The Open Systems View in Field Theory

Cuffaro and Hartmann have recently provided an extensive defense of the open systems view, according to which physical systems are best treated as fundamentally open, by arguing, in particular, that quantum systems should in general be taken to evolve non-unitarily over time. For all its merits, this defense faces one central limitation: little is known about the structure of non-unitary dynamics in the case of our best current theories. Yet there is cause for optimism: the standard effective field theory (EFT) framework, in which our best current theories are widely believed to be more reliably formulated, has been successfully generalized to an open EFT framework during the last decades. This paper defends the open systems view in the open EFT setting. We argue that the bottom-up open EFT framework, in which effective systems are treated as fundamentally open, is both more fundamental and more epistemically reliable than its top-down counterpart, in which effective systems are treated as derivatively open.