Each configuration of loops, i.e. state of space, can be described mathematically as a spin network. A spin network is a special type of graph, where the edges are labeled with integers. This representation is purely mathematical and does not provide a direct physical picture of space. The volume of a region of space is the number of nodes of the spin network that lie within the region times a unit on the order of the Planck volume. The area of a surface is the sum of the labels on the edges passing through the surface times a unit on the order of the Planck area.

A spin network evolves as the loops in the network interact. An evolving spin network is called a spin foam. Just as in classical general relativity, it is possible to define the future and past light cones for the events in a spin foam. In this case, time proceeds in discrete steps and there are only a finite number of events that an event could be a cause of after a specified number of time steps. In general relativity, time flows continuously and there are always an infinite number of events for which a given event could be a cause.