It seems from the paper discussed below that several characteristics of Bojowald's Big Bounce cosmology are exactly what Smolin needs to turn his Evolution of Universes from Black Hole baby universe creation hypotheis into a theory. This discussion is carried over from the Misc. subforum:
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 the bounce in time. 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.
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:
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.
So my interpretation of these results- Bojowald theory- is that baby universe creation bleed off energy long before unification energies are reached. I do not think that universe suffer the bounce. Dark energy considerations indicate nthat universes eventually expand out of existence at an accelerating rate.
Rather baby universes are created in the singularities of black holes once an energy threshold is achieved that is well below the unification energy. That threshold is where Bojowald's theory becomes non-unitary. The cration of new universes then prevents a further build up of energy in the black hole no matter how much additional matter (sic) is absorbed by the black hole.
Besides the obvious connection to Smolin's hypothesis, this result has the further implication that a theory unifying all forces up to Planck energies may not be necessary. Apparently the unified field never happens in nature. For example, vacuum production of virtual particles can now be predicted to happen at energies well below Planck energies. And space can become nonunitary at energies well below Planck energies, or likewise at distances well above the Planck length.
Richard Ruquist, PhD
79 Rice Street
Cambridge, Ma 02140