Gravity may seem simple in everyday life. Drop an apple, and it falls. On cosmic scales, though, gravity becomes one of science’s biggest stress tests. It governs the rise of galaxies, the behavior of galaxy clusters, and the overall architecture of the universe, yet some of the universe’s motions still do not add up.

That long-running mismatch is what drove University of Pennsylvania cosmologist Patricio A. Gallardo and his collaborators to ask a basic but profound question: what if gravity itself behaves differently across the largest distances in the universe?