A 3-D Holographic Display
ZonkerWilliam sends along a link to a Wired writeup on a novel 3-D holographic display developed at USC. Be sure to watch the video at the bottom of the page. "The process is not simple but can be defined through a few key concepts: Spinning mirrors, high-speed DLP Projections, and very precise math that figures out the correct axial perspective needed for a 360-degree image (even taking into account a viewer's positioning.)"
You can't put your hand through the image and disrupt it!
More accurately, if you try, your hand is likely to be destroyed by the mirror spinning at very high speeds. It's sort of like a force field...