Turing, Alan | Research & Encyclopedia Articles

Alan Mathison Turing (1912–1954), the founder of modern computer science and an important World War II cryptanalyst, was born in London on June 23. He died near Manchester, England, on June 7. His short life illustrates the ethical conflicts and ambiguities of scientific and technological aspirations.

Turing's early life was characterized by an intense enthusiasm for science that was only weakly supported by his upper-middle-class family. In 1931 he became an undergraduate at Cambridge University and read mathematics, demonstrating a rapidly emerging originality. At age twenty-four he settled an important problem in the foundations of mathematics, using a method that had much wider implications. Turing developed a precise way to characterize the concept of the "effectively calculable." This consisted of the "Turing machine," as the logician Alonzo Church immediately dubbed Turing's construction when reviewing it in 1937.

A Turing machine is an imaginary device with a finite number of possible configurations, a finite table of instructions for moving from one configuration to another, and the capacity to read, erase, and write a set of finitely many different symbols on a tape. With this structure Turing captured the idea of a finite mechanism, which he compared with the finite capacity of the human mind. By allowing unlimited space and time for working out the machine's operations, Turing was able to argue that such a device could encompass everything that could be achieved by a human calculator following a definite rule. Church endorsed Turing's argument that the concept of "effectively calculable" had been given a natural and convincing definition in terms of being computable by a Turing machine, a proposition now known as the Church-Turing thesis.

More recently there has been discussion of whether there could be, in the real universe or an imaginary one machines capable of operations beyond the scope of a Turing machine, and this debate has generated controversy about the correct interpretation of the Church-Turing thesis (Floridi 2003). At the time, however, Church simply characterized "computable" by reference to what could be done by any kind of machine of a finite size, and Turing similarly referred to that term as being synonymous with mechanical.

What is not in dispute is the fact that the Turing machine is still definitive as the foundation for computer science. By attacking an abstruse problem in the most rarefied and philosophical aspects of mathematics Turing arrived at the principle behind the dominant technology of the late twentieth century. Indeed, it was Turing who, seeing the practical potential of his ideas in 1945, was a leading designer and promoter of the electronic computer and its software.

However, this was possible only because of world events between 1938 and 1945 that gave Turing unique insight into practical computation and the promise of digital electronic technology. During the World War II Turing was the chief scientific figure in the successful British effort to decipher coded German communications, a project that became a joint Anglo-American operation after 1941. Turing's ingenious logical methods and theory of information measuring were used throughout the communications war, especially in the section he personally headed, which was responsible for reading U-boat signals.

By 1945 Turing thus possessed unrivaled theoretical and practical experience in the emergent field of information processing. He was disappointed by the practical progress of his plans at the National Physical Laboratory,the British government establishment to which he was appointed. He soon left to take up another, also disappointing, position at Manchester University. However, those short-term setbacks illustrated the fact that Turing's interest was never in the economic potential of computers but only in the long-term scientific question of what he called intelligent machinery, now usually referred to as artificial intelligence.

Is the computer in principle capable of rivaling human thought? That question was hinted at even in Turing's prewar references to human memory and states of mind but became much more prominent after 1945. In that period Turing went much further than he had in 1936, arguing that the computer could emulate all aspects of human thought, not merely those corresponding to a human being following a definite method. At that time he also spoke frequently about the physical basis of mental operations and informally described his work as "building a brain."

A crucial element in Turing's argument is that the computer is a practical form of a universal machine that is capable of performing any algorithm. According to this argument, if the function of the brain can be described as any sort of definite process, in principle a computer can simulate it. It is not suggested that the architecture of the brain should resemble that of a digital computer. Another vital part of Turing's argument is that programs that modify themselves can be considered as learning from experience. He expected them to show the features of surprise and originality that characterize the apparently "nonmechanical" aspects of human thought. Turing's famous 1950 paper (reprinted in Boden 1990) introduced the "imitation game," now called the Turing test, in an attempt to make an objective comparison between computational and human processes.

Interest in these issues has never flagged. The arguments of Roger Penrose (1989) have supplied important new ingredients. It is noteworthy that the interpretation of Gödel's theorem and the quantum-mechanical nature of matter, which are central to Penrose's arguments, are also issues that Turing found important and difficult to address.

The Turing test for intelligence can be accused of having been set up to evade questions of consciousness and responsibility: It is the problem of mind made into a game perhaps in the way codebreaking made it possible to think of World War II as a fascinating and exciting but bloodless game. In real life Turing struck everyone as a person of great integrity, not as a superficial or insensitive person. However, he did not offer an ethical view in his writing on mind and machines. It was the same with the war in which he played so important a role: Turing never spoke about motivation or political allegiance, though his actions showed a strong commitment to the defeat of Nazi Germany. His moral speech was generally directed against anything "phony." In this he was like G. H. Hardy, the Cambridge champion of pure mathematics, but whereas Hardy hated war and rejoiced if his work was "useless" for it, Turing applied mathematics to more effect in war than perhaps anyone else ever had.

After 1950 Turing devoted himself mainly to a mathematical theory of biological growth and form, a quest roughly parallel with the elucidation of DNA. This time he stated a motivation: to defeat the religious "argument from design" and vindicate the power of scientific explanation. However, in 1952 Turing was arrested as a homosexual, and after the ensuing trial he was sentenced to receive injections of estrogen, which was the advanced "scientific" treatment of that period. Turing rose to the crisis with a staunch defense of his personal liberty and equality that has become a standard of European human rights but in his time was an isolated position. He was even more isolated because of his unique access to sensitive Anglo-American military secrets. At the height of Cold War paranoia in June 1954 Turing found his life impossible. He died by taking cyanide.

That period has been dramatized for the stage and television (Whitemore 1986) in scenes in which a fictional Turing gives speeches to an audience, but the real person left his life without a word about the major ethical conflicts he faced. Although Turing was a farsighted and original thinker on fundamental scientific questions and an extraordinary personality, in his silence and unwillingness to pontificate he bore witness to a particular view of scientific practice.

Artificial Intelligence;; Computer Ethics;; Turing Tests;; Von Neumann, John.

Boden, Margaret A. (1990). The Philosophy of Artificial Intelligence. Oxford, UK: Oxford University Press. Classic papers, beginning with Turing's.

Davis, Martin. (2000). The Universal Computer: The Road from Leibniz to Turing. New York: Norton. A vivid exposition of Turing's 1936 work as the culmination of symbolic logic.

Floridi, Luciano. (2003). Blackwell Guide to the Philosophy of Computing and Information. Oxford, UK: Blackwell.

Hardy, G. H. (1940). A Mathematician's Apology. Cambridge, UK: Cambridge University Press. A classic essay on the ethics of mathematics from Turing's Cambridge background.

Hodges, Andrew. (1983). Alan Turing: The Enigma. London: Burnett; New York: Simon & Schuster. New editions: London, Vintage 1992; New York, Walker 2000.

Penrose, Roger. (1989). The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics. Oxford and New York: Oxford University Press. A serious challenge to Turing's theory of mind that shares Turing's materialist assumptions and base in mathematics.

Whitemore, Hugh. (1986). Breaking the Code. New York: Samuel French. A stage dramatization of Turing's life.

Hodges, Andrew. Alan Turing Website. Available at http:/www.turing.org.uk. Covers all aspects of Turing's life and work.

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