What dictates the temperature of a universe plunged into absolute darkness without stars?

Answer

The Cosmic Microwave Background (CMB)

In the absence of energetic input from fusion, the universe's temperature would be dictated by the ancient relic left over from the Big Bang, the CMB, currently measuring about 2.725 Kelvin.

What dictates the temperature of a universe plunged into absolute darkness without stars?

#Videos

Could Life Survive Without a Star? - YouTube

Planets Without Stars – Hidden Worlds in the Galaxy - YouTube

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