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Start swiping — it's freeGeneral relativity predicted that starlight passing near the sun would bend by a precise, measurable amount. Arthur Eddington tested it by photographing stars near the sun during the total eclipse of May 1919, from islands off West Africa and Brazil. The starlight shifted exactly as predicted — and when the Royal Society announced the result, Einstein went from a name physicists knew to a household one overnight.
A hallway one unit wide turns a sharp right angle. What is the largest-area two-dimensional shape — the 'sofa' — that can be slid flat around the corner without ever lifting it? The shape can be any outline at all, not just a rectangle. Mathematicians have chased this simple-sounding question since 1966.
The exact maximal shape is still not fully settled. The best confirmed lower bound is 'Gerver's sofa,' an 18-curve shape of area ≈2.2195 found by Joseph Gerver in 1992; in 2024 Jineon Baek posted a proof, still under review, that Gerver's sofa is in fact optimal. Leo Moser first posed the problem formally in 1966 for the Canadian Mathematical Congress's list of unsolved problems, and the hunt for the exact 'sofa constant' has remained a running joke and a serious open question in geometry ever since.
— Leo Moser, Moving furniture through a hallway (Problem 66-11) — SIAM Review, 1966
Glow, glitter, gleam, glisten, glint, glare: dozens of English words about light or shine start with 'gl-', far more than chance would predict. Linguist J.R. Firth coined the term 'phonestheme' in 1930 for sound clusters like this that carry a recognisable meaning without being a full morpheme - smaller than a word, but not meaningless the way an ordinary phoneme is. English has similar clusters for other senses, like 'sl-' for slippery motion in slide, slick and slither.
Anaximander, working in Miletus in the 6th century BC, proposed that everything originates from 'the apeiron' — a boundless, indefinite substance — rather than from any familiar element or divine will. It's considered the first recorded attempt to explain the natural world through a single, non-mythological principle.
In 1973, a Ruppell's vulture collided with a commercial aircraft over Ivory Coast at 11,300 metres (37,000 feet), knocking out one engine before the plane landed safely. Feather remains confirmed the species, which is rarely seen above 6,000 metres. It survives thin, oxygen-poor air using a specialized hemoglobin that binds oxygen far more efficiently than that of most other birds.