I've been reading a lot about space elevators being built from carbon nanotube thread and having lifters powered by lasers. I'm imagining it to be 50,000 long. Obviously this is fiction at the moment, but i was wondering... if there was such a structure, what would be the effects of gravity on someone in a lifter? At what point would the effects be felt? As the lifter was pushed/pulled further along the ribbon, how would gravity's force change along the journey. Also what kind of speed do you think would be reached on a 50,000 km long cable?