# Matter-dominated era

Matter-dominated era

The matter-dominated era was the epoch in the evolution of the Universe that began after the radiation-dominated era ended, when the Universe was about 70,000 years old. 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 5 billion years old, 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). [1]

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. ^ Zelik, M and Gregory, S: "Introductory Astronomy & Astrophysics", page 497. Thompson Learning, Inc. 1998

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