  Ludwig Boltzmann had a hunch that irreversibility exhibited by a macroscopic
system arises from the reversible dynamics of its microscopic constituents. He
derived a nonlinear integro-differential equation - now called the Boltzmann
equation - for the phase space density of the molecules of a dilute fluid. He
showed that the Second law of thermodynamics emerges from Newton's equations of
motion. However Boltzmann realized that stosszahlansatz, employed in the
derivation, smuggles in an element of stochasticity into the transport
equation. He then proposed a fully stochastic description of entropy which laid
the foundation for statistical mechanics. Recent developments, embodied in
different fluctuation theorems, have shown that Boltzmann's hunch was, in
essence, correct.
