Birthday of L.E.J. Brouwer (1881) — Fixed Points and Foundations

Luitzen Egbertus Jan Brouwer was born in Overschie, Netherlands on February 27, 1881. He proved one of the most beautiful theorems in all of mathematics: the Brouwer Fixed-Point Theorem. If you take a disc (or a ball, or any convex compact set) and map it continuously to itself, some point must map to itself. Stir a cup of coffee — at least one particle of liquid is in exactly the same position as before you stirred. Crumple a map of a country and lay it inside the original map's borders — some point lies exactly above its true location. Brouwer also founded mathematical intuitionism, arguing that mathematics exists only in the mind and that infinite objects must be constructed, not merely assumed.