He was born in Paddington to Civil Service[?] officer Julius Mathison Turing and his wife Ethel (née Stoney). 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 made a habit of stopping at street corners to read the serial numbers off of street lights. The love of numbers that gripped him at so early an age was to remain with him for life, leading him into a remarkable career distinguished by significant contributions to the fields of mathematics and computation.
Other stories about Turing's childhood also reveal a mind which enjoyed challenges and puzzles. While picnicking with his family, he traced the paths of flying bees and by using their paths as vectors determined the location of their hive, rewarding his family with honey for their repast. Another story, recounted in the quasi-historical novel Cryptonomicon, tells of a bicycle chain which, due to a broken link, would disengage from its gear every so many revolutions. Rather than take the simple route of replacing the chain, Turing counted the revolutions of the chain and when a derailment was imminent, stopped the bike and advanced it past the broken link. Later, he is said to have developed a mechanism to automatically advance the chain at the appropriate time.
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 at Marlborough College (a public school). At Marlborough, he first reported having problems with bullies. He went on to the Sherborne[?] boarding school at 13, where his first day was actually covered in the local press. There was a general strike in England, and Turing rode his bike sixty miles to school, stopping overnight at an inn.
Turing's natural inclination toward the sciences did not earn him respect with the teachers and administrators at Sherborne, whose definition of education did not value emphasis on the field of science. Prevailing sentiments were that a properly educated young Englishman should have a well rounded education in the Classics, not a narrow one. One of his form-masters referred to the hard sciences as "low cunning" and credited the Englishman's emphasis on religious studies for their victory in the First World War, not their scientific achievements. But despite this, Turing continued to show remarkable prowess in the studies he loved, solving advanced (for his age) problems without having even studied elementary calculus in 1927.
At this time in history, the field of physics was being reevaluated with the recent theories on quantum mechanics by Erwin Schrödinger and others, and Turing was again fascinated and enthralled by the field.
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. At King's College he finally found an institution where he could pursue his first love with all the diligence he had displayed from his childhood. He studied under G. H. Hardy, a well respected mathematician who held the Sadleirian Chair[?] at Cambridge. Cambridge was at this time a centre for mathematical research and study, and Turing found plenty of the challenge he so enjoyed.
It was in 1928 that David Hilbert and Kurt Gödel began their work in the field of theoretical mathematics, which were to lead into theories of computation and computability. Hilbert posed several questions about the completeness of mathematical theory, asking whether mathematics was complete, consistent and decidable. In attempting to answer these questions, Turing introduced Turing machines, formal devices capable of performing any conceivable mathematical problem once it was represented as an algorithm. However, the Turing machine was only a theoretical construct at that time and not a working implementation. It would remain for later researchers to solve the various practical difficulties required to make the computer a reality. Turing machines are to this day the central object of study in computational theory.
In his paper "On Computable Numbers, with an Application to the Entscheidungsproblem" (1936), he proved 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 that of Alonzo Church, 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.
He was a major participant in the code breaking efforts at Bletchley Park during the Second World War on cracking Nazi Enigma ciphers. He contributed several mathematical insights, both to breaking the Enigma code and the Fish teletype cyphers (machines made by both Lorenz and Siemens). The Fish insights were useful in the development of the special-purpose digital computer Colossus, which was developed by Max Newman and built at the Post Office Research Station at Dollis Hill by a team led by Thomas Flowers[?] in 1943 and used to crack Fish cyphers. Turing also designed advanced versions of the Polish "bombe" used to assist in finding keys for Enigma messages. These were electromechanical devices coupling several "Enigma machines" which were able to eliminate at high speed large numbers of possible key settings for blocks of Enigma traffic.
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 "intelligent".
Persecution 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, he was charged with "gross indecency and sexual perversion" (see sodomy law), 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 hormone injections, which lasted for a year, with side effects including the development of breasts during that period. In 1954, he died of poisoning after eating a cyanide-laced apple. Most believe that his death was intentional, and the death was ruled a suicide. His mother strenuously argued that the ingestion was accidental due to his careless storage of laboratory chemicals.
The Turing Award, awarded by the Association for Computing Machinery to a person for technical contributions to the computing community, is named for Alan Turing. The award is frequently referred to as the "Nobel Prize for computer science".