This question already has an answer here:
I know that thermodynamics 3rd law states that if a system in equilibrium is at zero temperature, its entropy is minimum.
Expansion of the universe made a transition from radiation dominated era (rde) to matter dominated era(mde). So the same question here occurred to me as well. But the answers did not satisfy me indeed. How is it possible that rde had lower entropy than today even if it was at higher temperature in the very early beginning of the universe? Isn't there any contradiction here?