The familiar optical illusion that makes a pencil look broken when half-dipped in water just took a new twist. A new experiment shows that when light bends at an interface (such as between water and air), the light's photons take a sideways shift depending on their polarization—something scientists didn't even suspect until a few years ago.
Physicists call the broken-pencil effect refraction. It's how lenses redirect light. When crossing at an oblique angle from air into glass or water, or between any two different transparent materials, light's path bends.