What is the ratio of cosmic microwave background photons to hydrogen atoms,on average,in our universe?
A) about 1 billion to 1
B) about 1 million to 1
C) about 1 to 100-very few microwave photons
D) about 1 to 1-equal numbers of photons and H atoms

Question

Quizplus · Accepted Answer

The cosmic microwave background (CMB) is a relic from the early universe, and there are about 1 billion CMB photons for every hydrogen atom. This high ratio is due to the universe's expansion and cooling, which has left a vast number of photons from the Big Bang.

What Is the Ratio of Cosmic Microwave Background Photons to Hydrogen