The earth vibrates with analogies: The Dirac sea and the geology of the vacuum.

ABSTRACT

The debate around analogy in modern physics that focuses on its role as a logical inference often correspondingly overlooks its historical dimension and the other equally important functions and aspects that are intertwined with this dimension. Inspired by a close investigation of the primary sources and archival material of a few historical actors, this paper lays out a framework on analogy-making which preserves as much as possible its historical complexity. While not losing sight of the logical role, our framework puts a special emphasis on the heuristic process, and aims at offering to the historian and philosopher of science as well as the physicist some tools to capture the subtle functions of analogical reasoning involved in such a process. After having traced it out theoretically, we make use of this framework to interpret the growth of the ideas of two remarkable physicists dealing with the multifaceted notion of vacuum in 20th century physics. We first consider the trajectory followed by John A. Wheeler, between the 1960s and 1970s, towards (in his own words) a "geology of the vacuum"; and then examine, starting from the hitherto neglected Japanese reception of the idea of Dirac sea in the early 1930s, the pathway that led Yoichiro Nambu to the discovery of spontaneous symmetry breaking.