The Method of Images in Cosmology
  We apply the method of images to the exact initial data for cosmological
models that contain a number of regularly arranged discrete masses. This allows
us to join cosmological regions together by throats, and to construct wormholes
in the initial data. These wormholes allow for the removal of the
asymptotically flat "flange" regions that would otherwise exist on the far side
of black holes. The method of images also provides us with a way to investigate
the definition of mass is cosmology, and the cosmological consequences of the
gravitational interaction energies between massive objects. We find evidence
that the interaction energies within clusters of massive objects do indeed
appear to contribute to the total energy budget in the cosmological regions of
the space-time.
