cosmic scale factor

Symbol: R. A measure of the size of the Universe as a function of time. R is related to the redshift parameter, z, by 1 + z = R (t ₀ )/R (t ₁ )

where t ₀ is the present time and t ₁ is the time at emission of the radiation. The quantity (1 + z) thus gives the factor by which the Universe has expanded in size between the time t ₁ and the present, t ₀. The proper distance between the origin and a point at a comoving coordinate r (i.e. in a system expanding with the Universe) is given by the product of R (t) and sin^–1r, r, or sinh^–1r depending on whether the Universe is closed, Euclidean, or open, respectively. R is also related to the Hubble constant H ₀ :

H ₀ = R ^–1(dR /dt )

单词	cosmic scale factor
释义	cosmic scale factor cosmic scale factor Symbol: R. A measure of the size of the Universe as a function of time. R is related to the redshift parameter, z, by 1 + z = R (t ₀ )/R (t ₁ ) where t ₀ is the present time and t ₁ is the time at emission of the radiation. The quantity (1 + z) thus gives the factor by which the Universe has expanded in size between the time t ₁ and the present, t ₀. The proper distance between the origin and a point at a comoving coordinate r (i.e. in a system expanding with the Universe) is given by the product of R (t) and sin^–1r, r, or sinh^–1r depending on whether the Universe is closed, Euclidean, or open, respectively. R is also related to the Hubble constant H ₀ : H ₀ = R ^–1(dR /dt )
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