Past eternal universe in inflationary models

[skydivephil]

Assuming inflation is true, we have this paper by Guth, Valenkin and Borde:
http://cdsweb.cern.ch/record/521154
which says that inflation can't be past eternal

and then we have this paper saying it can be made past eternal:
http://arxiv.org/abs/gr-qc/0301042

Can anyone explain to me the discrepancy in layman terms?

 

[Chronos]

Difference of opinon among respectable scientists. The eternal bounce scenario is not appealing because it inadequately explains how energy is recovered between cycles, imo.

 

[skydivephil]

Thanks for that Chronos, can you describe in layman terms what are the different assumptions that lead them to the different conclusions? is there a consensus on this question amonst other comsologists?