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Alan Turing

Alan Turing is often considered the father of modern computer science.


With the Turing test, Turing made a significant and characteristically provocative contribution to the debate regarding artificial intelligence: 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. During World War II, Turing worked at Bletchley Park, Britain's codebreaking centre and was for a time head of Hut 8, the section responsible for German Naval cryptanalysis. He devised a number of techniques for breaking German ciphers, including the method of the bombe, an electromechanical machine which could find settings for the Enigma machine.

After the war, he worked at the National Physical Laboratory, creating one of the first designs for a stored-program computer, although it was never actually built. In 1947 he moved to the University of Manchester to work, largely on software, on the Manchester Mark I then emerging as one of the world's earliest true computers.

In 1952, Turing was convicted of acts of gross indecency after admitting to a sexual relationship with a man in Manchester. He was placed on probation and required to undergo hormone therapy. When Alan Turing died in 1954, an inquest found that he had committed suicide by eating an apple laced with cyanide.

Childhood and youth Edit

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 (née Stoney) wanted Alan to be brought up in Britain, so they returned to Paddington, London, where Alan Turing was born June 23, 1912. 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.


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".[1]

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.


The computer room at King's is now named after Turing, who became a student there in 1931 and a Fellow in 1935.

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.

University and his work on computability Edit

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 was an undergraduate from 1931 to 1934, graduating with a distinguished degree, and in 1935 was elected a Fellow at King's on the strength of a dissertation on the Gaussian error function.


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 Gödel's 1931 results on the limits of proof and computation, substituting Gödel'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 undecidable: 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.


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 (Wittgenstein 1932/1976).

Cryptanalysis Edit

Turing flat


During World War II, Turing was a major participant in the efforts at Bletchley Park to break German ciphers. He contributed several insights into breaking both the Enigma machine and the Lorenz SZ 40/42 (a teletype cipher attachment codenamed "Tunny" by the British), and was, for a time, head of Hut 8, the section responsible for reading German Naval signals.

Since September 1938, Turing had been working part-time for the Government Code and Cypher School. Turing reported to Bletchley Park on 4 September 1939, the day after Britain declared war on Germany.[2]

The Turing-Welchman bombeEdit


Replica of a bombe machine

Within weeks of arriving at Bletchley Park,[2] Turing had devised an electromechanical machine which could help break Enigma: the bombe, named after the Polish-designed Bomba (cryptography)|bomba. The bombe, with an enhancement suggested by mathematician Gordon Welchman, became the primary tool used to read Enigma traffic.

The bombe searched for the correct settings of the Enigma rotors, and required a suitable "crib": a piece of matching plaintext and ciphertext. For each possible setting of the rotors, the bombe performed a chain of logical deductions based on the crib, implemented electrically. The bombe detected when a contradiction had occurred, and ruled out that setting, moving onto the next. Most of the possible settings would cause contradictions and be discarded, leaving only a few to be investigated in detail. Turing's bombe was first installed on 18 March 1940[citation needed]. Over 200 bombes were in operation by the end of the war[citation needed].

Hut 8 and Naval EnigmaEdit


In the spring of 1941, Turing proposed marriage to fellow Hut 8 co-worker Joan Clarke, although the engagement was broken off by mutual agreement in the summer.

In July 1942, Turing devised a technique termed Turingismus or Turingery for use against the Lorenz cipher. A frequent misconception is that Turing was a key figure in the design of the ossus computer; this was not the case.[3]

Turing travelled to the United States in November 1942 and liaised with US Navy cryptanalysts on Naval Enigma and bombe construction in Washington, and assisted at Bell Labs with the development of secure speech devices. He returned to Bletchley Park in March 1943. During his absence, Hugh Alexander had assumed the position of head of Hut 8, although Alexander had been de facto head for some time, Turing having little interest in the day-to-day running of the section. Turing became a general consultant for cryptanalysis at Bletchley Park.


In 1945, Turing was awarded the OBE for his wartime services.

Early computers and the Turing Test Edit


Turing achieved world-class Marathon Marathon standards. His best time of 2 hours, 46 minutes, 3 seconds, was only 11 minutes slower than the winner in the 1948 Olympic Games.

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 in Britain. 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, ACE was completed in his absence and executed its first program on May 10, 1950. 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 addressed 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, Alick Glennie, however, it is said that the program won a game against Champernowne's wife.

Pattern formation and mathematical biology Edit


Prosecution for homosexual acts and Turing's death Edit

Turing was a homosexual during a period when homosexual acts were illegal and homosexuality was regarded as a mental illness. In 1952, Arnold Murray, a 19 year old recent acquaintance of his (cf. Hodges' book pp.449-455) helped an accomplice to break into Turing's house, and Turing went to the police to report the crime. As a result of the police investigation, Turing acknowledged a sexual relationship with Murray, and they were charged with gross indecency under Section 11 of the Criminal Law Amendment Act of 1885. Turing was unrepentant and was convicted. He was given the choice between imprisonment and probation, conditional on him undergoing hormonal treatment designed to reduce libido. In order to avoid going to jail, he accepted the oestrogen hormone injections, which lasted for a year, with side effects including the development of breasts. His conviction led to a removal of his security clearance and prevented him from continuing consultancy for GCHQ on cryptographic matters.

In 1954, he died of cyanide poisoning, apparently from a cyanide-laced apple he left half-eaten. The apple itself was never tested for contamination with cyanide, and cyanide poisoning as a cause of death was established by a post-mortem. Most believe that his death was intentional, and the death was ruled a suicide. It is rumoured that this method of self-poisoning was in tribute to Turing's beloved film Snow White and the Seven Dwarfs (1937 film)|Snow White and the Seven Dwarfs. 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. The possibility of assassination has also been suggested[citation needed], owing to Turing's involvement in the secret service and the perception of Turing as a security risk due to his homosexuality.

In the book, Zeroes and Ones, author Sadie Plant speculates that the rainbow Apple logo with a bite taken out of it was a homage to Turing. This is unlikely as Gilbert Baker's rainbow pride flag, a gay pride emblem, was designed two years after the Apple logo, thus negating the possibility of it referring to Turing's sexuality.

Posthumous recognition Edit

Since 1966, the Turing Award has been 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.

In 1994 a stretch of the Manchester city inner ring road was named Alan Turing Way.

On 23 June 1998, on what would have been Turing's 86th birthday, Andrew Hodges, his biographer, unveiled an official English Heritage Blue Plaque on his childhood home in Warrington Crescent, London, now the Colonnade hotel [1], [2].

Alan Turing Memorial Closer

Alan Turing memorial statue in Sackville Park

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.

Turing Plaque

Plaque marking Turing's home

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


On October 28 2004 a bronze statue of Alan Turing sculpted by John W. Mills was unveiled at the University of Surrey [3]. 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.

The Polytechnic University of Puerto Rico named a computer laboratory for graduate studies the Turing Lab.

The University of Texas at Austin has an honours computer science program named the Turing Scholars.

The Plymouth State University of New Hampshire has named the server used by the computer science department after Turing.

The Boston GLBT pride organization,, named Turing their 2006 Honorary Grand Marshal



Turing biographies Edit

  • Andrew Hodges wrote a definitive biography Alan Turing: The Enigma in 1983 (see references below).
  • Leavitt, David (2005). The Man Who Knew Too Much: Alan Turing and the Invention of the Computer, New York: W. W. Norton. ISBN 0393052362.

Turing in fictionEdit

See also Edit


  1. Hodges, 1983, p. 26
  2. 2.0 2.1 Copeland, 2006, p. 378
  3. Copeland, 2006, pp. 382-383

References Edit

  1. REDIRECT Template:MacTutor

External links Edit

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