Excerpt from The MANIAC by Benjamin Labatut, plus links to reviews, author biography & more

Speak the truth, write with clarity, and defend it to your very end was Boltzmann's personal motto, and Paul, his disciple, took it to heart. The weight of the respect that Ehrenfest carried among so many outstanding physicists was due to his capacity to bring other people's ideas into sharp focus and capture their fundamental essence, transmitting this knowledge with such passion and vim that his audience was brought in to his thinking as if under a spell. "He lectures like a master. I have hardly ever heard a man speak with such fascination and brilliance. Significant phrases, witty points and dialectic are all at his disposal in an extraordinary manner. He knows how to make the most difficult things concrete and intuitively clear. Mathematical arguments are translated by him into easily comprehensible pictures," wrote the great German theoretical physicist Arnold Sommerfeld, who both appreciated and feared Ehrenfest's fame as the grand inquisitor of physics. Paul did not shy away from pointing out flaws in other people's arguments with the same pitiless criticism with which he would chastise himself; that role of his was particularly important during the fateful Solvay Conference of 1927, when classical physics and quantum mechanics faced off, forever changing the foundations of that branch of science. Ehrenfest mediated between the two major players-Einstein, who abhorred the weight that chance, indeterminacy, probability, and uncertainty were given in the new science of the quantum, and Bohr, who sought to enthrone a fundamentally different type of physics for the subatomic world. At one point, Ehrenfest took to the stage among the gaggle of some thirty-odd Nobel Prize winners screaming over each other in French, English, German, Dutch, and Danish and scribbled a couple of verses from the Bible on the blackboard: The Lord did there confound the languages of all the Earth. Everyone laughed, but the arguments continued to rage on for days, with quantum mechanics coming out victorious over the classical scheme of physics, in spite of, or perhaps due to, the fact that it was completely opposed to common sense. Although Ehrenfest was firmly on the side of the new, and much more open than his friend Einstein to the revolutionary principles coming from Bohr, Heisenberg, Born, and Dirac, he could not shake the feeling that a fundamental line had been crossed, that a demon, or perhaps a genie, had incubated in the soul of physics, one that neither his nor any succeeding generation would be able to put back in the lamp. If one were to believe the novel rules governing the inner realm of the atom, suddenly the entire world was no longer as solid and real as it once was. "Surely there is a special section in purgatory for professors of quantum mechanics!"

Paul wrote to Einstein when he returned from Solvay to Leiden, but all his attempts at humor could not slow his descent into the dark pit toward which he seemed to be spiraling down at a faster and faster pace, not least due to the strange direction that his hallowed discipline was taking, filled as it now was with logical contradictions, uncertainties, and indeterminacies that he could no longer explain to his beloved students, as he had no way of understanding them himself. In May 1931, Ehrenfest confessed his fears to Niels Bohr in a letter: "I have completely lost contact with theoretical physics. I cannot read anything anymore and feel myself incompetent to have even the most modest grasp about what makes sense in the flood of articles and books. Perhaps I cannot at all be helped anymore. Every new issue of the Zeitschrift für Physik or the Physical Review immerses me in blind panic. I know absolutely nothing!" Bohr wrote back to console his friend, pointing out that it was not just Ehrenfest, but the whole of the physics community that was having problems dealing with the latest discoveries, only to receive an even longer letter in return, in which Paul decried that he felt like a dog that, totally exhausted, was running after a streetcar carrying his master out of sight. Where some saw the quantum revolution as a protean fire sparking novel results at an unrelenting pace, Ehrenfest saw mostly stagnation and even degeneration: "Those awful abstractions! That incessant focus on tricks and techniques! The mathematical plague that erases all powers of imagination!" he cried out bitterly before his students in Leiden.

Excerpted from The MANIAC by Benjamin Labatut . Copyright © 2023 by Benjamin Labatut . All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.