So why might this be? It is not, I believe, any kind of coincidence, or trick of perception. And instead what I suspect is that it reflects a deep correspondence between simple programs and systems in nature.

When one looks at systems in nature, one of the striking things one notices is that even when systems have quite different underlying physical, biological or other components their overall patterns of behavior can often seem remarkably similar.

And in my study of simple programs I have seen essentially the same phenomenon: that even when programs have quite different underlying rules, their overall behavior can be remarkably similar.

So this suggests that a kind of universality exists in the types of behavior that can occur, independent of the details of underlying rules.

And the crucial point is that I believe that this universality extends not only across simple programs, but also to systems in nature. So this means that it should not matter much whether the components of a system are real molecules or idealized black and white cells; the overall behavior produced should show the same universal features.

And if this is the case, then it means that one can indeed expect to get insight into the behavior of natural systems by studying the behavior of simple programs. For it suggests that the basic mechanisms responsible for phenomena that we see in nature are somehow the same as those responsible for phenomena that we see in simple programs.

In this chapter my purpose is to discuss some of the most common phenomena that we see in nature, and to study how they correspond with phenomena that occur in simple programs.

Some of the phenomena I discuss have at least to some extent already been analyzed by traditional science. But we will find that by thinking in terms of simple programs it usually becomes possible to see the basic mechanisms at work with much greater clarity than before.

And more important, many of the phenomena that I consider—particularly those that involve significant complexity—have never been satisfactorily explained in the context of traditional science. But what we will find in this chapter is that by making use of my discoveries about simple programs a great many of these phenomena can now for the first time successfully be explained.