Could there perhaps ever be floating cities? If we could get the type of technology that sends rockets into space, and have the boosters running at a constant and equal velocity inversely, could this cause anything to levitate? If so, would this even be habitable? Considering that the fumes given off by such boosters is toxic, would there be a way to disperse of the fumes? In addition, this would be quite costly and probably not worth it. To expound, it would work with rocket boosters on top of a piece of land pushing downward with a velocity of at least 9.9m/s, and boosters at the bottom of a piece of land with a velocity of at least 9.9m/s. What do you guys think?