Paul Ehrenfest, Austrian-Dutch physicist and academic (d. 1933)
Paul Ehrenfest (18 January 1880 – 25 September 1933) was an Austrian-Dutch theoretical physicist, who made major contributions to the field of statistical mechanics and its relations with quantum mechanics, including the theory of phase transition and the Ehrenfest theorem. He bonded with Albert Einstein on a visit to Prague in 1912 and became a professor in Leiden, where he frequently hosted Einstein.