Topic

Science & Tech

150 cards. Tap one to open it in the feed – it continues with this topic from there.

Across topics there are also tags – or search all cards.

Colder than minus 273.15 degrees is impossible.
Temperature measures how much particles move. At −273.15 °C, which is 0 kelvin, thermal motion is at its minimum …
A solid that is more than 99 percent air.
Aerogel is made by removing the liquid from a gel without letting its skeleton collapse. What remains is a silica …
Every banana is slightly radioactive.
Bananas are rich in potassium, and about 0.012 % of it is the radioactive isotope potassium-40. One banana delivers …
No wind turbine can harvest more than 59 percent of the wind.
In 1919 Albert Betz showed that a turbine can't stop the air completely, or it would pile up and nothing would flow …
Counting seconds tells you how far away the storm is.
Sound moves through 20 °C air at about 343 metres per second; light arrives practically instantly. When you see …
Diamond and pencil lead are made of exactly the same stuff.
Both are pure carbon. In diamond, every atom bonds tightly to four neighbours in a three-dimensional lattice, hence the …
On Everest, water boils at about 70 degrees.
Water boils when its vapour pressure matches the air pressure. At sea level that happens at 100 °C. The higher you …
Fold a sheet of paper 42 times and you reach the Moon.
A sheet of paper is 0.1 millimetres thick. Every fold doubles the thickness. After 10 folds it's 10 centimetres, after …
How many piano tuners are in Chicago? Work it out.
Enrico Fermi estimated unknowns by breaking them into quantities he roughly knew: population, households, pianos per …
Planes fly because their wings shove air downward.
A wing is tilted slightly and curved on top. The oncoming air follows the surface and is deflected downward behind the …
23 people in a room, and two probably share a birthday.
With just 23 people, the chance that two share a birthday already exceeds 50 %. With 50 people it's 97 %. Intuition …
High tide happens on the side facing away from the Moon too.
The Moon pulls the near-side water more strongly than Earth's centre, and the centre more strongly than the far-side …
No, old window glass hasn't flowed downward.
A popular myth says glass is a slow liquid, which is why old church windows are thicker at the bottom. In fact, glass …
The gold in your ring was forged when dead stars collided.
Stars fuse elements in their cores only up to iron. Heavier ones like gold, platinum and uranium need extreme floods of …
Without Einstein, your sat-nav would drift 10 km per day.
GPS satellites carry atomic clocks and orbit at about 14,000 km/h, 20,000 km up. Their speed makes the clocks run …
The strongest known material was discovered with sticky tape.
Graphene is a single layer of carbon atoms in a honeycomb lattice, just one atom thick. In 2004, Andre Geim and …
Helium doesn't raise your pitch. Seriously.
With helium in your lungs, your vocal cords vibrate at exactly the same rate, so the pitch stays put. But sound travels …
The sky is blue because air loves to scatter blue.
Air molecules are far smaller than light waves and scatter short wavelengths much more than long ones, proportional to …
An induction hob heats the pan, not the surface.
Beneath the glass sits a copper coil carrying alternating current at roughly 25 to 50 kilohertz. Its magnetic field …
Astronauts on the ISS see 16 sunrises a day.
The International Space Station orbits about 400 kilometres up at roughly 27,600 km/h. One lap takes a little over 90 …
What a kilowatt-hour really is, in muscle power.
One kilowatt-hour is 3.6 million joules. That lifts a one-tonne car about 370 metres, heats roughly 10 litres of water …
Your fridge doesn't make cold. It moves heat.
A compressor squeezes a refrigerant, which gets hot and dumps that heat into your kitchen through the coils on the …
How an LED glows without getting hot.
An incandescent bulb heats a tungsten wire to about 2,500 °C; only around 5 % of the energy becomes light, the rest is …
The sunlight on your skin is eight minutes old.
Light travels through vacuum at exactly 299,792,458 metres per second. That number isn't measured, it's fixed: since …
How your phone battery stores power: as migrating ions.
A lithium-ion battery has two electrodes, graphite and a metal oxide, separated by an electrolyte. While charging …
Ten tonnes of air are resting on your desk.
Standard air pressure at sea level is 101,325 pascals, about 1 kilogram of force per square centimetre. On one square …
The compass has pointed south many times before.
Earth's magnetic field is generated by flowing liquid iron in the outer core. Over geological history it has flipped …
Why the microwave heats your soup but not the plate.
A microwave oven emits radio waves at 2.45 GHz. Water molecules are electric dipoles, so they flip back and forth about …
The Moon drifts 3.8 centimetres farther away every year.
Apollo astronauts left laser reflectors on the Moon. Since 1969, observatories have fired laser pulses at them and …
Three doors, one car: why switching doubles your odds.
A car sits behind one of three doors. You pick one; the host, who knows where the car is, opens another door showing a …
A teaspoon of this weighs more than a mountain range.
When a massive star explodes, its core can collapse into a neutron star: about 1.4 solar masses squeezed into a sphere …
The solar system's tallest mountain is too flat to admire.
Olympus Mons on Mars rises about 22 kilometres, roughly two and a half times the height of Everest. Its base spans …
Why giant movie ants would collapse on the spot.
Double a body's size and its surface area quadruples, but its volume and weight increase eightfold. Legs support weight …
Nobody sees the same rainbow you do.
Sunlight enters raindrops, reflects inside them and fans out into colours on the way out. Red light leaves the drop at …
Why a record is almost always followed by a weaker result.
Every measurement is skill plus chance. An extreme result usually included extreme luck, and luck doesn't repeat. The …
Why road salt melts ice while staying ice cold.
Dissolved particles disrupt the ice crystal lattice, so salt water freezes below 0 °C. Salt on ice dissolves into the …
The first black hole photo needed an Earth-sized telescope.
In 2019 the Event Horizon Telescope revealed the shadow of the black hole in galaxy M87, 55 million light-years away …
Soap cleans because its molecules have two faces.
A soap molecule has a water-loving head and a long fat-loving tail. In water, the tails burrow into grease droplets …
Why solar cells can never use 100 percent of the light.
A silicon cell only uses photons with energy above its band gap; red and infrared photons are wasted. Blue photons …
The Sun loses four million tonnes every second.
In the Sun's core, about 600 million tonnes of hydrogen fuse into helium every second. Roughly 0.7 % of that mass …
In some metals, current flows forever without loss.
In 1911 Heike Kamerlingh Onnes cooled mercury to 4.2 kelvin and watched its electrical resistance drop abruptly to …
A thermos works because there's nothing inside it.
Heat travels three ways: conduction, convection and radiation. A thermos has two walls with a vacuum between them. With …
Why your phone ignores gloves but feels wet fingers.
Modern displays are capacitive touchscreens: beneath the glass lies a grid of transparent electrodes that maintains a …
On Venus, a day lasts longer than a year.
Venus needs 225 Earth days to orbit the Sun but 243 Earth days for a single spin on its axis. It also rotates …
A probe from 1977 is still phoning home.
Voyager 1 launched in September 1977, flew past Jupiter and Saturn, and in 2012 became the first human-made object to …
Water is heaviest at 4 degrees. That saves fish.
Almost every substance gets denser as it cools. Water only does so down to 4 °C. Below that, hydrogen bonds arrange the …
Why your Wi-Fi crawls in the basement.
Wi-Fi mostly uses 2.4 GHz or 5 GHz. The lower frequency has longer waves, passes through walls better and reaches …
How bacteria run evolution in a matter of days.
Take an antibiotic and most bacteria die. A few happen to carry a mutation that protects them. Those survive and …
An animal that simply regrows a lost leg.
The axolotl, a Mexican salamander, regenerates entire limbs, parts of its heart and even sections of its brain, without …
This animal survived exposure to open space.
Tardigrades are mostly under a millimeter long and shrug off almost anything: vacuum, temperatures near -272 °C, brief …
Almost every supermarket banana is a clone.
The Cavendish variety is seedless and sterile; every plant is a cutting from the same genetic line. Until the 1950s the …
How to count to 31 on one hand.
In binary, each digit is worth twice the one before it: 1, 2, 4, 8, 16. The number 1011 means 8 + 0 + 2 + 1 = 11. Your …
Everything on your phone is made of yes and no.
A bit is the smallest unit of information: 0 or 1. Eight bits make a byte, which can hold 256 different values, enough …
The largest animal that ever lived is alive today.
Blue whales reach nearly 30 meters and up to around 190 tonnes, heavier than any known dinosaur. A blue whale heart …
Lightning is five times hotter than the Sun's surface.
A lightning channel heats the air to around 30,000 °C, roughly five times the Sun's surface temperature. The air …
Every cell holds two meters of thread.
Your genome has about 3.1 billion base pairs. Stretched out, the DNA of a single cell would run roughly two meters …
How your browser finds wikipedia.org.
Computers reach each other by numbers, the IP addresses. When you type a name, your device asks a DNS server, which …
Magnitude 7 isn't "a bit stronger" than 6.
The magnitude scale is logarithmic. One step up means ten times the ground motion and about 32 times the energy …
Beneath your feet it's as hot as the Sun's surface.
Earth's inner core is a ball of solid iron and nickel with a radius of about 1,220 kilometers. Its temperature is …
The most famous computer bug was an actual moth.
On September 9, 1947, technicians on the Harvard Mark II found a moth in a relay, taped it into the logbook and wrote …
Evolution wants nothing. It only sorts.
A common mistake: species "develop" traits because they need them. In reality, variants arise at random and the …
This shrimp punches faster than you can blink.
Mantis shrimp fling their clubs forward at over 80 km/h, cracking snail shells and, rarely, even aquarium glass. The …
A shark older than the United States.
Greenland sharks live in the cold North Atlantic and grow less than a centimeter per year. In 2016, researchers …
What the padlock in your address bar actually does.
With HTTPS, your browser and the website first exchange public keys and a certificate that vouches for the site's …
Your video arrives in thousands of separate pieces.
The internet doesn't send files whole; it chops them into packets, usually up to 1,500 bytes each. Every packet carries …
This crow builds hooks to get its lunch.
New Caledonian crows bend twigs into hooks and cut serrated probes from pandanus leaves to fish grubs out of wood. They …
A language model only ever guesses the next word.
Large language models like ChatGPT were trained on billions of sentences to predict the most likely next word fragment. …
You have fewer genes than a rice plant.
Humans carry only about 20,000 protein-coding genes. Before the Human Genome Project, estimates ran to 100,000. Rice …
You owe the microwave oven to a melted chocolate bar.
In 1945, engineer Percy Spencer at Raytheon was working on magnetrons, the transmitters in radar sets. He noticed a …
Every one of your cells houses former bacteria.
Mitochondria, the power plants of your cells, were free-living bacteria about two billion years ago. An ancestral cell …
Why doubling is so hard to picture.
In 1965 Gordon Moore noticed that the number of transistors on a chip doubled at a regular pace, roughly every two …
Most plants have business partners underground.
About 80 percent of land plant species live with mycorrhizal fungi. Fungal threads run through soil far more finely …
How a neural network learns from its mistakes.
A neural network is a mesh of computing nodes linked by millions to billions of numbers, the weights. To learn, it …
An octopus has three hearts and blue blood.
Two hearts push blood through the gills; the third supplies the body. That body heart stops while the animal swims …
Good websites never actually know your password.
Reputable services don't store your password but its hash: a fixed string that can't be reversed into the password. At …
How a leaf builds sugar out of air and light.
Chlorophyll captures light and uses it to split water, releasing the oxygen you breathe. The captured energy squeezes …
Fungi are closer relatives of yours than of plants.
Fungi and animals together form a group called Opisthokonta. Their last common ancestor lived after the plant lineage …
How continents move as fast as your fingernails grow.
Earth's crust is broken into seven large and many smaller plates floating on the slowly flowing mantle. Heat from …
Encryption explained with an open padlock.
Imagine handing out open padlocks that only your key can open. Anyone can lock a box with one, but only you can unlock …
The Sahara fertilizes the Amazon across an entire ocean.
Every year, winds carry many millions of tonnes of Saharan dust across the Atlantic, much of it from the Bodélé …
Oxygen was once Earth's deadliest pollutant.
About 2.4 billion years ago, cyanobacteria began releasing oxygen in bulk. For most life at the time the gas was toxic …
Earth's entire history compressed into one day.
Squeeze Earth's 4.54 billion years into 24 hours. The first life appears around 4 a.m. Multicellular animals don't show …
Humanity's most-manufactured object was invented in 1947.
In December 1947, John Bardeen, Walter Brattain and William Shockley at Bell Labs demonstrated the first working …
Without the greenhouse effect, Earth would be an ice ball.
Sunlight warms the ground, which sends the energy back as infrared radiation. Water vapor, CO₂ and methane let sunlight …
The question "Can machines think?" is 76 years old.
In 1950 Alan Turing proposed a game in his paper "Computing Machinery and Intelligence": a person chats in writing with …
The internet lies on the seafloor, not in space.
The vast majority of intercontinental data traffic runs through fiber-optic cables on the ocean floor, not via …
Dinosaurs aren't extinct. They're chirping outside.
Birds descend from small feathered predatory dinosaurs, the theropods, the group that also included Tyrannosaurus and …
James Watt didn't invent the steam engine.
Steam engines built by Thomas Newcomen were pumping water out of English mines from 1712. But they wasted enormous …
The web is not the internet.
The internet is the road network: cables, routers and protocols that have linked computers since the 1970s. The World …
Weather is mood, climate is personality.
Weather is what happens today: rain, 12 degrees, wind from the west. Climate is the statistics of that, usually …
You are living in the middle of an ice age.
Geologically, an ice age begins whenever permanent ice sheets exist at the poles. The current one, the Quaternary …
A fair-weather cloud weighs as much as a hundred elephants.
A typical cumulus cloud holds about half a gram of water per cubic meter. For a cloud one kilometer on each side, a …
How a second factor makes stolen passwords worthless.
A password is something you know. A second factor is something you have, like your phone with an authenticator app, or …
The siren never changes its pitch. You just hear it differently.
As an ambulance approaches, it squeezes its sound waves together: they arrive more densely and the tone sounds higher. …
Contrails are clouds made of exhaust water.
Burning kerosene produces water vapour. At 10 kilometres altitude it is about minus 50 degrees; the hot vapour cools …
The metal spoon isn't colder than the wooden one.
Both sit at room temperature, about 20 degrees. But your skin doesn't measure temperature – it measures how quickly …
How a QR code still works with a hole in the middle.
A QR code stores not just your data but Reed-Solomon check data too – like the check digits of an IBAN, only far more …
Why nobody knows the weather 30 days out.
In 1961 Edward Lorenz typed 0.506 instead of 0.506127 into his weather simulation. Shortly afterwards the weather …
A kettle is loudest just before it goes quiet.
At the bottom the water reaches 100 degrees while the top is still at 70. Steam bubbles form there, rise into cooler …
How a computer rolls dice when all it can do is calculate.
A computer knows no chance. It starts with a number, the seed, and runs it through a formula; each result becomes the …
For every human there are 2.5 million ants.
A 2022 analysis estimates 20 quadrillion ants on Earth, a 2 followed by 16 zeros. Together they weigh in at around 12 …
No tree can grow taller than about 130 metres.
A tree does not pump water. Evaporation in the leaves draws it up from the roots as one continuous thread. With every …
Jittering pollen proved that atoms exist.
In 1827 the botanist Robert Brown watched pollen particles twitch in water under his microscope, with nothing alive …
The blue glow in a reactor pool comes from particles outrunning light.
Nothing beats light in a vacuum. In water, though, light crawls at only 75 percent of its speed, and charged particles …
Stainless steel doesn't rust because it heals itself.
Steel counts as stainless once it contains at least 10.5 percent chromium. The chromium reacts with oxygen in the air …
Physics still isn't sure why ice is slippery.
The textbook story, that the pressure of a skate blade melts the ice, was refuted in 1939: it would make skating below …
Elephants carry 20 copies of a cancer-guard gene. You have one.
More cells, more divisions, more cancer, that is how it should go. Yet elephants with a hundred times your cell count …
The electrons in your cable crawl slower than a snail.
With one ampere flowing through a 2-millimetre copper wire, the electrons drift on average only 23 micrometres per …
Half the nitrogen in your body came out of a factory.
Since 1913 the Haber-Bosch process has squeezed nitrogen from air at 250 to 350 bar and around 500 °C into ammonia, the …
Sharks existed before trees did.
Sharks have been swimming the seas for around 400 million years. The first organism that counts as a tree …
Every party balloon loses helium to space for good.
Helium is so light that it escapes from the atmosphere into space. Only 5.2 parts per million of air are helium. Fresh …
The yellow in autumn leaves was there all summer.
Yellow and orange carotenoids sit in the leaf all year but are masked by green chlorophyll. In autumn the tree stops …
Properly stored honey keeps indefinitely.
Honey holds only about 18 percent water; the rest is sugar that pulls water out of any microbe. Add a pH of around 3.9 …
How baking powder puffs up a cake, and why baking soda alone can't.
Baking powder is sodium bicarbonate plus a dry acid plus a little starch against moisture. As soon as liquid joins …
How Bluetooth switches channels 1,600 times a second.
Bluetooth uses the 2.4 GHz band, the same as Wi-Fi and microwave ovens. To avoid drowning, it splits the band into 79 …
How a bat catches a mosquito in pitch darkness.
The bat calls in ultrasound, depending on species between 11 and 212 kilohertz, well above your hearing. From the delay …
How your phone turns four timestamps into a location.
GPS satellites orbit at about 20,180 km and constantly broadcast their position and the exact time. Your receiver …
How a nuclear plant makes electricity: with a steam engine.
In the reactor, uranium nuclei split and heat a coolant, usually water. That makes steam, directly or through a heat …
How headphones erase noise by producing more sound.
A microphone on the headphone measures outside noise. A chip calculates what part would reach your ear and plays …
How to soften rock-hard avocados in two days.
Bananas, apples, tomatoes and avocados keep ripening after harvest because they release the gas ethylene, a plant …
How astronomers measure star distances with a 300-million-kilometre ruler.
Hold a thumb up and blink each eye in turn: it jumps against the background. Stars do the same when Earth sits on the …
How your smoke detector sees smoke without having an eye.
Inside sits a dark chamber with an LED and a photodiode set at an angle to each other. In clean air the light beam …
How a ZIP file shrinks without losing a single bit.
Two tricks. First, the algorithm replaces repetitions with a back-reference: 'same as 200 characters ago, 15 characters …
The internet ran out of addresses in 2011.
An IPv4 address has 32 bits, so there are about 4.3 billion of them, for over 8 billion people and even more devices. …
On 19 January 2038 at 03:14:07, some computers will jump to 1901.
Many systems count time as seconds since 1 January 1970 and store the number in a signed 32-bit integer. The largest …
You taste fizz with your 'sour' cells, not with the bubbles.
On the sour-sensing cells of your tongue sits an enzyme, carbonic anhydrase 4. It turns dissolved CO2 into carbonic …
On the hottest pan, a water drop evaporates slowest.
At 150 °C a drop hisses away instantly. From about 193 °C the opposite happens: the underside flashes into steam and …
Bread crust, steak and coffee owe their flavour to the same reaction.
From roughly 140 to 165 °C, amino acids react with sugars into hundreds of new flavour and colour compounds: the …
On Mars, sunsets are blue.
By day the Martian sky is butterscotch, because iron-rich dust scatters the light. At sunset it flips: around the …
Check the units before you trust the number.
Every meaningful physical equation has the same units on both sides: metres stay metres, seconds stay seconds. If your …
Everything is poison. Only the amount matters.
The physician Paracelsus wrote in 1538: all things are poison, and the dose alone makes a thing not a poison. Too much …
A theory that can explain everything explains nothing.
Karl Popper, 1934: a statement is scientific only if some observation could refute it. A thousand white swans don't …
Disturb a system at equilibrium and it pushes back.
Henry Le Chatelier stated in 1884: change the pressure, temperature or concentration of an equilibrium and it shifts so …
No single water molecule is wet.
Wetness only appears when billions of molecules act together. An ant colony builds roads though no ant knows the plan …
A number without a plus-minus isn't a measurement, it's a claim.
Every measurement is uncertain, no matter how expensive the instrument. That is why labs worldwide agree: a result is …
More energy out than in? Look for the hidden source.
Two laws of thermodynamics have never been broken: energy does not arise from nothing, and heat flows by itself only …
Extraordinary claims require extraordinary evidence.
Carl Sagan made the line famous in 1980 in his series 'Cosmos', discussing alleged alien visits. The idea is older …
A '3-nanometre chip' has no part that measures 3 nanometres.
The number once meant the length of the transistor gate. Today it is a marketing name for a new generation with more …
The strongest known biological material is snail teeth.
Limpets rasp algae off rock, and their tiny teeth take it: in 2015 researchers measured tensile strengths of 3.0 to 6.5 …
A litre of osmium weighs 22.6 kilograms.
Osmium is the densest stable element: 22.587 grams per cubic centimetre, twice as dense as lead. Iridium trails by a …
A whip crack is a sonic boom.
The whip does not crack because it hits something. A wave runs from handle to tip, and because the cord keeps getting …
Why propellers look like bent bananas in phone photos.
Your phone's sensor doesn't capture the image all at once but line by line from top to bottom. If something moves fast …
Saturn would float in a bathtub, if the tub were big enough.
Saturn weighs 95 Earths but is so puffed up that its mean density is just 0.687 grams per cubic centimetre, about 30 …
Underwater, sound travels more than four times faster.
In air at 20 °C, sound covers 343 metres per second. In fresh water it is 1,481 m/s, in seawater about 1,500 m/s. The …
The Sun isn't yellow. It's white.
From space or high in the midday sky, the Sun shines white; its surface radiates at about 5,777 kelvin like a white-hot …
No straw on Earth works beyond ten metres in length.
When you suck, you create no pull, only low pressure: the air pressure outside pushes the drink upward. That pressure …
A tsunami in open sea is one metre tall and faster than a jet.
In the deep ocean a tsunami races at over 800 km/h yet stands only about one metre high, with a wavelength of up to 200 …
A jellyfish can turn itself back into a juvenile.
Turritopsis dohrnii is only about 4.5 millimetres across. When injured, starving or old, it rebuilds its cells and …
On Uranus, polar night lasts 42 years.
Uranus rolls around the Sun almost on its side: its axis is tilted by about 98 degrees, versus 23 for Earth. One orbit …
The hottest planet is not the one closest to the Sun.
Mercury orbits nearest the Sun, yet Venus is hotter: 464 °C on average at the surface, even though it receives only a …