Gravity follows Newton and Einstein's rules, even at cosmic scales

Key Points:

• Researchers from the University of Pennsylvania used data from the Atacama Cosmology Telescope (ACT) to test gravity across galaxy clusters separated by hundreds of millions of light-years, marking the largest-scale probe of gravity to date.
• Their findings, published in Physical Review Letters, confirm that gravity weakens with distance according to Newton's inverse square law and Einstein's general relativity, even on vast extragalactic scales.
• This result challenges alternative theories like Modified Newtonian Dynamics (MOND) that propose changes to gravity's laws to explain the unusually fast motions of stars and galaxies, reinforcing the need for dark matter as the source of the extra gravitational pull.
• Although the study strengthens the case for dark matter's existence, the true nature of dark matter remains unknown, representing a major open question in modern physics.
• Future observations of the cosmic microwave background and larger galaxy surveys are expected to further refine tests of gravity and deepen understanding of cosmic structure and dark matter.