Editing Scale factor (cosmology) (section)

===Matter-dominated era===
Between about 47,000 years and 9.8 billion years [[cosmic time|after the Big Bang]],<ref>Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.33, 6.41</ref> the [[energy density]] of matter exceeded both the energy density of radiation and the vacuum energy density.<ref>Zelik, M and Gregory, S: "Introductory Astronomy & Astrophysics", page 497. Thompson Learning, Inc. 1998</ref>

When the [[early universe]] was about 47,000 years old (redshift 3600), [[mass–energy equivalence|mass–energy]] density surpassed the [[radiant energy|radiation energy]], although the universe remained [[optical depth|optically thick]] to radiation until the universe was about 378,000 years old (redshift 1100). This second moment in time (close to the time of [[Recombination (cosmology)|recombination]]), at which the photons which compose the [[cosmic microwave background radiation]] were last scattered, is often mistaken{{pov inline|date=October 2020}} as marking the end of the radiation era.

For a matter-dominated universe the evolution of the scale factor in the [[Friedmann–Lemaître–Robertson–Walker metric]] is easily obtained solving the [[Friedmann equations]]:
<math display="block">a(t) \propto t^{2/3}</math>