ABSTRACT
Thermodynamic quantities are supposed to be constant when the system is in thermal equilibrium. If we measure them with higher and higher precision, however, there will come a point when we will notice that their values undergo small fluctuations. For example, the pressure is the force per unit area exerted by atoms on a boundary surface, and it fluctuates because of the randomness of atomic impacts. The internal energy fluctuates because of energy exchange with a heat reservoir, which proceeds via atomic collisions. These fluctuations appear as thermal noise, and indicate the granular structure of matter.
