The picture of some two dozen physicists, some of them pretending to be engaged in serious discussions, taken at the Hotel Metropole in Brussels in 1911 is one of the most reproduced images in the histories of early quantum physics. Indeed, the first Solvay conference in physics played a significant role in providing a forum in which a selection of European physicists could collectively discuss the potential and validity of the quantum hypothesis. Similarly, the fifth Solvay conference in 1927 is often represented as a pivotal moment in the transition to quantum mechanics. This book is one product of the ambitious Solvay Science Project dedicated to studying, preserving and digitizing the archives of the Solvay conferences and to gaining their recognition as part of the UNESCO World Heritage. The latter finally happened in 2023.

As for this book, the authors’ goal was to write a history of quantum physics and early quantum mechanics with the five Solvay conferences in physics between 1911 and 1927 as the backbone of their narrative, and with a particular emphasis on H.A. Lorentz’s role as president of the five meetings. We also learn a few aspects of the foundation and inner workings of the International Solvay Institute for Physics and its lesser-known programme of grants to subsidize research projects and instrumentation.

Let me start with the latter. Having recently worked on the history of another international institution (the International Union of Pure and Applied Physics, IUPAP), I understand the disappointment one may have with the scarcity of information in institutional archives, particularly concerning their beginnings. This book seems to show a similar limitation: the reader is left wanting more direct information about the early days of the institution and the behind-the-scenes preparation of the conferences. Indeed, there are a few documents regarding initial suggestions by the members of the Scientific Committee on which subjects to address at the meetings, but much of what is being said about the conferences, their preparation and their immediate impact relies on the published proceedings and on recollections by some of the attendees many decades later. At the same time – and this I would argue is a significant deficiency – there is hardly any reference to the relationship between the Solvay Institute and other scientific institutions of its day. The culture of internationalization and trans-national scientific societies was booming in the early twentieth century (both before and after the Great War), but by focusing only on the Solvay initiative this book might give the impression that this was a unique enterprise.

In their effort to stress the importance of the Solvay meetings, not only do the authors fail to draw a broader institutional, political and social context (besides the way Lorentz and others dealt with the postwar boycott of German scientists), they also often exaggerate the role of the conferences in their historical reconstruction of the history of quantum physics. More often than not, this reader is left with the impression that this is a reproduction of the standard history of quantum physics only with the novelty that the main theoretical and experimental developments are temporally set in relation to the Solvay meetings. To give just a few examples: ‘It is interesting to note that as the Third Physics Council came to a close … Arthur Holy Compton … was about to discover an effect that would be crucial to the quantum revolution’ (p. 132); or ‘the timing [of the fourth Physics Council] … was hardly favourable. Major advances that were to mark the last months of the “Old Quantum Theory” had not yet taken place’ (p. 138). Everything did indeed happen before or after one such scientific conference, but one is left wondering whether the authors are trying to depict a causal relationship between these meetings and some of the scientific milestones in the history of quantum physics. In other words, would the development of quantum physics have been any different had the Solvay meetings not taken place?

Finally, the storyline of the so-called ‘quantum revolution’ is not only based on well-established literature, but far too often built upon lengthy quotes (up to three pages long), mixing works by professional historians of science, reminiscences of some of the actors themselves at a later stage and introductory paragraphs of some of the original scientific papers, all of which are valid sources when approached critically and not simply at face value. In the context of the 2025 centenary of quantum mechanics, the idea behind this book was an interesting one; the outcome does not always meet those expectations.