🇬🇧Alan
Turing

The letter from his headmaster said, more or less, that if Alan Turing intended to remain at a school meant for educated gentlemen, he would need to learn to think in terms of classical languages and not merely of numbers. Turing was eleven. He had already, on his own, taught himself algebra without having been introduced to it formally. He was uninterested in the letter's argument. He remained interested in mathematics. The school's preference for Latin over logic was the sort of institutional priorities that Turing would spend his life politely declining to accommodate, until the institution in question was the British government and the accommodation it demanded was his own humanity, and then the politeness became something else entirely.

Alan Mathison Turing was born on June 23, 1912, in Maida Vale, London, to a family of the imperial civil service class — his father was an officer in the Indian Civil Service, and Alan spent significant parts of his childhood being boarded with family friends in England while his parents lived in India. He was a solitary, intense child, the kind who reads science books for pleasure and finds the social requirements of school baffling and slightly beside the point. At Sherborne School in Dorset, he found a single deep friendship with a fellow student named Christopher Morcom, who shared his love of science. Morcom died of tuberculosis in 1930, when both boys were seventeen. Turing was devastated in a way that people who knew him said he never entirely recovered from. He turned more deeply inward, and deeper into mathematics.

At King's College, Cambridge, he read mathematics and graduated with a first-class degree in 1934. Two years later, at twenty-four, he published "On Computable Numbers, with an Application to the Entscheidungsproblem" — a paper that answered, in the negative, a question posed by the mathematician David Hilbert about whether there exists a mechanical procedure that can determine the truth or falsehood of any mathematical statement. In answering the question, Turing invented a conceptual device — the Turing machine — that is the theoretical foundation of all modern computation. The paper did not describe an actual machine. It described an abstract logical structure, and in doing so it defined what computation means, what computers can in principle do, and what they cannot.

When war came in 1939, Turing reported to the Government Code and Cypher School at Bletchley Park, a Victorian estate in Buckinghamshire that had been converted into a codebreaking operation. The German military encrypted its communications using the Enigma machine — a device that could generate codes of almost inconceivable complexity. The number of possible settings ran to some 158 quintillion combinations. The British had been struggling with the cipher for months. Turing, working with a team that included Gordon Welchman, designed an electromechanical device called the Bombe that could systematically eliminate incorrect Enigma settings, narrowing the search to a manageable number. By the middle of the war, the British were regularly reading German naval communications, often within hours of transmission. Historians estimate that the intelligence gathered through Bletchley shortened the war by at least two years and saved millions of lives. Turing's work was the crucial contribution.

After the war, Turing continued working on what he called the "Automatic Computing Engine" — one of the first designs for a stored-program computer — and published, in 1950, his paper "Computing Machinery and Intelligence," which posed the question "Can machines think?" and proposed what became known as the Turing test as a practical criterion for machine intelligence. The paper founded the field of artificial intelligence. He was also, in his private life, a gay man in a country where homosexuality was a criminal offense. In 1952, following a burglary at his home, a police investigation led to his admission of a relationship with a man. He was charged with gross indecency — the same offense for which Oscar Wilde had been imprisoned half a century earlier. He was convicted. As an alternative to prison, he accepted a sentence of chemical castration via injections of synthetic estrogen. He died on June 7, 1954, from cyanide poisoning. A coroner ruled it suicide. He was forty-one. In 2013, Queen Elizabeth II granted him a posthumous royal pardon.