Niels Bohr’s Times, in Physics, Philosophy, and Polity

1. Ehrenfest71 on adiabatics. Paul Ehrenfest studied physics in his native Vienna, where his contact with Boltzmann (under whose guidance he obtained the Ph.D.) was decisive in directing him to his principal scientific devotion, statistical physics. As was noted earlier (5d, e) that was the branch of physics which had served Planck and Einstein as their prime tool in their earliest work on quantum theory. Ehrenfest studied their papers carefully. As a result he became probably the first after the founders to publish on quantum problems, beginning in 1905.72 These early papers already showed what Einstein later called 'his unusually well developed faculty to grasp the essence of a theoretical notion, to strip a theory of its mathematical accoutrements until the simple basic idea emerged with clarity. This capacity made him... the best teacher in our profession whom I have ever known.'73 He was respected by all who knew his work except by himself.