Abstract: | The macroscopic fluctuation theory is based on a single formula for the probability of joint fluctuations of thermodynamic variables and currents and its properties under time reversal. After giving an idea about its derivation we shall use it to introduce a natural generalization of the free energy and a new functional describing the thermodynamics of the time averaged currents. The singularities of these functionals are associated with phase transitions. An important consequence of the time reversal properties of the basic formula is that the hydrodynamic currents split into orthogonal parts having opposite time reversal behavior. Some applications will be discussed. |