of flow occur in both air and water. And with this in mind, what I decided was that rather than starting from detailed realistic models, I would instead start from models that were somehow as simple as possible—and were easy to set up as programs on a computer.

At the outset, I did not know how this would work, and how complicated the programs I would need would have to be. And indeed when I looked at various simple programs they always seemed to yield behavior vastly simpler than any of the systems I wanted to study.

But in the summer of 1981 I did what I considered to be a fairly straightforward computer experiment to see how all programs of a particular type behaved. I had not really expected too much from this experiment. But in fact its results were so surprising and dramatic that as I gradually came to understand them, they forced me to change my whole view of science, and in the end to develop the whole intellectual structure of the new kind of science that I now describe in this book.

The picture below shows a reproduction of typical output from my original experiment. The graphics are primitive, but the elaborate patterns they contain were like nothing I had ever seen before. At first I did not believe that they could possibly be correct. But after a while I became convinced that they were—and I realized that I had seen a sign of a quite remarkable and unexpected phenomenon: that even from very simple programs behavior of great complexity could emerge.

But how could something as fundamental as this never have been noticed before? I searched the scientific literature, talked to many people, and found out that systems similar to the ones I was studying had been named "cellular automata" some thirty years earlier. But despite a few close approaches, nobody had ever actually tried anything quite like the type of experiment I had.

Yet I still suspected that the basic phenomenon I had seen must somehow be an obvious consequence of some known scientific principle. But while I did find that ideas from areas like chaos theory and fractal geometry helped in explaining some specific features, nothing even close to the phenomenon as a whole seemed to have ever been studied before.

My early discoveries about the behavior of cellular automata stimulated a fair amount of activity in the scientific community. And

A reproduction of the computer printout that first gave me a hint of some of the central phenomena in this book.