The inflation theory states that for a brief period of time following the Big Bang, the universe expanded at an exponential rate. This period of time is said to have lasted from 10-36 seconds after the Big Bang to between 10-33 and 10-32 seconds. This is a mind-bogglingly brief period of time. Following this period of inflation, the universe continued to expand, but at a slower rate.
In January 1980, M.I.T. physicist Alan Guth proposed the inflation theory in an attempt to explain the lack of magnetic monopoles in the universe. It was Guth who proposed that as the early universe began to cool, it became trapped in a false vacuum with high energy density. His theory became known as “old inflation” when Andrei Linde, Andreas Albrecht and Paul Steinhardt created an updated model known as “slow-roll” or “new inflation.” In 2002, Guth, Linde, and Steinhardt were awarded the Dirac Prize for their contributions to the development of inflation theory.
The inflation theory is instrumental in explaining the cosmological principle, the notion that the distribution of matter in the universe is both homogeneous and isotropic. In other words, the part of the universe that humans can observe is representative of the universe as a whole, and that physical laws apply equally everywhere. Sir Isaac Newton was the first to express the cosmological principle.