Evidence of dark matter, and the interpretive role of general relativity

The use of general relativity to interpret dark-matter evidence is clarified.
• In one case, only the fact of gravitational lensing is used to detect dark matter.
• All viable theories of gravity include lensing.
• The accuracy of general relativity need not be assumed for evidence of dark matter.

Dark matter is hypothesized in large part to account for anomalous data in rotational speeds of galaxies and random motions in clusters of galaxies. But the anomalies could also be solved by revising the theory of gravity, rather than revising the distribution of mass. This situation of underdetermination would seem to be exacerbated by the use of the theory of gravity, the general theory of relativity, in interpreting the data. In an effort to clarify the status of both the theory of dark matter and the general theory of relativity, this paper describes the details of the role of the general theory of relativity in interpreting evidence for dark matter.