Jan J. Ostrowski

Is there proof that backreaction of inhomogeneities is irrelevant in cosmology

No. In a number of papers Green and Wald argue that the standard FLRW model approximates our Universe extremely well on all scales, except close to strong field astrophysical objects. In particular, they argue that the effect of inhomogeneities on average properties of the Universe (backreaction) is irrelevant. We show that this latter claim is not valid. Specifically, we demonstrate, referring to their recent review paper, that (i) their two-dimensional example used to illustrate the fitting problem differs from the actual problem in important respects, and it assumes what is to be proven; (ii) the proof of the trace-free property of backreaction is unphysical and the theorem about it fails to be a mathematically general statement; (iii) the scheme that underlies the trace-free theorem does not involve averaging and therefore does not capture crucial non-local effects; (iv) their arguments are to a large extent coordinate-dependent, and (v) many of their criticisms of backreaction frameworks do not apply to the published definitions of these frameworks. It is therefore incorrect to infer that Green and Wald have proven a general result that addresses the essential physical questions of backreaction in cosmology.

Evidence for an environment-dependent shift in the baryon acoustic oscillation peak

The Friedmann-Lemaitre-Robertson-Walker (FLRW) metric assumes comoving spatial rigidity of metrical properties. The curvature term in comoving coordinates is environment-independent and cannot evolve. In the standard model, structure formation is interpreted accordingly: structures average out on the chosen metrical background, which remains rigid in comoving coordinates despite nonlinear structure growth. The latter claim needs to be tested, since it is a hypothesis that is not derived using general relativity. We introduce a test of the comoving rigidity assumption by measuring the two-point auto-correlation function on comoving scales---assuming FLRW comoving spatial rigidity---in order to detect shifts in the baryon acoustic oscillation (BAO) peak location for Large Red Galaxy (LRG) pairs of the Sloan Digital Sky Survey Data Release 7. In tangential directions, subsets of pairs overlapping with superclusters or voids show the BAO peak. The tangential BAO peak location for overlap with Nadathur & Hotchkiss superclusters is

A relativistic model of the topological acceleration effect

4.3\pm1.6

Virialisation-induced curvature as a physical explanation for dark energy

Mpc/h less than that for LRG pairs unselected for supercluster overlap, and

Is the baryon acoustic oscillation peak a cosmological standard ruler

6.6\pm2.8

On the Green and Wald formalism

Mpc/h less than that of the complementary pairs. Liivamagi et al. superclusters give corresponding differences of

The background Friedmannian Hubble constant in relativistic inhomogeneous cosmology and the age of the Universe

3.7\pm2.9

On the relativistic mass function and averaging in cosmology

Mpc/h and

Mass Function of Galaxy Clusters in Relativistic Inhomogeneous Cosmology

6.3\pm2.6

Can an inhomogeneous metric be detected with the baryonic acoustic oscillation peak

Mpc/h, respectively. We have found moderately significant evidence (Kolmogorov--Smirnov tests suggest very significant evidence) that the BAO peak location for supercluster-overlapping pairs is compressed by about 6% compared to that of the complementary sample, providing a potential challenge to FLRW models and a benchmark for predictions from models based on an averaging approach that leaves the spatial metric a priori unspecified.