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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Dark-energy-dominated era ： ウィキペディア英語版 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.〔Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.33〕 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: :$a(t)\backslash propto\; \backslash exp(Ht)$ Here, the coefficient ''H'' in the exponential, the Hubble constant, is :$H\; =\; \backslash sqrt\; =\; \backslash sqrt.$ 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 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「Dark-energy-dominated era」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.