Chapter 9: Fundamental Physics

Section 2: The Notion of Reversibility

Directional reversibility [in cellular automata]

Even if successive time steps in the evolution of a cellular automaton do not correspond to an injective map, it is still possible to get an injective map by looking at successive lines at some angle in the spacetime evolution of the system. Examples where this works include the surjective rules 30 and 90.

From Stephen Wolfram: A New Kind of Science [citation]