friend said:
I wonder if quantum gravity effects can explain Inflation after the Big Bang? For example, in Loop Quantum Gravity, there are area and volume operators and eigenvalues, etc. Would there be jumps from one volume state to another with time? Thanks.
There have been papers on both sides of this issue. As a sample, here is a list of 48 papers:
http://arXiv.org/cits/gr-qc/0403106
These are the papers that cited an early work on this by Bojowald et al.
http://arXiv.org/abs/gr-qc/0403106
My personal opinion is that a brief inflationary period does arise in LQC---and is robust or generic. But this naturally arising brief inflation is not enough to produce the "60 e-folds" typically desired for inflation scenarios.
It seems that something must be put in by hand, to get the expansion by the factor e
60 believed necessary to explain flatness and isotropy.
So what I see happening is that in recent LQC work by e.g. Ashtekar and Singh, they put in an inflaton field to get the conventional amount of inflation. The amount that is automatically occurring in the LQC models is not enough. This is just my personal view, I think opinions about it differ.
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A separate issue is whether, in LQC, you actually need e
60-fold inflation. The "horizon problem" doesn't exist in a nonsingular model with a bounce because temperature equilibrium can have been achieved prior to bounce. A major motivation for inflation scenarios, namely the CMB temperature isotropy puzzle, is no longer so pressing. Whether and how much inflation is needed remains unresolved, as far as I know.
