Chapter 15.2 Today we traced the history of the Universe from the Big Bang up until almost the present day. Temperature is unimaginably hot. Temperature is unimaginably hot. Electrons and nuclei combine to form atoms.
Photons escape, forming cosmic microwave background.
To present Formation of galaxies, clusters and all the structure in the Universe. What happens is that the Universe expands, and as it does so, it cools. As the temperature decreases, so the concentration of energy decreases. As the energy decreases, first the forces are formed and then matter is formed. First it is simple matter, but then more complex matter can be formed.