Dark photons offer a new explanation for the double-slit experiment RUSSELL KIGHTLEY/SCIENCE PHOTO LIBRARY A core tenet of quantum theory was imperilled this year when a team of researchers put forward a radical new interpretation of an experiment about the nature of light. At the centre of the new work was the double-slit experiment, which was first conducted in 1801 by physicist Thomas Young, who used it to confirm that light acts like a wave. Classically, something that is a particle can never also be a wave, and vice versa, but in the quantum realm, the two aren’t mutually exclusive. In fact, all quantum objects exhibit so-called wave-particle duality. For decades, light seemed to be a prime example of this: experiments showed that it sometimes behaves as a particle called a photon and sometimes as a wave that produces effects like those that Young saw. But earlier this year, Celso Villas-Boas at the Federal University of São Carlos in Brazil and his colleagues proposed an interpretation of the double-slit experiment that only involves photons, effectively …