Ok this one is purely theoretical and I'm going to just make some assumptions. 1. No Debris will block the way. 2. Its A vacuum 3.The structure won't collapse. Ok, first we drill a hole through one side the earth and out the other. We then wrap the new whole in a superconducting coil of wire. At both ends of the wire attach a battery to collect the energy. Then drop the magnet. Would the magnet be slowed? I came up with this today and only researched a little on how magnetic generators generally work. Squares are magnets. The brown lines are the wires previously mentioned.