The CMB is a snapshot of the radiation in the universe at a redshift of z $\approx$1,000 when the universe was:
A) 1,000 times smaller than it is today
B) 10 times smaller than it is today
C) two times smaller than it is today
D) the same size as it is today
E) 10 times larger than it is today

Question

Quizplus · Accepted Answer

The redshift z is a measure of how much the universe has expanded since the CMB was emitted. A redshift of z=1,000 means the universe was 1,000 times smaller than it is today. Therefore, the best choice is A, where the universe was 1,000 times smaller than it is today when the CMB was emitted.

The CMB Is a Snapshot of the Radiation in the Universe