  The fluctuation relations, which characterize irreversible processes in
Nature, are among the most important results in non-equilibrium physics. In
short, these relations say that it is exponentially unlikely for us to observe
a time-reversed process and, thus, establish the thermodynamic arrow of time
pointing from low to high entropy. On the other hand, fundamental physical
theories are invariant under time-reversal symmetry. Although in Newtonian and
quantum physics the emergence of irreversible processes, as well as fluctuation
relations, is relatively well understood, many problems arise when relativity
enters the game. In this work, by considering a specific class of spacetimes,
we explore the question of how the time-dilation effect enters into the
fluctuation relations. We conclude that a positive entropy production emerges
as a consequence of both the special relativistic and the gravitational
(enclosed in the equivalence principle) time-dilation effects.
