Today's discoveries
Questions the platform found interesting since yesterday
Why do CPUs have cache?
Main memory is so slow relative to a modern processor that without a small, very fast copy of recently used data sitting next to the core, the processor would spend most of its life waiting.
Why are airplane windows round?
Sharp corners concentrate stress into a single point, and at cruising altitude a pressurised cabin pushes hard enough on that point to tear the fuselage open.
Why do batteries degrade?
Every charge cycle drives slow side reactions that permanently consume lithium and thicken an insulating film on the electrodes, so a little capacity is lost each time and never comes back.
Why do bank transfers take days to settle?
The message that money is coming arrives in seconds, but the banks only actually exchange the money in scheduled batches, and the gap between the promise and the exchange is the delay you experience.
Why do photos of propellers look bent?
Most digital cameras do not capture the whole image at one instant — they scan it line by line from top to bottom, so anything moving fast is recorded at a slightly different position in every row.
Why do 23 people give a 50% chance of a shared birthday?
Because you are not comparing 23 birthdays against 365 days — you are comparing 253 pairs of people against each other, and 253 chances at a 1-in-365 event is a coin flip.
Why do bruises change colour?
A bruise is blood spilt under the skin, and the colours are the stages your body's clean-up crew takes it apart in.
Why is cinema popcorn so expensive?
The ticket is priced low on purpose, and the popcorn quietly charges the people who enjoy the film most — because the cinema keeps almost all of the popcorn money and only a fraction of the ticket.
Why does bread go stale faster in the fridge?
Staling is starch slowly re-crystallising rather than bread drying out, and that crystallisation runs fastest at exactly the temperature a fridge holds.
Why do mirrors flip left and right but not up and down?
They do not flip left and right at all — they flip front and back, and you are the one who mentally rotates yourself to face your reflection.
Why is the ocean salty?
Rivers carry dissolved rock into the sea, and then only the water leaves again — evaporation takes the water and leaves the salt behind, over billions of years.
Why do leaves change colour in autumn?
The yellows and oranges were there all summer, hidden under green — and the tree dismantles the green deliberately to recover the nitrogen locked inside it before dropping the leaf.
Why do bridges have expansion joints?
Steel and concrete get longer when they warm up, and a bridge with nowhere to put that extra length will either buckle or tear itself apart.
Why don't antibiotics work on colds?
Antibiotics attack machinery that bacteria have and viruses do not — and a cold is a virus, which has almost no machinery of its own to attack.
Why are arches so strong?
An arch turns a downward load into a sideways squeeze, and stone is enormously strong in squeeze and almost useless in pull.
Why do computers use binary?
Because it is far easier to build a component that reliably tells apart two states than ten, and reliability is what matters when you are switching billions of times a second.
Why do websites need cookies?
The web was designed to forget you between every click, so a cookie is the note the site hands you to carry back, because it has no other way to know you are the same person.
Why do websites have names instead of numbers?
Machines route by number, people remember words, and the domain name system is the enormous distributed directory that translates between the two on every click.
Why do planes fly so high?
Thin air means less drag for the same lift, so an airliner burns far less fuel up high — and the altitude also buys smoother air, weather avoidance and time to react if something fails.
Why can't you divide by zero?
Division asks what you must multiply by to get back where you started, and multiplying by zero destroys that information — so the question either has no answer or has every answer.
Why can't a website tell you your forgotten password?
A well-built site never stored your password in the first place — only a one-way scramble of it, which can be checked against but cannot be turned back.
Why do prices end in .99?
People read prices left to right and stop paying attention early, so £9.99 lands in the mind as 'nine something' rather than 'basically ten'.
Why do tyres have treads?
Not for grip — a smooth tyre grips a dry road better. The grooves exist to give water somewhere to go, so the tyre can still touch the road in the rain.
Why do some countries drive on the left?
Left was the older custom across much of the world, and the countries that changed did so because of specific historical pressures — mainly Napoleon, and later the pull of neighbours and American vehicles.
Why does time seem to speed up as you get older?
Because you judge elapsed time largely by how much you remember of it, and a familiar year lays down far fewer distinct memories than a novel one.
Why is the Ship of Theseus a problem?
Because two perfectly reasonable rules for what makes something the same thing over time — continuity of matter and continuity of form — disagree, and nothing in the world settles which is right.
Why do some notes sound good together?
Notes whose frequencies stand in simple ratios share many of their overtones, so the ear has fewer clashing pairs to resolve — and the rest is what your culture has taught you to expect.
Why does food taste bland on planes?
The cabin is drier than a desert and pressurised to a mountain altitude, which dulls your sense of smell — and constant loud noise suppresses sweetness on top of it.
Why do carbon monoxide alarms matter when smoke alarms already exist?
Carbon monoxide has no smell, no colour and no smoke, and it binds to your blood hundreds of times more readily than oxygen — so nothing you can sense tells you it is there.
Why can a paracetamol overdose be deadly even when you feel fine?
The damage is done by a chemical your liver makes while breaking the drug down, and it destroys liver cells for a day or more before you feel anything at all.
Why do elevators have mirrors?
Mirrors were added because complaints about slow elevators dropped sharply when people had something to look at, which was far cheaper than making the elevators faster.
Why is the sky blue?
Air molecules scatter short-wavelength light far more strongly than long-wavelength light, so blue arrives at your eye from every direction of the sky while red passes straight through.
Why do onions make you cry?
Cutting the onion mixes two chemicals it kept apart, and the reaction makes a volatile gas that turns mildly acidic on the wet surface of your eye.
Why can't you tickle yourself?
Your brain predicts the sensations your own movements will produce and quietly turns them down, so a self-administered tickle arrives already expected and therefore not ticklish.
Why do 'mama' and 'papa' sound similar in almost every language?
Because babies everywhere babble the same easiest sounds first, and adults everywhere hear those sounds as being about them and adopt them as words.
Why don't birds get electrocuted on power lines?
Electricity only flows when there is a voltage difference across something, and a bird touching one wire has both feet at the same voltage, so there is nothing to push current through it.
Why do skyscrapers sway in the wind?
Because building one stiff enough not to sway would be absurdly expensive and no safer — swaying is how a tall building sheds wind energy instead of resisting all of it.
Why do we get a fever when we are ill?
A fever is not the infection overheating you — it is your body deliberately raising its own thermostat, because most of your defences work better warm and most invaders work worse.
Why do AI chatbots make things up?
They are built to produce text that fits, not text that is true, and a fluent invention fits just as well as a fact.
Why do we get goosebumps?
A tiny muscle at the base of every hair yanks the hair upright when you are cold or startled — useful if you are covered in fur, and left over in us because we are not.
Why is 0.1 + 0.2 not exactly 0.3?
One tenth cannot be written exactly in binary, any more than one third can be written exactly in decimal — so the computer stores a very close approximation and the small errors show up when you add them.
Why can't websites read files on your computer?
Browsers run every page inside a deliberately powerless sandbox, because the alternative — letting arbitrary code from strangers touch your filesystem — would make visiting a link as dangerous as running a downloaded program.
Why does Wi-Fi get slower through walls?
Walls absorb and reflect part of the radio signal, and rather than simply arriving quieter, a weakened signal makes your router switch to a slower, more repetitive way of encoding data so it can still be understood.
Why does water make a pan fire worse?
The oil is hotter than boiling water by hundreds of degrees, so the water flashes into steam instantly and blasts the burning oil upward and outward as a fireball.
Why do astronauts float if gravity is still there?
They are not beyond gravity — they are falling, continuously, and so is their spacecraft, so nothing pushes back against them.
Why does hot water sometimes freeze faster than cold water?
Sometimes it does and sometimes it does not — and after sixty years of attempts, nobody has produced an experiment that reliably shows it or a mechanism everyone accepts.
Why do phishing emails still work on careful people?
They do not target carelessness — they target context, arriving at a moment when the request they make is exactly what you were expecting.
Why are rockets launched eastward?
The Earth's surface is already moving east at up to about 1,670 km/h at the equator, and launching in that direction means the rocket starts with that speed for free.