Turing Machine

1937

Alan Turing (1912–1954)

Alan Turing, a young British mathematician, was responsible for one of the great advances that helped make modern digital computing possible and thus laid the groundwork for the later study of artificial intelligence. In 1936, in a paper entitled “On Computable Numbers,” Turing proposed a computational device designed to investigate the limitations of what can be computed, proving that a machine could calculate anything that was quantifiable and offering a workable definition of computation that was used as the basis for developing the modern digital computer program. In 1937, Turing’s hypothetical machine was christened a Turing machine.

Turing used his mathematical skills to help break the German military codes during World War II. He used a computational method modeled on his earlier theoretical work that guided a machine, named the bombe, through nearly all possible number-letter combinations until a comprehensible message was generated. Turing showed how the concept of computation can be expressed in terms of a system of rules. In her book Mind as Machine (2006), researcher Margaret Boden wrote that the significance of the exercise was to show how “abstract machines could be described in a standard logical form, and how they could be used to do elementary computations out of which all standard arithmetical operations could be constructed.”

In 1950, Turing asked the question, “Can a machine think?” He devised a thought experiment—the Turing test—in which a human judge has a “conversation” with another person and a machine; the conversation is conducted via a keyboard, and the participants are not visible to one another. The machine has passed the test if the judge cannot tell the difference between the respondents’ answers. Although only a thought experiment, the Turing test proved important for later developments in artificial intelligence.

SEE ALSO Cybernetics (1943), Logic Theorist (1956)

U.S. Navy version of the bombe device, developed by Alan Turing and used by British cryptologists against the German cipher machine Enigma–M4 to decipher encrypted messages during World War II.