What are e-foldings and how are they used in various fields of study?

[Mordred]

I've tried several searches on the term e-foldings, However I've been unable to find any decent write ups on the terminology or calculations. Surprisingly even Wiki doesn't have much on the subject.

 

[Drakkith]

Well, let's look at two articles from wiki.

First: http://en.wikipedia.org/wiki/E_folding

In science, e-folding is the time interval in which an exponentially growing quantity increases by a factor of e; it is the base-e analog of doubling time. This term is often used in theoretical physics, especially when cosmic inflation is investigated. Physicists often talk about the e-folding time scale that is determined by the proper time in which the length of a patch of space or spacetime increases by the factor e mentioned above.

Second: http://en.wikipedia.org/wiki/E_(mathematical_constant)

The number e is an important mathematical constant, approximately equal to 2.71828, that is the base of the natural logarithm.

If I'm reading this correctly, it appears that e-folding is simply the amount of time it takes for space to expand by approximately 2.71828 times its original size. Does that help at all?

 

[Mordred]

Ah yeah it does the second link provided the details I needed. I couldn't figure out how they derived the 2.71828 value thanks so much

 

[marcus]

Quite right! And log_e 10 = 2.3
So 60 e-folds is the same as 26 "ten-folds"

Distances increasing by a factor of e⁶⁰ is the same as their increasing
by a factor of 10²⁶