Which of these statements does NOT correctly describe the universe at the era of recombination?
A) The temperature of the universe was about 3 K.
B) The universe was about 380,000 years old.
C) The universe became transparent to radiation.
D) Electrons and protons combined to form neutral hydrogen atoms.

Question

Quizplus · Accepted Answer

The era of recombination occurred when the universe cooled enough for electrons and protons to combine and form neutral hydrogen atoms, making the universe transparent to radiation. This happened when the universe was about 380,000 years old, but the temperature was around 3000 K, not 3 K. The 3 K temperature is associated with the current temperature of the cosmic microwave background radiation, not the era of recombination.

Which of These Statements Does NOT Correctly Describe the Universe