Post #1925754

Astronomers have shown that the gravitational acceleration galaxy clusters exert on each other obeys an inverse square law, 1/r^n with n = 2.1±0.3, on distance scales of the order of 100-750 Mega light-years. This rules out many theories of “Modified Newtonian Dynamics”. They used the “kinematic Sunyaev-Zeldovich effect” (kSZ), a measure of how cosmic microwave background photons gain energy from electrons in motion (relative to the universe’s expansion), to determine how the velocities between pairs of galaxy clusters varied with their separation, in a sample of 227,837 galaxies. The kSZ is tricky, because there is also a temperature effect, but it is better for this than trying to use the Doppler shift for objects with a large cosmic red shift. Write-up in Science: https://www.science.org/content/article/newton-s-law-gravity-passes-its-biggest-test-ever The paper: https://arxiv.org/abs/2604.14327