Ars Technica: Two experiments on entangled photons have forced the photons to display both their wave-like and particle-like properties. Normally, an observation that reveals the wave-like properties prevents later observations from showing the particle-like properties—and vice versa. In both experiments, polarized photons were sent through a device where they initially encountered a beam splitter giving them equal chance to take either of two paths. On one of the paths, the polarization is rotated, and mirrors redirect both paths toward an intersection with two detectors beyond. If the intersection does not have a second beam splitter in place, both detectors click with equal frequency, because the photons behave like particles. If there is a beam splitter in the intersection, the photons behave like waves, travel down both paths, and interfere with themselves, resulting in only one of the detectors registering hits. In one of the experiments, measurements of one of the entangled photons after the first had been through the device could determine whether the first had encountered the second beam splitter or not. The other experiment manipulated the polarization of the photons in ways that allowed them to control whether the first photon was more wave-like or more particle-like.