Shereshevsky's finite-entropy conjecture for multidimensional cellular automata

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Let SS be a finite set, let d>1d>1, and let X=SZdX=S^{\mathbb{Z}^d}. A dd-dimensional cellular automaton is a continuous map T:X→XT:X\to X commuting with the shift action of Zd\mathbb{Z}^d, and its topological entropy is denoted by htop(T)h_{\mathrm{top}}(T). Shereshevsky's conjecture. A dd-dimensional cellular automaton with d>1d>1 cannot have finite, positive topological entropy; equivalently, its entropy is either zero or infinite. The conjecture was motivated by the absence of forward-expansive cellular automata in dimensions greater than one and was known for linear cellular automata, but this paper disproves it by constructing, for every dd, a dd-dimensional cellular automaton with finite, nonzero topological entropy.

References

Primary source

Tom Meyerovitch, “Finite entropy for multidimensional cellular automata”, arXiv:math/0703167 (2007).

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