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Encyclopedia > De Sitter universe

A de Sitter universe is a solution to Einstein's field equations of General Relativity which is named after Willem de Sitter. It is common to describe a patch of this solution as an expanding universe of the FLRW form where the scale factor is given by: For other topics related to Einstein see Einstein (disambiguation). ... Two-dimensional visualisation of space-time distortion. ... Willem de Sitter (May 6, 1872 – November 20, 1934) was a mathematician, physicist and astronomer. ... The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ...

a(t) = eHt,

where the constant H is the Hubble expansion rate and t is time. As in all FLRW spaces, a(t), the scale factor, describes the expansion of physical spatial distances. The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. ...

A de Sitter universe is one with no ordinary matter content but with a positive cosmological constant which sets the expansion rate, H. A larger cosmological constant leads to a larger expansion rate: The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) occurs in Einsteins theory of general relativity. ...

,

where the constants of proportionality depend on conventions. The cosmological constant is Λ and Mpl is the Planck mass. The Planck mass is the natural unit of mass, denoted by mP. mP = (c / G)1/2 ≈ 2. ...

Our universe may be approaching a de Sitter universe in the infinite future. If the current acceleration of our universe is due to a cosmological constant then as the universe continues to expand all of the matter and radiation will be diluted. Eventually there will be almost nothing left but the cosmological constant, and our universe will have become a de Sitter universe.

The exponential expansion of the scale factor means that the physical distance between any two non-accelerating observers will eventually be growing faster than the speed of light. At this point those two observers will no longer be able to make contact. Therefore any observer in a de Sitter universe would see horizons beyond which that observer can not see. If our universe is approaching a de Sitter universe then eventually we will not be able to observe any galaxies other than our own Milky Way. Cherenkov effect in a swimming pool nuclear reactor. ... This article is about a celestial body. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos) is the galaxy in which the Earth is found. ...

Another application of de Sitter space, is in the early universe during cosmic inflation. Many inflationary models are approximately de Sitter space and can be modeled by giving the Hubble parameter a mild time dependence. For simplicity, some calculations involving inflation in the early universe can be performed in de Sitter space rather than a more realistic inflationary universe. By using the de Sitter universe instead, where the expansion is truly exponential, there are many simplifications. Inflation is the idea—first proposed by Alan Guth (1981)—that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ...

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 De Sitter universe (136 words) A de Sitter universe is one with a positive cosmological constant and zero matter density. There is no Big Bang in a de Sitter universe - expansion is self-similar from an infinite time in the past to an infinite time in the future. The model has practical implications as an approximation during the future of the Universe when the cosmological constant is likely to dominate (assuming no changes from the present version of the standard Big Bang model), and during the early universe during a hypothesised period of inflation.
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