March 26, 2008
Holton begins by asserting the importance of historical research into "thematic" aspects of science, by which is meant things like the complex motivations and other personal factors at the level of individual scientists, as opposed to "analytic" aspects of the formal scientific theories themselves. This is certainly very sound, but this point of view is not developed very far, leading only to some very cursory illustrations, such as the observation that scientists always use some "preselection" when developing theories, such as, e.g., Plato's dictum that planetary motions should be described by circles (pp. 75-78), a vague but somewhat appealing parallel between modern art and modern science (pp. 79-83), and a suggestion that scientific revolutions "can usually be seen to be projections back to an idealized, purified state of the past" (p. 93, also pp. 194-196). Instead, the book soon turns into an excellent study of the genesis of special relativity, with some quantum mechanics and a tiny bit of Kepler thrown in for good measure.
Let us look at the relativity theory part. People who tell the story with a purely "analytic" mindset almost invariably emphasise the allegedly "crucial" experiment of Michelson. Holton's "thematic" study reveals a very different reality by identifying two far more important sources of influence on Einstein.
One rather unexpected influence is Föppl, an obscure physicist-engineer who wrote a textbook on Maxwell's theory. As a student Einstein was never taught Maxwell's theory as it was never offered as a course, which he regretted since he "seemed to conceive of himself as an experimentalist" (p. 239) and, according to his own account, "'worked most of the time in the physical laboratory, fascinated by the direct contact with experience,'" thus prompting him "'to study at home the works of Kirchhoff, Helmholtz, Hertz, etc.'" (p. 214). In the course of these studies he appears to have stumbled upon Föppl's book, which suited his interest in experiments and his philosophical leanings.
Einstein's study of electrodynamics led him to the following problem. "'According to Faraday, during the relative motion of a magnet with respect to a conducting circuit, an electric current is induced in the latter. It is all the same whether the magnet is moved or the conductor; only the relative motion counts according to the Maxwell-Lorentz theory. However, the theoretical interpretation of the phenomenon in these two cases is quite different ... The thought that one is dealing here with two fundamentally different cases was for me unbearable'" (pp. 381-382). This was a key motivation for Einstein in creating special relativity, as witnessed by the title "On the Electrodynamics of Moving Bodies" of his 1905 paper, and its first sentence: "It is known that Maxwell's electrodynamics---as usually understood at the present time---when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena."
This paper appears to be strongly influenced by Föppl, for, in a chapter entitled "The Electrodynamics of Moving Conductors," Föppl argues that this type of problem may require "'a deep-going revision of that conception of space which has been impressed upon human thinking in its previous period'" and that "'the decision on this question forms perhaps the most important problem of science of our time'" (p. 221).
A second major influence was Mach. Mach's philosophy of science was, in his own words, "'anti-meatphysical'" (p. 239). He admitted into science only concepts that can be directly observed and measured, and wished to banish things like the ether and the "'conceptual monstrosity of absolute space'" as being "'purely a thought-thing which cannot be pointed to in experience'" (p. 239). Einstein proudly acknowledged Mach's influence on his work. This influence may be seen "first, by Einstein's insistence from the beginning of his relativity paper that the fundamental problems of physics cannot be understood until an epistemological analysis is carried out, particularly so with respect to the meaning of the conceptions of space and time; and second, by Einstein's identification of reality with what is given by sensations, the 'events,' rather than putting reality on a plane beyond or behind sense experience" (p. 242). Although not relevant to the genesis of special relativity, it is interesting to see how Einstein gradually came to move away from Mach, eventually ending up as diametrically opposed to him, a conversion which was necessitated by the development of general relativity. "'Coming from sceptical empiricism of somewhat the kind of Mach's, I was made, by the problem of gravitation, into a believing rationalist, that is, one who seeks the only trustworthy source of truth in mathematical simplicity'" (p. 259).
Thus we see that these two factors (Föppl and Mach) explain very satisfactorily the thematic background of Einstein's 1905 paper. There seems to be no room for Michelson's experiment. Indeed, a detailed study reveals that "the role of the Michelson experiment in the genesis of Einstein's theory appears to have been so small and indirect that one may speculate that it would have made no difference to Einstein's work if the experiment had never been made at all" (p. 345).