An alternative, related to the 'rate of change' comment and perhaps the same thing is wolframphysics.org where time is indeed directional but owing to how rewrite rules apply on relations among a fixed number of space points in the universe. Among those relations is 'causes' for instance. He takes as his first guess on these points is the number of Planck points in the universe times 1000. He derives relativity and quantum mechanics out of this. The march of time is in his physics marching irreversably forward and causation (among other relations) could harmonize things.

Being a computation guy I like his model a lot.