There are unreachable states ("gardens of Eden" in the lingo) which means that (per the Garden of Eden Theorem) there exist states which are the successor of more than one possible state. This is an irreversibility (you cannot infer the previous state from the present one), implying an increase of entropy.
While this logic is technically correct its a very weird way to reason, since Garden of Eden patterns are very hard to find in CGL but sets of patterns which converge on the next step are trivially easy to find (e.g. the block and the two common pre-blocks all become blocks on the next step).
I don't see how that matters: if there exist any states for which it is impossible to infer the previous state, that is a loss of information and therefore an increase in entropy.
I agree it's hard to know "the" way to map the 2nd law onto an arbitrary universe and see how it applies, but based on some heuristics (checking for irreversibility, agent-perceived flow of time) it seems like Life doesn't violate it.
Many experts suspect that there is no polynomial-time solution to the so-called NP-complete problems, though no-one has yet been able to rigorously prove this and there remains the possibility that a polynomial-time algorithm will one day emerge. However unlikely this is, today I would like to invite LW to play a game I played with with some colleagues called what-would-you-do-with-a-polynomial-time-solution-to-3SAT? 3SAT is, of course, one of the most famous of the NP-complete problems and a solution to 3SAT would also constitute a solution to *all* the problems in NP. This includes lots of fun planning problems (e.g. travelling salesman) as well as the problem of performing exact inference in (general) Bayesian networks. What's the most fun you could have?