THE LABORATORY OF THE MIND Thought Experiments in the Natural Sciences James Robert Brown London and New York First published 1991 This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” Paperback edition first published in 1993 by Routledge 11 New Fetter Lane London EC4P 4EE Simultaneously published in the USA and Canada by Routledge 29 West 35th Street, New York, NY 10001 © 1991 James Robert Brown All rights reserved. No part of this book may be reprinted or reproduced or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. British Library Cataloguing in Publication Data Brown, James Robert The laboratory of the mind. 1. Science. Philosophical perspectives I. Title II. Series 501 Library of Congress Cataloging in Publication Data Brown, James Robert. The laboratory of the mind: thought experiments in the natural sciences/James Robert Brown. p. cm.—(Philosophical issues in science) Includes bibliographical references and index. 1. Physics—Philosophy. 2. Quantum theory. 3. Science—Methodology. 4. Rationalism. 5. Knowledge, Theory of. I. Title. II. Series. Q175.B7965 1991 530′.01–dc20 90–47820 ISBN 0-203-97915-X Master e-book ISBN ISBN 0-415-05470-2 (Print Edition) 0-415-09579-4 pbk For Kathleen who doesn’t believe a word of it CONTENTS Preface and Acknowledgements viii 1 ILLUSTRATIONS FROM THE LABORATORY OF 1 THE MIND 2 THE STRUCTURE OF THOUGHT 33 EXPERIMENTS 3 MATHEMATICAL THINKING 49 4 SEEING THE LAWS OF NATURE 75 5 EINSTEIN’S BRAND OF VERIFICATIONISM 99 6 QUANTUM MECHANICS: A PLATONIC 127 INTERPRETATION Afterword 155 Notes 159 Bibliography 165 Index 175 PREFACE AND ACKNOWLEDGEMENTS Like most philosophers, I encountered a bit of rationalism (Plato and Descartes) and a bit of empiricism (Hume) in my first formal introduction to the subject. And like most students of philosophy I found the rationalists endlessly fascinating, but not in the least believable. It seemed obvious to me, as it does to most, that all our knowledge is based upon sensory experience. Then one day I heard about Galileo’s thought experiment showing that all bodies must fall at the same rate—I almost fell out of my chair. It was a wonderful intellectual experience. Suddenly, traditional rationalism seemed a live option; perhaps my philosophical heroes—Plato, Descartes, and Leibniz—were on the right track after all. All of this remained on the back burner until a couple of years ago when I got around to looking at thought experiments in general. I was surprised by two things. First, that there is remarkably little literature on the subject. People often use the expression ‘thought experiments’, but hardly anyone has thought seriously (or at least written extensively) about them. The second thing I was surprised at was that my old rationalist sentiments stood up; if anything, they have been reinforced by looking at this topic anew. I have long held a platonistic view of mathematics; I now hold a platonistic view of physics as well. In brief, the book is as follows. The first chapter introduces the subject by giving several examples of thought experiments. A multitude of cases is necessary since I have no definition of thought experiment to work with; we need a variety of paradigm instances. But this is not the only reason for describing several specimens. They are such a pleasure to contemplate that it’s an opportunity not to be missed. With lots of examples under our belt we can begin to talk about how they work. This task is begun in chapter two, which offers a ix taxonomy of thought experiments. Some commentators say thought experiments do this or that or some other thing. Actually they do several quite distinct things and chapter two tries to classify their diverse uses. Chapter three is a defence of platonism in mathematics. It serves as a model of how I’d like theorizing about thought experiments to go. Platonism in the philosophy of mathematics, though a minority view, is eminently respectable, whereas a priorism about the physical world is likely be dismissed out of hand. So the point of the third chapter is to carry empiricist-, naturalist-, and physicalist- minded readers as gently as possible into chapter four which contends that we really do have some a priori knowledge of nature. Of course, the great bulk of our knowledge must be accounted for along empiricist lines; but there is, I contend, the odd bit that is a priori and it comes from thought experiments. Not all thought experiments generate a priori knowledge. Only a very select class is capable of doing so. This a priori knowledge is gained by a kind of perception of the relevant laws of nature which are, it is argued, interpreted realistically. Just as the mathematical mind can grasp (some) abstract sets, so the scientific mind can grasp (some of) the abstract entities which are the laws of nature. The next two chapters function as a kind of test of my platonist outlook, though I hope there is some independent interest in these final chapters as well. A novel interpretation of Einstein is offered in chapter five. It attempts to make sense of what is commonly thought to be Einstein’s ‘youthful empiricism’ and his ‘mature realism’ as well as accounting for the role of thought experiments in his scientific work. Chapter six surveys some of the philosophical problems of quantum mechanics and some of the interpretations which have been proposed to solve them. Though my discussion of thought experiments has been mainly about the epistemology of science, much ontological machinery has been developed. Laws of nature, understood as real entities in their own right, are now put to work to give an account of quantum phenomena—not just thought experiments about quantum phenomena, but the actual measurement results themselves—which is realistic and does not violate the locality requirements of special relativity. It is a commonplace at this point in a preface for authors to say that they are less interested in having their own views stand up to close scrutiny than in stimulating interest in their chosen subjects. x Of course, such remarks are largely disingenuous. Nobody wants to be shot down in flames—certainly I don’t; yet the chance of this happening is great since the central views put forward here are far removed from mainstream thinking about how either science or nature work. Even if some of my claims are on the right track, the details are bound to be seriously flawed. At best this work is a first attempt at a (modern) rationalist interpretation of science. So it is probably wise for me also to take the disingenuous route and declare that I am content to provoke interest in the subject of thought experiments, and to hope that readers are more than usually indulgent. I mentioned that there is very little literature on the subject of thought experiments. This lamentable state of affairs is about to change radically. Two other books are soon to be published: Nicholas Rescher (ed.), Thought Experiments, and Roy Sorensen, Thought Experiments. I have seen some of the contributions to the first and they have played a role in my developing views. This is especially true of John Norton’s excellent essay, Thought Experiments in Einstein’s Work’. In several places below I borrow from it or argue against it. Norton’s is one of the most intelligent and persuasive pieces going on this subject. Unfortunately, I found out about Roy Sorensen’s book too late to let it have any impact on this one—though it certainly would have if I’d read it earlier. It’s a rich, readable, and wide-ranging work, bound to be influential over the long haul. If an antidote to my gung-ho platonism should be needed, then it can be found in either Norton’s empiricism or Sorensen’s naturalism. Both are warmly recommended. Much of the material in this book was presented to various audiences in Canada, Dubrovnik, Yugoslavia, Lanzhou, China, and Moscow. In every case I am grateful to my hosts and numerous critics. Some of this work stems from earlier essays: ‘Thought Experiments since the Scientific Revolution’, International Studies in the Philosophy of Science, 1986, ‘Einstein’s Brand of Verificationism’, International Studies in the Philosophy of Science, 1987, and ‘π in the Sky’, A.Irvine (ed.), Physicalism in Mathematics, Kluwer, 1989. There are a large number of individuals who deserve special mention: Igor Akchurin, Brian Baigrie, John L.Bell, Lars Bergström, Harvey Brown, Robert Butts, John Carruthers, Paul Forster, Rolf George, David Gooding, Ian Hacking, Andrew Irvine, Dominick Jenkins, Randell Keen, André xi Kukla, Igal Kvart, Lin Li, Ma Jin-Song, Penelope Maddy, Elena Mamchur, James McAllister, Cheryl Misak, Margaret Morrison, William Newton-Smith, John Norton, Kathleen Okruhlik, David Papineau, Kent Peacock, Michael Ruse, David Savan, Valerie Schweitzer, William Seager, Roy Sorensen, Demetra Sfendoni- Mentzou, Jacek Urbaniec, Alasdair Urquhart, Wang Jian-Hua, Kathleen Wilkes, and Polly Winsor. I’m grateful to them all. Finally, I am extremely grateful to David Kotchan who did the diagrams. Note to paperback edition I have taken this opportunity to correct a few slips and misprints. I am especially grateful to Kent Peacock who pointed many of these out to me. 1 ILLUSTRATIONS FROM THE LABORATORY OF THE MIND Thought experiments are performed in the laboratory of the mind.