  Fluctuation theorems, which have been developed over the past 15 years, have
resulted in fundamental breakthroughs in our understanding of how
irreversibility emerges from reversible dynamics, and have provided new
statistical mechanical relationships for free energy changes. They describe the
statistical fluctuations in time-averaged properties of many-particle systems
such as fluids driven to nonequilibrium states, and provide some of the very
few analytical expressions that describe nonequilibrium states. Quantitative
predictions on fluctuations in small systems that are monitored over short
periods can also be made, and therefore the fluctuation theorems allow
thermodynamic concepts to be extended to apply to finite systems. For this
reason, fluctuation theorems are anticipated to play an important role in the
design of nanotechnological devices and in understanding biological processes.
These theorems, their physical significance and results for experimental and
model systems are discussed.
