When we stand in front of a mirror and wave, our reflection waves back at us. Something similar applies to elementary particles. In particle physics, there are "mirrors" that scientists use as a tool to better understand the behavior of particles. These mirrors are called symmetries.
Like all mirrors, symmetries can also break – among other things, due to quantum effects. In such cases, however, there seems to be a way to save them: the axion can protect the symmetry. So far, though, this particle exists only in theory; it has not yet been detected experimentally. Lucy Komisel from the Max Planck Institute for Physics explains the powers of the axion and how theoretical particle physicists also develop practical solutions.