Matter-dominated era

The matter-dominated era was the epoch in the evolution of the Universe that began when the radiation-dominated era ended, when the Universe was about 47,000 years old.[1] Although it was often said that we still live in the matter-dominated era, it is more correct to say that when the Universe was about 9.8 billion years old,[2] this era ended and was replaced by the dark-energy-dominated era. This change of the perspective occurred when the cosmological constant or dark energy was first observed in the late 1990s.

In the matter-dominated era, the energy density of matter exceeds the energy density of radiation in the universe (and it should exceed the vacuum energy density i.e. dark energy, too).[3]

For a matter dominated universe the evolution of the scale factor in the Friedmann-Lemaitre-Robertson-Walker metric is easily obtained solving the Friedmann equations:

$a(t)\propto t^{{2/3}}$

References

1. ^ Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.41
2. ^ Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.33
3. ^ Zelik, M and Gregory, S: "Introductory Astronomy & Astrophysics", page 497. Thompson Learning, Inc. 1998