Naming Names in QED

I’m doing edits on the QED chapter of the book-in-progress today, and I’m struck again by the apparent randomness of the way credit gets attached to things. QED is a rich source of examples of this, but two in particular stand out, one experimental and the other theoretical.

On the experimental side, it’s interesting to note that one of the two experimental effects that really galvanized the theoretical effort leading to QED bears the name of a particular person, while the other does not. Ask any physicist about the origin of QED, and they will almost certainly be able to cite the “Lamb shift” as one of the motivations– “Lamb” in this case is Willis Lamb, a theorist who was recruited for radar research during WWII, and was inspired by that to do an experimental measurement of the hydrogen spectrum using the new tools provided as a side benefit from the war effort. His measurement, with Robert Retherford, a grad student at Columbia, conclusively showed that there is a shift in the energy levels of hydrogen from what the simplest application of the Dirac equation would predict. This resolved an experimental debate that had been simmering for a decade or so, and forced theorists to grapple with a bunch of problems that they had been able to ignore to that point.

But the Lamb shift wasn’t the only new and problematic result reported at the famous Shelter Island conference in 1947. It wasn’t even the only ground-breaking result out of Columbia University– also at the meeting, I.R. Rabi reported the measurement of another small deviation from the simplest prediction, by John Nafe and Edward Nelson, showing some odd discrepancies in the magnetic behavior of hydrogen. This was the effect that, according to comments in The Second Creation by Mann and Crease, particularly inspired Julian Schwinger to work on his version of QED (since all but a tiny piece of the Lamb shift could be explained by a non-relativistic calculation that Hans Bethe did on the train home after the Shelter Island meeting). Schwinger’s calculation of this particular effect gave a compact expression that’s carved on his tombstone: α/2 π.

The second effect is known as “the anomalous magnetic moment of the electron,” or if people want to be compact, “g-2” (as the mathematical symbol expressing the important quantity is a lowercase g, and the expected value from Dirac’s equation is exactly 2, so g-2 is the discrepancy that must be explained by QED). The names of Nafe and Nelson would likely draw a blank stare from most of the same physicists who would instantly recognize the important of the Lamb shift. In fact, I had to look their names up for this post, which I did by Googling “Lamb and Retherford” in the Google Books version of The Second Creation and reading forward to where the anomalous magnetic moment was mentioned.

Despite being of equal historical importance, one of the critical experimental effects is named for (one of) its discoverer(s), and the other is not. It’s kind of weird, when you think about it. There are a lot of reasons for this, some having to do with science– Nafe and Nelson didn’t immediately interpret their result as an anomalous magnetic moment, and some later measurements were needed to show that that’s what was going on– others with sociology– Lamb remained an important player in physics, and was well-known in the community while the others were of lower status and didn’t necessarily stick with physics (Nafe went into geology, Nelson’s name is too common for Google to turn up much, and Retherford only has a stub of a bioigraphy). The comparison of the two is a useful reminder of the essential arbitrariness of the way credit gets handed out in physics (see also a famous boson that I’m thoroughly sick of).

On the theory side, the interesting issue has to do with Sin-Itiro Tomonaga. While Julian Schwinger and Richard Feynman were well connected to the physics community, and invited to the Shelter Island workshop to hear about new developments, Tomonaga was working in isolation in the devastation of post-war Japan, and learned of the Lamb shift from a newspaper article. Once he heard about it, though, he and his students quickly rushed through a calculation of the effect, getting the correct answer, which they sent off to Robert Oppenheimer in the US who had just returned from the Pocono conference where Schwinger and Feynman announced their versions of QED. Oppenheimer wrote back immediately recommending they write up a paper, alerted his colleagues to Tomonaga’s work, and made sure the eventual paper was published. Nearly twenty years later, Tomonaga shared a Nobel Prize with Schwinger and Feynman for developing QED.

Of course, the Nobels are famously limited to three recipients, and there’s a fourth figure who could easily have been in there with them: Freeman Dyson. In fact, in what’s generally regarded as the definitive history of this, Silvan Schweber’s QED and the Men Who Made It, Dyson comes off as arguably the most important of the four. He’s the one who, thanks to a summer school Schwinger ran and a long car trip he took with Feynman, was able to show that the three forms of QED were mathematically equivalent, and did a lot of the heavy lifting to make QED useful for non-geniuses. While Tomonaga was unquestionably earlier, Dyson’s eventual contribution was far more important. And yet, Tomonaga shared a Nobel, and Dyson did not.

There are a lot of interesting angles to this particular story, because they go against some stereotypes. The last time I wrote about the history of QED, I immediately got a pissy comment accusing me of saying that only well-connected white males matter in science. Of course, the story of Tomonaga and Dyson is an obvious counterexample– Dyson is white, male, and well-connected, while Tomonaga was only one of those at the time. And Oppenheimer’s central role in the story is also fascinating– he was, after all, the head of the Manhattan Project that produced the atomic bombs dropped on Tomonaga’s home country, and he and Dyson famously butted heads about QED for a while at Princeton.

Sadly, I haven’t seen a really good discussion of this episode. Schweber’s book includes an apologetic note that he really doesn’t know all that much about Tomonaga, and both it and the new Oppenheimer bio quote a letter somebody wrote at the time (it might even have been Dyson, I don’t recall) attributing the whole thing to anti-nationalism– that Tomonaga was being celebrated as a way to restrain American hubris in the post-war era. They pretty much leave it at that, which I find kind of disappointing. I’d like to see a more in-depth look at the whole Tomonaga-Oppenheimer-Dyson story (though I have so many other things to do that I haven’t made much of an attempt to find one– I’d be a little surprised if there hasn’t been a history-of-science thesis written about this at some point).

And that’s about as much procrastination as I can justify wringing out of this particular story. Back to editing…