Because of the travel time of light, astronomers see more distant parts of the universe as they were when the universe was younger, but they cannot see back "into" times when the universe was opaque and light could not travel freely. Using photons, then, what is the furthest back in time that astronomers can when they look out into the universe?
A) 1/1 millionth seconds after the start of the Big Bang
B) 380,000 years after the start of the Big Bang
C) 3 minutes after the start of the Big Bang
D) 3000 years after the start of the Big Bang

Question

Quizplus · Accepted Answer

The furthest back in time that astronomers can see using photons is 380,000 years after the start of the Big Bang. This is when the universe cooled enough for protons and electrons to combine into neutral hydrogen, making the universe transparent to light for the first time.

Because of the Travel Time of Light, Astronomers See More