An advanced version of the famous double-slit experiment has directly measured a single photon in two places at once – or at least, that’s the claim made by a team of physicists who say these results could destroy the concept of a multiverse. This interpretation remains highly contested, however, with other physicists arguing that the experiment can’t really tell us anything new about the nature of reality.

The double-slit experiment, first performed in 1801, has played a key role in the development of quantum mechanics. It shows…