Ryogo Kubo

Ryogo Kubo was born in Tokyo in 1920 and became one of the leading figures of twentieth-century statistical physics. Working in the post-war Japanese physics community, he developed the systematic theory of how systems near equilibrium respond to small external forces.

In 1957 Kubo formulated linear-response theory and proved the fluctuation–dissipation theorem in full generality, expressing transport coefficients such as electrical conductivity in terms of equilibrium time-correlation functions of the corresponding fluctuations. The Kubo formula made precise the idea that a system's spontaneous fluctuations and its dissipative response are two aspects of the same underlying dynamics, with k_BT the link between them.

Kubo was also a celebrated teacher and author. His textbooks on thermodynamics and statistical mechanics, with their extensive worked problems, educated generations of physicists around the world.

He received many honours, including the Boltzmann Medal in 1977, and remained a central figure in statistical physics until his death in 1995.