1889 – 1969
Léon Brillouin (1889–1969) was a French physicist who made foundational contributions to quantum mechanics, solid-state physics, and information theory. He is best known for Brillouin zones and Brillouin scattering, and for his landmark analysis connecting physical entropy with information, most fully developed in his 1956 work *Science and Information Theory*. His resolution of Maxwell's Demon paradox—showing that any measurement act is thermodynamically costly—remains a touchstone in philosophy of physics.
Demonstrated that Maxwell's Demon cannot circumvent the second law because measurement requires entropy-increasing energy expenditure
Developed the concept of Brillouin zones, foundational to solid-state and condensed matter physics
Co-developed the WKB (Wentzel–Kramers–Brillouin) approximation in quantum mechanics
Established the formal connection between Shannon information entropy and Boltzmann thermodynamic entropy (negentropy principle)
Authored *Science and Information Theory* (1956), a seminal text linking physics and information science