Lars Onsager (27.02.1903-5.10.1976) was an American chemist and physicist, one of the creators of non-equilibrium thermodynamics, a member of the National Academy of Sciences (1947). He was born in Oslo (Norway). He graduated from the Norwegian Higher Technical School in Trondheim (1925). From 1928 he lived in the USA. In 1928-33 he worked at Brown University, in 1933-45 at Yale University. In 1945-72 he was professor of theoretical chemistry at the University of Miami.
His research concerned the theory of electrolytic conductivity, the theory of dielectrics and semiconductors, metals, liquids, the thermodynamics of irreversible processes, the statistics of crystals and hydrodynamics. In 1926 he derived an equation relating the equivalent conductivity of an electrolyte solution to its concentration (the Onsager equation).
In 1931 he proved one of the basic theorems of the thermodynamics of irreversible processes, on the symmetry properties of the kinetic coefficients (the Onsager theorem), established the linear dependence of generalised thermodynamic fluxes and potentials (the principle of linearity), and in 1932 the reciprocal relations (the Onsager relations), which express the equality of the cross coefficients (the principle of reciprocity). These two principles became the basis of the theory of non-equilibrium processes that he developed and stimulated the creation of non-equilibrium thermodynamics. He discovered a reversible reaction (the Onsager reaction) that is of great importance for the thermodynamics of irreversible processes (Nobel Prize in Chemistry, 1968). He developed a theory of the thermodynamic properties of a plane lattice (the Onsager theory). In 1944 he extended the statistical theory of phase transitions.
In 1949 he predicted the appearance of quantised vortices in the superfluid component of liquid helium moving at a supercritical velocity, at temperatures below the phase transition point.
A member of a number of academies of sciences and scientific societies. The B. Rumford and H. Lorentz medals and others.