wolram said:
How do QG people evolve particles into the theory?
initially they didn't worry about particles
they just focused on the simpler problem of getting a quantum theory of spacetime geometry
and they put matter into the picture by hand, when they wanted to include that. usually just some simple generic stuff (not worrying about what kind of particles)
around 2005 several things happened that changed this simple situation
1. Alain Connes has an elegant geometrical way of generating the Standard Model and two Danes (Aastrup and Grimstrup) got the idea of taking the LQG configuration space as a basis and building a Connes-style geometry on it----so they started working on combining the Standard Model of particle physics with LQG. It's a major undertaking. They have made some progress on this is the past two years.
2. Also around 2005, Laurent Freidel discovered a form of LQG-spinfoam that seems to have the Feynman diagrams of usual Quantum Field Theory latent in it. According to him, if you gradually turn off gravity by gradually making Newton constant G go to zero, then what appears is particle physics in flat space. This takes more work to make precise and this is one of the things Freidel and others have been pursuing in the past couple of years. One difficulty has been recovering in full 4D some things that work in 3D.
3. Also in 2005 Lee Smolin took note of some work by Bilson-Thompson (a young Australian particle physicist). He realized that B-T's version of the Standard Model particles could be realized in terms of twists and tangles in LQG SPIN NETWORKS.
So B-T was invited to Perimeter Institute and a number of people there have been working on that idea of matter for a couple of years as well.