New Work on the Problem of Time - a podcast by MCMP Team

Oliver Pooley (Oxford) gives a talk at the MCMP Colloquium (22 January, 2014) titled "New Work on the Problem of Time". Abstract: A central aspect of the "Problem of Time" in canonical general relativity is the result of applying to the theory Dirac's seemingly well-established method of identifying gauge transformations in constrained Hamiltonian theories. This "orthodox" move identifies transformations generated by the first-class constraints as mere gauge. Applied to GR the strategy yields the result that the genuine physical magnitudes of the theory (so identified) do not take on different values at different times. In the context of quantum gravity, this orthodoxy underwrites the derivation of the timeless Wheeler–DeWitt equation. It is thus intimately connected to one of the central interpretative puzzles of the canonical approach to quantum gravity, namely, how to make sense of a profoundly timeless quantum formalism. This talk reviews several disparate challenges to the technical underpinning of the orthodox view that are starting to gain prominence. Three issues, in particular, will be surveyed. One, explored in the work of Salisbury and collaborators and Pitts, concerns the true relationship between transformations identified as gauge symmetries in the context of a Lagrangian formalism and transformations generated by first-class constraints. A second, explored in the work of Barbour, Gryb and Thébault, concerns whether physical magnitudes are required to commute with all first-class constraints in order for a Hamiltonian theory to be manifestly deterministic. Taking on board the lessons from these two areas is not always sufficient to address all apparent indeterminism in the Hamiltonian formalism. The third topic concerns how this should be addressed.

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