ALAN TURING: THE ENIGMA
THE BOOK THAT INSPIRED THE FILM THE IMITATION GAME
Andrew Hodges is Tutor in Mathematics at Wadham College, Oxford University. His classic text of 1983, since translated into several languages, created a new kind of biography, with mathematics, science, computing, war history, philosophy and gay liberation woven into a single personal narrative. Since 1983 his main work has been in the mathematics of fundamental physics, as a colleague of Roger Penrose. But he has continued to involve himself with Alan Turing’s story, through dramatisation, television documentaries and scholarly articles. Since 1995 he has maintained a website at www.turing.org.uk to enhance and support his original work.
TO THEE OLD CAUSE!
The dedication, epigraphs and epitaph, are taken from the Leaves of Grass of Walt Whitman.
‘Alan Turing was by any reckoning one of the most remarkable Englishmen of the century. A brilliant mathematician at Cambridge in the ’30s, Turing discovered that his was precisely the kind of intelligence needed by Britain during the war and became the presiding genius at Bletchley Park, the boffin centre which cracked the German Enigma code. (A character in McEwan’s The Imitation Game was loosely based on him.) There he became obsessed by the notion of machine intelligence and was, in effect, the father of the modern computer. Mistrust and bureaucracy, however, frustrated many of his plans after the war, when Turing was to discover that though he was the master of his own sphere, politically he remained as he was in 1941 – a servant. A homosexual, Turing found his own morality and scientific ideas increasingly at odds with the values of the state which he served. Eventually, he committed suicide. Andrew Hodges’s book is of exemplary scholarship and sympathy. Intimate, perceptive and insightful, it’s also the most readable biography I’ve picked up in some time’
Richard Rayner, Time Out
‘Researched and written extraordinarily well. It is a first-class contribution to history and an exemplary work of biography’
Nature
‘Life and work are both made enthralling by Hodges, himself a scientist’
Sunday Times
‘This rather shadowy figure has now finally been lifted into the light of day … it has to be said that Andrew Hodges has put together an extraordinary story’
Sunday Telegraph
‘This book has a great deal to offer: clear technical descriptions set against their backgrounds; the story of a man largely at odds with the system he lived in; and the puzzle of Alan Turing himself’
Times Higher Education Supplement
‘Andrew Hodges, in this fine biography Alan Turing: The Enigma, brings Turing the thinker and Turing the man alive for the reader and thus allows us all to share in the privilege of knowing him’
Financial Times
‘This is not a book to be argued about. It is a book to be read’
New Scientist
‘A major work at any level. Recommended’
Personal Computing World
‘An almost perfect match of biographer and subject…. [A] great book.’
Ray Monk, Guardian
‘A captivating, compassionate portrait of a first-rate scientist who gave so much to a world that in the end cruelly rejected him. Perceptive and absorbing, Andrew Hodges’s book is scientific biography at its best.’
Paul Hoffman, author of The Man Who Loved Only Numbers
‘A remarkable and admirable biography.’
Simon Singh, author of The Code Book and Fermat’s Enigma
ANDREW HODGES
Alan Turing: The Enigma
The Book That Inspired the Film The Imitation Game
Princeton University Press
Princeton and Oxford
Published in the United States by Princeton University Press
41 William Street, Princeton, New Jersey 08540
press.princeton.edu
Copyright © Andrew Hodges 1983
Preface copyright © Andrew Hodges 2014
Andrew Hodges has asserted his right under the Copyright, Designs and Patents Act 1988 to be identified as the author of this work
This book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, resold, hired out, or otherwise circulated without the publisher’s prior consent in any form of binding or cover other than that in which it is published and without a similar condition, including this condition, being imposed on the subsequent purchaser
First published by Burnett Books Ltd
in association with Hutchinson Publishing Group 1983
Unwin Paperbacks edition 1985
Reprinting 1985 (twice), 1986, 1987 (twice)
First published by Vintage in 1992
This edition published in the United Kingdom in 2014 by Vintage
Random House, 20 Vauxhill Bridge Road, London SW1V 2SA
A Penguin Random House Company
Library of Congress Control Number: 2014952514
ISBN: 978-0-691-16472-4
Printed on acid-free paper. ∞
Printed in the United States of America
1 3 5 7 9 10 8 6 4 2
Contents
List of Plates
ix
Foreword by Douglas Hofstadter
xi
Preface
xv
PART ONE: THE LOGICAL
1 Esprit de Corps to 13 February 1930
3
2 The Spirit of Truth to 14 April 1936
60
3 New Men to 3 September 1939
141
4 The Relay Race to 10 November 1942
202
BRIDGE PASSAGE to 1 April 1943
305
PART TWO: THE PHYSICAL
5 Running Up to 2 September 1945
325
6 Mercury Delayed to 2 October 1948
394
7 The Greenwood Tree to 7 February 1952
491
8 On the Beach to 7 June 1954
574
Postscript
665
Author’s Note
666
Notes
680
Acknowledgements
714
Index
715
List of Plates
1 Alan’s father, Julius Turing (John Turing)
Alan Turing with his brother John, St Leonard’s, 1917 (John Turing)
Alan with his mother in Brittany, 1921 (John Turing)
2 Colonel and Mrs Morcom with Christopher, 1929 (Rupert Morcom)
Alan Turing with two school contemporaries, 1931 (Peter Hogg)
Alan Turing in 1934 (John Turing)
3 Alan Turing with his parents, 1938 (John Turing)
Sailing at Bosham, 1939 (John Turing)
4 The naval Enigma machine
5 A Colossus machine in operation at Bletchley Park, 1944–5 (HMSO)
The Delilah terminal, 1945 (HMSO)
6 Robin Gandy in 1953 (Robin Gandy)
Finish of a three-mile race, possibly 1946 (King’s College, Cambridge)
The Pilot ACE computer in 1950
7 The prototype Manchester computer, 1949 (Department of Computer Science, University of Manchester)
Alan Turing at the console of the Ferranti Mark I computer, 1951 (Department of Computer Science, University of Manchester)
8 Alan Mathison Turing, Fellow of the Royal Society, 1951 (King’s College, Cambridge and The Royal Society)
Alan’s father, Julius Turing, in about 1907.
On the beach : Alan
and his brother John at St Leonard’s in 1917.
On the cliffs: Alan and his mother at St Lunaire Brittany, in 1921 (see page 14).
Colonel Morcom, Mrs Morcom and Christopher on holiday, summer 1929.
George Madure, Peter Hogg and Alan setting out on their hike, Easter 1931 (see page 75).
Alan Turing in a Guildford street, a chance snapshot taken in 1934.
A brushed-up Alan with his father and mother and a family friend (right) outside 8 Ennismore Avenue in 1938.
Boy and buoys at Bosham, August 1939 (see page 200). From the front: Alan, Bob, Karl and Fred Clayton.
The naval Enigma machine with its lid raised to show the four rotors.
The Colossus in operation at Bletchley Park, 1944—5, showing the rapid punched tape input mechanism.
In contrast, the complete Delilah terminal fitted easily onto a table top (note the scale).
The key unit, with lid removed to show both rotors and multivibrators.
Robin Gandy in Summer 1953, on holiday in France.
A sporting second in a three-mile race: possibly the event of 26 December 1946 (see page 444).
The pilot ACE computer, on show at the NHL, in November 1950. Jim Wilkinson is the right hand figure.
The prototype Manchester computer. The six racks shown are essentially those of the ‘baby machine’ which ran its first program in June 1948 ; by June 1949 when this photograph was taken, the machine had roughly doubled in size.
Alan Turing with two Ferranti engineers at the console of the ‘Mark I’ computer at Manchester, 1951.
Alan Mathison Turing on election to Fellowship of the Royal Society, 1951.
Foreword
Is a mind a complicated kind of abstract pattern that develops in an underlying physical substrate, such as a vast network of nerve cells? If so, could something else be substituted for the nerve cells – something such as ants, giving rise to an ant colony that thinks as a whole and has an identity – that is to say, a self? Or could something else be substituted for the tiny nerve cells, such as millions of small computational units made of arrays of transistors, giving rise to an artificial neural network with a conscious mind? Or could software simulating such richly interconnected computational units be substituted, giving rise to a conventional computer (necessarily a far faster and more capacious one than we have ever seen) endowed with a mind and a soul and free will? In short, can thinking and feeling emerge from patterns of activity in different sorts of substrate – organic, electronic, or otherwise?
Could a machine communicate with humans on an unlimited set of topics through fluent use of a human language? Could a language-using machine give the appearance of understanding sentences and coming up with ideas while in truth being as devoid of thought and as empty inside as a nineteenth-century adding machine or a twentieth-century word processor? How might we distinguish between a genuinely conscious and intelligent mind and a cleverly constructed but hollow language-using facade? Are understanding and reasoning incompatible with a materialistic, mechanistic view of living beings?
Could a machine ever be said to have made its own decisions? Could a machine have beliefs? Could a machine make mistakes? Could a machine believe it made its own decisions? Could a machine erroneously attribute free will to itself? Could a machine come up with ideas that had not been programmed into it in advance? Could creativity emerge from a set of fixed rules? Are we – even the most creative among us – but passive slaves to the laws of physics that govern our neurons?
Could machines have emotions? Do our emotions and our intellects belong to separate compartments of our selves? Could machines be enchanted by ideas, by people, by other machines? Could machines be attracted to each other, fall in love? What would be the social norms for machines in love? Would there be proper and improper types of machine love affairs?
Could a machine be frustrated and suffer? Could a frustrated machine release its pent-up feelings by going outdoors and self-propelling ten miles? Could a machine learn to enjoy the sweet pain of marathon running? Could a machine with a seeming zest for life destroy itself purposefully one day, planning the entire episode so as to fool its mother machine into ‘thinking’ (which, of course, machines cannot do, since they are mere hunks of inorganic matter) that it had perished by accident?
These are the sorts of questions that burned in the brain of Alan Mathison Turing, the great British mathematician who spear-headed the science of computation; yet if they are read at another level, these questions also reveal highlights of Turing’s troubled life. It would require someone who shares much with Turing to plumb his life story deeply enough to do it justice, and Andrew Hodges, an accomplished British mathematical physicist, has succeeded wonderfully in just that venture.
This biography of Turing, painstakingly assembled from innumerable sources, including conversations with scores of people who knew Turing at various stages of his life, provides a picture as vivid as one could hope of a most complex and intriguing individual. Turing’s was a life that merits deep study, for not only was he a major player in the science of the twentieth century, but his interpersonal behavior was unconventional and caused him great grief. Even today, society as a whole has not learned how to grapple with Turing’s brand of nonconformism.
Hodges’s rich and engrossing portrait is not the first book about Turing; indeed, Turing’s mother, Sara Turing, wrote a sketchy memoir a few years after her son’s death, presenting an image of him as a lovable, eccentric boy of a man, filled with the joy of ideas and driven by an insatiable curiosity about questions concerning mind and life and mechanism. Although that little book has some merits and even some charm, it also whitewashes a great deal of the true story. Andrew Hodges explores Turing’s mind, body, and soul far more deeply than Sara Turing ever dared to, for she wore conventional blinders and did not want to see, let alone say, how poorly her son fit into the standard molds of British society.
Alan Turing was homosexual – a fact that he took no particular pains to hide, especially as he grew older. For a boy growing up in the 1920s and for a grown man in the subsequent few decades, being homosexual – especially if one was British and a member of the upper classes – was an unmentionable, terrible, and mysterious affliction.
Atheist, homosexual, eccentric, marathon-running English mathematician, A. M. Turing was in large part responsible not only for the concept of computers, incisive theorems about their powers, and a clear vision of the possibility of computer minds, but also for the cracking of German ciphers during the Second World War. It is fair to say that we owe much to Alan Turing for the fact that we are not under Nazi rule today. And yet this salient figure in world history has remained, as the book’s title says, an enigma.
In this biography, Andrew Hodges has painted an extraordinarily detailed and devoted portrait of a multifaceted man whose honesty and decency were too much for his society and his times, and who brought about his own downfall. Beyond the evident empathy that Hodges feels for his subject, there is another level of depth and understanding in this book, one that makes all the difference in a biography of a scientific figure: scientific accuracy and clarity. Hodges has done an admirable job of presenting to the lay reader each idea in detail, and most likely this is so because, as is obvious to a reader, he himself is passionately intrigued by all the ideas that fascinated Turing.
Alan Turing: The Enigma is a first-rate presentation of the life of a first-rate scientific mind, and given that this particular mind was attached to a body that had a mind of its own, the full story is an important document for social reasons as well. Alan Turing would probably have shuddered had he ever suspected that the tale of his personal life would one day be presented to the public at large, but he is in good hands: it is hard to imagine a more thoughtful and compassionate portrait of a human being than this one.
Douglas Hofstadter
Preface
On 25 May 2011, the President of the United States, Barack Obama, speaking to the par
liament of the United Kingdom, singled out Newton, Darwin and Alan Turing as British contributors to science. Celebrity is an imperfect measure of significance, and politicians do not confer scientific status, but Obama’s choice signalled that public recognition of Alan Turing had attained a level very much higher than in 1983, when this book first appeared.
Born in London on 23 June 1912, Alan Turing might just have lived to hear these words, had he not taken his own life on 7 June 1954. He perished in a very different world, and his name had gone unmentioned in its legislative forums. Yet even then, in its secret circles, over which Eisenhower and Churchill still reigned, and in which the names of NSA and GCHQ were spoken in whispers, Alan Turing had a unique place. He had been the chief backroom boy when American power overtook British in 1942, with a scientific role whose climax came on 6 June 1944, just ten years before that early death.
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 round 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, that 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. Such is mathematical culture, and such was his life, presenting a real difficulty to minds set in literary, artistic or political templates.
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