What Happens if You Cut a Photon in Half? The Answer Is Trippy

Physicists tend to think of light in terms of photons: massless, elementary particles “carrying” the forces of nature. And elementary particles, like the photon, are indivisible. That is, there is no such thing as half a photon. Or is there? That was the question that three theoretical physicists tried to answer in a recent paper published in Physical Review Letters, bluntly titled “Truncated Photon.” To be clear, the team understands that elementary particles like photons can’t be cut into two. But consider this quantum shortcut: photons exhibit the behaviors of both waves and particles. As it turns out, there is a way to split a photon using this property—although, in typical quantum weirdness, the product of this isn’t anything you’d expect. “Despite being a simple question, it appears that it has not been asked before,” the physicists, from the University of Oslo in Norway, wrote in the paper. The dual nature of light as both a particle and a wave was most famously demonstrated by British physicist Thomas Young in 1801. The double-slit experiment, as it came to be called, showed how, when you shine a beam of light (“particles”) through two parallel slits on a screen, you’d get