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Science

1,604 cards. Each one is a 40-second story with a five-minute read behind it. Page 9 of 27.

481. The US Army searched for a brainwashed prisoner and never found oneBrainwashing entered English in a Miami newspaper in October 1950 and soon dominated Cold War headlines. Yet a 1956 US Army report concluded that exhaustive research by several ag…
482. Empty fishing nets off Ghana pushed hunters deeper into its forestsWhen foreign and local trawlers depleted West African fish stocks, people in Ghana turned to wild animals for protein. More than 30 years of records tie falling fish supplies to s…
483. Cambridge University Press turned down the Oxford English DictionaryIn the Victorian era, lexicographer James Murray pitched Cambridge University Press a vast new dictionary. The press said no, so he took it to Oxford, where it became the Oxford E…
484. Candida albicans reads one word of the genetic code differently from nearly all lifeIn almost every organism, the DNA triplet CUG tells the cell to add the amino acid leucine to a protein. In the common yeast Candida albicans it means serine instead. That quirk m…
485. The chemical once in lava lamps, fire extinguishers and dry shampooFor about 70 years carbon tetrachloride was sold as the safe cleaner, a non-flammable swap for gasoline. It filled fire extinguishers, weighted the wax in lava lamps and even went…
486. Every heartbeat is a 0.8-second relay timed by a built-in delayAt a resting rate of around 70 to 75 beats a minute, one full heartbeat lasts about 0.8 seconds. In that sliver of time four chambers fill, squeeze and seal in strict order, and t…
487. Heart muscle wrings out blood like someone twisting a damp clothLayers of muscle around the heart's left ventricle run at right angles to one another. When they contract together, the chamber shortens, narrows and twists all at once, much like…
488. Your wrist bones harden in a spiral order that can reveal your ageA newborn's wrist contains no true bone, only cartilage. The eight small carpal bones start hardening after birth in a roughly spiral sequence, beginning with the capitate and ham…
489. The world's leading cause of blindness is usually curable with surgeryCataracts, a clouding of the eye's lens, leave around 12 to 15 million people blind worldwide and over 200 million with impaired sight. Replacing the cloudy lens with an artificia…
490. Bornean orangutans build beds with pillows and hold leafy umbrellas in the rainEach night a Bornean orangutan weaves a fresh nest from branches, sometimes adding a roof, a pillow and a blanket of leaves. Youngsters learn the craft by watching their mothers. …
491. Bladder cancer is often first noticed as painless blood in the urineEach year about 500,000 people learn they have bladder cancer, most after spotting blood in their urine without any pain. Tobacco smoking causes roughly half of all cases, and the…
492. The blood-brain barrier keeps over 98 percent of small-molecule drugs out of the brainAround 1900, Paul Ehrlich injected dyes into animals and found they coloured every organ except the brain. The reason is the blood-brain barrier, a lining of tightly sealed cells …
493. Charles Drew scaled up plasma processing from test tubes to mass production in wartimeIn August 1940 New York hospitals began collecting blood so its plasma could be shipped to Britain. Charles Drew, the project's medical supervisor, turned laboratory test-tube met…
494. Your muscles alone may contain 9,000 to 19,000 kilometres of capillariesAugust Krogh once estimated that the capillaries in a heavily muscled human body might stretch about 100,000 kilometres. Later studies, using better density figures and average ad…
495. Biometric systems either confirm who you claim to be or search for who you areA fingerprint scanner can work in two very different ways. In verification mode it compares your print with one stored template to confirm you are who you claim to be; in identifi…
496. Biophysics turns the tools of physics on life, down to single moleculesRichard Feynman once imagined repair machines so tiny that a patient could swallow the doctor. That 1959 idea belongs to biophysics, the field that aims the methods of physics at …
497. A 45-degree slope is a 100 percent grade, and a vertical wall is infiniteGrade is usually quoted as rise over run times 100, which leads to a quirk: a 45-degree hill is a 100 percent grade, and as the slope nears vertical the percentage races toward in…
498. Bees build hexagons because six-sided cells tile a surface using the least wallRegular hexagons fit together with no gaps, three meeting at every corner, and a hexagonal grid keeps its lines as short as possible when filling a large area. That is why honeyco…
499. Euclid never measured distance with numbers, only with matching line segmentsThe straight-line distance between two points is named after Euclid, yet in his Elements distances were not numbers at all. Two segments were simply equal or not. Linking distance…
500. Three turns are always enough to point any object in any directionLeonhard Euler showed that any orientation of a rigid body, however twisted, can be reached with just three rotations about coordinate axes. His three angles remain a standard way…
501. Calculus worked brilliantly for two centuries before anyone could justify itNewton and Leibniz built calculus on infinitesimals, numbers somehow infinitely close to zero, and used it to explain why planets move in ellipses. The philosopher George Berkeley…
502. Proving four colours suffice for any map took 124 years and a computerIn October 1852 Francis Guthrie, colouring a map of English counties, noticed he never needed more than four colours to keep neighbouring counties distinct. His question baffled A…
503. In four dimensions, you can untie any knot in a piece of stringAdd a fourth direction at right angles to the usual three and strange things happen. A knotted string can be slipped free by nudging it along the new axis, while flat surfaces suc…
504. Asking whether a gram is bigger than an hour is physically meaninglessYou can compare metres with feet, or seconds with years, because each pair measures the same kind of thing. But grams and hours belong to different dimensions, so no conversion li…
505. One number tells you what a polynomial's roots look like without solving itThe discriminant is built from a polynomial's coefficients alone, yet it reveals whether roots repeat and whether they are real. For a quadratic it is the familiar b squared minus…
506. A Dutch cocoa tin gave its name to the picture inside a pictureIn 1904 Droste cocoa boxes showed a nurse bearing hot chocolate and a box of Droste cocoa on her tray, which showed the same nurse, carrying the same box, and so on. That endlessl…
507. Measuring the edge of an ellipse needed a whole new family of functionsFinding the length of a circle's rim is easy, but squash it into an ellipse and ordinary formulas fail. The integrals that arise, first studied by Giulio Fagnano and Leonhard Eule…
508. The error function got its name from the mathematics of measurement mistakesIn 1871 the mathematician J. W. L. Glaisher named a stubborn integral the error function, because it answered a practical question from the theory of errors: how likely is a measu…
509. Archimedes wanted a sphere inside a cylinder carved on his tombAround 225 BCE Archimedes proved that a sphere holds exactly two-thirds the volume of the snugly fitting cylinder around it, and has two-thirds of its surface area too. He was so …
510. Cinema screens went wide because Hollywood feared losing audiences to televisionUntil 1953 nearly every sound film was shot in the almost-square Academy ratio. Then television, with a very similar shape, began stealing moviegoers. Studios fought back by stret…
511. A deck of playing cards is a Cartesian product in disguiseTake the 13 card ranks from ace down to two and the four suits, then pair every rank with every suit. You get exactly 52 combinations, one for each card in a standard deck. Mathem…
512. A cathedral is defined by a chair, not by its size or grandeurWhat makes a church a cathedral is not soaring towers or stained glass but a single piece of furniture: the bishop's seat, or cathedra. A tiny chapel holding that throne qualifies…
513. Three chords can harmonise every note of a major scaleWild Thing by The Troggs gets by on just three chords, and it is hardly unusual. In any major key, the chords built on the first, fourth and fifth notes of the scale together cont…
514. Mathematicians measure how sharply a curve bends by watching its tangent turnImagine driving along a winding road at a steady speed and noting how fast your steering direction swings. That rate of turning is exactly what mathematicians call curvature. A st…
515. An affine space is geometry after you forget where the origin isTwo people add arrows on the same map, but each secretly believes a different point is the centre. Their sums disagree, except in one special case: when the weights add up to exac…
516. Your ankle is built like a carpenter's mortise and tenon jointWoodworkers join timber by slotting a tongue into a snug rectangular socket. The human ankle uses the same trick, and it is the only joint in the body to do so. That design explai…
517. Iron is where the fusion inside giant stars finally stopsIron is the most common element on Earth by mass, and the reason lies in dying stars. Fusion in the most massive stars runs up the periodic table until it reaches iron and then st…
518. Astronomers found a methanol cloud 288 million miles across drifting in spaceMethanol, the simplest alcohol, turns up in camping stoves, windscreen fluid and the chemistry of plastics. It also floats between the stars. In 2006 radio astronomers at Jodrell …
519. Make a polymer chain ten times longer and its melt gets over a thousand times thickerPlastic bags, silk, DNA and rubber tyres share one design: enormous molecules built from small units repeated thousands of times. Chain length changes everything. Beyond the point…
520. Elizabeth I paid 300 pounds in gold to learn how to grow saltpetreFor centuries, whoever controlled saltpetre controlled gunpowder. England had no supply of its own, so in 1561, at war with Spain and cut off from imports, Elizabeth I paid a Germ…
521. Most of modern mathematics rests on a handful of rules about setsWhen paradoxes cracked the early theory of sets, mathematicians rebuilt it from a short list of axioms. The result, Zermelo-Fraenkel set theory with the axiom of choice, is now th…
522. Zorn's lemma lets mathematicians finish constructions that never actually endSuppose you are building something step by step, you have not finished after infinitely many steps, and nothing seems to stop you from continuing. A single statement from set theo…
523. Why any two sides of a triangle always outrun the thirdIn any triangle, two sides added together are at least as long as the third. Euclid proved it in Book I of the Elements, and the same rule now helps define what it means to measur…
524. Type theory began as Russell's fix for a paradox and now runs proof softwareImagine a collection of every set that fails to include itself: it ends up both belonging to itself and not. Bertrand Russell's answer to that paradox was a hierarchy of types, an…
525. The 1872 curve that is continuous everywhere yet smooth nowhereMathematicians including Gauss had assumed a continuous curve could only have isolated sharp points. On 18 July 1872 Karl Weierstrass presented a function to the Royal Academy of …
526. Why slope is written m, and why vertical lines have noneSlope is just rise over run: how far a line climbs for each step sideways. Nobody is sure why mathematicians label it m, but the letter appears in English as early as 1844, and th…
527. Smooth is not the same as analytic: the ladder of differentiabilityIn analysis, smoothness counts how many times a function can be differentiated before something breaks. The absolute value function is continuous but has a sharp corner, so it fai…
528. Sobolev spaces: where equations find solutions that classical calculus cannotSome important partial differential equations have no solutions among ordinary differentiable functions, yet do have them once derivatives are understood in a looser, weak sense. …
529. Square numbers hide odd sums, odd divisors and a mental arithmetic trickAdd up the first few odd numbers and you always land on a perfect square: 1 plus 3 plus 5 plus 7 plus 9 makes 25. Squares are also the only positive whole numbers with an odd coun…
530. Stokes' theorem: add up the swirl across a surface to get the circulation at its edgePicture a vector field crossing a surface bounded by a closed loop. Stokes' theorem says the total circulation around that loop equals the sum of all the local rotation, or curl, …
531. From Euclid to Leibniz: the long hunt for the line that just touchesA tangent is the straight line that just touches a curve at one point, heading the same way. Pinning that down took roughly two millennia, from Euclid's circles around 300 BC thro…
532. Taylor's theorem: how a few derivatives let a polynomial impersonate a functionCharles Babbage's difference engine computed sines, cosines and logarithms by working with just the first 7 terms of their Taylor series. The trick rests on Taylor's theorem: near…
533. A test that always says positive catches every case and is uselessImagine a bogus kit that reads positive for everyone. It never misses a sick person, so its sensitivity is a perfect 100 percent. It also flags every healthy person. That thought …
534. Add two sine waves of the same pitch and you always get anotherMix two sine waves that share a frequency, whatever their sizes or timing, and the result is still a clean sine wave at that frequency. No other periodic wave shape behaves this w…
535. Matrix calculus has two rival spelling systems, and mixing them breaks answersMatrix calculus bundles hundreds of partial derivatives into tidy vectors and matrices, which is why statisticians and machine learning engineers lean on it. The catch: practition…
536. If your average speed was 60, at some instant you were doing exactly 60Drive smoothly from one town to another and, somewhere along the way, your speedometer must have shown precisely your average speed for the trip. That everyday certainty is the me…
537. Fermat's Last Theorem fell because two distant branches of mathematics turned out to matchAndrew Wiles did not attack Fermat's Last Theorem head-on. He proved a large part of a claim that elliptic curves, a kind of cubic equation, always correspond to highly symmetric …
538. Non-decreasing and not decreasing mean very different thingsIn mathematics, a function that never goes down is called non-decreasing, and it is allowed to sit flat for a while. A function that is merely not decreasing could zigzag up and d…
539. The nautilus steers its depth with a shell full of sealed chambersA nautilus lives inside a coiled shell that it keeps extending, sealing off each outgrown room behind a wall. A hatchling has about 4 chambers; an adult can have 30 or more, threa…
540. Why Link could never carry more than 255 rupeesIn the original Legend of Zelda, the hero's wallet capped out at 255 rupees, and Pac-Man breaks down at level 256. Neither number is arbitrary. One byte of 8 bits holds exactly 25…

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