The remarkable thing is, what we've been able to do, is to make from this very... structurally simple underlying set of ideas, we've been able to bui… - Stephen Wolfram

Problem 9. What is the correspondence between cellular automata and continuous systems?
Cellular automatat are discrete in several respects. First, they consist of a discrete spatial lattice of sites. Second, they evolve in discrete steps. And finally, each site has only a finite discrete set of possible values.
The first two forms of discreteness are addressed in the numerical analysis of approximate solutions to, say, differential equations. ...
The third form of discreteness in cellular automata is not so familiar from numerical analysis. It is an extreme form of round-off, in which each "number" can have only a few possible values (rather than the usual 2¹⁶ or 2³²).

What's happened is, for 300 years people basically said, "If you want to make a model of things in the world, mathematical equations are the best place to go. In the last 15 years: it doesn't happen. New models... most often are made with programs, not with equations. ...Was that ...going to happen anyway? Was that a consequence of my particular work and my particular book? It's hard to know for sure. ...Was there a chain of academic references? Probably not.

It was the spring of 1978 and I was 18 years old. I’d been publishing papers on particle physics for a few years, and had gotten quite known around the international particle physics community (and, yes, it took decades to live down my teenage-particle-physicist persona). I was in England, but planned to soon go to graduate school in the US, and was choosing between Caltech and Princeton. And one weekend afternoon when I was about to go out, the phone rang. In those days, it was obvious if it was an international call. “This is Murray Gell-Mann”, the caller said, then launched into a monologue about why Caltech was the center of the universe for particle physics at the time.