Announcement of a “Day of Philosophy of Physics” at the University of Paris 7, Denis Diderot, next Friday, 28 June 2013, with speakers Jeremy Butterfield, Nazim Bouatta, Gabriel Catran, Oliver Pooley, Christian Wüthrich:
“Journée Philosophie de la physique au séminaire Philosophie et Physique du Laboratoire SPHERE”
Friday, 28 June 2013, salle Luc Valentin, 454A (for details on the location, see below).
Program and abstracts:
9h45 : Welcome
10h: Jeremy Butterfield (University of Cambridge): Reduction and Emergence in the Context of Renormalization.
11h: Nazim Bouatta (University of Cambridge): Easing into Fields and Strings: Emergence, Background Independence and all that.
14h: Gabriel Catren (CNRS/Université Paris Diderot): Towards a Group-Theoretical Quantum Ontology.
15h: Oliver Pooley (University of Oxford): On the alleged link between general covariance and background independence.
16h: Christian Wüthrich (University of California at San Diego): Time and Space in Causal Set Theory.
In previous work, I argued that reduction and emergence are compatible. I took reduction of theories a la Nagel: as deduction, usually using judiciously chosen definitions (bridge-laws). And I took emergence as behaviour or properties that are novel (by some salient standard). My idea was: reduction and emergence are often combined by one theory being deduced as a limit of another. In this talk, I will extend my previous framework to renormalization. I will argue that the explanation, using renormalization group ideas, of why non-renormalizable terms dwindle at long distances amounts to a family of Nagelian reductions. That is: a renormalization scheme that defines a flow to lower energies amounts to a set of definitions that enable deductions, from a theory describing high-energy physics, of a low-energy theory. Because the same scheme shows how many similar high-energy theories flow to correspondingly similar low-energy theories, we have a unified family of Nagelian reductions.
Theories of quantum gravity have been a recent focus of interest for philosophers of physics. Indeed, the fact that space-time geometry and diffeomorphism invariance can be said to emerge from quantum gravity has made them a natural focus, and a source for case studies, for the philosophical contrast between reduction and emergence, and related topics such as explanation. In this talk we will restrict ourselves to the so-called gauge/gravity correspondence: whose gauge theory is mercifully well-understood (at least in principle), and whose various limits and regimes have been much studied, including those on the way to the ‘t Hooft limit. We will also relate this example to the wider issues, which remain topical within the philosophy of space-time, about how best, in a field theory, to define and so to understand background independence.
We shall propose a group-theoretical quantum ontology based on an analysis of the relationships between quantum mechanics and 1) the theory of constrained Hamiltonian systems (or gauge theories), and 2) Kirillov’s orbit method for constructing irreducible unitary representations of some Lie groups.
The view that the requirement of general covariance is a constraint on a theory’s formulation, and not on its physical content, has its origins in Kretschmann’s 1917 criticisms of Einstein’s original presentation of the general theory of relativity (GR). At least in the literature on classical GR, it has since become the mainstream view. On the face of it, the view is in tension with claims made by several physicists working on quantum gravity, especially loop quantum gravity. Rovelli, for example, claims that GR’s background independence is “expressed by”, “coded in” or “technically realised by” the theory’s (active) diffeomorphism invariance. The aim of the talk is to get clear on the content and correctness of claims like Rovelli’s. I hope to show that the “no content” view of general covariance is essentially correct and that the differences between GR and pre-relativistic theories are often overplayed.
Causal set theory offers an elegant and philosophically rich, though admittedly inchoate, approach to quantum gravity. After presenting its basic theoretical framework, I will show how space and time vanish from the fundamental picture it offers. The absence of space and time from the theory raises the serious question of whether such a theory can be empirically coherent at all, i.e, whether its truth would not undermine any justification we may have for believing it. If it can be shown that spacetime re-emerges from the fundamental structure in the appropriate limit, I will argue, then the threat of empirical incoherence is averted and it can be appreciated how space and time emerge from what there is, fundamentally, according to causal set theory. I shall close by sketching the prospects of the antecedent of this conditional claim.
Salle Luc Valentin, 454A
Université Paris Diderot-Paris 7
4, rue Elsa Morante
Métro: Ligne 14, RER C, arrêt: Bibliothèque-François Mitterrand. Autobus: 62 89 325 64.