This Friday we have Seth's former advisor Jeremy Butterfield visiting. https://en.wikipedia.org/wiki/Jeremy_Butterfield He works on philosophy of physics and during the 11am group meeting will tell us about his work on symmetry and duality. He will also give a talk at 1:30pm in room 6c-442. Here are the details. title: Deriving time evolution in general relativity : a philosopher's perspective. Joint work with Henrique Gomes, Cambridge. Abstract: Abstract: This talk will advertise three results that give, in a broadly general-relativistic framework, sufficient conditions for time-evolution being generated by the ADM Hamiltonian. The philosophical background is functionalism. Roughly speaking, it is the idea that one specifies an entity or concept by its web of relations to other entities and concepts. Recently philosophers have debated 'spacetime functionalism': "spacetime is as spacetime does". Thus their focus is on how the physics of matter and radiation contributes to determining, or perhaps even determines or explains, chrono-geometry: a Machian theme. The results are as follows:--- (i) The recovery of geometrodynamics, i.e. general relativity's usual ADM Hamiltonian, from requirements on deformations of hypersurfaces in a Lorentzian spacetime; due to Hojman, Kuchar and Teitelboim (1976: Annals of Physics); (ii) The deduction from judicious assumptions about matter and radiation in a 4-dimensional manifold that there is an (appropriately related) Lorentzian metric; due to Schuller, Duell, Giesel et al. (2012, 2018: Physical Review D); (iii) The deduction of a Lorentzian metric and of general relativity's usual ADM Hamiltonian, assuming (not a 4-manifold: but merely) that how a 3-geometry changes over time should be locally definable (Gomes and Shyam 2016: Journal of Mathematical Physics; and at 1608.08236). Thus the overall aim of the talk is to give a philosophical background to Gomes and Shyam, 1608.08236. _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip