Max Planck

Max Karl Ernst Ludwig Planck was born in Kiel in 1858 and studied in Munich and Berlin, where he was taught by Helmholtz and Kirchhoff. His earliest research, in the 1880s, was in thermodynamics, the subject of his doctoral dissertation on the second law.

As a young thermodynamicist Planck tightened the Kelvin statement of the second law into the precise, modern form now known as the Kelvin–Planck statement, and he clarified the meaning of entropy and irreversibility with a rigour that became a model for the field. His thermodynamic instincts would prove decisive in what came next.

In 1900, studying the spectrum of blackbody radiation, Planck found he could match the data only by assuming that energy is exchanged in discrete packets, or quanta, of size E = hν. This act of desperation, as he later called it, cracked thermodynamics open into quantum mechanics and earned him the 1918 Nobel Prize in Physics. His full profile belongs to the quantum branch of physics; here he appears for his foundational work on the second law.

Planck remained in Germany through both world wars, a figure of great personal integrity amid catastrophe; his son Erwin was executed by the Nazi regime in 1945. He died in 1947, and Germany's principal research organisation, the Max Planck Society, bears his name.