At present, the energy density of matter greatly exceeds that of radiation. But in the early universe, radiation energy was dominant. Why was this?
A)Dark matter had not yet formed to add to the matter energy density.
B)The radiation temperature was high enough to prevent the transformation of radiation into matter; photon Y matter + antimatter.
C)Radiation was at a much greater temperature (and energy) and density than now.
D)Large numbers of antiparticles existed and combined with matter particles to form photons.

Question

Quizplus · Accepted Answer

In the early universe, the temperature and energy density of radiation were much higher than they are now, which made radiation energy dominant over matter energy.

At Present, the Energy Density of Matter Greatly Exceeds That