As part of this year’s celebration of the centenary of quantum mechanics, we present this adaptation of an article that was published in the April 2025 issue of Physics Today, an AIP publication, with the title, “Demythologizing quantum history.” It was written by Ryan Dahn, a historian of science and a senior associate editor at Physics Today.
The United Nations has proclaimed 2025 to be the International Year of Quantum Science and Technology. Official pronouncements about the IYQ tend to emphasize forward-looking technological applications of quantum science, such as computing and cryptography. They refer only obliquely to the reason why this year was chosen: that it is, allegedly, the centennial of the development of quantum mechanics.
This week, one of the most prominent IYQ meetings is taking place on the German island of Helgoland, featuring many distinguished figures in recent quantum science, including 2022 Nobel laureates Alain Aspect, John Clauser, and Anton Zeilinger. In keeping with IYQ’s emphasis, the meeting focuses on the future of quantum science and technology. But the location of the conference is a nod to a particular and popular origin myth: that Werner Heisenberg developed matrix mechanics, a first formulation of a fully foundational quantum theory, on a visit to the island in June 1925.
By any estimation, 1925 was a pivotal year. At that time, the deficiencies of what historians now term the old quantum theory were apparent. Based on Bohr’s atomic model, which was refined by Arnold Sommerfeld and others, the old theory could not accurately model the spectra of anything heavier than ionized helium. So, 1925 marked the turning point toward the quantum mechanics we know today: a theory that remains part of the backbone of our understanding of the universe. It therefore does make sense to celebrate the centennial this year. But—appropriately enough, given the subject matter—the more one tries to locate a precise origin of modern quantum mechanics, the more indeterminate the very idea becomes.
A view of the main island of the Helgoland archipelago around the turn of the twentieth century, as seen from a neighboring island.
Library of Congress, Prints and Photographs Division, Washington, DC
The birth of a myth
Despite efforts from historians to tell a nuanced story about the birth of modern quantum mechanics, the tale about Helgoland that’s seeped into the broader consciousness seems to stem from Heisenberg himself. As the German physicist related on several occasions, most notably in his 1969 memoirs, he had reached an impasse in his investigations of several problems in the old quantum theory in June 1925 when he was stricken by a bad bout of seasonal allergies. Seeking relief, Heisenberg decamped from his position at the University of Göttingen in Germany to the nearly pollenless island of Helgoland in the North Sea.
Free from distractions and fortified by long walks and swims, Heisenberg devoted himself to his work attacking the inconsistencies in the old theory. One evening, he made the crucial breakthrough: energy conservation had to hold true in his new quantum theory just as it did in classical physics. After working through the night carrying out calculations, he was quickly able to finish drafting a paper upon returning home.
On July 29, Heisenberg submitted his paper , whose title translates as “On a quantum theoretical reinterpretation of kinematic and mechanical relations,” to the Zeitschrift für Physik, a relatively new German journal that had gained a reputation for publishing cutting-edge research. In the popular narrative, the Umdeutung (“reinterpretation”) paper, as it’s typically referred to after its original German title, birthed the matrix formulation of quantum mechanics and almost single-handedly initiated a dynamic period of feverish work that culminated in the creation of modern quantum theory in an astonishingly short amount of time. By 1927, it was mature enough that Bohr and Einstein were debating its philosophical implications at the Fifth Solvay Conference on Physics. And a few years later, Heisenberg would receive the 1932 Nobel Prize in Physics “for the creation of quantum mechanics.”
But the veracity of the Helgoland story is dubious at best. It has its roots in Heisenberg’s memoirs, Der Teil und das Ganze, which were published in English in 1971 under the title of Physics and Beyond . But memory is notoriously unreliable. Heisenberg admitted in the book’s preface that it wasn’t a “historically accurate retelling of all the various events in every detail” and that he only intended to depict the “broader picture.” Far too many writers have taken his account as gospel.
Contemporary evidence confirms that Heisenberg spent about 10 days on Helgoland in June 1925. It’s not clear how much he accomplished there. As Anthony Duncan and Michel Janssen note in their recent magisterial history of the 1920s quantum revolution, Heisenberg probably did much of the work on the Umdeutung paper before and after his brief visit to Helgoland.
Moreover, as they point out, several letters he wrote to Wolfgang Pauli in June and July of that year indicate that Heisenberg was not confident in his theory at first. He was so unsure of his results that he gave his finished manuscript to Max Born, who supervised his 1924 habilitation at the University of Göttingen, to look over and decide whether it was worth submitting. That’s not exactly what you’d expect from someone who allegedly had a eureka moment.
Werner Heisenberg, center, accompanied by Enrico Fermi, left, and Wolfgang Pauli, at the Como Conference in 1927.
Photograph by Franco Rasetti, courtesy AIP Emilio Segrè Visual Archives, Segrè Collection
Moreover, the Umdeutung paper is notoriously obscure. Something of a cottage industry among technically oriented historians of physics has developed that attempts to explain both the content of the paper and its intellectual backstory. Tellingly, the various exegeses of the Umdeutung paper invariably dwarf the slender 15-page original. An early and widely cited 1977 article on the topic by historian and philosopher Edward MacKinnon, for example, runs to 52 pages, while Duncan and Janssen devote an entire 46-page chapter of their book to it.
It was only after other researchers recognized that Heisenberg’s clunky calculations could be elegantly rewritten using the mathematical language of matrices—a formalism unknown at the time to nearly all physicists, including Heisenberg—that his work began to assume the form in which it is taught today. Born was immediately captivated on reading Heisenberg’s Umdeutung paper, and he soon roped the mathematically talented Pascual Jordan—one of his former doctoral students—into a collaboration. They submitted their paper on the topic, whose title translates as “On quantum mechanics,” to the Zeitschrift für Physik on September 27, 1925. It was only in that article that matrix mechanics started to resemble something that today’s physicists are likely to understand.
Even before finalizing the paper, Born and Jordan began collaborating with Heisenberg on a follow-up article that was submitted to the Zeitschrift für Physik on November 16 that same year. Often referred to as the “three-man paper,” it was arguably the most crucial milestone of that year: historian of science Max Jammer termed it the “first comprehensive exposition of the foundations of modern quantum mechanics in its matrix formulation.” Heisenberg admitted that the Royal Swedish Academy of Sciences should have split the 1932 Nobel Prize: after receiving the news about the award, he wrote separately to Born and Jordan stating that he was sorry the three had not shared it.1
An important lesson
The lesson about the collaborative origins of quantum mechanics extends well beyond the three-man paper. Historians estimate that between 1925 and 1927, almost 200 papers were published—many of which were authored by long-forgotten individuals—that advanced the new theory and applied it to various problems in atomic dynamics.
One prominent example is US physicist Carl Eckart, who asserted the equivalence of the matrix and wave formulations of quantum mechanics independently of Erwin Schrödinger. Working in California, Eckart submitted his paper in June 1926 to a then-obscure journal called Physical Review, some three months after Schrödinger sent off his famous equivalency paper to the Annalen der Physik in Germany. Ironically, most scholars now agree that both Eckart’s and Schrödinger’s proofs were incomplete and that it was actually John von Neumann, building on their and others’ work, who conclusively showed in a series of publications in the late 1920s and early 1930s that the two formulations were equivalent.
Carl Eckart.
AIP Emilio Segrè Visual Archives
Lucy Mensing, who was working in Göttingen when Heisenberg, Born, and Jordan made their breakthrough in 1925, quickly became acquainted with the new quantum mechanics and may have been the first individual to apply the theory to diatomic molecules. Mensing followed up her pathbreaking article by collaborating with Pauli—who had supervised her dissertation in Hamburg—on presenting a quantum understanding of the electric polarizability of those molecules.2 Physicist Gernot Münster terms the article a “milestone in applied quantum mechanics.”
Another physicist working in Göttingen during the quantum revolution of the mid-1920s was Hertha Sponer. She went on to publish a number of works, including an influential two-volume set on spectroscopy in 1935-36 that experimentally confirmed predictions of quantum mechanics. Unlike Mensing, who soon left physics, Sponer remained in academia for the long haul. As a woman in Nazi-ruled Germany, she had little hope of obtaining an academic position, so she ended up emigrating, first to Norway in 1934 and then in 1936 to the US, where she received a tenured position at Duke University.3
Eckart, Mensing, and Sponer are just the tip of the iceberg: there are many other early quantum innovators who aren’t part of the standard canon. If we’re going to recognize the 100th anniversary of quantum mechanics this year, let’s broaden the scope of our celebration. At the very least, let’s avoid the type of hero worship emblematized by the Helgoland myth.
The author thanks Michel Janssen for providing helpful comments that prevented the inadvertent propagation of several quantum myths.
Non-linked references
1. Heisenberg to Born, November 25, 1933, file 1/3/2/4, papers of Professor Max Born, Churchill Archives Centre, University of Cambridge; Jordan to Heisenberg, June 6, 1934, file 1515/2, Werner Heisenberg papers, Archives of the Max Planck Society, Berlin.
2. L. Mensing and W. Pauli, “Über die Dielektrizitätskonstante von Dipolgasen nach der Quantenmechanik” Physikalische Zeitschrift 27 (1926): 509–512.
3. Mensing is profiled by Gernot Münster and Michel Janssen, and Sponer by Elise Crull in the volume to be released this month, Women in the History of Quantum Physics: Beyond Knabenphysik, Patrick Charbonneau, Michelle Frank, Margriet van der Heijden, and Daniela Mondaldi, eds. (Cambridge University Press, 2025).
Other citations in this piece may be found in the links above and in the original article.
Ryan Dahn
American Institute of Physics
rdahn@aip.org
Sign up to receive the Weekly Edition and other AIP newsletters by email here.
More from AIP
