What was the temperature of the universe at the time the universe became transparent to radiation?
A) 300,000 K
B) 30 billion K
C) 3 K
D) 3000 K

Question

Quizplus · Accepted Answer

The universe became transparent to radiation at a temperature of about 3000 K, a period known as the recombination era, when electrons and protons combined to form neutral hydrogen, allowing photons to travel freely.

What Was the Temperature of the Universe at the Time