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This thread is distinct from discussion of the mainstream media coverage of the letter that just appeared in Nature Physics.
I just want to get more precise about the actual issues.
So far, not having a subscription, I don't have access to the advance online publication in Nature Physics (NP), but there is a preprint of a longer article at arxiv which cites the letter and mentions some relevant conclusions.
http://arxiv.org/abs/0706.1057
Effective equations for isotropic quantum cosmology including matter
Martin Bojowald, Hector Hernandez, Aureliano Skirzewski
42 pages
The NP letter is reference [29] in this paper. See for example pages 34 and 37
==quote==
...In such a situation, it is important to know the precise state,
i.e. all parameters c1, c2, α1, α2, δ1 and δ2, in order to determine the quantum nature of
the bounce. However, the relevant squeezing parameters cannot be fully determined from
using the state at only one side of the bounce [29] due to exponential suppression factors
of some of the integration constants in (29)–(32) if one restricts φ to a fixed sign. Thus,
the precise quantum nature of the bounce may always depend on what assumptions one
makes for a state...
...
At first perturbative order, there is no strong back-reaction for a Wheeler-DeWitt quantization,
or for most of a single collapsing or expanding branch in a loop quantization.
But quantum back-reaction effects are noticeable for squeezed states around
the bounce of loop quantum cosmology due to the influence of the growing branch on the
collapsing one. Since squeezing parameters of a bouncing state are not determined by
properties in one of the two large volume regime only [29], no general statement about
the presence of a semiclassical bounce is available. There are quantum parameters whose
influence is negligible at large volume but which will become important near a bounce and
determine its fate.
==endquote==
I just want to get more precise about the actual issues.
So far, not having a subscription, I don't have access to the advance online publication in Nature Physics (NP), but there is a preprint of a longer article at arxiv which cites the letter and mentions some relevant conclusions.
http://arxiv.org/abs/0706.1057
Effective equations for isotropic quantum cosmology including matter
Martin Bojowald, Hector Hernandez, Aureliano Skirzewski
42 pages
The NP letter is reference [29] in this paper. See for example pages 34 and 37
==quote==
...In such a situation, it is important to know the precise state,
i.e. all parameters c1, c2, α1, α2, δ1 and δ2, in order to determine the quantum nature of
the bounce. However, the relevant squeezing parameters cannot be fully determined from
using the state at only one side of the bounce [29] due to exponential suppression factors
of some of the integration constants in (29)–(32) if one restricts φ to a fixed sign. Thus,
the precise quantum nature of the bounce may always depend on what assumptions one
makes for a state...
...
At first perturbative order, there is no strong back-reaction for a Wheeler-DeWitt quantization,
or for most of a single collapsing or expanding branch in a loop quantization.
But quantum back-reaction effects are noticeable for squeezed states around
the bounce of loop quantum cosmology due to the influence of the growing branch on the
collapsing one. Since squeezing parameters of a bouncing state are not determined by
properties in one of the two large volume regime only [29], no general statement about
the presence of a semiclassical bounce is available. There are quantum parameters whose
influence is negligible at large volume but which will become important near a bounce and
determine its fate.
==endquote==
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