In this frame the particle horizon is seen to shrink.
So, the picture during inflation is that the spacetime background expands at an accelerating pace.
This resolves the horizon problem, since causal regions in the early universe are stretched to regions much larger than the Hubble distance..
The most significant assumption is that very shortly after the Big Bang, the universe expanded very rapidly for a short period of time.
Much faster than normal expansion due to Big Bang.
It was an exponential expansion and occurred around 10−32 seconds after Big Bang and lasted for tiny fraction of second..
Inflation is now considered an extension of the Big Bang theory since it explains the above puzzles so well, while retaining the basic paradigm of a homogeneous expanding universe.
Moreover, Inflation Theory links important ideas in modern physics, such as:
The Cosmic Inflation Theory was developed by particle physicist Alan Guth during the early 1980s to deal with the three problems presented by the Big Bang Theory.
He theorized that the reason why the Universe appears to be flat is because of the extremely fast rate at which it grew.
The inflationary universe theory suggests that the early universe experienced a time of rapid and exponential expansion.
This period of expansion occurred before the expansion that would be called the “Big Bang.” .
