If all Alan Turing had done was answer, in the negative, a vexing question in the arcane realm of mathematical logic, few nonspecialists today would have any reason to remember him. But the method Turing used to show that certain propositions in a closed logical system cannot be proved within that system--a corollary to the proof that made Kurt Godel famous--had enormous consequences in the world at large. For what this eccentric young Cambridge don did was to dream up an imaginary machine--a fairly simple typewriter-like contraption capable somehow of scanning, or reading, instructions encoded on a tape of theoretically infinite length. As the scanner moved from one square of the tape to the next--responding to the sequential commands and modifying its mechanical response if so ordered--the output of such a process, Turing demonstrated, could replicate logical human thought.
The device in this inspired mind-experiment quickly acquired a name: the Turing machine. And so did another of Turing's insights. Since the instructions on the tape governed the behavior of the machine, by changing those instructions, one could induce the machine to perform the functions of all such machines. In other words, depending on the tape it scanned, the same machine could calculate numbers or play chess or do anything else of a comparable nature. Hence his device acquired a new and even grander name: the Universal Turing Machine.
Does this concept--a fairly rudimentary assemblage of hardware performing prodigious and multifaceted tasks according to the dictates of the instructions fed to it--sound familiar? It certainly didn't in 1937, when Turing's seminal paper, "On Computable Numbers, with an Application to the Entscheidungsproblem," appeared in Proceedings of the London Mathematical Society. Turing's thoughts were recognized by the few readers capable of understanding them as theoretically interesting, even provocative. But no one recognized that Turing's machine provided a blueprint for what would eventually become the electronic digital computer.
So many ideas and technological advances converged to create the modern computer that it is foolhardy to give one person the credit for inventing it. But the fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine.
Turing's 1937 paper changed the direction of his life and embroiled a shy and vulnerable man ever more directly in the affairs of the world outside, ultimately with tragic consequences.
Alan Mathison Turing was born in London in 1912, the second of his parents' two sons. His father was a member of the British civil service in India, an environment that his mother considered unsuitable for her boys. So John and Alan Turing spent their childhood in foster households in England, separated from their parents except for occasional visits back home. Alan's loneliness during this period may have inspired his lifelong interest in the operations of the human mind, how it can create a world when the world it is given proves barren or unsatisfactory.