Alan Turing: The Enigma

ALAN TURING: THE ENIGMA

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. He is an active contributor to the mathematics of fundamental physics, as a follower of Roger Penrose. See
www.turing.org.uk
for further material.

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 his 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

THE CENTENARY EDITION

With a foreword by Douglas
Hofstadter and a new preface by the author

ANDREW HODGES

Alan Turing: The Enigma

Published in the United States by Princeton University Press, 41 William Street, Princeton, New Jersey 08540 press.princeton.edu

First published in 2012 by Vintage, Random House, 20 Vauxhall Bridge Road, London SW1V 2SA
www.vintage-books.co.uk

Copyright © 1983 by Andrew Hodges
Preface to the 2012 Centenary edition copyright © 2012 by Andrew Hodges
Foreword
copyright © 2000 by Douglas Hofstadter

All Rights Reserved

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

Library of Congress Control Number 2012935958
ISBN 978-0-691-15564-7

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

Foreword by Douglas Hofstadter

Preface to the 2012 Centenary edition

PART ONE: THE LOGICAL

1   Esprit de Corps
to 13 February 1930

2   The Spirit of Truth
to 14 April 1936

3   New Men
to 3 September 1939

4   The Relay Race
to 10 November 1942

BRIDGE PASSAGE
to 1 April 1943

PART TWO: THE PHYSICAL

5   Running Up
to 2 September 1945

6   Mercury Delayed
to 2 October 1948

7   The Greenwood Tree
to 7 February 1952

8   On the Beach
to 7 June 1954

Postscript

Author’s Note

Notes

Acknowledgements

Index

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, August 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. Finish of a three-mile race, 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)
   Robin Gandy in 1953 (Robin Gandy)
   
8. Alan Mathison Turing, Fellow of the Royal Society, 1951 (King’s College, Cambridge and The Royal Society)
   

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 spearheaded 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 to the Centenary Edition

On 25 May 2011, the President of the United States, Barack Obama, speaking to the parliament 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. In that very different world, his name had gone unmentioned in its legislative forums. Yet in the secret world, over which Eisenhower and Churchill still reigned, and in which the newly reorganised NSA and GCHQ were the holy of holies, their names to be whispered, 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.