Karen Crowther: Emergence, Reduction, and Correspondence in the Context of Quantum Gravity

Karen Crowder introduces her project on quantum gravity, focusing on the principles of quantum gravity and its relationship with general relativity. She discusses the criteria for a successful quantum gravity theory, including its ability to recover general relativity in relevant domains and the emergence of space-time from quantum gravity. The importance of understanding different types of theory relationships such as emergence, reduction, and correspondence is highlighted, with an aim to explore these concepts in the context of quantum gravity.

The speaker delves into the significance of theory relationships in quantum gravity, particularly emergence, reduction, and correspondence. She explains that these relationships are crucial for defining the criteria of acceptance for a quantum gravity theory. The literature has mainly focused on emergence, but the speaker aims to explore the roles and distinctions of all three concepts, suggesting that correspondence might be a more relevant focus for further exploration.

The paragraph discusses the concept of correspondence in the context of scientific theory development. Correspondence is seen as a relationship between two theories that successfully describe the same domain, aiming to establish consistency between them. The speaker introduces different types of correspondence relations and their roles in physics, such as heuristic roles in theory development and justification roles in theory acceptance. The paragraph emphasizes the practical interest in correspondence relations when the success of one theory in a domain has yet to be demonstrated.

The speaker presents an account of reduction and correspondence, explaining that reduction is a special case of correspondence where the more fundamental theory subsumes the domain of success of the less fundamental theory. The conception of reduction is domain subsumption, and the aim is to show that all physical phenomena described by the older theory are also covered by the newer, more fundamental theory. Correspondence, in this context, serves as a shortcut to results and plays various roles in the development and acceptance of scientific theories.

This section explores the heuristic roles of correspondence in the development of quantum gravity. It discusses how correspondence can guide the construction of new theories by inferring parts of the theory from older, more established theories. The speaker provides examples from quantum gravity, such as the use of general relativity as a guiding principle in loop quantum gravity and causal set theory, highlighting how these theories aim to recover general relativity and retain features that contribute to their empirical support.

The speaker discusses the role of correspondence in justifying new theories and making predictions. Correspondence can serve as a constraint on theory development, a means of confirmation, or as an explanation for the success of older theories. The paragraph also touches on the idea of predictions, where the new theory may recover aspects of the older theory that are responsible for its success, providing indirect support for the new theory.

The paragraph examines the efficiency roles of correspondence and reduction, which justify the continued use of older theories by their compatibility with newer theories. It also discusses how newer theories may reveal redundancy in older theories, showing which aspects are unnecessary for the success of the older theory. The speaker notes that while these roles are not yet applicable to quantum gravity, there is an assumption of mutual justification, particularly in the recovery of general relativity.

The speaker introduces the concept of emergence, explaining that it is not required in quantum gravity but is often assumed to hold. Emergence suggests that general relativity is novel and robust compared to the physics of quantum gravity. The paragraph explores different approaches to emergence, comparing the fundamental structures of quantum gravity with those of general relativity and discussing the potential for quantum gravity to be more autonomous, similar to critical phenomena in statistical physics.

In conclusion, the speaker summarizes her accounts of fundamentality, correspondence, and reduction, emphasizing their importance in defining quantum gravity and establishing the consistency of theories. She reflects on the roles these concepts play in the development, acceptance, and justification of scientific theories, particularly in the context of quantum gravity. The speaker also acknowledges the complexity of these relationships and the need for further exploration and understanding.

The final paragraph captures an open discussion on the nature of theoretical relationships in physics, particularly focusing on the concepts of space-time and the recovery of general relativity within quantum gravity. The conversation touches on the importance of understanding the structure of space-time, the challenges of linking theoretical pieces, and the potential for novel phenomena that are not described by existing theories. The discussion also considers the role of testability and the need for unique predictions in scientific theories.