Meinard Kuhlmann

Ontological aspects of quantum field theory

Approaches to Ontology: Candidate General Ontologies for Situating Quantum Field Theory (P Simons) Quanta, Tropes, or Processes: Ontologies for QFT Beyond the Myth of Substance (J Seibt) Analytical Ontologists in Action: A Comment on Seibt and Simons (M Kuhlmann) How Do Field Theories Refer to Entities in a Field? (S Y Auyang) Field Ontologies for QFT: A Naive View of the Quantum Field (A Wayne) Comments on Paul Tellers Book, An Interpretive Introduction to Quantum Field Theory (G Fleming) So What Is the Quantum Field? (P Teller) Relativity, Measurement and Renormalization: On the Nature of Measurement Records in Relativistic Quantum Field Theory (J A Barrett) No Place for Particles in Relativistic Quantum Theories? (H Halvorson & R Clifton) Events and Covariance in the Interpretation of Quantum Field Theory (D Dieks) Measurement and Ontology: What Kind of Evidence Can We Have for Quantum Fields? (B Falkenburg) Renormalization and the Disunity of Science (N Huggett) Gauge Symmetries and the Vacuum: The Interpretation of Gauge Symmetry (M Redhead) Comment on Redhead: The Interpretation of Gauge Symmetry (M Drieschner et al.) Is the Zero-Point Energy Real? (S Saunders) Two Comments on the Vacuum in Algebraic Quantum Field Theory (M Redei).

Quantum Field Theory

Quantum field theory (QFT) shares many of its philosophical problems with quantum mechanics. This applies in particular to the quantum measurement process and the connected interpretive problems, to which QFT contributes hardly any new aspects, let alone solutions. The question as to how the objects described by the theory are spatially embedded was already also discussed for quantum mechanics. However, the new mathematical structure of QFT promises new answers, which renders the spatiotemporal interpretation of QFT the pivotal question. In this chapter, we sketch the mathematical characteristics of QFT and show that a particle as well as a field interpretation breaks down.

Explaining Financial Markets in Terms of Complex Systems

Large changes of financial market prices without exogenous causes deviate significantly from the Gaussian behavior of random variables. This indicates that financial markets should be treated as complex systems, for which nonlinear interactions of its subunits/agents are crucial. I focus on how the complex systems perspective impacts the notion of explanations in economics. The mechanistic model seems to fit the bill, but problems surface on closer scrutiny. One characteristic of complex systems is that their behavior is surprisingly independent from microscopic details. Thus, mechanistic explanations in the microreductionist manner seem unavailable. Despite these conflicts, I defend a modified structural mechanistic approach.

Chronology and Outlook

The following chronology places emphasis on the basics and on interpretations of quantum physics; it should not be considered to be a history of quantum physics as a whole. In particular, the special developments within quantum field theory, and the advances in particle physics which grew out of them, are not included. However, along with the interpretations which were given a detailed treatment in earlier chapters (Copenhagen, GRW, Everett, Bohm), a number of other approaches are briefly mentioned here. They could not be treated in detail in the rest of the book.

A Mechanistic Reading of Quantum Laser Theory

Quantum laser theory proceeds in a way that seems at variance with the mechanistic model of explanation. First, as is typical for a complex systems theory, the detailed behavior of the component parts plays a surprisingly subordinate role. In particular, the so-called “enslaving principle” seems to defy a mechanistic reading. Moreover, being quantum objects, the “parts” of a laser are neither located in space nor describable as separate entities. I want to show that, despite these apparent obstacles, quantum laser theory constitutes a good example of a mechanistic explanation in a quantum physical setting, provided that one broadens the notion of mechanism. One may feel that such adjustments are ad hoc and question-begging. However, I will argue that the necessary adjustments are far more natural and less drastic than one may expect. Among other things I suggest that the structural similarities between semiclassical and quantum laser theory support a mechanistic reading of the latter.

Position measurements on quantum mechanical particles in bound states

Abstract The statistical interpretation of quantum mechanics and its possible conflict with the conservation of energy in the case of measurements on bound systems is described. A semi-classical solution to the problem given by Heisenberg is quantitatively reconstructed and proved not to solve the problem. Finally an approach within the quantum theory of measurement is made and shown to yield promising results.