Passport photo of Alan Turing at age 16

Alan Mathison Turing (1912 – 1954) was a British mathematician, logician, cryptanalyst and computer scientist. He was highly influential in the development of computer science, giving a formalisation of the concepts of "algorithm" and "computation" with the Turing machine, which can be considered a model of a general purpose computer. Turing is widely considered to be the father of theoretical computer science and artificial intelligence.

During World War II, Turing worked for the Government Code and Cypher School (GC&CS) at Bletchley Park, Britain's codebreaking centre. For a time he led Hut 8, the section responsible for German naval cryptanalysis. He devised a number of techniques for breaking German ciphers, including the bombe method, an electromechanical machine that could find settings for the Enigma machine.

After the war, he worked at the National Physical Laboratory, where he designed the ACE (Automatic Computing Engine), among the first designs for a stored-program computer. In 1948 Turing joined Max Newman's Computing Laboratory at Manchester University, where he assisted development of the Manchester computers and became interested in mathematical biology.

Turing was prosecuted for homosexuality in 1952, when such acts were still criminalised in the UK. He accepted treatment with female hormones (chemical castration) as an alternative to prison. Turing died in 1954, 16 days before his 42nd birthday, from cyanide poisoning. An inquest determined his death a suicide; his mother and some others believed it was accidental. On 10 September 2009, following an Internet campaign, British Prime Minister Gordon Brown made an official public apology on behalf of the British government for "the appalling way he was treated."

In May 2012, a private member's bill was put before the House of Lords to grant Turing a statutory pardon. In July 2013, it gained government support; however, instead of calling for the second reading of the bill through the House of Commons, the government opted for a posthumous pardon under the royal prerogative of mercy, which was signed on 24 December 2013 with immediate effect.

His parents enrolled him at St Michael's, a day school at 20 Charles Road, St Leonards-on-Sea, at the age of six. The headmistress recognised his talent early on, as did many of his subsequent educators.

In 1926, at the age of 13, he went on to Sherborne School, a well known independent school in the market town of Sherborne in Dorset. Turing's natural inclination toward mathematics and science did not earn him respect from some of the teachers at Sherborne, whose definition of education placed more emphasis on the classics. Despite this, Turing continued to show remarkable ability in the studies he loved, solving advanced problems in 1927 without having studied even elementary calculus. In 1928, aged 16, 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.

After Sherborne, Turing studied as an undergraduate from 1931 to 1934 at King's College, Cambridge, from where he gained first-class honours in mathematics. In 1935, at the young age of 22, he was elected a fellow at King's on the strength of a dissertation in which he proved the central limit theorem.

In June 1938, he obtained his PhD from Princeton; his dissertation, Systems of Logic Based on Ordinals, introduced the concept of ordinal logic and the notion of relative computing, where Turing machines are augmented with so-called oracles, allowing a study of problems that cannot be solved by a Turing machine.

From September 1938, Turing had been working part-time with the GCCS, the British code breaking organisation. He concentrated on cryptanalysis of the Enigma, with Dilly Knox, a senior GCCS codebreaker. Soon after the July 1939 Warsaw meeting at which the Polish Cipher Bureau had provided the British and French with the details of the wiring of Enigma rotors and their method of decrypting Enigma messages, Turing and Knox started to work on a less fragile approach to the problem. The Polish method relied on an insecure indicator procedure that the Germans were likely to change, which they did in May 1940. Turing's approach was more general, using crib-based decryption for which he produced the functional specification of the bombe (an improvement of the Polish Bomba) which proved very instrumental in deciphering the Enigma-machine.

In July 1942, Turing devised a technique termed Turingery (or jokingly Turingismus) for use against the Lorenz cipher messages produced by the Germans' new Geheimschreiber (secret writer) machine.

A Turing machine is a hypothetical device that manipulates symbols on a strip of tape according to a table of rules. Despite its simplicity, a Turing machine can be adapted to simulate the logic of any computer algorithm, and is particularly useful in explaining the functions of a CPU inside a computer.

At age 18, after the death of a close friend of his (Christopher Morcom), He became an atheist and adopted the conviction that all phenomena, including the workings of the human brain, must be materialistic, but he still believed in the survival of the spirit after death.

An Enigma machine was any of a family of related electro-mechanical rotor cipher machines used in the twentieth century for enciphering and deciphering secret messages. Enigma was invented by the German engineer Arthur Scherbius at the end of World War I. Early models were used commercially from the early 1920s, and adopted by military and government services of several countries — most notably by Nazi Germany before and during World War II. Several different Enigma models were produced, but the German military models are the most commonly discussed.

In 1941, Turing proposed marriage to Hut 8 co-worker Joan Clarke, a fellow mathematician and cryptanalyst, but their engagement was short-lived. After admitting his homosexuality to his fiancée, who was reportedly "unfazed" by the revelation, Turing decided that he could not go through with the marriage.

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, putting forth the Turing hypothesis of pattern formation. His central interest in the field was understanding Fibonacci phyllotaxis, the existence of Fibonacci numbers in plant structures.

Since 1966, the Turing Award has been given annually by the Association for Computing Machinery for technical or theoretical contributions to the computing community. It is widely considered to be the computing world's highest honour, equivalent to the Nobel Prize.

The logo of Apple Computer is often erroneously referred to as a tribute to Alan Turing, with the bite mark a reference to his method of suicide. Both the designer of the logo and the company deny that there is any homage to Turing in the design of the logo. Stephen Fry has recounted asking Steve Jobs whether the design was intentional, saying that Jobs' response was, "God, we wish it were."

The Alan Turing Year, 2012, marks the celebration of the life and scientific influence of Alan Turing on the occasion of the centenary of his birth on 23 June 1912.

Source and more information:
Wikipedia article Alan Turing

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