Alan Mathison Turing (23 June 1912 – 7 June 1954) was a British mathematician who is generally recognized as the father of computer science. He also made contributions to cryptography, and artificial intelligence.
Inventing computer science is not the same as inventing the computer. The invention of the computer—that is, a device that can automatically process data algorithmically, goes back to the non-electronic "analytical engine" devised (but never actually built) by Charles Babbage and Ada Lovelace. Actual electronic computers were invented by John Atanasoff in the 1930s and J. Presper Eckert and John Mauchly in the 1940s, among others. Alan Turing was associated with one of the early engineering efforts in the 1940s to make practical computers, the "ACE" (Automatic Computing Engine) project at the UK's National Physical Laboratory, but it was bested by the ENIAC, EDSAC, and EDVAC projects elsewhere.
Alan Turing's claim to fame came from the invention of the field of Computer science. He took the concepts of mathematical logic and recursive function theory, from such people and Alonzo Church and Kurt Gödel , and showed that a certain type of automatic computing device, called a Turing machine, was deeply connected to those concepts. His major paper on the subject was the 1937 paper On Computable Numbers, with an Application to the Entscheidungsproblem, in the Proceedings of the London Mathematical Society. ("Entscheidungsproblem" is a German word for "decision problem", a term that logicians were using.) The concepts of Decidability, the Halting problem, and the Turing machine, all staples of college-level computer science, originated with him.
Turing is also known for his contributions to the Allied war effort in World War II with the work of breaking the Nazi Enigma codes. He formuated the "Turing Test" as a criterion for determining whether a computer can actually exhibit humanlike intelligence.
There is a prestigious annual "Turing Award", considered the computer science equivalent of the Nobel Prize, named after him, and a separate annual invited "Turing Lecture" in the UK. There are buildings named after him, and statues of him at Bletchley Park, where the wartime cryptography work was done, and in Manchester.
Turing was sent to Sherborne School in Dorset, a private school for boys, where he showed great aptitude for maths and science, no interest in any other subject, and a lack of social skills. His spelling and handwriting remained poor throughout life. However he obtained a place at King's College, Cambridge University where he became a follower of John Maynard Keynes. He did postgraduate work and then in 1936 went to study at Princeton University in the USA. His mother later wrote of him "in dress and habits he tended to be slovenly".
The Turing Machine
At Princeton, Turing proposed the concept of a "Universal Machine". Turing had first proposed that the operations needed to calculate any formula could be broken down into a base set of instructions (or primitive recursive functions) that could, in principle, be followed by a machine: the "Turing Machine". Once fully formalized, the calculations needed to derive the instructions themselves were capable of being run by a Turing Machine. The looped logic allowed the conception of a Turing Machine that could create its own instruction and, in principle, run a huge variety of calculations. Turing then used the concept of Universal Turing Machine to prove the undecidability of the halting problem. After gaining his PhD in June 1938, he returned to Cambridge University.
During World War II Turing was assigned to the codebreaking unit at Bletchley Park, where he worked on the decoding of the German's Enigma machine. Turing's contribution to the war effort has been massively exaggerated. He was actually only one of hundreds of people working at Bletchley, including John Tiltman the chief cryptographer, who was in charge of all projects, and the mathematicians Bill Tutte, Max Newman and Tommy Flowers. Other members of the team Turing worked in included R.V. Jones and Peter Calvocoressi. Work on breaking the Enigma code had started long before the war, and cryptographers from all over Europe including Poland, had done the ground work.
In June 1938, Sir Stewart Menzies, the chief of MI6, received a message that the Polish Intelligence Service had encountered a man who had worked as a mathematician and engineer at the factory in Berlin where the Germans were producing the Enigma Machine. The man, Richard Lewinski (not his real name), was a Polish Jew who had been expelled from Nazi Germany because of his religion. He offered to sell his knowledge of the machine in exchange for £10,000, a British passport and a French resident permit. Lewinski claimed that he knew enough about Enigma to build a replica, and to draw diagrams of the heart of the machine - the complicated wiring system in each of its rotors. Menzies suspected that Lewinski was a German agent who wanted to "lure the small British cryptographic bureau down a blind alley while the Germans conducted their business free from surveillance". Menzies suggested that Alfred Dilwyn Knox, a senior figure at the Government Code and Cypher School, should go to interview Lewinski. He asked Turing to go with him. They were soon convinced that he had a deep knowledge of the machine and he was taken to France to work on producing a model of the machine. 
Turing's work on Enigma was greatly helped in May 1941 by the lucky capture of an Enigma machine from a German U-boat, which pushed the project forward by several years.
In the later part of WW2, because of the capture of the Enigma machine, the Nazis shifted from using the Enigma code to using a far more complicated one. They called it the Lorenz cipher and the Bletchley control nicknamed it Tunny, or the Fish. While the Enigma code machine had only three wheels, the Tunny machine had twelve, and had other random tricks built into it to make decoding so difficult that even a mathematician could hardly calculate all the possible combinations. The code changed with every letter of the same message. In the later part of the war, from 1943 onwards, Tunny, not Enigma, was the code that the Germans depended on for their top-most secrets and attack plans. Tutte and Flowers worked on breaking the Tunny code.
Bill Tutte, the principal mathematician who undertook the work on Tunny, came from a humble background, being the son of a gardener and a cook, and he went to a grammar school - unlike Turing who had been to an elite private school. From there Tutte won a scholarship to university where he studied chemistry. He was aged only 24 when he arrived at Bletchley. His feats of deduction and analysis were extraordinary and have been described as a "miracle". Because the sheer quantity of data to be processed was overwhelming, Professor Max Newman suggested that they try to build a calculating machine along the lines suggested by Turing. Turing took no other part in the Tunny project. Turing's first machine did not work very well and the successful machine, "Colossus" was built by Tommy Flowers. He was a Post Office telephone engineer from a working-class background. He used electric circuits and vacuum tubes (called "valves" at the time). Because all this work was top secret, even after the war ended, neither of them could talk about what they had done or get credit for it.
In his 1950 paper "Computing Machinery and Intelligence", Turing proposed a test (apparently heavily influenced by Logical Positivism) for establishing whether a computer could think, which he called the Imitation Game. This test, now known as the Turing test, is still widely considered to be the best test of whether a machine exhibits characteristics of artificial intelligence.
Sexuality and prosecution
Turing's reputation has been inflated by those who wish to glorify him as a "gay genius" and "gay martyr". While at Cambridge University, where homosexuality was prevalent, he had intimate relationships with other men. In December 1951, when working as a mathematics lecturer at Manchester University, he went to the police and complained that a young man who had spent the night at his house had stolen a sum of money from him. The police questioned the young man, 19-year-old Arnold Murray, who told them that Turing had picked him up in a public house and taken him home for homosexual purposes, then illegal. This meant that the police had no choice but to prosecute Turing, who was not given a custodial sentence, but ordered by the court to undergo chemical treatment. As a result of the conviction, Turing lost his security clearance for government work. A year later, he was found dead, prompting speculation that he committed suicide.
Death and posthumous reputation
Turing was found dead by his housekeeper on June 8, 1954. The cause of death after an autopsy was determined to be cyanide poisoning; however, there was also a half eaten apple beside the bed. The apple was not tested for traces of cyanide. Turing's death has been cause for much speculation, as parts of it seem accidental; for instance, the poisoning seems more consistent with inhalation than ingestion, leading some to believe that he accidentally inhaled fumes while sleeping from an apparatus of his set up in the spare room. Some speculate that Turing wished his death to appear accidental in order to spare his mother's grief. This is called plausible deniability.
These events have been dramatized in Hugh Whitemore's play Breaking the Code and in the Hollywood film The Imitation Game both of which have contributed to the growing myth of a "gay martyr". The inaccuracy of that picture is measured by the fact that there were many university lecturers in this period who were openly homosexual and no steps were taken against them. There were also many cases of heterosexuals committing suicide because of sex-scandals, the most famous being Dr Stephen Ward, who was mixed up in the Profumo affair in 1963, and may have been wrongly convicted.
- Computing Machinery and Intelligence
- Oddballs and Eccentrics. Shaw, Karl. Edison, New Jersey: Castle Books, 2004.
- Steven Homer, Alan L. Selman: Computability and Complexity Theory, p. 35
- The Biography of Alan Turing, turing.org
- http://www.computerweekly.com/video/Unsung-heroes-of-IT-The-story-of-Bill-Tutte-and-Tommy-Flowers https://www.telegraph.co.uk/news/obituaries/1393587/Professor-Bill-Tutte.html http://www.stephenkettle.co.uk/turing.html
- The housekeeper found him the morning after he had died
- Hodges, Andrew (1983). Alan Turing : the Enigma. London: Burnett Books. ISBN 0-09-152130-0.
- Pease, Roland (23 June 2012). "Alan Turing: Inquest's suicide verdict 'not supportable'". BBC News.