i have a three part question. how does light act leaving, traveling between, and entering a galaxy? we have come to the conclusion that the speed and direction of of traveling light is effected by its surroundings. i'm wondering what that looks like at a galactic scale. first, leaving a galaxy, can the mass and speed of said galaxy propel the light out in all directions? how fast would that be? next, is the space outside a galaxy really like a massive vacuum? finally, could the spinning galaxy pull in the light? how fast? could some of it bounce back out (like if the space shuttle botched it's approach)? how would it act in reference to the stellar population at the time of entry?