Paul Ehrenfest was an Austrian and 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.
Wikipedia
“You will get your difficulties with the point electron.”
as quoted by Hendrik Casimir in an interview http://www.aip.org/history/ohilist/4550_1.html by Thomas Kuhn, Léon Rosenfeld, Aage Bohr and Erik Ruedinger at the Institute for Theoretical Physics, Copenhagen, 5 and 6 July, 1963.
Attributed
about the theory of general relativity, in a letter dated November 24, 1919, to Albert Einstein.
