No i am thinking of a warp drive. The Alcubierre drive or space time metric in particular. It the sort of metrics that lead to closed timelike space curvature or whatever (its been a while), ie time travel. In all these cases various things are not conserved that are wildly held to be conserved, requires negative energy etc.
Sure math can be predictive. But that leads you in the direction of a experiment, it is the experiment that matters. I can get imaginary results for calculations for throwing a ball, that does not make the ball imaginary. Even more interesting is that we have fudged the math a lot in the past, because it works. Later mathmaticians make it more rigioirs. In otherwords we design the math to fit the universe we live in.