more formal level, it also implies that everything we can observe can be captured by a causal network. And as I will discuss a little below, I suspect that the idea of causal invariance for such a network will then be what turns out to account for some key features of quantum theory.

The basic picture of our universe that I have outlined in the past few sections is a network whose connections are continually updated according to some simple set of underlying rules. In the past one might have assumed that a system like this would be far too simple to correspond to our universe. But from the discoveries in this book we now know that even when the underlying rules for a system are simple, its overall behavior can still be immensely complex.

And at the lowest level what I expect is that even though the rules being applied are perfectly definite, the overall pattern of connections that will exist in the network corresponding to our universe will continually be rearranged in ways complicated enough to seem effectively random.

Yet on a slightly larger scale such randomness will then lead to a certain average uniformity. And it is then essentially this that I believe is responsible for maintaining something like ordinary space—with gradual variations giving rise to the phenomenon of gravity.

But superimposed on this effectively random background will then presumably also be some definite structures that persist through many updatings of the network. And it is these, I believe, that are what correspond to particles like electrons.

As I discussed in the last two sections [14, 15], causal invariance of the underlying rules implies that such structures should be able to move at a range of uniform speeds through the background. Typically properties like charge will be associated with some specific pattern of connections at the core of the structure corresponding to a particle, while the energy and momentum of the particle will be associated with roughly the number of nodes in some outer region around the core.

So what about interactions? If the structures corresponding to different particles are isolated, then the underlying rules will make them persist. But if they somehow overlap, these same rules will usually make some different configuration of particles be produced.