As the temperature in the early universe decreased, pair production reactions were confined to particles of smaller and smaller mass while annihilation reactions were unaffected. Why this difference?
A)Particles and antiparticles contain a certain amount of mass-energy independent of their temperature whereas the energy of a photon depends on its temperature.
B)Photons contain a certain amount of mass-energy independent of their temperature whereas the energy of particles and antiparticles depend on its temperature.
C)When particles collide, the interaction raises their temperature, but this does not happen when gamma-ray photons interact.
D)When gamma-ray photons collide, the interaction raises their temperature, but this does not happen when particles interact.

Question

Quizplus · Accepted Answer

Particles and antiparticles have a rest mass that determines the minimum energy (related to temperature) required for their creation. Photons, being massless, have energies that can vary with temperature, but this doesn't affect their existence in the same way it does for massive particles.

As the Temperature in the Early Universe Decreased, Pair Production