What is the cosmic microwave background radiation?
A) uniform background of radiation from electrons spiraling in weak intergalactic magnetic fields
B) radiation left over from the Big Bang after the universe expanded and cooled
C) almost uniform background of radiation from distant, unresolved, overlapping galaxies
D) radiation from a very tenuous, ionized gas that fills the universe equally in all directions

Question

Quizplus · Accepted Answer

The cosmic microwave background radiation is the afterglow radiation left over from the Big Bang. It is the remnant heat from the time the universe became cool enough for protons and electrons to combine into neutral atoms, leading to the photons being able to travel freely through space. This event significantly cooled the universe, leaving behind the cosmic microwave background radiation as a snapshot of the infant universe.

What Is the Cosmic Microwave Background Radiation