Confirmation of general relativity on large scales from weak lensing and galaxy velocities

TL;DR

This study tests general relativity on large cosmological scales using weak lensing and galaxy velocities, finding results consistent with Einstein's theory but with uncertainties that still allow some alternative models.

Contribution

It provides the first measurement of the EG parameter on large scales, confirming general relativity predictions within current uncertainties.

Findings

EG = 0.39 +/- 0.06, consistent with GR

Excludes tensor-vector-scalar gravity models

Permits f(R) gravity models due to uncertainties

Abstract

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 effect3. 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 $\approx$ 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(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.