Birthday of François Arago (1786) — Mathematics Predicts the Bright Spot

Dominique François Jean Arago was born in Estagel, France on February 26, 1786. In 1818, Siméon Denis Poisson attempted to ridicule the wave theory of light by deriving an absurd consequence: if light were a wave, a perfectly circular shadow of a disc should have a bright spot exactly at its centre. This seemed so ridiculous that it should disprove the wave theory. Arago immediately went to his laboratory and looked — the bright spot was there. Mathematics had predicted a physical phenomenon that no one had ever seen, purely from equations. Poisson's reductio ad absurdum had become Arago's greatest discovery.