Can light itself cast a shadow? It may sound like a philosophical riddle, but researchers have found that under certain conditions, a laser beam can act like an opaque object and cast a shadow. The discovery challenges the traditional understanding of shadows and opens new possibilities for technologies that could use a laser beam to control another laser beam.

A new experiment has demonstrated something that sounds physically impossible – light itself casting a shadow. It turns out that if you manipulate a laser just right, then hit it side-on with another light source,

With the help of a ruby cube and two laser beams, researchers made one ray of light cast a shadow when illuminated by the other

To ask if a beam of light can make a shadow sounds like a sort of Zen paradox, but physicists have demonstrated the possibility. They used a laser beam to block another laser beam, albeit with some crystalline assistance.

The blue laser light was directed at one side of the ruby, where it passed through and cast a cool glow upon a screen, while a narrow beam of green laser light passed perpendicular to the first from another. A diagram and photograph of the experiment.