Philosophy of Physics Dimensions of Philosophy Series Norman Daniels and Keith Lehrer, Editors Philosophy of Physics, Lawrence Sklar Metaphysics, Peter van Inwagen Theory of Knowledge, Keith Lehrer Philosophy of Law: An Introduction to Jurisprudence, Revised Edition, Jeffrie G. Murphy and Jules L. Coleman Philosophy of Social Science, Alexander Rosenberg Introduction to Marx and Engels: A Critical Reconstruction, Richard Schmitt FORTHCOMING Philosophy of Biology, Elliott Sober Philosophy of Science, Clark Glymour Philosophy of Mind, Jaegwon Kim Contemporary Continental Philosophy, Bernd Magnus Political Philosophy, Jean Hampton Normative Ethics, Shelly Kagan Philosophy of Religion, Thomas V. Morris Philosophy of Education, Nel Noddings Also by Lawrence Sklar Space, Time, and Spacetime Philosophy and Spacetime Physics Philosophy of Physics Lawrence Sklar U niversity of M ichigan CRC Press Taylor & Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business Dimensions of Philosophy Series First published 1992 by Westview Press Published 2018 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 CRC Press is an imprint of the Taylor & Francis Group, an informa business Copyright © 1992 Taylor & Francis Group LLC No claim to original U.S. Government works This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. 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QC6.S578 1992 SSO'.Ol— dc20 92-18759 CIP ISBN 13: 978-0-8133-0625-4 (pbk) For P at and R ubby Contents Acknowledgments 1 Introduction : P h il o s o p h y a n d t h e P h y sic a l S c ien ces The Relation of Science to Philosophy, 1 Modern Physics and Philosophy, 3 Philosophy of Physics and General Philosophy, 7 The Aim and Structure of This Book, 9 2 S p a c e , T im e, a n d M o tio n Traditional Philosophical Problems of Space and Time, 11 The Debate Between Newton and Leibniz, 19 From Space and Time to Spacetime, 25 Gravity and the Curvature of Spacetime, 40 How Do We Know the True Geometry of the World? 53 What Kind of Being Does Spacetime Have? 69 Further Readings, 90 3 T h e Introduction o f P ro ba bility in to P h ysic s Philosophers on Probability and Statistical Explanation, 92 From Thermodynamics to Statistical Mechanics, 109 The Problem of Irreversibility and Attempts to Solve It, 121 The Problem of "The Direction of Time," 147 Further Readings, 155 X Contents 4 T h e Q u a n t u m P ictu re o f t h e W o rld 1 5 7 The Experimental Basis of Quantum Theory, 157 Early Attempts to Interpret the Theory: The Uncertainty Principle, 164 What Is Measurement in Quantum Theory? 179 The Problem of Hidden Variables and Determinism, 202 The Inseparability of Systems, 213 Further Readings, 225 5 R efle c t io n s o n t h e Interdependence o f Philosophy and Science 2 2 7 References 2 3 3 About the Book and Author 2 3 7 Index 2 3 9 Acknowledgments For a work of this sort, designed to survey the current state of the field, the sources of intellectual influence are far too many to mention in an acknowledgments section. The suggested readings at the ends of the three major chapters will indicate to the reader where I have found the sources of many important ideas in the philosophy of physics. Discussions with many people over the years have helped me to get my ideas in order on the topics presented here. Jim Joyce and Bob Bat- terman have been of great help, and I have learned much from John Earman, Clark Glymour, David Malament, Paul Horwich, and Michael Friedman. Michele Vaidic provided invaluable help in putting the manuscript together. Spencer Carr and the two referees of Westview Press helped greatly in improving the early draft of the manuscript, especially with regard to style and organization. Marian Safran, copy editor, provided much-appreciated help in bringing the manuscript to its final form. Research that contributed to the material in Chapter 3 was supported in part by the National Science Foundation, whose aid is gratefully ac­ knowledged. Thanks are due also to the University of Michigan for a grant that helped defray some of the costs of manuscript preparation. Lawrence Sklar 1 Introduction: Philosophy and the Physical Sciences The Relation of Science to Philosophy The demarcation of the natural sciences from philosophy has been a long and gradual process in Western thought. Originally, in­ quiry into the nature of things consisted in an amalgamation of what would now be thought of as philosophy: general considerations of the broadest sort about the nature of being and the nature of our cognitive access to it, and what would now be considered to be the specific sci­ ences: the amassing of observational fact and the formulation of general and theoretical hypotheses to explain it. If we look at the fragmentary remains of the works of the pre-Socratic philosophers, we find not only important and ingenious attempts to apply reason to broad metaphys­ ical and epistemological questions but also the first crude, if extraor­ dinarily imaginative, physical theories concerning the nature of matter and its changing aspects. By the time of classical Greek philosophy, we can already see some splitting of the two disciplines. Aristotle in his metaphysical works is plainly doing what would now be done by philosophers. But in much of his biological, astronomical, and physical works, we find methods of inquiry familiar to us now in the practice of scientists. As the special sciences such as physics, chemistry, and biology have increased in number, commanded more and more resources, and de­ veloped highly individual methodologies, they have demonstrated abil­ ity to describe and explain the fundamental features of the world in which we live. Because of the success of the practitioners of the special sciences, many question whether there is anything left for philosophers to do at all. Some philosophers believe that there are areas of inquiry that are radically distinct from those of the particular sciences, for ex­ ample, inquiry into the nature of God, of "being itself," or of some- 1 2 Introduction thing else again. Other philosophers have sought in varying ways for a remaining area of inquiry for philosophy more closely connected to the natural sciences in their latter-day, sophisticated, development. An older view, waning in popularity over the centuries but never disappearing entirely, holds that there is a way of knowing the world that need not rest upon observational or experimental inquiry at its foundations, the method of the specific sciences. The older view was partly influenced by the existence of pure logic and mathematics, whose firmly established truths do not seem to rest for their warrant on any observational or experimental ground. The hope has endured—from Plato and Aristotle to Leibniz and the other rationalists, through Kant and the idealists, and even to the present time—that were we but smart and thoughtful enough, we could establish a body of propositions de­ scriptive of the world, yet known with the certainty with which we claim to know truths of logic and mathematics. These would be be­ lievable independently of any inductive support from particular ob­ served facts. Were such a body of knowledge available to us, would it not be the goal aimed at over the centuries by the discipline tradition­ ally called philosophy? A more contemporary view is that philosophy's role is to serve, not as some ground for the sciences or as some extension of them, but rather as their critical observer. The idea here is that the particular sci­ entific disciplines use concepts and methods. The relationships of the concepts to one another, although implicit in their use in science, may fail to be explicitly clear to us.