I am thinking of a time period between two events: 1. After the annihilation of most protons/neutrons with all anti-protons/anti-neutrons, and 2. Before the annihilation of electrons and positrons.During this period the temperature decreases from T1 to T2. T1 is the highest temperature at which (almost?) no photons have the (approximate?) energy equivalent of two protons. T2 is the lowest temperature at which (almost?) all photons have the (approximate?) energy equivalent of two electrons. Also during this period there are no anti-protons/anti-neutrons, and a great many electrons and positrons. I would much appreciate some help in calculating how the ratio between the number of electrons and the number of protons decreases as a function of the decreasing temperature.