Physicists have found evidence challenging the century-old assumption that the universe is uniform on large scales. Three new preprint papers propose tests and analyze data showing the standard FLRW model may be flawed. The results could help resolve major cosmological puzzles.
Physicists have long modeled the universe assuming it is homogeneous and isotropic on the largest scales, a principle embedded in the FLRW model developed in the 1920s by Alexander Friedmann, Georges Lemaître, Howard Robertson, and Arthur Geoffrey Walker. This simplification allows cosmologists to interpret observations without detailing every galaxy. However, three preprint papers published this month question these assumptions, suggesting the universe is lumpier than thought. Timothy Clifton at Queen Mary University of London and Asta Heinesen at the University of Copenhagen proposed a test using combinations of cosmic distance formulas derived from supernovae observations and matter density fluctuations. These combinations should yield zero under the FLRW model; any nonzero result indicates a problem. Heinesen and Sofie Marie Koksbang at the University of Southern Denmark applied the test to existing data. They derived distances without FLRW assumptions and used AI-based symbolic regression to fit formulas, obtaining a clear nonzero outcome. “I was surprised by our result because it breaks with much of what’s come before,” Heinesen said. Clifton added, “It suggests that the universe may not be as simple as it appears,” opening new possibilities. The findings have not yet met cosmologists' full statistical threshold for discovery and require more data. Still, a lumpy universe could explain discrepancies like the varying expansion rate, mismatches between early and current cosmic history, and hints of evolving dark energy, as these would be averages not holding universally, Clifton noted. Subodh Patil at the University of Leiden praised the approach: “My first impression is, fantastic, they’re asking the right questions,” though he urged caution against overinterpretation.