Paul Ehrenfest classified phase transitions based on the behavior of the (density of) free energy f as a function of other thermodynamic variables (see ref.
And while studying with
Paul Ehrenfest in Leiden, Holland, he met Albert Einstein, who liked and admired Fermi.
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Paul Ehrenfest 1880-1933 An intense physicist with a debilitating streak of self-doubt who could rarely see the valuable gift he offered to physics, and a passionate friend to both Einstein and Bohr.
His research dealt with the interrelated developments of quantum mechanics and statistical thermodynamics, and usually concentrated on the work of individual physicists, such as the development of Ludwig Boltzmann's statistical ideas, Josiah Willard Gibb's early work in thermodynamics,
Paul Ehrenfest's contributions to the quantum theory, the origins of Erwin Schrodinger's wave mechanics, and the life and work of Niels Bohr and Albert Einstein.
One of the unsung heroes of the quantum movement is
Paul Ehrenfest, whose hospitality and spacious living room served as a meeting place for high-level discussions among colleagues and visitors, a catalytic role that once brought Bohr and Einstein together for a week-long discussion, each occupying one of the two spare bedrooms in the Erhrenfest household.
of Pennsylvania) profiles seven of those figures, including the aforementioned Delbruck and Bohr, as well as
Paul Ehrenfest, Lise Meitner, Werner Heisenberg, Wolgang Pauli, and Paul Dirac, describing their activities at the meeting and setting them within the wider context of their lives and careers in the pre-dawn of the nuclear era.
The attendees included Bohr, Paul Dirac, Werner Heisenberg, Lise Meitner, Max Delbruck, and
Paul Ehrenfest. Wolfgang Pauli, another Bohr-meeting regular who happened to miss the 1932 get-together, is profiled as well.
The quite extraordinary intellectual insight of Maxwell, Boltzmann and Gibbs in combining deterministic mechanics for micro-states with a probabilistic or statistical theory of observables (macro-states) and their equally brilliant early critics, like Henri Poincare, Ernst Zermelo and Tatiana and
Paul Ehrenfest, provided a host of delicate and profound conceptual problems, which though much clarified and elaborated are as central now to the proper understanding of the physical Universe as they were a hundred years ago.
Other entries cover Einstein's most notable contemporaries, including Niels Bohr,
Paul Ehrenfest, and Robert Oppenheimer.