Cosmological inflation is a theory in cosmology that proposes a rapid and exponential expansion of the universe in the first fraction of a second after the Big Bang. It is believed to have occurred due to a hypothetical field called the inflaton field, which caused the universe to expand faster than the speed of light.
One of the main pieces of evidence for cosmological inflation is the observation of the cosmic microwave background radiation, which is the leftover radiation from the Big Bang. The pattern of this radiation supports the idea of inflation, as it shows a near-perfectly uniform distribution across the entire universe.
The horizon problem is the issue of how different regions of the universe, which are now too far apart to have ever been in contact, have the same temperature. Inflation solves this problem by allowing these regions to have been in contact before the rapid expansion, thus explaining the uniformity of the cosmic microwave background.
Yes, there are various models of cosmological inflation that have been proposed to explain different aspects of the universe. Some of the most well-known models include the chaotic inflation model, the new inflation model, and the eternal inflation model.
The multiverse theory suggests that there are multiple universes, each with its own set of physical laws and properties. Inflation is often used to explain the existence of these parallel universes, as the rapid expansion during inflation could have created "bubbles" that eventually became separate universes with their own unique properties.