Quantum Theory , livre ebook

Quantum
Theory
a philosopher’s overview
salvator cannavoQuantum TheoryQuantum Theory
A Philosopher’s Overview
SALVATOR CANNAVOPublished by State University of New York Press, Albany
© 2009 State University of New York
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Library of Congress Cataloging-in-Publication Data
Cannavo, S. (Salvator)
Quantum theory : a philosopher’s overview / Salvator Cannavo.
p. cm.
Includes bibliographical references and index.
ISBN 978-0-7914-9347-2 (hardcover : alk. paper)
1. Quantum theory—Philosophy. I. Title.
QC174.13.C36 2009
530.12—dc22 2008027670
10 9 8 7 6 5 4 3 2 1Contents
Preface vii
1. The Quantum and Classical Theories: A Crucial Difference of
Theory-Type 1
Quantum Theory 1Classical y 2
The “Unfi nished” Quantum Theory 3
2. Quantum Puzzles: A Clash with the Traditional Realism of
Natural Science 7
The Core Formalism 7
The Hypostatization of the Core Formalism 8
The Nondeterministic Part of the Quantum Formalism 9
Wave-Particle Duality in Quantum Experiments 9
Superposition 14
The Measurement Problem 15
The Projection Postulate: Wave Collapse 17
3. More Quantum Puzzles 23
Quantum Uncertainty 23
Virtual Pair Production 29
Phase Entanglement 30
Quantum-Theoretic Description and Completeness 31
Bell’s Inequality: The Unyielding Challenge to
Traditional Scientifi c Realism 34
4. Interpretation 39
The Problem of Interpretation: Old and Persistent 39
Objective Realism in Physical Science 39
Hidden Variable Interpretations: Highly Problematic 42
Copenhagenism: No Less Problematic 51vi Contents
5. Fresh Starts 57
The Many Worlds Interpretation: New and Old Problems 57
The Many Minds Interpretation: More Problems 62
Decoherence Theory: Somewhat Promising 69
GRW Theory 75Positivism 77
Interpretation in a Fuller Sense: Ontic Interpretation 78
6. Explanatory and Algorithmic Nomologicals: Of Which Kind is
Quantum Theory? 81
Nomological Types 81Scientifi c Explanation 83
Causation and Explanation 84
Quantum Theory; Born Algorithmic 85
Settling for Prediction 87
Dirac Transformation Theory 90
Symmetry in Scientifi c Theorizing 91
Abstract Symmetrizing 95
7. A Modest Proposal 97
Interpretation: A Failed Program 97
Away from Interpretation 100
Hidden Variables Are OK 101
No End to Science 102
8. Quantumization: The Quantum Supplementation of
Explanatory Theory 105
The Quantum-Theoretic Context 105
Quantum Electrodynamics 106
Quantum Field Theory 107
String Theory 109
9. Beyond Quantumization 119
A Deeper Incorporation 119
Conclusion 122
Notes 131
Bibliography 161
Index 165Preface
My interest in the foundations and philosophy of quantum theory
was fi rst sparked by J. M. Jauch who taught our graduate course in
quantum mechanics at Princeton University. But this was only the
beginning. The seminars and teas that were occasionally held in
Fine Hall and which we graduate students were privileged to attend
were the ultimate in stimulation and fascination. The participants
were Princeton faculty and members of the Institute for Advanced
Studies. And it was an unforgettable experience to see some of the
very architects of quantum theory express themselves impromptu on
how to understand or “interpret” it. Most remarkably the issues that
arose then are the issues of interpretation that persist to this very
day. In essence, therefore, the conceptualization of this book began
at that time.
The actual writing, however, jumpstarted with my own lectures
on quantum theory at the City University of New York. My thoughts
in this area evolved further with papers in the philosophy of science
that I read to the Teilhard de Chardin Conference at Brooklyn College
of CCNY, to the Royal Institute of Philosophy at the University of
Southern California, to the Long Island Philosophical Society, and to
the Academy for the Humanities and the Sciences at the Graduate
Center of the City University of New York. This last lecture was a lead
paper on “The Reality Problem in Quantum Mechanics,” and it was this
reading followed by the long and searching philosophical discussion
that followed that helped shape the main themes in this book.
Among the features that any scientifi c theory about the physical
world is expected to have, two are basic, though not both required.
First, the theory must make prediction possible. That is, by means of
its mathematical formalism and, on the basis of the initial state of a
physical system at some given time, the theory must enable one to
compute the state of that system at some future time. Secondly, but
not required, a theory may also be expected to provide for explanation.
viiviii Preface
That is, it may be expected to enable one to say, either in causal terms
or in terms of some sort of unifi cation, how the change from one
state to another comes about. While all physical theories must predict
successfully (this goes into granting them confi rmation and eventual
acceptance), not all can (nor must they) explain what they predict.
In this general regard, one need hardly note that the notion of
“explaining” ranges over a variety of senses, such as that of subsuming
under more general principles, explicating, justifying, and more. This,
however, need not delay us. Explaining, either in causal terms or in
terms of some sort of unifi cation is one of these senses and the one
concerning us here.
In order for a physical theory to explain. it must, as an addition
to its formalism, make the existential or, as we might say, “ontological”
claim that there exist physical entities to which some terms of the
theory make general reference. The entities must be either capable
of interacting dynamically over space and time (e.g., masses, particles,
forces, charges, fi elds) or they must be relatable in other essential
respects. Moreover, in order that the resulting explanations do what
they’re supposed to do—namely, enlighten our grasp or understanding
of the “how and why” of things—the posited existential subject matter
must itself be coherent and therefore intelligible. This means it must,
at least in some respects, be observer independent or objective,
existentially stable, uniquely locatable in physical space-time, and
preferably susceptible only to proximate or local infl uences rather than
to unmediated, instantaneous, and therefore, mysterious ones. To
this, one might cautiously add that what an explanatory theory tells us
about the physical world must, to some suffi cient extent, be intuitable.
Indeed, what we are describing here is what one might more succinctly
call a “reality” model, and the coordination of such a model with the
formalism of a theory is what we are calling the ontology or interpretation
of the theory.
After one hundred years of astoundingly successful prediction,
quantum theory has yet to fi nd itself such an interpretation in this sense
and on which there is general agreement. Paradoxically, therefore, y—perhaps the most elegantly structured mathematical
edifi ce in the history of science—predicts but does not explain what it
so accurately predicts.
Some might want to say at this point that the idea of framing a
physical theory in such a way as to invest it with the sort of content
we are describing and therefore with explanatory power is no more
than the arbitrary imposition of classical notions and content on
an essentially nonclassical theory. We shall argue, however, that any Preface ix
such concern would be a misguided one. The power of a theory to
explain is not merely a feature limited to classical physics operating
in classical contexts but a feature for delivering something essential to
an understanding of the physical world—something epistemically basic
and quite apart from any distinction between classical and nonclassical
modes of description. In fact there are, as will be discussed in the main
text, quantum-type theories, for example, quantum electrodynamics,
quantum fi eld theory, and string theory that—whatever their present
stage of development—are explanatory in a sense that is philosophically
satisfying, though requiring a degree of liberalization or “tolerance” in
the underlying realism.
Though falling short of suffi cient physical content for explanation,
quantum theory must nevertheless be tied to observational subject
matter (scintillations, clicks, photographic patterns, etc.). If it weren’t,
it would be not physics but only a mathematical system for relating
abstract symbols. This subject matter, however, does not, by itself,
comprise a coherent physical model or interpretation. True,
quantumtheoretic terms, are customarily understood to refer to a variety of
entities and their attributes (particles, spin, momentum, location,
energy, etc.). This “quantum subject matter,” however, immediately
tests our understanding with its strangeness. We fi nd ourselves dealing
with such physical oddities as entities that have no unique locations,
particles that have spins but no dimensions, unsettling discontinuities
and much, much more to perplex us. Indeed, the quantum formalism,
which, in itself, seriously blocks physical interpretations, is framed in a
space of variable dimensions whose abstract constructions cannot be
simply coordinated with much more than raw observational results
and the parameters of given experiments. Any attempt, for example,
to assign concrete ex