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(* = RP's parentheses)
The
accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. In 1998 observations of
Type Ia supernovae suggested that the expansion of the
universe is speeding up.
[1][2] In the past few years, these observations have been corroborated by several independent sources: the
cosmic microwave background[
citation needed],
gravitational lensing[
citation needed],
age of the universe[
citation needed] and
large scale structure[
citation needed], as well as improved measurements of the
supernovae[3][4].
An expanding universe means that density drops.
(*Not if the accelerating expansion of matter is the cause of the spatial acceleration)
If acceleration continues eventually all galaxies beyond our own
local supercluster will
redshift so far that it will become hard to detect them, the distant universe will turn dark.
(*Not if the accelerating expansion of matter is the cause of the spatial acceleration)
Models attempting to explain accelerating expansion include the
(*recently re-engaged, formerly abandoned) cosmological constant,
quintessence, and phantom energy, with the latest
WMAP data favoring the cosmological constant. The most important property of dark energy is that it has negative
pressure which is distributed relatively
homogeneously in space.
Phantom energy in a scenario known as the
Big Rip causes an exponentially increasing
divergent expansion, which overcomes the gravitation of the local group and tears apart our
Virgo supercluster, it then tears apart the milky way galaxy, our solar system, and finally even atoms. Measurements of acceleration are thought crucial to determining the
ultimate fate of the universe, however we should expect the implications of such a major discovery to develop slowly over many years in the same way the big bang model has continued to develop.
The density of
dark matter (*The newly adopted name for the reinstated Cosmological Constant) in an expanding universe disappears more quickly than
dark energy (see
Equation of State (Cosmology)) and, eventually, the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant for a cosmological constant).
[edit] See also[edit] References- <LI id=_note-0>^ Goldhaber, G. and Perlmutter, S, "A study of 42 type Ia supernovae and a resulting measurement of Omega(M) and Omega(Lambda)", Physics Reports-Review section of Physics Letters 307 (1-4): 325-331 Dec. 1998 <LI id=_note-1>^ Garnavich PM, Kirshner RP, Challis P, et al. "Constraints on cosmological models from Hubble Space Telescope observations of high-z supernovae" Astrophysical Journal 493 (2): L53+ Part 2 Feb. 1 1998 <LI id=_note-Leibundgut>^ B. Leibundgut, J. Sollerman (2001). "A cosmological surprise: the universe accelerates". Europhysics News 32 (4). Retrieved on 2007-02-01.
- ^ "Confirmation of the accelerated expansion of the Universe", Centre National de la Recherche Scientifique, September 19, 2003. Retrieved on 2006-11-03.
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