New Guth paper-reviewing by-now-familiar scenario

[marcus]

new Guth paper--reviewing by-now-familiar scenario

http://arxiv.org/abs/hep-th/0702178
Eternal inflation and its implications
Alan H. Guth
21 pages, 5 figures. Talk presented at the "2nd International Conference on Quantum Theories and Renormalization Group in Gravity and Cosmology (IRGAC 2006)," Barcelona, Spain, 11-15 July 2006, to be published in J. Phys. A

"I summarize the arguments that strongly suggest that our universe is the product of inflation. The mechanisms that lead to eternal inflation in both new and chaotic models are described. Although the infinity of pocket universes produced by eternal inflation are unobservable, it is argued that eternal inflation has real consequences in terms of the way that predictions are extracted from theoretical models. The ambiguities in defining probabilities in eternally inflating spacetimes are reviewed, with emphasis on the youngness paradox that results from a synchronous gauge regularization technique. Although inflation is generically eternal into the future, it is not eternal into the past: it can be proven under reasonable assumptions that the inflating region must be incomplete in past directions, so some physics other than inflation is needed to describe the past boundary of the inflating region."

 

[heusdens]

Although inflation is generically eternal into the future, it is not eternal into the past: it can be proven under reasonable assumptions that the inflating region must be incomplete in past directions, so some physics other than inflation is needed to describe the past boundary of the inflating region."

Even if the calculated past is not eternal (as calculated by some method) is there any possible way of having an upper bound defined at which inflation started?

If no such upper bound can be given, it means inflation did not have to start somewhere in the past.

 

[marcus]

.. is there any possible way of having an upper bound defined at which inflation started?
..

Yes. what one calculates depends on the QG model one uses.

If one uses LQC then the model evolves deterministically back in time, through the epoch where the classical singularity was, into an epoch of gravitational collapse.

In this model, inflation starts at the time of the bounce: that is, about 14 billion years ago.

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To clarify: I didn't post Guth's abstract because I think his ideas are reasonable or persuasive. Personally I don't find 'eternal inflation' very convincing.
It's as if some people---Guth, Linde---got one good idea 30 years ago and can't stop talking about it, so it gets kind of magnified in importance, for them.
I posted the abstract because some people DO find eternal inflation, bubbles etc etc, appealing so that a new Guth paper about it could be of interest to them.