If two galaxies are separated by a large distance such that radiation transmitted from the mid-point between the two galaxies never reaches either galaxy due to the expansion of space, how can the expansion of space at the mid-point ever affect the distance between the two galaxies. i.e. how does the information that space has expanded at the mid-point reach the two galaxies? I have a hard time picturing what the expansion of space means. I'm trying to picture little boxes of space pushing on each other but it doesn't seem to work because of having a finite propagation speed. I'll try asking my question another way. Suppose there's two galaxies 100 million light years apart. I don't know what the expansion rate is but suppose that in one second, the distance between the two galaxies increases by one kilometer. Is there any delay between the expansion of space and the reduction in the gravitational force from one galaxy to the other? Is there any delay between the expansion of space and the increase in distance between the two galaxies?