Is light made of particles or waves? The answer, according to quantum physics, is both. Depending on the situation, particles of light—and particles of matter too—sometimes contradict themselves and act like waves. But between these two extremes, there’s a range of behaviors. Scientists have now demonstrated those intermediates in a conspicuous way.
The new research is a variation on the so-called double-slit experiment, a staple of introductory quantum theory courses. In the classic version, light passes through two slits in an opaque screen and hits another screen some distance away. Crests and troughs of light waves emerging from each slit add together or cancel each other out, depending on how they overlap, and create an interference pattern of light and dark stripes on the screen. This phenomenon has been demonstrated not only with photons but also with electrons, and even whole atoms.