In physical cosmology the inflationary epoch was the period in the evolution of the early universe when, according to inflation theory, the universe underwent an extremely rapid exponential expansion. This rapid expansion increased the linear dimensions of the early universe by a factor of at least 1026 (and possibly a much larger factor), and so increased its volume by a factor of at least 1078.
The expansion is thought to have been triggered by the phase transition that marked the end of the preceding grand unification epoch at approximately 10−36 seconds after the Big Bang. One of the theoretical products of this phase transition was a scalar field called the inflaton field. As this field settled into its lowest energy state throughout the universe, it generated a repulsive force that led to a rapid expansion of the fabric of space-time. This expansion explains various properties of the current universe that are difficult to account for without such an inflationary epoch.
It is not known exactly when the inflationary epoch ended, but it is thought to have been between 10−33 and 10−32 seconds after the Big Bang. The rapid expansion of space meant that elementary particles remaining from the grand unification epoch were now distributed very thinly across the universe. However, the huge potential energy of the inflation field was released at the end of the inflationary epoch, repopulating the universe with a dense, hot mixture of quarks, anti-quarks and gluons as it entered the electroweak epoch.