  It will be shown, how the Boltzmannian ideas on statistical physics can be
naturally applied to nonequilibrium thermodynamics. A similar approach for
treating nonequilibrium phenomena has been successfully used by Einstein and
Smoluchowski treating fluctuations. It will be argued, that due to the
reversibility of the microscopic equations, all processes - also macroscopic
ones - must at least in principle be reversible. Also, a clear conceptual
distinction between equilibrium and nonequilibrium states is not possible in
the Boltzmannian framework, which is just the reason why these concepts should
apply to nonequilibrium. In the present manuscript we derive a Fluctuation
Theorem from the equation S=k ln P, where P is the probability of a state. The
recently discovered Fluctuation Theorems are some of the few exact results
valid far from equilibrium. Two assumptions are needed for the derivation:
First, the process shall happen on certain time-scales that are large compared
with the time, during which the system memorizes its initial conditions.
Second, the entropy production rate averaged over all realizations of the
process shall be constant during the process. We will finally point out, why a
solution to the problem of macroscopic irreversibility invoking causality - as
it was recently suggested in connection with the Fluctuation Theorem - cannot
live up to its task.
