There is a deeply entrenched view in philosophy and physics, the closed systems view, according to which isolated systems are conceived of as fundamental. On this view, when a system is under the influence of its environment this is always described in terms of a coupling between it and a separate system, which taken together are isolated. There is an alternative, the open systems view, according to which systems interacting with their environment are conceived of as fundamental, and the environment’s influence is represented via the dynamical equations that govern the system of interest’s evolution. In this paper we propose (although the formalism is not original to us) a theoretical framework which we call the general quantum theory of open systems (GT), within which one can make sense of the dynamics of open quantum systems in fundamental terms, and we argue that the open systems view, as formalized in GT, is fundamental in quantum theory.
There is a deeply entrenched view in philosophy and physics, the closed systems view, according to which isolated systems are conceived of as fundamental. On this view, when a system is under the influence of its environment this is always described in terms of a coupling between it and a separate system, which taken together are isolated. There is an alternative, the open systems view, according to which systems interacting with their environment are conceived of as fundamental, and the environment’s influence is represented via the dynamical equations that govern the system of interest’s evolution. In this paper we propose (although the formalism is not original to us) a theoretical framework which we call the general quantum theory of open systems (GT), within which one can make sense of the dynamics of open quantum systems in fundamental terms, and we argue that the open systems view, as formalized in GT, is fundamental in quantum theory.
There is a deeply entrenched view in philosophy and physics, the closed systems view, according to which isolated systems are conceived of as fundamental. On this view, when a system is under the influence of its environment this is always described in terms of a coupling between it and a separate system, which taken together are isolated. There is an alternative, the open systems view, according to which systems interacting with their environment are conceived of as fundamental, and the environment’s influence is represented via the dynamical equations that govern the system of interest’s evolution. In this paper we propose (although the formalism is not original to us) a theoretical framework which we call the general quantum theory of open systems (GT), within which one can make sense of the dynamics of open quantum systems in fundamental terms, and we argue that the open systems view, as formalized in GT, is fundamental in quantum theory.
Abstract There is a deeply entrenched view in philosophy and physics, the closed systems view, according to which isolated systems are conceived of as fundamental. On this view, when a system is evolving under the influence of its environment, this is always described in terms of a coupling between it and a separate system which taken together are isolated. In this chapter, we introduce the theoretical framework that we call standard quantum theory (ST), formulated in accordance with the closed systems view, and we consider approaches to interpreting the formalism of ST that take it to be complete in some sense. Broadly speaking, these can be grouped into two families. The first includes (neo-)Bohrian and related approaches, the second (neo-)Everettian. We argue, from the point of view of each, that although ST is formulated in accordance with the closed systems view, it is nevertheless ontologically committed to open systems in a way that other, for instance, classical, theoretical frameworks are not. We close with the suggestion that philosophical and foundational progress may be made through the adoption of an alternative theoretical framework, which might in principle involve a change in corresponding view, within which one can make sense of open systems dynamics in fundamental terms.
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.
In this chapter we shall deal with the quantum dynamics of an open system. By open quantum system we mean here a system which interacts with an environment (see Sec. 9.4): since we are not interested in the dynamics of the environment, we shall have to describe the evolution of the system in some “effective” way. In particular, if we consider only the evolution of the system, it will be non-unitary, and this will represent the subject of this chapter. As we know, Hamiltonian quantum dynamics is unitary and changes pure states into pure states. On the other hand, non-unitary dynamics changes an initially pure state into a mixture, which must be described by a density matrix (see Ch. 5). In the case of macroscopic systems, the coupling with the environment may be arbitrarily reduced and therefore its influence can be made correspondingly small (see Sec. 1.1). Microscopic systems, however, always couple to the environment and this coupling cannot be considered negligible. This is the reason why the quantum theory of open systems is one of the most important and fundamental chapters of quantum mechanics that, though born in quantum optics, has many implications in almost all fields of physics. The present chapter can be seen as a further development of the measurement theory (see Ch. 9), as open systems manifest a decoherent dynamics (see in particular Sec. 9.4).
Abstract The study of open systems is a cornerstone of many scientific disciplines outside physics. Across the biological, social, and cognitive sciences, systems are commonly understood in terms of their interactions with an environment. This is because, at a fundamental level, the entities studied in these disciplines are rarely, if ever, isolated. While openness is often taken as a given in the special sciences, physics has historically developed with a strong emphasis on closed-system modelling. The success of Newtonian mechanics, classical thermodynamics, and quantum mechanics has to a large extent relied on the ability to isolate and describe systems in terms of well-defined boundary conditions. However, recent developments suggest that the importance of open systems is gaining increasing recognition even within physics. In this introduction we introduce the general topic of open systems in physics and the open systems view, and we summarise each of the other chapters of the volume.
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.