Combinatorial dynamics in quantum gravity

Abstract

We describe the application of methods from the study of discrete dynanmical systems to the problem of the continuum limit of evolving spin networks. These have been found to describe the small scale structure of quantum general relativity and extensions of them have been conjectured to give background independent formulations of string theory. We explain why the the usual equilibrium critical phenomena may not be relevant for the problem of the continuum limit of such theories and why, instead, the continuum limits of such theories are likely to be governed by non-equilibrium critical phenomena such as directed percolation. The fact that such non-equilibrium critical phenomena can be self-organized implies the possibility that the classical limit of quantum theories of gravity may exist without fine tuning of parameters.