The Aether around the Electron 1899-1904

For the Lorentzian (and Larmorian) theories of the electron, matter, optics, the aether and the electromagnetic fields to interact as required, the aether had to be undetectable.  As we have seen (in the post “Reality Dragged from the Aether”), Larmor worked this requirement out independently in 1900 while this requirement only became clear to Lorentz in 1904 after elaborating his theory of the electron in the context of Kaufmann’s experiments and Abraham’s explanations of them. 

Basically, for Larmor and Lorentz, the aether had to be undetectable because Lorentz invariance (and the associated “contraction” of matter) concealed it.  Much to Abraham’s horror, this concealed action of the aether meant that there were forces in the universe other than electromagnetism and the entire thrust of physics in 1903 was to set aside the discredited mechanical world view and build up a picture of the universe based purely on electromagnetism.  As Janssen and Mecklenberg point out in their “Electromagnetic Models of the Electron and the Transition from Classical to Relativistic Mechanics”:

A choice had to be made between the objectives of Lorentz and Abraham.  One could not eliminate all signs of the Earth’s motion through the aether and reduce all physics to electrodynamics at the same time.  Special Relativity was initially conflated with Lorentz’s theory because it too seemed to focus on the undetectability of motion at the expense of electromagnetic purity.

But when Kaufmann began his series of experiments in 1901 to determine the effect of an electron’s velocity on its mass, the need for such a choice was not yet part of the theoretical problems of the electron.  Miller points out that Kaufmann was following up on Wilhelm Wien’s 1900 outline of a research program to build an alternative to Hertz’s 1894 proposal to develop a completely mechanical description of the universe, which had not proved fruitful.  Wien thought experiments to resolve the increasing mass of the electron as the electron’s velocity increased to one third the speed of light as presented in Lenard’s work with cathode rays was the place to begin building an electromagnetic picture of how the universe was constructed. (see A. I. Miller, Albert Einstein’s Special Theory of Relativity. Pages 46 and 47).  Lorentz in 1901 was not so sure about how to deal with the relation of an electron’s “real” mass (“mechanical” = “real” at this point for Lorentz) to its “apparent” (or “electromagnetic”) mass.

Kaufmann, on the other hand, thought it could all be clarified with his experimental work thus pushing aside the “sterile,” mechanical imagery of the world and beginning anew with the electron as the primordial building-block of the universe.  Rather than being sterile, the electron was stunningly fecund; it appeared to explain luminous vapors, the Zeeman Effect, Planck’s constant, stellar aberration, electrolysis, the photoelectric effect and radioactive decay.  It’s strange that Kaufmann doesn’t seem to have mentioned X-rays, but since he was going to be using beta-rays (electrons) from radium decay in his experiments maybe adding X-rays to the list might have seemed excessive and, of course, in 1901 the nature of X-rays was still not clear except for the general notion that they were not electrons.

As Miller sets the stage on page 48 of Albert Einstein’s Special Theory of Relativity, Kaufmann wanted to use beta-rays since they went up to three times faster than cathode rays (ie the electrons of cathode rays were measured traveling at speeds up to 0.3c, about one third the speed of light while beta-ray electrons had been measured at speeds of up to 0.9c).  In 1899, William Sutherland put that close-to-light-speediness in the context of the concerns of the time, pointing out, “The electrons stream through the aether with nearly the velocity of light and yet provoke no noticeable resistance.  What wonder, then, that any aetherial resistance to planetary motion has remained beyond our ken!”  At such high speeds, the additional mass that the electrons acquired due to their velocities would be open to exact measurement by tracing the effects on their trajectories by using electrical and magnetic fields of known strength.   For cathode rays these kinds of measurements had determined the ratio (at least) of the electron’s charge to its mass.  But what if the field of the charge, interacting with other fields, determined the mass?  Miller notes that J. J. Thomson had worked out this possibility as early as 1881, work that was clarified by Thomson and Heaviside in 1889 and Searle in 1897.  Kaufmann used Searle’s expression for the mass increase caused by the movement of a spherical body with a uniform surface charge distribution as his basic phenomenological reference point in describing the meaning of the curves that his beta-rays (presumed to be spherical electrons)  produced on photographic emulsions after passing through a set of parallel fields.

Miller says (page 54) that in the process of making sense of Kaufmann’s data: “…on 11 January 1902, Kaufmann’s colleague at Goettingen, Max Abraham, proposed the first field-theoretical description of an elementary particle.”  Abraham revised the mass calculation implied by Searle’s work and noted a little later in 1902 that, given his description of the electron, “however continuously the aether manages to fill space, electricity has an atomistic structure.”

From there on into the interior of Abraham’s electron, things get very strange even in Miller’s lucid account.  If I understand correctly what is going on with what Abraham called “the Lorentz-Poincaré equation,” Lorentz and Poincaré had proposed a formal function G of the aether to account for all the energy involved in moving electrons.  For them, it was a sort of theoretical book-keeping function to sustain the conservation of energy over all of space and time.  Abraham used this same function, calling it the “electromagnetic momentum density,” G, but took it to be a real and direct impact within the aether in the present set of local time frames (ie not in a theoretically infinite time) caused by moving electrons.

It might be worth noting that some of these early approaches to the electron suggest some of the methods that eventually were used later in the century to account for events surrounding electrons and energy (e.g. “the Dirac little delta function” that touches briefly at infinity as a normalizing distribution), but the whole range of the electron’s energy states are very hard to describe without special relativity and the kind of transformations and virtual interactions suggested in the quantum electrodynamics of the later 1940s.  Larmor, Abraham, Lorentz, Kaufmann and Poincaré had run into a set of interrelated problems, such as what would later be described as virtual particles and the self-energy of the electron, that were impossible to unravel without special relativity and some kind of quantum approach.  Moreover, many components of their world-picture (or as Janssen and Mecklenberg put it, their dreams) – the electron as a fundamental building block involved in all forces, the aether, local versus universal time and so on – were more hinderances than helpful things.

Speaking of unraveling, at this point in the parallel explanations of Abraham’s theory of the electron, Janssen and Mecklenberg have an enormous footnote which we will use to escape from this post with some cliff-hanging conclusions.  First, you can see Lorentz’s contraction and aetherial book-keeping as a set of methods for keeping the aether out of local expressions of electron energy.  Second and similarly, you can see Abraham’s use of electromagnetic momentum that includes the aether as a way of shrinking the effects of the aether into the electron.  In both cases the effects of the aether are removed from descriptions of the electron, though with odd and specific effects on the surface dynamics of the electron itself – ie.  The Lorentz electron deforms and the Abrahamic electron has some problems dealing with its momentum (ie the electromagnetic momentum is not the only momentum involved in the electron’s movement).  The cliff-hanger is that Planck, Ehrenfest and Einstein worked this out in 1907 as we will see and there is even another loose end involving what is sometimes called Poincaré Pressure and three letters that Miller discovered at the Algemeen Rijksarchief, The Hague, in the early 1970s.