



When a thermodynamic system is in contact with a heat reservoir, heat transfer may occur between the system and the reservoir. As a result of processes of this type, the energy of the system fluctuates with time. The Boltzmann probability addresses the question: "If the reservoir has a Kelvin temperature, T, what is the probability of the system having an energy, E?" Statistical thermodynamics provides the answer: P(E)_{T} = exp (  E/kT) , where k is Boltzmann's constant (8.6 x 10^{}^{5}eV/K).  