865,100 research outputs found

    Bohmian Histories and Decoherent Histories

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    The predictions of the Bohmian and the decoherent (or consistent) histories formulations of the quantum mechanics of a closed system are compared for histories -- sequences of alternatives at a series of times. For certain kinds of histories, Bohmian mechanics and decoherent histories may both be formulated in the same mathematical framework within which they can be compared. In that framework, Bohmian mechanics and decoherent histories represent a given history by different operators. Their predictions for the probabilities of histories therefore generally differ. However, in an idealized model of measurement, the predictions of Bohmian mechanics and decoherent histories coincide for the probabilities of records of measurement outcomes. The formulations are thus difficult to distinguish experimentally. They may differ in their accounts of the past history of the universe in quantum cosmology.Comment: 7 pages, 3 figures, Revtex, minor correction

    Learning Histories

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    {Excerpt} How can we gauge the successes and failures of collective learning? How can the rest of the organization benefit from the experience? Learning histories surface the thinking, experiments, and arguments of actors who engaged in organizational change. In the corporate world, the precedence ascribed to individual learning can run counter to organizational learning, the process by which an organization and its people develop their capabilities to create a desired future. Without doubt, developing capabilities is a precondition of a desired future; however, if the essence of a learning organization is that it actively identifies, creates, stores, shares, and uses knowledge to anticipate, adapt to, and maybe even shape a changing environment, the driving concern must be reflection, communication, and collective sense makingfor action across its personnel. (Proponents of organizational learning grumble that people in organizations perform collectively yet still learn individually from incomplete, heterogeneous information to which they ascribe different meaning.) Intra-organizational interaction for learning cannot depend on serendipity: it must be encouraged, facilitated, recognized, and rewarded. Increasingly, narration is deemed a good vessel for bridging knowledge and action in the workplace

    Quantum Histories

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    There are good motivations for considering some type of quantum histories formalism. Several possible formalisms are known, defined by different definitions of event and by different selection criteria for sets of histories. These formalisms have a natural interpretation, according to which nature somehow chooses one set of histories from among those allowed, and then randomly chooses to realise one history from that set; other interpretations are possible, but their scientific implications are essentially the same. The selection criteria proposed to date are reasonably natural, and certainly raise new questions. For example, the validity of ordering inferences which we normally take for granted --- such as that a particle in one region is necessarily in a larger region containing it --- depends on whether or not our history respects the criterion of ordered consistency, or merely consistency. However, the known selection criteria, including consistency and medium decoherence, are very weak. It is not possible to derive the predictions of classical mechanics or Copenhagen quantum mechanics from the theories they define, even given observational data in an extended time interval. Attempts to refine the consistent histories approach so as to solve this problem by finding a definition of quasiclassicality have so far not succeeded. On the other hand, it is shown that dynamical collapse models, of the type originally proposed by Ghirardi-Rimini-Weber, can be re-interpreted as set selection criteria within a quantum histories framework, in which context they appear as candidate solutions to the set selection problem. This suggests a new route to relativistic generalisation of these models, since covariant definitions of a quantum event are known.Comment: 19 pages, TeX with harvmac. Contribution to Proceedings of the 104th Nobel Symposium, ``Modern Studies of Basic Quantum Concepts and Phenomena'', Gimo, June 1997. To appear in Physica Script

    Entangled Histories

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    We introduce quantum history states and their mathematical framework, thereby reinterpreting and extending the consistent histories approach to quantum theory. Through thought experiments, we demonstrate that our formalism allows us to analyze a quantum version of history in which we reconstruct the past by observations. In particular, we can pass from measurements to inferences about "what happened" in a way that is sensible and free of paradox. Our framework allows for a richer understanding of the temporal structure of quantum theory, and we construct history states that embody peculiar, non-classical correlations in time.Comment: 16 pages, 1 figure. v2: typo corrected, minor stylistic changes. v3: minor stylistic changes, final version for publication in Nobel Symposium NS 15

    Quantum causal histories

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    Quantum causal histories are defined to be causal sets with Hilbert spaces attached to each event and local unitary evolution operators. The reflexivity, antisymmetry, and transitivity properties of a causal set are preserved in the quantum history as conditions on the evolution operators. A quantum causal history in which transitivity holds can be treated as ``directed'' topological quantum field theory. Two examples of such histories are described.Comment: 16 pages, epsfig latex. Some clarifications, minor corrections and references added. Version to appear in Classical and Quantum Gravit

    Histories of hating

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    This roundtable discussion presents a dialogue between digital culture scholars on the seemingly increased presence of hating and hate speech online. Revolving primarily around the recent #GamerGate campaign of intensely misogynistic discourse aimed at women in video games, the discussion suggests that the current moment for hate online needs to be situated historically. From the perspective of intersecting cultural histories of hate speech, discrimination, and networked communication, we interrogate the ontological specificity of online hating before going on to explore potential responses to the harmful consequences of hateful speech. Finally, a research agenda for furthering the historical understandings of contemporary online hating is suggested in order to address the urgent need for scholarly interventions into the exclusionary cultures of networked media

    Decoherent Histories Quantum Mechanics with One 'Real' Fine-Grained History

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    Decoherent histories quantum theory is reformulated with the assumption that there is one "real" fine-grained history, specified in a preferred complete set of sum-over-histories variables. This real history is described by embedding it in an ensemble of comparable imagined fine-grained histories, not unlike the familiar ensemble of statistical mechanics. These histories are assigned extended probabilities, which can sometimes be negative or greater than one. As we will show, this construction implies that the real history is not completely accessible to experimental or other observational discovery. However, sufficiently and appropriately coarse-grained sets of alternative histories have standard probabilities providing information about the real fine-grained history that can be compared with observation. We recover the probabilities of decoherent histories quantum mechanics for sets of histories that are recorded and therefore decohere. Quantum mechanics can be viewed as a classical stochastic theory of histories with extended probabilities and a well-defined notion of reality common to all decoherent sets of alternative coarse-grained histories.Comment: 11 pages, one figure, expanded discussion and acknowledgment