 Supposing that the actual physical world is a giant, discrete automaton, are there philosophically interesting conclusions to be drawn? A first one has already been partially explored in connection with Life: if nature is a CA, it has to be a universal CA, given that universal computers (e.g., the one on which you are probably reading this entry) uncontroversially exist in the physical world. Then its evolution is algorithmically irreducible, given the Halting Problem. Notwithstanding the opportunity of devising approximate forecast tools, we are left with a universe whose evolution is unpredictable for a reason quite different from the ones commonly adduced by resorting to standard physics, such as quantum effects or random fluctuations: it is unpredictable just because of its computational complexity. 