Browse

Why two almost-in-tune notes throb, and how tuners use the wobble Play two notes that are almost in tune and you hear one note that swells and fades: wah-wah-wah. Neither string is wobbling. The throb, called a beat, appears… Music & Sound5 min read27 Sep How one extra digit on your bank card catches your typos The last digit of your bank card number isn't part of your account. It's a check digit, computed from the other fifteen by a recipe an IBM engineer patented in… Computing5 min read27 Sep Why one more candle lights a dark room but vanishes in a bright one Add one candle to a dark room and everything changes. Add one to a room with a hundred and nobody notices. Your senses don't measure differences in amounts… Mind5 min read27 Sep Hang a chain, flip it upside down, and you have the perfect arch In 1675 Robert Hooke hid a building secret in an anagram. Decoded after his death, it said: as hangs a flexible cable, so, inverted, stand the touching pieces… Engineering5 min read27 Sep The winner's curse: why whoever wins an auction has usually overpaid In 1983, MBA students bid on jars of coins worth exactly $8. On average they underestimated the jars, guessing $5.13. Yet the winning bids averaged $10.01, so… Economics5 min read27 Sep Stale bread isn't dry: its starch has quietly turned back into crystals Bread left on the counter turns hard and crumbly, and it looks like it dried out. It mostly didn't. In 1852 Jean-Baptiste Boussingault showed that bread sealed… Food Science4 min read27 Sep Why the sky is blue and sunsets are red: it's the same light The blue sky and the red sunset are the same effect, seen from two angles. Air molecules scatter short, blue wavelengths far more than long, red ones: about… Physics4 min read27 Sep Autumn leaves don't turn yellow. The yellow was there all summer Autumn leaves don't really turn yellow. The yellow carotenoids were in the leaf all summer, hidden under green chlorophyll. In autumn the tree dismantles its… Biology5 min read27 Sep How Eratosthenes measured the whole Earth with a stick and a shadow Around 240 BC, Eratosthenes, head of the Library of Alexandria, measured the size of the whole Earth with a stick and a shadow. At noon on midsummer, sticks in… History4 min read27 Sep Why seven shuffles are enough to mix a deck of cards A 52-card deck can be put in about 8 × 10^67 different orders, yet a few quick shuffles leave a lot of the old order behind. In 1992 Dave Bayer and Persi… Maths4 min read27 Sep Why Mars sometimes walks backwards across the sky Every 26 months or so, Mars slows down, stops, and drifts backwards against the stars for a couple of months before carrying on. Ancient astronomers built… Earth & Space4 min read27 Sep Why the most common words are the shortest: Zipf's two laws of language Count the words in almost any long text and a strange pattern appears: the most common word turns up about twice as often as the second, three times as often… Language5 min read26 Sep