What significant event occurred about 400,000 years after the start of the Big Bang?
A) All of the galaxies seen today formed.
B) Electrons and nuclei combined to form neutral atoms.
C) Quarks became confined.
D) The formation of helium stopped.

Question

Quizplus · Accepted Answer

About 400,000 years after the Big Bang, the universe cooled enough for electrons and nuclei to combine and form neutral atoms, a period known as recombination. This event allowed photons to travel freely, leading to the cosmic microwave background radiation we observe today.

What Significant Event Occurred About 400,000 Years After the Start