John Baez
October 11, 2005
Towards a Spin Foam Model of Quantum Gravity
Spin foam models include several
different classes of physical theories: lattice gauge theories,
dynamical triangulation models of quantum gravity, "chain
mail" quantum field theories, and topological string theories.
Is there a spin foam model of quantum gravity in 4 dimensions? To
address this question, we review recent work on causal dynamical
triangulations and the renormalization group. This
suggests that quantum gravity is a welldefined theory with the
curious property that spacetime is effectively 4dimensional at large
distance scales, but 2dimensional at very short distance scales.
This is just what one might expect from a spin foam model,
since spacetime is fundamentally 2dimensional in these theories.
We discuss properties a spin foam model should have in order to approximate
general relativity at large distance scales.
You can see the transparencies of this talk, and also a video of it:
Here are some of the papers alluded to in this talk, in
the order they're mentioned:

Florian Conrady,
Geometric spin foams, YangMills theory and backgroundindependent
models

Daniele Oriti,
Spin foam
models of quantum spacetime

Alejandro Perez,
Spin foam models
of quantum gravity

Carlo Rovelli,
Quantum Gravity, chapter 9.3

Jan Ambjørn, J. Jurkiewicz and Renate Loll,
Reconstructing the universe

Oliver Lauscher and Martin Reuter,
Fractal
spacetime structure in asymptotically safe gravity

Abhay Ashtekar, Donald Marof, Jose Mourao and Thomas
Thiemann,
Constructing Hamiltonian quantum theories from path integrals
in a diffeomorphism invariant context

Fotini Markopoulou and Lee Smolin,
Quantum geometry with intrinsic local causality

Etera Livine and Daniele Oriti,
Implementing causality in the spin foam quantum geometry

Daniele Oriti,
The Feynman propagator for spin foam quantum gravity

Carlo Rovelli,
Graviton propagator from backgroundindependent quantum gravity
Here are some general introductions to spin foams:
© 2005 John Baez
baez@math.removethis.ucr.andthis.edu