Updated: October 21, 2020
Inflation (Cosmic) is a theory put forth (originally, by Alan Guth in his 1980 paper) to explain why, if the universe is full of mass, is it not curved in some way? Instead, it’s flat (see: Curvature).
This isotropy in its temperature/geometry seems to contradict Thermodynamics in that we should see varying pockets of temperature around us since it would take time for the heat to dissipate throughout the universe.
The theory of Cosmic Inflation gets around this issue by stating that the baby universe expanded faster than light, which prevented anisotropy.
Faster than light expansion? #
FTL expansion is possible with a loophole in Einstein’s General theory: light’s speed limit only applies to things within the universe, not the universe itself. The difference is subtle.
If you accept the theory of Inflation you must also accept (at least in its current incancation) its corrolaries: multiverses.