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The uncertain art of reconstructing history

4 January 2023

For historians, interpreting what is left unsaid in a letter can be as important as understanding the words on the page itself.

One stereotypical image of a historian is someone poring over dusty volumes in search of some pure truth. There’s some accuracy in that vision—I’ve looked at a lot of musty tomes and crumbling documents over the years—but the reality is that there’s almost never a singular truth out there to be found. People are complex and unpredictable, and what one person sees as the truth may seem like a misrepresentation to someone else.

I learned an early lesson in humanity’s fundamental unknowability about eight years ago, when I began carrying out research for my PhD dissertation on the German physicist Pascual Jordan (1902–80). One of the founders of quantum mechanics in the 1920s, Jordan worked in close collaboration with such prominent Jewish physicists as Max Born, Wolfgang Pauli, and James Franck. Despite his friendships with those men, Jordan joined the Nazi Party in 1933 and proceeded to propagandize for its cause, even after the regime’s genocidal intentions were revealed. He was no opportunist; he had been publishing in far-right journals under a pseudonym since 1930. That dissonance in his life story was what brought me to Jordan. How could someone who held his Jewish friends and collaborators in high esteem join the Nazi Party and agitate in its favor?

You can learn more about Jordan’s paradoxical life in my article “Nazis, émigrés, and abstract mathematics,” in Physics Today’s January 2023 issue. It details the story behind one of his most-cited papers, a mathematical article he wrote in 1933 with Eugene Wigner and John von Neumann, two Hungarian Jewish mathematical physicists who had been educated in Germany. Titled “On an algebraic generalization of the quantum mechanical formalism,” the paper outlined a form of nonassociative algebra that was later named after Jordan. (Jordan hoped that his algebra would help further generalize quantum theory. That was not to be. But the study of his algebras now comprises an entire subfield of mathematics.) The collaboration among Jordan, Wigner, and von Neumann occurred under circumstances that were anything but ordinary. The article was written as Jordan was joining the Nazi Party and as Wigner and von Neumann were preparing to move to the US to avoid Nazi persecution.

Pascual Jordan, 1934.
Pascual Jordan stands at a blackboard during a conference in the 1930s at the Institute for Theoretical Physics (now the Niels Bohr Institute) at the University of Copenhagen. Credit: Photograph by Paul Ehrenfest Jr, courtesy of the AIP Emilio Segrè Visual Archives, Weisskopf Collection

When I began poking through Jordan’s unpublished papers in various archives, I hoped to find a smoking gun: some buried document, diary, or manuscript that would perfectly explain his motivations. I slowly realized that this mythical piece of evidence didn’t exist—and probably never had. Instead, as I pored through letters and manuscripts, I gradually picked up bits and pieces of revealing information. In my article, I reconstruct the story of the three-man collaboration using a few of those historical tidbits: seven letters Jordan wrote to Wigner and von Neumann along with Jordan’s original draft manuscript of their joint paper.

Archival vicissitudes

My sources were located in collections of personal papers, which are typically donated to research institutions by the individuals or their families. In my case, I was lucky, because Jordan, Wigner, and von Neumann all have personal archives—at the Berlin State Library, Princeton University Library, and the Library of Congress, respectively—that are publicly available. In many cases, the papers of famous individuals remain in private hands or have been destroyed. And if you aren’t a famous scientist, your papers probably won’t be of interest to most libraries.

It’s quite remarkable that the sources I’ve used have survived. Wigner brought Jordan’s letters with him from Europe when he emigrated to the US and then held onto them for more than six decades before his death in 1995. Jordan’s letters to von Neumann also crossed the Atlantic, and he held on to them for more than 20 years before his death in 1957. The draft manuscript of the article is one of the very few items in Jordan’s archive that dates from before 1945.

The interior of Berlin State Library showing bookshelves, tables, and large windows
The main reading room of the Berlin State Library’s building on Potsdamer Strasse. Pascual Jordan’s papers were housed here when the author carried out his research in 2014–16, but they were moved in 2020 to the library’s other building, which is located on the stately boulevard Unter den Linden. Credit: Lessormore, Wikimedia Commons, CC BY-SA 4.0

That last point is perhaps the most remarkable of all. Like those of many German scientists, Jordan’s papers did not survive the Nazi era unscathed. A cache of correspondence with Jewish colleagues that Jordan hid during the Nazi era out of fear that the Gestapo would search his apartment seems to have been destroyed in a wartime bombing raid; he lost countless other papers, manuscripts, and books during the war; his apartment in the German city of Rostock was requisitioned and probably plundered by Soviet forces after the war; he or his family may have destroyed documents relating to his Nazi ties in the postwar period; and—something not to be underestimated—Jordan was never a pack rat. (Some people are savers. He wasn’t.) And yet, the manuscript to the Jordan-Wigner-von Neumann paper survives in his archive!

Piecing together a narrative

As I note in the article, quite a bit of correspondence between Jordan, Wigner, and von Neumann is missing. That is typical. After all, do you keep every letter or email you receive? None of the letters Wigner and von Neumann sent to Jordan survived. Some letters that Jordan sent to Wigner and von Neumann appear to be lost as well.

Moreover, especially before the war, Jordan had a habit of leaving his letters undated. When I found a trove of letters Jordan sent to Wigner in 1933 in the Princeton University Library, I quickly realized that they were out of order. I was able to roughly date them by looking closely at clues in the text. Some were obvious: In one letter to von Neumann, Jordan thanks his friend for a prior letter dated 18 July 1933, which means that the letter I was reading must have been written after that date.

Other clues required deeper contextual understanding. In my article, I analyze a letter from Jordan to Wigner that inquires whether scholars like Max Zorn, a mathematician, and Walter Gordon, a physicist, had been dismissed because of their religious or political beliefs. The law that enabled the Nazis to purge universities of Jewish and left-leaning scholars was promulgated on 7 April 1933. So the letter must have been written after 7 April. But because of mass confusion over, among other things, who exactly was to be considered a Jew, the authorities were forced to issue several clarifying decrees. That meant that the purge of scholars from universities didn’t begin in earnest until later in the month. For that reason, I’ve dated that letter to late April. But it could have been written in May.

Exterior photo of the Harvey S. Firestone Memorial Library, which is the main building of Princeton University Library
The Harvey S. Firestone Memorial Library, the main building of the Princeton University Library, houses Eugene Wigner’s personal papers. Credit: Andreas Praefcke, CC BY 3.0

I can’t say with certainty that my dating and ordering of the letters is correct. In the letter to von Neumann that dates from after 18 July 1933, for example, Jordan tells von Neumann to ask Wigner about a letter that discusses an equation Jordan abbreviated as “(⁎).” One of the surviving letters to Wigner does indeed contain an equation that Jordan abbreviated with that symbol.

But Jordan doesn’t define (⁎) in the letter to von Neumann. It seems clear that (⁎) is referring to the same equation in both letters, and thus that the letter Jordan sent to Wigner is, in fact, the very letter that he mentions in his late July letter to von Neumann. That conclusion, of course, implies that the letter to Wigner that first defines (⁎) was sent before the letter to von Neumann. Yet one could argue that there might be another letter, now lost, that contains a different equation that Jordan abbreviated as (⁎). As you can see, it can be difficult to reconstruct past events.

Interpreting tone

Even trickier than dating undated letters or identifying abbreviated equations is reading between the lines. And make no mistake; Jordan’s letters to Wigner and von Neumann must be read like that. On 28 February 1933, the day after the German Reichstag burned down in an arson attack whose origins remain mysterious, the Nazi government issued what became known as the Reichstag Fire Decree. Among many other intrusions on civil liberties, the decree allowed the government to snoop on private correspondence. Many people quickly stopped writing about certain topics in letters or discussed them in a subtle, circumspect manner.

The Nazi purge of Jewish and left-leaning scholars like Wigner and von Neumann was one of those sensitive topics. So when Jordan inquired about Zorn and Gordon, one must consider what was being implied or left unsaid. Maybe he asked about Zorn and Gordon—but not Wigner himself or von Neumann—to subtly ask about Wigner’s own status as well. It may have been safer to inquire about a third party than to ask directly. Similarly, after inquiring about Zorn and Gordon, Jordan tells Wigner that he was “very sad” that they wouldn’t be able to meet in person, because there were “so many things I would like to talk with you about.” I interpret that statement as implying that Jordan wanted to talk to Wigner about the dismissals and was saddened to hear that scholars like Wigner and von Neumann were being sacked.

As with the dating of the letters, though, it’s possible to interpret such passages differently. Maybe Jordan just wanted to meet with Wigner to talk about mathematics, physics, and their collaborative work. Maybe he really wasn’t that concerned about his friends’ fate.

I’m confident that I’ve correctly interpreted Jordan’s letters to Wigner and von Neumann, and I certainly hope you’ll agree with my version of the story. But it’s instructive to consider the possible fallibility of the historian. Too often, we still think there is one incontrovertible truth in history that’s waiting to be uncovered. In the vast majority of cases, that’s simply untrue. Evidence is always incomplete; inferences must be made. There’s almost always room for an alternate interpretation. But should we expect anything else? Humans are complicated and contradictory. Why should history be any less so?

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