Alan Turing: The Enigma (2 page)

Alan Turing played a central part in world history. Yet it would be misleading to portray his drama as a power play, or as framed by the conventional political issues of the twentieth century. He was not political as defined by contemporary intellectuals, revolving as they did around alignment or non-alignment with the Communist party. Some of his friends and colleagues were indeed party members, but that was not his issue. (Incidentally, it is equally hard to find money-motivated ‘free enterprise’, idolised
since the 1980s, playing any role in his story.) Rather, it was his individual freedom of mind, including his sexuality, which mattered − a question taken much more seriously in the post-1968 and even more in the post-1989 era. But beyond this, the global impact of pure science rises above all national boundaries, and the sheer timelessness of pure mathematics transcends the limitations of his twentieth-century span. When Turing returned to the prime numbers in 1950 they were unchanged from when he left them in 1939, wars and superpowers notwithstanding. As G. H. Hardy famously said, they are so. This is mathematical culture, and such was his life, presenting a real difficulty to minds set in literary, artistic or political templates.

Yet it is not easy to separate transcendence from emergency: it is striking how leading scientific intellects were recruited to meet the existential threat Britain faced in 1939. The struggle with Nazi Germany called not just for scientific knowledge but the cutting edge of abstract thought, and so Turing’s quiet logical preparations in 1936-8 for the war of codes and ciphers made him the most effective anti-Fascist amongst his many anti-Fascist contemporaries. The historical parallel with physics, with Turing as a figure roughly analogous to Robert Oppenheimer, is striking. This legacy of 1939 is still unresolved, in the way that secret state purposes are seamlessly woven into intellectual and scientific establishments today, a fact that is seldom remarked upon.

The same timelessness lies behind the central element of Alan Turing’s story: the universal machine of 1936, which became the general-purpose digital computer in 1945. The universal machine is the focal, revolutionary idea of Turing’s life, but it did not stand alone; it flowed from his having given a new and precise formulation of the old concept of algorithm, or mechanical process. He could then say with confidence that all algorithms, all possible mechanical processes, could be implemented on a universal machine. His formulation became known immediately as ‘the Turing machine’ but now it is impossible not to see Turing machines as computer programs, or software.

Nowadays it is perhaps taken rather for granted that computers can replace other machines, whether for record-keeping, photography,
graphic design, printing, mail, telephony, or music, by virtue of appropriate software being written and executed. No-one seems surprised that industrialised China can use just the same computers as does America. Yet that such universality is possible is far from obvious, and it was obvious to no-one in the 1930s. That the technology is digital is not enough: to be all-purpose computers must allow for the storage and decoding of a program. That needs a certain irreducible degree of logical complexity, which can only be made to be of practical value if implemented in very fast and reliable electronics. That logic, first worked out by Alan Turing in 1936, then implemented electronically in the 1940s, and nowadays embodied in microchips, is the mathematical idea of the universal machine.

In the 1930s only a very small club of mathematical logicians could appreciate Turing’s ideas. But amongst these, only Turing himself had the practical urge as well, capable of turning his hand from the 1936 purity of definition to the software engineering of 1946: ‘every known process has got to be translated into instruction table form …’ (p. 326). One of Turing’s 1946 colleagues, Donald Davies, later developed such instruction tables (as Turing called programs) for ‘packet switching’ and these grew into the Internet protocols. Giants of the computer industry did not see the Internet coming, but they were saved by Turing’s universality: the computers of the 1980s did not need to be re-invented to handle these new tasks. They needed new software and peripheral devices, they needed greater speed and storage, but the fundamental principle remained. That principle might be decribed as the law of information technology: all mechanical processes, however ridiculous, evil, petty, wasteful, or pointless, can be put on a computer. As such, it goes back to Alan Turing in 1936.

That Alan Turing’s name has not from the start been consistently associated with praise or blame for this technological revolution is due partly to his lack of effective publication in the 1940s. Science absorbs and overtakes individuals, especially in mathematics, and Alan Turing swam in this anonymising culture, never trying to make his name, although frustrated at not being taken seriously. In fact, his competitive spirit went instead into marathon running at near-Olympic level. He omitted to write that monograph on ‘the theory and practice of computing’ which would have stamped his name on the emergent post-war computer world. In 2000 the leading mathematical logician Martin Davis, whose work since 1949 had greatly developed Turing’s theory of computability, published a book
¹
which was in essence just what Turing could have written in 1948, explaining the origin of the universal machine of 1936, showing how it became the stored-program computer of 1945, and making it clear that John von Neumann must have learnt from Turing’s 1936 work in formulating his better-known plan. Turing’s very last publication, the
Science News
article of 1954 on computability, demonstrates how ably he could have written such an analysis. But even there, on terrain that was incontestably his own discovery, he omitted to mention his own leading part.

Online search engines,
which work with such astonishing speed and power, are algorithms, and so equivalent to Turing machines. They are are also descendants of the particular algorithms, using sophisticated logic, statistics and parallel processing, that Turing expertly pioneered for Enigma-breaking. These were search engines for the keys to the Reich. But he asked for, and received, very little public credit for what has subsequently proved an all-conquering discovery: that all algorithms can be programmed systematically, and implemented on a universal machine. Instead, he nailed his colours to the mast of what he called ‘intelligent machinery’, but which came to be called Artificial Intelligence after 1956. This far more ambitious and contentious research programme has not developed as Turing hoped, at least as yet. Why did Turing go so public on AI, and make so little of himself
as an established maestro of algorithms and the founder of programming? Partly, because AI was for him the really fundamental scientific question. The puzzle of mind and matter was the question which drove him most deeply. But to some extent he must have been a victim of his own suppressed success. The fact that he knew so much of the algorithms of the secret war, and that the war had made the vital link between logic and electronics, cramped his style and constrained his communication. In his 1946 report his guarded allusion to the importance of cryptographic algorithms (p. 332) reflects an inhibition that must have infected all that came later.

Only after thirty years did the scale and depth of wartime cryptanalysis at Bletchley Park begin to leak out, allowing a serious assessment of Alan Turing’s life to be attempted. This point coincided with the break-out of cryptology theory into an expanding computer science, with a re-assessment of the Second World War in general, and with the impact of 1970s sexual liberation. The 1968 social revolution, which Turing anticipated, had to happen before his story could be liberated. (Even so, the change in UK vetting and military law came only in the 1990s, and a legal principle of equality was not established until 2000. ‘Don’t ask don’t tell’ ended only while I was writing this Preface in 2011, showing how the issues of chapter 8 have remained literally unspeakable in the US military.) Alan Turing’s story shows the first elements of this liberating process in the Norway of 1952, since the men-only dances he heard about (p. 476) were probably organised by the fledgling Scandinavian gay organisation. In addition to the gay-themed novels mentioned on p. 487, Norman Routledge recalled in 1992 how Turing expected him to read André Gide in French. One regret, voiced in note 8.31, is that his letters to Lyn Newman did not survive (they were destroyed by John Turing). Their content can be guessed from what in 1957 she wrote to a friend: ‘Dear Alan, I remember his saying to me so simply & sadly “I just can’t believe it’s as nice to go to bed with a girl as with a boy” and all I could say was “I entirely agree with you − I also much prefer boys.”’ This
interchange, then confined to a discreet privileged circle, could now be a TV chat show joke, with a happy resonance of the repartee of his famous imitation game. But Alan Turing’s simple openness came decades too early.

It is not difficult to imagine the hostility and stigma of those days, for such hatred and fear is still, whether in Africa, the Middle East, or the United States, a major cultural and political force. It is harder now to imagine a world where persecution was not just asserted but taken as an unquestionable axiom. Alan Turing faced the impossible irony that his demand for honesty ran up against the two things, state security and homosexuality, which were the most fraught questions of the 1950s. It is not surprising that it proved impossible to contain them in a single brain. His death left a jagged edge in history, something no-one (with the extraordinary exception of his mother) wanted to talk about. My fusion of these elements into a single narrative certainly encountered criticism in 1983. But nous avons changé tout cela: since then, his life and death have been as celebrated as those of any scientific figure. Hugh Whitemore’s play Breaking the Code, based on this book, and featuring leading performers, pushed at the envelope of public acceptability. It made Alan Turing’s life a popular story in 1986, reinforced by a television version in 1997. By that time the internet had transformed personal openness. In a curious way Turing had anticipated this use of his technology, already hinted at in the risqué text-messaging of his imitation game. The love letters created by the Manchester computer (p. 478), and his message about the Norwegian youth, rendered as a nerdy computer print-out (p. 482), suggest a Turing who would have relished the opportunity for electronic communication with like-minded people.

In 2009 the British prime minister, Gordon Brown, made a statement of apology for Turing’s trial and punishment in 1952-54, framed by a wider vision of how the values of post-war European civil society had been won with his secret help. This statement was enlisted through a popular web-based petition, something impossible in 1983, but already then being mooted as the sort of thing the
‘mighty micro’ could bring about. My own comments (p. 539) in the concluding Author’s Note about future revision of printed text reflected this mood. And indeed from 1995 onwards my website has supplied updating material. In this light it is surprising that such a long volume has remained continuously in print since 1983. But perhaps one thing a traditional stack of paper still makes possible is an immersion in story-telling, and this time-consuming experience was one I certainly supplied.

As narrator I adopted a standpoint of a periscope looking just a little ahead of Alan Turing’s submerged voyage, punctuated by just a few isolated moments of prophecy. The book bears in mind that what is now the past, the 1940s and 1950s, was once the completely unknown future. This policy required an unwarranted confidence that readers would wade through the pettier details of Alan Turing’s family origins and early life, before being given any reason why this life had any significance. But it has had the happy outcome that the text has not dated as do texts resting on assertions about ‘what we know now’. So although so much has changed, the story that follows can be read without having to subtract 1983-era comment. (Of course, this is not true of the Notes, which now show what sources were available in 1983, but do not indicate a guide to ‘further reading’.)

After a further thirty years, how would I re-assess Alan Turing’s pure scientific work and its significance? My book made no attempt to trace the legacy of Turing’s work after 1954; that would be far too large a task. But naturally, the expansion of scientific discovery continually forces fresh appraisals of Turing’s achievement. His morphogenesis theory, since 2000 more actively pursued as a physico-chemical mechanism, would now require more material on the various different approaches and models. As another example, Turing’s strategy of combining top-down and bottom-up approaches to AI, and the neural nets he sketched in 1948, have acquired new significance. There has been a parallel explosion in quality and quantity of the history of science and technology since the 1970s, with many detailed studies of Turing’s papers and many
more expected with the 2012 stimulus. Topics that attracted scant attention in 1983 are now the subject of lively debate.

But I would not take a radically different point of view. My division of the book into Logical and Physical was already radical, reflecting a rejection of conventional description of him as a pure logician, and portraying him as always, and increasingly, involved in the nature of the physical world. This fundamental perception could now be asserted with even greater confidence. He came to the ideas of 1936 with an unusual knowledge of quantum mechanics, and this is now a more interesting connection, for since the mid-1980s quantum computing and quantum cryptography have become important extensions of Turing’s ideas. Likewise, the renewed interest in quantum mechanics in Turing’s last year, whose significance was correctly signalled with a supersized footnote (p. 512) could now be linked more closely with his 1950 and 1951 arguments about computers and minds. These issues have arisen sharply since 1989, when Roger Penrose
²
discussed the significance for minds of the uncomputable numbers Turing had discovered. Penrose himself suggested an answer which related Turing machines to a radical new view of quantum mechanics. Writing now, I would draw more attention to what is now called the
physical Church-Turing thesis
. Did Turing consider that the scope of the computable includes everything that can be done by any physical object? And what would this mean for his philosophy of the mind? In this light, Church’s 1937 review (p. 123) of Turing’s work has more importance than I noted. Turing’s decisive shift of focus to what could be done by algorithms, stated on page 108, I would now move from 1936 to 1941 (at p. 212). Turing’s argument about infallibility (p. 361) would deserve more analysis, as also his use of ‘random’ elements, and a number of general statements about thinking and doing in my text. But sharper sensitivity to these questions would bring out few if any new answers; it would only make more acute the questions about what Turing really thought.