User:WritingMan/Timescape cosmology
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Inhomogeneous cosmology refers to physical cosmologies (astronomical models of the physical universe's origin and evolution) that, unlike the currently widely accepted standard cosmological model, assume 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.[1] 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 standard 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 type Ia supernovae were independently observed in 1998 to be further away than our calculations showed they should be, it was concluded that the expansion of the universe is accelerating, and dark energy, a repulsive energy inherent in space, was proposed to explain the acceleration. While still unexplained in nature and origin, dark energy is widely accepted as comprising almost 70% of the universe's energy density.
By contrast, 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.[2][3] For example, in 2007, David Wiltshire proposed a model (timescape cosmology) in which backreactions have causing 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.[4][5] Timescape cosmology may also imply that the expansion of the universe is in fact slowing.[1]
Inhomogeneous cosmologies are the subject of sometimes caustic debate and are not considered significant by the majority of astronomers and cosmologists. Proponents of such cosmologies have been described as "rebels" or, by Buchert himself, "backreactionistas."[6]