# How many years of expansion occurred during inflation?

During inflation, expansion happens at a very rapid rate.

How many years of expansion did it fast forward through?

Meaning, if it weren't for inflation, how many years would it take for the universe to expand at its basic rate from the big bang to the size of the universe after inflation?

• The expansion that the Universe went through during inflation isn't usually measured in 'years-at-normal-rate', presumably because it doesn't make any sense to talk about a normal rate when that's simply not what happened. It is measured in e-folds; experimental data requires that inflation lasted for about $60$ e-folds, aka the Universe expanded by a factor $e^{60}$ or more. – Danu Mar 6 '14 at 6:53
• There are a lot of different models though, and the number of e-folds they are capable of producing can easily go up to $100$ or maybe even more: we are unable to observationally tell the difference anyhow because of the limited size of the observable Universe. – Danu Mar 6 '14 at 7:20

We have few hard theories about inflation, but suppose the universe expanded by $e^{60}$ as Danu suggests in his comment, then the number of doubling times is $60/ln(2) \approx 87$. The time it will take the current universe to double in size 87 times is about 990 billion years.
You can obviously adapt this sum for whatever number of $e$-foldings your preferred theory of inflation predicts.
• @John Rennie : I am not so sure about this. $\\$ The Hubble Time, 11.4Gyrs that you refer to, is the time that it would take the universe to expand by one e-fold today. This is not a constant number, but a timescale that changes with the scale of the universe. Namely, the time that it would take the universe to expand by one e-fold tomorrow will be (slightly) bigger. So your calculation is incorrect I think. Please correct me if I am wrong... – Flint72 May 9 '14 at 15:06