  In this paper a new form of duality for probabilistic cellular automata (PCA)
is introduced. Using this duality, an ergodicity result for processes having a
dual is proved. Also, conditions on the probabilities defining the evolution of
the processes for the existence of a dual are provided. The results are applied
to wide classes of PCA which include multi-opinion voter models, competition
models and the Domany-Kinzel model.
