Founder Effects in Physics

The legacy of Dan Kleppner and Norman Ramsey

Jun 23, 2025

One of my long-standing half-assed ideas for a Thing that probably won’t get written is a historical article called “Wolfgang Pauli: Grandfather of the Arxiv.” The conceit being that there’s a fairly direct line tracing back from the modern institution of the Arxiv preprint server where researchers freely share their articles to the letter networks of the early days of quantum mechanics, in which Wolfgang Pauli was a central node. Any history of the crucial period is full of references to the voluminous correspondence between the principal figures, sharing draft papers and batting around ideas that would become other seminal papers, often citing letters to or from Pauli.

I like putting Pauli in that role because it seems an odd fit— he was infamously acerbic and opinionated, and on a couple of occasions actually squashed potentially important ideas with his initial negative reaction. Kindlier folks like Sommerfeld or Ehrenfest might seem to make more sense, personality-wise (though Paul Ginsparg, the actual founder of the Arxiv, is actually kind of Pauli-esque…). Pauli’s also only really famous within physics circles, not to the outside world, so in terms of fame, Bohr might be a better fit, or if you wanted to make a play for contemporary pop-cultural resonance, you could throw Oppenheimer in there in his stead, particularly given his role in elevating Tomonaga’s work on QED. Or you could go with the ultimate evergreen reference, and tie it to the story of Einstein recognizing and elevating Satyendra Nath Bose’s work on the statistics of photons.

Whatever specific face you want to put on it, though, I think there’s a decent argument to be made that the rise of the Arxiv is rooted in something specific to physics. For many years, there were attempts to promote one service or another as “An Arxiv for life sciences,” and they always struggled to gain traction. Meanwhile, the Arxiv rolled on, steadily expanding its coverage of physics, a field renowned within academia for the arrogance of its practitioners. For all our reputation for incredible self-regard, though, the institutional culture of physics was amenable to the open sharing of research in a way that other fields were not. That comes from somewhere, and I think it’s at least arguable that the letter networks of the early 1900s are a piece.

(The biggest obstacle to actually writing this (other than, you know, my day job) is that I don’t speak or read German, which means I’d have limited and second-hand access to the actual correspondence of Pauli and the rest…)

Anyway, I was thinking about this over the weekend because I learned that Dan Kleppner of MIT passed away recently. Kleppner was the Ph.D. advisor of my Ph.D. advisor, Bill Phillips, and did pioneering work involving hydrogen masers, Rydberg atoms, and Bose-Einstein Condensation.

He was also an absolutely massive influence on the field of atomic, molecular, and optical (AMO) physics through the large number of students he mentored, but probably overshadowed in that respect by his own Ph.D. advisor, Norman Ramsey, whose academic descendants are everywhere. It’s hard to find an AMO physicist from the US who doesn’t have a connection that can be traced back to Ramsey1.

The influence from these two isn’t just formal academic stuff, though, it’s also cultural. As a student in AMO physics in the 1990s, I remember being struck by how collegial the field was, in contrast to some of the horror stories I would hear about grad student life in other (sub)fields. There was competition between labs, to be sure, but also a sense that everyone was to a large extent engaged in a common enterprise, so it was never all that cutthroat. There was a lot of sharing of preliminary results, and even a fair number of cases where people more or less agreed to avoid stepping on each other’s results.

The first research paper I was an author on was very similar to work being done in a lab in Japan, and they not only let us know what they were doing, they held off submitting their paper on it for a couple of weeks so we could submit ours at the same time. A couple years later, they offered to do the same again, but that time they were farther ahead of us, and we told them to go ahead and send it in, and we’d publish later. (That meant we had to do more work to justify getting a second paper about that topic into a good journal, but it came out great in the end…) This kind of thing went on even in subfields that were a bit more intense— I remember a postdoc getting upset that one of the major groups had delayed starting a particular project by “only” six months because they knew somebody else was working on that, and noting that was a weird thing to get annoyed about, since they weren’t under any obligation to delay their work at all. Within the world of AMO physics, though, that was not an absurd expectation.

When I was writing about the history of laser cooling a year or so ago, and interviewing physicists from the field, almost everybody I talked to cited Ramsey as a big reason for this. He was a towering figure in the field, and also personified class. He visited our lab when I was in grad school and took some time to talk to a nobody of a grad student. Whenever I heard him give a talk, he was extremely gracious about spreading credit around, and while he had some very funny stories about Big Names in physics, there were never sharp edges to them— pointing to foibles, yes, but never anything actually disparaging.

Kleppner could be a bit more acerbic— if he thought something was a dumb idea, he’d absolutely let you know— but was also generous with his time and gracious about crediting other people. You can see a bit of his graciousness in this interview posted by MIT, when he talks about his time at Williams. He pretty clearly did not care for the social aspects— a not uncommon reaction for academically inclined students in that era— but bends over backwards to praise the faculty. He maintained a good connection with the school, and graciously turned up for a good number of “Ephs at DAMOP” photos even when the gap between him and the next oldest graduate was three decades2.

That kind of tone-setting does a lot to shape the culture of a field. It wasn’t just those two, of course— people in Europe also cite Alfred Kastler and Herbert Walther in similar tones, though I can’t speak to them as much. Charles Townes and Art Schawlow3 are also very highly regarded. Put all of that together, and you end up with a field that’s a very pleasant place to work, by the standards of academic science.

Kleppner was also influential in terms of writing about physics— for years he did an intermittent column in Physics Today where he largely talked about physics history. I’ve gotten a lot of mileage out of basically recapitulating his 2005 article about Einstein’s early work on a statistical approach to photons, so he’s a major influence on my side hustles as well as my formal academic career. On the bad (but not actually bad) side, I heard him give a talk at DAMOP where he took the blame for the “Referee 2” problem— he was working with APS on the problem of publication delays, and noted that while they initially sent papers to a single referee, a significant percentage of papers required an appeal to a second reviewer. “Why don’t we just send them to two referees from the start?” he said4…

I reached out to Dan when I was doing those laser cooling stories, and he said “Ask me again in a few months,” by which time I had finished the articles and got buried in Chair stuff. I regret never following up on that, because I bet he would’ve had some good stories to share.

Anyway, Dan was an excellent physicist but also a really good person and his passing is a great loss. He, like Ramsey before him, was an enormous positive influence on the culture of AMO physics, and that’s an outstanding legacy to leave behind.

Kind of a bummer for a Monday, I know, but it is what it is. Anyway, if you like this sort of thing, here’s a button:

And if you have Thoughts about Ramsey, Kleppner, or physics culture in general, the comments will be open:

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