This topic is a little "out there" but what are you thoughts on this being possible someday? I'm doing some research for my Hard SF world and don't want to use anything unplausible. If possible any guesses as to if it'd only need power to turn it on, off and change altitude, not to maintain levitation at the desired altitude? What physical mechanism would allow repulsion against gravitational fields? Could gravity be manipulated not only in the negative but create positive gravity "lasers" to tear objects apart or just pull them to you like sci-fi "tractor beams"? Thanks for the help if you can.