Eugene Vaynberg

Dark matter in astrophysics offers a rare treat for philosophers of science. When they look at the contemporary science of dark matter, they see reports of a widely accepted theoretical posit indispensable to our best theories and models but without an accepted experimental confirmation of its existence. Nearly all astrophysicists and cosmologists believe that dark matter exists and makes up approximately a quarter of the mass-energy content of the universe. However, they seem to know almost nothing about its nature, cannot directly observe it, and have been unable to detect the products of any interactions with any of the candidate dark matter particles. This project addresses the apparent tension between the impressive knowledge taken to have been obtained in contemporary sciences of the cosmos and the methodological and theoretical limitations in obtaining such knowledge. To do so, this dissertation investigates the ways in which astronomers and astrophysicists are making progress by looking more closely at their experimental practices and actual theoretical commitments. More specifically, the goal is to determine how this bears on longstanding philosophical questions of scientific realism and the nature of scientific experimentation. Ultimately, I argue that astronomers do conduct traditional, interventionist experiments and that we can be realists about dark matter. These two views offer a way of thinking differently about how scientists can and do obtain knowledge about inaccessible and unobservable targets systems.

A number of philosophers claim that realism about dark matter in cosmology is unwarranted because there has been no empirical confirmation of a dark matter particle. This demand is misguided. I argue that we should take the theoretical concept of dark matter as described in our best cosmological model (ΛCDM) at face value. Since there is no theoretical or nomological requirement that dark matter be a particle, we should better assess the implications of dark matter detection via gravitational lensing. The result is that realism about dark matter is a viable position.