I know this is a commonly adressed topic, but it is one in which things are hazy to me. If the universe is finite (which we don't know), and flat (which we are becoming ever more increasingly certain about), then how could a light beam fired from a point in the universe not ever reach its starting point? I know that most make analogies, like balloons, but this is for a universe with some curvature. If a light beam is fired to the farthest reaches of space, then it is commonly said that the beam would end up where it started. However, this scenario seems to me as to be described only from a stand-point of the beam curving its way around the spherical shape of the universe. If one were to imagine a flat universe witha finite size, then a light beam would travel to the farthest reaches of space, and then what? It certainly can't curve back in and reverse its trajectory.. the universe is flat, remember. It wouldn't be able to reverse its trajectory, so what would happen to it? Thanks.