Inflationary Theory is a concept in cosmology that suggests the universe underwent a rapid expansion shortly after the Big Bang. This expansion, which occurred in a fraction of a second, helped to explain the uniformity of the universe and the distribution of galaxies. It proposes that the universe expanded exponentially, smoothing out any irregularities. The theory was first introduced by physicist Alan Guth in the 1980s. It addresses several key issues in cosmology, such as the flatness problem and the horizon problem, by suggesting that this rapid inflationary phase created the large-scale structure we observe today.