ABSTRACT
Thermodynamics is the only discipline that contemplates the presence of an arrow of time in our universe. The Second Law of Thermodynamics introduces entropy to describe the sense of the arrow of time. In our universe, the irreversible transformations determine an increase of entropy, whereas the reversible transformations do not. Entropy was introduced in the Industrial Age when scientists and entrepreneurs were trying to optimize the efficiency of their machines. When energy is dissipated in heat, entropy grows up. Then, the mechanical statistics investigation showed that entropy is related to the microscopic degrees of freedom. When entropy rises, the number of microstates becomes larger. Since we are unable to collect accurate information about the microstates, a growth of entropy means an increase in our uncertainty about the microscopic state of our system. During the more recent Information Age, the link between entropy and uncertainty has been strengthened. After revealing the intimate meaning of entropy, it is spontaneous to try to violate the Second Law of Thermodynamics. Different attempts have been made, which are described in this chapter. Only when the Fluctuation Theorem holds, it is possible to observe a spontaneous decrease in entropy.
