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Posted by Richard Ruquist on October 19, 2004 13:57:17 UTC

The link to Contrasting Cosmologies is a paper I missed, perhaps because its content was not obvious from its title. For me this is a very important criticism of Loop Quantum Cosmology per Bojowald by Coule. As the critique is related to standard cosmologies and string cosmologies, it is also a review paper. I will transfer this discussion to the Big Bang subforum, as it is a more appropriate there.

Coule criticizes several features of the LQG cosmology for the Big Bounce, which now replaces the Big Bang. However, I believe that the criticisms are actually strengths once Smolin couples Bojowald's theory to his Black Hole Universe creation hypothesis. In that case the bounce is replaced by a black hole. So lets list the criticisms:

1. Coule says the Big Bounce in unstable and permits baby universe creation. So this obviously is just what Smolin needs to describe baby universe creation in black holes.

2. Coule says that Bojowald theory predicts a reduction in entropy as the Big Bounce is approach from behind, so to speak, in time- actually before. This again is exactly what Smolin needs to counter a principal criticism of his hypothesis. If entropy did not reset to zero or something small compared to the mother universe, the result would be chaos in just a few generations. This is a definite plus in Bojowald theory for Smolin.

3. Coule says that the force of gravity should unify with the other forces in the Big Bounce whereas the Bojowald theory predicts that it stays relatively weak. I say that there is no reason apriori to require unification of all forces at any time in any universe. Perhaps that is just how nature works and Bojowald cosmology predicts it. Of course, I will have to abandon my claim that the unified 26-d field is achieved in the singularity of black holes even though that is a possible mechanism to reduce entropy. Baby universes can apparently be born at much lower energies.

4. Coule says that the unitary condition is violated by the Bojowald theory. From my readings of Hoyle's more recent theories of a steady state universe, Hoyle now proves that matter can only be created in regions where the unitarey condition is violated. I expect that same argument applies to baby universe creation.

5. There are a few more that I forget, even though I just read the paper.

For completeness the link and paper abstract are copied below:

http://xxx.lanl.gov/abs/gr-qc/0312045
Contrasting Quantum Cosmologies
Authors: D.H. Coule
Comments: 21 pages, dispute with astro-ph/0311015 addressed
We compare the recent loop quantum cosmology approach of Bojowald and co-workers with earlier quantum cosmological schemes. Because the weak-energy condition can now be violated at short distances, and not necessarily with a high energy density, a number of possible instabilities are suggested: flat space unstable to expansion or baby universe production. Or else a Machian type principle is required to prevent such behaviour. Allowing a bounce to prevent an approaching singularity seems incompatible with other standard notions concerning the arrow of time and unitarity.
Preventing rapid oscillations in the wavefunction appears in conflict with more general scalar-tensor gravity.
Other approaches such as ``creation from nothing'' or from some quiescent state, static or time machine, are also assessed on grounds of naturalness and fine tuning.


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