arXiv subjects

Karen Crowther

Publications and source records attributed to Karen Crowther.

8 recordsLinked to original sources

arXiv2025

Another 100 Years of Quantum Interpretation?

Interpretation is not the only way to explain a theory's success, form and features, and nor is it the only way to solve problems we see with a theory. This can also be done by giving a reductive explanation of the theory, by reference to a newer, more accurate, and/or more fundamental theory. We are seeking a theory of quantum gravity, a more fundamental theory than both quantum mechanics and general relativity, yet, while this theory is supposed to explain general relativity, it's not typically been thought to be necessary, or able, to explain quantum mechanics -- a task instead assigned to interpretation. Here, I question why this is. I also present a new way of assessing the various interpretations of quantum mechanics, in terms of their heuristic and unificatory potential in helping us find a more fundamental theory.

physics.hist-ph↗

arXiv2025

Why Do We Want a Theory of Quantum Gravity?

The search for a new scientific theory is typically prompted by an encounter with something in the world that cannot be explained by current theories. This is not the case for the search for a theory of quantum gravity, which has been primarily motivated by theoretical and philosophical concerns. This Element introduces some of the motivations for seeking a theory of quantum gravity, with the aim of instigating a more critical perspective on how they are used in defining and constraining the theory sought. These motivations include unification, incompatibilities between general relativity and quantum field theory, consistency, singularity resolution, and results from black hole thermodynamics.

gr-qc↗

arXiv2021

Four Attitudes Towards Singularities in the Search for a Theory of Quantum Gravity

Singularities in general relativity and quantum field theory are often taken not only to motivate the search for a more-fundamental theory (quantum gravity, QG), but also to characterise this new theory and shape expectations of what it is to achieve. Here, we first evaluate how particular types of singularities may suggest an incompleteness of current theories. We then classify four different `attitudes' towards singularities in the search for QG, and show, through examples in the physics literature, that these lead to different scenarios for the new theory. Two of the attitudes prompt singularity resolution, but only one suggests the need for a theory of QG. Rather than evaluate the different attitudes, we close with some suggestions of factors that influence the choice between them.

gr-qc↗

arXiv2019

As Below, So Before: `Synchronic' and `Diachronic' Conceptions of Spacetime Emergence

Typically, a less fundamental theory, or structure, emerging from a more fundamental one is an example of synchronic emergence. A model (and the physical state it describes) emerging from a prior model (state) upon which it nevertheless depends is an example of diachronic emergence. The case of spacetime emergent from quantum gravity and quantum cosmology challenges these two conceptions of emergence. Here, I propose two more-general conceptions of emergence, analogous to the synchronic and diachronic ones, but which are potentially applicable to the case of emergent spacetime: an inter-level, hierarchical conception, and an intra-level, `flat' conception. I then explore whether, and how, these ideas may be applicable in the case of several putative examples of relativistic spacetime emergent from the non-spatiotemporal structures described by different approaches to quantum gravity, and of spacetime emergent from a non-spatiotemporal `big bang' state according to different examples of quantum cosmology.

physics.hist-ph↗

arXiv2019

What we cannot learn from analogue experiments

Analogue experiments have attracted interest for their potential to shed light on inaccessible domains. For instance, `dumb holes' in fluids and Bose-Einstein condensates, as analogues of black holes, have been promoted as means of confirming the existence of Hawking radiation in real black holes. We compare analogue experiments with other cases of experiment and simulation in physics. We argue---contra recent claims in the philosophical literature---that analogue experiments are not capable of confirming the existence of particular phenomena in inaccessible target systems. As they must assume the physical adequacy of the modelling framework used to describe the inaccessible target system, arguments to the conclusion that analogue experiments can yield confirmation for phenomena in those target systems, such as Hawking radiation in black holes, beg the question.

physics.hist-ph↗

arXiv2017

Inter-theory Relations in Quantum Gravity: Correspondence, Reduction, and Emergence

Relationships between current theories, and relationships between current theories and the sought theory of quantum gravity (QG), play an essential role in motivating the need for QG, aiding the search for QG, and defining what would count as QG. Correspondence is the broad class of inter-theory relationships intended to demonstrate the necessary compatibility of two theories whose domains of validity overlap, in the overlap regions. The variety of roles that correspondence plays in the search for QG are illustrated, using examples from specific QG approaches. Reduction is argued to be a special case of correspondence, and to form part of the definition of QG. Finally, the appropriate account of emergence in the context of QG is presented, and compared to conceptions of emergence in the broader philosophy literature. It is argued that, while emergence is likely to hold between QG and general relativity, emergence is not part of the definition of QG, and nor can it serve usefully in the development and justification of the new theory.

physics.hist-ph↗

arXiv2017

Renormalizability, fundamentality and a final theory: The role of UV-completion in the search for quantum gravity

Principles are central to physical reasoning, particularly in the search for a theory of quantum gravity (QG), where novel empirical data is lacking. One principle widely adopted in the search for QG is UV completion: the idea that a theory should (formally) hold up to all possible high energies. We argue---\textit{contra} standard scientific practice---that UV-completion is poorly-motivated as a guiding principle in theory-construction, and cannot be used as a criterion of theory-justification in the search for QG. For this, we explore the reasons for expecting, or desiring, a UV-complete theory, as well as analyse how UV completion is used, and how it should be used, in various specific approaches to QG.

physics.hist-ph↗

arXiv2014

Appearing Out of Nowhere: The Emergence of Spacetime in Quantum Gravity

Quantum gravity is understood as a theory that, in some sense, unifies general relativity (GR) and quantum theory, and is supposed to replace GR at extremely small distances (high-energies). It may be that quantum gravity represents the breakdown of spacetime geometry described by GR. The relationship between quantum gravity and spacetime has been deemed "emergence", and the aim of this thesis is to investigate and explicate this relation. After finding traditional philosophical accounts of emergence to be inappropriate, I develop a new conception of emergence by considering physical case studies including condensed matter physics, hydrodynamics, critical phenomena and quantum field theory understood as effective field theory. This new conception of emergence is independent of reduction and derivation. Instead, a low-energy theory is understood as emergent from a high-energy theory if it is novel and autonomous compared to the high-energy theory, and the low-energy physics is dependent (in a particular, minimal sense) on the high-energy physics (this dependence is revealed by the techniques of effective field theory and the renormalisation group). These ideas are important in exploring the relationship between quantum gravity and GR, where GR is understood as an effective, low-energy theory of quantum gravity. Without experimental data or a theory of quantum gravity, we rely on principles and techniques from other areas of physics to guide the way. As well as considering the idea of emergence appropriate to treating GR as an effective field theory, I investigate the emergence of spacetime (and other aspects of GR) in several concrete approaches to quantum gravity, including examples of the condensed matter approaches, the "discrete approaches" (causal set theory, causal dynamical triangulations, quantum causal histories and quantum graphity) and loop quantum gravity.

physics.hist-ph↗