The Matter Era

The Matter era one in which matter acts pretty much as it does now. It began 300 to 500 thousand years after the Big Bang, when the temperature of the background radiation had dropped to around 3000 degrees K, cooler than the surface of the sun, but still hot enough to melt and vaporise most subtsances. The universe had a radius of one and a half million light years - in other words it was much bigger than our galaxy is now (although still a tiny fraction of the size of the modern universe).

When the temperature dropped to about 3000 K, it was cool enough for electrons to form into atoms with the hydrogen and helium nuclei. The previous state of plasma no longer ensured. The lack of interaction with matter by the photons caused a sudden drop in the pressure acting on the matter. The universe becomes transparent to radiation. The radiation and the matter decouple, which means they are no longer in thermal equilibrium with each other. The universe becomes matter-dominated. Electrons and protons recombine into hydrogen atoms, and matter as we know it, with electrons circling atomic nucleis, appears.

With the radiation pressure gone it became possible for matter to collapse into stars and galaxies under gravitational attraction. Before this time the radiation pressure would have promptly re-expanded any clumps which tried to form. This was also the time about which the energy density of the radiation was exceeded by that of the matter.

The first generation of stars (population III) formed from clouds of interstellar gas. Thus began the Stelliferous era. Massive stars create the chemical elements within their cores and return them to the interstellar medium when they explode as supernovae. There is a period of element formation that lasts for some 100 million to one or two billion years.

Parting Company

The Plank Era

The Inflationary Era

The Quark-Lepton Era

The Radiation Era

The Matter Era