Thus, for example, in the early part of this chapter I will discuss the so-called Second Law of Thermodynamics or Principle of Entropy Increase: the observation that many physical systems tend to become irreversibly more random as time progresses. And I will show that the essence of such behavior can readily be seen in simple programs.

More than a century has gone by since the Second Law was first formulated. Yet despite many detailed results in traditional physics, its origins have remained quite mysterious. But what we will see in this chapter is that by studying the Second Law in the context of simple programs, we will finally be able to get a clear understanding of why it so often holds—as well as of when it may not.

My approach in investigating issues like the Second Law is in effect to use simple programs as metaphors for physical systems. But can such programs in fact be more than that? And for example is it conceivable that at some level physical systems actually operate directly according to the rules of a simple program?

Looking at the laws of physics as we know them today, this might seem absurd. For at first the laws might seem much too complicated to correspond to any simple program. But one of the crucial discoveries of this book is that even programs with very simple underlying rules can yield great complexity.

And so it could be with fundamental physics. Underneath the laws of physics as we know them today it could be that there lies a very simple program from which all the known laws—and ultimately all the complexity we see in the universe—emerges.

To suppose that our universe is in essence just a simple program is certainly a bold hypothesis. But in the second part of this chapter I will describe some significant progress that I have made in investigating this hypothesis, and in working out the details of what kinds of simple programs might be involved.

There is still some distance to go. But from what I have found so far I am extremely optimistic that by using the ideas of this book the most fundamental problem of physics—and one of the ultimate problems of all of science—may finally be within sight of being solved.