4.2. Relic abundances

The rapid expansion of the inflationary stage rapidly dilutes the unwanted relic particles, because the energy density during inflation falls off more slowly (as a^-2 or slower) than the relic particle density. Very quickly their density becomes negligible.

This resolution can only work if, after inflation, the energy density of the Universe can be turned into conventional matter without recreating the unwanted relics. This can be achieved by ensuring that during the conversion, known as reheating, the temperature never gets hot enough again to allow their thermal recreation. Then reheating can generate solely the things which we want. Such successful reheating allows us to get back into the hot big bang Universe, recovering all its later successes such as nucleosynthesis and the microwave background.