"First, Will, you don’t need to have a closed loop. There’s really no physical reason why you couldn’t leave the ends unconnected. It wouldn’t have a stable orbit anyway, so in either scenario you’d need some method of orbital adjustment. And you’d build it in segments of some length, with some kind of barrier at the end of each segment. The barrier wouldn’t even have to go right to the center, as long as the segments were already rotating. Spillover would be trivial."