Paul Teller

This article explains why Bohr does not need to discuss the projection postulate or the "problem of measurement". Beginning with a thumbnail sketch of Bohr 's general views, it is argued that Bohr interprets the state function as giving a statistical summary of experimental outcomes. Against the objection that Bohr was too much a microrealist to endorse such an instrumentalist statistical interpretation it is suggested that he rejected the issue of microrealism as not well formed. It is shown that on his statistical interpretation Bohr does not need the projection postulate or face the usual problem of measurement

Huggett and Weingard's critical review provides an opportunity to continue the interpretive examination of quantum field theory in terms of some specific issues as well as comparison of alternative approaches to the subject. This note recasts their example of inequivalent Fock spaces in an effort to further clarify what it illustrates. Questions are addressed about the role of analogy in developing quantum field theory and about the conflict between formal vs. concrete methods in both physics and its interpretation, continuing the well-known historical debate between Pierre Duhem and Clark Maxwell. Huggett and Weingard's examination very usefully occasions clarification on some points of exposition which, it is hoped, will make An Interpretive Introduction to Quantum Field Theory a more useful resource for understanding this subject

In response to Cushing it is urged that the vicissitudes of quantum field theory do not press towards a nonrealist attitude towards the theory as strongly as he suggests. A variety of issues which Redhead raises are taken up, including photon localizability, the wave-particle distinction in the classical limit, and the interpretation of quantum statistics, vacuum fluctuations, virtual particles, and creation and annihilation operators. It is urged that quantum field theory harbors an unacknowledged inconsistency connected with the fact that the zero point energy has observable consequences, while to avoid infinities it must be "thrown away". Finally, Redhead's conception of ephemerals is pressed and the paper concludes with the suggestion that the particle concept largely drops out of quantum field theory.

Many in philosophy understand truth in terms of precise semantic values, true propositions. Following Braun and Sider, I say that in this sense almost nothing we say is, literally, true. I take the stand that this account of truth nonetheless constitutes a vitally useful idealization in understanding many features of the structure of language. The Fregean problem discussed by Braun and Sider concerns issues about application of language to the world. In understanding these issues I propose an alternative modeling tool summarized in the idea that inaccuracy of statements can be accommodated by their imprecision. This yields a pragmatist account of truth, but one not subject to the usual counterexamples. The account can also be viewed as an elaborated error theory. The paper addresses some prima facie objections and concludes with implications for how we address certain problems in philosophy.

This paper digests technical commonplaces of quantum field theory to present an informal interpretation of the theory by emphasizing its connections with the harmonic oscillator. The resulting "harmonic oscillator interpretation" enables newcomers to the subject to get some intuitive feel for the theory. The interpretation clarifies how the theory relates to observation and to quantum mechanical problems connected with observation. Finally the interpretation moves some way towards helping us see what the theory comes to physically. The paper also argues that, in important respects, interpretive problems of quantum field theory are problems we know well from conventional quantum mechanics. An important exception concerns extending the puzzles surrounding the superposition of properties in conventional quantum mechanics to an exactly parallel notion of superposition of particles. Conventional quantum mechanics seems incompatible with a classical notion of property on which all quantities always have definite values. Quantum field theory presents an exactly analogous problem with saying that the number of "particles" is always definite

This paper challenges “traditional measurement-accuracy realism”, according to which there are in nature quantities of which concrete systems have definite values. An accurate measurement outcome is one that is close to the value for the quantity measured. For a measurement of the temperature of some water to be accurate in this sense requires that there be this temperature. But there isn’t. Not because there are no quantities “out there in nature” but because the term ‘the temperature of this water’ fails to refer owing to idealization and failure of specificity in picking out concrete cases. The problems can be seen as an artifact of vagueness, and so doing facilitates applying Eran Tal’s robustness account of measurement accuracy to suggest an attractive way of understanding vagueness in terms of the function of idealization, a way that sidesteps the problems of higher order vagueness and that shows how idealization provides a natural generalization of what it is to be vague.

This volume does not succeed in encapsulating the legacy of Logical Positivism. Much more than 291 pages would not suffice for the things of value the movement has left us. Logical Positivism has clarified old doctrines and provided us with new ones. It has encouraged new standards of care, clarity, and philosophical honesty. These in turn have fostered what I believe to be the movement's greatest legacy: a clear understanding of the difficulties with the prima facie attractive doctrines associated with the movement. This is a propitious basis on which to extend our inquiries. What the volume does provide is a fair sample of the legacy's contemporary effect on the philosophy of science. Besides the three historical sketches, the papers review known difficulties with Logical Positivist views and present new doctrines inspired by foregoing critical examination. None of the criticisms is new, and for the most part they have been more clearly and thoroughly presented elsewhere. The papers which attempt to work out new ideas are below the standard we all would like to see in (and contribute to) the literature, but up to the standard of what we usually find. Consequently, the volume is best used as a source for particular authors' views on particular subjects.

If we take the state function of quantum mechanics to describe belief states, arguments by Stairs and Friedman-Putnam show that the projection postulate may be justified as a kind of minimal change. But if the state function takes on a physical interpretation, it provides no more than what I call a fortuitous approximation of physical measurement processes, that is, an unsystematic form of approximation which should not be taken to correspond to some one univocal "measurement process" in nature. This fact suggests that the projection postulate does not provide a proper locus for interpretive investigation. Readers will also find section 3's analysis of fortuitous approximations of independent interest and presented without the perils of quantum mechanics

Quantum mechanics is a subject that has captured the imagination of a surprisingly broad range of thinkers, including many philosophers of science. Quantum field theory, however, is a subject that has been discussed mostly by physicists. This is the first book to present quantum field theory in a manner that makes it accessible to philosophers. Because it presents a lucid view of the theory and debates that surround the theory, An Interpretive Introduction to Quantum Field Theory will interest students of physics as well as students of philosophy. Paul Teller presents the basic ideas of quantum field theory in a way that is understandable to readers who are familiar with non-relativistic quantum mechanics. He provides information about the physics of the theory without calculational detail, and he enlightens readers on how to think about the theory physically. Along the way, he dismantles some popular myths and clarifies the novel ways in which quantum field theory is both a theory about fields and about particles. His goal is to raise questions about the philosophical implications of the theory and to offer some tentative interpretive views of his own. This provocative and thoughtful book challenges philosophers to extend their thinking beyond the realm of quantum mechanics and it challenges physicists to consider the philosophical issues that their explorations have encouraged.

In practice theoretical terms are open-ended in not being attached to anything completely specific. This raises a problem for scientific realism: If there is no one completely specific kind of thing that might be in the extension of “atom”, what is it to claim that atoms exist? A realist’s solution is to say that in theoretical contexts of mature atom-theories there are things that play the role of atoms as characterized in that theory-context. The paper closes with a laundry list of problems that this more careful statement of scientific realism still faces.