Why did the formation of particle-antiparticle pairs (such as protons and antiprotons) from gamma rays come to an end in the first second after the start of the Big Bang?
A) Expansion of the universe carried the gamma rays too far apart for them to collide and form particle-antiparticle pairs.
B) The gamma-ray energy decreased as the universe expanded.
C) The universe became transparent to radiation, so gamma rays and particles no longer interacted.
D) The formation of particle-antiparticle pairs exhausted the supply of gamma rays, preventing further formation of particle-antiparticle pairs.

Question

Quizplus · Accepted Answer

As the universe expanded, it cooled, leading to a decrease in the energy of gamma rays. This reduced energy was insufficient to create particle-antiparticle pairs.

Why Did the Formation of Particle-Antiparticle Pairs (Such as Protons