  One could begin a study like the present one by simply postulating that our
universe is four-dimensional. There are ample reasons for doing this.
Experience, observation and experiment all point to the fact that we inhabit a
four-dimensional universe. Another approach would be to show that
four-dimensions arise naturally from a reasonable model of the universe or
multiverse. After reviewing the causal set approach to discrete quantum gravity
in Section~1, we shall discuss the emergence of four-dimensions in Section~2.
We shall see that certain patterns of four arise that suggest the introduction
of a 4-dimensional discrete manifold. In the later sections we shall discuss
some consequences of this introduced framework. In particular, we will show
that quantum amplitudes can be employed to describe a multiverse dynamics.
Moreover, a natural unitary operator together with energy, position and
momentum operators will be introduced and their properties studied.
