Cosmic test shows gravity follows Newton and Einstein across galaxy clusters

Patricio A. Gallardo and colleagues at the University of Pennsylvania investigated how gravity behaves over the largest observable distances by studying the imprint of moving galaxy clusters on the cosmic microwave background. Using data from the Atacama Cosmology Telescope, they measured the gravitational interaction between clusters separated by hundreds of millions of light-years. Their findings, reported in Physical Review Letters and summarized by one outlet, demonstrate that the force weakens with distance in line with Newton's inverse-square law and Einstein's general relativity.

This result challenges theories that modify gravity on cosmic scales, such as Modified Newtonian Dynamics, and bolsters the hypothesis that dark matter provides the missing mass. Although the composition of dark matter remains unknown, the study narrows the range of viable explanations for the rapid motions observed in galaxies and clusters. The authors note that upcoming improvements in CMB observations and larger galaxy surveys will allow even more precise tests of gravity on the grandest structures.