Dark-energy-dominated era

In physical cosmology, the dark-energy-dominated era refers to the last 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 9.8 billion years old.^[1] 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–Lemaître–Robertson–Walker metric is easily obtained solving the Friedmann equations:

$a(t)\propto \exp(Ht)$

Here, the coefficient H in the exponential, the Hubble constant, is

$H = \sqrt{8\pi G \rho_\mathrm{full} / 3} = \sqrt{\Lambda / 3}.$

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. The current density of the observable universe is of the order of 9.44 x 10⁻²⁷kg m⁻³ and the age of the universe is of the order of 13.8 billion years, or 4.358 x 10¹⁷s. The Hubble parameter, H, is ~70.88 km s⁻¹Mpc⁻¹. (The Hubble time is 13.79 billion years.) The value of the cosmological constant, Λ, is ~2 x 10⁻³⁵s⁻².

See also

• Quintessence (physics)
• Dark energy
• Chronology of the universe

References

1. ↑ Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.33