Communication complexity and intrinsic universality in cellular automata

The notions of universality and completeness are central in the theories of computation and computational complexity. However, proving lower bounds and necessary conditions remains hard in most cases. In this article, we introduce necessary conditions for a cellular automatonto be "universal", according to a precise notion of simulation, related bothtothe dynamics of cellular automata and to their computational power. This notion of simulation relieson simple operations of space-time rescaling and it isintrinsictothe modelofcellular automata. Intrinsic universality, the derived notion, is stronger than Turing universality, but more uniform, and easier to define and study. Our approach builds upon the notion ofcommunication complexity, which was primarily designed to study parallel programs, and thus is, as we show in this article, particulary well suited to the study of cellular automata: it allowed us to show, by studying natural problems on the dynamics of cellular automata, that several classes of cellular automata, as well as many natural (elementary) examples, were not intrinsically universal.