Voids as Alternatives to Dark Energy and the Propagation of Gamma Rays
  through the Universe
  We test the opacity of a void Universe to TeV energy gamma rays having
obtained the extra-galactic background light in that Universe using a simple
model and the observed constraints on the star formation rate history. We find
that the void Universe has significantly more opacity than a Lambda-CDM
Universe, putting it at odds with observations of BL-Lac objects. We argue that
while this method of distinguishing between the two cosmologies contains
uncertainties, it circumvents any debates over fine-tuning.
