Science fiction and comics are full of mutants and aliens whose superpowers defy various laws of physics. Shape-changers who can alter their mass, people who can fly -- in space, even! -- and guys who can produce extreme cold or heat on cue. But in real life, the ability to negate just one of the laws of physics, whenever you felt like it, could turn you into a god. Which law of physics would you like to have a personal on/off switch for?