From what cosmic epoch do the photons in the cosmic background radiation originate?
A)the end of the Planck era
B)during the era of nucleosynthesis
C)during the era of galaxy formation
D)the end of the era of nuclei
E)the moment of the Big Bang

Question

Quizplus · Accepted Answer

The photons in the cosmic background radiation originate from the end of the era of nuclei, when the universe cooled enough for electrons to combine with nuclei to form neutral atoms, allowing photons to travel freely.

From What Cosmic Epoch Do the Photons in the Cosmic