Turing, Alan M

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Turing, Alan M.

British Mathematician and Cryptographer

Alan Mathison Turing was one of the leading theoreticians in computer science. Turing was something of a visionary in that his hypothetical "Turing Machine" set the standard for the description of computation and its relation to human computing.


Turing was born on June 23, 1912, to upper-middle-class parents in London, England. He was educated in traditional British schools including St. Michael's, a day school, where he learned Latin; Hazelhurst, a preparatory boarding school, where he studied to pass Great Britain's Common Entrance exam; Sherbourne, a high-school-level boarding institution, where he prepared for university admission; and finally, King's College, Cambridge, for university.

Upon graduation from the university, he won a research scholarship of 200 British pounds per year, which enabled him to stay on another year and try for a King's fellowship. This required a dissertation, which he wrote on the Gaussian error function, the Central Limit Theorem in statistics. In 1935 he was one of forty-five students who won the King's fellowship. This enabled him to attend Princeton University in the United States.

At Princeton he had contact with John von Neumann (19031957), who is widely credited as the inventor of the "stored program" computer, although this concept pre-dated him through the work of Charles Babbage (17911871). Turing also worked with Alonzo Church (19031995), one of the leading logicians of the day during his time at Princeton. He eventually earned his Ph.D. from Princeton in 1938. His dissertation, "Systems of Logic Based on Ordinals," was on the axioms of mathematics.

The Turing Machine

In 1936 Turing wrote an article describing a general machine for computation. It is taken as a description of a hypothetical computing machine, although Turing had in mind the human computer performing a typical calculation or computation. He suggested that the machine would need a tape of indefinite length to serve as a data storage device; a set of instructions; the ability to read, write, and manipulate cells on the tape; and the ability to move forward and backward along the tape. With this system, a single symbol would be stored in a cell, with the computing device able to read the value in the cell, write to the cell, or erase the value stored there. It would take action based on the contents of the cell, write, erase, move forward or backward.

The Turing Machine is widely regarded as the general model of a computing device, and its basic premise is sometimes still used to determine whether a computation or other problem can be solved by a general purpose computer. If it can be solved using the Turing Machine principles and methods, it can be done with a general-purpose computer.

Although the concept of the Turing Machine was not immediately accepted, nor even widely known in its day, it has come to be the standard in computing theory. As a result, the Association of Computing Machinery (ACM) has instituted an award in Turing's name which is given to the most accomplished practitioners and theoreticians of its field.

Turing's Career

Turing worked with or was friends with many of the leading scientists of his day including Donald Michie (1923), who became famous for his work in machine learning; Claude Shannon (19162001), the developer of mathematical communication theory; E.C. Titchmarsh (18991963), an Oxford mathematician; and M.V. Wilkes (1913), among others. He met Shannon at Bell Laboratories, where he worked for a time with the speech encryption unit during World War II.

As a war-time cryptographer, Turing worked for the British government, deciphering codes for Allied military operations. This occurred at Bletchley Park, for the Government Code and Cypher School. He also worked for the government secret service, in speech encryption, and was an envoy to Washington, D.C., as a liaison for the encryption and decryption effort.

After the war, Turing went to work at the National Physical Laboratory, and then, in 1948, at the University of Manchester, where he worked with one of the early computers. Although he developed a plan for an early computer, the ACE, or Automatic Computing Engine, it was never implemented.

Turing also devised "a Turing test" that is still used to determine humanlike behavior in the development of artificial intelligence, albeit imperfectly. He indicated that a computer and a person (or a male and a female) could be isolated in a separate room and interrogated by an "observer." If the observer, asking whatever questions he or she wanted, could not tell the difference between the answers given by the two, then there was no difference in their behavior. This is, of course, not entirely certain, but it gives an operational definition of "humanlike" behavior, in determining if indeed a computer "can think."

Turing was appointed to the Order of the British Empire, and, in 1951, elected a fellow of the Royal Society. Although he was considered a slow student during his early schooling, Turing was later acknowledged as one of the innovative thinkers of his time. He received a number of honors during his lifetime, but he has received greater acclaim in the decades since his death.

Personal Life

Turing was avidly interested in solitary pursuits such as bicycling, running, and general exploration of the countryside. He was said to have been a playful sort, once he trusted a person's friendship, although it is also reported that this was not always an easy accomplishment.

At one point, Turing was engaged to be married to Joan Clark, a colleague at Bletchley Park, although this never materialized. He was also befriended by and was a friend to Lyn Newman, the wife of Max Newman, a professor of mathematics at Cambridge.

Turing's professional life was complicated by the fact that he was an avowed homosexual in an era when this was not publicly accepted. In 1952 he was arrested and subsequently required to undergo treatment, which led to a certain amount of embarassment, though he tried to minimize this. He continued to work at Manchester on several projects: the computer, mathematics, and his interest in human cognition and the development of living things. However, this period was to be shortlived. Turing died a short time later, on June 7, 1954.

The circumstances of Turing's death are unresolved. He died of cyanide poisoning; a partially eaten apple was found nearby his body, but it was never examined. Although Turing's mother attributed the death to a tragic accident, the coroner's office ruled it a suicide.

see also Artificial Intelligence; Codes; Mathematics; Turing Machine.

Roger R. Flynn


Hodges, Andrew. Alan Turing: The Enigma of Intelligence. London: Unwin Paperbacks, 1983.

Internet Resources

The Alan Turing Homepage. <http://www.turing.org.uk/turing/>