars are made of. Then she writes, in her own thesis, that her result is probably not real.
The Sun and gravityAn astronaut floats in the International Space Station. Why?
The Solar SystemOn 24 August 2006, Pluto ceased to be a planet. It had not moved.
The Earth and the MoonFive mirrors have been placed on the Moon. For more than fifty years, scientists have been firing lasers at them.
The rocky planetsWhich is the hottest planet in the Solar System?
The giant planetsNeptune, the most distant of the planets, is known as a deep-blue ball.
Dwarf planets, asteroids and cometsThere is an object in the solar system that has changed category twice without ever moving a metre.
Black holes and extreme phenomenaThis image went around the world: a blurry orange ring surrounding a black disc. The image of the black hole in the galaxy M87, published on 10 April 2019.
Light and distances in space“The stars we see in the sky may already be dead.” This familiar sentence is false.
Space exploration and satellitesWhen a phone shows its position on a map, it is trusting two theories written in 1905 and 1915.
Reading the sky: telescopes, observatories and astronomies of the worldMore than two thousand years ago, in Babylon, scribes recorded eclipses on clay tablets.
Searching for Life Elsewhere: What We Look At, and What We Think We SeeFor decades, serious astronomers reported seeing lines on Mars — and some saw in them canals dug by a civilisation.
2 Societies and cultures
The Diversity of Peoples and CulturesHow many peoples are there on Earth?
Territories, Sovereignties and GovernmentsHow many countries are there in the world?
Childhood, education and the transmission of knowledgeSchool is neither the only way of passing knowledge from one generation to the next, nor the oldest.
Languages and means of communicationHow many languages are there in the world?
Facing the elements: how humanity sheltersThe igloo is not the home of the Inuit. It is a winter shelter, built in a single region of the Arctic, by a people who have several other kinds.
City and countryside: where does one end and the other begin?A seemingly simple question: exactly what share of humanity lives in cities today?
Transport networksA simple box of cereal may have travelled in a metal crate whose doors nobody opened for the whole journey.
Getting dressed: material, rank, workThe oldest known thread is more than thirty thousand years old. The Scottish costume, believed to be immemorial, is about three hundred.
Agriculture, livestock farming and fishing: between myths and scientific dataThere is no single cradle of agriculture.
Food on the move: how cooking travels, changes and invents itselfAmong familiar cuisines, the most “traditional” one is quite likely to be less than five centuries old.
The economy, trade and systems of exchangeTo obtain what they do not have, humans have devised many means. Only one of them is called “buying”.
Beliefs and philosophiesFrom one end of the world to the other, beliefs give very different answers. The questions, much less so.
The invention of categories and the journeys of objectsIn a record shop or a music app, there is a “world music” section.
Coming together: festivals, games and ritualsIn sport, nothing seems older than the Olympic flame, lit at Olympia and carried by runners all the way to the stadium.
3 History and exchanges
The origins of Homo sapiens: the lesson of Jebel IrhoudIn 1961, Moroccan miners looking for barite uncovered a skull. It is almost complete, which is extremely rare.
The Neolithic revolutionsThere is a story that gets told, then its opposite, then the opposite of the opposite. All three in less than thirty years.
The first states, writing systems and citiesThe oldest written text we know of is neither a poem, nor a prayer, nor a law.
Exchange networks and metallurgyWas iron metallurgy invented in sub-Saharan Africa, or did it arrive there from the north? Nobody can yet say for certain.
Great political entities and philosophiesIn the third century, a prophet of the Persian Empire named Mani drew up a list of the four greatest powers in the world.
The great centres of learning and tradeThe House of Wisdom in Baghdad, the academy where scholars supposedly translated Greek books together, never existed in that form.
Caravan routes and transcontinental exchangeIn 1324, a West African king crosses Egypt on his way to Mecca. He hands out so much gold there that the price of the metal falls in Cairo.
When the continents began to tradeIt is often said that in 1492 a navigator discovered America.
Political revolutions and technical upheavalsIn 1804, after thirteen years of war, Haiti became the first country in the world born of a successful uprising of enslaved people.
Empires, plantations and resistanceOver three hundred and sixty-six years, about 12.5 million people were forcibly embarked from Africa to the Americas.
World conflicts and the crises of the twentieth centuryCommon estimates put the death toll of the Second World War at between 55 and 70 million people.
Decolonisation and the new sovereigntiesIn 2011, a trial in London forced the British government to admit that it held twenty thousand files from thirty-seven former colonies.
Contemporary globalisation and interdependenciesThe label on a T-shirt prompts a simple question: how many people worked on it, and where?
Humanity facing the challenges of the twenty-first centuryThe world’s population passed eight billion on 15 November 2022. The forecast for what comes next has been revised three times in five years.
4 Matter and energy
States of matterHow many states of matter are there?
Atoms and moleculesA little over a hundred years ago, some leading scientists did not believe in atoms.
The periodic table and the elementsIn 1869 and 1870, two chemists arranged the elements in the same way, less than a year apart, without having consulted each other.
Chemical reactions and mixturesSalt poured into water disappears. The iron of a nail that rusts disappears too. Yet these are not at all the same thing.
Nuclear physics and radioactivityChristmas 1938, in Sweden. A woman walks in the snow with her nephew and understands, within a few hours, what will change the course of the century.
Water and its physical propertiesIce floats. Almost nothing else does that.
Forces, motion and gravityA false idea held for more than two thousand years, ever since the philosophers of ancient Greece — and such a reasonable one.
Energy and its transformations“In physics today, we have no knowledge of what energy is.” — Richard Feynman
Heat and ThermodynamicsFrom the eighteenth century to the middle of the nineteenth, heat was believed to be an invisible fluid.
Light and OpticsIn 1666, a young man who had withdrawn to the family farm because of the plague designed an experiment capable of proving him wrong.
Sound and WavesThe same noise can measure 150 dB in water and 90 dB in air. Yet it is exactly the same energy.
Electricity and CircuitsElectrons in a wire advance at barely four tenths of a millimetre per second. Yet the light comes on as soon as you press the switch.
Magnetism and ElectromagnetismNorth is moving, and airports have had to repaint the numbers on their runways.
The Electromagnetic SpectrumOne day in 1800, an astronomer placed a thermometer where there was nothing to see. The mercury began to rise.
5 The animal world
The classification and evolution of animalsHow many species of animals and plants are there on Earth?
Insects, arachnids and myriapodsIf an encyclopaedia followed the number of species, most of its pages would go to six-legged animals.
Molluscs, crustaceans and marine invertebratesNine out of ten marine species do not yet have a name.
Fish and sharksSharks kill a few people a year. Humans kill tens of millions of them.
Amphibians and reptilesFive hundred and one species of frogs, toads and salamanders have declined because of a single fungus. Ninety are probably extinct.
BirdsThere are dinosaurs in our gardens.
Rodents and small mammalsDid rats spread the Black Death? Everyone believes so; yet researchers are still debating it today.
Carnivores: felids, canids, ursidsThe alpha wolf does not exist.
Large herbivores and ungulatesA landscape deprived of its large herbivores does not become wild again. It becomes another landscape, and a poorer one.
Marsupials and monotremesIn 1799, an English scholar took a pair of scissors and cut into the skin of a dead animal to make sure nobody was playing a trick on him.
PrimatesWe are not descended from present-day apes.
Marine mammalsIn 1830, there were about twenty-seven thousand of them in the western South Atlantic. By the mid-1950s, four hundred and fifty remained.
Animal adaptations and defencesThe porcupine did not want its quills, nor the cuttlefish its ink, nor the chameleon its colour.
Social behaviour and migrationFor a very long time, nobody knew where birds went in winter.
6 The plant world
Plant structure and photosynthesisHumans do not see plants.
Reproduction, flowers and seedsIn 1862, Darwin announced the existence of a moth that no one had ever seen.
The fungal kingdom and decompositionA fungus is not a plant. It is closer to us than to a tree.
Trees and how the forest worksThe fungal networks that connect the roots of trees exist. This is not in dispute.
The vegetation of deserts and arid environmentsAntarctica is a desert. Antarctica is not a desert.
Grassland and savanna plantsSome of the world’s great grasslands and savannas have been maintained by humans, using fire, for a very long time.
Mountain and polar floraClimbing a mountain takes you, in a few hours, through what you would cross by travelling thousands of kilometres towards the pole.
Tropical forests and their biodiversityNo, the Amazon does not produce twenty per cent of the planet’s oxygen: three words were lost along the way.
Wetlands, swamps and coastlinesPeatlands cover 3 to 4% of the land surface, but store up to a third of the planet’s soil carbon.
Marine plants and algaeThe ocean produces half of the Earth’s oxygen. But marine life consumes roughly as much.
Cultivated plants and human foodWhat we eat comes from at least eleven places in the world, where communities domesticated plants entirely independently.
Medicinal and useful plantsA plant does not make medicines: it makes defence molecules.
Plant defences and symbiosesA plant cannot run away.
Microorganisms: bacteria, viruses, protistsIt was long repeated that the human body contains ten times more bacteria than human cells.
7 Earth and climate
The internal structure of the EarthThe deepest hole ever dug by humankind goes down twelve kilometres. That is about two thousandths of the distance to the centre of the Earth.
Plate tectonics and continental driftIn 1952, a woman who was not allowed on board ship found, drawing by hand, the proof that the continents move.
Earthquakes and tsunamisThe death toll of an earthquake depends far less on its strength than on the way the buildings were constructed.
Volcanoes and volcanismAn eruption can cool the entire planet for more than a year.
Rocks, minerals and crystalsThe rarity of a stone is not always a fact of nature.
Fossils and the history of rocksIn 2022, a statue was unveiled in Lyme Regis, on the English coast, after a campaign led by an eleven-year-old girl.
The atmosphere and the layers of the skyA man wanted to reassure the public. He compared his measurements for the year with those from twenty years earlier, expecting them to be identical.
Climate, the seasons and climate zonesA cold day tells us nothing about the climate. Neither does a hot year.
Weather and extreme eventsFor a long time, the only honest answer to “is this heatwave due to climate change?” was: nothing can be said about an isolated event.
The water cycle, rivers and oceansThere is no less water on Earth than there was a thousand years ago.
Erosion, ice and the shaping of landscapesThe idea that ice ages follow variations in the Earth’s orbit was set aside for decades: nobody knew how to test it.
Major ecosystems and biomesThe Earth has nine major natural environments. Or fourteen. Or seventeen. Or thirty.
Human impact and climate changeOn climate, there is not one disagreement but two, and they are not of the same kind.
Protecting the planet and the ecological transitionA global problem of the atmosphere has already been solved once. We know why, because we measured it.
8 The human body
The cell, the unit of lifeIn 1951, cells were taken from Henrietta Lacks and then used for research, without either her or her family being consulted.
Skin, hair and nailsShaving does not make hair grow back coarser: this was measured as early as 1928.
The skeleton and the jointsA baby has more bones than an adult.
The muscular systemWhat is the most powerful muscle in the human body?
The nervous system and the spinal cordWhen you pull your hand away from a burning-hot surface, the pain has often not yet been felt.
The brain, memory and thoughtThree very widespread claims about the brain are false, and were corrected long ago.
The five senses and perceptionHow many senses does a human being have?
Breathing and the lungsWhat triggers the urge to breathe is not, first and foremost, a lack of oxygen.
Blood circulation and the heartAround 1242, a physician born near Damascus described the passage of blood through the lungs. Europe would not read his text for nearly seven centuries.
Digestion, nutrition and eliminationEven upside down, swallowed food reaches the stomach.
Diseases, epidemics and smallpoxIn 1721, an enslaved man explains in Boston how to protect oneself from smallpox. The scholar who listens to him is mocked.
The immune system and defence against disease“Boost your natural defences” is an advertising slogan, not a medical term.
Reproduction and geneticsThe story often told about the discovery of DNA is disputed.
Growth, development and sleepHaving trouble falling asleep early and trouble getting up, in adolescence, is not laziness.
9 Numbers, measures and techniques
Counting: number systems around the worldWriting the number twenty is easy. Writing it as a Babylonian scribe did four thousand years ago is much less so.
Zero, large numbers and calculationThere is a digit that counts nothing. And yet, without it, almost nothing works.
Shapes, geometry and symmetryYou need to mark out a right angle in a field, without a set square.
Measuring: lengths, weights, volumesHow long is a metre?
Measuring time: calendars and clocks of the worldA year lasts three hundred and sixty-five days. Except when it lasts three hundred and sixty-six.
Chance, data and large numbersWhen you throw a die, there is no knowing what will come up. Over a thousand throws, the outcome can be predicted with astonishing precision.
The first technical gestures: stone, bone, woodOn the face of it, all you would need to do is strike two stones together.
Fire, furnaces and metallurgyThis whole page comes down to a single question: how hot can you get?
Mastering water: wells, qanats, canals, irrigationIn Western Asia, water flows from the mountain to the village without a single pump, through an underground tunnel dug by hand.
Building: materials, vaults, timber frames, earthquakesA wall stands up on its own. The difficulty is the hole you make in it.
Preserving and processing foodIn the Andes, the frost at night and the sun by day make it possible to keep potatoes for years.
Fibres, textiles, dyes and cordageAsked to name an important invention, people probably think of the wheel, fire or printing.
The media of knowledge: tablets, papyrus, paper, printing pressesWhat do you write on when paper does not exist?
Calculating machines, computing and the digital worldBefore it was a machine, a computer was a person.
The sources for each entry are given in the notes at the end of the page.