Cosmic-scale gravity test confirms Newtonian law, bolstering dark-matter theory

A team of astronomers conducted the largest-scale test of gravity to date, analyzing the motions of galaxy clusters hundreds of millions of light-years apart using observations from the Atacama Cosmology Telescope. Their findings, reported in Physical Review Letters, indicate that the force of gravity diminishes with distance exactly as described by Newton’s inverse-square law and incorporated into Einstein’s general relativity.

This result narrows the viability of modified-gravity theories like MOND, which predict a slower decline. Consequently, the evidence further supports the presence of an invisible dark-matter component that accounts for the excess gravitational pull in galaxies and clusters. Lead researcher Patricio A. Gallardo of the University of Pennsylvania highlighted that while the study strengthens the dark-matter case, it does not reveal the particle’s nature. Future cosmic-microwave-background measurements and larger galaxy surveys aim to test gravity with even finer precision.