Ludwig Boltzmann (20.02.1844 - 5.09.1906) was an Austrian theoretical physicist, one of the founders of classical statistical physics and a member of the Austrian Academy of Sciences (1895). He was born in Vienna. He graduated from the University of Vienna (1866). He was professor at the universities of Graz (1869-73 and 1876-89), Vienna (1873-76, 1894-1900 and from 1903), Munich (1889-94) and Leipzig (1900-02).
His main work was in the field of the kinetic theory of gases, thermodynamics and the theory of radiation. In 1866 he derived the law of the distribution of gas molecules by velocity (Boltzmann statistics). The formula for the equilibrium Boltzmann distribution became the basis of classical statistical physics. In 1871 he put forward the ergodic hypothesis. Applying statistical methods to the kinetic theory of ideal gases, he derived (1872) the fundamental kinetic equation of gases, which is the basis of physical kinetics. He related the entropy of a physical system to the probability of its state (1872) and proved the statistical nature of the second law of thermodynamics, giving it a formulation of his own, which struck a blow at the idealist hypothesis of the heat death of the Universe. In 1872 he formulated the H-theorem (Boltzmann's H-theorem), which, together with his statistical interpretation of the second law of thermodynamics, became the basis of the theory of irreversible processes.
He was the first to apply the principles of thermodynamics to radiation. Using J. Maxwell's hypothesis of light pressure, in 1884 he discovered theoretically the law of thermal radiation, according to which the energy radiated by a black body is proportional to the fourth power of the body's absolute temperature. This law had been established experimentally in 1879 by J. Stefan (the Stefan — Boltzmann law). In 1884 he deduced the existence of light pressure from thermodynamic considerations.
He also gave attention to the philosophical questions of natural science, and he fought actively against the energeticists in defence of atomistic theory and, in the theory of knowledge, against the Machists. V. I. Lenin assessed Boltzmann's philosophical views favourably. The continual attacks of the opponents of the kinetic theory of gases gave Boltzmann a persecution mania. That may be why he took his own life.
His work also concerned mathematics, mechanics, optics, hydrodynamics, the theory of elasticity, the theory of the electromagnetic field and so on.
A member of many academies of sciences, and in particular a corresponding member of the St Petersburg Academy of Sciences (1899).