Hector (and James),
going back to the remark by James -- if the universe is a computer (or, better, a computation), it needs power supply, and needs to be programmed -- I agree with the reply that there is no need to program it for a purpose, and not need to inject information during the computation. A lot of interesting things emerge in computations that are not the result of a purposeful design, and are 'closed', that is, not interacting with the outside, as many experiments have shown.
But we are left with the question of the 'power supply'. As a supporter of the digital/computational universe conjecture, I like to assume that everything must emerge from the universal computation (i.e., from spacetime): particles, matter, energy, up to life, and whatever else is going to emerge next. But don't we need some sort of energy to keep the computation running, step by step? How do we avoid the circularity of energy requiring energy to exist?
Perhaps a possible answer would be: we don't need energy to run the Computation because there is no actual, physical, Digital Computer that runs it, in the same way as we do not require power for an Analog Computer to run, say, the Navier-Stokes or Einstein equations, under an analog-based understanding of the universe.
An alternative answer, along the lines of Tegmark's Mathematical Universe Hypothesis, would be that the Computation does not unfold step by step: it is already all there, time being a sort of illusion (I wonder whether the fact that time and energy are conjugate variables plays a role here).
In any case, if we insist that the computational steps 'really happen', and that they require some non-null effort, hopefully not from metaphysical entities like angels (after all, angels don't sweat), it would be wise to keep it to the bare minimum. In this respect, a prefix-free universal Turing machine (as suggested by Hector), or a Turmite, or a network mobile automaton (as discussed in my contribution), all based on the operation of a simple, localized control head, are preferable to a cellular automaton, with its global operation mode. (By the way, to my knowledge, the first to push for the localized control head idea in a physical context has been S. Wolfram.)
Hector, James, what do you think?