Alan Turing

Virtual Consumer column from Ethical Consumer magazine Sep-Oct 2012

This year there are celebrations to mark 100 years since the birth of Alan Turing.

Turing was famous for three things, all huge achievements. He helped decipher Nazi messages as part of the famous ‘Project Ultra’ team at Bletchley Park during the Second World War. This is probably what he is best known for.  Turing was a brilliant mathematician, which helps when you are trying to crack codes. But his stroke of genius was to build a machine - the “bombe” - which could work systematically through combinations to test whether they could have been produced by the German ‘Enigma’ coding machine. Churchill famously said “It was thanks to Ultra that we won the war”.

But it was before the war that Turning made the contribution that led many to call him the father of modern computing. He conceived of a machine that could follow instructions and manipulate data stored on an infinite tape. He proved mathematically that this ‘Turing machine’ could calculate anything that can be calculated by following a sequence of logical steps. A modern computer doesn’t work in the same way as a Turing machine, but it can do anything a Turing machine can do (and vice versa). They are equivalent, which is why modern computers are described as ‘Turing complete’.

This notion, that a machine is defined by how it behaves externally, rather than by its internal workings, led Turing to his third great insight. If a machine can be defined by what it is capable of doing, what if it is capable of behaving like an intelligent being? Would that make it equivalent? This was a radical thought at the time, although we have become more used to the idea since that machines might behave in intelligent ways. He invented a way to test if a machine meets this criterion. In the ‘Turing test’ you communicate with a human and a machine by typing. You can ask any question. The machine passes the test if you cannot tell which is which. Philosophers have been arguing ever since about what it means if a machine ever passes the test: is it intelligent? Is it conscious? Would it be unethical to turn it off?

There is perhaps a fourth thing that Turing is famous for. In 1952 he was prosecuted for being gay, which was illegal at the time. Two years later he committed suicide, probably by taking a bite from a poisoned apple, although this is not certain. It’s often said that the Apple logo, with its missing bite, is a tribute to Turing, although this is denied by the company. A shame because he was a man worth paying tribute to, and his prosecution was no way to treat someone who did so much to help defeat Nazism - a point noted by Gordon Brown when as prime minister he apologised on behalf of the UK Government in 2009.