Alan Turing: The Enigma The Centenary Edition

by Andrew Hodges

  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 Penrose2 discussed the significance for minds of the uncomputable numbers Turing had discovered. Penrose himself suggested an answer which related Turing machines to a radic
al 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.

  Much more positive detail could now be given regarding his secret wartime work. Even in the 1992 preface to the Vintage edition, new material could be given from the third volume of F. H. Hinsley’s official history of British Intelligence. But since the mid-1990s, raw American and British documents on Second World War cryptanalysis have been officially released, and it has been possible to elucidate the internal story with far more details than Hinsley allowed. What has emerged has only enhanced the quality and significance of Bletchley Park work, and of Turing as its chief scientific figure. The Park itself is now a famous visitor attraction, though its lesson, that reason and scientific methods were the heroes of the hour, has not really caught on.

  These documents show how on 1 November 1939 Turing could announce ‘the machine now being made at Letchworth, resembling, but far larger than the Bombe of the Poles (superbombe machine).’ That prefix ‘super’ dramatised the advance that my explanation (p. 183) was unable, for lack of supporting narrative detail, to highlight as the crucial breakthrough. Turing’s own 1940 report on the Enigma-breaking methods clarified how he made this advance, called ‘parallel scanning’. All of this is now working physically in the rebuilt Bombe at the Bletchley Park Museum. In addition to the document release, members of the original cryptanalytic team have written fully about the technical work, such as the details of the bigram tables which made the Naval Enigma so much more challenging, and the statistical Banburismus method. The super-fast bombes, the break into the Lorenz cipher, and the now-famous Colossus are all open to study, a great deal being due to the inspiring work of the late Tony Sale. The description in this book is now unnecessarily hazy. On the other hand, there was no room for any more codebreaking technicalities in the book, and the reader will not be seriously misled by its summary.

  In particular, these revelations have only reinforced the significance of the ‘Bridge Passage’ between the logical and the physical, Turing’s top-level liaison visit to the United States in the winter of 1942-3. His report of 28 November 1942 from Washington, now released, documents the difficult and anomalous position he faced, including an initial confinement to Ellis Island (p. 242). He was not overawed by the US Navy: ‘I am persuaded that one cannot very well trust these people where a matter of judgment in cryptography is concerned.’ Something that I had heard only as rumour in 1983 has been confirmed: on 21 December a train brought Turing to Dayton, Ohio, where the US Bombes were under construction. There is also more revealed on his initiation into the most secret US speech encipherment technology. There is more on his response to it, the Delilah speech scrambler − an interim report dated 6 June 1944, and a later complete description. As a precursor of the mobile phone, this belongs to the future, whilst the Enigma was a mediocre adaptation of 1920s mechanical engineering. This new material only underlines that in the post-war period, Turing had a unique knowledge of the most advanced American technology, as it emerged from victory in 1945.

  This fact draws further attention to the question of what he did for GCHQ after 1948. In the 1992 preface I floated the suggestion that this might have been connected with the now famous Venona problem of Soviet messages. But there has been no comparable release of GCHQ or MI5 documents on 1948-54 to indicate the nature of his work, or to show how the British (and American) State dealt with the arrest and trial. The recently published history of GCHQ3 opens by saying that ‘Today it is more important than ever — yet we know almost nothing about it’.

  No Turing Diaries have emerged to reveal the enigma of Alan Turing’s inner life, or to pose new puzzles; no new lovers have told stories. No great treasure troves of correspondence have come to light. But a few gems of personal writing surfaced too late for the 1983 book, and were included in the 1992 preface. They are given again here.

  A cosy continuity between King’s College, Cambridge, and the pre-war codebreaking establishment is evoked by some brief letters placed in the King’s archive in 1990. ‘Dilly Knox, who is my boss, sends you greetings,’ wrote Turing on 14 September 1939 to the Provost, John Sheppard. ‘It is always a joy to have you here’, wrote back the Provost, encouraging him to visit. The economist J. M. Keynes, who looked after the question of Turing’s fellowship for the duration of the war, also knew the older generation of codebreakers (and indeed had apparently enjoyed an intimate relation with the ‘boss’). These connections lend further colour to my description (p. 148) of how in 1938 Turing’s interest in ciphers could have been transmitted to the British government, thus making possible his fateful appointment.

  The following account, which in 1983 was only available in Polish, also concerns the early months of the war.4 It settles the question raised in note (4.10) as to whether Turing was the personal emissary who took the new perforated sheets to the Polish and French cryptanalysts. Indeed he was: there is no mistaking his voice in this account of their farewell supper.

  In a cosy restaurant outside Paris staffed by Deuxième Bureau workers, the cryptologists and the chiefs of the secret decryptment center, Bertrand and Langer, wished to spend an evening in a casual atmosphere free of everyday concerns. Before the dishes ordered and the choice wine selected for the occasion had been served, the attention of the diners was drawn to a crystal flower glass with flowers, placed on the middle of the tablecloth. They were delicate rosy-lilac flowers with slender, funnel-shaped calyces. It was probably Langer who uttered their German and then their Polish names: “Herbstzeitlose … Zimowity jesienne….”

  This meant nothing to Turing, as he gazed in silence at the flowers and the dry lanceolate leaves. He was brought back from his reverie, however, by the Latin name, Colchicum autumnale (autumn crocus, or meadow saffron), spoken by mathematician-geographer Jerzy Rózycki.

  “Why, that’s a powerful poison!” said Turing in a raised voice.

  To which Rózycki slowly, as though weighing each word, added: “It would suffice to bite into and suck at a couple of stalks in order to attain eternity.”

  For a moment there was an awkward silence. Soon, however, the crocuses and the treacherous beauty of the autumnal flowers were forgotten, and an animated discussion began at the richly laid table. But despite the earnest intention of the participants not to raise professional questions, it proved impossible to get completely away from Enigma. Once again, there was talk of the errors committed by German operators and of the perforated sheets, now machine-rather than handmade, which the British sent in series from Bletchley to the Poles working at Gretz-Armainvillers, outside Paris. The inventor of the perforated sheets, Zygalski, wondered why their measurements were so peculiar, with each little square being about eight and a half millimeters on a side.

  “That’s perfectly obvious,” laughed Alan Turing. “It’s simply one-third of an inch!”

  This remark in turn gave rise to a dispute as to which system of measures and currency, the traditionally chaotic British one or the lucid decimal system used in France and Poland, could be regarded as the more logical and convenient. Turing jocularly and eloquently defended the former. What other currency in the world was as admirably divided as the pound sterling, composed of 240 pence (20 shillings, each containing 12 pence)? It alone enabled three, four, five,
six or eight persons to precisely, to the penny, split a tab (with tip, generally rounded off to a full pound) at a restaurant or pub.

  The dark tone of Turing’s knowledge of poisonous plants, arising unexpectedly in the midst of secret work and mathematical banter, recalls the manner of his death. The shock of that event is vividly portrayed by another first-account, that written by Turing’s housekeeper Mrs Clayton on the night of Tuesday 8 June 1954:

  My dear Mrs Turing

  You will by now have heard of the death of Mr Alan. It was such an awfull shock. I just didn’t know what to do. So I flew across to Mrs Gibson’s and she rang Police & they wouldn’t let me touch or do a thing & I just couldn’t remember your address. I had been away for the weekend and went up tonight as usual to get his meal. Saw his bedroom light on the lounge curtains not drawn back, milk on steps & paper in door. So I thought he’d gone out early & forgot to put his light off so I went & knocked at his bedroom door. Got no answer so walked in, Saw him in bed he must have died during the night. The police have been up here, again tonight for me to make a statement & I understand the inquest will be Thursday. Shall you or Mr [John] Turing be coming over[?] I feel so helpless & not able to do anything. The Webbs removed last Wed. & I don’t know their new address yet. Mr & Mrs Gibson saw Mr Alan out walking Mon. evening he was perfectly all right then. The weekend before he’d had Mr Gandy over for the weekend & they seemed to have had a really good time. The Mr & Mrs Webb came to dinner Tues. & Mrs Webb had aftern[oon] tea with him Wed. the day she removed. You do know you have my very deepest sympathy in your great loss & what I can do to help at this end you know I will continue to do so.