I dunno where to post this so here it is. I've googled it, found something interesting by USC Graphic lab, turns out it's a rotating mirror, emulating a holographic displayer, but fair enough, it's still quite amazing. http://www.wired.com/gadgetlab/2008/06/usc-lab-creates/ Is there anything that does not require specific medium? For example, projecting in the middle of the air? I know it may not be scientifically possible.