Alan Turing

In simple terms

Alan Turing was a British mathematician who, in 1936, described an imaginary machine that could compute anything any computer could ever compute. That idea — the Turing machine — became the foundation of computer science. He also led the team that broke the German Enigma cipher during World War II.

More detail

Turing’s main contributions:

• 1936 — “On Computable Numbers”: introduced the Turing machine, an abstract model of computation, and proved there are well-defined problems no algorithm can solve (the halting problem).
• 1940–1945 — Bletchley Park: designed the Bombe, an electromechanical machine that broke the German Enigma cipher and helped shorten the war.
• 1948–1950 — Manchester: worked on some of the earliest stored-program computers and wrote one of the first programming manuals.
• 1950 — “Computing Machinery and Intelligence”: proposed what is now called the Turing test as a way to think about machine intelligence.

Turing was prosecuted in 1952 under UK laws then in force against homosexuality and died in 1954. He received a posthumous royal pardon in 2013.

Why it matters

Almost every idea in modern computer science — computability, complexity, automatic programming, AI — traces back, in part, to Turing.

Real-world examples

• The Turing Award is the highest honour in computer science, named in his recognition.

• The Turing test is still invoked (rightly or wrongly) in debates about AI capability.

• The Turing Award (computing’s Nobel) has been awarded to figures including Donald Knuth, Tim Berners-Lee, Frances Allen, Vint Cerf, Whitfield Diffie and Martin Hellman, and most recently Yoshua Bengio, Geoffrey Hinton, and Yann LeCun.

Common misconceptions

• “Turing built the first computer.” He didn’t; the Bombe was a specialised codebreaking device, and other people (Konrad Zuse, John Atanasoff, the ENIAC team) built early general-purpose machines. Turing’s biggest contribution was theoretical.

Learn next

The idea that made him famous — see Turing machine.