Alan Turing: The Enigma The Centenary Edition

by Andrew Hodges

  Wiener regarded Alan as a cybernetician, and indeed ‘cybernetics’ came close to giving a name to the range of concerns that had long gripped him, which the war had given him an opportunity to develop, and which did not fit into any existing academic category. In spring 1947, on his way to Nancy, Wiener had been able to ‘talk over the fundamental ideas of cybernetics with Mr Turing,’ as he explained in the introduction to his book.

  By 1949 an American supremacy was virtually taken for granted in science as in everything else, and it was a sign of the times that on 24 February 1949 the popular magazine News Review,11 presenting a digest of what Wiener had to say, should explain with pride how British scientists had been able to supply ‘valuable data’ to the American professor when he had flown in. It was as a planet round the Wiener sun that Alan appeared, the photograph of his young and slightly nervous profile standing in marked contrast to the ponderous features of Wiener and the massive visage of the biologist J. B. S. Haldane.

  In reality Alan was more than a match for Wiener, and although genuinely sharing many common interests, their outlooks were different. Wiener had an empire-building tendency which rendered almost every department of human endeavour into a branch of cybernetics. Another difference lay in Wiener’s total lack of a sense of humour. While Alan always managed to convey his solid ideas with a light English touch of wit, Wiener delivered with awesome solemnity some pretty transient suggestions, to the general effect that solutions to fundamental problems in psychology lay just around the corner, rather than putting them at least fifty years in the future. Thus in Cybernetics it was seriously suggested that McCulloch and Pitts had solved the problem of how the brain performed visual pattern recognition. The cybernetic movement was rather liable to such over-optimistic stabs in the dark. One story going around, which later turned out to be a hoax, but which found its way into serious literature,12 was of an experiment supposed to measure the memory capacity of the brain by hypnotising bricklayers and asking them such questions as ‘What shape was the crack in the fifteenth brick on the fourth row above the damp course in such and such a house?’. Alan’s reaction to these cybernetic tales was one of amusement.

  Another point of difference lay in the fact that Wiener was openly concerned about the economic implications of cybernetic technology. The war, for him, had not changed a conviction that machines should be made to work for people rather than vice versa. His comment that factory robots would put the people they replaced in the position of competing against slave labour, and his daring description of the principle of competition as a ‘shibboleth’, put him on the extreme left of 1948 American opinion. It was no accident that on his visit to Britain Wiener had consulted the left-wing luminaries of science, J.D. Bernal and H. Levy, as well as Haldane.

  But the academic debate that followed Cybernetics in Britain was not concerned with this question, nor indeed with anything to do with the use of computers, or the harnessing of wartime technology to peaceful and constructive ends, or the relative merits of cooperation and competition. When the News Review called cybernetics a ‘frightening science’ it was not the economic consequences but the threat to traditional beliefs that it feared. Post-war reaction to planning and austerity, conservative rather than commercial, was reflected in the almost Victorian terms of reference which the intellectuals also accepted. This was true of Alan Turing as much as anyone; these were terms close to his own struggle of the 1930s over problems of thought and feeling. Times had changed, however, and so it was not a bishop but a brain surgeon who led the British intellectual reaction to the claims of machinery to thought. The eminent Sir Geoffrey Jefferson delivered an address,13 The Mind of Mechanical Man, as the Lister Oration on 9 June 1949.

  Jefferson held a Chair of Neurosurgery at Manchester, and knew about the Manchester computer development from talking about it with Williams. But most of his impressions came from Wiener, whose emphasis was still placed on the similarity of the nerve-cells of the brain to the components of a computer.* On this level the analogy was pretty feeble, and not much advanced by Wiener’s comparisons between computer malfunctions and nervous diseases. The Turing ideas of discrete state machines and universality were required to lend precision and substance to the cybernetic claim. Some of Wiener’s assertions were rather easy to attack; but Jefferson did go further than just knocking them down, playing some strong commonsense cards, such as:

  But neither animals nor men can be explained by studying nervous mechanics in isolation, so complicated are they by endocrines, so coloured is thought by emotion. Sex hormones introduce peculiarities of behaviour often as inexplicable as they are impressive (as in migratory fish).

  Jefferson liked talking about sex. But his Oration was concluded by flights of rhetoric which only begged the question. An oft-quoted passage held that

  Not until a machine can write a sonnet or compose a concerto because of thoughts and emotions felt, and not by the chance fall of symbols, could we agree that machine equals brain – that is, not only write it but know that it had written it. No mechanism could feel (and not merely artificially signal, an easy contrivance) pleasure at its successes, grief when its valves fuse, be warmed by flattery, be made miserable by its mistakes, be charmed by sex, be angry or miserable when it cannot get what it wants.

  Jefferson ended by ‘ranging myself with the humanist Shakespeare rather than the mechanists, recalling Hamlet’s lines: “What a piece of work is man! How noble in reason! How infinite in faculty”’, and so forth. Shakespeare was often exhibited in these discussions as proof of the speaker’s exquisite human sensibilities. However, Jefferson had done a good deal to improve upon the ‘piece of work’ himself, not only by mending the broken heads of two world wars but as an exponent in the late 1930s of the frontal lobotomy.

  This was the ‘heads in the sand’ argument, resting upon the assumption that a machine, because its components were non-biological, was incapable of creative thinking. ‘When we hear it said that wireless valves think,’ Jefferson said, ‘we may despair of language.’ But no cybernetician had said the valves thought, no more than anyone would say that the nerve-cells thought. Here lay the confusion. It was the system as a whole that ‘thought’, in Alan’s view, and it was its logical structure, not its particular physical embodiment, that made this possible.

  The Times14 seized upon Jefferson’s concession that

  A machine might solve problems in logic, since logic and mathematics are much the same thing. In fact, some measures to that end are on foot in my university’s department of philosophy [sic].

  Their reporter telephoned Manchester, where Alan rose to the bait and chatted away without inhibition:

  ‘This is only a foretaste of what is to come, and only the shadow of what is going to be. We have to have some experience with the machine before we really know its capabilities. It may take years before we settle down to the new possibilities, but I do not see why it should not enter any one of the fields normally covered by the human intellect, and eventually compete on equal terms.

  I do not think you can even draw the line about sonnets, though the comparison is perhaps a little bit unfair because a sonnet written by a machine will be better appreciated by another machine.’

  Mr Turing added that the university was really interested in the investigation of the possibilities of machines for their own sake. Their research would be directed to finding the degree of intellectual activity of which a machine was capable, and to what extent it could think for itself.

  This embarrassing definition of what ‘the university’ was ‘really interested in’ provoked a swish of the cane from the Catholic public school:15

  …If one may judge from Professor Jefferson’s Lister oration …responsible scientists will be quick to dissociate themselves from this programme. But we must all take warning from it. Even our dialectical materialists would feel necessitated to guard themselves, like Butler’s Erewhonians, against the possible hostility of the machines. And those of
us who not only confess with our lips but believe in our hearts that men are free persons (which is unintelligible if we have no unextended mind or soul, but only a brain) must ask ourselves how far Mr Turing’s opinion are shared, or may come to be shared, by the rulers of our country.

  Yours &c. ILLTYD TRETHOWAN

  Downside Abbey, Bath, June 11.

  The rulers of Great Britain did not divulge their opinions. But Max Newman wrote to The Times to correct the impression left by Alan’s heady prophecies, dousing them with a laborious explanation of the Mersenne prime problem. Jefferson proved a good publicity agent for Manchester, for The Times published photographs of the adolescent machine, and the Illustrated London News followed on 25 June. By chance, these happened to upstage the grand opening of the EDSAC in Cambridge.

  Wilkes’ team had made rapid progress, and had already completed the building of an EDVAC-type computer, with mercury delay line storage, well ahead of any American development. It had a storage capacity of only thirty-two delay lines, and its digit time was two microseconds, twice that of the planned ACE. But it worked; and if the ‘baby machine’ at Manchester was the first working electronic stored program computer, the EDSAC was the first to be available for serious mathematical work.*

  Alan attended the inaugural conference, and gave a talk on 24 June 1949 entitled Checking a Large Routine16 He described a sophisticated procedure, appropriate for long programs in which it would be easy to lose track of the fate of numbers in store. Illustrating his points, he did some sums on the blackboard, and lost everyone by writing the numbers backwards as he was used to doing at Manchester. ‘I do not think that he was being funny, or trying to score off us,’ wrote Wilkes,17 ‘it was simply that he could not appreciate that a trivial matter of that kind could affect anybody’s understanding one way or the other.’ It was a ‘fussy little detail’, which perhaps masked the irony of the fact that while the EDSAC people had only begun to write programs in May 1949, soon discovering the idea of the sub-routine, Alan had been writing and perhaps checking them for years.

  Meanwhile the ACE did survive after all. Alan had resigned at the lowest ebb. Then Thomas, who was in charge of the electronics, resigned, and his successor, F.M. Colebrook, proved to have a very different attitude. In fact, as soon as Thomas was gone, the mathematicians moved into the engineers’ building. Thanks to Colebrook an unheard-of relaxation took place, and the two groups were soon working together in a sort of assembly line. The speed of progress attained in building the machine was comparable with that envisioned in Alan’s original proposal. By mid-1949 they had a delay line working and the wiring of the control was finished in October. The machine, the ‘Pilot ACE’, was based on the Turing ‘Version V’, just as Huskey’s premature effort had been. It retained the ‘distributed’ processing that distinguished it from the von Neumann system which used an accumulator. They also kept megacycle speed, which made it the fastest in the world. Meanwhile Sir Charles Darwin retired in 1949. Max Newman took the view that he had done Darwin a good turn in taking Alan away, and Alan would agree with this. When he went to the official opening of the Pilot ACE in November 1950 he was particularly generous in telling Jim Wilkinson how much better they had done than would have been possible had he stayed. Certainly the Pilot ACE would not have been possible at all had not Alan gone. But he must also have known that it represented only a shadow of his original vision.18

  Womersley managed to rewrite the history of the ACE project after Alan had left. For it was Womersley’s story that Colebrook gave to the Executive Committee meeting on 13 November 1949:

  Mr Colebrook then referred to the organisational history of the Automatic Computing Engine project. The work on this originated with Dr Turing’s paper … ‘On Computable Numbers with an Application to the Entscheidung Problem’ [sic] and Mr Womersley began thinking about the logical design in 1938 after reading Dr Turing’s paper and after discussions with Professor Hartree. Mr Womersley came to the Laboratory early in 1944, and the following year visited the United States to see the Harvard and ENIAC machines. Professor Newman came to see Mr Womersley in 1945 and introduced Dr Turing, who very soon afterwards joined the staff of the Laboratory.

  This was the only mention of Alan’s part in the project. The account continued to explain that

  In 1946, work on the Automatic Computing Engine was started and it was arranged for the experimental work to be done by the Post Office and the theoretical work, including the programming of the machine, at the Laboratory. Because of slow progress at the Post Office, a section was started at NPL in 1947 to build the ACE machine.

  Skilfully passing over the Thomas period, Colebrook described the progress made in 1948 and 1949. He then contrasted the Pilot ACE with ‘the machine originally proposed’, and announced that

  The actual size of the ace as originally contemplated was the outcome of long consideration by Mr Womersley and Professor von Neumann during Mr Womersley’s visit to the United States.

  Already by 1950, Alan Turing was an unperson, the Trotsky of the computer revolution.

  But he was never one to complain, once he had made his decision. In many ways his position at Manchester was parallel to that at Hanslope, in terms of status and class and struggles over equipment. One difference was the harshness of the Manchester environment, which surely exacerbated his rudeness. Another was that in 1943 his move sideways and downwards had gained for him practical experience with electronics. In 1948 it gained for him the use of a computer. And this remained a paramount consideration. He had conceived of a universal machine, and now he could work or play with one of the two that existed in the world of 1949. There was a method in his madness.

  For the time being he contented himself with paying off some scores to old days that would vindicate the power of the universal machine. The first thing he did was to revive the zeta-function calculation. The gear wheels that had been cutting when the phoney war broke in could now be replaced by instructions on the tape of a universal machine, in the phoney peace of 1950. It did not go quite according to plan, this being partly the machine’s fault and partly his own:19

  In June 1950 the Manchester University [prototype] Electronic Computer was used to do some calculations concerned with the distribution of the zeros of the Reimann zeta-function. It was intended in fact to determine whether there are any zeros not on the critical line in certain particular intervals. The calculations had been planned some time in advance, but had in fact to be carried out in great haste. If it had not been for the fact that the computer remained in serviceable condition for an unusually long period from 3 p.m. one afternoon to 8 a.m. the following morning it is probable that the calculations would never have been done at all. As it was, the interval 2π.632
  …The interval 1414
  This was an unusual joint exercise, on which Kilburn stood by all night. Alan would hold up the output teleprinter tape to the light to read:

  The content of a tape may afterwards automatically be printed out if desired [sic] … the output consisted mainly of numbers in the scale of 32 …writing the most significant digit on the right. More conventionally the scale of 10 can be used, but this would require the storage of a conversion routine, and the writer was entirely content to see the results in the scale of 32, with which he is sufficiently familiar.

  Another old score, that of the Enigma, was also paid off at about this time:20

  I have set up on the Manchester computer a small programme using only 1000 units of storage, whereby the machine supplied with one sixteen figure number replies
with another within two seconds. I would defy anyone to learn from these replies sufficient about the programme to be able to predict any replies to untried values.

  He had, in other words, devised a cipher system which he reckoned impregnable even with the help of known plain-text. The lumbering wheels of the Second World War were already heading towards the same obsolescence as that of his zeta-function machine.

  There were some other hints of a continued interest in cryptology. Another item that he demanded from the engineers as a hardware function of the Mark I Ferranti machine was what they called a ‘sideways adder’. It would count the number of ‘1’ pulses in a 40-bit sequence. This would have no application in a numerical program, but would be very useful in one where the digits coded ‘yes’ or ‘no’ answers to some Boolean question, and it was required to count the ‘yes’ answers – just what the Colossus had done. Such applications might possibly have been spare-time interests of his own. However, it was during this period, as the international situation hardened, that he found himself consulted by GCHQ. It would indeed have been remarkable had they not consulted the person who knew more about cryptology and the potential of electronic computers than did anyone else. And had he not described cryptanalysis as the most ‘rewarding’ field for the application of programming? Few, however, were in a position to perceive this fact, the subject being more secret than ever.

  A hark-back to cryptology also featured in his discussions with a young American, David Sayre, in this period. A graduate of the wartime MIT Radiation Laboratory, Sayre was now at Oxford studying molecular biology with Dorothy Hodgkin. Having worked with F.C. Williams during the war, he made a visit to Manchester to see the computer, explaining that it might help in X-ray crystallography, Williams passed him on to Alan, who showed an unusual kindness and geniality, making Sayre21 ‘perfectly at ease with him’. They talked for two and a half days, interrupted only when ‘the telephone would ring to say that the machine was free for a few minutes in case he wanted to use it, and he would gather up sheaves of paper and ribbons of punched paper tapes …and disappear for a bit.’