Dozens of academic and technical departments worldwide are named after Turing. Winston Churchill famously said that Turing had made the single biggest contribution to Allied victory in the war against Nazi Germany. The biopic based on his life – The imitation game – was the highest-grossing independent movie of 2014. Accolades for the British mathematician, logician, cryptanalyst, philosopher, computer scientist and mathematical biologist are endless. The blue plaque at his birthplace in London’s Maida Vale simply reads “founder of computer science and cryptographer”. But none of these fully encapsulate the enigmatic and complex scientist that seemed to pack so much into his short life of 41 years.
Born in 23 June 1912, there was nothing specific in Alan Mathison Turing’s circumstances that predicted a path into a life of science. His father was in the Indian civil service, while his uncle HD Turing was an authority on trout fishing. Perhaps a hint of what was to come lies more in his mother’s side, in the form of physicist George Johnstone Stoney, a distant relative famous for introducing the word ‘electron’ as “the fundamental unity quantity of electricity”. But, for the main part, the Turings followed the professions, notably the law. According to his biographer Andrew Hodges, Turing’s childhood was largely that of being fostered in English homes with his brother while his parents were away in India. It was an existence in which “nothing encouraged expression, originality, or discovery. Science for him was an extra-curricular passion, first shown in primitive chemistry experiments. But he was given, and read, later commenting on its seminal influence, a popular book called Natural Wonders Every Child Should Know. An unpromising career at the ancient and exalted Sherborne School resulted in his headmaster reporting: “If he is to be solely a scientific specialist, he is wasting his time at a public school.”
Things looked up for Turing as an undergraduate at King’s College Cambridge where, aside from his academic pursuits, he threw himself into rowing, running and sailing. Armed with a first in mathematics, he was made a fellow at King’s in 1935. A year later he was to deliver his paper ‘On computable numbers, with an application to the Entscheidungsproblem’, that introduced the idea of the ‘Universal Machine’ (now the ‘Universal Turing Machine’) that was acknowledged by the foremost mathematician of his time, John von Neumann, as establishing the central concept of the modern computer. The Turing Machine was also to become the foundation of the modern theory of computation and computability. During 1936-8, Turing was at Princeton University in the US, where he studied cryptology, worked on an electro-mechanical binary multiplier while obtaining his PhD. Although he was offered a job at Princeton by von Neumann he returned to Cambridge where, without a lectureship, he remained a fellow of King’s as a logician and number theorist, during which time he attended lectures by Austrian philosopher Ludwig Wittgenstein and worked part-time at the Government Code and Cypher School (GC&CS) that was later to become GCHQ.
“The idea behind digital computers may be explained by saying that these machines are intended to carry out any operations which could be done by a human computer” - Alan Turing
Turing reported for duty at Bletchley Park, the wartime station of GC&CS, on 4 September 1939, the day after the UK declared war on Germany. It was his role in breaking German ciphers that was to form the bedrock of the Turing legend, which is neatly encapsulated in historian Asa Briggs’ assertion that: “You needed exceptional talent, you needed genius at Bletchley and Turing’s was that genius.” Initially, Turing worked on cryptanalysis of Enigma (an encryption device used in the early- to mid-20th century to protect commercial, diplomatic and military communication) alongside senior GC&CS codebreaker Dilly Knox. It was at this time he produced the functional specification of the bombe, a development and refinement of the Polish bomba kryptologiczna electro-mechanical decryption machine. Fellow code-breaker Jack Good thought Turing’s work on the bombe as his ‘most important contribution.’ By the end of the war, 200 such machines were in operation and had made the reading of Luftwaffe signals routine. Turing also worked on the more complex German naval communications that were considered unbreakable, a challenge he decided to take on “because no one else was doing anything about it and I could have it to myself”.
Turing’s section at Bletchley that deciphered U-boat messages – ‘Hut 8’ – became a cornerstone of the organisation’s success. Turing’s image was to become what Hodges calls “the genius loci at Bletchley Park, famous as ‘Prof’, shabby, nail-bitten, tie-less, sometimes halting in speech and awkward of manner, the source of many hilarious anecdotes about bicycles, gas masks, and the Home Guard; the foe of charlatans and status-seekers, relentless in long shift work with his colleagues”. In marked contrast to his somewhat eccentric exterior image, the ‘Prof’ (who was never actually a university professor), became an all-purpose consultant to the by now enormous Bletchley Park machine. He also wrote two papers discussing mathematical approaches to code-breaking that were of such value to the GC&CS (and later GCHQ) that they weren’t released to the National Archives until 2012.
With the war coming to an end, in 1945 Turing moved to Richmond, where he concentrated on the design of the Automatic Computing Engine (ACE) at the National Physical Laboratory (NPL), presenting a paper in February 1946 outlining the first detailed design of a stored-program computer. He envisaged a machine that would be able to switch between functions such as numerical work, code-breaking, file handling and chess-playing. In 1947 his Abbreviated Code Instructions marked the beginning of programming language. But the ACE project was never built due to lack of cooperation, leaving Turing, who had expected to encounter the collaborative war-time spirit he’d experienced at Bletchley, deeply frustrated.
Heading back to the University of Cambridge once more, Turing redirected his efforts away from mathematics and technology in favour of neurology and physiology, out of which came a paper that anticipated neural nets. Meanwhile, at Manchester University, funds had been secured via a Royal Society grant to build a computer that would demonstrate Turing’s principle of the stored program. In October 1948 Turing stepped into the role of deputy director of the computing laboratory at Manchester, and while this job title was deliberately vague and his status within the organisation uncertain, he at least had a clear role in electronics programming. By 1950 he was using the computer for his own research, which he described as the mathematical theory of morphogenesis: the theory of growth and form in biology. This was a change in direction that returned Turing to his childhood interest in biological structures, when he had spent time ‘watching the daisies grow.’ The resulting paper – ‘The chemical basis of morphogenesis’ – is one of the founding documents of the discipline of non-linear dynamical theory.
After being elected to Fellowship of the Royal Society in July 1951, Turing became involved in a sequence of events that led to him being put on trial charged with gross indecency under Section 11 of the Criminal Law Amendment Act 1885. In essence, he was being tried for committing acts of homosexuality for which – despite pleading guilty on the advice of his brother and other lawyers – he felt neither guilt nor remorse, having previously acknowledged his homosexuality during the police investigation into a burglary at Turing’s house. Convicted of the charge, Turing was offered the choice between imprisonment and probation, the latter of which carried the condition of his agreement to undergo drug therapy in the form of injections of the synthetic oestrogen stilboestrol. The year-long treatment caused serious effects to Turing’s health that he took in relatively good humour. The conviction also stripped him of the security clearance required to continue working as a cryptographic consultant with the UK government and prevented him from visiting the US.
The rest is history. On 8 June 1954 Alan Turing was found dead. The cause of death was cyanide poisoning, and an inquest determined that he had committed suicide. While there have been rigorous attempts by his biographers to provide alternative explanations, and while Turing’s mother certainly believed that the scientist had died by accident, the carefully orchestrated suicide by poisoned apple, that so closely resembled a scene from Walt Disney’s Snow White (Turing’s favourite fairy tale), seems to leave little room to doubt the inquest’s finding. On 24 December 2013, Queen Elizabeth II signed a pardon for Turing’s conviction.