A remarkable international collaboration has just completed Women in the History of Quantum Physics: Beyond Knabenphysik (WiHQP), a nearly 500-page volume edited by Patrick Charbonneau, Michelle Frank, Margriet van der Heijden, and Daniela Monaldi and published by Cambridge University Press. The book is organized in rough chronological order around the biographies of sixteen figures:

• Williamina Fleming (by Maria McEachern and Bretislav Friedrich)
• H. Johanna van Leeuwen (by Miriam Blaauboer and Margriet van der Heijden)
• Hertha Sponer (by Elise Crull)
• Lucy Mensing (by Gernot Münster and Michel Janssen)
• Jane Dewey (by Adriana Minor)
• Laura Chalk (by Daniela Monaldi)
• Elizabeth Monroe Boggs (by Patrick Charbonneau)
• Katharine Way (by Stefano Furlan)
• Sonja Ashauer (by Barbra Miguele and Ivã Gurgel)
• Chien-Shiung Wu (by Michelle Frank)
• Grete Hermann (by Andrea Reichenberger)
• Lídia Salgueiro and others at the University of Lisbon (by Ana Simões and Maria Paula Diogo)
• Carolyn Parker (by Charnell Chasten Long)
• Freda Friedman Salzman (by Jens Salomon)
• Maria Lluïsa Canut (by Marta Jordi Taltavull)
• Ana María Cetto Kramis (by Mar Rivera Colomer)

In their introduction, the editors note that they intentionally did not include chapters on well-known figures such as Marie Curie, Lise Meitner, and Maria Goeppert Mayer. This choice was not so much because they wanted to focus on bringing more obscure figures into the scientific pantheon, but because their aim is to build a more expansive and realistic history of physics that is unbound from an exclusive focus on pantheonic achievement.

Illuminating a broader history of quantum physics

The editors point out that there are histories of certain areas of physics that are built largely around the banner achievements of single individuals—particularly Isaac Newton’s foundational work in mechanics and Albert Einstein’s in relativity. Quantum physics, they observe, is different in that it is widely recognized as a collaborative accomplishment. Nevertheless, they insist that popular historical accounts of quantum physics remain structured around a line of heroic theoretical and conceptual advances.

In a bare outline, such accounts typically encompass a series of contributions that built up what is known as the “old” quantum theory, which, during the revolutionary period of 1925 to 1927, was then reformulated and extended into the “new” quantum theory that still prevails. Milestones generally include Max Planck’s introduction of the quantum concept, Einstein’s application of it to the photoelectric effect, Niels Bohr’s atomic model and correspondence principle, Louis de Broglie’s wave-particle duality, and then, in quick succession, matrix mechanics, Erwin Schrödinger’s wave mechanics, Werner Heisenberg’s uncertainty principle, and Bohr’s principle of complementarity.

The rapid development, audaciousness, and mathematical ingenuity of the new quantum theory led some at the time to refer to the endeavor as Knabenphysik, or “boys’ physics.” The editors point out that the term was intended to highlight the youth and energy of many of the figures involved, with any implicit assumptions about gender left unnoted.

Yet, the signal achievements of quantum mechanics were enabled by contemporaneous progress in more traditional areas of physics, and those areas were in turn spurred along by the new theoretical ideas. The WiHQP editors note that historians have appreciated this point for a long time, quoting John Heilbron’s path-breaking historiographical analysis from 1968: “The development of quantum physics was intimately linked to that of other branches of physical science, particularly statistical mechanics, the study of radioactivity, spectral analysis, and the theory of atomic structure.”

The community that produced this larger body of work stretched well beyond the figures we might most associate with the term Knabenphysik. The editors highlight Alexei Kojevnikov’s 2020 book, The Copenhagen Network: The Birth of Quantum Mechanics from a Postdoctoral Perspective , as identifying a group of more than eighty key players. These people were generally as young as the core figures who receive the most attention, and some of them were in fact women, not boys.

A record of experimental and theoretical achievement

In examining the contributions of the community that Margaret Rossiter has referred to as “less-well-known women,” WiHQP aims to probe both the nature of work that women and men did in and around quantum physics, as well as the experiences specific to women in that milieu.

While the most well-known women in this history stand out as almost solitary figures in a field dominated by men, broadening the scope shows that less-well-known women, though well outnumbered, were neither extremely rare nor especially marginal. Many of the women featured in WiHQP made significant or even major contributions to both the experimental and theoretical shifts taking place in physics. Some of these contributions were neglected in their time, though some gained broad recognition.

On the experimental side, quantum physics was built in large part around the need to explain spectroscopic observations. The chapter on Williamina Fleming’s work at the Harvard College Observatory, directed by Edward Pickering, sets the stage by highlighting her observation of peculiar spectral lines for helium. These served as a proving ground for Bohr’s work on the atom, though Fleming’s role was obscured beneath the label given to them: the Pickering series. In the mid-1920s, Jane Dewey and Laura Chalk undertook spectroscopic work on the Stark effect that was in direct conversation with developments in quantum mechanics. Hertha Sponer did extensive spectroscopic work and achieved recognition for the two-volume book she published on the subject in the mid-1930s.

On the theoretical side, Johanna van Leeuwen demonstrated in her 1919 doctoral thesis that various types of magnetism could not be explained in terms of classical mechanics. However, it turned out Bohr had already come to a similar conclusion in a little-noticed part of his own doctoral thesis in 1911; by the late 1930s, the result came to be referred to as the “Bohr-Van Leeuwen theorem.” In the mid-1920s, Lucy Mensing devised some of the first applications of the new quantum mechanics to problems in atomic and molecular physics left unresolved in the old quantum theory. In the 1930s, mathematician and philosopher Grete Hermann offered a critique of John von Neumann’s proof that there cannot be hidden variables governing the probabilistic behavior of quantum systems. That work has only recently gained broader notice with the flourishing of quantum information science.

A fuller picture of women’s careers and perspectives

The women in WiHQP had a wide range of experiences in the physics profession as well as differing reactions to those experiences. Although Mensing’s early work was on the cutting edge of quantum mechanics, she was conscious of the limited professional opportunities for women in the field. After she grew frustrated with her follow-on work and the cutthroat professional atmosphere she encountered, she left physics soon after marrying another physicist and later expressed little regret about her path. Similarly, after Chalk made important contributions around the same time, she scaled back her professional work when she got married. Later in life, she expressed contentment and claimed not to have experienced serious professional discrimination.

Dewey’s experimental accomplishments were similar to Chalk’s, but her attitude toward her career was decidedly different. The daughter of philosopher and educational reformer John Dewey, she came from a background that prized the advancement of women. She received a fellowship to go to Copenhagen, but, despite her promising work there, she had trouble advancing her research after returning to the United States. She ultimately did find a permanent place as a chief physicist with the Ballistics Research Laboratory at the Aberdeen Proving Ground. Around when she retired in 1970, she sent a pessimistic letter to Barnard College’s alumni magazine opposing coeducation so as to keep young women sheltered for a while from the reality of their lower professional status.

The turbulence of the early-to-mid-twentieth century often had profound and unpredictable effects on women’s careers. As Rossiter observed, by the 1920s the entry of women into the physical sciences had grown to such a point that it sparked backlash, particularly in Germany and other countries that descended into fascism. Yet, as Ana Simões and Maria Paula Diogo document in their chapter, progress was just possible, even under hostile regimes such as Portugal’s Estado Novo dictatorship, where an unusually large group of women managed to take root at the University of Lisbon.

Many women escaping conditions in Europe went to the United States, which could be a haven—Sponer, for instance, obtained a tenured position at Duke University—but advancement was still difficult and variable. The deprivations of the Great Depression led administrators to explicitly allocate scarce jobs to men. Then, the demands of World War II led to jobs for figures such as Chien-Shiung Wu, who went on to a highly successful career, and Carolyn Parker, who became the first black woman to earn an advanced degree in physics in the US, though her advancement then stalled in the face of illness and she died prematurely. Following the war, alongside overt discrimination, anti-nepotism rules proved a serious barrier to women scientists in the US, as many were married to other scientists, who tended to be given the higher-status positions. As late as the early 1970s, Freda Friedman Salzman had to fight these rules and ultimately won, but only a few years before her own untimely death.

Many additional insights can be found in WiHQP, and the authors plan to continue their work, with talks and articles listed on their website . AIP is partnering with the collaboration to offer additional materials on our website.

William Thomas
American Institute of Physics
wthomas@aip.org

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