The thing that bugs me about his theory is that it just assumes the existence of time. That patterns within the network are replaced according to certain rules.

The thing that bugs me about his theory is that it just assumes the existence of time. That patterns within the network are replaced according to certain rules. And it seems that this replacement rule corresponds to time at the high level. His low level model seems to require propagation / evolution without being able to model it. Whatever enacts the replacement rule is an external force that acts upon his network, and so falls outside his definition of the universe. I guess it's a limitation of the cellular automata model. You have to assume that something outside of the system "steps" the simulation forward.