History of darkmatter in galaxies

Abstract

The phrase dark matter goes back to 1922, and the concept of things that exist but are not, or cannot be, seen to the ancients. Here is one version of how the phrase was gradually restricted to kinds of matter not capable of electromagnetic interactions, how evidence for its existence very gradually accumulated, and how a number of watershed events have brought the astronomical community to near consensus that there is dark matter on many scales, but that its nature remains uncertain. The acceptance of dark matter in the universe has been described as a paradigm shift but also has many of the characteristics of normal science, in which data are acquired in response to existing ideas and those ideas gradually modified in light of the data. The approach is largely chronological, but with frequent looks ahead to see how various parts of the story turn out. It is not claimed that present understanding is complete or final.