Dark Matter in Zwicky's Cosmology: Towards an Epistemological Reconstruction

TL;DR

This paper reexamines Zwicky's 1933 work on galaxy cluster mass discrepancies, suggesting dark matter was an early cosmological indicator linked to General Relativity, not just an ad hoc hypothesis.

Contribution

It offers a new contextualized interpretation of Zwicky's work, emphasizing its cosmological motivations and its potential role as an early sign of General Relativity.

Findings

Dark matter was central in Zwicky's epistemic context.

The observed mass discrepancy was consistent with early cosmological expectations.

Dark matter may indicate early support for General Relativity.

Abstract

A new contextualised reading of Fritz Zwicky's 1933 article ''The redshift of extragalactic nebulae'' about the virial analysis of the velocity dispersion of galaxies in the Coma cluster leads to a reconsideration of the traditional discourse on the introduction of dark matter. We argue that this component of matter was not only already on the stage of the scientific debates of the time, but also, in a more concealed form, played a central role in Zwicky's epistemic context. We thus reject the narration that dark matter is the result of a ``na{\"i}ve'' astrophysical observation and emphasise the cosmological motivations that prompted Zwicky to presciently search for it. Moreover, with regard to its abundance, we argue that the discrepancy between the observed amount of luminous matter in the Coma Cluster and Zwicky's higher mass estimate derived from virial analysis was not, in fact, astonishing. What Zwicky described as a surprising excess of dark matter was of precisely the order of magnitude he had set out to identify. Consequently, we challenge the widespread view that dark matter was merely an ad hoc hypothesis introduced to rescue Newtonian theory. Instead, we suggest it may represent one of the earliest cosmological indications supporting a new emerging theory of gravitation: General Relativity. This reinterpretation contributes to ongoing debates in the philosophy of science concerning the epistemic status of ad hoc hypotheses.