Encyclopedia > Scale factor

  Article Content

Scale factor

The scale factor is a variable which represents the relative expansion of the Universe. It relates physical coordinates (also called proper coordinates) to comoving coordinates.

<math> L = \lambda \; a(t) </math>


  • <math>L</math> = physical distance

  • <math>\lambda</math> = a distance in comoving units

  • <math>a(t)</math> ( lub <math>S(t)</math> ) - the scale factor

The scale factor could in principle either have length units or be dimensionless.

Most commonly in modern usage, it is chosen to be dimensionless, with

<math> a(t_0) = 1</math>
where <math>t_0</math> 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:

<math> {\dot{a}(t) \over a(t)}</math>

where the dot represents a time derivative.

See also: cosmology astronomy

All Wikipedia text is available under the terms of the GNU Free Documentation License

  Search Encyclopedia

Search over one million articles, find something about almost anything!
  Featured Article

... and 13338 are female. The population density of the community is 18 inhabitants per km². External links Ludvika (http://www.ludvika.se) - Official ...

This page was created in 24.4 ms