What Has Science Done?

Tuesday, June 21, 2005

Questions about an Annus Mirabilis

Having a propensity to ask history laden questions in physics classes often gets me to go digging in the science library for an answer, when I should be doing problem sets. One problem that has been recently vexing me is an idea that Einstein's work in quantum theory helped pave the way for relativity theory. This may look at first glance as if I had pulled this out of the air, particular with the current problem in theoretical physics of reconciling the underlying assumptions of relativity theory and quantum mechanics. After having Alexandre Pais, a physicist and biographer, recommend as a potential source, I came upon an article for the hundredth anniversary of Einstein's birth in the Reviews of Modern Physics (Vol.51 863-914). Reading it set my mind further wondering if there was a connection which Einstein would have most vehemently denied, since he kept discussions of quantum theory and of relativity separate from each other.

So in part this posting is to be both a recount of what I have read so far on the subject, that is the genesis of relativity theory, as well as to petition any knowledgeable physicists/historians out there who could help me out in answering this conundrum.

I have taken over the past year two courses in intermediate electrodynamics, which I know is a drop in the bucket compared to some, but I am working with what I've got. At the end of the year, we naturally went over Special Relativity with discussions of Lorentz transforms of E&M fields and the ease of using four vectors. David Griffiths' text, Introduction to Electrodynamics, was our textbook for the two classes. I also, because I like being interdisciplinary got to write a paper on the reception of Special Relativity in the United States, which forced me to do some background reading into how the came about in the first place. Three things struck me in the course of my study, one: that few historical commentators ever commented on the importance of Faraday's Law and the Flux Rule when talking about the genesis of SR, two: that Einstein through his reasoning was able to discard so easily the concept of a luminiferous ether as superfluous when so many of his contemporaries were unable to, and three: that a discussion of synchronized clocks which is crucial for relativity resembles so much a lesson in ballistics.

The first is not particularly relevant to this discussion, more for a need to vent about the obsession historians particularly in the US have with the Michelson Morley interferometer experiments, and in the course missing a whole lot more crucial material. Oh and this is not to say Einstein didn't know about the experiment, for one of Lorentz's 1895 papers was called "The Michelson interferometer experiment," so whether Einstein read the original paper I think is inconsequential. The two other points are important, though one may chalk them up to a mere lack of experience with this material. The ether was a particulate substance that permeated all the universe and whose oscillations (in whatever manner that was) were electric and magnetic field oscillations. And when Maxwell and his followers described light as an electromagnetic wave, the already vaguely defined ether now gained another phenomena to its historical grab bag. In order to keep from drawing this out too far, I will cut straight to the chase and say I believe that Einstein's work on quanta was further corroboration for his dismissal of the ether hypothesis in special relativity, and that an acceptance of the quantum hypothesis may have facilitated an exceptance of special relativity. This is a working hypothesis and obviously needs a bit more fleshing out, but I think it is a worthwhile line of inquiry.

The Pais article I mentioned before is so interesting (well the whole thing is) because a small section is devoted to Relativity and Quantum Theory. Pais brings up a number of obvious areas to mention quantum or relativity in the discussions of the other theory, but Einstein does not.

In his first relativity paper (1905c) Einstein noted: "It is remarkable that the energy and frequency of a light complex vary with the state of motion of the observer according to the same law." Here was an obvious opportunity to refer to the relation E = hv of his paper on light-quanta, finished a few months earlier . But Einstein did not do that. Also in the September paper (1905d) he referred to radiation but not light-quanta. In his 1909 address to Salzburg (1909a) Einstein discussed his ideas both on relativity theory and on quantum theory but kept these two areas well separated. As we have seen, in his 1917 paper (1917a) Einstein ascribed to light-quanta an energy E = hv and a momentum p = hv / c. This paper concludes with the following remark. "Energy and momentum are most intimately related; therefore a theory can only then be considered justified if it has been shown that according to it, the momentum transferred by radiation to matter leads to motions as required by thermodynamics." Why is only thermodynamics mentioned; why not also relativity?.

None of this is proof of the matter, but it should raise doubts about how much Einstein was able to keep the two theories separate in his own head despite his public claims to the contrary. Pais proposes that "Einstein kept the quantum theory apart from relativity theory is that he considered the former to be provisional (as he said (1912d) already in 1911) while, on the other hand, relativity to him was revealed truth." I would love to get some feedback on this peculiar topic, which though doesn't seem to have possibility of resolving problems in physics, does shine a new light on an impressive achievement of human intellect.