The existence of the cosmic microwave background radiation tells us that the early universe was:
A) much hotter than it is today.
B) much colder than it is today.
C) composed entirely of radiation at early times.
D) composed entirely of stars at early times.

Question

Quizplus · Accepted Answer

The cosmic microwave background radiation is an afterglow of the big bang, which was a hot and dense event. Therefore, the existence of this radiation tells us that the early universe was much hotter than it is today.

The Existence of the Cosmic Microwave Background Radiation Tells Us