[Fermilab scientists] have found more evidence that sub-atomic particles, called muons, are not behaving in the way predicted by the current theory of sub-atomic physics.

Scientists believe that an unknown force could be acting on the muons.

All of the forces we experience every day can be reduced to just four categories: gravity, electromagnetism, the strong force and the weak force. These four fundamental forces govern how all the objects and particles in the Universe interact with each other.

The findings have been made at a US particle accelerator facility called Fermilab. They build on results announced in 2021 in which the Fermilab team first suggested the possibility of a fifth force of nature.