where is the physical distance, is the distance in comoving units, and is the scale factor.
The scale factor could, in principle, have units of length or be dimensionless. Most commonly in modern usage, it is chosen to be dimensionless, with the current value equal to one: , where t is counted from the birth of the universe and is the present age of the universe: .
The evolution of the scale factor is a dynamical question, determined by the equations of general relativity, which are presented in the case of a locally isotropic, locally homogeneous universe by the Friedmann equations.
The Hubble parameter is defined:
where the dot represents a time derivative.
External links
This article is licensed under the GNU Free Documentation License.
Last updated on Monday June 23, 2008 at 01:26:14 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
where is the physical distance, is the distance in comoving units, and is the scale factor.
The scale factor could, in principle, have units of length or be dimensionless. Most commonly in modern usage, it is chosen to be dimensionless, with the current value equal to one: , where t is counted from the birth of the universe and is the present age of the universe: .
The evolution of the scale factor is a dynamical question, determined by the equations of general relativity, which are presented in the case of a locally isotropic, locally homogeneous universe by the Friedmann equations.
The Hubble parameter is defined:
where the dot represents a time derivative.
External links
This article is licensed under the GNU Free Documentation License.
Last updated on Monday June 23, 2008 at 01:26:14 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
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