  We study a simple model of spin network evolution motivated by the hypothesis
that the emergence of classical space-time from a discrete microscopic dynamics
may be a self-organized critical process. Self organized critical systems are
statistical systems that naturally evolve without fine tuning to critical
states in which correlation functions are scale invariant. We study several
rules for evolution of frozen spin networks in which the spins labelling the
edges evolve on a fixed graph. We find evidence for a set of rules which
behaves analogously to sand pile models in which a critical state emerges
without fine tuning, in which some correlation functions become scale
invariant.
