The Wikipedia article on the subject is quite good:kashiark said:What exactly is cosmological inflation? Just a hypothesis that the rate of expansion is increasing? What is negative-pressure vacuum energy density? If the universe is expanding faster than the speed of light, how do any photons reach us from anywhere other than our sun? Thanks in advance!
Cosmological inflation is a theory that proposes the rapid expansion of the universe in the first fraction of a second after the Big Bang. It suggests that during this time, the universe expanded at an exponential rate, increasing its size by an enormous amount. This theory helps explain certain observations in the universe, such as the uniformity of the cosmic microwave background radiation and the large-scale structure of the universe.
According to the theory, a hypothetical field called the inflaton field was responsible for driving the rapid expansion of the universe. As the field expanded, it released large amounts of energy, causing the universe to expand at an exponential rate. This expansion stopped when the field decayed, and the energy was converted into particles and radiation.
One of the main pieces of evidence for inflation is the observed uniformity of the cosmic microwave background radiation. This radiation is a remnant of the Big Bang and is expected to have a uniform distribution. Inflation also helps explain the large-scale structure of the universe, such as the formation of galaxies and galaxy clusters.
While there is strong evidence supporting the theory of inflation, there are also some challenges. One of the biggest challenges is the lack of direct observational evidence for the inflaton field. Some scientists also question the initial conditions required for inflation to occur and the potential for the theory to be tested by future observations.
Cosmological inflation is often considered an extension of the Big Bang theory. It helps explain certain observations that the Big Bang theory alone cannot, such as the uniformity of the cosmic microwave background radiation. Inflation does not replace the Big Bang theory but rather provides a mechanism for the rapid expansion of the universe in its early stages.