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Alan Turing

1912–1954 · British

Computing — theoretical computer science and artificial intelligence

Alan Turing was an English mathematician whose 1936 paper on computable numbers defined the abstract Turing machine and founded the theory of computation. At Bletchley Park in the Second World War he led the attack on German naval Enigma and designed the Bombe codebreaking machine, and afterwards he designed the ACE computer, proposed the Turing test for machine intelligence and pioneered mathematical biology. Prosecuted in 1952 for homosexual acts, he died of cyanide poisoning in 1954; he received a posthumous royal pardon in 2013 and appears on the Bank of England £50 note.

How to spot them

▸Turing machine; 'On Computable Numbers'; the Entscheidungsproblem; the halting problem
▸Bletchley Park, Hut 8, the Bombe and naval Enigma
▸The Turing test or 'imitation game'; 'Can machines think?'
▸Morphogenesis; the ACE at the National Physical Laboratory; Manchester
▸Royal pardon 2013; £50 note 2021; The Imitation Game (2014) with Benedict Cumberbatch

Key discoveries & works

On Computable Numbers, with an Application to the Entscheidungsproblem (1936)

Defined the universal computing machine and showed some problems cannot be decided by any algorithm

The Bombe (electromechanical Enigma-breaking machine) (1939–40)

Designed at Bletchley Park, building on the Polish bomba, with improvements by Gordon Welchman

Computing Machinery and Intelligence (1950)

Published in Mind; asks 'Can machines think?' and proposes the imitation game

Automatic Computing Engine (ACE) design (1945–46)

Detailed design for a stored-program computer at the National Physical Laboratory

The Chemical Basis of Morphogenesis (1952)

Explained biological patterns such as spots and stripes by reaction–diffusion

Key ideas

Universal Turing machine: one machine can simulate any other, the theoretical basis of the stored-program computer
Undecidability: no general algorithm can decide whether an arbitrary program halts (the halting problem, as later formulated)
Church–Turing thesis: anything effectively calculable can be computed by a Turing machine
Turing test: a machine counts as thinking if its conversation cannot be told apart from a human's

Quick-fire facts

•Born in Maida Vale, London; educated at Sherborne School and King's College, Cambridge
•PhD from Princeton (1938) under Alonzo Church
•Head of Hut 8 at Bletchley Park, responsible for German naval Enigma
•Appointed OBE in 1946 and elected a Fellow of the Royal Society in 1951
•A fine long-distance runner, he ran a marathon in 2 hours 46 minutes in 1947
•Convicted of gross indecency in 1952 and subjected to chemical castration; died at Wilmslow in June 1954, the inquest ruling suicide
•Gordon Brown made a government apology in 2009; he received a royal pardon in 2013, and the 2017 'Alan Turing law' pardoned others
•The ACM's Turing Award, often called the Nobel Prize of computing, has been given since 1966
•His portrait went on the Bank of England £50 note in June 2021, released on his birthday, 23 June
•Biography Alan Turing: The Enigma by Andrew Hodges; play Breaking the Code by Hugh Whitemore

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Sources

MacTutor History of Mathematics, University of St Andrews — Alan Mathison Turing
Andrew Hodges — Alan Turing: The Enigma