Folks;
Here's another recent paper from Uni of British Columbia:
'Precision Cosmology Defeats Void Models for Acceleration, (July 2010)'
http://arxiv.org/abs/1007.3725
...which puts another 'popular' hypothesis to the test. (Would seem to be relevant to demonstrating Science's open-mindedness to well thought out, alternative ideas).
Unfortunately, its too big to post as an attachment, but hopefully one can get a feeling for the article from the below quotes. (You can also download a pdf from the link above).
Some interesting quotes:
The Introduction:
"The suggestion that we occupy a privileged position near the centre of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy. Putting aside the philosophical problems with this scenario, we perform the most complete and up-to-date comparison with cosmological data. We use supernovae and the full cosmic microwave background spectrum as the basis of our analysis. We also include constraints from radial baryonic acoustic oscillations, the local Hubble rate, age, big bang nucleosynthesis, the Compton y-distortion, and for the first time include the local amplitude of matter fluctuations, σ8. These all paint a consistent picture in which voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an “old age problem”, and predict much less local structure than is observed."
The Conclusions:
"We have performed the most complete and up-to-date analysis of the proposal to explain the acceleration of the Universe with a large, nonlinear void. Our main results can be summarized as follows:
• Models which fit both the CMB and SNe have an extremely low local Hubble rate of h0 = 0.45 ± 0.02 and are very old, with an age of around 18.5– 19 Gyr. Both of these are inconsistent with observations.
• The radial BAO scale is suppressed in the outer void region compared to ΛCDM and is a poor fit to data.
• The Compton y-distortion constraint from COBE rules out wider, deeper voids even if the overdense shell is tuned to minimize y. Generic shells are inconsistent with the COBE limit and all void models are ruled out at high significance in conjunction with radial BAO data.
• The local amplitude of matter fluctuations is extremely low in void models, with σ8 = 0.49 ± 0.04. This is due to the suppression of growth compared to ΛCDM, and is strongly incompatible with estimates from local galaxy clusters.
• The primordial power spectrum would need to be highly tuned and far from scale-invariant in order to attempt to alleviate some of these problems. We considered running of the spectral index and a broken power law and these were insufficient to change our conclusions.
• We uncovered a class of models with multi-valued distance-redshift relations. While unusual and interesting to study, they again did not alter our conclusions.
Thus it appears that void models for acceleration are overwhelmingly at odds with several types of observations."
"Finally, we note that two of the most important assumptions in cosmology are those of the cosmological and Copernican principles. Therefore, in confronting void models, which blatantly violate both of these principles, with observations, we do more than just examine an unusual approach to the mystery of acceleration. We put the foundations of modern cosmology themselves to the test."
Great stuff !!
Cheers