'This is a schematic of the wings' motion,' Nilis said. 'See the way the wings change their shape. You have to think of spacetime as the natural medium of the craft. It is like—like a bacterium embedded in water. To a small enough creature, water is as viscous as treacle, and in such sticky stuff swimming is difficult, because if your recovery stroke is the same as your impulsive stroke you pull yourself back to where you started. So what bacteria do is adopt different geometrical shapes, during the first and second parts of the stroke, to pull themselves forward. It's called a geometric phase, a closed sequence of different shapes.
'Pirius, the nightfighter is embedded in spacetime as surely as any bacterium in water. By pulsing through their sequence of shapes, the wings of the nightfighter are clearly using a geometric phase to control and direct the ship's motion. It's a shape-shifting drive—nothing like a rocket, no need for anything like reaction mass to be thrown out the back of your ship—really quite remarkable. And quite unlike the principles on which human sublight drives are based.'
-Exultant, Ch. 11