https://phys.org/news/2018-06-cosmic-voids-galaxy-clusters-upend.html

As far as we know, gravity works according to Albert Einstein's general theory of relativity, but the theory has not yet been precision-tested at very great distances and in sparse areas.

Researchers Martin Sahlén at the Department of Physics and Astronomy at Uppsala University and Joseph Silk at Johns Hopkins University, Institut d'Astrophysique de Paris, Université Paris Diderot and the University of Oxford, have calculated how small deviations from Einstein's theory of relativity at large distances might affect the number, size and density of cosmic voids and galaxy clusters.