Banned because I've been thinking about this physics problem for a week or so, and it's bugging the hell out of me. It deals with the conservation of energy for a number of disparate phenomena, all of which are what we would consider "teleportation": this could be wormholes, quantum tunneling, or any other way of traveling from one place to another without physically going there.
It's kind of hard to explain, so I'll just provide an incredibly basic example, using for simplicity's sake a pair of idealized "portals" that could stand in for any of the above effects- anything that enters one side of one portal comes out the other side of the other. Basically, the portals from Portal.
Let's say that there are two portals, one on the ceiling and one directly under it on the floor, with a large amount of space in between, enough so that a reasonable object could achieve terminal velocity and then some. There is a mass of water in between the two, so that it constantly falls through the bottom one and emerges from the top- basically, an infinite waterfall. This presents a problem, or more accurately a miracle- if I were to move a waterwheel underneath the waterfall (assuming no water splashed out) and plug it into my laptop, I would have a perpetual motion machine! (Which is, of course, a blatant violation of the laws of thermodynamics)
In more general terms, the problem is this: science tells us that there exist phenomena which can translocate matter from one position to another with a constant expenditure of energy (a wormhole crossing over the same distance will require the same mass to create regardless of which direction it is pointed). However, depending on the position, that object can have either greater or lesser potential energy than at its previous position, which can then be released back into the universe- thus, energy could be created (or destroyed) by the process of translocation.