The "Alcubierre drive" isn't an engineering design for a method of propulsion. It's just a nickname for a certain valid solution of the Einstein field equations

The "Alcubierre drive" isn't an engineering design for a method of propulsion. It's just a nickname for a certain valid solution of the Einstein field equations. Like, in classical terms, you can get a repulsive force to come out of Newton's law of gravitation if you plug in a negative mass. But that doesn't mean you've designed a hoverboard.