Abstract We argue that there is a temporal analogue of the open systems view expounded by Cuffaro and Hartmann (2024), suggesting that we should not think of the universe as breaking down into autonomous time-slices whose instantaneous evolution is always independent from events at other times. Employing the definitions proposed by Cuffaro and Hartmann, we argue that there are good reasons to think that the temporally open systems view should be regarded as ontically fundamental. We use the failure of narratability in quantum mechanics to demonstrate that generically, quantum histories cannot be decomposed into autonomous temporal slices; we discuss the status of temporal closure 39in several interpretations of quantum mechanics; and finally, we consider the consequences of the temporally open systems view for the question about whether the state of the universe as a whole is pure.
Abstract We argue that there is a temporal analogue of the open systems view expounded by Cuffaro and Hartmann (2024), suggesting that we should not think of the universe as breaking down into autonomous time-slices whose instantaneous evolution is always independent from events at other times. Employing the definitions proposed by Cuffaro and Hartmann, we argue that there are good reasons to think that the temporally open systems view should be regarded as ontically fundamental. We use the failure of narratability in quantum mechanics to demonstrate that generically, quantum histories cannot be decomposed into autonomous temporal slices; we discuss the status of temporal closure 39in several interpretations of quantum mechanics; and finally, we consider the consequences of the temporally open systems view for the question about whether the state of the universe as a whole is pure.
Abstract How should we interpret physical theories, and especially quantum theory, if we drop the assumption that we should treat it as an exact description of the whole universe? I expound and develop the claim that physics is about the study of autonomous, but not necessarily isolated, dynamical systems, and that when applied to quantum mechanics this entails that in general we should take quantum systems as having mixed states and non-unitary dynamics. I argue that nonetheless unitary dynamics continues to have a special place in physics, via the empirically-well-supported reductionist principles that non-unitarity is to be explained by restriction to a subsystem of a larger unitary system and that microscopic physics is governed by unitary and largely known dynamics. I contrast this position with the ‘Open Systems View’ advocated recently by Michael Cuffaro and Stephan Hartmann.
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.
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.
It is argued that those who defend the Everett, or ‘many-worlds’, interpretation of quantum mechanics should embrace what we call the general quantum theory of open systems (GT) as the proper framework in which to conduct foundational and philosophical investigations in quantum physics. GT is a wider dynamical framework than its alternative, standard quantum theory (ST). This is true even though GT makes no modifications to the quantum formalism. GT rather takes a different view, what we call the open systems view, of the formalism; i.e., in GT, the dynamics of systems whose physical states are fundamentally represented by density operators are represented as fundamentally open as specified by an in general non-unitary dynamical map. This includes, in principle, the dynamics of the universe as a whole. We argue that the more general dynamics describable in GT can be physically motivated, that there is as much prima facie empirical support for GT as there is for ST, and that GT could be fully in the spirit of the Everett interpretation—that there might, in short, be little reason for an Everettian not to embrace the more general theoretical landscape that GT allows one to explore.
Abstract In defending the fundamentality of the open systems view for quantum theory, Cuffaro and Hartmann (2024) articulate an account of frameworks in physics. They argue that the general quantum theory of open systems is a more fundamental framework than standard quantum theory. In this chapter, we articulate an account of frameworks using the examples of quantum field theory and statistical mechanics. We argue that what makes frameworks useful in physics is the combination of generality and abstractness of frameworks. In particular, their abstractness makes them poor targets for metaphysical analysis; the more concrete levels of theories or models are the appropriate target for ontological fundamentality claims.
Abstract In the classical framework, not only can systems be identified by their space-time location, but they also possess mutually independent existences: they are individuals in the philosophical meaning of the concept. In the quantum domain, by contrast, matters are no so easy. Quantum systems cannot be labelled. Nor can they be assigned precise trajectories. Moreover, after interacting, quantum systems become interrelated in a way that does not diminish with either time or space: quantum correlations challenge the independent existence of the subsystems of a composite quantum system. Therefore, in the quantum framework the identification of open systems is a subtle issue. In this chapter I will emphasise the relative nature of open quantum systems in standard quantum mechanics by pointing out how this relativity is manifested under different forms: the relativity of entanglement, the identification of systems in decoherence, and the many ways in which a quantum system can be decomposed. Therefore, any view that considers open quantum systems as fundamental must take this relativity into account. The general purpose is to argue that the closed systems view and the open-system view are complementary approaches that need not be considered rival.