The peculiar notion of exchange forces—I: Origins in quantum mechanics, 1926–1928

Abstract

Exchange forces lie at the base of some of the most striking explanatory successes of modern physics.An exchange interaction, for instance, is held to be responsible in some key sense for the chemical bond.An exchange force is the origin of ferromagnetism, providing the force that lines up individual spins into an overall pattern.In nuclear physics an exchange force is characteristic for the description of nucleon-nucleon forces.And, in perhaps the most far-reaching example, an exchange interaction is taken as definitional for the quantum field-theoretic description of nature, in which not only the fundamental forces (gravity, electromagnetism, the weak and strong nuclear forces), but also such non-fundamental ones as that operative between pairs of superconducting electrons in a lattice, are traced to the exchange of field quanta.In all these cases, moreover, exchange forces are a peculiarly quantum mechanical phenomenon, something characteristic of the new era that began in 1925 and continues into the present.And as a peculiarly quantum mechanical phenomenon, they are central to the new understanding of matter and force that was ushered in by the theory.For such a central concept, the historical origins of exchange forces are distinctly unclear.What was the path by which these diverse manifestations of exchange-in atomic physics, in condensed matter, in nuclear physics, in quantum field theory-came to go by the same name?Indeed, what is the common thread running through all these uses?The very notion of exchange is nebulous.Consider the following definition from a technical dictionary: exchange [QUANT MECH] (1) Operation of exchanging the space and spin coordinates in a Schrodinger--Pauli wave function representing two identical particles; this operation must leave the wave function unchanged, except possibly for a sign.(2) Process of exchanging a real or virtual particle between two other particles.'Here two distinct meanings of the term 'exchange' are on offer.The first notion

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