While it is widely agreed that decoherence will not solve the measurement problem, decoherence has been used to explain the “emergence of classicality” and to eliminate the need for a Copenhagen edict that some systems simply have to be treated as classical via a quantum-classical “cut”. I argue that decoherence still relies on such a cut. Decoherence accounts derive classicality only in virtue of their incompleteness, by omission of part of the entangled system of which the classical-appearing subsystem is a (...) part. I argue that this omission is only justified by implicit classical assumptions that objectify a subsystem and are employed via either a traditional Copenhagen cut or a functionally equivalent imposition of separability on a system in a non-separable state. I argue that decoherence cannot derive classicality without assuming it in some other form, and I provide an analysis of when it is appropriate to make these otherwise implicit classical assumptions by adopting a minimalistic Copenhagen-style approach to measurement. Finally, I argue that, ironically, the conditions for making these assumptions may be better satisfied in standard measurement situations than in cases of environmental monitoring. (shrink)

I discuss the quantum mechanical theory of consciousness and freewill offered by Stapp (1993, 1995, 2000, 2004). First I show that decoherence-based arguments do not work against this theory. Then discuss a number of problems with the theory: Stapp's separate accounts of consciousness and freewill are incompatible, the interpretations of QM they are tied to are questionable, the Zeno effect could not enable freewill as he suggests because weakness of will would then be ubiquitous, and the holism of measurement in (...) QM is not a good explanation of the unity of consciousness for essentially the same reason that local interactions may seem incapable of accounting for it. (shrink)

According to Zurek, decoherence is a process resulting from the interaction between a quantum system and its environment; this process singles out a preferred set of states, usually called “pointer basis”, that determines which observables will receive definite values. This means that decoherence leads to a sort of selection which precludes all except a small subset of the states in the Hilbert space of the system from behaving in a classical manner: environment-induced-superselection—einselection —is a consequence of the process of decoherence. (...) The aim of this paper is to present a new approach to decoherence, different from the mainstream approach of Zurek and his collaborators. We will argue that this approach offers conceptual advantages over the traditional one when problems of foundations are considered; in particular, from the new perspective, decoherence in closed quantum systems becomes possible and the preferred basis acquires a well founded definition. (shrink)

In this paper we argue that the formalisms for decoherence originally devised to deal just with closed or open systems can be subsumed under a general conceptual framework, in such a way that they cooperate in the understanding of the same physical phenomenon. This new perspective dissolves certain conceptual difficulties of the einselection program but, at the same time, shows that the openness of the quantum system is not the essential ingredient for decoherence. †To contact the authors, please write to: (...) Mario Castagnino, CONICET-IAFE, Universidad Nacional de Buenos Aires, Casilla de Correos 67, Sucursal 28, 1428 Buenos Aires, Argentina; Roberto Laura, IFIR-Universidad Nacional de Rosario, Av. Pellegrini 250, 2000 Rosario, Argentina; Olimpia Lombardi, CONICET-Universidad Nacional de Buenos Aires, C. Larralde 3440, 6°D, 1430, Buenos Aires; e-mail: [email protected]. (shrink)

The existence of quantum correlates of consciousness (QCC) is doubtful from a scientific perspective. But even if their existence were verified, philosophical problems would remain. On the other hand, there could be more to QCC than meets the sceptic's eye: • QCC might be useful or even necessary for a better understanding of conscious experience or quantum physics or both. The main reasons for this are: the measurement problem (the nature of observation, the mysterious collapse of the wave function, etc.), (...) ostensibly shared features of quantum phenomena and conscious phenomena (e.g., complementarity, nonspatiality, acausality, spontaneity, and holism) and connections (ontology, causation, and knowledge), the qualia problem (subjectivity, explanatory gap etc.). But there are many problems, especially questions regarding realism and the nature and role of conscious observers; • QCC are conceptually challenging, because there are definitory problems and some crucial ontological and epistemological shortcomings. It is instructive to compare them with recent proposals for understanding neural correlates of consciousness (NCC). QCC are not sufficient for a quantum theory of mind, nor might they be necessary except perhaps in a very broad sense; • QCC are also empirically challenging. Nevertheless, QCC could be relevant and important for the mindbody problem: QCC might reveal features that are necessary at least for behavioral manifestations of human consciousness. But QCC are compatible with very different proposals for a solution of the mind-body problem. This seems to be both advantageous and detrimental. QCC restrict accounts of nomological identity. The discovery of QCC cannot establish a naturalistic theory of mind alone. But there are also problems with QCC in the framework of other ontologies. (shrink)

According to Zurek, decoherence is a process resulting from the interaction between a quantum system and its environment; this process singles out a preferred set of states, usually called “pointer basis”, that determines which observables will receive definite values. This means that decoherence leads to a sort of selection which precludes all except a small subset of the states in the Hilbert space of the system from behaving in a classical manner: environment-induced-superselection (einselection) is a consequence of the process of (...) decoherence. The aim of this paper is to present a new approach to decoherence, different from the mainstream approach of Zurek and his collaborators. We will argue that this approach offers conceptual advantages over the traditional one when problems of foundations are considered; in particular, from the new perspective, decoherence in closed quantum systems becomes possible and the preferred basis acquires a well founded definition. (shrink)

This work is a critique of the program of "environment-induced decoherence" as advocated by Zurek, Zeh and Joos, among others. In particular, the alleged relevance of decoherence for a solution of the "measurement problem" is subjected to a detailed philosophical analysis. In the first chapter, an attempt is made to unravel what exactly this "measurement problem" amounts to for the decoherence theorists. The second chapter reviews the standard decoherence literature. The third chapter starts with a brief discussion of the philosophical (...) implications of the decoherence program, followed by a non-standard reconstruction of the decoherence argument that aims to uncover some (mostly hidden) assumptions underlying the approach. It is argued that different subsets of these assumptions result in different versions of the decoherence argument. Next, these assumptions are investigated in more detail, and a number of open problems for the decoherence approach is formulated, in addition to the well-known "problem of outcomes". These problems concern the interpretational relevance of the preferred basis, the role and status of the ignorance interpretation of mixed states, imperfect decoherence and the role of the environment and the definition of subsystems. The fourth chapter addresses the question to what extent the embedding of decoherence in an Everett-like interpretational framework, such as Zurek's "existentional interpretation" and Wallace's structural-realistic version of the many-worlds interpretation, helps to resolve these problems. The main conclusions are formulated in the fifth chapter. Namely: 1) decoherence cannot address the "preferred-basis problem" without adding new interpretational axioms to the standard formalism, 2) the the locality principle (that says that the environment is the "irrelevant" part and should therefore be ignored) is not only problematic but also interpretationally superfluous, 3) the decoherence approach, when formulated in terms of the standard interpretation of quantum mechanics, is predicated on a solution of the "problem of outcomes" and thus cannot claim to account (even partially) for the latter, and 4) that the results of the decoherence program do not increase the plausibility of a realist interpretation of the quantum state. (shrink)