Alan Turing

Early Life

Alan Mathison Turing was born in London on June 23, 1912. He showed an early talent for mathematics and science and later attended Sherborne School. There he became close to fellow pupil Christopher Morcom, who shared his scientific interests. Morcom's sudden death in 1930, when Turing was 17, affected him deeply and led Turing to reflect on questions about mind, matter and consciousness. In 1931 Turing entered King's College, Cambridge, where he studied mathematics.

The Turing Machine

At Cambridge in 1936, Turing imagined a simple theoretical machine — the 'Turing machine' — that could compute anything that is computable. He used it to prove that some mathematical problems cannot be solved by any algorithm, solving Hilbert's Entscheidungsproblem. This concept became the mathematical foundation of all computer science. The same year, he travelled to Princeton to study with Alonzo Church, who had arrived at equivalent results by a different route.

Breaking Enigma

During the Second World War, Turing worked at Bletchley Park, Britain's codebreaking centre, and became a leading member of the team attacking German Naval Enigma. Building on important pre-war breakthroughs by Polish cryptanalysts, Turing developed the initial design for the British Bombe, while Gordon Welchman's diagonal-board modification greatly increased its effectiveness. The Bombe helped codebreakers search rapidly for possible Enigma settings rather than directly reading messages by itself.

Turing also developed Banburismus, a statistical technique used against Naval Enigma, and later devised a statistical method known as 'Turingery' for attacking the German Lorenz teleprinter cipher. The wider codebreaking effort at Bletchley Park provided vital Allied intelligence and is widely credited with helping to shorten the war.

The Turing Test

In his 1950 paper 'Computing Machinery and Intelligence', Turing opened with the question 'Can machines think?' but argued that the question was too ambiguous to answer directly. Instead, he proposed an 'imitation game' in which a human interrogator communicates by text and tries to distinguish a machine from a person. This idea later became known as the Turing Test and remains one of the best-known concepts in the history of artificial intelligence.

After the War

After the war, Turing joined the National Physical Laboratory in 1945, where he designed the Automatic Computing Engine (ACE), an ambitious electronic stored-program computer. In 1948 he moved to the University of Manchester, becoming Deputy Director of the Computing Machine Laboratory and contributing to programming, machine intelligence and the use of the Manchester computers.

Turing also explored computer chess. In 1947 he devised a pioneering chess-playing program at a time when no suitable computer existed to run it, so the method was tested manually. In 1952 he published 'The Chemical Basis of Morphogenesis', proposing that interacting and diffusing chemicals could generate biological patterns. He later investigated phyllotaxis, including patterns found in plants.

A Tragic End and a Royal Pardon

In 1952, Turing was prosecuted because he was gay, at a time when relationships between men were illegal in Britain. He was placed on probation and required to undergo medical treatment. Turing died on June 7, 1954, aged 41. The official inquest ruled his death a suicide, although the exact circumstances have remained debated. He was granted a posthumous royal pardon in 2013. In 2021, the Bank of England issued a £50 note featuring his portrait, and the prestigious A.M. Turing Award is named in his honour.