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Why a country that's worse at everything still gains from trade: Ricardo's comparative advantage How can a country that is worse at everything still gain from trade? Ricardo's 1817 England-and-Portugal example says the answer is not who is faster, but what… Economics4 min read26 Oct Why bread rises: yeast only inflates the bubbles your kneading put there Yeast doesn't blow bubbles into dough. It only inflates the ones your kneading already folded in. That means the number of bubbles is fixed early, and the… Food Science4 min read25 Oct Why the sky is blue and the sunset red: Rayleigh scattering and the length of the air The sky is blue and the sunset is red, yet the sunlight is the same. Air scatters short blue waves about four times more strongly than long red ones, a… Physics4 min read25 Oct Why predators boom after the prey do: Lotka–Volterra and the Adriatic fish puzzle After the First World War, an Italian biologist noticed something odd in Adriatic fish catches: with less fishing, the share of predators had gone up, not… Biology4 min read24 Oct How a stick's shadow measured the whole Earth: Eratosthenes, a well and 5,000 stadia Two sticks, one shadow and one distance were enough for Eratosthenes to size the whole planet around 240 BC. On the summer solstice the noon Sun shone straight… History4 min read24 Oct Why random dice rolls draw a perfect fractal: the chaos game and the Sierpiński triangle Pick three dots, then keep jumping halfway towards a randomly chosen one. It sounds like it should leave a grey smudge, but after a few thousand jumps a… Maths3 min read24 Oct Why the Moon changes shape: always half lit, and only part of it faces you Ask why the Moon changes shape and most people blame the Earth's shadow. It is a natural guess, and it is wrong: the Moon is half lit by the Sun all the time… Earth & Space4 min read24 Oct Why a sentence can nest forever on paper but not in your head: centre-embedding The rat the cat the dog chased killed ate the malt. It is perfectly grammatical, and almost nobody can read it. English lets you tuck one clause inside another… Language4 min read23 Oct Why you hear a note that isn't there: the missing fundamental Play only 220, 330 and 440 hertz and most people hear a note at 110 hertz — a frequency that is not in the sound at all. This is the missing fundamental: the… Music & Sound5 min read23 Oct Why one flipped bit can be found and fixed: Hamming's error-correcting code A single flipped bit can turn a good file into garbage, yet a machine can find and repair it without ever seeing the original. In 1950 Richard Hamming, tired… Computing4 min read23 Oct Why you stumble naming the ink of a clashing colour word: the Stroop effect Name the ink colour of the word GREEN printed in red and you stumble, even though the rule is trivial. In 1935 John Ridley Stroop timed it: naming the ink of… Mind3 min read23 Oct Why bridges are made of triangles: a square folds, a triangle cannot A square made of four pinned rods folds flat at the slightest push, but a triangle of three rods cannot change shape at all. That one fact is why bridges… Engineering3 min read22 Oct