A University of Toronto experiment showing that photons can spend a negative amount of time inside a cloud of atoms has been published in Physical Review Letters, clearing peer review more than a year and a half after the result first circulated as a preprint. The work, led by Aephraim Steinberg with first author Daniela Angulo and Griffith University theorist Howard Wiseman, found that photons sent straight through a cloud of cold rubidium can register a negative atomic-excitation time, appearing to exit before they enter, and that the atoms themselves report the same negative figure when probed during transit.
The peer-reviewed paper, published in April, drops the somewhat provocative framing of the September 2024 arXiv draft for a narrower title, with the team again stressing that the effect is fully explained by standard physics, with no faster-than-light signaling involved.
