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.
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.
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.
Based on a number of experimentally verified physical observations, it is argued that the standard principles of quantum mechanics should be applied to the Universe as a whole. Thus, a paradigm is proposed in which the entire Universe is represented by a pure state wavefunction contained in a factorisable Hilbert space of enormous dimension, and where this statevector is developed by successive applications of operators that correspond to unitary rotations and Hermitian tests. Moreover, because by definition the Universe contains everything, it is argued that these operators must be chosen self-referentially; the overall dynamics of the system is envisaged to be analogous to a gigantic, self-governing, quantum computation. The issue of how the Universe could choose these operators without requiring or referring to a fictitious external observer is addressed. The processes by which conventional physics might be recovered from this fundamental, mathematical and global description of reality are particularly investigated. Specifically, it is demonstrated that by considering the changing properties, separabilities and factorisations of both the state and the operators as the Universe proceeds though a sequence of discrete computations, familiar notions such as classical distinguishability, particle physics, space, time, special relativity and endo-physical experiments can all begin to emerge from the proposed picture. A pregeometric vision of cosmology is therefore discussed, with all of physics ultimately arising from the relationships occurring between the elements of the underlying mathematical structure.
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.
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.
Since its inception, the intricate mathematical formalism of quantum mechanics has empowered physicists to describe and predict specific physical events known as quantum processes. However, this success in probabilistic predictions has been accompanied by a profound challenge in the ontological interpretation of the theory. This interpretative complexity stems from two key aspects. Firstly, quantum mechanics is a fundamental theory that, so far, is not derivable from any more basic scientific theory. Secondly, it delves into a realm of invisible phenomena that often contradicts our intuitive and commonsensical notions of matter and causality. Despite its notorious difficulties of interpretation, the most widely accepted set of views of quantum phenomena has been known as the Copenhagen interpretation since the beginning of quantum mechanics. According to these views, the correct ontological interpretation of quantum mechanics is incompatible with ontological realism in general and with philosophical materialism in particular. Anti-realist and anti-materialist interpretations of quantum matter have survived until today. This paper discusses these perspectives, arguing that materialistic interpretations of quantum mechanics are compatible with its mathematical formalism, while anti-realist and anti-materialist views are based on wrong philosophical assumptions. However, although physicalism provides a better explanation for quantum phenomena than idealism, its downward reductionism prevents it from accounting for more complex forms of matter, such as biological or sociocultural systems. Thus, the paper argues that neither physicalism nor idealism can explain the universe. I propose then a non-reductionistic form of materialism called inclusive materialism. The conclusion is that the acknowledgment of the qualitative irreducibility of ontological emergent levels above the purely physical one does not deny philosophical materialism but enriches it.