Talk by Oliver Pooley at MCMP (Jan 22)

[Dardashti, Radin]

Speaker: Oliver Pooley (Oxford)
Wednesday 22nd Jan 2014
Location: Ludwigstr. 31 room 021
Time: 18:15 - 19:45

Title:  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.