Abstract
<jats:title>Abstract</jats:title> <jats:p>If open systems are metaphysically fundamental, as Cuffaro and Hartmann (2024) have proposed, then what is the fate of the system that corresponds to the entire physical universe? One option is that the universe exists without being metaphysically fundamental. This amounts to priority pluralism, the converse of Schaffer’s priority monism (2009). Monism itself has often been defended by appeal to quantum physics. We first ask how Cuffaro and Hartmann’s proposal manages to avoid existing arguments from quantum physics to priority monism, then raise some worries about their own argument from quantum physics to the open systems view. In any case, a real but derivative universe remains puzzling. We suggest an alternative metaphysics for the open systems view which does not include a complete cosmos. Metaphysical realists about the content of physical theories typically assume that there is such a thing as the totality of physical reality: a well-defined physical entity on which the fundamental laws of nature operate holistically. We explore some potential consequences for the metaphysics of physics of dropping this assumption and embracing a picture of physical reality as indefinitely extensible.</jats:p>