Life's Greatest Secret by Matthew Cobb Read Free Book Online

such a ‘Brain’ would be capable of more than just doing complicated sums: ‘Shannon wants to feed not just data to a Brain, but cultural things! He wants to play music to it!’ Turing exclaimed in a letter. 18 More significantly, the two men also exchanged their ideas about signal transmission, how to measure the content of communication, and how to incorporate uncertainty into their mathematical procedures. Turing had developed the concept of ‘decibans’, which were a measure of the uncertainty contained in a message; Shannon was on the brink of defining the ‘binary digit’ or ‘bit’, which could have two states – 0 or 1 – and was at the heart of postwar computing. At the beginning of March, Turing returned to England on the hazardous north Atlantic crossing, the only civilian on a 4,300-strong troop ship. The next time the two men met was after the war, in Manchester, where Turing was working on Baby, the world’s first stored-program computer.
    Shannon was part of the Bell Labs team working with the MIT Rad Lab on fire control. Like Wiener, Shannon’s job was to come up with a method for predicting the location of the target, and the two men discussed this question several times. Bigelow later recalled that Wiener was extremely generous, exchanging ideas with the younger man, sharing his insights. Eventually Wiener’s generosity began to wear off and – perhaps because of his amphetamine abuse – he started to react in a paranoid fashion to Shannon’s visits, telling close friends that Shannon was ‘coming to pluck my brains’, and doing his best to avoid the visitor. 19
    Although Shannon was clearly inspired by some aspects of Wiener’s work in the Yellow Peril, he had already begun thinking about the nature of communication and how to describe it mathematically. He was not the first person to do this; in the late 1920s Ralph Hartley and Harry Nyquist had studied how telegraph messages were transmitted, but they did not approach the problem from a probabilistic point of view, nor did they include random variation – noise – as a factor affecting transmission accuracy. In 1945, Shannon wrote a document for the D-2 division of the NRDC, entitled ‘A mathematical theory of cryptography’, in which he summarised his ideas about communication and what it involved. He called the stuff that was communicated ‘information’, and described the nature of its fundamental unit, which he termed the ‘bit’. For obvious reasons the paper was immediately stamped ‘secret’, but after the war a version of it was published and it was eventually declassified in 1957. 20
    The final element of the ideas about information that were coming into form around the war years was an exploration of Maxwell’s Demon by the German physicist Leo Szilárd. This thought experiment was devised in 1871 by the British physicist James Clerk Maxwell, with the aim of showing how it was theoretically possible to violate the second law of thermodynamics. Maxwell imagined a demon that without effort could open a door between two chambers, allowing the more energetic molecules into one side, thereby increasing the temperature in that chamber and decreasing entropy in the system – something the second law said was impossible. Szilárd’s solution, which he devised in 1929, was that the demon would have to be able to measure the speed of the molecules, and to do this would require the expenditure of energy and therefore an increase in entropy. If the demon and the chamber were taken as a whole, the entropy of the system would not decline, and the second law remained intact. Although Szilárd did not use the term information, his theoretical discussion linked entropy and measures of knowledge in a way that proved significant.
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    At the beginning of 1945, Wiener and fellow mathematician John von Neumann organised a meeting of the newly formed Teleological Society. The aim of the society was to study ‘how purpose is realised