Alcubierre warp drive theory

If you need equal parts positive gravity in front of the ship and equal part negative gravity behind the ship couldn't you then instead of using exotic matter to create negative and positive gravity in front of and behind of a ship couldn't you just displace the neutral gravity from in front of the ship to the back of the ship to create the negative and positive "vacuum" I'm by no means a physicist so please forgive me if it's a dumb question.