Discussion: What is the ontology of quantum field theory?

The panel discussion begins with an introduction to the various themes in the philosophy of quantum field theory (QFT). The moderator highlights three main areas of debate: particle ontology, field ontology, and the concept of effective field theories. They also touch on the historical development of QFT and the different ontological stances taken by physicists. The aim is to stimulate a comprehensive discussion on these ontological questions, inviting speakers and attendees to contribute their perspectives.

The first speaker emphasizes the importance of maintaining a pragmatic and flexible approach to ontological commitments in physics. They argue against 'naturalistic metaphysics' that seeks to fix the ontology of current, incomplete physical theories, as this could hinder future development. Instead, they propose viewing ontological commitments as malleable and responsive to the goals and understanding of physicists.

The second speaker, a physics student, candidly admits their initial lack of a precise definition for 'ontology' and shares their thought process in formulating a working definition for the discussion. They propose that reality in QFT is based on observable outcomes of experiments, suggesting that the theory's components can be considered 'real' to the extent that they accurately predict experimental results.

The third speaker discusses the historical context of QFT and the importance of considering different interpretations of the theory. They highlight the tension between continuous and discrete views of reality in physics and the role of no-go theorems in shaping our understanding of QFT. They also stress the need for collaboration between philosophers and physicists to address ontological questions effectively.

The fourth speaker explores the relationship between interpretation and ontology in QFT, suggesting that interpretation can extend beyond empirical predictions. They argue for the importance of considering effective or emergent content of theories as part of the interpretive process, which can inform future work in physics without necessarily committing to a single ontology.

The fifth speaker delves into the complexities of interpreting quantum theories, particularly the issue of macro objectification and the measurement problem. They discuss the challenges of reconciling quantum superpositions with our macroscopic reality and the implications for ontology. The speaker also touches on the mutual constraints between ontological problems and the solutions offered by different interpretations of QFT.

The sixth speaker addresses the sociological impact of physicists' interpretations, especially how they are often misconstrued as ontological claims by the media. They caution against the oversimplification of complex theories for public consumption and the potential for this to create confusion about the nature of scientific theories and their ontological implications.

The seventh speaker engages with the concept of fundamental elements in theories, using the example of Newtonian gravity and its eventual displacement by general relativity. They discuss the importance of recognizing when elements of a theory are fundamentally flawed and how this can inform the development of new theories.

The eighth speaker contrasts the unified view of quantum field theories with the dappled world of effective field theories, where different energy scales may require different descriptions. They discuss the challenges of applying theories beyond their domains of empirical support and the philosophical implications of this for our understanding of the fundamental nature of reality.

The ninth speaker acknowledges the uncertainty surrounding the fundamentals of quantum field theory, particularly in relation to the standard model. They emphasize the importance of being cautious about ontological claims and considering the failures of a theory as well as its successes when contemplating its fundamental nature.

The tenth speaker views quantum field theory as a flexible framework that can be adapted to various contexts and purposes. They discuss the variation in how QFT is applied and the importance of understanding the contexts in which it is used, suggesting that the theory's adaptability is a key aspect of its interpretive and ontological considerations.

The eleventh speaker reflects on the historical development of quantum theory interpretations and the operational approach often taken in the foundations of quantum mechanics. They suggest that while we await a more comprehensive theory, an operational stance may be a pragmatic strategy, focusing on empirical data and avoiding ontological disputes.

In the final paragraph, the discussion turns to the ontology of general relativity as a point of comparison for quantum field theory. The panel is challenged to consider whether there is a consensus on the ontology of general relativity, which is generally considered a well-understood theory, and to reflect on the reasons for the lack of consensus in the case of quantum field theory.