By switching the dielectric constant of a metamaterial, physicists have time-reflected electromagnetic waves being carried within it. The didn’t turn back time Cher-style, but the signal carried by the waves underwent both a reversal in order and frequency lengthening. Besides confirming a possibility theoreticians have been toying with for 60 years, the work could allow greater control over the way waves and matter interact. It could prove useful in photonics, the quest to replace electricity in information technology with light, allowing for an astonishing increase in speed.