The iPhone may be getting lots of attention, but Steve Jobs has no corner on "multi-touch" displays, which allow a person to use multiple fingers to do things like zoom in and out of pictures. At New York University's Courant Institute of Mathematical Sciences, research scientist Jeff Han has developed an effective way to make large, very high-­resolution screens that accommodate 10, 20, or even more fingers. Applications could include interactive white boards, touch-screen tables, and digital walls.

In Han's setup, a digital projector shines an image on a six-­millimeter-thick clear acrylic screen. Touch sensitivity comes from infrared light-emitting diodes attached to the edges of the screen. Normally, the diodes' light reflects internally and stays trapped within the acrylic. Once fingers or other objects touch the acrylic, though, the light diffuses at the point of contact and scatters outside the surface. A camera behind the screen detects these changes. Simple image-processing software can interpret the scattering, in real time, as discrete touches and strokes.