  The second law of thermodynamics imposes an increase of macroscopic entropy
with time in an isolated system. Microscopically, however, the entropy
production can be negative for a single, microscopic realization of a
thermodynamic process. The so-called fluctuation theorems provide exact
relations between the stochastic entropy consumption and generation. Here, we
analyse pixel-to-pixel fluctuations in time of small-scale magnetic fields
(SSMF) in the quiet Sun observed with the SDO/HMI instrument. We demonstrate
that entropy generated by SSMF obeys the fluctuation theorems. In particular,
the SSMF entropy consumption probability is exactly exponentially smaller than
the SSMF entropy generation probability. This may have fundamental implications
for the magnetic energy budget of the Sun.
