  The laws of thermodynamics apply to biophysical systems on the nanoscale as
described by the framework of stochastic thermodynamics. This theory provides
universal, exact relations for quantities like work, which have been verified
in experiments where a fully resolved description allows direct access to such
quantities. Complementary studies consider partially hidden, coarse-grained
descriptions, in which the mean entropy production typically is not directly
accessible but can be bounded in terms of observable quantities. Going beyond
the mean, we introduce a fluctuating entropy production that applies to
individual trajectories in a coarse-grained description under time-dependent
driving. Thus, this concept is applicable to the broad and experimentally
significant class of driven systems in which not all relevant states can be
resolved. We provide a paradigmatic example by studying an experimentally
verified protein unfolding process. As a consequence, the entire distribution
of the coarse-grained entropy production rather than merely its mean retains
spatial and temporal information about the microscopic process. In particular,
we obtain a bound on the distribution of the physical entropy production of
individual unfolding events.
