Wayne Myrvold: Collapse Theories for Relativistic QFT: Problems and Prospects

The speaker opens the quantum field theory conference, reflecting on the significant progress made in the field since the last event a decade ago. They highlight the intention to revisit foundational topics and philosophical discussions, emphasizing the inclusion of both young scholars and original contributors. The speaker also introduces organizational details, such as food arrangements and budgetary constraints affecting dinner invitations, and acknowledges the efforts of the organizing team led by Debra Fox.

The speaker discusses the shift in scientific realism towards interpreting quantum field theories as effective theories, despite their non-fundamental nature. They address the challenge of being a realist about quantum theory, especially in reconciling quantum mechanics with macroscopic objects and the measurement problem. The speaker also introduces a classification of approaches to address these issues, based on Bell's distinction between whether the quantum state and unitary evolution are complete or not.

The speaker delves into the concept of collapse theories within quantum mechanics, focusing on the debate surrounding the completeness of the quantum state and the implications for realism. They discuss the idea of hidden variables, the potential misrepresentation of quantum states, and the challenges of maintaining the quantum state as given by unitary evolution. The talk also touches on the possibility of a relativistic dynamical collapse theory and its potential issues.

The speaker transitions the discussion to the complexities of formulating collapse theories in the context of relativistic quantum field theories. They explore the challenges of adapting non-relativistic collapse theories to a relativistic framework and the need to reconcile these theories with the principles of special relativity. The speaker also introduces the concept of local beables and the issues of particle production from the vacuum.

The speaker addresses the problem of vacuum excitations in relativistic collapse theories, where an infinite number of particles are produced per unit time from the vacuum. They discuss the implications of this issue and the challenges it poses to the development of a sensible relativistic collapse theory. The speaker also references the work of Daniel Bernoulli and Philip Pearl in creating a relativistic collapse theory that avoids this problem.

The speaker examines the spectrum condition, which is a requirement for the positive energy of any space-time region in quantum field theory. They discuss the implications of this condition for the stability of the vacuum and the deterministic evolution of the vacuum state. The speaker also highlights the challenges of constructing a non-trivial stochastic evolution that respects the spectrum condition.

The speaker discusses the construction of a relativistic collapse theory by introducing non-standard fields and deviating from the standard Hilbert space. They explain how the introduction of pointer fields that couple to matter fields allows for a stable vacuum while still permitting non-trivial collapse outside of the vacuum. The speaker also raises the question of the physical motivation behind these theoretical constructs.

The speaker explores the role of pointer fields in collapse theories, which are introduced to facilitate the collapse of the quantum state to eigenstates of mass density. They discuss the unusual commutation relations of these fields and how they affect the evolution of matter fields. The speaker also considers the possibility that these pointer fields might indicate a deeper level of reality beyond ordinary matter.

The speaker discusses the possibility of testing collapse theories through entanglement experiments and the challenges associated with detecting superpositions of macroscopic objects. They mention the potential for energy non-conservation as a testable prediction of these theories and the current experimental bounds that have not yet ruled out the proposed parameters.

The speaker ponders the philosophical implications of collapse theories and the theoretical considerations that arise from their construction. They address the question of whether these theories should be taken seriously and what the introduction of pointer fields might suggest about the nature of reality. The speaker also considers the possibility of alternative theories that might work in curved space-time rather than flat Minkowski space-time.