Alan Turing

• 1. Introduction

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  Alan Turing once chained his tea mug to a radiator pipe at Bletchley Park so it could not be stolen. In the first week of every June he cycled to the office in a service gas mask, fending off hay fever pollen. His bicycle chain slipped at regular intervals, so rather than have it mended he counted the turns of the pedals and stepped off in time to fix it by hand. These were the eccentricities of a man his colleagues simply called Prof. The cognitive scientist Douglas Hofstadter described him as an atheist, homosexual, eccentric, marathon-running mathematician. Born in Maida Vale in London on the 23rd of June 1912, Turing died on the 7th of June 1954, aged 41, from cyanide poisoning. Between those two dates sits a life that touched the foundations of computing, the cracking of German ciphers, the patterns on a leopard's fur, and a criminal trial that ended in chemical castration. How does one mind reach so far. And why was a man Hofstadter credits with helping ensure we are not under Nazi rule today never fully recognised while he lived.

• 2. A Genius And A Loss

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  In 1922, a 10-year-old Turing discovered a book called Natural Wonders Every Child Should Know by Edwin Tenney Brewster. He credited it with opening his eyes to science. The headmistress of St Michael's, the primary school he attended from the age of six, put it plainly. She had clever boys and hardworking boys, she said, but Alan was a genius. At Sherborne School, which he entered in 1926 aged 13, his gifts did not impress teachers who prized the classics. His headmaster warned his parents that if he was to be solely a scientific specialist, he was wasting his time at a public school. Turing pressed on regardless, solving advanced problems in 1927 without having studied even elementary calculus. By 1928 he had encountered Albert Einstein's work and may have deduced Einstein's questioning of Newton's laws of motion from a text that never made it explicit. At Sherborne he formed a deep friendship with a fellow pupil, Christopher Collan Morcom, born on the 13th of July 1911. Morcom has been described as Turing's first love. The friendship was cut short when Morcom died in February 1930 from complications of bovine tuberculosis, contracted after drinking infected cow's milk. Turing coped with the grief by working harder on the science and mathematics they had shared. He wrote to Morcom's mother that he could not have found anywhere another companion so brilliant and yet so charming and unconceited. Years later, on the eve of the third anniversary of the death, he wrote to her again, signing himself her affectionate Alan.

• 3. The Machine On Paper

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  On the 28th of May 1936, Turing delivered a 36-page paper titled On Computable Numbers, with an Application to the Entscheidungsproblem. It has been called easily the most influential math paper in history. The decision problem at its heart had been posed by the German mathematician David Hilbert in 1928. Turing answered it using a hypothetical device so simple it could be imagined on paper, now known as a Turing machine. He proved there was no solution to the decision problem by first showing that the halting problem is undecidable. One cannot decide algorithmically whether such a machine will ever stop. The American logician Alonzo Church reached equivalent conclusions at almost the same time using his lambda calculus, publishing his own work that same month. Turing's approach was considerably more accessible and intuitive. His paper included a Universal Machine, capable of performing the tasks of any other computation machine. John von Neumann acknowledged that the central concept of the modern computer was due to Turing's paper. From September 1936 to July 1938 Turing studied under Church at Princeton University. There he obtained his PhD in June 1938 with a dissertation titled Systems of Logic Based on Ordinals. Von Neumann wanted to hire him as a postdoctoral assistant, but Turing went back to the United Kingdom.

• 4. The Codebreaker

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  On the 4th of September 1939, the day after the United Kingdom declared war on Germany, Turing reported to Bletchley Park. The historian and wartime codebreaker Asa Briggs said you needed genius at Bletchley, and Turing's was that genius. Turing made five major cryptanalytical advances during the war. The first was specifying the bombe, an electromechanical machine that searched for the correct settings of an Enigma message. A four-rotor U-boat variant had on the order of ten to the power of twenty-two states. The first bombe was installed on the 18th of March 1940. Turing chose to tackle the German naval use of Enigma, he said, because no one else was doing anything about it and he could have it to himself. In December 1939 he solved the essential part of the naval indicator system. That same night he conceived of Banburismus, a sequential statistical technique that used a measure of evidence he called the ban. He later devised Turingery against the Lorenz cipher, and a portable secure voice scrambler codenamed Delilah. By late 1941, frustrated by limited staff and bombes, Turing and three colleagues wrote directly to Winston Churchill. The biographer Andrew Hodges later wrote that the letter had an electric effect. Churchill fired back a memo headed ACTION THIS DAY, ordering that they have all they want on extreme priority. More than two hundred bombes were in operation by the end of the war. The official war historian Harry Hinsley estimated this work shortened the war in Europe by more than two years.

• 5. The Runner

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  Turing's tryout time for the marathon was only 11 minutes slower than the British silver medallist Thomas Richards' Olympic race time of 2 hours 35 minutes. He was a talented long-distance runner who tried out for the 1948 British Olympic team but was hampered by an injury. While working at Bletchley he occasionally ran the 40 miles to London when he was needed for meetings. He was Walton Athletic Club's best runner, a fact discovered when he passed the group while running alone. Asked why he ran so hard in training, he replied that his job was so stressful the only way he could get it out of his mind was by running hard. Running, he said, was the only way he could get some release. The same restless determination had shown itself years earlier. When the first day of term at Sherborne coincided with the 1926 General Strike, the young Turing rode his bicycle unaccompanied 60 miles from Southampton to Sherborne, stopping overnight at an inn.

• 6. Minds And Machines

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  On the 19th of February 1946, Turing presented a paper that was the first detailed design of a stored-program computer, the Automatic Computing Engine, at the National Physical Laboratory. Von Neumann's incomplete First Draft of a Report on the EDVAC had predated it but was much less detailed. The superintendent John R. Womersley said Turing's paper contained a number of ideas that were Dr. Turing's own. The Pilot ACE, built in his absence, executed its first program on the 10th of May 1950. In 1948 Turing was appointed to the University of Manchester, where he worked on software for the Manchester Mark 1 and wrote its first Programmer's Manual. There he addressed the problem of artificial intelligence in a paper titled Computing Machinery and Intelligence. He proposed an experiment that became known as the Turing test. A computer could be said to think, he argued, if a human interrogator could not tell it apart through conversation from a human being. He suggested it would be better to simulate a child's mind and subject it to a course of education than to build a program simulating the adult mind. A reversed form of his idea is now everywhere on the internet as the CAPTCHA test. Working with his former undergraduate colleague D.G. Champernowne, Turing began writing a chess program in 1948 for a computer that did not yet exist. By 1950 it was completed and dubbed the Turochamp. Lacking a powerful enough machine, in 1952 Turing ran it himself by flipping through the pages of the algorithm, taking about half an hour per move. According to Garry Kasparov, the program played a recognizable game of chess.

• 7. Spots And Stripes

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  In January 1952, at the age of 39, Turing published his masterpiece The Chemical Basis of Morphogenesis. He was fascinated by morphogenesis, the development of patterns and shapes in living organisms. He proposed that a system of chemicals reacting and diffusing across space, a reaction-diffusion system, could account for the main phenomena of morphogenesis. The idea was a catalyst that produced more of itself, paired with an inhibitor that slowed it down. If the two diffused at different rates, some regions would be dominated by one and some by the other. Lacking a powerful computer in 1951, Turing solved the equations by hand using linear approximations. His calculations produced a uniform mixture that oddly enough had regularly spaced fixed red spots. The Russian biochemist Boris Belousov had performed experiments with similar results but could not get his papers published, because contemporaries believed such a thing violated the second law of thermodynamics. One early application came from James Murray, explaining the spots and stripes on the fur of cats, large and small. Later research suggested Turing's mechanism could partially explain feathers, hair follicles, the branching pattern of lungs, and even the left-right asymmetry that places the heart on the left side of the chest. A study in 2023, presented by the American Physical Society, grew chia seeds in trays and tweaked the factors in the Turing equations. Patterns resembling those in natural environments emerged, believed to be the first time experiments with living vegetation verified his insight.

• 8. Conviction And Reckoning

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  In December 1951, Turing met Arnold Murray, a 19-year-old unemployed man, outside the Regal Cinema on Manchester's Oxford Road. In January 1952 they began an intimate relationship. After Turing's house was burgled that month, he reported the crime, and during the investigation acknowledged the relationship. Homosexual acts were criminal offences, and both men were charged with gross indecency under Section 11 of the Criminal Law Amendment Act 1885. The case, Regina v. Turing and Murray, came to trial on the 31st of March 1952. Turing was convicted and chose probation conditional on hormone treatment, a procedure commonly referred to as chemical castration. He accepted injections of stilboestrol, a synthetic oestrogen, continued for one year. The treatment rendered him impotent and caused breast tissue to form. The conviction stripped him of his security clearance and barred his cryptographic consultancy for GCHQ. On the 8th of June 1954, his housekeeper found him dead at his house at 43 Adlington Road in Wilmslow. An apple lay half-eaten beside his bed. The inquest determined suicide, though the philosopher Jack Copeland later argued the autopsy findings were more consistent with accidental inhalation of cyanide fumes from an electroplating apparatus in his spare room. His nephew Dermot Turing notes he had just written a list of tasks for his return to the office. His mother never accepted the verdict of suicide. Decades later, the reckoning came. After a petition gathered more than 30,000 signatures, the prime minister Gordon Brown apologised in 2009, saying we're sorry, you deserved so much better. Queen Elizabeth II signed a pardon on the 24th of December 2013, only the fourth royal pardon granted since the Second World War. The campaign by the Manchester MP John Leech became the informal Alan Turing law, contained in the Policing and Crime Act 2017, which pardoned 75,000 other men and women. On the 23rd of June 2021, Turing's birthday, his portrait first appeared on the Bank of England 50-pound note.