3.2 Early disagreement about how to explain elementary particles by field theory

In his book on Einstein’s relativity, Max Born, in 1920, had asked about the forces hindering “an electron or an atom” to disintegrate.

“Now, these objects are tremendous concentrations of energy in the smallest place; therefore, they will house huge curvatures of space or, in other words, gravitational fields. The idea that they keep together the dispersing electrical charges lies close at hand.”52View original Quote ([19Jump To The Next Citation Point], p. 235)

Thus, the idea of a program for building the extended constituents of matter from the fields the source of which they are, was very much alive around 1920. However, Pauli’s remark after Weyl’s lecture in Bad Nauheim (86. Naturforscherversammlung, 19–25 September 1920) [245] showed that not everybody was a believer in it. He claimed that in bodies smaller than those carrying the elementary charge (electrons), an electric field could not be measured. There was no point of creating the “interior” of such bodies with the help of an electric field. Pauli:

“None of the present theories of the electron, also not Einstein’s (Einstein 1919 [70Jump To The Next Citation Point]), up to now did achieve solving satisfactorily the problem of the electrical elementary quanta; it seems obvious to look for a deeper reason for this failure. I wish to see this reason in the fact that it is altogether not permitted to describe the electromagnetic field in the interior of an electron as a continuous space function. The electrical field is defined as the force on a charged test particle, and if no smaller test particles exist than the electron (vice versa the nucleus), the concept of electrical field at a certain point in the interior of the electron – with which all continuum theories are working – seems to be an empty fiction, because there are no arbitrarily small measures. Therefore, I’d like to ask Mr. Einstein whether he approves of the opinion that a solution of the problem of matter may be expected only from a modification of our perception of space (perhaps also of time) and of electricity in the sense of atomism, or whether he thinks that the mentioned reservations are unconvincing and is of the opinion that the fundaments of continuum theory must be upheld.”53View original Quote

Pauli referred to Einstein’s paper about elementary particles and field theory in which he had exchanged his famous field equations for traceless equations with the electromagnetic field tensor as a source. Einstein’s answer is tentative and evasive: We just don’t know yet54.

“With the progressing refinement of scientific concepts, the manner by which concepts are related to (physical) events becomes ever more complicated. If, in a certain stage of scientific investigation, it is seen that a concept can no longer be linked with a certain event, there is a choice to let the concept go, or to keep it; in the latter case, we are forced to replace the system of relations among concepts and events by a more complicated one. The same alternative obtains with respect to the concepts of time- and space-distances. In my opinion, an answer can be given only under the aspect of feasibility; the outcome appears dubious to me.”55View original Quote

In the same discussion Gustav Mie came back to Förster’s idea of an asymmetric metric but did not like it

“[...] that an antisymmetric tensor was added to the symmetric tensor of the gravitational potential, which represented the six-vector of the electromagnetic field. But a more precise reasoning shows that in this way no reasonable world function is obtained.”56View original Quote

It is to be noted that Weyl, at the end of 1920, already had given up on a possible field theory of matter:

“Finally I cut loose firmly from Mie’s theory and arrived at another position with regard to the problem of matter. To me, field physics no longer appears as the key to reality; in contrary, the field, the ether, for me simply is the totally powerless transmitter of causations, yet matter is a reality beyond the field and causes its states.”57View original Quote (letter of Weyl to F. Klein on 28 December 1920, see [293], p. 83)

In the next year, Einstein had partially absorbed Pauli’s view but still thought it to be useful to apply field theory to the constituents of matter:

“The physical interpretation of geometry (theory of the continuum) presented here, fails in its direct application to spaces of submolecular scale. Yet it retains part of its meaning also with regard to questions concerning the constitution of elementary particles. Because one may try to ascribe to these field concepts [...] a physical meaning even if a description of the electrical elementary particles which constitute matter is to be made. Only success can decide whether such a procedure finds its justification [...].”58View original Quote [72Jump To The Next Citation Point]

During the twenties Einstein changed his mind and looked for solutions of his field equations which were everywhere regular to represent matter particles:

“In the program, Mr. Einstein expressed during his two talks given in November 1929 at the Institut Henri Poincaré, he wished to search for the physical laws in solutions of his equations without singularities – with matter and the electromagnetic field thus being continuous. Let us move into the field chosen by him without too much surprise to see him apparently follow a road opposed to the one successfully walked by the contemporary physicists.”59View original Quote ([36Jump To The Next Citation Point], p. 17 (1178))

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