Quantumfieldtheory (QFT) combines quantum mechanics with Einstein's special theory of relativity and underlies elementary particle physics. This book presents a philosophical analysis of QFT. It is the first treatise in which the philosophies of space-time, quantum phenomena, and particle interactions are encompassed in a unified framework. Describing the physics in nontechnical terms, and schematically illustrating complex ideas, the book also serves as an introduction to fundamental physical theories. The philosophical interpretation both upholds (...) the reality of the quantum world and acknowledges the irreducible cognitive elements in its representation. The interpretation is based on an analysis of our ways of thinking as the are embedded in the logical structure of QFT. The author argues that philosophical categories are significant only if they play active and essential roles in our knowledge and hence constitute part of the theories in actual use. Thus she regards physical theories as primary, extracts their categorical structure, and uses it to rethink key philosophical questions. Among the questions this book tries to answer are: What are the quantum properties independent of measurements? How do we refer to individual things in a continuous field? How do theories relate to objects? What are the general conditions of the world and of our ways of thinking that make possible our knowledge of the microscopic realm, which is so intangible and counterintuitive? As a penetrating analysis of vital themes in contemporary science, the book will engage the interest of students and professionals in physics and philosophy alike. (shrink)
Quantumfieldtheory, one of the most rapidly developing areas of contemporary physics, is full of problems of great theoretical and philosophical interest. This collection of essays is the first systematic exploration of the nature and implications of quantumfieldtheory. The contributors discuss quantumfieldtheory from a wide variety of standpoints, exploring in detail its mathematical structure and metaphysical and methodological implications.
Methods developed in a previous paper are employed to define an exact correspondence between the states of a deterministic cellular automaton in 1+1 dimensions and those of a bosonic quantumfieldtheory. The result may be used to argue that quantumfield theories may be much closer related to deterministic automata than what is usually thought possible.
I argue that algebraic quantumfieldtheory (AQFT) permits an undisturbed view of the right ontology for fundamental physics, whereas standard (or Lagrangian) QFT offers different mutually incompatible ontologies.My claim does not depend on the mathematical inconsistency of standard QFT but on the fact that AQFT has the same concerns as ontology, namely categorical parsimony and a clearly structured hierarchy of entities.
Quantumfieldtheory (QFT) presents a genuine example of the underdetermination of theory by empirical evidence. There are variants of QFT—for example, the standard textbook formulation and the rigorous axiomatic formulation—that are empirically indistinguishable yet support different interpretations. This case is of particular interest to philosophers of physics because, before the philosophical work of interpreting QFT can proceed, the question of which variant should be subject to interpretation must be settled. New arguments are offered for basing (...) the interpretation of QFT on a rigorous axiomatic variant of the theory. The pivotal considerations are the roles that consistency and idealization play in this case. *Received June 2009; revised August 2009. †To contact the author, please write to: Department of Philosophy, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada; e‐mail: dlfraser@uwaterloo.ca. (shrink)
Although the philosophical literature on the foundations of quantumfieldtheory recognizes the importance of Haag’s theorem, it does not provide a clear discussion of the meaning of this theorem. The goal of this paper is to make up for this deficit. In particular, it aims to set out the implications of Haag’s theorem for scattering theory, the interaction picture, the use of non-Fock representations in describing interacting fields, and the choice among the plethora of the (...) unitarily inequivalent representations of the canonical commutation relations for free and interacting fields. (shrink)
The availability of unitarily inequivalent representations of the canonical commutation relations constituting a quantization of a classical fieldtheory raises questions about how to formulate and pursue quantumfieldtheory. In a minimally technical way, I explain how these questions arise and how advocates of the Hilbert space and of the algebraic approaches to quantumtheory might answer them. Where these answers differ, I sketch considerations for and against each approach, as well as (...) considerations which might temper their apparent rivalry. (shrink)
I examine some problems standing in the way of a successful 'field interpretation' of quantumfieldtheory. The most popular extant proposal depends on the Hilbert space of 'wavefunctionals.' But since wavefunctional space is unitarily equivalent to many-particle Fock space, two of the most powerful arguments against particle interpretations also undermine this form of field interpretation.
Algebraic quantumfieldtheory provides a general, mathematically precise description of the structure of quantumfield theories, and then draws out consequences of this structure by means of various mathematical tools -- the theory of operator algebras, category theory, etc.. Given the rigor and generality of AQFT, it is a particularly apt tool for studying the foundations of QFT. This paper is a survey of AQFT, with an orientation towards foundational topics. In addition (...) to covering the basics of the theory, we discuss issues related to nonlocality, the particle concept, the field concept, and inequivalent representations. We also provide a detailed account of the analysis of superselection rules by Doplicher, Haag, and Roberts (DHR); and we give an alternative proof of Doplicher and Robert's reconstruction of fields and gauge group from the category of physical representations of the observable algebra. The latter is based on unpublished ideas due to J. E. Roberts and the abstract duality theorem for symmetric tensor *-categories, a self-contained proof of which is given in the appendix. (shrink)
Philosophical interpretations of theories generally presuppose that a theory can be presented as a consistent mathematical formulation that is interpreted through models. Algebraic quantumfieldtheory (AQFT) can fit this interpretative model. However, standard Lagrangian quantumfieldtheory (LQFT), as well as quantum electrodynamics and nuclear physics, resists recasting along such formal lines. The difference has a distinct bearing on ontological issues. AQFT does not treat particle interactions or the standard model. This (...) paper develops a framework and methodology for interpreting such informal theories as LQFT and the standard model. We begin by summarizing two minimal epistemological interpretation of non-relativistic quantum mechanics (NRQM): Bohrian semantics, which focuses on communicables; and quantum information theory, which focuses on the algebra of local observables. Schwinger's development of quantumfieldtheory supplies a unique path from NRQM to QFT, where each step is conceptually anchored in local measurements. LQFT and the standard model rely on postulates that go beyond the limits set by AQFT and Schwinger's anabatic methodology. The particle ontology of the standard model is clarified by regarding the standard model as an informal modular theory with a limited range of validity. (shrink)
I analyse the conceptual and mathematical foundations of Lagrangian quantumfieldtheory (QFT) (that is, the ‘naive’ (QFT) used in mainstream physics, as opposed to algebraic quantumfieldtheory). The objective is to see whether Lagrangian (QFT) has a sufficiently firm conceptual and mathematical basis to be a legitimate object of foundational study, or whether it is too ill-defined. The analysis covers renormalisation and infinities, inequivalent representations, and the concept of localised states; the conclusion (...) is that Lagrangian QFT (at least as described here) is a perfectly respectable physical theory, albeit somewhat different in certain respects from most of those studied in foundational work. (shrink)
An epistemological interpretation of quantum mechanics hinges on the claim that the distinctive features of quantum mechanics can be derived from some distinctive features of an observational basis. Old and new variations of this theme are listed. The program has a limited success in non-relativistic quantum mechanics. The crucial issue is how far it can be extended to quantumfieldtheory without introducing significant ontological postulates. A C*-formulation covers algebraic quantumfield (...) class='Hi'>theory, but not the standard model. Julian Schwinger’s anabatic methodology extended a strict measurement-based formulation of quantum mechanics through fieldtheory. His extension also excluded the quark hypothesis and the standard model. Quarks and local gauge invariance are postulates that go beyond the limits of an epistemological interpretation of quantum mechanics. The ontological significance ascribed to these advances depends on the role accorded ontology. (shrink)
Much attention has been directed to the philosophical implications of quantumfieldtheory (QFT) in recent years; this paper attempts a survey in low-technical terms. First the relations of QFT to other kinds of theory, classical and quantum, particle and field, are discussed. Then various formulations of QFT are introduced, along with related interpretations. Finally a review is made of some of the most interesting foundational problems.
The metaphysical commitments of quantumfieldtheory are examined. A thesis of underdetermination as between field and particle approaches to the "elementary particles" is argued for but only if a disputed notion of transcendental individuality is admitted. The superiority of the field approach is further emphasized in the context of heuristics.
I discuss issues concerning the philosophical foundations andimplications of quantumfieldtheory, renormalization inparticular. A new understanding of the correspondence principle,an unexpected role of perturbation theory and, most of all, acriterion to reduce the set of consistent theories frominfinitely many to finitely many, are the key concepts of atheoretical set-up that appears to overcome in a natural wayvarious consistency problems of quantum mechanics and offerseveral hints for further developments.
The recent work of Paul Teller and Sunny Auyang in the philosophy of QuantumFieldTheory (QFT) has stimulated the search for the fundamental entities in this theory. In QFT, the classical notion of a particle collapses. The theory does not only exclude classical, i.e., spatiotemporally identifiable particles, but it makes particles of the same type conceptually indistinguishable. Teller and Auyang have proposed competing ersatz-ontologies to account for the 'loss of particles': field quanta vs. (...)field events. Both ontologies, however, suffer from serious defects. While quanta lack numerical identity, spatiotemporal localizability, and independence of basis-representations, events--if understood as concrete measurement events--are related to the theory only statistically. I propose an alternative solution: The entities of QFT are events of the type 'Quantum system, S, is in quantum state, Ψ '. These are not point events, but Davidsonian events, i.e., they can be identified by their location within the causal net of the world. (shrink)
In this paper I put forward a suggestion for identifying causality in micro-systems with the specific quantumfield theoretic interactions that occur in such systems. I first argue — along the lines of general transference theories — that such a physicalistic account is essential to an understanding of causation; I then proceed to sketch the concept of interaction as it occurs in quantumfieldtheory and I do so from both a formal and an informal (...) point of view. Finally, I present reasons for thinking that only a quantumfield theoretic account can do the job — in particular I rely on a theorem by D. Currie and to the effect that interaction cannot be described in (a Hamiltonian formulation of) Classical Mechanics. Throughout the paper I attempt to suggest that the widespread scepticism about the ability of quantumtheory to support a theory of causality is mistaken and rests on several misunderstandings. (shrink)
Entanglement has long been the subject of discussion by philosophers of quantumtheory, and has recently come to play an essential role for physicists in their development of quantum information theory. In this paper we show how the formalism of algebraic quantumfieldtheory (AQFT) provides a rigorous framework within which to analyse entanglement in the context of a fully relativistic formulation of quantumtheory. What emerges from the analysis are new (...) practical and theoretical limitations on an experimenter's ability to perform operations on a field in one spacetime region that can disentangle its state from the state of the field in other spacelike-separated regions. These limitations show just how deeply entrenched entanglement is in relativistic quantumfieldtheory, and yield a fresh perspective on the ways in which the theory differs conceptually from both standard non-relativistic quantumtheory and classical relativistic fieldtheory. (shrink)
In this paper we critically review the various attempts that have been made to understand quantumfieldtheory. We focus on Teller's (1990) harmonic oscillator interpretation, and Bohm et al.'s (1987) causal interpretation. The former unabashedly aims to be a purely heuristic account, but we show that it is only interestingly applicable to the free bosonic field. Along the way we suggest alternative models. Bohm's interpretation provides an ontology for the theory--a classical field, with (...) a quantum equation of motion. This too has problems; it is not Lorentz invariant. (shrink)
The status of the vacuum in relativistic quantumfieldtheory is examined. A sharp distinction arises between the global vacuum and the local vacuum. The concept of local number density is critically assessed. The global vacuum state implies fluctuations for all local observables. Correlations between such fluctuations in space-like separated regions of space-time are discussed and the existence of correlations which are maximal in a certain sense is remarked on, independently of how far apart those regions may (...) be. The analogy with the mirror-image correlations in the singlet state of two spin-1/2 particles is explained. The connection between these maximal correlations and the well-known violation of the Bell inequality in the vacuum state is discussed, together with the way in which the existence of these correlations might be exploited in developing a vacuum version of the Einstein-Podolsky-Rosen argument. The recent relativistic formulation of the Einstein-Podolsky-Rosen argument by Ghirardi and Grassi is critically assessed with particular reference to the vacuum case. (shrink)
This paper digests technical commonplaces of quantumfieldtheory 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 quantumfieldtheory 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. Quantumfieldtheory presents an exactly analogous problem with saying that the number of "particles" is always definite. (shrink)
The physics and metaphysics of quantumfieldtheory Content Type Journal Article Category Book Review Pages 1-3 DOI 10.1007/s11016-011-9609-2 Authors Federico Laudisa, Department of Human Sciences “R. Massa”, University of Milan-Bicocca, Piazza Ateneo Nuovo 1, 20126 Milan, Italy Journal Metascience Online ISSN 1467-9981 Print ISSN 0815-0796.
This dissertation reconsiders some traditional issues in the foundations of quantum mechanics in the context of relativistic quantumfieldtheory (RQFT); and it considers some novel foundational issues that arise first in the context of RQFT. The first part of the dissertation considers quantum nonlocality in RQFT. Here I show that the generic state of RQFT displays Bell correlations relative to measurements performed in any pair of spacelike separated regions, no matter how distant. I also (...) show that local systems in RQFT are "open" to influence from their environment, in the sense that it is generally impossible to perform local operations that would remove the entanglement between a local system and any other spacelike separated system. The second part of the dissertation argues that RQFT does not support a particle ontology -- at least if particles are understood to be localizable objects. In particular, while RQFT permits us to describe situations in which a determinate number of particles are present, it does not permit us to speak of the location of any individual particle, nor of the number of particles in any particular region of space. Nonetheless, the absence of localizable particles in RQFT does not threaten the integrity of our commonsense concept of a localized object. Indeed, RQFT itself predicts that descriptions in terms of localized objects can be quite accurate on the macroscopic level. The third part of the dissertation examines the so-called observer-dependence of the particle concept in RQFT -- that is, whether there are any particles present must be relativized to an observer's state of motion. Now, it is not uncommon for modern physical theories to subsume observer-dependent descriptions under a more general observer-independent description of some underlying state of affairs. However, I show that the conflicting accounts concerning the particle content of the field cannot be reconciled in this way. In fact, I argue that these conflicting accounts should be thought of as "complementary" in the same sense that position and momentum descriptions are complementary in elementary quantum mechanics. (shrink)
Philosophical reflection on quantumfieldtheory has tended to focus on how it revises our conception of what a particle is. However, there has been relatively little discussion of the threat to the ‘reality’ of particles posed by the possibility of inequivalent quantizations of a classical fieldtheory, i.e. inequivalent representations of the algebra of observables of the field in terms of operators on a Hilbert space. The threat is that each representation embodies its (...) own distinctive conception of what a particle is, and how a ‘particle’ will respond to a suitably operated detector. Our main goal is to clarify the subtle relationship between inequivalent representations of a fieldtheory and their associated particle concepts. We also have a particular interest in the Minkowski versus Rindler quantizations of a free Boson field, because they respectively entail two radically different descriptions of the particle content of the field in the very same region of spacetime. We shall defend the idea that these representations provide complementary descriptions of the same state of the field against the claim that they embody completely incommensurable theories of the field. (shrink)
This paper explores various functions of idealizations in quantumfieldtheory. To this end it is important to first distinguish between different kinds of theories and models of or inspired by quantumfieldtheory. Idealizations have pragmatic and cognitive functions. Analyzing a case-study from hadron physics, I demonstrate the virtues of studying highly idealized models for exploring the features of theories with an extremely rich structure such as quantumfieldtheory and (...) for gaining some understanding of the physical processes in the system under consideration. (shrink)
Many of the "counterintuitive" features of relativistic quantumfieldtheory have their formal root in the Reeh-Schlieder theorem, which in particular entails that local operations applied to the vacuum state can produce any state of the entire field. It is of great interest then that I.E. Segal and, more recently, G. Fleming (in a paper entitled "Reeh-Schlieder meets Newton-Wigner") have proposed an alternative "Newton-Wigner" localization scheme that avoids the Reeh-Schlieder theorem. In this paper, I reconstruct the (...) Newton-Wigner localization scheme and clarify the limited extent to which it avoids the counterintuitive consequences of the Reeh-Schlieder theorem. I also argue that there is no coherent interpretation of the Newton-Wigner localization scheme that renders it free from act-outcome correlations at spacelike separation. (shrink)
Huggett and Weingard's critical review provides an opportunity to continue the interpretive examination of quantumfieldtheory 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 quantumfieldtheory 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 QuantumFieldTheory a more useful resource for understanding this subject. (shrink)
If the general arguments concerning the involvement of variation and selection in explanations of “fit” are valid, then variation and selection explanations should be appropriate, or at least potentially appropriate, outside the paradigm historistic domains of biology and knowledge. In this discussion, I wish to indicate some potential roles for variation and selection in foundational physics – specifically in quantumfieldtheory. I will not be attempting any full coherent ontology for quantumfieldtheory (...) – none currently exists, and none is likely for at least the short term future. Instead, I wish to engage in some partially speculative interpretations of some interesting results in this area with the aim of demonstrating that variation and selection notions might play a role even here. If variation and selection can survive in even as inhospitable and non-paradigmatic a terrain as foundational physics, then it can survive anywhere. (shrink)
Based partly on proving that algebraic relativistic quantumfieldtheory (ARQFT) is a stochastic Einstein local (SEL) theory in the sense of SEL which was introduced by Hellman (1982b) and which is adapted in this paper to ARQFT, the recently proved maximal and typical violation of Bell's inequalities in ARQFT (Summers and Werner 1987a-c) is interpreted in this paper as showing that Bell's inequalities are, in a sense, irrelevant for the problem of Einstein local stochastic hidden (...) variables, especially if this problem is raised in connection with ARQFT. This leads to the question of how to formulate the problem of local hidden variables in ARQFT. By giving a precise definition of hidden-variable theory within the operator algebraic framework of quantum mechanics, it will be argued that the aim of hidden-variable investigations is to determine those classes of quantum theories whose elements represent a statistical content that cannot be reduced in a given way. In some particular way to be stated, a proposition will be stated which distinguishes quantumfield theories whose statistical content cannot be reduced without violating some relativistic locality principle. (shrink)
This paper is intended to be an introductory survey of subjects related to the problems dealt with in the three other papers in this symposium on quantumfieldtheory. A brief history of quantum electrodynamics is given and some of the objections to it are stated. A brief history of quantumfield theories from the 1970's to the present is then provided. Finally, a sketch of some of the philosophical work that has been done (...) on quantumfield theories is presented. The object of the paper is to explain why philosophers of physics have tended to neglect quantumfield theories and to point out several of the conceptual issues raised by quantumfield theories that call out for further analysis. (shrink)
A resolution of the quantum measurement problem would require one to explain how it is that we end up with determinate records at the end of our measurements. Metaphysical commitments typically do real work in such an explanation. Indeed, one should not be satisfied with one's metaphysical commitments unless one can provide some account of determinate measurement records. I will explain some of the problems in getting determinate records in relativistic quantumfieldtheory and pay particular (...) attention to the relationship between the measurement problem and a generalized version of Malament's theorem. (shrink)
What does quantumfieldtheory (QFT) tell us about the furniture of the world? Seventeen essays gathered in the four parts of Ontological Aspects of QuantumFieldTheory address this question from different angles and with different objectives. Together, they form a wide-ranging and up-to-date volume that makes a valuable contribution to an ongoing discussion, which, due to the comprehensive introduction by the editors, can be of interest to experts and novices alike.
Alfred North Whitehead in his book Process and Reality describes the history of the universe in terms of a process of ‘creative advance into novelty.’ This advance is produced by a collection of happenings called ‘actual occasions’, or ‘actual entities’. Each actual entity has an associated actual world, and it arises from its own peculiar actual world. (PR 284). Two occasions are termed ‘contemporary’ if neither lies in the actual world of the other. A key issue is whether the words (...) in Process and Reality commit Whitehead to the relativity-theory idea that, at least in our present epoch, the creative advance into novelty is not serially ordered, or whether, alternatively, the logical developments in Part IV entail, at a deep metaphysical level, that the facts specified by two contemporary occasions become fixed and settled in some definite order. Irresolution on this basic question renders Whitehead’s theory obscure and plagued with controversy. I argue, in opposition to another paper in this issue, that Whitehead endorses the relativistic viewpoint, and consistently adheres to it. This makes Whitehead’s theory compatible with relativistic quantumtheory. Combining Whitehead’s relativistic process theory with relativistic quantumfieldtheory is therefore possible, and it holds the promise of producing a rationally coherent understanding far richer than what is provided by either theory alone of the relationships between the physically described aspects of the universe and human knowledge and intentions. (shrink)
In a pair of articles (1996, 1997) and in his recent book (1998), Miklos Redei has taken enormous strides toward characterizing the conditions under which relativistic quantumfieldtheory is a safe setting for the deployment of causal talk. Here, we challenge the adequacy of the accounts of causal dependence and screening off on which rests the relevance of Redei's theorems to the question of causal good behavior in the theory.
This paper shows how different axiomatic and constructive approaches within quantumfieldtheory can be understood in terms of the so-called ,picture theory' of Heinrich Hertz. Each approach will count as a different picture due to the different status of the various concepts (symbols) they are employing, like observables, gauge invariance, confinement or the space-time continuum. An important difference with the original Hertzian approach is the fact that the different approaches in quantumfield (...) class='Hi'>theory have partially overlapping, partially supplementing domains of application. This also marks some of the parallels and differences with contemporary debates on structural realism and model-theoretic approaches in the philosophy of physics. The objection that the talk about different pictures just relies on the fact that quantumfieldtheory is unfinished will be countered. Finally, the Hertzian approach will be briefly elaborated and embedded into its philosophical successor projects of Cassirer and Goodman. German Dieser Aufsatz zeigt, wie verschiedene axiomatische und konstruktive Ansätze in der Quantenfeldtheorie mit Hilfe der sogenannten ,,Bildtheorie“ von Heinrich Hertz verstanden werden können. Aufgrund der unterschiedlichen Stellungen der verschiedenen Konzepte (Symbole), die diese Ansätze benutzen - wie etwa Observable, Eichinvarianz, Confinement oder Raum-Zeit-Kontinuum - wird jeder als ein eigenes Bild zu betrachten sein. Ein wichtiger Unterschied zu Hertz' ursprünglicher Fassung der Bildtheorie sind dabei die unterschiedlichen Anwendungsbereiche der Ansätze in der Quantenfeldtheorie. Diese überschneiden sich zum Teil, zum Teil ergänzen sie einander. Dadurch ergeben sich für die bildtheoretische Interpretation wichtige Parallelen und Unterschiede zu anderen Positionen in der Philosophie der Physik, insbesondere zum Strukturrealismus und zur Modell-Theorie. Neben diesen diskutiere ich den Einwand, dass die Redeweise von verschiedenen Bildern in der Quantenfeldtheorie nur deshalb möglich sei, weil die Theorie noch nicht abgeschlossen ist. Schließlich erweitere ich die Hertzsche Bildtheorie und setze sie dabei in Beziehung zu ihren philosophischen Nachfolgeprojekten bei Cassirer und Goodman. (shrink)
In relativistic quantumfieldtheory the notion of a local operation is regarded as basic: each open space-time region is associated with an algebra of observables representing possible measurements performed within this region. It is much more difficult to accommodate the notions of events taking place in such regions or of localized objects. But how can the notion of a local operation be basic in the theory if this same theory would not be able to (...) represent localized measuring devices and localized events? After briefly reviewing these difficulties we discuss a strategy for eliminating the tension, namely by interpreting quantumtheory in a realist way. To implement this strategy we use the ideas of the modal interpretation of quantum mechanics. We then consider the question of whether the resulting scheme can be made Lorentz invariant. (shrink)
The general context of this paper is the locality problem in quantumtheory. In a recent issue of this journal, Redei (1991) offered a proof of the proposition that algebraic Lorentz-covariant quantumfieldtheory is past stochastic Einstein local. We show that Redei's proof is either spurious or circular, and that it contains two deductive fallacies. Furthermore, we prove that the mentioned theory meets the stronger condition of stochastic Haag locality.
In response to Cushing it is urged that the vicissitudes of quantumfieldtheory 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 quantumfieldtheory 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 quantumfieldtheory. (shrink)
If $\{{\cal A}(V)\}$ is a net of local von Neumann algebras satisfying standard axioms of algebraic relativistic quantumfieldtheory and $V_1$ and $V_2$ are spacelike separated spacetime regions, then the system $({\cal A}(V_1),{\cal A}(V_2),\phi)$ is said to satisfy the Weak Reichenbach's Common Cause Principle iff for every pair of projections $A\in{\cal A}(V_1)$, $B\in{\cal A}(V_2)$ correlated in the normal state $\phi$ there exists a projection $C$ belonging to a von Neumann algebra associated with a spacetime region $V$ (...) contained in the union of the backward light cones of $V_1$ and $V_2$ and disjoint from both $V_1$ and $V_2$, a projection having the properties of a Reichenbachian common cause of the correlation between $A$ and $B$. It is shown that if the net has the local primitive causality property then every local system $({\cal A}(V_1),{\cal A}(V_2),\phi)$ with a locally normal and locally faithful state $\phi$ and open bounded $V_1$ and $V_2$ satisfies the Weak Reichenbach's Common Cause Principle. (shrink)
If the general arguments concerning theinvolvement of variation and selection inexplanations of ``fit'' are valid, then variationand selection explanations should beappropriate, or at least potentiallyappropriate, outside the paradigm historisticdomains of biology and knowledge. In thisdiscussion, I wish to indicate some potentialroles for variation and selection infoundational physics â specifically inquantum fieldtheory. I will not be attemptingany full coherent ontology for quantum fieldtheory â none currently exists, and none islikely for at least the short term future. Instead, (...) I wish to engage in some partiallyspeculative interpretations of some interestingresults in this area with the aim ofdemonstrating that variation and selectionnotions might play a role even here. Ifvariation and selection can survive in even asinhospitable and non-paradigmatic a terrain asfoundational physics, then it can surviveanywhere. (shrink)
Relativistic quantumfield theories (RQFTs) are invariant under the action of the Poincaré group, the symmetry group of Minkowski spacetime. Non-relativistic quantumfield theories (NQFTs) are invariant under the action of the symmetry group of a classical spacetime; i.e., a spacetime that minimally admits absolute spatial and temporal metrics. This essay is concerned with cashing out two implications of this basic difference. First, under a Received View, RQFTs do not admit particle interpretations. I will argue that (...) the concept of particle that informs this view is motivated by nonrelativistic intuitions associated with the structure of classical spacetimes, and hence should be abandoned. Second, the relations between RQFTs and NQFTs also suggest that routes to quantum gravity are more varied than is typically acknowledged. The second half of this essay is concerned with mapping out some of this conceptual space. (shrink)
Nick Huggett and Robert Weingard (1994) have recently proposed a novel approach to interpreting field theories in physics, one which makes central use of the fact that a field generally has an infinite number of degrees of freedom in any finite region of space it occupies. Their characterization, they argue, (i) reproduces our intuitive categorizations of fields in the classical domain and thereby (ii) provides a basis for arguing that the quantumfield is a field. (...) Furthermore, (iii) it accomplishes these tasks better than does a well-known rival approach due to Paul Teller (1990, 1995). This paper contends that all three of these claims are mistaken, and suggests that Huggett and Weingard have not shown how counting degrees of freedom provides any insight into the interpretation or the formal properties of field theories in physics. (shrink)
A fully micro realistic, propensity version of quantumtheory is proposed, according to which fundamental physical entities - neither particles nor fields - have physical characteristics which determine probabilistically how they interact with one another (rather than with measuring instruments). The version of quantum "smearon" theory proposed here does not modify the equations of orthodox quantumtheory: rather, it gives a radically new interpretation to these equations. It is argued that (i) there are strong (...) general reasons for preferring quantum "smearon" theory to orthodox quantumtheory; (ii) the proposed change in physical interpretation leads quantum "smearon" theory to make experimental predictions subtly different from those of orthodox quantumtheory. Some possible crucial experiments are considered. (shrink)
Acclaimed mathematical physicist and natural philosopher Luciano Boi expounds the quantum vacuum, exploring the meaning of nothingness and its relationship with ...
We review the dissipative quantum model of the brain and present recent developments related to the role of entanglement, quantum noise and chaos in the model.
The essays in the first part, Approaches to Ontology, explore different philosophical frameworks in which the ontology of QFT could fruitfully be examined. Despite their differences, they all agree that traditional ontologies, in particular substance-attribute ontology, are unsuitable for QFT. Peter Simons begins by pointing out why substance-attribute ontology, applied set theory, fact ontology, occurrent ontologies, and trope theory are inadequate ontologies for QFT and then puts forward his own suggestion: factored ontology. The main idea of this ontology (...) is to posit basic features (so-called ‘factors’) and to view objects as suitable combinations of some of these factors. He presents an outline of a version of a factored ontology, called PACIS, which he and his collaborators have developed over the last fifteen years and which they have – in their view successfully – applied to different domains in the natural and the social sciences. Given this success, Simons is confident that this framework will also prove fruitful in the case of QFT. However, he does not give any further argument for this claim and does not make an attempt at formulating a concrete factor 1 ontology of QFT. He merely puts forward his framework as a conceptual tool and leaves it to the philosopher of physics to work out an interpretation of QFT in its terms. (shrink)
This essay considers the extent to which a concept of emergence can be associated with Effective Field Theories (EFTs). I suggest that such a concept can be characterized by microphysicalism and novelty underwritten by the elimination of degrees of freedom from a high-energy theory, and argue that this makes emergence in EFTs distinct from other concepts of emergence in physics that have appeared in the recent philosophical literature.
The idea that science aspires to and routinely achieves truths about the world has been challenged in recent writings. Rather than beginning with a theory of scientific development, or of scientific explanation, we begin with a consideration of truth claims in ordinary discourse, particularly with Davidson's truth-functional semantics. Next we consider the way in which some framework features of ordinary language discourse are extended to and modified in scientific discourse. Two areas are treated in more detail: quantum (...) class='Hi'>theory, and the peculiar problem of semantic entailment it involves; and quantumfieldtheory. These supply a basis for criticizing some historicist and logicist treatments of the truth of scientific claims. (shrink)
Nature seems to be such that we can describe it accurately with quantum theories of bosons and fermions alone, without resort to parastatistics. This has been seen as a deep mystery: paraparticles make perfect physical sense, so why don't we see them in nature? We consider one potential answer: every paraparticle theory is physically equivalent to some theory of bosons or fermions, making the absence of paraparticles in our theories a matter of convention rather than a mysterious (...) empirical discovery. We argue that this equivalence thesis holds in all physically admissible quantumfield theories falling under the domain of the rigorous Doplicher-Haag-Roberts approach to superselection rules. Inadmissible parastatistical theories are ruled out by a locality-inspired principle we call Charge Recombination. (shrink)
Most philosophical discussion of the particle concept that is afforded by quantumfieldtheory has focused on free systems. This paper is devoted to a systematic investigation of whether the particle concept for free systems can be extended to interacting systems. The possible methods of accomplishing this are considered and all are found unsatisfactory. Therefore, an interacting system cannot be interpreted in terms of particles. As a consequence, quantumfieldtheory does not support the (...) inclusion of particles in our ontology. In contrast to much of the recent discussion on the particle concept derived from quantumfieldtheory, this argument does not rely on the assumption that a particulate entity be localizable. (shrink)
In [3] John S. Bell proposed how to associate particle trajectories with a lattice quantumfieldtheory, yielding what can be regarded as a |Ψ|2-distributed Markov process on the appropriate configuration space. A similar process can be defined in the continuum, for more or less any regularized quantumfieldtheory; such processes we call Bell-type quantumfield theories. We describe methods for explicitly constructing these processes. These concern, in addition to the definition (...) of the Markov processes, the efficient calculation of jump rates, how to obtain the process from the processes corresponding to the free and interaction Hamiltonian alone, and how to obtain the free process from the free Hamiltonian or, alternatively, from the one-particle process by a construction analogous to “second quantization.” As an example, we consider the process for a second quantized Dirac field in an external electromagnetic field. (shrink)
The theoretical physicist Paul Dirac rejected, explicitly on aesthetic grounds, a successful theory known as quantum electrodynamics (QED), which is the prototype for the family of theories known as quantumfield theories (QFTs). Remarkably, the theoretical physicist Steven Weinberg, also largely on aesthetic grounds, supports QED and other QFTs. In order to evaluate these opposing aesthetic views a short introduction to the physical properties of QFTs is presented together with a detailed analysis of the aesthetic claims (...) of Dirac and Weinberg. It turns out that Dirac rejected QED, without regard to its success, because this theory fails to yield to what he perceived as beautiful mathematics, whereas Weinberg's support of QFTs is founded primarily on the physical concepts of the theories. In particular, he relies on symmetries that are the basis for the construction of the extremely successful current fundamental theories of particles physics. This success was decisive in leading to Weinberg's conviction of the beauty of QFTs. As a result of the evaluation of these approaches, the factors causing scientists to perceive a theory as being a fundamentally beautiful theory are discussed in detail. (shrink)
The permutation symmetry of quantum mechanics is widely thought to imply a sort of metaphysical underdetermination about the identity of particles. Despite claims to the contrary, this implication does not hold in the more fundamental quantumfieldtheory, where an ontology of particles is not generally available. Although permutations are often defined as acting on particles, a more general account of permutation symmetry can be formulated using superselection theory. As a result, permutation symmetry applies even (...) in field theories with no particle interpretation. The quantum mechanical account of permutations acting on particles is recovered as a special case. (shrink)
In this paper I put forward a new micro realistic, fundamentally probabilistic, propensiton version of quantumtheory. According to this theory, the entities of the quantum domain - electrons, photons, atoms - are neither particles nor fields, but a new kind of fundamentally probabilistic entity, the propensiton - entities which interact with one another probabilistically. This version of quantumtheory leaves the Schroedinger equation unchanged, but reinterprets it to specify how propensitons evolve when no (...) probabilistic transitions occur. Probabilisitic transitions occur when new "particles" are created as a result of inelastic interactions. All measurements are just special cases of this. This propensiton version of quantumtheory, I argue, solves the wave/particle dilemma, is free of conceptual problems that plague orthodox quantumtheory, recovers all the empirical success of orthodox quantumtheory, and at the same time yields as yet untested predictions that differ from those of orthodox quantumtheory. (shrink)
While for the majority of physicists the problem of the deciphering of the brain code, the intelligence code, is a matter for future generations, the author boldly and forcefully disagrees. Breaking with the dogma of classical logic he develops in the form of the conversion postulate a concrete working hypothesis for the actual thought mechanism. The reader is invited on a fascinating mathematical journey to the very edges of modern scientific knowledge. From lepton and quark to mind, from cognition to (...) a logic analogue of the Schrodinger equation, from Fibonacci numbers to logic quantum numbers, from imaginary logic to a quantum computer, from coding theory to atomic physics - the breadth and scope of this work is overwhelming. Combining quantum physics, fundamental logic and coding theory this unique work sets the stage for future physics and is bound to titillate and challenge the imagination of physicists, biophysicists and computer designers. Growing from the author's matrix operator formalization of logic, this work pursues a synthesis of physics and logic methods, leading to the development of the concept of infophysics. The experimental verification of the proposed quantum hypothesis of the brain is presently in preparation in cooperation with the Cavendish Laboratory, Cambridge, UK, and, if proved positive, would have major theoretical implications. Even more significant should be the practical applications in such fields as molecular electronics and computer science, biophysics and neuroscience, medicine and education. The new possiblities that could be opened up by quantum level computing could be truly revolutionary. The book aims at researchers and engineers in technical sciences as well as in biophysics and biosciences in general. It should have great appeal for physicists, mathematicians, logicians and for philosophers with a mathematical bent. (shrink)
This paper will examine the implications of an extended “fieldtheory of information,” suggested by Wolfhart Pannenberg, specifically in the Christian understanding of creation. The paper argues that the Holy Spirit created the world as field, a concept from physics, and the creation is directed by the logos utilizing information. Taking into account more recent developments of information theory, the essay further suggests that present creation has a causal impact upon the information utilized in creation. In (...) order to adequately address Pannenberg's hypothesis that the logos utilizes information at creation the essay will also include an introductory examination of Pannenberg's Christology which shifts from a strict “from below” Christology, to a more open “third way” of doing Christology beyond “above” and “below.” The essay concludes with a brief section relating the implications of an extended “fieldtheory of information” to creative inspiration, as well as parallels with human inspiration. (shrink)
Recent developments in quantumtheory have focused attention on fundamental questions, in particular on whether it might be necessary to modify quantum mechanics to reconcile quantum gravity and general relativity. This book is based on a conference held in Oxford in the spring of 1984 to discuss quantum gravity. It brings together contributors who examine different aspects of the problem, including the experimental support for quantum mechanics, its strange and apparently paradoxical features, its underlying (...) philosophy, and possible modifications to the theory. (shrink)
According to a Received View, relativistic quantumfield theories (RQFTs) do not admit particle interpretations. This view requires that particles be localizable and countable, and that these characteristics be given mathematical expression in the forms of local and unique total number operators. Various results (the Reeh-Schlieder theorem, the Unruh Effect, Haag's theorem) then indicate that formulations of RQFTs do not support such operators. These results, however, do not hold for nonrelativistic QFTs. I argue that this is due to (...) the absolute structure of the classical spacetimes associated with such theories. This suggests that the intuitions that underlie the Received View are non-relativistic. Thus, to the extent that such intuitions are inappropriate in the relativistic context, they should be abandoned when it comes to interpreting RQFTs. (shrink)
