Astrophysics (Index)About

radiation era

(radiation-dominated era, primordial fireball)
(early universe era when radiation pressure dominated)

Radiation era (aka radiation-dominated era or primordial fireball) refers to a period after the Big Bang when the energy density of electromagnetic radiation was greater than the energy density of matter. As the universe expanded, some thousands of years after the Big Bang (one source says 47,000 years), this reversed, and subsequent time is termed the matter era or matter-dominated era. As the universe expanded, radiation energy density changed at a rate proportional to R-4 whereas that of matter changed at a rate proportional to R-3, allowing for the reversal (where R is the scale factor, an increasing number indicating the relative size of the universe as time passes).


(cosmology)
Further reading:
https://en.wikipedia.org/wiki/Scale_factor_(cosmology)#Radiation-dominated_era
https://pages.uoregon.edu/jimbrau/astr123/Notes/Chapter27.html

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