We present a brief history of decoherence, from its roots in the foundations of classical statistical mechanics, to the current spin bath models in condensed matter physics. We analyze the philosophical import of the subject matter in three different foundational problems, and find that, contrary to the received view, decoherence is less instrumental to their solutions than it is commonly believed. What makes decoherence more philosophically interesting, we argue, are the methodological issues it draws attention to, and (...) the question of the universality of quantum mechanics. (shrink)
Interference phenomena are a well-known and crucial feature of quantum mechanics, the two-slit experiment providing a standard example. There are situations, however, in which interference effects are (artificially or spontaneously) suppressed. We shall need to make precise what this means, but the theory of decoherence is the study of (spontaneous) interactions between a system and its environment that lead to such suppression of interference. This study includes detailed modelling of system-environment interactions, derivation of equations (‘master equations’) for the (reduced) (...) state of the system, discussion of time-scales etc. A discussion of the concept of suppression of interference and a simplified survey of the theory is given in Section 2, emphasising features that will be relevant to the following discussion (and restricted to standard non-relativistic particle quantum mechanics.[1] A partially overlapping field is that of decoherent histories, which proceeds from an abstract definition of loss of interference, but which we shall not be considering in any detail. (shrink)
Given the impressive success of environment-induced decoherence (EID), nowadays no interpretation of quantum mechanics can ignore its results. The modal-Hamiltonian interpretation (MHI) has proved to be effective for solving several interpretative problems but, since its actualization rule applies to closed systems, it seems to stand at odds of EID. The purpose of this paper is to show that this is not the case: the states einselected by the interaction with the environment according to EID (the elements of the “pointer (...) basis”) are the eigenvectors of an actual-valued observable belonging to the preferred context selected by the MHI. (shrink)
This paper relates both to the metaphysics of probability and to the physics of time asymmetry. Using the formalism of decoherent histories, it investigates whether intuitions about intrinsic time directedness that are often associated with probability can be justified in the context of no-collapse approaches to quantum mechanics. The standard (two-vector) approach to time symmetry in the decoherent histories literature is criticised, and an alternative approach is proposed, based on two decoherence conditions ('forwards' and 'backwards') within the one-vector formalism. (...) In turn, considerations of forwards and backwards decoherence and of decoherence and recoherence suggest that a time-directed interpretation of probabilities, if adopted, should be both contingent and perspectival. (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: olimpiafilo@arnet.com.ar. (shrink)
This work examines whether the environmentally-induced decoherence approach in quantum mechanics brings us any closer to solving the measurement problem, and whether it contributes to the elimination of subjectivism in quantum theory. A distinction is made between ,collapse, and ,decoherence,, so that an explanation for decoherence does not imply an explanation for collapse. After an overview of the measurement problem and of the open-systems paradigm, we argue that taking a partial trace is equivalent to applying the projection (...) postulate. A criticism of Zurek's decoherence approach to measurements is also made, based on the restriction that he must impose on the interaction between apparatus and environment. We then analyze the element of subjectivity involved in establishing the boundary between system and environment, and criticize the incorporation of Everett's branching of memory records into the decoherence research program. Sticking to this program, we end by sketching a proposal for ‘environmentally-induced collapse’. (shrink)
Can we explain the laws of thermodynamics, in particular the irreversible increase of entropy, from the underlying quantum mechanical dynamics? Attempts based on classical dynamics have all failed. Albert (1994a,b; 2000) proposed a way to recover thermodynamics on a purely dynamical basis, using the quantum theory of the collapse of the wavefunction of Ghirardi, Rimini and Weber (1986). In this paper we propose an alternative way to explain thermodynamics within no-collapse interpretations of quantum mechanics. Our approach relies on the standard (...) quantum mechanical models of environmental decoherence of open systems, e.g. Joos and Zeh (1985) and Zurek and Paz (1994). (shrink)
This work examines whether the environmentally-induced decoherence approach in quantum mechanics brings us any closer to solving the measurement problem, and whether it contributes to the elimination of subjectivism in quantum theory. A distinction is made between ,collapse, and ,decoherence,, so that an explanation for decoherence does not imply an explanation for collapse. After an overview of the measurement problem and of the open-systems paradigm, we argue that taking a partial trace is equivalent to applying the projection (...) postulate. A criticism of Zurek's decoherence approach to measurements is also made, based on the restriction that he must impose on the interaction between apparatus and environment. We then analyze the element of subjectivity involved in establishing the boundary between system and environment, and criticize the incorporation of Everett's branching of memory records into the decoherence research program. Sticking to this program, we end by sketching a proposal for âenvironmentally-induced collapseâ. (shrink)
According to the environment-induced approach to decoherence (EID), the split of the Universe into the degrees of freedom which are of direct interest to the observer (the system) and the remaining degrees of freedom (the environment) is absolutely essential for decoherence. However, the EID approach offers no general criterion for deciding where to place the “cut” between system and environment: the environment may be “external” (a bath of particles interacting with the system of interest) or “internal” (such as (...) collections of phonons or other internal excitations). The main purpose of this paper is to argue that decoherence is a relative phenomenon, better understood from a closed-system perspective according to which the split of a closed quantum system into an open subsystem and its environment is just a way of selecting a particular space of relevant observables of the whole closed system. In order to support this claim, we shall consider the results obtained in a natural generalization of the simple spin-bath model usually studied in the literature. Our main thesis will lead us to two corollaries. First, the problem of identifying the system that decoheres is actually a pseudo-problem, which vanishes as soon as one acknowledges the relative nature of decoherence. Second, the usually supposed link between decoherence and energy dissipation is misguided. As previously pointed out, energy dissipation and decoherence are different phenomena, and we shall argue for this difference on the basis of the relative nature of decoherence. (shrink)
Decoherence results from the dissipative interaction between a quantum system and its environment. As the system and environment become entangled, the reduced density operator describing the system "decoheres" into a mixture (with the interference terms damped out). This formal result prompts some to exclaim that the measurement problem is solved. I will scrutinize this claim by examining how modal and relative-state interpretations can use decoherence. Although decoherence cannot rescue these interpretations from general metaphysical difficulties, decoherence may (...) help these interpretations to pick out a preferred basis. I will explore whether decoherence solves nagging technical problems associated with selecting a preferred basis. (shrink)
In this paper we argue that the emergence of the classical world from the underlying quantum reality involves two elements: self-induced decoherence and macroscopicity. Self-induced decoherence does not require the openness of the system and its interaction with the environment: a single closed system can decohere when its Hamiltonian has continuous spectrum. We show that, if the system is macroscopic enough, after self-induced decoherence it can be described as an ensemble of classical distributions weighted by their corresponding (...) probabilities. We also argue that classicality is an emergent property that arises when the behavior of the system is described from an observational perspective. (shrink)
This work examines whether the environmentally-induced decoherence approach in quantum mechanics brings us any closer to solving the measurement problem, and whether it contributes to the elimination of subjectivism in quantum theory. A distinction is made between 'collapse' and 'decoherence', so that an explanation for decoherence does not imply an explanation for collapse. After an overview of the measurement problem and of the open-systems paradigm, we argue that taking a partial trace is equivalent to applying the projection (...) postulate. A criticism of Zurek's decoherence approach to measurements is also made, based on the restriction that he must impose on the interaction between apparatus and environment. We then analyze the element of subjectivity involved in establishing the boundary between system and environment, and criticize the incorporation of Everett's branching of memory records into the decoherence research program. Sticking to this program, we end by sketching a proposal for 'environmentally-induced collapse'. (shrink)
General results about restrictions on measurements from inside are applied to quantum mechanics. They imply subjective decoherence: For an apparatus it is not possible to determine whether the joint system consisting of itself and the observed system is in a statistical state with or without interference terms; it is possible that the apparatus systematically mistakes the real pure state of the joint system for the decohered state. We discuss the relevance of subjective decoherence for quantum measurements and for (...) the problem of Wigner's friend. (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)
We discuss a recent proposal by Albert (1994a; 1994b; 2000, ch. 7) to recover thermodynamics on a purely dynamical basis, using the quantum theory of the collapse of the wave function by Ghirardi, Rimini, and Weber (1986). We propose an alternative way to explain thermodynamics within no-collapse interpretations of quantum mechanics. Our approach relies on the standard quantum mechanical models of environmental decoherence of open systems (e.g., Joos and Zeh 1985; Zurek and Paz 1994). This paper presents the two (...) approaches and discusses their advantages. The problems faced by both approaches will be discussed in a sequel (Hemmo and Shenker 2003). (shrink)
In realistic situations where a macroscopic system interacts with an external environment, decoherence of the quantum state, as derived in the decoherence approach, is only approximate. We argue that this can still give rise to facts, provided that during the decoherence process states that are, respectively, always close to eigenvectors of pointer position and record observable are correlated. We show in a model that this is always the case.
We discuss a recent proposal by Albert (1994a,b; 2000, Chapter 7) to recover thermodynamics on a purely dynamical basis, using the quantum theory of the collapse of the wave function of Ghirardi, Rimini and Weber (1986). We propose an alternative way to explain thermodynamics within no-collapse interpretations of quantum mechanics. Our approach relies on the standard quantum mechanical models of environmental decoherence of open systems, \eg Joos and Zeh (1985) and Zurek and Paz (1994). This paper presents the two (...) approaches and discusses their advantages. The problems they face will be discussed in a sequel (Hemmo and Shenker 2002b). (shrink)
The decoherent histories formalism, developed by Griffiths, Gell-Mann, and Hartle (in Phys. Rev. A 76:022104, 2007; arXiv:1106.0767v3 [quant-ph], 2011; Consistent Quantum Theory, Cambridge University Press, 2003; arXiv:gr-qc/9304006v2, 1992) is a general framework in which to formulate a timeless, ‘generalised’ quantum theory and extract predictions from it. Recent advances in spin foam models allow for loop gravity to be cast in this framework. In this paper, I propose a decoherence functional for loop gravity and interpret existing results (Bianchi et al. (...) in Phys. Rev. D 83:104015, 2011; Phys. Rev. D 82:084035, 2010) as showing that coarse grained histories follow quasiclassical trajectories in the appropriate limit. (shrink)
State-reduction and the notion of actuality are compared to passage through time and the notion of the present; already in classical relativity the latter give rise to difficulties. The solution proposed here is to treat both tense and value-definiteness as relational properties or facts as relations; likewise the notions of change and probability. In both cases essential characteristics are absent: temporal relations are tenselessly true; probabilistic relations are deterministically true.The basic ideas go back to Everett, although the technical development makes (...) use of the decoherent histories theory of Griffiths, Omnès, and Gell-Mann and Hartle. Alternative interpretations of the decoherent histories framework are also considered. (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 to account for it. (shrink)
NGC 1300 (shown in figure 1) is a spiral galaxy 65 million light years from Earth.1 We have never been there, and (although I would love to be wrong about this) we will never go there; all we will ever know about NGC 1300 is what we can see of it from sixty-five million light years away, and what we can infer from our best physics. Fortunately, “what we can infer from our best physics” is actually quite a lot. To (...) take a particular example: our best theory of galaxies tells us that that hazy glow is actually made up of the light of hundreds of billions of stars; our best theories of planetary formation tell us that a sizable fraction of those stars.. (shrink)
Quantum mechanical entangled configurations of particles that do not satisfy Bell’s inequalities, or equivalently, do not have a joint probability distribution, are familiar in the foundational literature of quantum mechanics. Nonexistence of a joint probability measure for the correlations predicted by quantum mechanics is itself equivalent to the nonexistence of local hidden variables that account for the correlations (for a proof of this equivalence, see Suppes and Zanotti, 1981). From a philosophical standpoint it is natural to ask what sort of (...) concept can be used to provide a “joint” analysis of such quantum correlations. In other areas of application of probability, similar but different problems arise. A typical example is the introduction of upper and lower probabilities in the theory of belief. A person may feel uncomfortable assigning a precise probability to the occurrence of rain tomorrow, but feel comfortable saying the probability should be greater than ½ and less than ⅞. Rather extensive statistical developments have occurred for this framework. A thorough treatment can be found in Walley (1991) and an earlier measurement-oriented development in Suppes (1974). It is important to note that this focus on beliefs, or related Bayesian ideas, is not concerned, as we are here, with the nonexistence of joint probability distributions. Yet earlier work with no relation to quantum mechanics, but focused on conditions for existence has been published by many people. For some of our own work on this topic, see Suppes and Zanotti (1989). Still, this earlier work naturally suggested the question of whether or not upper and lower measures could be used in quantum mechanics, as a generalization of.. (shrink)
The conceptual structure of orthodox quantum mechanics has not provided a fully satisfactory and coherent description of natural phenomena. With particular attention to the measurement problem, we review and investigate two unorthodox formulations. First, there is the model advanced by GRWP, a stochastic modification of the standard Schrödinger dynamics admitting statevector reduction as a real physical process. Second, there is the ontological interpretation of Bohm, a causal reformulation of the usual theory admitting no collapse of the statevector. Within these two (...) seemingly quite different approaches, we discuss in a comparative manner, several points: The meaning of the state vector, the status of quantum probability, the legitimacy of attributing macro objective properties to physical systems, and the possibility of retrieving the classical limit. Finally, we consider aspects of non-locality and relevant difficulties with formulating a relativistic generalization of the two approaches. (shrink)
In a previous paper (Hemmo and Shenker 2003) we discussed a recent proposal by Albert (2000, Ch. 7) to recover thermodynamics on a purely dynamical basis, using the quantum theory of the collapse of the quantum state of Ghirardi, Rimini and Weber (1986). We proposed an alternative way to explain thermodynamics within no collapse interpretations of quantum mechanics. In this paper some difficulties faced by both approaches are discussed and solved: the spin echo experiments, and the problem of extremely light (...) gases. In these contexts, we point out several ways in which the above quantum mechanical approaches as well as some other classical approaches to the foundations of statistical mechanics may be distinguished experimentally. (shrink)
We propose a technical reformulation of the measurement problem of quantum mechanics, which is based on the postulate that the final state of a measurement is classical; this accords with experimental practice as well as with Bohr’s views. Unlike the usual formulation (in which the post-measurement state is a unit vector in Hilbert space), our version actually opens the possibility of admitting a purely technical solution within the confines of conventional quantum theory (as opposed to solutions that either modify this (...) theory, or introduce unusual and controversial interpretative rules and/or ontologies).To that effect, we recall a remarkable phenomenon in the theory of Schrödinger operators (discovered in 1981 by Jona-Lasinio, Martinelli, and Scoppola), according to which the ground state of a symmetric double-well Hamiltonian (which is paradigmatically of Schrödinger’s Cat type) becomes exponentially sensitive to tiny perturbations of the potential as ħ→0. We show that this instability emerges also from the textbook wkb approximation, extend it to time-dependent perturbations, and study the dynamical transition from the ground state of the double well to the perturbed ground state (in which the cat is typically either dead or alive, depending on the details of the perturbation).Numerical simulations show that adiabatically arising perturbations may (quite literally) cause the collapse of the wave-function in the classical limit. Thus, at least in the context of a simple mathematical model, we combine the technical and conceptual virtues of decoherence (which fails to solve the measurement problem but launches the key idea that perturbations may come from the environment) with those of dynamical collapse models à la grw (which do solve the measurement problem but are ad hoc), without sharing their drawbacks: single measurement outcomes are obtained (instead of merely diagonal reduced density matrices), and no modification of quantum mechanics is needed. (shrink)
David Bourget has raised some conceptual and technical objections to my development of von Neumann’s treatment of the Copenhagen idea that the purely physical process described by the Schrödinger equation must be supplemented by a psychophysical process called the choice of the experiment by Bohr and Process 1 by von Neumann. I answer here each of Bourget’s objections.
Contrary to the widespread belief, the problem of the emergence of classical mechanics from quantum mechanics is still open. In spite of many results on the ¯h → 0 asymptotics, it is not yet clear how to explain within standard quantum mechanics the classical motion of macroscopic bodies. In this paper we shall analyze special cases of classical behavior in the framework of a precise formulation of quantum mechanics, Bohmian mechanics, which contains in its own structure the possibility of describing (...) real objects in an observer-independent way. (shrink)
It is standardly assumed in discussions of quantum theory that physical systems can be regarded as having well-defined Hilbert spaces. It is shown here that a Hilbert space can be consistently partitioned only if its components are assumed not to interact. The assumption that physical systems have well-defined Hilbert spaces is, therefore, physically unwarranted.
This is a preliminary version of an article to appear in the forthcoming Ashgate Companion to the New Philosophy of Physics.In it, I aim to review, in a way accessible to foundationally interested physicists as well as physics-informed philosophers, just where we have got to in the quest for a solution to the measurement problem. I don't advocate any particular approach to the measurement problem (not here, at any rate!) but I do focus on the importance of decoherence theory (...) to modern attempts to solve the measurement problem, and I am fairly sharply critical of some aspects of the "traditional" formulation of the problem. (shrink)
Probabilities may be subjective or objective; we are concerned with both kinds of probability, and the relationship between them. The fundamental theory of objective probability is quantum mechanics: it is argued that neither Bohr's Copenhagen interpretation, nor the pilot-wave theory, nor stochastic state-reduction theories, give a satisfactory answer to the question of what objective probabilities are in quantum mechanics, or why they should satisfy the Born rule; nor do they give any reason why subjective probabilities should track objective ones. But (...) it is shown that if probability only arises with decoherence, then they must be given by the Born rule. That further, on the Everett interpretation, we have a clear statement of what probabilities are, in terms of purely categorical physical properties; and finally, along lines laid out by Deutsch and Wallace, that there is a clear basis in the axioms of decision theory as to why subjective probabilities should track these objective ones. These results hinge critically on the absence of hidden-variables or any other mechanism (such as state-reduction) from the physical interpretation of the theory. The account of probability has traditionally been considered the principal weakness of the Everett interpretation; on the contrary it emerges as one of its principal strengths. (shrink)
I argue that a dual-aspect theory of consciousness, associated with a particular class of quantum states, can provide a consistent account of consciousness. I illustrate this with the use of coherent states as this class. The proposal meets Chalmers 'requirements of allowing a structural correspondence between consciousness and its physical correlate. It provides a means for consciousness to have an effect on the world (it is not an epiphenomenon, and can thus be selected by evolution) in a way that supplements (...) and completes conventional physics, rather than interfering with it. I draw on the work of Hameroff and Penrose to explain the consistency of this proposal with decoherence, while adding details to this work. The proposal is open to extensive further research at both theoretical and experimental levels. (shrink)
In this paper I assess the prospects for combining contemporary Everettian quantum mechanics (EQM) with branching-time semantics in the tradition of Kripke, Prior, Thomason and Belnap. I begin by outlining the salient features of ‘decoherence-based’ EQM, and of the ‘consistent histories’ formalism that is particularly apt for conceptual discussions in EQM. This formalism permits of both ‘branching worlds’ and ‘parallel worlds’ interpretations; the metaphysics of EQM is in this sense underdetermined by the physics. A prominent argument due to Lewis (...) (On the Plurality of Worlds, 1986 ) supports the non-branching interpretation. Belnap et al. (Facing the Future: Agents and Choices in Our Indeterministic World, 2001 ) refer to Lewis’ argument as the ‘Assertion problem’, and propose a pragmatic response to it. I argue that their response is unattractively ad hoc and complex, and that it prevents an Everettian who adopts branching-time semantics from making clear sense of objective probability. The upshot is that Everettians are better off without branching-time semantics. I conclude by discussing and rejecting an alternative possible motivation for branching time. (shrink)
I address the problem of indefiniteness in quantum mechanics: the problem that the theory, without changes to its formalism, seems to predict that macroscopic quantities have no definite values. The Everett interpretation is often criticised along these lines, and I shall argue that much of this criticism rests on a false dichotomy: that the macroworld must either be written directly into the formalism or be regarded as somehow illusory. By means of analogy with other areas of physics, I develop the (...) view that the macroworld is instead to be understood in terms of certain structures and patterns which emerge from quantum theory (given appropriate dynamics, in particular decoherence). I extend this view to the observer, and in doing so make contact with functionalist theories of mind. (shrink)
We develop and defend the thesis that the Hilbert space formalism of quantum mechanics is a new theory of probability. The theory, like its classical counterpart, consists of an algebra of events, and the probability measures defined on it. The construction proceeds in the following steps: (a) Axioms for the algebra of events are introduced following Birkhoff and von Neumann. All axioms, except the one that expresses the uncertainty principle, are shared with the classical event space. The only models for (...) the set of axioms are lattices of subspaces of inner product spaces over a field K. (b) Another axiom due to Soler forces K to be the field of real, or complex numbers, or the quaternions. We suggest a probabilistic reading of Soler's axiom. (c) Gleason's theorem fully characterizes the probability measures on the algebra of events, so that Born's rule is derived. (d) Gleason's theorem is equivalent to the existence of a certain finite set of rays, with a particular orthogonality graph (Wondergraph). Consequently, all aspects of quantum probability can be derived from rational probability assignments to finite "quantum gambles". (e) All experimental aspects of entanglement- the violation of Bell's inequality in particular- are explained as natural outcomes of the probabilistic structure. (f) We hypothesize that even in the absence of decoherence macroscopic entanglement can very rarely be observed, and provide a precise conjecture to that effect .We also discuss the relation of the present approach to quantum logic, realism and truth, and the measurement problem. (shrink)
The decision-theoretic account of probability in the Everett or many-worlds interpretation, advanced by David Deutsch and David Wallace, is shown to be circular. Talk of probability in Everett presumes the existence of a preferred basis to identify measurement outcomes for the probabilities to range over. But the existence of a preferred basis can only be established by the process of decoherence, which is itself probabilistic.
Confused ideas about the weirdness of quantum mechanics have sometimes been blamed for the spread of anti-realist positions in philosophy. In this seminar, I shall re-examine the relation between realism and quantum theory. My goal is to argue that one can remain a realist in a reasonably familiar sense, while adopting a theory which amounts to a form of idealism. After sketching the abstract mathematical structure of quantum theory, I will introduce realism and consider some of its problems and some (...) counter-arguments. Next I will look at why quantum theory needs an interpretation and at some of the features common to many proposed interpretations. Then I will discuss some of the gaps in decoherence theory, when it is considered as an interpretation of quantum theory, and I will end with a sketch of my own realist version of idealism in which the fundamental entities are structures which define minds, and the fundamental laws govern the stochastic developments of those structures. (shrink)
For nearly six decades, the conscious observer has played a central and essential rôle in quantum measurement theory. I outline some difficulties which the traditional account of measurement presents for material theories of mind before introducing a new development which promises to exorcise the ghost of consciousness from physics and relieve the cognitive scientist of the burden of explaining why certain material structures reduce wavefunctions by virtue of being conscious while others do not. The interactive decoherence of complex quantum (...) systems reveals that the oddities and complexities of linear superposition and state vector reduction are irrelevant to computational aspects of the philosophy of mind and that many conclusions in related fields are ill founded. (shrink)
Proposals for quantum computation rely on superposed states implementing multiple computations simultaneously, in parallel, according to quantum linear superposition (e.g., Benioff, 1982; Feynman, 1986; Deutsch, 1985, Deutsch and Josza, 1992). In principle, quantum computation is capable of specific applications beyond the reach of classical computing (e.g., Shor, 1994). A number of technological systems aimed at realizing these proposals have been suggested and are being evaluated as possible substrates for quantum computers (e.g. trapped ions, electron spins, quantum dots, nuclear spins, etc., (...) see Table 1; Bennett, 1995; and Barenco, 1995). The main obstacle to realization of quantum computation is the problem of interfacing to the system (input, output) while also protecting the quantum state from environmental decoherence. If this problem can be overcome, then present day classical computers may evolve to quantum computers. (shrink)
A simple exactly solvable model is given of the dynamical coupling between a person’s classically described perceptions and that person’s quantum mechanically described brain. The model is based jointly upon von Neumann’s theory of measurements and the empirical findings of close connections between conscious intentions and synchronous oscillations in well separated parts of the brain. A quantum-Zeno-effect-based mechanism is described that allows conscious intentions to influence brain activity in a functionally appropriate way. The robustness of this mechanism in the face (...) of environmental decoherence effects is emphasized. (shrink)
It is emphasized that a many-worlds interpretation of quantum theory exists only to the extent that the associated basis problem is solved. The core basis problem is that the robust enduring states specified by environmental decoherence effects are essentially Gaussian wave packets that form continua of non-orthogonal states. Hence they are not a discrete set of orthogonal basis states to which finite probabilities can be assigned by the usual rules. The natural way to get an orthogonal basis without going (...) outside the Schroedinger dynamics is to use the eigenstates of the reduced density matrix, and this idea is the basis of some recent attempts by many-worlds proponents to solve the basis problem. But these eigenstates do not enjoy the locality and quasi-classicality properties of the states defined by environmental decoherence effects, and hence are not satisfactory preferred basis states. This core problem is obscured by approaches that treat the universe as a quantum computer, but it needs to be addressed and resolved before a many-worlds-type interpretation can be said to exist. (shrink)
Abstract: This paper assesses the Everettian approach to the measurement problem, especially the version of that approach advocated by Simon Saunders and David Wallace. I emphasise conceptual, indeed metaphysical, aspects rather than technical ones; but I include an introductory exposition of decoherence. In particular, I discuss whether---as these authors maintain---it is acceptable to have no precise definition of 'branch' (in the Everettian kind of sense). (A version of this paper will appear in a CTNS/Vatican Observatory volume on Quantum Theory (...) and Divine Action, ed. Robert Russell et al.). (shrink)
Among the alternatives of non-relativistic quantum mechanics (NRQM) there are those that give different predictions than quantum mechanics in yet-untested circumstances, while remaining compatible with current empirical findings. In order to test these predictions, one must isolate one’s system from environmental induced decoherence, which, on the standard view of NRQM, is the dynamical mechanism that is responsible for the ‘apparent’ collapse in open quantum systems. But while recent advances in condensed-matter physics may lead in the near future to experimental (...) setups that will allow one to test the two hypotheses, namely genuine collapse vs. decoherence, hence make progress toward a solution to the quantum measurement problem, those philosophers and physicists who are advocating an information-theoretic approach to the foundations of quantum mechanics are still unwilling to acknowledge the empirical character of the issue at stake. Here I argue that in doing so they are displaying an unwarranted double standard. r 2007 Elsevier Ltd. All rights reserved. (shrink)
Gödel’s incompleteness applies to any system with recursively enumerable axioms and rules of inference. Chaitin’s approach to Gödel’s incompleteness relates the incompleteness to the amount of information contained in the axioms. Zurek’s quantum Darwinism attempts the physical description of the universe using information as one of its major components. The capacity of quantum Darwinism to describe quantum measurement in great detail without requiring ad-hoc non-unitary evolution makes it a good candidate for describing the transition from quantum to classical. A baby-universe (...) diffusion model of cosmic inflation is analyzed using quantum Darwinism. In this model cosmic inflation can be approximated as Brownian motion of a quantum field, and quantum Darwinism implies that molecular interaction during Brownian motion will make the quantum field decohere. The quantum Darwinism approach to decoherence in the baby-universe cosmic-inflation model yields the decoherence times of the baby-universes. The result is the equation relating the baby-universe’s decoherence time with the Hubble parameter, and that the decoherence time is considerably shorter than the cosmic inflation period. (shrink)
Q0 Why this FAQ? Q1 Who believes in many-worlds? Q2 What is many-worlds? Q3 What are the alternatives to many-worlds? Q4 What is a "world"? Q5 What is a measurement? Q6 Why do worlds split? What is decoherence? Q7 When do worlds split? Q8 When does Schrodinger's cat split? Q9 What is sum-over-histories? Q10 What is many-histories? What is the environment basis? Q11 How many worlds are there? Q12 Is many-worlds a local theory? Q13 Is many-worlds a deterministic theory? (...) Q14 Is many-worlds a relativistic theory? What about quantum field theory? What about quantum gravity? Q15 Where are the other worlds? Q16 Is many-worlds (just) an interpretation? Q17 Why don't worlds fuse, as well as split? Do splitting worlds imply irreversible physics? Q18 What retrodictions does many-worlds make? Q19 Do worlds differentiate or split? Q20 What is many-minds? Q21 Does many-worlds violate Ockham's Razor? Q22 Does many-worlds violate conservation of energy? Q23 How do probabilities emerge within many-worlds? Q24 Does many-worlds allow free-will? Q25 Why am I in this world and not another? Why does the universe appear random? Q26 Can wavefunctions collapse? Q27 Is physics linear? Could we ever communicate with the other worlds? Why do I only ever experience one world? Why am I not aware of the world (and myself) splitting? Q28 Can we determine what other worlds there are? Is the form of the Universal Wavefunction knowable? Q29 Who was Everett? Q30 What are the problems with quantum theory? Q31 What is the Copenhagen interpretation? Q32 Does the EPR experiment prohibit locality? What about Bell's Inequality? Q33 Is Everett's relative state formulation the same as many-worlds? Q34 What is a relative state? Q35 Was Everett a "splitter"? Q36 What unique predictions does many-worlds make? Q37 Could we detect other Everett-worlds? Q38 Why quantum gravity? Q39 Is linearity exact? (shrink)
In Everett’s many worlds interpretation, quantum measurements are considered to be decoherence events. If so, then inexact decoherence may allow large worlds to mangle the memory of observers in small worlds, creating a cutoff in observable world size. Smaller world are mangled and so not observed. If this cutoff is much closer to the median measure size than to the median world size, the distribution of outcomes seen in unmangled worlds follows the Born rule. Thus deviations from exact (...)decoherence can allow the Born rule to be derived via world counting, with a finite number of worlds and no new fundamental physics. (shrink)
The integration of recent work on decoherence into a so-called modal interpretation offers a promising new approach to the measurement problem in quantum mechanics. In this paper I explain and develop this approach in the context of the interactive interpretation presented in Healey (1989). I begin by questioning a number of assumptions which are standardly made in setting up the measurement problem, and I conclude that no satisfactory solution can afford to ignore the influence of the environment. Further, I (...) argue that there are good reasons to believe that on a modal interpretation environmental interactions rapidly ensure that a quantummechanically describable apparatus indeed records a definite result following a measurement interaction. (shrink)
I consider the question of the direction of time in the context of the Everett interpretation of quantum mechanics. I focus on the special role of decoherence in the recovery of time asymmetric behaviour, such as the collapse of the quantum state and the thermodynamic regularities. The discussion is based on results in the consistent histories approach (Gell-Mann and Hartle 1993) and in decoherence theory (Zurek and Paz 1994). Finally, I compare the status of the direction of time (...) in Everett and in a recent proposal by Albert (2001) based on the collapse theory of Ghirardi, Rimini and Weber (1986). (shrink)
The rotating discs argument (RDA) against perdurantism has been mostly discussed by metaphysicians, though the argument of course appeals to ideas from classical mechanics, especially about rotation. In contrast, I assess the RDA from the perspective of the philosophy of physics. I argue for three main conclusions. The first conclusion is that the RDA can be formulated more strongly than is usually recognized: it is not necessary to ‘imagine away’ the dynamical effects of rotation. The second is that in (...) general relativity, the RDA fails because of frame-dragging. The third conclusion is that even setting aside general relativity, the strong formulation of the RDA can after all be defeated, namely, by the perdurantist taking objects in classical mechanics (whether point-particles or continuous bodies) to have only temporally extended (i.e. non-instantaneous) temporal parts, which immediately blocks the RDA. Admittedly, this version of perdurantism defines persistence in a weaker sense of ‘definition’ than pointilliste versions that aim to define persistence assuming only instantaneous temporal parts. But I argue that temporally extended temporal parts (i) can do the jobs within the endurantism–perdurantism debate that the perdurantist wants temporal parts to do and (ii) are supported by both classical and quantum mechanics. Introduction The story so far 2.1 The RDA 2.2 Intrinsic properties and the idea of velocity 2.2.1 The intrinsic–extrinsic distinction 2.2.2 Velocity to the rescue? 2.3 ‘Naturalism’ 2.4 The accompaniments of rotation 2.5 Two kinds of reply: against the consensus Describing rotation 3.1 Rotation is kinematic 3.2 Beware of rigidity 3.3 An improved RDA: allowing the actual accompaniments 3.4 The RDA fails in general relativity Perdurantism without tears: the classical case 4.1 Rejecting instantaneous temporal parts 4.2 Replying to the RDA 4.2.1 ‘Kinematics’ 4.2.2 ‘Dynamics’ 4.2.3 An ‘anti-pointilliste’ objection and reply 4.3 Intrinsic properties of non-instantaneous temporal parts 4.3.1 Can the perdurantist appeal to them? 4.3.2 Temporal intrinsicality at an instant is rare 4.3.3 A better reason for temporal intrinsicality 4.4 Non-instantaneous parts can do the jobs 4.4.1 Humean supervenience revisited 4.4.2 The problem of change 4.4.3 Puzzles of coincidence 4.5 Instantaneous velocity is hardly extrinsic Support from decoherence in quantum theory 5.1 Classical and quantum: relativizing the intrinsic–extrinsic distinction 5.1.1 Unitarity: momentum as temporally intrinsic 5.2 Position and existence as nomically extrinsic. (shrink)
In Everett’s many-worlds interpretation, where quantum measurements are seen as decoherence events, inexact decoherence may let large worlds mangle the memories of observers in small worlds, creating a cutoff in observable world measure. I solve a growth–drift–diffusion–absorption model of such a mangled worlds scenario, and show that it reproduces the Born probability rule closely, though not exactly. Thus, inexact decoherence may allow the Born rule to be derived in a many-worlds approach via world counting, using a finite (...) number of worlds and no new fundamental physics. (shrink)
A variety of ideas arising in decoherence theory, and in the ongoing debate over Everett's relative-state theory, can be linked to issues in relativity theory and the philosophy of time, specifically the relational theory of tense and of identity over time. These have been systematically presented in companion papers (Saunders 1995; 1996a); in what follows we shall consider the same circle of ideas, but specifically in relation to the interpretation of probability, and its identification with relations in the Hilbert (...) Space norm. The familiar objection that Everett's approach yields probabilities different from quantum mechanics is easily dealt with. The more fundamental question is how to interpret these probabilities consistent with the relational theory of change, and the relational theory of identity over time. I shall show that the relational theory needs nothing more than the physical, minimal criterion of identity as defined by Everett's theory, and that this can be transparently interpreted in terms of the ordinary notion of the chance occurrence of an event, as witnessed in the present. It is in this sense that the theory has empirical content. (shrink)
An outline for a modal interpretation in terms of possible worlds is presented. The so-called Schmidt histories are taken to correspond to the physically possible worlds. The decoherence function defined in the histories formulation of quantum theory is taken to prescribe a non-classical probability measure over the set of the possible worlds. This is shown to yield dynamics in the form of transition probabilities for occurrent events in each world. The role of the consistency condition is discussed.
This work-in-progress paper consists of four points which relate to the foundations and physical realization of quantum computing. The first point is that the qubit cannot be taken as the basic unit for quantum computing, because not every superposition of bit-strings of length n can be factored into a string of n-qubits. The second point is that the “No-cloning” theorem does not apply to the copying of one quantum register into another register, because the mathematical representation of this copying is (...) the identity operator, which is manifestly linear. The third point is that quantum parallelism is not destroyed only by environmental decoherence. There are two other forms of decoherence, which we call measurement decoherence and internal decoherence, that can also destroy quantum parallelism. The fourth point is that processing the contents of a quantum register “one qubit at a time” destroys entanglement. (shrink)
I analyse two different methods for the retrieval of a classical notion of spacetime from the theory of quantum cosmology in terms of the different means they employ to bring about the necessary loss of coherence. One method employs a direct coarse graining of the appropriate phase space, whereas the other method is based on decohering the system by the interaction with an environment. Although these methods are equivalent on a phenomenological level, I argue that conceptually the decoherence approach (...) is superior. The coarse graining approach construes the necessary loss of coherence in epistemic terms, whereas the method based on decohering the system by interaction with an environment provides a dynamical explanation for the emergence of classical notions of spacetime. On the latter account the emergence of classical behaviour is an objective property of the physical system under consideration, in contradistinction with the subjective coarse graining account of the retrieval of a classical spacetime in terms of measurements made by an observer. (shrink)
We study the process of observation (measurement), within the framework of a `perspectival' (`relational', `relative state')version of the modal interpretation of quantum mechanics. We show that if we assume certain features of discreteness and determinism in the operation of the measuring device (which could be a part of the observer's nerve system), this gives rise to classical characteristics of the observed properties, in the first place to spatial localization. We investigate to what extent semi-classical behavior of the object system itself (...) (as opposed to the observational system) is needed for the emergence of classicality. Decoherence is an essential element in the mechanism of observation that we assume, but it turns out that in our approach no environment-induced decoherence on the level of the object system is required for the emergence of classical properties. (shrink)
: The oft-repeated claim that life is ‘ written into ’ the laws of nature is examined and criticised. Arguments are given in favour of life spreading between near-neighbour planets in rocky impact ejecta (transpermia), but against panspermia, leading to the conclusion that if life is indeed found to be widespread in the universe, some form of life principle or biological determinism must be at work in the process of biogenesis. Criteria for what would constitute a credible life principle are (...) elucidated. I argue that the key property of life is its information content, and speculate that the emergence of the requisite information-processing machinery might require quantum information theory for a satisfactory explanation. Some clues about how decoherence might be evaded are discussed. The implications of some of these ideas for ‘ fine-tuning ’ are discussed. (shrink)
We make a first attempt to axiomatically formulate the Montevideo interpretation of quantum mechanics. In this interpretation environmental decoherence is supplemented with loss of coherence due to the use of realistic clocks to measure time to solve the measurement problem. The resulting formulation is framed entirely in terms of quantum objects without having to invoke the existence of measurable classical quantities like the time in ordinary quantum mechanics. The formulation eliminates any privileged role to the measurement process giving an (...) objective definition of when an event occurs in a system. (shrink)
These two books, both by distinguished authors, are excellent. Though they are written by and for physicists, they are an invaluable resource for philosophers interested in the grand theme of how classical physical phenomena emerge from the quantum realm. Both individually and taken together, they are fine representatives of the present state of knowledge about this theme, and about many more specific topics falling under it. They are also pedagogic, though aimed at an advanced level—graduate students and beyond, in physics (...) and mathematics. Thus, they are packed with sophisticated expositions of such topics as quantum Brownian motion, and decoherence in quantum field theory (Joos 2003), the rigorous definition of macroscopic observables and of their evolution laws in quantum statistical physics (Sewell 2002), and the rigorous treatment of open quantum systems (Joos 2003; Sewell 2002). So overall, they provide an invaluable overview of a large and lively research area of physics. But the books are also different in several ways. The first book, by Joos et al., has six authors, all theoretical physicists based in Germany and part of the ‘Heidelberg school’ of decoherence physics, which has grown up in the last twenty-five years under the tutelage of Heinz-Dieter Zeh. The second book is a monograph: Sewell is a British mathematical physicist, most of whose work has been in the algebraic approach to quantum statistical mechanics. Other, less obvious, differences follow on from these. By and large, the material in Decoherence is both more familiar and more accessible to philosophers of physics. And for reviewing the books for philosophers of physics, it will be a convenient strategy to spell out the three reasons for this contrast. But as we shall see, Quantum Mechanics being more difficult need not mean it is less valuable. First, decoherence processes of the kinds that Joos, et al., mostly discuss are now well-known to philosophers of quantum theory, not least through the work of the Heidelberg school itself (and the acclaimed first edition of this book) and of the ‘Los Alamos school’ of Zurek and coauthors. Indeed, Joos’ own Chapter 3, “Decoherence through Interaction with the.... (shrink)
How come quantum theory has anything to do with mind? Is your theory refutable? What is the point of all the technical detail? Do you suggest that the operation of the brain involves large scale quantum coherence? Isn't large scale quantum coherence necessary to solve the problem of the unity of consciousness? How does a many-minds interpretation survive Occam's razor? What, briefly, is your current philosophical position? What is your understanding of the relationship between mind and brain for split-brain patients? (...) Do you believe that the mind can survive the death of the brain? No journal reference is given for several of the recent papers on your home page. Where will these papers be printed? How are the “source” and “pdf” versions of the papers on your home page produced and viewed? Why does the page with your photograph behave oddly in some browsers? Where can I find an elementary introduction to the interpretation of quantum theory? Doesn't decoherence theory solve all the problems of the interpretation of quantum theory? How do the ambiguities of decoherence affect the many-worlds interpretation? Could you expand on your answers to the two previous questions? Why isn't the conventional interpretation of quantum theory adequate? What about the Bohm interpretation? What about consistent histories? Does the present many-minds interpretation solve all the problems? (shrink)
The relationship between classical and quantum theory is of central importance to the philosophy of physics, and any interpretation of quantum mechanics has to clarify it. Our discussion of this relationship is partly historical and conceptual, but mostly technical and mathematically rigorous, including over 500 references. For example, we sketch how certain intuitive ideas of the founders of quantum theory have fared in the light of current mathematical knowledge. One such idea that has certainly stood the test of time is (...) Heisenberg's `quantum-theoretical Umdeutung (reinterpretation) of classical observables', which lies at the basis of quantization theory. Similarly, Bohr's correspondence principle (in somewhat revised form) and Schroedinger's wave packets (or coherent states) continue to be of great importance in understanding classical behaviour from quantum mechanics. On the other hand, no consensus has been reached on the Copenhagen Interpretation, but in view of the parodies of it one typically finds in the literature we describe it in detail. On the assumption that quantum mechanics is universal and complete, we discuss three ways in which classical physics has so far been believed to emerge from quantum physics, namely in the limit h -> 0 of small Planck's constant (in a finite system), in the limit N goes to infinity of a large system with $N$ degrees of freedom (at fixed h), and through decoherence and consistent histories. The first limit is closely related to modern quantization theory and microlocal analysis, whereas the second involves methods of C*-algebras and the concepts of superselection sectors and macroscopic observables. In these limits, the classical world does not emerge as a sharply defined objective reality, but rather as an approximate appearance relative to certain ``classical" states and observables. Decoherence subsequently clarifies the role of such states, in that they are ``einselected", i.e. robust against coupling to the environment. Furthermore, the nature of classical observables is elucidated by the fact that they typically define (approximately) consistent sets of histories. This combination of ideas and techniques does not quite resolve the measurement problem, but it does make the point that classicality results from the elimination of certain states and observables from quantum theory. Thus the classical world is not created by observation (as Heisenberg once claimed), but rather by the lack of it. (shrink)
Why don't we see large macroscopic objects in entangled states? Even if the particles composing the object were all entangled and insulated from the environment, we shall still find it almost always impossible to observe the superposition. The reason is that as the number of particles n grows, we need an ever more careful preparation, and an ever more carefully designed experiment, in order to recognize the entangled character of the state of the object. An observable W that distinguishes all (...) the unentangled states from some entangled states is called a witness. We consider witnesses on n quantum bits (qbits), and use the following normalization: A witness W satisfies |tr(Wr)|<= 1 for all separable states r, while ||W|| >1, with the norm being the maximum among the absolute values of the eigenvalues of W. Although there are n-qbit witnesses whose norm is exponential in n, we conjecture that for a large majority of such witnesses ||W||<=O[(nlogn)^1/2]. We prove this conjecture for the family of extremal witnesses introduced by Werner and Wolf (Phys. Rev. A 64, 032112 (2001)). Assuming the conjecture is valid we argue that multiparticle entanglement can be detected only if a system has been carefully prepared in a very special state. Otherwise, multiparticle entanglement lies below the threshold of detection, even if it exists, and even if decoherence has been ``turned off''. (shrink)
The classical space-time structure is derived from the structure of an abstract infinite dimensional separable Hilbert space S. For this S is first realized as a Hilbert space H* of functions of abstract parameters. Such a realization is associated with the process of measuring position of macroscopic particles naturally occurring in the universe. The process of decoherence and collapse induced by the measurement is in return associated with the choice of a "decohered" submanifold M of realization H*. The submanifold (...) M is then identified with the classical space-time. The mathematical formalism is developed which permits to recover the usual Riemannian geometry on space-time in terms of the Hilbert structure on S. The specific functional realizations of S are shown to produce space-times of different geometry and topology. (shrink)
A short review of some recent developments in the philosophy of physics is presented. I focus on themes which illustrate relations and points of common interest between philosophy of physics and three of its ‘neighboring’ fields: Physics, metaphysics and general philosophy of science. The main examples discussed inthese three ‘border areas’ are (i) decoherence and the interpretation of quantum mechanics; (ii) time in physics and metaphysics; and (iii) methodological issues surrounding the multiverse idea in modern cosmology.
Ruetsche (1996) has argued that van Fraassen's (1991) Copenhagen Variant of the Modal Interpretation (CVMI) gives unsatisfactory accounts of measurement and of state preparation. I defend the CVMI against Ruetsche's first argument by using decoherence to show that the CVMI does not need to account for the measurement scenario which Ruetsche poses. I then show, however, that there is a problem concerning preparation, and the problem is more serious than the one Ruetsche focuses on. The CVMI makes no substantive (...) predictions for the everyday processes we take to be measurements. (shrink)
The following introduction offers a broad survey of the history of quantum physics. It then outlines the position of each contributor in this Special Focus Section concerning the collapse of the quantum wave function and defines three important terms (Hilbert space, Schrödinger’s cat, and decoherence) used in discussing this topic.
We propose a technical reformulation of the measurement problem of quantum mechanics, which is based on the postulate that the final state of a measurement is classical; this accords with experimental practice as well as with Bohr's views. Unlike the usual formulation (in which the post-measurement state is a a unit vector in Hilbert space, such as a wave-function), our version actually admits a purely technical solution within the confines of conventional quantum theory (as opposed to solutions that either modify (...) this theory, or introduce unusual and controversial interpretative rules and/or ontologies). To that effect, we recall a remarkable phenomenon in the theory of Schroedinger operators (discovered in 1981 by Jona-Lasinio, Martinelli, and Scoppola), according to which the ground state of a symmetric double-well Hamiltonian (which is paradigmatically of Schroedinger's Cat type) becomes exponentially sensitive to tiny perturbations of the potential as h -> 0. We show that this instability emerges also from the textbook WKB approximation, extend it to time-dependent perturbations, and study the dynamical transition from the ground state of the double well to the perturbed ground state (in which the cat is typically either dead or alive, depending on the details of the perturbation). Numerical simulations show that, in an individual experiment, certain (especially adiabatically rising) perturbations may (quite literally) cause the collapse of the wavefunction in the classical limit. Thus we combine the technical and conceptual virtues of dynamical collapse models a la GRW (which do solve the measurement problem) with those of decoherence (in that our perturbations come from the environment) without sharing their drawbacks: although single measurement outcomes are obtained (instead of merely diagonal reduced density matrices), no modification of quantum mechanics is needed. (shrink)
There have been many attempts to undertand the connections between quantum theory and Whiteheadian process philosophy. However, due to the ontological considerations, it is very important to specify which interpretation of quantum theory one embraces before inquiring into the details of Whitehead`s philosophy of organism. In this article, I argue that Ghirardi-Rimini-Weber (GRW) collapse interpretation of quantum theory serves as a suitable point of departure for future endeavors. Comparisons with many-worlds interpretation and decoherence approach have also been provided.
Time flows. This oft-lamented fact of human existence seems plain enough, but is remarkably difficult to explain scientifically. Physical theory follows a greater goal—symmetry—and the directional nature of time is left adrift. The phenomenon must nevertheless be explained.Scientists since Isaac Newton have searched classical mechanics for answers, but precious little progress has been made on his mystical ideas. The discoveries of thermodynamics, though clearly relevant, have posed more problems than they have solved.Now a new solution presents itself through quantum mechanics. (...) The intimate relation between thermodynamics and time is not in doubt, but now quantum theory is explaining how the laws of entropy arise from a stranger reality. The theory of decoherence begins to explain time as a holistic quantum concept. (shrink)
By the relational realist interpretation of wave function collapse, the quantum mechanical actualization of potentia is defined as a decoherence-driven process by which each actualization (in “orthodox” terms, each measurement outcome) is conditioned both by physical and logical relations with the actualities conventionally demarked as “environmental” or external to that particular outcome. But by the relational realist interpretation, the actualization-in-process is understood as internally related to these “enironmental” data per the formalism of quantum decoherence. The concept of “actualization (...) via wave function collapse” is accounted for solely by virtue of these presupposed logical relations—the same logical relations otherwise presupposed by the scientific method itself—and thus requires no “external” physical-dynamical trigger: e.g., the Gaussian hits of GRW, acts of conscious observation, etc. By the relational realist interpretation, it is the physical and logical relations among quantum actualities (quantum “final real things”) that drives the process of decoherence and, via the latter, the logically conditioned actualization of potentia. In this regard, the relational realist interpretation of quantum mechanics is a praxiological interpretation; that is, these physical and logical relations are ontologically active relations, contributing not just to the epistemic coordination of quantum actualizations, but to the process of actualization itself. (shrink)
Decoherence and entanglement : new concepts and perspectives -- Quantum-like models in cognitive science and economics -- Invited presentations -- Contributed presentations -- Post-conference papers.
I examine G.B. Bagci’s arguments for the Ghirardi-Rimini-Weber (GRW) interpretation of non-relativistic quantum mechanics as ideally suited for Whitehead’s philosophy. Much of Bagci’s claims are in response to Michael Epperson, who argues in the same vein in favor of decoherence accounts (Omnès; Zureck). Pace Epperson, I do not think that decoherence is the final arbiter here, and instead I contrast GRW with several other accounts addressing foundational problems of quantum theory (Finkelstein; Green; Peres and Terno; etc.), which also (...) account for relativistic covariance, while GRW does not. I argue that such latter research programs align themselves in a more convincing manner with Whitehead’s scheme, in epistemic as well as metaphysical senses, than GRW. (shrink)
The population, molecular and submolecular (quantum) levels of oncogenesis are considered. The quantum description takes into account the nonlocal Einstein- Podolsky-Rosen correlations, interactions at-the-distance, quantum entanglement and macroscopic quantum coherence. In this approach, cancerogenesis is initiated by destruction of the quantum entanglement of the DNA molecules due to mutation, which leads to appearance of an oncogen and a local decoherence of the organism. In the genetic approach a cancer is the gene disease, whereas in the quantum approach — a (...) disease of the living system. On the basis of the Humphreys criteria, an attempt of the ontological classification of bio- and ontogenesis is made. Those phenomena can be considered in terms of the coherent, synchronic and holistic emergence. (shrink)
The consistent histories reformulation of quantum mechanics was developed by Robert Griffiths, given a formal logical systematization by Roland Omn\`{e}s, and under the label `decoherent histories', was independently developed by Murray Gell-Mann and James Hartle and extended to quantum cosmology. Criticisms of CH involve issues of meaning, truth, objectivity, and coherence, a mixture of philosophy and physics. We will briefly consider the original formulation of CH and some basic objections. The reply to these objections, like the objections themselves, involves a (...) mixture of physics and philosophy. These replies support an evaluation of the CH formulation as a replacement for the measurement, or orthodox, interpretation. (shrink)
This paper suggests an epistemic interpretation of Belnap’s branching space-times theory based on Everett’s relative state formulation of the measurement operation in quantum mechanics. The informational branching models of the universe are evolving structures defined from a partial ordering relation on the set of memory states of the impersonal observer. The totally ordered set of their information contents defines a linear “time” scale to which the decoherent alternative histories of the informational universe can be referred—which is quite necessary for assigning (...) them a probability distribution. The “historical” state of a physical system is represented in an appropriate extended Hilbert space and an algebra of multi-branch operators is developed. An age operator computes the informational depth of historical states and its standard deviation can be used to provide a universal information/energy uncertainty relation. An information operator computes the encoding complexity of historical states, the rate of change of its average value accounting for the process of correlation destruction inherent to the branching dynamics. In the informational branching models of the universe, the asymmetry of phenomena in nature appears as a mere consequence of the subject’s activity of measuring, which defines the flow of time-information. (shrink)
