Alan Turing Born (1912)
Alan Mathison Turing was born on June 23, 1912, in Maida Vale, London. He became the most consequential mathematician and computer scientist of the twentieth century — the man who conceived the theoretical basis of the modern computer, helped crack Nazi Germany's Enigma codes during World War II, and laid the groundwork for the field of artificial intelligence. He was also prosecuted by the British government for homosexuality in 1952, chemically castrated as a condition of avoiding prison, and found dead in June 1954 in circumstances that were ruled a suicide. He was 41 years old.
The Turing Machine
Turing showed exceptional mathematical ability from childhood, though his unconventional thinking often frustrated his teachers. He studied mathematics at King's College, Cambridge, where he was elected a Fellow in 1935. In 1936, at the age of 24, he published "On Computable Numbers, with an Application to the Entscheidungsproblem" — a paper that resolved one of the most important open questions in mathematics (David Hilbert's decision problem) by inventing a theoretical model of computation: what we now call the Turing Machine. A Turing Machine is an abstract device that manipulates symbols on a strip of tape according to a table of rules. In this simple model, Turing demonstrated that any computation that can be described algorithmically can in principle be carried out by such a machine — and that some problems, including Hilbert's Entscheidungsproblem, are mathematically undecidable. This paper, written before electronic computers existed, described the logical architecture that all computers would follow. Turing went on to Princeton, earning a PhD under the logician Alonzo Church, before returning to Britain — just in time for the war.
Did You Know?
The Turing Test — Turing's proposed test for machine intelligence, described in his 1950 paper "Computing Machinery and Intelligence" — begins with the question "Can machines think?" Turing reframed this as a practical question: if a human interrogator cannot reliably distinguish between responses from a human and responses from a machine in a text-based conversation, the machine could be said to demonstrate intelligence. The test has been criticized and refined by philosophers and computer scientists for 75 years and has never been definitively "passed" to universal satisfaction. But no other concept has done more to focus serious thinking about what intelligence means and whether machines can achieve it.
Bletchley Park and the Enigma
When World War II began, Turing joined the Government Code and Cypher School at Bletchley Park, the top-secret British codebreaking center. Germany's military communications were encrypted using the Enigma machine — an electromechanical cipher device that could produce astronomical numbers of possible configurations. Polish mathematicians had cracked an earlier version of Enigma and shared their methods with Britain just before the war. Turing built on their work, developing the Bombe — an electromechanical machine that could rapidly test Enigma settings to find the day's key. Working with Gordon Welchman and others, he transformed Bletchley's ability to crack German naval and military codes. The intelligence derived from these decryptions — code-named Ultra — has been credited by historians with shortening the war by two to four years. Turing also worked on breaking the Lorenz cipher, which encrypted Hitler's messages to his high command. The full extent of Turing's contributions remained classified for decades after the war.
Persecution and Posthumous Pardon
After the war, Turing worked at the National Physical Laboratory, where he designed one of the first stored-program computers, and then at the University of Manchester. In 1950 he published "Computing Machinery and Intelligence," introducing the Turing Test. In 1952, he reported a burglary to police and inadvertently disclosed that he was in a relationship with a man. He was charged with "gross indecency" under the same law that had been used to prosecute Oscar Wilde. Convicted and given the choice between imprisonment and chemical castration via hormonal injections, he chose the latter. He was found dead on June 7, 1954, with a half-eaten apple beside him. The coroner ruled suicide by cyanide poisoning. The Apple Computer logo is sometimes said to honor Turing, though the company has denied any intentional connection. In 2009, British Prime Minister Gordon Brown issued an official apology for the government's treatment of Turing. In 2013, Queen Elizabeth II granted him a posthumous royal pardon. In 2021, his image appeared on the British £50 note. The debt owed to Alan Turing — by every person who uses a computer, every researcher in artificial intelligence, every democracy that benefited from Allied victory — can scarcely be calculated.