Inhomogeneous cosmologies assume that the backreactions of denser structures, as well as those of very empty voids, on space-time are significant enough that when not taken into account, they distort our understanding of time and our observations of distant objects. Following Thomas Buchert's publication of equations in 1997 and 2000 that derive from general relativity but also allow for the inclusion of local gravitational variations, a number of cosmological models were proposed under which the acceleration of the universe is in fact a misinterpretation of our astronomical observations and in which dark energy is unnecessary to explain them. For example, in 2007, David Wiltshire proposed a model (timescape cosmology) in which backreactions have caused time to run more slowly or, in voids, more quickly, thus giving the supernovae observed in 1998 the illusion of being further away than they were. Timescape cosmology may also imply that the expansion of the universe is in fact slowing.