After the Big Bang, as the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?
A) Protons and neutrons combined to form nuclei such as deuterium and helium.
B) Neutrinos ceased to interact with normal matter.
C) Dark matter ceased to interact with normal matter.
D) Photons began to travel freely through the universe.
E) Lithium and other light elements were formed by the fusion of hydrogen and helium.

Question

Quizplus · Accepted Answer

As the universe cooled and protons and electrons combined to make the universe neutral, photons began to travel freely through the universe. Before this time, photons were constantly interacting with charged particles, which prevented them from freely moving through space. This allowed the Cosmic Microwave Background Radiation to be released, which we observe today as the afterglow of the Big Bang.

After the Big Bang, as the Universe Cooled and Protons