The existence of the cosmic 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 background radiation is leftover radiation from the Big Bang, when the universe was extremely hot and dense. The fact that it is present today indicates that the early universe was much hotter than it is now.

The Existence of the Cosmic Background Radiation Tells Us That