Lambda in Modern Use

Lambda has one of the more varied modern technical histories of any Greek letter, none of it connected to the ancient ox-goad meaning of its Semitic root lamedh, covered elsewhere in this atlas. Physicists use lowercase lambda for wavelength, one of the most widely taught uses of any Greek letter in an introductory science classroom, and Albert Einstein used an uppercase Lambda for the cosmological constant he introduced into his equations of general relativity in 1917, a term still central to modern cosmology's account of the universe's accelerating expansion. In computer science, the mathematician Alonzo Church chose lambda in the 1930s to name lambda calculus, a formal system for expressing computation through function definition and application that underlies the design of many modern programming languages.

Outside the sciences, the Gay Activists Alliance in New York adopted a stylised lambda as a symbol of the gay rights movement in 1970, reportedly chosen for its use in chemistry to denote a catalyst for change, and the symbol spread through LGBT organisations internationally over the following decade, an entirely modern adoption with no ancient precedent. In the older Milesian numeral system, covered elsewhere in this atlas, lambda holds the value thirty, a role that plays no part in any of these later scientific or political adoptions of the letter.