Dark matter plays a central role in our understanding of modern cosmology. But despite its significance, many of the scientists active in this area of research know relatively little about its interesting history, and how it came to be accepted as the standard explanation for a wide variety of astrophysical observations. Most publications and presentations on this topic – whether at a technical or a popular level – either ignore the long history of this field or condense it into a brief anecdotal account, typically centered around the work on galaxy clusters by Fritz Zwicky in the 1930s and on galactic rotation curves by Vera Rubin in the 1970s. Only a small number of scientists, and an even smaller number of historians, have endeavoured to systematically analyze the development of the dark matter problem from an historical perspective, and it is surprisingly hard to find articles and books that do justice to the fascinating history of dark matter.
The aim of this article is to provide a review of the theoretical arguments and observations that led to the establishment of dark matter among the pillars of modern cosmology, as well as of the theories that have been proposed to explain its nature. Although we briefly discuss some early ideas and recent developments, the focus of this review is the 20th century, beginning with the first dynamical estimates of dark matter's abundance in the Universe, and to its role in the current standard cosmological model, and the strategies that have been pursued to reveal its particle nature.
The first part of this article is largely based on the analysis of primary sources, mainly scanned versions of scientific articles and books published in the 19th and 20th centuries, freely accessible via NASA ADS and the Internet Archive Project. We study the emergence of the concept of dark matter in the late 19th century and identify a series of articles and other sources that describe the first dynamical estimates for its abundance in the known Universe (Chapter II). We then discuss the pioneering work of Zwicky within the context of the scientific developments of the early 20th century. And although his work clearly stands out in terms of methodology and significance, we find that his use of the term “dark matter” was in continuity with the contemporary scientific literature. We then go on to follow the subsequent development of the virial discrepancy that he discovered, with particular emphasis on the debate that took place around this issue in the 1960s (Chapter III).
The second part of this article focuses on more recent developments, which gave us the opportunity to complement the analysis of the primary sources with extensive discussions with some of the pioneering scientists who contributed to the advancement of this field of research. We discuss the history of galactic rotation curves, from the early work in the 1920s and 1930s to the establishment of flat rotation curves in the 1970s, placing the famous work of Bosma and Rubin and collaborators in 1978 within the broader context of the theories and observations that were available at that time (Chapter IV). We then discuss the theories that have been put forward to explain the nature of dark matter, in terms of fundamental particles (Chapter V), astrophysical objects (Chapter VI), or manifestations of non-Newtonian gravity or dynamics (Chapter VII).
Finally, we discuss how the emergence of cosmology as a science in the 1960s and 1970s, the advent on numerical simulations in the 1980s, and the convergence between particle physics and cosmology, led most of the scientific community to accept the idea that dark matter was made of non-baryonic particles (Chapter VIII), and prompted the development of new ideas and techniques to search for dark matter candidates, many of which are still being pursued today (Chapter IX).
One of the main difficulties in reconstructing the history of dark matter is that the key developments took place in a continuously changing landscape of cosmology and particle physics, in which scientists were repeatedly forced to revise their theories and beliefs. The authors of this review are not professional historians, but scientists writing for other scientists. And although we have taken great care in reconstructing the contributions of individuals and groups of scientists, we have little doubt that that our work falls short of the standards of the historical profession. We nevertheless hope that this article will contribute to a better understanding and appreciation of the history of dark matter among our fellow astronomers and physicists, and that it will foster an interest among professional historians in this rich and fascinating field of research.