Alan Mathison Turing (June 23, 1912–June 7, 1954) was a British mathematician, logician, and cryptographer, and is considered to be one of the fathers of modern computer science. He provided an influential formalisation of the concept of algorithm and computation: the Turing machine. He formulated 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 he worked on breaking German cyphers, particularly the Enigma machine; he was the director of the Naval Enigma section at Bletchley Park for some time. After the war, he designed one of the earliest electronic programmable digital computers at the National Physical Laboratory and, shortly thereafter, actually built another early machine at the University of Manchester. He also, amongst many other things, made significant and characteristically provocative contributions to the discussion "Can machines think?"
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 (née Stoney) wanted Alan to be born in Britain, so they returned to Paddington where Alan was eventually born. His father's Indian Civil Service commission was still active, and during Turing's childhood years his father travelled between England and India, leaving his family to stay with friends in England due to concerns over the dangers of 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 recognised his genius early on, as did many of his subsequent educators at Marlborough College (a public school). At Marlborough, he first reported having problems with bullies. In 1926, and 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 the sciences did not earn him respect with the teachers and administrators at Sherborne, whose definition of education placed more emphasis on the classics rather than the area of science. But despite this, Turing continued to show remarkable ability in the studies he loved, solving advanced (for his age) problems in 1927 without having even studied elementary calculus.
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 his final examinations several times, and went on to the college of his second choice, King's College, Cambridge, rather than his first choice, Trinity. He studied under G. H. Hardy, a well respected mathematician who held the Sadleirian Chair at Cambridge, then a centre for mathematical research and study, from 1931 to 1934. In 1935 he was elected a Fellow at King's College.
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 unsolvable: 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 the World War II he was a major participant in the efforts at Bletchley Park on cracking Nazi cyphers. He contributed several mathematical insights, both to breaking the Enigma cypher machine and the Fish teletype cyphers (teletype cypher machines made by both Lorenz Electric and Siemens & Halske). The Fish insights were useful in the development of the first digital programmable electronic computer Colossus, which was designed by Max Newman and team, and built at the Post Office Research Station at Dollis Hill by a team led by Thomas Flowers in 1943. It was used to crack Fish cyphers (in particular the Lorenz machine traffic).
To help crack the Enigma machine, Turing designed the bombe, an electromechanical machine - named in recognition of the Polish-designed bomba - which could be used to eliminate large numbers of candidate Enigma keys. For each possible setting, a chain of logical deductions was implemented electrically. 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 Allied codebreakers to read Enigma traffic.
Turing's codebreaking work was kept secret until the 1970s; not even his close friends knew about it.
Work on early computers; the Turing Test
From 1945 to 1948 he was at the National Physical Laboratory, where he worked on the design of ACE (Automatic Computing Engine). 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 1952 Turing wrote a chess program. Lacking a computer powerful enough to execute it, he simulated the computer, taking about half an hour per move. One game was recorded; the program lost to a colleague of Turing.
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 during that period. 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.
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 Manchester University 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 (http://portal.surrey.ac.uk/press/oct2004/281004a/) of Alan Turing sculpted by John W. Mills was unveiled at the Surrey University. The statue marks the 50th anniversary of Turing's death. It portrays Turing carrying his books across the campus.
Turing in literature