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In physical cosmology, the age of the universe is the time elapsed since the Big Bang. The current measurement of the age of the universe is billion years ( years) within the Lambda-CDM concordance model.〔 〕〔C. R. Lawrence, JPL, for the Planck Collaboration, Astrophysics Subcommittee, NASA HQ (18 March 2015) "Planck 2015 Results" (See page 29 of pdf) http://science.nasa.gov/media/medialibrary/2015/04/08/CRL_APS_2015-03-18_compressed2.pdf〕〔http://www.teachastronomy.com/astropedia/article/Precision-Cosmology〕 The uncertainty of 21 million years has been obtained by the agreement of a number of scientific research projects, such as microwave background radiation measurements by the Planck satellite, the Wilkinson Microwave Anisotropy Probe and other probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time. == Explanation == The Lambda-CDM concordance model describes the evolution of the universe from a very uniform, hot, dense primordial state to its present state over a span of about 13.8 billion years of cosmological time. This model is well understood theoretically and strongly supported by recent high-precision astronomical observations such as WMAP. In contrast, theories of the origin of the primordial state remain very speculative. If one extrapolates the Lambda-CDM model backward from the earliest well-understood state, it quickly (within a small fraction of a second) reaches a singularity called the "Big Bang singularity". This singularity is not understood as having a physical significance in the usual sense, but it is convenient to quote times measured "since the Big Bang" even though they do not correspond to a physically measurable time. For example, "10−6 seconds after the Big Bang" is a well-defined era in the universe's evolution. If one referred to the same era as "13.8 billion years minus 10−6 seconds ago", the precision of the meaning would be lost because the minuscule latter time interval is swamped by uncertainty in the former. Though the universe might in theory have a longer history, the International Astronomical Union〔 〕 presently use "age of the universe" to mean the duration of the Lambda-CDM expansion, or equivalently the elapsed time since the Big Bang in the current observable 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「Age of the universe」の詳細全文を読む スポンサード リンク
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