1. FIRST FRAME. t = 10 -2 s »T = 10 11 K »Density (mostly radiation, not matter) = 4x10 9 times the density of water. »Average photon energy is 10 MeV (1 eV = 1.6x10 -19 J) »BUT, only one “nucleon” (neutron or proton) for every 10 9 photon (still true now). »Pair production occurs for E > 1.022 MeV, so antielectrons are common. »Neutrinos and antineutrinos are also common. »Mass-energy of “nucleons” is 938 MeV, so protons and neutrons are common. »Neutron/proton mass difference is about 1 MeV, so equal numbers of each. »Equality maintained by collisions with electrons and “neutrinos”.

2. SECOND FRAME. t = 10 -1 s »T = 3x10 10 K »Density = 3x10 7 times the density of water. »Average photon, electron, neutrino energies too small to maintain exact n/p balance. »Now about 62% protons and 38% neutrons.

3. THIRD FRAME. t = 1 s »T = 10 10 K »Density = 4x10 5 times the density of water. »Neutrinos “decouple” (Note: this means there is a cosmic neutrino background!) »Now about 76% protons and 24% neutrons. »Still too hot for nuclei to form!

4. FOURTH FRAME. t = 10 s »T= 3x10 9 K »Photon energies too small to create pairs, so antielectrons begin to disappear rapidly. »Now about 83% protons and 17% neutrons. »Stable nuclei (like helium) could exist, if they were formed. »BUT, formation of He delayed due to fragility of “deuterium” ( 2 H)

5. FIFTH FRAME. t = 100 s »T = 10 9 K »Now about 87% protons and 13% neutrons. »Decay of the free neutron important (10% decay every 100 s) »Deuterium bottleneck passed…elements rapidly cooked up (to Be). »Heavier elements not made due to stability gaps at mass 5 and mass 8. »Fraction of 4 He by weight = 26%