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Overview
On Physics and Philosophy is an accessible, mathematics-free reflection on the philosophical meaning of the quantum revolution, by one of the world's leading authorities on the subject. D'Espagnat presents an objective account of the main guiding principles of contemporary physics-in particular, quantum mechanics-followed by a look at just what consequences these should imply for philosophical thinking.
The author begins by describing recent discoveries in quantum physics such as nonseparability, and explicating the significance of contemporary developments such as decoherence. Then he proceeds to set various philosophical theories of knowledge—such as materialism, realism, Kantism, and neo-Kantism—against the conceptual problems quantum theory raises. His overall conclusion is that while the physical implications of quantum theory suggest that scientific knowledge will never truly describe mind-independent reality, the notion of such an ultimate reality—one we can never access directly or rationally and which he calls "veiled reality"—remains conceptually necessary nonetheless.
Product Details
| ISBN-13: | 9780691158068 |
|---|---|
| Publisher: | Princeton University Press |
| Publication date: | 04/07/2013 |
| Edition description: | Reprint |
| Pages: | 520 |
| Sales rank: | 918,260 |
| Product dimensions: | 6.00(w) x 9.00(h) x 1.70(d) |
About the Author
Read an Excerpt
On Physics and Philosophy
By Bernard d'Espagnat
Princeton University Press
Copyright © 2006 Princeton University PressAll right reserved.
ISBN: 978-0-691-11964-9
Chapter One
BROAD OVERVIEW1-1 A General Picture
ADMITTEDLY THE new world-view that soared in the early seventeenth century originated from Copernicus' discovery but it is not to be questioned that the change from Aristotelian to Galilean physics played an essential part in its development. Aristotle had kept close to raw data obtained through the senses. He saw that all moving bodies not subjected to any force finally stop, and he raised this observed fact to the level of a basic principle of knowledge. He observed that living beings have all sorts of different shapes, qualitatively differing from one another, and he therefore took the notion of a wide variety of fundamental forms as a guideline for his philosophy. Hence, for him, there were a great abundance and variety of concepts, all of them lying, so to speak, on the same level. Hence also he gave considerable care to detailed qualitative descriptions, counterbalanced by a marked weakness concerning anything physically quantitative. With Galileo, Descartes, etc., on the contrary, the idea that came to the forefront was that of a hierarchy of concepts. Within their approach there are basic and nonbasic ones, and the latter must be accounted for in terms of the former, so that, in the end,the description of the physical world should be entirely expressed in terms of just a few basic notions linked together by quantitative laws. And we know, of course, that within classical physics as well as in all other sciences this is the conception that finally prevailed.
The difference just sketched between the Aristotelian and the Cartesian-Galilean approaches is quite well known. But what often remains unnoticed is that, notwithstanding this difference, the approaches in question had an important feature in common. In fact, they shared the view that the basic concepts (the nonderived ones) are either obvious ones or, at least, idealizations of obvious ones; that they are familiar notions- "clear and distinct ideas" as Descartes said-whose unquestionable validity is fully guaranteed by commonsense (i.e., by God, according to the same). It is often-and rightly-stressed that Galileo, Descartes, and Newton brought mathematics into physics. But an often overlooked point is that they made use of mathematics primarily for imparting quantitative content to developments exclusively bearing on objects designated by means of familiar concepts. Descartes was bent on describing the whole of the physical world by "figures and motions" and referred to "the pipes and springs that cause the effects of the natural bodies." Newton spoke of material points, that is, (basically) idealized grains or specks. Even Pascal, in his fable of the mite, clearly took it for granted that the domain of validity of the familiar concepts extends to the whole range of conceivable scales, from the infinitely great to the infinitesimally small.
Were they right? Yes of course, in a sense. Pioneers they were and, as such, their most urgent task was to explore the ins and outs of such a natural idea. Moreover, the idea in question proved spectacularly fruitful. Still today, there are many fields of study in which it is possible to describe data and processes by the sole means of basically familiar concepts and in which this is obviously the best way to carry on fruitful research. Consider, for example, molecular biology. Molecular biologists have to do with large molecules whose behavior-for well-known reasons following from the very rules of quantum physics-practically obeys the laws of classical physics. Consequently it is possible and natural to think of them as having rigid atomic structures, fixed shapes (including hooks), and so on; in short, to reason about them as if they were component parts of a clockwork or a machine. This mode of thought opened the way to quite a host of predictions, many of which proved brilliantly successful. No wonder that many biologists are tempted to raise it to the level of an absolute; to view it as yielding the proper canvas for a description of "the Real itself," including thought.
All this naturally leads to a mechanistic world-view styled naïve-to be sure-within philosophical circles but stamped with commonsense and taken therefore by the majority of well-informed people to be by far the most sensible one. Think, for a moment, of an attorney, a senior executive, an engineer, or even a scientist working in some highly specialized field other than theoretical physics. Such people-most of our contemporaries indeed-have to do, all day long, with machines of all kinds, that is, with human-made devices of which the clock is the example par excellence. No wonder that they spontaneously lean toward a generalized mechanistic world-view, in spite of all that the philosophers may write and say! It is therefore fully understandable that such a type of natural philosophy should remain, so to speak, the instinctive one in the minds of both the enlightened laymen and a majority of scientists. The idea that the World- or, at least, its physical part-is of the nature of some gigantic machinery seems infinitely plausible indeed.
And still, the opposite is true! In a move that was slow at first but progressively speeded up, physics taught us, not only that the human mind is able to operate well outside the framework of familiar concepts, but also that it absolutely must do so. Of all sciences, only physics, apparently, yields this message. But it does. And the fact that it does may well be taken to constitute one of its main contributions to the development of thought.
For brevity's sake, let me illustrate this by but one example, that of particle creation in high-energy collisions. This phenomenon is explored and investigated in laboratories where large particle accelerators are available and observed in bubble chambers in which moving particles produce tracks. Two protons are accelerated. Each one has a given motion, a given velocity, and hence a given energy. They collide and they then part from one another. At that time we observe that, even though they are still in existence and did not break up, other particles have appeared, which are "really true" particles-possessing masses, electric charges, and so on-that have been created in the collision, at the expense of the incident protons' total energy. This, at least, is what we see. Admittedly, the phenomenon is quite in agreement with the celebrated E=mc law expressing mass-energy equivalence. But if we insisted on describing it by the sole means of familiar concepts we would have to say that the incident particle motion was changed into particles. Now, motion is a property of objects, so that what we would thereby refer to would be nothing else than the transformation of a property of objects into objects. Such an idea lies entirely outside the realm of our familiar concepts. Within the set of the latter there are, on the one hand, objects and, on the other hand, properties of objects; and no element of either one of these subsets ever transforms into an element of the other one. The very idea of such a transformation looks just as absurd as that of changing the height of the Eiffel tower into another Eiffel tower. Or as the view that, when two taxis collide, they may both emerge undamaged, accompanied by five or six other taxis arising from the initial kinetic energy of the former. All this makes it crystal clear that contemporary physics forces upon us the use of basic concepts lying outside the realm of the familiar ones, with the sole help of which Descartes (and the other "founding fathers" of modern science) originally claimed that physics would describe the World.
Are we then faced with an enigma exceeding the powers of understanding? Quite on the contrary, theoretical physicists not only know how to deal with this creation phenomenon but also had predicted it, on the basis of their equations. Which shows that, when applied to physics, mathematics makes it possible to really reach beyond all familiar concepts; to actually coin new concepts. This reminds us of Pythagoras' famous saying: "Numbers are the essence of things." A sentence to be understood, of course, as "mathematics are the essence-the very essence-of things."
This, to be sure, is not the proper place for entering into a detailed account of how physics manages to describe the creation phenomenon. Already at this stage let us note, however, that it offers several ways of doing so, grounded on quite different basic concepts. The existence of this diversity should not disconcert us, but it is important that we should be aware of it, since it casts quite a serious doubt on the very possibility of univocally determining, by means of physics, a list of the truly basic notions. Which, in turn, makes it unlikely that Pythagorism is the "last word" of our story. Indeed the diversity in question is a good example of a philosophically important phenomenon-called "incomplete determination of theory by experience"-that we shall frequently have to take into consideration. With respect to the case under study, it so happens that the mathematical formalism yields not one but three distinct theories, all of them grounded on the general quantum rules, yielding essentially the same observational predictions, but widely differing concerning the ideas they call forth. They are called the "theory of the Dirac sea," "Feynman graph theory," and "quantum field theory."
We shall soon get acquainted with the two first named ones (sections 2-6 and 2-7), and shall then have the opportunity of observing how widely both depart from the Cartesian ideal of a description using only familiar concepts. But, for the time being, let us focus our attention on quantum field theory.
Unquestionably more general than the first one-Dirac's-this theory is, in a way more basic than the second one-Feynman's-which primarily appears as a powerful method of calculating, grounded, as its author himself stressed, precisely on the very rules of quantum field theory. To form a broad idea of the general guiding lines of the latter let us begin by observing that the notion of creation is not a scientific one: We do not know how to capture it, and even less quantify it. It is therefore appropriate to try and reduce it to something we can master. Now we do master the notions of a system state and changes thereof. We know how to calculate transition rates from one state to another. And the brilliant idea, the breakthrough, just came from this. It consisted in considering that the existence of a particle is a state of a certain "Something," that the existence of two particles is another state of this same "Something," and so on. Of course, the absence of a particle is also a state of this "Something." Then, the creation of a particle is nothing else than a transition from one state of this "Something" to another, and therefore we may hope to be able to treat it quantitatively. It is just as simple as that! In practice- believe it-the matter is appreciably more complex. Quantum field theory textbooks are big, fat objects, full of formulas, many of which are in no way beautiful. But by plodding through the latter it proved possible to account for observed phenomena with a precision that, in some cases, extends to the seventh decimal. Which, really, is "not too bad"!
The reader will be spared the calculations. Instead, let him or her reflect on the just described basic idea of the quantum field theory. True, the problem of the "real nature" of the "Something" that it brings-at least implicitly-into play is, as we shall see, an inordinately delicate one. However, concerning it, one point at least seems rather clear. It is that the cornerstone role tacitly attributed to it somehow suggests the presence, within the core of present-day physics, of a wholeness of some sort, radically foreign to classical physics. The point is that classical science was very much in favor of what may be adequately said to be a multitudinist world-view. In other words, it favored a conception of Nature in which basic Reality-matter, as it was called-was constituted of a myriad simple elements-essentially localized "atoms" or "particles"-embedded in fields, and hence interacting by means of forces decreasing when distance increased. The first two of the above mentioned theoretical approaches still are more or less compatible with such a view, although, as we shall see, they considerably weaken it by attributing to the particles behaviors that the mind cannot imagine. On the other hand, the-more general- quantum field theory is radically at variance with it. Not only is it true that, in it, the particles no longer play the role of the constitutive material of the Universe. What is more, the only "entity" that, in it, might conceivably be thought to constitute basic Reality is the "Something," of which we saw that it is fundamentally the only one of its species.
The idea that, here, is seen to come to light (though dimly as yet) is, to repeat, the notion of a wholeness of some sort. Within elementary particle physics wholeness, admittedly, remains ambiguous since while, say, manifest in one formulation, it is evanescent in the other two-in spite of the fact that all three are equivalent and proceed from the same-quantum- formalism. This perhaps explains why, when quantum mechanics appeared, the notion in question was clearly apprehended by neither the epistemologists nor even the physicists, with the perhaps unique exception of Schrödinger. But theoretical as well as experimental advances gradually made people realize that it constitutes an inherent part of the very quantum formalism and has quite specific experimental consequences.
Nowadays the common name nonseparability serves to designate both the just mentioned mathematical features of the formalism and the corresponding observable effects. A most important point is to be noted concerning it. It is the fact that the range of validity of the notion it designates is even wider than that of the presently accepted theory. Indeed, it has been established that in one at least of its main aspects-nonlocality-it will certainly remain true, even if the quantum formalism must, one day, be replaced by some other, more general, one. As will be seen (chapter 3), this follows from the Bell theorem and the experiments-such as Aspect's-associated with it, for the results of the latter are incompatible with some consequences of the inverse hypothesis-locality, and this quite independently of any theory whatsoever.
To be sure, scientists and even physicists go on expressing themselves in terms of particles, molecules, and so on, all words calling forth the idea of individual, localized objects depending less on one another as the distances between them grow greater. In short, they go on making use of a multitudinist language. And from their angle they are right for, as we saw, this amounts to referring to a model that is, by far, the most convenient one in an enormous variety of cases. But, by now, it appears more and more clearly that it is merely a model. With due reservations a comparison could be ventured here with Ptolemy's geocentric model, which also works quite well on specific problems. In both cases, to raise the model to the level of a description of "what really is" is scientifically illegitimate.
In this respect, let it be noted that the question "reality or just model?" never comes to light in the articles physicists write. The latter wisely remain on "secure ground," which means that their theoretical constructions, elaborate as they may be at the level of equations and methods, are left by them very much "open" regarding concepts. In fact, when they work on such constructions the condition they impose on them is just that they should be highly general models, correctly accounting for what we observe in a great variety of experiments. Consequently it is without qualms that they ground them-tacitly at least-on the basic principles of "standard" quantum mechanics, without being in the least worried by the fact that, as we shall see, some of these principles impart a fundamental role to such notions as "measurement" and "preparation of system states." Now, this fact-the occurrence of a reference to human action within the very axioms of physics-is sometimes explicitly stated. Often it is kept implicit. But in any case it implies that the theories built up in this way markedly depart from a principle that was one of the main guidelines of all classical ones. I mean the rule that basic scientific statements should be expressed in a radically objectivist language, making no reference whatsoever, be it explicit or implicit, to us ("operators" or "measurers").
(Continues...)
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Table of Contents
Preface to the English Edition xiForeword 1
PART 1: PHYSICAL FACTS AND RELATED CONCEPTUAL PROBLEMS
CHAPTER 1: Broad Overview 131-1. A General Picture 131-2. Some Useful Definitions 21
CHAPTER 2: Overstepping the Limits of the Framework of Familiar Concepts 322-1. Introduction 322-2. From Aristotle's Ontology to Descartes' Near Realism and Galilean Ontology 322-3. A Small Digression on Ontology 342-4. A Gradual Overstepping 372-5. Trajectories and Misleading "Pieces of Evidence" 382-6. On the Existence or Nonexistence of Hidden Things: Particles and Dirac's Sea 412-7. A "Fabricated" Ontology 462-8. Indications for What Follows 48
CHAPTER 3: Nonseparability and Bell's Theorem 513-1. Correlation at-a-Distance: Bell's Theorem 513-2. Locality and the Bell Theorem 583-3. Discussion and Philosophical Implications 71
CHAPTER 4: Objectivity and Empirical Reality 894-1. Strong Objectivity and Weak Objectivity (Alias Intersubjectivity) 894-2. The Measurement Problem and Empirical Reality 1014-3. "Quantum Rules" and "von Neumann's Chain" 110
CHAPTER 5: Quantum Physics and Realism 1135-1. Strong Objectivity and Realism 1135-2. Intersubjective Agreement 1275-3. Intersubjective Agreement and Empirical Reality 1275-4. Conceptual Glimpses; Carnap, Quine, Primas; Relative Ontologies 129
CHAPTER 6: Universal Laws and the "Reality" Question 1346-1. The "Theoretical Framework" Notion 1346-2. Antiuniversalism and "Realism about Entities" 1366-3. "Pythagorism" ("Einsteinism") 1426-4. Remarks Concerning Two "Macrorealisms" 1456-5. Quantum Mechanics as a Universal Theoretical Framework 1466-6. Antirealism 148
CHAPTER 7: Antirealism and Physics; the Einstein-Podolsky-Rosen Problem; Methodological Operationalism 1527-1. "Value of a Quantum Physical Quantity" in the Antirealist Framework 1527-2. Operationalism (Alias "Instrumentalism") 1567-3. On "Meaning" and "Prediction" 166
CHAPTER 8: Measurement and Decoherence, Universality Revisited 1688-1. Introduction 1688-2. Decoherence 1778-3. Decoherence and State Robustness 1898-4. The Everett-Zurek Semirealist Approach 1908-5. Universality Revisited 192
CHAPTER 9: Various Realist Attempts 1969-1. Introduction 1969-2. On Our Intellectual Craving for Realism 1969-3. The Broglie-Bohm Approach 1999-4. The So-Called "Modal" Interpretation 2069-5. The Heisenberg Representation: It Does Not, by Itself, Yield a Solution 2099-6. Feynman's Reformulation and the Corresponding "Fabricated Ontology" 2119-7. A "Realism of Signification" 2169-8. Nonlinear Realist Quantum Theories 2209-9. Outlook 222
CHAPTER 10: Schrödinger's Cat, Wigner's Friend, and Veiled Reality 22510-1. Introduction 22510-2. Of Pointers and Cats 22510-3. Wigner's Friend 22810-4. The Veiled Reality Hypothesis 236
PART 2: A PHILOSOPHICAL ANALYSIS
CHAPTER 11: Science and Philosophy 24911-1. The Impossible Split 24911-2. Epistemology in the Late Twentieth Century 25011-3. A Critical Glance at Some Claims 25511-4. Physics and Linguistics 25811-5. Sociologism 26111-6. The End of Certainties? 263
CHAPTER 12: Materialisms 26512-1. Introduction 26512-2. Dialectical Materialism 26512-3. The So-Called "Scientific" Materialism 26612-4. "Neomaterialism" and Physics 27212-5. The Purely Philosophical Aspects of Neomaterialism 27612-6. Materialism and Wisdom 281
CHAPTER 13: Suggestions from Kantism 28213-1. Introduction 28213-2. A Look at Kantism 28213-3. Facing the Refusal of the Independent Reality Notion 29113-4. Kant and Our Contemporaries 306
CHAPTER 14: Causality and Observational Predictability 31214-1. Introduction 31214-2. Causes and Laws 31214-3. Determinism and Causality 31514-4. Determinism and Chaos 31614-5. Quantum Indeterminacy 31914-6. Predictability and Reliability Revisited 32614-7. The Influence Notion Revisited 330
CHAPTER 15: Explanation and Phenomena 33315-1. Introduction 33315-2. The Notion of Explanation 33315-3. Back to the "Explanatory Power of Predictive Rules" Question 34215-4. Empirical Reality and Abstractions, Explanation, and Empirical Causality 34415-5. The Rainbow Analogy 34715-6. Removing the "Paradox of the Dinosaurs" 35115-7. The "False Explanation" Question 352
CHAPTER 16: Mind and Things 35416-1. Empiricism, Positivism, and So On 35416-2. Phenomenalism 35516-3. Ambiguities about Innatism 36616-4. Poincaré, Conventionalism, and Structural Realism 368
CHAPTER 17: Pragmatic-Transcendental versus Veiled Reality Approaches 37617-1. Introduction 37617-2. Replies to Michel Bitbol's and Hervé Zwirn's Objections 37617-3. The Pragmatic-Transcendental Approach 39617-4. A Few Notes on Zwirn's Approach 402
CHAPTER 18: Objects and Consciousness 40518-1. Introduction 40518-2. Truth: Definitions and Criteria 40618-3. Objects and "Orders," or "Levels," of Reality 40818-4. A Few Remarks Concerning Sensations 41118-5. On the Question of the Plurality of Minds 426
CHAPTER 19: The "Ground of Things" 42919-1. Introduction 42919-2. Mystery, Affectivity, and Meaning 42919-3. Do Things Have a "Ground"? Pro and Con Received Arguments 43419-4. Some Consequences of the Evolution of Physics 44319-5. The Veiled Reality Conception Reexamined 449
APPENDIX 1: The Bell Theorem 465A. Proof 465B. A Simplified Proof 470C. A Glance at the Experimental State of Things 473D. Historical Comments and a Short Bibliography 474
APPENDIX 2: Consistent Histories, Counterfactuality, and Bell's Theorem 477APPENDIX 3Correlation-at-a-Distance in the Broglie-Bohm Model 483
References 485Name Index 493Subject Index 497
What People are Saying About This
D'Espagnat has performed an intellectual feat by distilling the essential conceptual puzzles of quantum mechanics into a few core principles without relying on any mathematical formalism, and in a very readable style at that. At the same time, this book is not some trendy everyman's guide to the exotic features of quantum physics, with some philosophical commentary—but a work of mature scholarship.
— Jeffrey Bub, University of Maryland, author of "Interpreting the Quantum World"
Here, d'Espagnat discusses virtually all the central philosophical issues related to quantum mechanics and its interpretation. The book is nontechnical, presupposing no previous knowledge of science or philosophy. It is a pleasure to read.
— Andrew Z. Wayne, University of Guelph, coeditor of "Ontological Aspects of Quantum Field Theory"
"This book is a monument to d'Espagnat's excellent work and style; it is surely the most complete book to have been written on this subject and one likely to last a long time, at least until we come to fully understand the remaining mysteries in the field."—Roland Omnès, Professor Emeritus of Theoretical Physics, Université de Paris-Sud"Bernard d'Espagnat is an accomplished theoretical physicist and philosopher, whose two disciplines are interrelated in the present book. He conclusively argues that features of quantum mechanics—particularly the Uncertainty Principle, the nonlocality exhibited by entangled systems, and the measurement problem—revolutionize epistemology and metaphysics. His novel and lucid philosophy, called 'veiled realism,' criticizes Kant's doctrine of synthetic a priori knowledge but shares the thesis that scientific knowledge provides empirical regularities while pointing to an underlying 'noumenal' reality whose structure is not revealed."—Abner Shimony, Professor Emeritus of Philosophy and Physics, Boston University"With exceptional scientific, historical, and philosophical insights, d'Espagnat examines the implications of recent developments in quantum physics for philosophy and the implications of philosophical reflections for the understanding of fundamental physics. D'Espagnat's book not only challenges ingrained ways of thinking; it is indeed a visionary and critical reorientation for both physics and philosophy."—Tian Yu Cao, Boston University"D'Espagnat has performed an intellectual feat by distilling the essential conceptual puzzles of quantum mechanics into a few core principles without relying on any mathematical formalism, and in a very readable style at that. At the same time, this book is not some trendy everyman's guide to the exotic features of quantum physics, with some philosophical commentary—but a work of mature scholarship."—Jeffrey Bub, University of Maryland, author of Interpreting the Quantum World"Here, d'Espagnat discusses virtually all the central philosophical issues related to quantum mechanics and its interpretation. The book is nontechnical, presupposing no previous knowledge of science or philosophy. It is a pleasure to read."—Andrew Z. Wayne, University of Guelph, coeditor of Ontological Aspects of Quantum Field Theory"This book takes the theme of d'Espagnat's influential Veiled Reality and develops it into a 'world view,' as he calls it. This extensive treatment is rich in detailed arguments, deft rebuttal of rival viewpoints, and historical perspectives."—Arthur G. Zajonc, Amherst College, coauthor of The Quantum Challenge
Bernard d'Espagnat is an accomplished theoretical physicist and philosopher, whose two disciplines are interrelated in the present book. He conclusively argues that features of quantum mechanics—particularly the Uncertainty Principle, the nonlocality exhibited by entangled systems, and the measurement problem—revolutionize epistemology and metaphysics. His novel and lucid philosophy, called 'veiled realism,' criticizes Kant's doctrine of synthetic a priori knowledge but shares the thesis that scientific knowledge provides empirical regularities while pointing to an underlying 'noumenal' reality whose structure is not revealed.
— Abner Shimony, Professor Emeritus of Philosophy and Physics, Boston University
This book is a monument to d'Espagnat's excellent work and style; it is surely the most complete book to have been written on this subject and one likely to last a long time, at least until we come to fully understand the remaining mysteries in the field.
— Roland Omnes, Professor Emeritus of Theoretical Physics, Universite de Paris-Sud
This book takes the theme of d'Espagnat's influential Veiled Reality and develops it into a 'world view,' as he calls it. This extensive treatment is rich in detailed arguments, deft rebuttal of rival viewpoints, and historical perspectives.
— Arthur G. Zajonc, Amherst College, coauthor of "The Quantum Challenge"
With exceptional scientific, historical, and philosophical insights, d'Espagnat examines the implications of recent developments in quantum physics for philosophy and the implications of philosophical reflections for the understanding of fundamental physics. D'Espagnat's book not only challenges ingrained ways of thinking; it is indeed a visionary and critical reorientation for both physics and philosophy.
— Tian Yu Cao, Boston University