In the process of light propagating to the surroundings, if there is no energy loss, then it will propagate forever. The universe we see will be brighter, and it will become brighter and brighter. The hotter it is; light can only be retained in the universe if it is transformed into another kind of matter. That is, after the light is at rest, it becomes matter with zero rest mass, that is, dark matter and dark energy in the universe.