FIGURE 1. Averaging the Universe.

These three curves represent the same distribution of matter on three different averaging scales. The blue curve shows considerable detail; the pink one is averaged on a medium scale to show the overall inhomogeneity; and the red one is averaged on a very large scale to show the uniform cosmological average. The effective general-relativistic field equations describing the behaviour of the Universe will be different at each of these scales; the essential question in assessing the role of inhomogeneities is how the averaging of the small-scale terms adds up to affect the dynamics of the large-scale averaged depiction.