Chapter 12: The Principle of Computational Equivalence

Section 6: Computational Irreducibility

Formulas [and computational irreducibility]

It is always in principle possible to build up some kind of formula for the outcome of any process of evolution, say of a cellular automaton (see page 618). But for there to be computational reducibility this formula needs to be simple and easy to evaluate—as it is if it consists just of a few standard mathematical functions (see note above; page 1098).

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