I How Can Data Constrain the Number of e-Folds During Inflation?

[windy miller]

Is there any way to constrain with data how many e folds went on during inflation ( or during our era of inflation in the case of eternal inflation)?

 

[bapowell]

Is there any way to constrain with data how many e folds went on during inflation ( or during our era of inflation in the case of eternal inflation)?

There's no way to collect data on inflation that occurred prior to the last 60 e-folds or so, since such length scales are outside today's cosmological horizon.

 

[kimbyd]

Sort of. It depends upon the inflation model.

Basically, for a given inflation model, different numbers of e-folds of inflation result in different spectral tilt (that is, the power spectrum's shape is slightly altered by the number of e-folds).

However, this can't be done in general. This depends upon a very specific model of inflation. Other models, with other dynamics, will show very different numbers in terms of the number of e-folds. I'm not currently aware of any methodology to measure the number of e-folds directly.

 

[Chronos]

Most theorists would agree no less than 50 e-folds are necessary, many prefer 60.

 

[bapowell]

It's not so much a matter of it being "necessary"...when you begin considering fewer than 50 efolds or so, you begin to have real problems satisfying the flatness and entropy constraints.

 

[Chronos]

I mean necessary in the sense of modeling a universe consistent with the observational constraints you hint at.