Inhomogeneous cosmology

An inhomogeneous cosmology is a physical cosmological theory (an astronomical model of the physical universe's origin and evolution) which, unlike the currently widely accepted cosmological concordance model, assumes that inhomogeneities in the distribution of matter across the universe affect local gravitational forces (i.e., at the galactic level) enough to skew our view of the Universe.^[3] When the universe began, matter was distributed homogeneously, but over billions of years, galaxies, clusters of galaxies, and superclusters have coalesced, and must, according to Einstein's theory of general relativity, warp the space-time around them. While the concordance model acknowledges this fact, it assumes that such inhomogeneities are not sufficient to affect large-scale averages of gravity in our observations. When two separate studies^[4][5] claimed in 1998-1999 that high redshift supernovae were further away than our calculations showed they should be, it was suggested that the expansion of the universe is accelerating, and dark energy, a repulsive energy inherent in space, was proposed to explain the acceleration. Dark energy has since become widely accepted, but it remains unexplained. Accordingly, some scientists continue to work on models that might not require dark energy. Inhomogeneous cosmology falls into this class.

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.^[6][7] 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.^[8][9] Timescape cosmology may also imply that the expansion of the universe is in fact slowing.^[3]