Alan Turing

Overview

Alan Mathison Turing (1912–1954) was a British mathematician and logician. His work touched three areas that matter to AI and computing: a precise account of what a computer can do, codebreaking in the Second World War, and the question of whether machines can think. He was born in London on 23 June 1912. He died at his home in Wilmslow, Cheshire, on 7 June 1954, and the inquest ruled his death a suicide.^[2]

Education and early research

He studied mathematics at King’s College, Cambridge, graduating in 1934 with first-class honours. In 1935 he was elected a Fellow of King’s for a dissertation in probability theory.^[2]

In 1936 he published “On Computable Numbers, with an Application to the Entscheidungsproblem”. The paper described computation through an abstract machine, now called the Turing machine. It has a tape divided into cells, a head that reads and writes one cell at a time, and a fixed table of rules that says what to do next. The model is simple, yet it can express any step-by-step calculation, which is why it is still used to define what can be computed. The paper also described a universal machine that can imitate any other such machine, and it showed that the Entscheidungsproblem, a question posed by David Hilbert, has no general solution.^[1]

He then went to Princeton University, where he earned a PhD in 1938 under Alonzo Church. His thesis was titled “Systems of Logic Based on Ordinals”.^[1]

Wartime codebreaking

From 1939 to 1945 Turing worked at Bletchley Park, Britain’s codebreaking centre, on the German Enigma cipher. He led Hut 8, which handled naval Enigma messages. For this wartime work he was appointed an OBE in 1946.^[2]

Designing computers

From 1945 to 1947 he worked at the National Physical Laboratory, where he designed the Automatic Computing Engine (ACE) and presented the design in February 1946. In 1948 he moved to the University of Manchester as deputy director of the Computing Machine Laboratory.^[2]

Machine intelligence

In 1948 Turing wrote a National Physical Laboratory report titled “Intelligent Machinery”. In October 1950 he published “Computing Machinery and Intelligence” in the philosophy journal Mind. In it he proposed the imitation game, now known as the Turing test. A judge exchanges written messages with a person and a machine, and must work out which is which. The test turns the question “can machines think?” into a question about whether a machine’s conversation can be told apart from a human’s. Those two works made Turing a founding figure of artificial intelligence.^[1][3]

Later work and recognition

Turing was elected a Fellow of the Royal Society in 1951. In 1952 he published “The Chemical Basis of Morphogenesis”, a mathematical theory of how biological patterns form.^[1]

In 1952 he was also prosecuted for a homosexual relationship. He accepted chemical castration, in the form of oestrogen injections, as a condition of probation, and he lost his security clearance.^[1]

Legacy

In 2009 the UK government apologised, with Prime Minister Gordon Brown speaking on its behalf. In 2013 Queen Elizabeth II granted him a royal pardon. The Bank of England’s £50 note, which features his portrait, was first released on 23 June 2021, the anniversary of his birth.^[2]

Turing’s 1936 model is still the standard way of defining computability, and his 1950 question continues to shape debates about machine intelligence. His life also shows how wartime service and later persecution can both become part of a scientist’s public record.