For many years, cosmologists believed that the universe from the very beginning looked like an expanding ball of fire. This explosive beginning of the universe was called the big bang. Fifteen years ago a different scenario of the universe evolution was proposed. The main idea of the new scenario was that the universe at the very early stages of its evolution came through the stage of inflation, exponentially rapid expansion in an unstable vacuum-like state. As a result, the universe within a very short time became exponentially large. At the end of inflation the energy of the vacuum-like state rapidly transformed into thermal energy, the universe became hot, and its subsequent evolution could be described by the standard big bang theory.
Updated on March 17, 2020