As we look at more distant regions of space, we see those regions as they existed at earlier times, but our farthest views are blocked by a "wall"-beyond which the universe is opaque. What event occurred at the time marked by this wall?
A)Electrons and protons combined to form neutral hydrogen atoms, making the universe transparent for the first time.
B)Quarks combined to form neutrons and protons, removing $\gamma$ -ray absorbers for the first time.
C)Gravity froze out as a separate force.
D)Electrons and protons combined to form helium atoms, removing major absorbers of electromagnetic radiation from the universe for the first time.

Question

Quizplus · Accepted Answer

The wall that blocks our farthest views of the universe is known as the cosmic microwave background radiation (CMBR), which was created when the universe became transparent for the first time. Before this event, the universe was filled with a hot, dense, ionized plasma that absorbed all electromagnetic radiation. As the universe expanded and cooled, electrons and protons combined to form neutral hydrogen atoms, which no longer interacted with this radiation, making the universe transparent for the first time. The CMBR is the afterglow of this event and provides important evidence for the Big Bang theory.

As We Look at More Distant Regions of Space, We γ\gammaγ

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