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**A**lan Mathison Turing (June 23, 1912 - June 7, 1954) was a British mathematician, logician, cryptographer, and is often considered a father of modern computer science. With the Turing Test, he made a significant and characteristically provocative contribution to the debate regarding synthetic consciousness: whether it will ever be possible to say that a machine is conscious and can think. He provided an influential formalisation of the concept of algorithm and computation with the Turing machine, formulating the now widely accepted “Turing” version of the Church-Turing thesis, namely that any practical computing model has either the equivalent or a subset of the capabilities of a Turing machine.

Turing’s contributions during World War II were never publicly acknowledged during his lifetime because his work was classified. At Bletchley Park he was a pivotal player in breaking German cyphers, becoming the head of Hut 8, the group tasked with breaking Naval Enigma.

After the war, he designed one of the earliest electronic programmable digital computers at the National Physical Laboratory and actually built another early machine at the University of Manchester. The Turing Award was created in his honour.

Turing was later tried and convicted for “gross indecency and sexual perversion” because of his homosexuality. He began a government-mandated hormonal treatment programme and died shortly thereafter in what is generally considered to have been a suicide.

**Childhood and youth**

Turing was conceived in 1911 in Chatrapur, India. His father, Julius Mathison Turing, was a member of the Indian civil service. Julius and wife Ethel (nee Stoney) wanted Alan to be brought up in Britain, so they returned to Paddington, London. His father’s civil service commission was still active, and during Turing’s childhood years his parents travelled between Guildford, England and India, leaving their two sons to stay with friends in England, rather than risk their health in the British colony. Very early in life, Turing showed signs of the genius he was to display more prominently later. He is said to have taught himself to read in three weeks, and to have shown an early affinity for numbers and puzzles.

His parents enrolled him at St. Michael’s, a day school, at six years of age. The headmistress recognized his genius early on, as did many of his subsequent educators. In 1926, at the age of 14, he went on to the Sherborne boarding school in Dorset. His first day of term coincided with a general strike in England, and so determined was he to attend his first day that he rode his bike unaccompanied over sixty miles from Southampton to school, stopping overnight at an inn - a feat reported in the local press.

Turing’s natural inclination toward mathematics and science did not earn him respect with the teachers at Sherborne, a famous and expensive public school (a British private school with charitable status), whose definition of education placed more emphasis on the classics. His headmaster wrote to his parents: “I hope he will not fall between two schools. If he is to stay at Public School, he must aim at becoming educated. If he is to be solely a Scientific Specialist, he is wasting his time at a Public School,” (Alan Turing: The Enigma by Andrew Hodges, Walker Publishing Company edition (2000), p. 26).

But despite this, Turing continued to show remarkable ability in the studies he loved, solving advanced problems in 1927 without having even studied elementary calculus. In 1928, aged sixteen, Turing encountered Albert Einstein’s work; not only did he grasp it, but he extrapolated Einstein’s questioning of Newton’s laws of motion from a text in which this was never made explicit.

Turing’s hopes and ambitions at school were raised by his strong feelings for his friend Christopher Morcom, with whom he fell in love, though the feeling was not reciprocated. Morcom died only a few weeks into their last term at Sherborne, from complications of bovine tuberculosis, contracted after drinking infected cow’s milk as a boy. Turing was heart-broken.

**College and his work on computability**

Due to his unwillingness to work as hard on his classical studies as on science and mathematics, Turing failed to win a scholarship to Trinity College, Cambridge, and went on to the college of his second choice, King’s College, Cambridge. He studied under G. H. Hardy, a respected mathematician, who held the Sadleirian Chair at Cambridge, then a center for mathematical research and study, from 1931 to 1934. In 1935 he was elected a Fellow at King’s College. Hardy was a member of the infamous Cambridge Apostles, which gained notoriety during this period from the Cambridge Spy Ring scandal. Oddly, but perhaps the better for him, Turing was either not invited to join the circle, or declined the invitation.

Alan Turing, on the steps of the bus, with members of the Walton Athletic Club, 1946.

In his momentous paper “On Computable Numbers, with an Application to the Entscheidungsproblem” (submitted on May 28, 1936), Turing reformulated Kurt Godel’s 1931 results on the limits of proof and computation, substituting Godel’s universal arithmetics-based formal language by what are now called Turing machines, formal and simple devices. He proved that such a machine would be capable of performing any conceivable mathematical problem if it were representable as an algorithm, even if no actual Turing machine would be likely to have practical applications, being much slower than alternatives. Turing machines are to this day the central object of study in theory of computation. He went on to prove that there was no solution to the Entscheidungsproblem by first showing that the halting problem for Turing machines is uncomputable: it is not possible to algorithmically decide whether a given Turing machine will ever halt. While his proof was published subsequent to Alonzo Church’s equivalent proof in respect to his lambda calculus, Turing’s work is considerably more accessible and intuitive. It was also novel in its notion of a “Universal (Turing) Machine,” the idea that such a machine could perform the tasks of any other machine. The paper also introduces the notion of definable numbers.

Most of 1937 and 1938 he spent at Princeton University, studying under Alonzo Church. In 1938 he obtained his Ph.D. from Princeton; his dissertation introduced the notion of hypercomputation where Turing machines are augmented with so-called oracles, allowing a study of problems that cannot be solved algorithmically.

Back in Cambridge in 1939, he attended lectures by Ludwig Wittgenstein about the foundations of mathematics. The two argued and disagreed vehemently, with Turing defending formalism and Wittgenstein arguing that mathematics is overvalued and does not discover any absolute truths.

**Cryptanalysis (code breaking)**

During World War II he was a major participant in the efforts at Bletchley Park to break German ciphers. Turing’s codebreaking work was kept secret until the 1970s; not even his close friends knew about it. He contributed several mathematical insights into breaking both the Enigma machine and the Lorenz SZ 40/42 (a teletype cipher attachment codenamed “Tunny” by the British).

Turing realised that it was not necessary to test all the possible combinations to crack the Enigma machine. He proved that it was possible to test for the correct settings of the rotors (approximately one million combinations) without having to consider the settings of the plugboard (approximately 157 million combinations). Whilst still a formidable task, one million combinations was achievable using an electromechanical machine - the bombe, named after the Polish-designed bomba - which could be used to eliminate large numbers of candidate Enigma settings. For each possible setting, a chain of logical deductions was implemented electrically, and it was possible to detect when a contradiction had occurred and rule out that setting. Turing’s bombe, with an enhancement suggested by mathematician Gordon Welchman, was the primary tool used by British and American codebreakers to read Enigma traffic, with over 200 bombes in operation by the end of the war. The design and production of the machine itself was undertaken by Harold Keen of the British Tabulating Machine company. For a time, Turing was head of Hut 8, the section responsible for cryptanalysing German Naval signals. Turing also invented the technique of Banburismus to assist in breaking Enigma.

Turing devised some methods for attacking Tunny, termed Turingismus or Turingery, although other methods were also used. To assist in the codebreaking, the first digital programmable electronic computer was developed, Colossus. Turing, however, was not directly involved - Colossus was designed and built at the Post Office Research Station at Dollis Hill by a team led by Thomas Flowers in 1943.

In the later part of the war, Turing undertook (with engineer Donald Bayley) the design of a portable machine codenamed Delilah to allow secure voice communications, teaching himself electronic theory at the same time. Intended for different applications, Delilah lacked the ability to be used over long-distance radio transmissions. Delilah was completed too late to be used in the war. While Turing demonstrated it to officials by encoding/decoding a recording of a Winston Churchill speech, it was not adopted for use.

**Work on early computers and the Turing Test**

From 1945 to 1947 he was at the National Physical Laboratory, where he worked on the design of ACE (Automatic Computing Engine). He presented a paper on February 19, 1946, which was the first complete design of a stored-program computer. Although he succeeded in designing the ACE, there were delays in starting the project and he became disillusioned. In late 1947 he returned to Cambridge for a ’sabbatical’ year. While he was at Cambridge work on building the ACE stopped before it was ever begun. In 1949 he became deputy director of the computing laboratory at the University of Manchester, and worked on software for one of the earliest true computers - the Manchester Mark I. During this time he continued to do more abstract work, and in “Computing machinery and intelligence” (Mind, October 1950), Turing tackled the problem of artificial intelligence, and proposed an experiment now known as the Turing test, an attempt to define a standard for a machine to be called “sentient". In 1948, Turing, working with his former undergraduate colleague, D.G. Champernowne, began writing a chess program for a computer that did not yet exist. In 1952, lacking a computer powerful enough to execute the program, Turing played a game in which he simulated the computer, taking about half an hour per move. The game was recorded; the program lost to a colleague of Turing, however, it is said that the programme won a game against Champernowne’s wife.

**Work on pattern formation and mathematical biology**

Turing worked from 1952 until his death in 1954 on mathematical biology, specifically morphogenesis. He published one paper on the subject called “The Chemical Basis of Morphogenesis” in 1952. His central interest in the field was understanding Fibonacci phyllotaxis, the existence of Fibonacci numbers in plant structures. He used reaction-diffusion equations which are now central to the field of pattern formation. Later papers went unpublished until 1992 when Collected Works of A.M. Turing was published.

**Prosecution for homosexuality and Turing’s death**

Prosecution of Turing for his homosexuality crippled his career. In 1952, his male lover helped an accomplice to break into Turing’s house and commit larceny. Turing went to the police to report the crime. As a result of the police investigation, Turing was said to have had a sexual relationship with a 19-year-old man, and Turing was charged with “gross indecency and sexual perversion.” He unapologetically offered no defence, and was convicted. Following the well-publicised trial, he was given a choice between incarceration and libido-reducing hormonal treatment. He chose the oestrogen hormone injections, which lasted for a year, with side effects including the development of breasts.

In 1954, he died of cyanide poisoning, apparently from a cyanide-laced apple he left half-eaten. Most believe that his death was intentional, and the death was ruled a suicide. His mother, however, strenuously argued that the ingestion was accidental due to his careless storage of laboratory chemicals. Friends of his have said that Turing may have killed himself in this ambiguous way quite deliberately, to give his mother some plausible deniability.

**Recognition**

A statue of Turing was unveiled in Manchester on June 23, 2001. It is in Sackville Park, between the University of Manchester building on Whitworth Street and the Canal Street gay village. To mark the 50th anniversary of his death, a memorial plaque was unveiled at his former residence, Hollymeade, in Wilmslow on June 7, 2004.

The Turing Award is given by the Association for Computing Machinery to a person for technical contributions to the computing community. It is widely considered to be the equivalent of the Nobel Prize in the computing world.

The Alan Turing Institute was initiated by UMIST and University of Manchester in Summer 2004.

A celebration of Turing’s life and achievements was held at the University of Manchester on 5 June 2004; it was arranged by the British Logic Colloquium and the British Society for the History of Mathematics.

On October 28, 2004 a bronze statue of Alan Turing sculpted by John W. Mills was unveiled at Surrey University. The statue marks the 50th anniversary of Turing’s death. It portrays Turing carrying his books across the campus.

Holtsoft produces a programming language named for Turing. The language is designed for beginner programmers and has no direct access to the hardware.

**Turing in fiction**

Turing appears as a character in the World War II sections of Neal Stephenson’s Cryptonomicon.

In another one of Stephenson’s books, The Diamond Age, there is a very good explanation of Turing’s work put into the format of a child’s book.

The play Breaking the Code by Hugh Whitemore deals with the life and death of Turing.

“Turing Police” (Artificial Intelligence law enforcers) appear in William Gibson’s Neuromancer.

In White Wolf Game Studio’s World of Darkness role-playing universe, Turing was a leading member of the mage faction known as the Virtual Adepts.

An FBI agent named Alan Turing appears in the webcomic Questionable Content as a homage to Turing.

Appears in Enigma by Robert Harris

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