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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.〔Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.41〕 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,〔Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.33〕 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).〔Zelik, M and Gregory, S: "Introductory Astronomy & Astrophysics", page 497. Thompson Learning, Inc. 1998〕 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: : == References == 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Matter-dominated era」の詳細全文を読む スポンサード リンク
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