Working paper, Santa Fe Institute, 1998. Ten of the papers appeared as a special Proceedings issue of Complexity, Vol. The Proceedings Editors were J. Hartle, P. Hut, and J. F. Traub. There are two formal systems that concern us. One is the mathematical model which is chosen by the scientist.
Continuous models are common in fields varying from physics to economics.
The real or complex number field is assumed. The second formal model is the model of computation . Computer scientists tend to favor the Turing Machine model. For scientific problems the real-number model has a number of advantages. The pros and cons of the real-number model versus the Turing Machine model are given in Chapter 8 of Complexity and Information .