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Why the night sky is dark: Olbers' paradox and the light that hasn't arrived yet Go outside and look between the stars: it's dark. That's strange. In an endless, unchanging universe, every line of sight would end on a star, and the whole… Earth & Space4 min read3 Nov Why a microwave leaves cold spots: a standing wave 12.2 cm long, and a chocolate bar that measures the speed of light Microwave ovens fill a metal box with radio waves 12.2 cm long. The waves bounce off the walls and add up into a standing wave, a frozen pattern of hot spots… Food Science5 min read1 Nov Why an elephant doesn't eat 200,000 times more than a mouse: Kleiber's three-quarter law A mouse is 200,000 times lighter than an elephant, yet the elephant burns only about 9,000 times more energy. In 1932 Max Kleiber found that resting metabolic… Biology5 min read31 Oct How astronomers find planets by their shadow: the dip in starlight Most planets around other stars are far too faint to see directly, so astronomers watch the star instead. When a planet crosses its face, a tiny dark disc… Earth & Space4 min read30 Oct Why honey never spoils: it isn't the sugar, it's the missing water Honey is rich, sweet and nutritious, so why don't bacteria and moulds move in? Because microbes need free water, and honey's sugar holds almost all of it… Food Science4 min read29 Oct Why a small ball on a big ball shoots up nine times higher: the two-step bounce Drop a tennis ball on top of a basketball and the small ball can fly far above the height it fell from. Nothing is cheating: it is a two-step bounce. The floor… Physics4 min read28 Oct Why Russians have two blues: how a colour word can speed up your eyes Russian has two basic words for blue, goluboy (light) and siniy (dark), and in a 2007 experiment Russian speakers were about 124 milliseconds faster at telling… Language4 min read27 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 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 Why a dot vanishes when you look away from it: the blind spot where the optic nerve exits Close one eye, stare at a cross, and a dot a hand's width away simply vanishes. That is your blind spot: the place where the optic nerve leaves each eye, with… Mind4 min read19 Oct Why light bends in water: the lifeguard's shortest-time path (Fermat's principle) A lifeguard runs faster than she swims, so the quickest route to a swimmer is not a straight line. It bends at the shoreline, and the bend follows one tidy… Physics4 min read18 Oct Why common letters get short codes in a ZIP file: Huffman coding ASCII spends 8 bits on every letter, whether it is a common e or a rare z. In 1951 a graduate student, David Huffman, found a way to give frequent symbols… Computing4 min read12 Oct