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Neal Stephenson 


Alan Turing (1912-1954)
Alan Mathison Turing was born on 23rd June 1912 to Julius Mathison Turing and Ethel Sara Turing. Alan was the second child of the couple; he had an elder brother named John.

Alan Turing is now thought of as the godfather of modern computing science but he was unappreciated in his own lifetime particularly in the early years. He was born into the British upper middle class where science was looked down upon rather boys should grow up to become lawyers as John Turing did. Turing's mother was worried that his interest in science may have prevented his acceptance into public school. He was however despite her fears accepted at Sherborne School, but the headmaster thought he would be wasting his time and that Turing would not amount to much.

Whatever his school and peers may have thought of him, upon finishing school Turing was accepted at King's College, Cambridge in 1931. Cambridge University proved to be the ideal environment for Alan Turing and allowed him to explore both his intellectual pursuits and his homosexuality.

He received in 1934 a distinguished degree and then a fellowship of King's College the following year. This would have seemed to secure a future as an eccentric professor of mathematics, but Turing's true interest was to lead him elsewhere. Turing's future lay in the field of symbolic logic, furthering the work of Bertrand Russell and Alfred N Whitehead and their three volume Principia Mathematica. In 1935, he began to tackle Hilbert's Entscheidungsproblem, which asked:

Could there exist a mechanical process by which it could be decided if any given mathematical assertion was provable?

Analysis of this problem drove his thoughts to the conception of a theoretical machine able to perform elementary operations. Any mathematical method could be encapsulated in such a machine because any mathematical method can be broken down into a series of elementary operations. His theoretical machine became known as a Turing Machine. A further development of this idea is of a machine that would be equivalent to any possible Turing Machine such a machine would be a Universal Turing Machine.

He concluded that the answer to the Entscheidungsproblem was no, such a decision procedure does not exist. Turing's work was presented in a paper, On Computable Numbers with an Application to the Entscheidungsproblem. The history of mathematics has seen many coincidences, progress made by different people on the same subject working in complete isolation from the other person. In one such coincidence Turing's work was similar to that presented slightly earlier by Alonzo Church at Princeton University but Turing's approach was original, unique and of much importance to mathematics.

In September 1936, Princeton University saw the arrival of Alan Turing who had enrolled as a graduate student. Whilst at Princeton Turing came to the attention of a leading mathematician John von Neumann who had read the paper 'On Computable Numbers' that finally saw publication in December 1936. Turing had impressed von Neumann greatly, and so when he had finished his studies von Neumann offered him a temporary post at Princeton. However, Turing declined the offer and returned to England and Cambridge.

The year 1939 saw increasing tensions in Europe and it was thought that Britain might be facing the threat of war. It was decided that the operations of the Government Code and Cipher School should be expanded and moved to Bletchley Park, a country estate in Buckinghamshire. The now larger GC&CS needed to attract people to work at Bletchley Park and so Alan Turing began to work there on a part time basis. On 3rd September 1939, World War II started and Turing became a full time cryptanalyst at Bletchley Park this began the most important period of his life.

Bletchley Park is now widely known as the organisation responsible for the cracking of Germany's Enigma encryption system, and Alan Turing was to make a huge contribution to this effort. The initial work for the cracking of Enigma had actually been carried out by Polish cryptanalysts during the previous decade who had created a machine they named the Bombe. This work was built upon by the British and under direction from Turing; a new and improved version of the Bombe was constructed. The Bombe was capable of breaking an Enigma encrypted text through brute force (trying many possibilities until the correct one is hit upon). The decrypted Enigma texts were codenamed Ultra. The work at Bletchley Park was of utmost secrecy and remained so for decades so Turing was not able to tell his parents of his work or of his importance to the war effort.

In February 1942, a disaster befell the cryptanalysts of Bletchley Park they discovered that they could no longer decrypt messages sent using the German Navy's version of the Enigma. This was because the machines had been altered to make them more complicated and hence far more complicated to break, this new version was codenamed Shark. The advantage that the Allies had held was swept away and it seemed that the war of the Atlantic might be lost. This crisis forced the brilliant minds of Bletchley Park particularly Turing's to focus and try to discover a solution.

Although not responsible for the insight that broke Shark Turing was again instrumental to the Allies codebreaking efforts during this period. He conceived of an electro-mechanical computing device, the size of three wardrobes and containing 1500 vacuum tubes it was named Colossus. The machines construction was finished in December 1943 and although primarily constructed to break Shark it was often used to crack the Nazi's most heavily encrypted messages sent by the high command. Colossus is one of the contenders for the title of first digital computer but it was not a Universal Turing Machine.

In the meantime, Turing was working on a method for the encipherment of speech signals in order for Churchill and Roosevelt to communicate securely over the telephone. With the war all but won and his success with Colossus Turing's mind turned again to his Universal Turing Machine. Turing was intrigued by the possibility of being able to construct his machine; he wrote a paper about his design for what was in effect a modern digital computer.

Yet again in his life his publication was pre-empted by that of an American this time John von Neumann and his plan for a digital computer. However, unbeknownst to both Turing and von Neumann there was another plan for a digital computer that was under way during this period, built by Mauchly and Eckert it was called ENIAC and was completed in 1946. Fortunately, for Turing the American publication by von Neumann allowed him to gather support for a British project to rival the Americans to be built at the National Physical Laboratory. Turing was appointed as a Senior Principal Scientific Officer at the National Physical Laboratory so that he could oversee the project.

However, the end of the war also saw the end of the wartime spirit of cooperation and the return of the typical British bureaucracy. Turing's plan never saw fruition at the NPL and so he left to become the Deputy Director of the computing laboratory at Manchester University in October 1948. With various computing projects underway in various organisations it became clear that Turing was no longer critical to the building of a digital computer and he become sidelined from his own project. His mind began to dwell on more prosaic subjects such as artificial intelligence and in 1950; he published Computing Machinery and Intelligence. Turing's sexuality had been an open secret for many years, but the advent of the Cold War saw increasing paranoia by those in power and because he was homosexual he had his security clearance revoked.

His sexuality or more precisely the authorities attitude towards it would be the downfall of Turing that led to his death. Whilst giving a statement to the police following a burglary at his home he casually mentioned that his lover was a man. The police promptly arrested him and he was tried for homosexual practices on 31st March 1952, offering no defence as he believed that he had done nothing wrong he was found guilty. He accepted a series of hormone injections intended to quell his libido rather than face imprisonment.

During this period Alan Mathison Turing became increasingly depressed and finally committed suicide by eating a cyanide-coated apple. His body was discovered in bed at his home by his cleaner on the 8th June 1954.

If you are interested in Alan Turing and would like to learn more about him why not visit http://www.turing.org.uk/turing/ or read this excellent book about his life.
Alan Turing: The Enigma

by Andrew Hodges

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