MCMP – Philosophy of Physics

Edward Anderson (Paris Diderot and Cambridge) gives a talk in the colloquium "Journeys in Platonia: Celebrating 50 Years Since The End of Time" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Kendall’s Shape Statistics as a Classical Realization of Barbour-type Timeless Records Theory Approach to Quantum Gravity". Abstract: I already showed that Kendall’s shape geometry work was the geometrical description of Barbour’s relational mechanics’ reduced configuration spaces (alias shape spaces). I now describe the extent to which Kendall’s subsequent statistical application to such as the ‘standing stones problem’ realizes further ideas along the lines of Barbour-type timeless records theories, albeit just at the classical level.

Harvey Brown (Oxford) gives a talk in the colloquium "Journeys in Platonia: Celebrating 50 Years Since The End of Time" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Leibniz, Mach and Barbour". Abstract: My comments will be concerned with the way that Leibniz's and Mach's thinking on the nature of space have influenced Julian Barbour's approach to the formulation of dynamical theories.

Jean Bricmont (Université catholique de Louvain) gives a talk at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "From the microscopic to the macroscopic world". Abstract: The derivation of the laws describing the macroscopic world from those governing the microscopic one is a very difficult problem. The root of the difficulty is sometimes seen as arising from the fact that the first set of laws are often time-irreversible, while the second ones are time-reversible. The goal of the talk will be to explain precisely these notions (macroscopic, microscopic, (ir)reversibility) and why this difference does not constitute an insuperable difficulty. We will also discuss the role of probability in the derivation of the macroscopic laws from the microscopic ones and criticize several misleading attempts at justifying this derivation.

John D. Norton (Pittsburgh) gives a talk at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "The Neglect of Fluctuations in the Thermodynamics of Computation". Abstract: The thermodynamics of computation assumes that thermodynamically reversible processes can be realized arbitrarily closely at molecular scales. They cannot. Overcoming fluctuations so that a molecular scale process can be completed creates more thermodynamic entropy than the small quantities tracked by Landauer's Principle. This no go result is the latest instance of a rich history of problems posed by fluctuations for thermodynamics.

James Owen Weatherall (California) gives a talk at the MCMP Colloquium (19 July, 2013) titled "Inertial Motion, Explanation, and the Foundations of Classical Spacetime Theories". Abstract: There is an influential view in physics and philosophy of physics, originating with Einstein and Eddington, that holds that general relativity is distinctive in the history of physics because it can be used to "explain" inertial, or unforced, motion. In this talk, I will describe how a reformulation of Newtonian gravitation may be used to provide insight into claims concerning the (allegedly) distinctive explanatory resources of relativity theory. I will then argue that Newtonian gravitation can be understood to explain inertial motion in much the same way as general relativity. However, a careful comparative study of the status of inertial motion in the two theories reveals that neither explanation is as clean or straightforward as adherents to the view noted above believe. I will conclude by presenting a view about the interdependencies of the central principles of physical theories that I will argue provides some insight into a sense in which inertial motion is explained in both of these theories.

Michael Stöltzner (South Carolina) gives a talk at the MCMP Colloquium (17 July, 2013) titled "Feynman Diagrams as Models". Abstract: While Feynman considered his diagrams as pictorial representation of (real and virtual) physical processes, Dyson took then as a mere bookkeeping tool for mathematical expressions in a perturbation series. This split perspective has persisted since, especially when Feynman diagrams gradually extended their sway into modern particle physics. I argue that the modern debates on models in science can build a bridge between both perspectives by granting Feynman diagrams some explanatory autonomy and representative features. While a single Feynman diagram remains isomorph to a mathematical expression, it also represents a family of diagrams that model a measurable physical effect.

Dean Rickles (Sydney) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Dualities and Physical Content". Abstract: A duality expresses a reltionship between a pair of putatively distinct physical theories. Theories are said to be dualwhen they generate "the same physics", where same physics is parsed in terms of, e.g., having the same amplitudes, expectation values, observable spectra, and so on. Hence, theories related by dualities can look very different while making exactly the same predictions about observatle phenomena. Indeed, such theories can look sufficiently different that would-be interpreters would surely consider them to be representations of very different possible worlds. In this talk I will be concerned with the question of whether dualites reflect some deep aspect of reality, or whether they are simply a formal device that aids computations in difficult contexts (functioning in much the same way as a change of variables). This links quite naturally to problems of underdetermination, and also to the issue of what we mean by theory in such contexts. I defend a rather deflationary account fo the philosophical implications of dualities. Since the underdetermination is taken to apply to structurally distinct theories (that is, it is structure that is underdetermined), I will also consider whether dualities pose a problem for structural realists.

Ioan Muntean (Fort Wayne) comments on Dean Rickles' "Dualities and the Physical Content of Theories" at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013).

Karen Crowther (Sydney) comments on Daniele Oriti's "Dissappearance and Emergence of Space and Time in Quantum Gravity" at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013).

Daniele Oriti (Potsdam) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Disappearance and Emergence of Space and Time in Quantum Gravity". Abstract: We recall the hints for the disappearance of continuum space and time at microsopic scales, coming from classical and semi-classical gravitational physics. These include arguments for discreteness or for a fundamental non-locality, in a quantum theory of gravity. We compare how these ideas are realized in specific quantum gravity approaches, and focus in particular on the group field theory formalism, itself strictly related to other approaches, in particular loop quantum gravity. Next, we consider the emergence of continuum space and time from the collective behaviour of discrete, pre-geometric and non-spatio-temporal atoms of quantum space. After discussing the notion of emergence, with Bose condensates as one paradigmatic examples, and some specific cenceptual difficulties with the notion of emergent spacetime, we argue for spacetime as a kind fo cendsate, result of a phase transition, physically identified with the big bang. We then illustrate recent results, in the context of the group field theory framework, establishing a tentative procedure for the emergence of cosmological (homogeneous) spacetime and their effective quantum dynamics from fundamental, pre-geometric models. Last, we re-examine the conceptual issues raised by the emergent spacetime scenario in light of this concrete example.