Joseph Larmor and the ring current model of an electron

Joseph Larmor is surely not among the more famous participants in the Solvay Conferences. He only joined the 1921 Conference, together with Charles Glover Barkla and others, and his one and only substantial intervention there is limited to some remarks and questions following a presentation by H.A. Lorentz on the Theory of Electrons, during which Lorentz highlights all of the issues in regard to what was then supposed to be the understanding of what an electron actually is (which, in my not-so-humble-view, is still pretty much the state of our current understanding of it).

I find his one intervention (and Lorentz’ reply to it) very interesting though, and so that’s why I am writing about it here. I am not aware of any free online English translations of the proceedings of the Solvay Conferences (nor of any translation of Lorentz’ paper in particular) but you may be luckier than me when googling: if you find it, please do let me know. In the meanwhile, I am happy to freely translate part of Larmor’s rather short intervention after Lorentz’ presentation from French to English:

“I understand that Mr. Lorentz was given the task to give an overview of how electrons behave inside of an atom. That requires an overview of all possible theories of the electron. That is a highly worthwhile endeavor which, in itself, would already justify the holding of this Conference. However, Mr. Lorentz might have paid more attention to the viewpoint that the electron has some structure, and that its representation as a simple distribution of electric charge can only be provisional: electrons explain electricity, but electricity does not explain electrons. However, the description of an electron in terms of a charge distribution is, for the time being, all we can imagine. In the past, we thought of the atom as an indivisible unit – a fundamental building block – and we imagined it as a swirling ring. That idea is gone now, and the electron has now taken the place of the atom as an indestructible unit. All we can know about it, is how it influences other bodies. If this influence is transmitted all across the aether, we need to be able to express the relations between the electron and the aether[1], or its force field in the space that surrounds it. It may have other properties, of course, but physics is the science that should analyze the influence or force of one body upon others.

The question we should raise here is whether or not an electron formed by a perfectly uniform current ring can grab onto the aether in a physical sense, and how it does so if its configuration does not change.” (Joseph Larmor, 1921, boldface and italics added)

Larmor then talks about the (possible) use of the energy-momentum tensor to address the latter question, which is a very technical discussion which is of no concern to us here. Indeed, the question on how to use tensors to model how an electron would interact with other charges or how it would create an electromagnetic field is, effectively, a rather standard textbook topic now and, in case you’d be interested, you can check  my blog on it or, else, (re-)read Chapters 25, 26 and 27 of Feynman’s Lectures on electromagnetism.

What grabbed my attention here was, effectively, not the technicality of the question in regard to the exact machinery of the electromagnetic force or field. It was Larmor’s description of the electron as a perpetual or persistent current ring (the French reference to it is this: un electron formé par un courant annulaire parfaitement uniforme), and his language on it, which indicates he thought of it as a rather obvious and natural idea! Hence, Parson’s 1915 toroidal ring model – the precursor to Schrödinger’s Zitterbewegung model and modern-day ring current models – was apparently pretty well established at the time! In fact, Rutherford’s lecture on the Structure of the Atom at the 1921 Conference further confirms this, as he also talks about Parson’s électron annulaire (ring electron) and the apparent magnetic properties of the electron (I will talk about Rutherford’s 1921 Solvay lecture in my next post).

Larmor’s belief that the electron was not pointlike should, of course, not surprise us in light of his rather famous work on the quantum-mechanical precession of the magnetic moment of an electron, but I actually wasn’t aware of Joseph Larmor’s own views in regard to its possible reality. In fact, I am only guessing here but his rather strong views on its reality may explain why the scientific committee − which became increasingly dominated by scientists in favor of the Bohr-Heisenberg interpretation of physical reality (basically saying we will never be able to understand it)  − did not extend an invitation to Larmor to attend the all-important Solvay conferences that would follow the 1921 Conference and, most notably, the 1927 Conference that split physicists between realists and… Well… Non-realists, I guess. 🙂

Lorentz’ immediate reaction to Larmor mentioning the idea of a swirling ring (in French: un anneau tourbillon), which is part of his reply to Larmor’s remarks, is equally interesting:

“There is a lot to be said for your view that electrons are discontinuities in the aether. […] The energy-momentum formulas that I have developed should apply to all particles, with or without structure. The idea of a rotating ring [in French: anneau tournant] has a great advantage when trying to explain some issues [in the theory of an electron]: it would not emit any electromagnetic radiation. It would only produce a magnetic field in the immediate space that surrounds it. […]” (H.A. Lorentz, 1921, boldface and italics added)

Isn’t that just great? Lorentz’ answer to Larmor’s question surely does not solve all of the problems relating to the interpretation of the electron as a current ring, but it sure answers that very basic question which proponents of modern quantum mechanics usually advance when talking about the so-called failure of classical physics: electrons in some electron orbital in an atom should radiate their energy out, but so they do not. Let me actually quote from Feynman’s Lectures on Quantum Mechanics here: “Classically, the electrons would radiate light and spiral in until they settle down right on top of the nucleus. That cannot be right.”

Surely You’re Joking, Mr. Feynman! Here is the answer of the classical quantum theorists: superconducting rings of electric current do not radiate their energy out either, do they?

[1] Larmor believed an aether should exist. We will re-quote Robert B. Laughlin here: “The word ‘ether’ has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. […] The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo.”

On the concept of the aether, we can also usefully translate part of Lorentz’ answer to Larmor: “As for the aether, even the physicists who still talk about it have stripped the concept of anything it might have in common with matter. I was a believer in an immobile aether myself but I realize that, because of relativity, we cannot talk about any force acting on the aether. However, I still think of the aether as the seat of electromagnetic energy (in French, le siège de l’énergie électromagnétique). Now, we can all think of the components of the energy-momentum tensor like we want, but if we think of some of them being real in some sense, then all of them should be real in the same sense.”

Post scriptum: I should really stop duplicating posts between this and my other blog site on physics. Hence, I beg the readers who want to keep following me to do so on my ideez.org site. I think I’ll devote it a historical analysis of how useful and not-so-useful ideas in physics have evolved over the past hundred years or so, using the proceedings of the Solvay Conferences as the material for analysis.