The photons from the microwave background have not interacted with matter since theuniverse was how old?
A)4,000,000,000 years old
B)4,000,000 years old
C)400,000 years old
D)4,000 years old
E)4 seconds old

Question

Quizplus · Accepted Answer

The photons from the microwave background have not interacted with matter since the universe was around 400,000 years old. This is when the universe became transparent, allowing photons to travel freely through space without being absorbed or scattered by matter. The photons from the cosmic microwave background were last scattered by matter when the universe was about 400,000 years old. This is known as the time of recombination, when the universe became transparent to radiation and the photons were able to travel freely without scattering off of charged particles.

The Photons from the Microwave Background Have Not Interacted with Matter