The cosmic microwave background radiation was emitted when the universe had a size about 1/1,000 of today's value.What was the temperature of the microwave background radiation at the epoch of recombination?
A) 30 K
B) 300 K
C) 3000 K
D) 30,000 K
E) 300,000 K

Question

Quizplus · Accepted Answer

The temperature of the cosmic microwave background radiation at the epoch of recombination was approximately 3000 K. This is when electrons and protons combined to form neutral hydrogen, allowing photons to travel freely.

The Cosmic Microwave Background Radiation Was Emitted When the Universe