 Darkenergydominated era

The darkenergydominated era refers to one of the three phases of the known universe, the other two being the matterdominated era and the radiationdominated era. The darkenergydominated era began after the matterdominated era, i.e. when the Universe was about 5 billion years old. As other forms of the matter – dust and radiation – dropped to very low concentrations, the cosmological constant term started to dominate the energy density of the Universe.
For a darkenergydominated universe, the evolution of the scale factor in the FriedmannLemaitreRobertsonWalker metric is easily obtained solving the Friedmann equations:
Here, the coefficient H in the exponential, the Hubble constant, is
This exponential dependence on time makes the spacetime geometry identical to the de Sitter Universe, and only holds for a positive sign of the cosmological constant, the sign that was observed to be realized in Nature anyway. As the current density of the observable universe is of the order of 9.44 x 10^{−27}kg m^{−3}, and the age of the universe is of the order of 13.7 billion years, or 4.32339 x 10^{17}s, the present scale factor a(t) is ~2.699738. The Hubble parameter, H, is ~70.88 km s^{−1}Mpc^{−1}. (The Hubble time is 13.79 billion years.) The value of the cosmological constant, Λ, is ~2 x 10^{−35}s^{−2}.
See also
http://map.gsfc.nasa.gov/news/
Categories: Physical cosmology
 Physics stubs
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