Scale factor (cosmology)

The scale factor is a parameter of the cosmological Friedmann - Lemaître - Robertson -Walker model. It is a function of time, and outputs the relative expansion of the universe, ie it Establishes a relationship between physical coordinates and comoving coordinates L:

The scale factor can, in principle, the unit of length or dimensionless. In modern cosmology, it is usually chosen dimensionless, so that:

Where t of the origin of the universe is measured, and the present age of the universe ( 13.7 ± 0.2 ) billion years represents.

The temporal evolution of the scale factor is determined by the formulas of general relativity, which are represented by the Friedmann equations in the case of a locally isotropic and locally homogeneous universe.

The scale factor and its temporal change define the Hubble parameter: