Ehrenfest’s adiabatic hypothesis in Bohr’s quantum theory

Enric Pérez, Blai Pié Valls
It is widely known that Paul Ehrenfest formulated and applied his adiabatic hypothesis in the early 1910s. Niels Bohr, in his first attempt to construct a quantum theory in 1916, used it for fundamental purposes in a paper which eventually did not reach the press.
He decided not to publish it after having received the new results by Sommerfeld in Munich. Two years later, Bohr published “On the quantum theory of line-spectra.” There, the adiabatic hypothesis played an important role, although it appeared with another name: the principle of mechanical transformability. In the subsequent variations of his theory, Bohr never suppressed this principle completely.
We discuss the role of Ehrenfest’s principle in the works of Bohr, paying special attention to its relation to the correspondence principle. We will also consider how Ehrenfest faced Bohr’s uses of his more celebrated contribution to quantum theory, as well as his own participation in the spreading of Bohr’s ideas…
…


The Tragic Fate of Physicist Paul Ehrenfest

Physics is not immune from tragedy. Even brilliant minds sometimes grapple with inner demons. The worst situations involve not just the physicists themselves but also their families. Consider the tragic case of Paul Ehrenfest and his son Wassik.
Wassik Ehrenfest was a friendly boy with Down Syndrome who, like many children of his time with that condition, spent much of his life in hospitals and institutions. He lived for some time in a facility in Jena, Germany that was progressive for its age but expensive. Little is known of his life, except through his correspondence with his parents. Encouraged by his teachers, he sent many postcards to his parents to show them what he was learning. When the Nazis rose to power in spring 1933, he was transferred to the Waterink Institute for Afflicted Children in Amsterdam, Holland, founded by educational reformer Jan Waterink….
…