# Dark Energy Dominated Era

Dark Energy Dominated Era

The Dark-Energy-Dominated Era refers to one of the three phases of the known universe, the other two being the Matter-Dominated Era and the Radiation-Dominated Era. The Dark-Energy-Dominated Era began after the Matter-Dominated 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 dark-energy-dominated universe, the evolution of the scale factor in the Friedmann-Lemaitre-Robertson-Walker metric is easily obtained solving the Friedmann equations::$a\left(t\right)propto exp\left(Ht\right)$Here, the coefficient "H" in the exponential, the Hubble constant, is:$H = sqrt\left\{8pi G ho_\left\{full\right\} / 3\right\} = csqrt\left\{Lambda / 3\right\}.$This exponential dependence on time makes the spacetime geometry identical to 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.

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