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Physical cosmology

Key topics

Universe · Big Bang Age of the universe Timeline of the Big Bang Ultimate fate of the universe

Early universe

Inflation · Nucleosynthesis GWB · Neutrino Background Cosmic microwave background Expanding universe Redshift · Hubble's law Metric expansion of space Friedmann equations FLRW metric Structure formation Shape of the universe Structure formation Galaxy formation Large-scale structure Components Lambda-CDM model Dark energy · Dark matter History Timeline of cosmology... Cosmology experiments Observational cosmology 2dF · SDSS CoBE · BOOMERanG · WMAP Scientists Einstein · Hawking . Friedman · Lemaître · Hubble · Penzias · Wilson · Gamow · Dicke · Zel'dovich · Mather · Smoot · others

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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^[3], gravitational lensing^{[citation needed]}, age of the universe^{[citation needed]} and large scale structure^{[citation needed]}, as well as improved measurements of the supernovae.^[4][5]

An expanding universe means that density drops. 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.

Models attempting to explain accelerating expansion include the cosmological constant, quintessence, and phantom energy, with the latest WMAP data favouring 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 in an expanding universe disappears more quickly than dark energy (see equation of state) 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).

• High-z Supernova Search Team
• Supernova Cosmology Project
• Brian P. Schmidt

1. ^ 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
2. ^ 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
3. ^ arXiv:astro-ph/0604051v2
4. ^ B. Leibundgut, J. Sollerman (2001). "A cosmological surprise: the universe accelerates". Europhysics News 32 (4). Retrieved on 2007-02-01. 
5. ^ "Confirmation of the accelerated expansion of the Universe", Centre National de la Recherche Scientifique, September 19, 2003. Retrieved on 2006-11-03.