  Spontaneous symmetry breaking (SSB) is a key concept in physics that for
decades has played a crucial role in the description of many physical phenomena
in a large number of different areas, like particle physics, cosmology, and
condensed-matter physics. SSB is thus an ubiquitous concept connecting several,
both "high" and "low" energy, areas of physics and many textbooks describe its
basic features in great detail. However, to study the dynamics of symmetry
breaking in the laboratory is extremely difficult. In condensed-matter physics,
for example, tiny external disturbances cause a preference for the breaking of
the symmetry in a particular configuration and typically those disturbances
cannot be avoided in experiments. Notwithstanding these complications, here we
describe an experiment, in which we directly observe the spontaneous breaking
of the temporal phase of a driven system with respect to the drive into two
distinct values differing by $\pi$.
