Tuesday, September 29th
Hal Haggard, Bard CollegeEffective Spin Foams & the Flatness Problem
PDF of the talk (10M)
Audio+Slides of the talk (360M)
SRT (Subtitles) of the talk (70K)
The spin foam approach to quantum gravity emanates from loop quantum gravity and from treating space-time as a whole. Initially, loop quantum gravity was formulated in what is known as the "canonical" approach in which space-time is treated as a bunch of spaces that evolve. Space is represented by quantum states known as spin networks that are networks of lines with intersections and with numbers associated to them. If you can imagine one of those spatial networks sweeping forward in time, the result looks like a foam, hence the name spin foams. How the spin networks evolve as they sweep forward determines the dynamics of the theory, something known as "the vertex", because it involves the creation of new intersections in the spin network. There have been over time several proposals for such vertices, trying to capture as best as possible the quantum dynamics of general relativity
Regge Calculus is an approach to classical general relativity. In it, space-times are approximated by flat sections, pretty much like a geodesic dome approximates a sphere through its flat sections. It has the advantage that it cuts down the infinite number of degrees of freedom of a field theory like general relativity to a finite number. Due to this it can also be used to treat the theory numerically.
This talk used a Regge Calculus approach to define a new "vertex" for spin foams. It inherits the convenience of Regge Calculus as a computational tool. Several numerical experiments were carried out successfully and there are proposals for new ones to come.
