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A response by James Gunn to a letter to the editor about his article "A Singular Conundrum: How odd is our universe?" in the September 28, 2007 issue is presented.

ABSTRACT We present measurements of galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey III (SDSS-III). These use the Data Release 9 (DR9) CMASS sample, which contains 264 283 massive galaxies covering 3275 square degrees with an effective redshift z = 0.57 and redshift range 0.43 < z < 0.7. Assuming a concordance ΛCDM cosmological model, this sample covers an effective volume of 2.2 Gpc3, and represents the largest sample of the Universe ever surveyed at this density [ABSTRACT FROM AUTHOR]

We present the power spectrum of the reconstructed halo density field derived from a sample of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) Seventh Data Release (DR7). The halo power spectrum has a direct connection to the underlying dark matter power for , well into the quasi-linear regime. This enables us to use a factor of ∼8 more modes in the cosmological analysis than an analysis with , as was adopted in the SDSS team analysis of the DR4 LRG sample. The observed halo power spectrum for is well fitted by our model: for 40 degrees of freedom for the best-fitting Λ cold dark matter (ΛCDM) model. We find for a power-law primordial power spectrum with spectral index ns and fixed, consistent with cosmic microwave background measurements. The halo power spectrum also constrains the ratio of the comoving sound horizon at the baryon-drag epoch to an effective distance to . Combining the halo power spectrum measurement with the Wilkinson Microwave Anisotropy Probe ( WMAP) 5 year results, for the flat ΛCDM model we find and . Allowing for massive neutrinos in ΛCDM, we find eV at the 95 per cent confidence level. If we instead consider the effective number of relativistic species Neff as a free parameter, we find . Combining also with the Kowalski et al. supernova sample, we find and for an open cosmology with constant dark energy equation of state w. The power spectrum and a module to calculate the likelihoods are publicly available at . [ABSTRACT FROM AUTHOR]

Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, EG, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to ‘galaxy bias’ (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of EG different from the general relativistic prediction because, in these theories, the ‘gravitational slip’ (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect. Here we report that EG = 0.39 ± 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of EG ≈ 0.4. The measured value excludes a model within the tensor–vector–scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f() theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models. [ABSTRACT FROM AUTHOR]