The search continues Bernhard Lauss (left) and Géza Zsigmond examined around 25 billion neutrons at PSI’s ultracold neutron source. They have largely ruled out the hypothesis that neutrons spontaneously turn into mirror neutrons. (Courtesy: Paul Scherrer Institute PSI/Markus Fischer)"> The search continues Bernhard Lauss (left) and Géza Zsigmond examined around 25 billion neutrons at PSI’s ultracold neutron source. They have largely ruled out the hypothesis that neutrons spontaneously turn into mirror neutrons. (Courtesy: Paul Scherrer Institute PSI/Markus Fischer)

Could a mirror world – in which every type of elementary particle has a corresponding mirror particle – exist in parallel to our ordinary world? For now, the answer is probably no, but in exploring this question, physicists at the Ultracold Neutron (UCN) Physics Group at the Paul Scherrer Institute (PSI) in Switzerland, say they have refuted this hypothesis with the best precision yet.…