Alan Turing, a great scientist

My Times column:

Tomorrow the House of Lords gives a second reading to Lord Sharkey’s Bill to pardon Alan Turing, the mathematician, computer pioneer and code-cracking hero of the Second World War.

In 1952 Turing was prosecuted for being gay (he had reported a burglary to the police and made it no secret that the burglar was a friend of his consensual lover). Convicted of “gross indecency” he was offered prison or oestrogen injections to reduce his libido; he chose the latter but then committed suicide at the age of 41.

That Turing deserved an apology in his lifetime for this appalling treatment is not in doubt. What will be debated tomorrow is whether a posthumous pardon from today’s Government is right, or may be a further insult to his memory. After all, the word pardon implies that his crime is still a crime, which it is not, and it will do nothing for the victim (especially since he was an atheist), and do nothing to untarnish his reputation, which history has already fully untarnished. Also it could be unfair to other, less famous convicted gay men and may even seem to rewrite history rather than leaving it starkly to reproach us. By rights, Turing should be pardoning the Government, but that’s not possible.

So it is not easy to judge if a pardon is the right thing. For my part, I think a greater matter is at issue — whether we have done enough to recognise Turing’s scientific reputation and how we put that right. It becomes clearer by the day that, irrespective of his tragic end and even of his secret war service, he ranks for the momentous nature of his achievements with the likes of Francis Crick and Albert Einstein in the 20th-century scientific pantheon. This was not just a moderately good scientist made famous by persecution; this was the author of a really big idea.

In 1936, aged 24, Turing wrote: “We may now construct a machine to do the work of this computer.” It makes no sense today, but that’s because of what Turing wrought. In 1933 a computer was a person, usually a woman, who knew how to compute. Machines existed to help her — calculating machines, cash registers, telephone switchboards — but only to do specific things. A general purpose computer that could be “programmed” was an idea that had not even been thought.

What Turing understood was that a sufficiently well designed machine — what we would now call a Turing machine — could do almost anything, because both its data and instructions could be fed into it in the form of numbers. His paper, called “On computable numbers with an application to the Entscheidungsproblem”, was addressed to an esoteric question in mathematics being debated between two Germans, David Hilbert and Kurt Gödel. It was in the method he used to tackle the question that Turing made his startling insight.

It seems obvious now that you can feed information into a computer and change its “state of mind” — make it a word processor or a video player or a spreadsheet. But this was brand new in 1936. It was the great Hungarian mathematician John von Neumann who took Turing’s insight and turned it into a universal architecture for computers — memory and processor, data and programs — that we all know.

Like most scientific ideas, it would have occurred to somebody else at some point, but might have taken several more years. Another way of thinking about what Turing achieved is that the development of computing was not just a matter of technology — it needed a philosophical breakthrough, too.

Indeed, as the philosopher Daniel Dennett points out in his new bookIntuition Pumps and Other Tools for Thinking, Turing stands alongside Charles Darwin in one respect. One of Darwin’s critics, Robert Mackenzie Beverley, had scoffed: “In the theory with which we have to deal, Absolute Ignorance is the artificer; so that we may enunciate as the fundamental principle of the whole system, that, in order to make a perfect and beautiful machine, it is not requisite to know how to make it.”

To which Dennett replies: “Exactly!” That’s the extraordinary Darwinian insight. Complexity is built from the bottom up, without any understanding. Turing says something very similar, according to Dennett: “In order to be a perfect and beautiful computing machine, it is not requisite to know what arithmetic is.” Lumps of silicon and copper can book airline tickets and simulate economies — they do not have to be specialised as travel agents or economists. This also had implications for the study of the human brain, which came to be seen at least partly as general purpose hardware running software called culture.

When the war broke out, Turing’s genius proved as practical as it had been ethereal in the 1930s. His crucial contributions to three successive computing innovations at Bletchley Park — the “bombe” machines for replicating the settings of the German Enigma encryption machine, the later cracking of the naval Enigma machine enabling U-boat traffic to be read, and finally the Colossus computer that broke the Germans’ “tunny” cipher machine — provided Churchill with the famous “ultra” decrypts that almost certainly shortened the war and saved millions of lives in battlefields, ships and camps.

For this he was appointed OBE, but secrecy shrouded his work until long after his death, so he wasn’t known to be a hero, let alone the man who saved so many lives. He moved to what would become GCHQ, but in the paranoid days after Burgess and Maclean fled east, his homosexuality conviction categorised him as a security risk.

Turing’s postwar achievements at the National Physical Laboratory and Manchester University were pretty special too. He helped to design the Pilot ACE, Britain’s first modern computer and the equal to anything in the US at the time. Manchester now proudly commemorates him in Alan Turing Way, near the Etihad Stadium — an initiative of the former council leader (now MP) Graham Stringer, himself a scientist. Mr Stringer reckons Turing’s computable numbers insight ranks him alongside John Dalton and Ernest Rutherford in the roll call of scientific fame.

Turing also began to push new ideas in embryology, including a theory as to why the pattern of sunflower seeds follows the Fibonacci series (1,1,2,3,5,8,13,21 ... you add the previous two numbers to get the next one). Lovely science all of it, but nothing compared with computable numbers.

So don’t let the pardon get in the way of recognising one of the great scientific geniuses of all time. Put Alan Turing on banknotes or a plinth in Trafalgar Square.