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• • • In and, dark energy is an unknown form of which is to permeate all of space, tending to the. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is at an. Assuming that the is correct, the indicate that dark energy contributes 68.3% of the total energy in the present-day. The mass–energy of and contribute 26.8% and 4.9%, respectively, and other components such as and contribute a very small amount. The density of dark energy (~ 7 × 10 −30 g/cm 3) is very low, much less than the density of ordinary matter or dark matter within galaxies.

However, it dominates the mass–energy of the universe because it is uniform across space. Two proposed forms for dark energy are the, representing a constant energy density filling space homogeneously, and such as or, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant.

The cosmological constant can be formulated to be equivalent to the of space i.e. Scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow.

Contents • • • • • • • • • • • • • • • • • • • • • • • • • History of discovery and previous speculation [ ] Einstein's cosmological constant [ ] The 'cosmological constant' is a constant term that can be added to of General Relativity. If considered as a 'source term' in the field equation, it can be viewed as equivalent to the mass of empty space (which conceptually could be either positive or negative), or '. The cosmological constant was first proposed by as a mechanism to obtain a solution of the gravitational that would lead to a static universe, effectively using dark energy to balance gravity. Einstein gave the cosmological constant the symbol Λ (capital lambda). The mechanism was an example of, and it was later realized that Einstein's static universe would not be stable: local inhomogeneities would ultimately lead to either the runaway expansion or contraction of the universe. The is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion. Likewise, a universe which contracts slightly will continue contracting.

These sorts of disturbances are inevitable, due to the uneven distribution of matter throughout the universe. Further, observations made by in 1929 showed that the universe appears to be expanding and not static at all. Einstein reportedly referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder.

Boa Kpop Selection Download Yahoo. Inflationary dark energy [ ] and proposed in 1980 that a negative pressure field, similar in concept to dark energy, could drive in the very early universe. Inflation postulates that some repulsive force, qualitatively similar to dark energy, resulted in an enormous and exponential expansion of the universe slightly after the.

Such expansion is an essential feature of most current models of the Big Bang. However, inflation must have occurred at a much higher energy density than the dark energy we observe today and is thought to have completely ended when the universe was just a fraction of a second old.

It is unclear what relation, if any, exists between dark energy and inflation. Even after inflationary models became accepted, the cosmological constant was thought to be irrelevant to the current universe. Nearly all inflation models predict that the total (matter+energy) density of the universe should be very close to the critical density.

During the 1980s, most cosmological research focused on models with critical density in matter only, usually 95% and 5% ordinary matter (baryons). These models were found to be successful at forming realistic galaxies and clusters, but some problems appeared in the late 1980s: in particular, the model required a value for the lower than preferred by observations, and the model under-predicted observations of large-scale galaxy clustering. These difficulties became stronger after the discovery of anisotropy in the by the spacecraft in 1992, and several modified CDM models came under active study through the mid-1990s: these included the and a mixed cold/hot dark matter model. Free Fursona Wolf Template. The first direct evidence for dark energy came from supernova observations in 1998 of in et al.