Editing Cosmic inflation (section)

== Overview ==
{{main|Expansion of the universe|Inflaton}}
Around 1930, [[Edwin Hubble]] discovered that light from remote galaxies was [[redshift]]ed; the more remote, the more shifted. This implies that the galaxies are receding from the Earth, with more distant galaxies receding more rapidly, such that galaxies also recede from each other. This [[expansion of the universe]] was previously predicted by [[Alexander Friedmann]] and [[Georges Lemaître]] from the theory of [[general relativity]]. It can be understood as a consequence of an initial impulse, which sent the contents of the universe flying apart at such a rate that their mutual gravitational attraction has not reversed their increasing separation.

Inflation may have provided this initial impulse. According to the [[Friedmann equations]] that describe the dynamics of an expanding universe, a [[perfect fluid|fluid]] with sufficiently negative pressure exerts gravitational repulsion in the cosmological context. A [[field (physics)|field]] in a positive-energy [[false vacuum]] state could represent such a fluid, and the resulting repulsion would set the universe into exponential expansion. This ''inflation'' phase was originally proposed by [[Alan Guth]] in 1979 because the exponential expansion could dilute exotic relics, such as [[magnetic monopoles]], that were predicted by [[grand unified theories]] at the time. This would explain why such relics were not seen. It was quickly realized that such accelerated expansion would resolve the [[horizon problem]] and the [[flatness problem]]. These problems arise from the notion that to look like it does ''today'', the Universe must have started from very [[fine tuned universe|finely tuned]], or "special", initial conditions at the Big Bang.