    But the Principle of Computational Equivalence asserts that this is not the case, and that in fact almost any system whose behavior is not obviously simple will exhibit universality and will perform sophisticated computations even with typical simple initial conditions.

So the result is that computational irreducibility can in the end be expected to be common, so that it should indeed be effectively impossible to outrun the evolution of all sorts of systems.

One slightly subtle issue in thinking about computational irreducibility is that given absolutely any system one can always at least nominally imagine speeding up its evolution by setting up a rule that for example just executes several steps of evolution at once.

But insofar as such a rule is itself more complicated it may in the end achieve no real reduction in computational effort. And what is more important, it turns out that when there is true computational reducibility its effect is usually much more dramatic.

The pictures on the next page show typical examples based on cellular automata that exhibit repetitive and nested behavior. In the patterns on the left the color of each cell at any given step is in effect found by tracing the explicit evolution of the cellular automaton up to that step. But in the pictures on the right the results for particular cells are instead found by procedures that take much less computational effort.

These procedures are again based on cellular automata. But now what the cellular automata do is to take specifications of positions of cells, and then in effect compute directly from these the colors of cells.

The way things are set up the initial conditions for these cellular automata consist of digit sequences of numbers that give positions. The color of a particular cell is then found by evolving for a number of steps equal to the length of these input digit sequences.

And this means for example that the outcome of a million steps of evolution for either of the cellular automata on the left is now determined by just 20 steps of evolution, where 20 is the length of the base 2 digit sequence of the number 1,000,000.

And this turns out to be quite similar to what happens with typical mathematical formulas in traditional theoretical science. For the point of such formulas is usually to allow one to give a number as

From Stephen Wolfram: A New Kind of Science [citation]