MCMP – Philosophy of Physics

Chris Timpson (Brasenose College, Oxford) gives a talk at the Workshop on Quantum Computation, Quantum Information, and the Exact Sciences (30-31 January, 2015) titled "Quantum Information: Conceptual and Ontological Aspects". Abstract: In this talk I will explore some ways of thinking about what quantum information is. This topic has a certain intrinsic interest, but it is also important when trying to assess in a careful way what role the concept of information might have to play in fundamental physics. I shall argue for a view which is fairly ontologically deflationary about quantum information (this has significant impact on how we should understand the slogan ‘information is physical’ and for informational immaterialist views) and which sees quantum and classical (Shannon) information both as species of a single genus.

Elena Castellani (Florence) gives a talk at the MCMP Colloquium (28 January, 2015) titled "Dualities". Abstract: Dualities are a key, intriguing ingredient in mathematics, logic and physics. This talk is concerned with physical dualities, in particular those dualities that have played "a central role in mapping out the structure of theoretical physics" in the past two decades (quoting Polchinski, 2015). Despite the importance of duality in field and string theory, philosophers are just starting to pay the due attention to the subject. This talk is meant as an introduction to discussing the significance of physical dualities, by pointing out the different relevant functions they play and the kinds of philosophical issues they connect or give rise to (in particular: theoretical equivalence and ontological indeterminacy).

Gia Dvali (LMU-MPI & NYU) gives a talk at the MCMP Colloquium (14 January, 2015) titled "Corpuscular structure of geometry". Abstract: We review some recent ideas on quantum-corpuscular structure of gravitational metric backgrounds, such as black holes and cosmological spaces. We show how this picture sheds light on seemingly-mysterious properties, such as, black hole information processing and evaporation, as well as how it excludes eternal de Sitter space. This picture sheds a very different light on notion of "holography" and cosmological constant problem.

Karim Thebault (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "A New Prescription for the Quantization of Refoliation Invariant Field Theories". Abstract: Imagine a loaf of bread that we can irregularly cut up into a sequence of slices. The loaf is spacetime and the slices are instantaneous spatial surfaces. A foliation is a parameterization of a spacetime by a time ordered sequence of spatial slices. In a field theory such a parametrization can be local in the sense that it is defined for every point on every spatial slice. Diffeomorphism invariance implies that spacetimes described by general relativity that are related by refoliations are physically equivalent. Classically the symmetry is therefore directly connectable to the idea that only the coordinate-free information contained in a spacetime geometry has a physical basis. The implications of this symmetry for quantization are notoriously problematic. Here we offer a new prescription for the canonical quantization of gravity that side-steps the issues with refoliations via the adoption of the 'shape dynamics’ reformulation. We then offer our thoughts as to whether this is a satisfactory resolution for the problem for understanding refoliation symmetry in the context of a quantum field theory of gravity.

Ben Feintzeig (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Unitary Inequivalence in Classical Systems". Abstract: I provide an algebraic formulation of classical field theories and use this to probe our interpretation of algebraic theories more generally. I show that the problem of unitarily inequivalent representations, as discussed in Ruetsche (2011), arises in classical theories just as in quantum theories, and I argue that this gives reason to not be a Hilbert Space Conservative when interpreting algebraic theories.

Brian Padden (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Relativistic Quantum Particles the Feynman Way". Abstract: It is often believed, especially in light of theorems by Malament and others, that there is no relativistic theory of localizable quantum particles. However, an example of exactly such a theory seems to exist, and in fact occupies an important place in the storied history of quantum field theory: Feynman’s path integral approach to quantum electrodynamics. We introduce Feynman’s theory and show that, up to a few minor issues, it is satisfactory. Then, we turn to the theorems stating that such a theory is impossible and discuss which premises are violated by the Feynman theory.

Samuel Fletcher (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Classical Field Theory and Intertheoretic Reduction". Abstract: In 1986, Ehlers set out a program on how to understanding the approximative relationships between different physical theories. However, he essentially only investigated the case of classical and relativistic spacetime theories, which have a number of special features that distinguish them from broader classes of physical theories. To what extent, then, can the Ehlers program be successful? I outline some of the challenges facing the program's generalization and argue that they can largely be overcome for classical field theories.

Sarita Rosenstock (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "On Fiber Bundle and Holonomy Interpretations of Yang-Mills Theories". Abstract: In the philosophy of Yang-Mills theories, there is an ongoing debate between rival interpretations that can be grouped into two rough categories: “holonomy interpretations” (supported by, e.g., Healey, Belot, and Lyre) and “fiber bundle interpretations” (supported by, e.g., Arntzenius, Maudlin, and Leeds). I present a theorem that I interpret as providing a precise sense in which these interpretations are equivalent.

James Weatherall (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December) titled "Fiber Bundles, Yang-Mills Theory, and General Relativity". Abstract: I articulate and discuss a geometrical interpretation of Yang-Mills theory. Analogies and disanalogies between Yang-Mills theory and general relativity are also considered.

Meinard Kuhlmann (Mainz) gives a talk at the MCMP Colloquium (10 December, 2014) titled "A Trope Bundle Interpretation of Algebraic Quantum Field Theory". Abstract: Algebraic quantum field theory (AQFT) is a conceptually lucid reformulation of the conventional theory of quantum fields. I consider AQFT to be the appropriate starting point for ontological considerations about QFT because, like the philosophical discipline of ontology, AQFT strives for a clear, justified and parsimonious separation of basic and derived classes of entities. I argue that the one-category theory of particularized properties or 'tropes', which analyses all other entities in terms of the basic category of tropes, yields the most appropriate ontological reading of AQFT. Among other things I will show that trope ontology and AQFT have essential structural similarities. I argue in particular that the trope-ontological conception of objects as bundles of tropes is related to the pivotal net structure of observable algebras in AQFT. Eventually, I show that the identification of trope-like entities in AQFT is best achieved via the notion of representations in the algebraic theory of superselection sectors, where the notion of inequivalent irreducible representations allows for a neat distinction of essential and non-essential properties/tropes.