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| ===Dark energy dominates=== | ===Dark energy dominates=== | ||
| As the Universe expands, the density of ] declines more quickly than the density of ] (see ]) 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). | As the Universe expands, the density of ] declines more quickly than the density of ] (see ]) 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).<br /> | ||
| At the present moment of time, the density of dark energy is surpassing the density of matter: | |||
| <blockquote> | |||
| As the expansion continues, it is expected that dark energy—a mysterious force that causes the expansion of the universe to accelerate—will become most important. Over the past 10 years, observations of the universe have shown that the expansion is accelerating, suggesting that the gradual transition from the current matter-dominated phase to the dark-energy era is underway. We're right on the cusp between the matter-dominated and dark energy-dominated epochs.<ref></ref> | |||
| </blockquote> | |||
| ==Implications== | |||
| ===Fusion of Planckian pixels=== | |||
| At the Planck scale, the fabric of space-time is made of tiny units rather like pixels. If space-time is a grainy hologram, then you can think of the universe as a sphere whose outer surface is papered in Planck length-sized squares, each containing one bit of information. The ] says that the amount of information papering the outside must match the number of bits contained inside the volume of the universe. According to Craig Hogan, director of Fermilab's Center for Particle Astrophysics in Batavia, Illinois, when this information is projected from the surface into the volume of the universe, each bit gets magnified and blurred. The volume of the expanding universe increases ten times faster than the surface area (m<sup>3</sup> : m<sup>2</sup> = 10). That is why instead of 10<sup>−35</sup>m, a Planckian pixel of space currently has the size of 10<sup>−16</sup>m.<ref> New Scientist, 15 January 2009</ref><ref> New Scientist, 2 September 2009</ref><br /> | |||
| ==See also== | ==See also== | ||
Revision as of 20:28, 14 September 2009
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The accelerating universe is the observation that the universe appears to be expanding at an increasing rate. In 1998 observations of Type Ia supernovae suggested that the expansion of the universe is accelerating.
Corroboration
In the past few years, these observations have been corroborated by several independent sources: the cosmic microwave background, gravitational lensing, age of the universe and large scale structure, as well as improved measurements of the supernovae.
Density drops
An expanding universe means that density drops due to continual space being added between all matter. If acceleration continues, eventually all galaxies beyond our own Local supercluster will redshift so far that it will become hard to detect them, and the distant universe will turn dark.
Explanatory models
Models attempting to explain accelerating expansion include some form of dark energy: cosmological constant, quintessence, or 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.
Divergent expansion
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.
Dark energy dominates
As the Universe expands, the density of dark matter declines more quickly than the density of 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).
At the present moment of time, the density of dark energy is surpassing the density of matter:
As the expansion continues, it is expected that dark energy—a mysterious force that causes the expansion of the universe to accelerate—will become most important. Over the past 10 years, observations of the universe have shown that the expansion is accelerating, suggesting that the gradual transition from the current matter-dominated phase to the dark-energy era is underway. We're right on the cusp between the matter-dominated and dark energy-dominated epochs.
Implications
Fusion of Planckian pixels
At the Planck scale, the fabric of space-time is made of tiny units rather like pixels. If space-time is a grainy hologram, then you can think of the universe as a sphere whose outer surface is papered in Planck length-sized squares, each containing one bit of information. The holographic principle says that the amount of information papering the outside must match the number of bits contained inside the volume of the universe. According to Craig Hogan, director of Fermilab's Center for Particle Astrophysics in Batavia, Illinois, when this information is projected from the surface into the volume of the universe, each bit gets magnified and blurred. The volume of the expanding universe increases ten times faster than the surface area (m : m = 10). That is why instead of 10m, a Planckian pixel of space currently has the size of 10m.
See also
References
- 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
- 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
- arXiv:astro-ph/0604051v2
- B. Leibundgut, J. Sollerman (2001). "A cosmological surprise: the universe accelerates". Europhysics News. 32 (4): 121. doi:10.1051/epn:2001401. Retrieved 2007-02-01.
- "Confirmation of the accelerated expansion of the Universe". Centre National de la Recherche Scientifique. September 19, 2003. Retrieved 2006-11-03.
- Simple answer to dark mystery
- Our world may be a giant hologram New Scientist, 15 January 2009
- Noise from the edge of the universe New Scientist, 2 September 2009