Radiation-Dominated Era
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The Radiation-Dominated Era refers to one of the three phases of the known universe, the other two being the Matter-Dominated Era and the Dark Energy Dominated Era. The Radiation-Dominated Era occurred from 3 seconds after the universe's creation until it was about 380,000 years old. The era is marked by radiation being the primary force in the universe.
For a radiation dominated universe the evolution of the scale factor in the Friedmann-Lemaitre-Robertson-Walker metric is easily obtained solving the Friedmann equations: