When realism made a difference: The constitution of matter and its conceptual enigmas in late 19th century physics

Abstract

The late 19th century debate among German-speaking physicists about theoretical entities is often regarded as foreshadowing the scientific realism debate. This paper brings out differences between them by concentrating on the part of the earlier debate that was concerned with the conceptual consistency of the competing conceptions of matter—mainly, but not exclusively, of atomism. Philosophical antinomies of atomism were taken up by Emil Du Bois-Reymond in an influential lecture in 1872. Such challenges to the consistency of atomism had repercussions within the physics community, as can be shown for the examples of Heinrich Hertz and Ludwig Boltzmann. The latter developed a series of counter-arguments, culminating in an ingenious attempt to turn the tables on the critics of atomism and prove the inconsistency of non-atomistic conceptions of nature. Underlying this controversy is a disagreement over specific goals of physical research which was considered crucially relevant to the further course of physical inquiry. It thereby exemplifies an attitude towards the realism issue that can be contrasted with a different, more neutral attitude of construing the realism issue as merely philosophical and indifferent with respect to concrete research programs in physics, which one also occasionally finds expressed in the 19th century controversy and which may be seen as the prevailing attitude of the 20th century debate.

Introduction

In late 19th century physics, especially in the German-speaking countries, a long and persistent debate about what we now call theoretical entities unfolded.¹ Some physicists (including Ernst Mach, Wilhelm Ostwald and Gustav Kirchhoff) sought to eliminate from physical theory all elements that they considered mere hypothetical constructs. They advocated physics without pictures, which meant that descriptions in terms of directly measurable quantities were in principle preferable. Others argued that physics without pictures was impossible, but conceded that physical pictures were not in exact correspondence to nature, but would only bear a partial resemblance to the phenomena. (This line of thought was elaborated by Heinrich Hertz and Ludwig Boltzmann and is related to earlier ideas by Hermann von Helmholtz.)

These controversies are generally regarded as foreshadowing the scientific realism debate in 20th century philosophy of science (cf. Nagel, 1961, pp. 118–119; Niiniluoto, 2002, Chapter 1; Popper, 1956, to name just a few prominent examples). This appraisal often explicitly includes those parts of the debate that were concerned with atomism and the argumentative efforts of atomism's most fervent advocate, Ludwig Boltzmann (see, e.g., Blackmore, 1999; Nye, 1976). My aim in this paper is to highlight a side of the debate which Boltzmann and others were involved in that is seldom discussed, viz., the concerns about the conceptual consistency of atomism. I want to accentuate the fact that an important concern for at least some of the participants of the debate was the legitimacy in principle of the use of atomistic conceptions in physics. I will analyze this controversy as a debate about legitimate concrete goals of fundamental research in physics. This disagreement over goals was perceived as immediately relevant to concrete research programs. While this analysis points to a certain continuity with the later realism debate, which has also been analyzed as a controversy over the aims of science, it also permits the diagnosis of some significant differences, as I will try to show in the concluding section.