Computers and their software are the most complex things ever made by man. However, computation is based on the operations of the simplest mechanisms ever discovered. Computers work with bits and simple gates that implement trivial Boolean functions such as the 2-input NAND gate [1] . The biggest and most complex computer processors and memories can be built by wiring together nothing beyond multiple copies of 2 input NAND gates. Many identical simple circuits can be wired together to make complex computer processors, and complex computer programs are built out of sequences of simple instructions.
Fundamental physics is complex and we are looking for simple models that might be at the bottom. We know, because of Turing’s argument [2] , that any discrete process can be modeled exactly by any universal computer.
Digital Philosophy suggests that the search for fundamental physical models should begin in the realms of greatest simplicity. For example, the bit as a unit of state is considerably simpler than a real number or even a rational number. Of course, it is possible that a 3‑state or 4‑state system might result even greater overall simplicity. In order to explore DP we must choose a set of reasonable assumptions and not worry too much about every such choice. The laws of Automata Theory encourage this approach because we know that every kind of discrete behavior can be exhibited by any universal computer (or automaton) even though, at a fundamental level, the computer performs sequences of nothing but simple operations on bits.
(Last revised 15-Oct-01)