Scale factor (cosmology)

Expansion of the universe parameter

The expansion of the universe is parametrized by a dimensionless scale factor a {\displaystyle a} . Also known as the cosmic scale factor or sometimes the Robertson–Walker scale factor, this is a key parameter of the Friedmann equations. In the early stages of the Big Bang, most of the energy was in the form of radiation, and that radiation was the dominant influence on the expansion of the universe.

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