Alan Turing
1912–1954, London, England, Wilmslow, Cheshire, England
British mathematician and logician who defined the abstract computing machine that bears his name, laying the theoretical foundation of computer science, and played a central role in wartime efforts to break German Enigma ciphers.
Alan Turing entered King's College, Cambridge, in 1931 and was elected a fellow there in 1935 for work proving the central limit theorem, which he discovered independently, unaware it was already known. In 1936 he published 'On Computable Numbers, with an Application to the Entscheidungsproblem', introducing an abstract device — now called a Turing machine — that reads and writes symbols on a tape according to a finite table of rules. He used it to prove that no algorithm can decide, for every statement in first-order logic, whether it is logically valid (equivalently, whether it is provable in a sound and complete formal system), settling Hilbert's Entscheidungsproblem in the negative and giving the first rigorous, machine-independent definition of what it means to compute.
After doctoral study at Princeton under Alonzo Church, Turing returned to Britain and, from 1939, worked at the Government Code and Cypher School at Bletchley Park. There he was central to breaking the German Enigma cipher, co-designing the electromechanical Bombe used to decrypt Luftwaffe and, later, naval Enigma traffic — work that shortened the war and was kept secret for decades.
Workplaces: King's College, Cambridge, Government Code and Cypher School, Bletchley Park, University of Manchester
United Kingdom