Because of the travel time of light,we see more distant parts of the universe as they were when the universe was younger,but we 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 we can see as we look out into the universe?
A) 1/1,000,000 seconds after the start of the Big Bang
B) 500,000 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 we can see using photons is the Cosmic Microwave Background Radiation (CMB), which was emitted about 380,000 years after the Big Bang. However, it took about 500,000 years for the universe to become transparent to photons, so any radiation emitted before that was scattered by charged particles in the universe and cannot be seen directly. Therefore, B) 500,000 years after the start of the Big Bang is the best choice for the furthest back in time that we can see using photons.

Because of the Travel Time of Light,we See More Distant