  This article is based on the covariant causal set ($c$-causet) approach to
discrete quantum gravity. A $c$-causet $x$ is a finite partially ordered set
that has a unique labeling of its vertices. A rate of change on $x$ is
described by a covariant difference operator and this operator acting on a wave
function forms the left side of the wave equation. The right side is given by
an energy term acting on the wave function. Solutions to the wave equation
corresponding to certain pairs of paths in $x$ are added and normalized to form
a unique state. The modulus squared of the state gives probabilities that a
pair of interacting particles is at various locations given by pairs of
vertices in $x$. We illustrate this model for a few of the simplest nontrivial
examples of $c$-causets. Three forces are considered, the attractive and
repulsive electric forces and the strong nuclear force. Large models get much
more complicated and will probably require a computer to analyze.

General Relativity and Quantum Cosmology