On this is … this is one of the strangest solo projects I've ever seen. "Volumetric Display using an Acoustically Trapped Particle". Dude has two speakers facing each other, they emit a wave that contains enough force a light foam bead is forced to levitate in the air between them, then by varying it he can move it around, and by changing the light of an LED shining on it he can give it color. He can draw basic 3D shapes and persistence of vision makes them appear real. https://www.youtube.com/watch?v=hCC1C5KIeUA