Consciousness

• seCtIon FoUR: eVoLUtIon
  at the time, yet it has taken its place in
  history as the first general-purpose, pro-
  grammable calculating machine.
  Among the ideas that were fundamental
  to such machines was Boolean algebra,
  invented by the English mathematician
  George Boole. As a young man, working
  as an assistant teacher in Doncaster in
  1833, Boole went walking one day on
  the Town Fields. There he had a sud-
  den insight: one of the famous ‘eureka’
  moments of science. He saw that just as
  mathematical principles could explain
  the function of cogs in machines, so they
  might be able to explain what he called
  ‘the laws of thought’, and he believed
  that in this way mathematics might
  solve the mysteries of the human mind.
  He showed how logical problems could
  be expressed as algebraic equations and
  therefore solved by mechanical manipu-
  lation of symbols according to formal rules. This required only two values, 0 and
  1, or false and true, and the rules for combining them. Boole did not succeed in
  solving the mystery of mind, as he had hoped, but Boolean algebra was funda-
  mental to the computer revolution.
  In the 1930s, the American mathematician and founder of information theory,
  Claude Shannon, realised that Boolean algebra could be used to describe the
  behaviour of arrays of switches, each of which has only two states, on or off. He
  used a binary code and called each unit of information a ‘binary digit’ or ‘bit’. All
  this made possible the idea that logical operations could be embodied in the
  workings of a machine.

As so often happens, it was the pressures of war that drove on the invention of

computing machinery. The first general-purpose computers were built in the Sec-

ond World War to decode German ciphers and to calculate the tables needed to

guide ballistics. The master code-breaker, though this was only revealed thirty

years after the war ended, was the brilliant English mathematician Alan Turing.

Turing worked on algorithms, that is, sets of step-by-step instructions for oper-

ations to be performed. Problems are said to be ‘computable’ if they can be

formulated and solved by using an appropriate algorithm. Turing proposed the

idea of a simple machine that could move an indefinitely long tape backwards

and forwards one square and print or erase numbers on it. He showed that this

simple machine could specify the steps needed to implement all computational

algorithms.

The principle underlying this is an abstract machine, now known as the Tur-

ing machine. An important aspect of this idea is that the abstract machine

has ‘multiple realisability’ and ‘substrate-neutrality’. That is, it can use tapes or

FIGURE 12.1 • The mechanical Turk was the first
ever chess-playing machine. His
hands were moved by intricate
machinery under the table,
but the real player was hidden
inside. The online crowdsourcing
marketplace is named after him
(Photo: AKG London).