Every action in physics is governed by some kind of push or pull. As far as we know, these all fall into one of just four categories; electromagnetism, gravity, and two kinds of nuclear force.

Yet there could well be forces hidden deep within the tiny storms of particle dynamics that have been simply too subtle to easily detect.

Physicists from Germany, Switzerland, and Australia have now placed new restrictions on where one example of a ‘fifth’ force may be hiding in the hearts of atoms, exchanging whispers between electrons and neutrons.