About half a million ultracold neutrons (around 2 miiliKelvin above absolute zero) were let into a container and allowed to bounce around. Isolated neutrons have a half life of 881 seconds. The number going into, and then the number coming out of the container after 300 seconds, were counted. The number coming out depended on the direction of a small magnetic field applied to the container.
The authors had no explanation under conventional physics. Neutron decay should not depend on the direction of a small magnetic field. They raise the theory that some of the neutrons are turning into “mirror neutrons” that exist in a mirror universe parallel to ours. This needs much more testing, especially to find if some other factor in the experiment is causing the measurement change (see: faster than light neutrinos). If all other possibilities are eliminated, then new physics like mirror universes might be accepted as an explanation.”