Multiple Choice
When did the universe cool to a temperature of 3 K?
A) 1 second after the start of the Big Bang, when pair production ceased
B) 500,000 years after the Big Bang, when the universe became transparent to radiation
C) 3 minutes after the start of the Big Bang, when primordial nuclear reactions ceased
D) very recently
Correct Answer:
Verified
Correct Answer:
Verified
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