According to Einstein’s general theory of relativity, any matter or energy can drive cosmic expansion. But as space expands, all the familiar kinds of matter and energy become less dense as they spread out in a roomier universe. As their densities fall, the expansion of the universe should slow down, not speed up.

Dark Energy May Be Weakening, Major Astrophysics Study Finds

https://www.quantamagazine.org/dark-energy-may-be-weakening-major-astrophysics-study-finds-20240404/