Here's a thought experiment with a few questions: Space expands, probably at accelerating rate. We can make a thought experiment like this: there's a star surrounded by billions of light-years of empty space (say 4300 Mpc radius, well beyond the size of what we see - it's a thought experiment). On the outer layer of our empty space are solar cells collecting the energy of the star at all wavelengths at 100% efficiency. At that distance Hubble's law states the run-away speed would be above c (assuming 70km/s/Mpc value of Hubble's constant and assuming the law is valid over such distances and that it's linear in nature) So... what's the sum of the energy collected by all solar cells? If light never reaches the solar cells then the total energy output of the star at that distance will be Zero... I suppose? So the star has event horizon even though it's not a black hole? And if the energy from the star was sent "somewhere" but never reached the solar cells then what happened to it?