The Electron: 1905-1906

To continue Miller’s exposition, on page 226 he observes that Kaufmann was the first person to mention Einstein’s relativity paper in print.  Kaufmann described Einstein’s view as being formally equivalent (for Kaufmann’s purpose – measuring the change in the mass of an electron as its speed approached that of light) to Lorentz’s theory of the electron.  But, said Kaufmann, Einstein avoided the Lorentzian problem of velocity relative to the aether – which had never been measured and yet was implied by the contraction of the electron (and other “molecular forces”) in relation to this unknown (and for Lorentz, unmeasurable) coordinate system or stationary matrix of forces.  Miller points out that Kaufmann considered Einstein’s space-time formulations to be phenomenological improvements that got around Lorentz’s problem with a measurable impact (contraction) derived from a source that could not be measured due to the contraction of electrons as they moved relative to the aether. 

In any case, according to Kaufmann’s interpretation of his experimental results, the Lorentz-Einstein theory of the electron led to predictions that deviated farther from the experiment than did those of Abraham’s theory.  In 1906, Planck reviewed Kaufmann’s experimental confirmation of Abraham’s theory and said that the results were not a clear disproof of the Lorentz-Einstein theory.  In their discussion, Planck and Abraham referred to the Einsteinian theory as a “relativity theory” – the first use of that term.  Abraham insisted that the relativity theory must have serious problems because it relied on unknown forces outside of those recognized by electromagnetic theory.  Nevertheless, Planck said his sympathies were with the relativistic theory, even if it did imply that there were forces in the universe other than electromagnetism.

At this point, I’m afraid I have to detour into a slightly retrospective view of what the problems are with a non-relativistic or only partly relativistic description of the energy-momentum of a system – something that maybe only is completely clear in General Relativity (where this blog isn’t going if I can help it).  It’s a problem that Einstein will begin to clarify in 1907 – but what were people thinking of on that topic in 1900-1906?

Among other things that came up as physicists tried to describe the energy-momentum of a charged system as it approached the speed of light (but without a relatively complete relativistic picture) were:

  1. Lorentz driven “to the end of his Latin” (out of his wits?  Having his last nerve stepped on?  To distraction?) with trying to account for Kaufmann’s ever-changing results that suggested a rigid electron just moved right on through a mass-changing aether as Abraham’s theory suggested
  2. 2)     Poincaré developed the notion of a stress-force (usually now called “Poincaré Pressure”) inside the electron that exactly counter-balanced whatever external forces were acting to overload and disperse the electron via deformation or some other mechanism.  As Abraham noted, this non-electromagnetic force was needed if the electron was deformable in relation to an unobservable aether and he stressed that his rigid electron in a mass-changing aether did not have this problem
  3. BUT for Poincaré (for a while anyway, 1900-1904 according to Wikipedia on “Electromagnetic mass”) and Abraham, this left the problem of how the energy (speed) and momentum (mass) were related to the field forces represented by the aether.  Poincaré suggested an imaginary “fictitious” aether fluid circulation as a sort of book-keeping arrangement where energy and momentum could be exchanged and Abraham suggested an almost relativistic relation of energy and mass.
  4. And that brings us almost to 1907 when things began to get a little clearer as Einstein began to work out the details of special relativity with Ehrenfest and Planck. 
X-Ray Crystallography from Wikipedia