Chapter 9: Fundamental Physics

Section 8: The Relationship of Space and Time

Spacetime symmetric rules

With k=2 and the neighborhoods shown here, only the additive rules 90R, 105R, 150R and 165R are space-time symmetric. For larger k and larger neighborhoods, there presumably begin to be non-additive rules with this property.

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