Scale factor (Universe)
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>
where:
- <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 cosmology astronomy
