Artist's concept of a bias drive spacecraft. Credit: Popular Science.
Principle of the bias drive.
Credit: Popular Science.
The bias drive would alter the properties of space itself. It could reduce normal gravity on one side to produce thrust. Imagine a boat made from a block of wood with one pointed end and the other indented. The block is floating on water, and you drop detergent on it. Because the soap changes the surface tension of the water, the boat is pushed along.
Compare with the induction ring.