- TL;DR Summary
- The model of eternal cosmological inflation states that once inflation begins, it generically never ends. But in any patch of space within this eternal inflating universe, inflation always effecively ends after a finite amount of time. From cosmological data we can only deduce a minimum amount of time (or e-foldings) must have happened before our universe was formed, but is there any data or anything within the theory that can tell us anything about how long inflation has lasted?
In so far I know eternal inflation can only constraint the minimum duration that inflation happened to produce the properties of the universe we can experimentally test (a minimum of some 60 e-folds, or in time, at least some 10^-30 seconds), but as eternal inflation is generically eternal to the future, is there some upper bound to the duration of the inflationary process, is there any theoretical or experimental data that can constraint the upper bound, or is that duration unbounded (can grow to infinity)?