3,930 research outputs found
Consistent histories, quantum truth functionals, and hidden variables
A central principle of consistent histories quantum theory, the requirement
that quantum descriptions be based upon a single framework (or family), is
employed to show that there is no conflict between consistent histories and a
no-hidden-variables theorem of Bell, and Kochen and Specker, contrary to a
recent claim by Bassi and Ghirardi. The argument makes use of ``truth
functionals'' defined on a Boolean algebra of classical or quantum properties.Comment: Latex 10 pages, no figure
Cosmogenesis and Collapse
Some possible benefits of dynamical collapse for a quantum theory of
cosmogenesis are discussed. These are a possible long wait before creation
begins, creation of energy and space, and choice of a particular universe out
of a superposition.Comment: For a festschrift in Foundations of Physics in honor of Daniel
Greenberger and Helmut Rauch in Foundations of Physics. This updates the
previous version by adding an appendix (Appendix B) which contains the exact
solution of a partial differential equation of importance in the pape
Are collapse models testable with quantum oscillating systems? The case of neutrinos, kaons, chiral molecules
Collapse models provide a theoretical framework for understanding how
classical world emerges from quantum mechanics. Their dynamics preserves
(practically) quantum linearity for microscopic systems, while it becomes
strongly nonlinear when moving towards macroscopic scale. The conventional
approach to test collapse models is to create spatial superpositions of
mesoscopic systems and then examine the loss of interference, while
environmental noises are engineered carefully. Here we investigate a different
approach: We study systems that naturally oscillate --creating quantum
superpositions-- and thus represent a natural case-study for testing quantum
linearity: neutrinos, neutral mesons, and chiral molecules. We will show how
spontaneous collapses affect their oscillatory behavior, and will compare them
with environmental decoherence effects. We will show that, contrary to what
previously predicted, collapse models cannot be tested with neutrinos. The
effect is stronger for neutral mesons, but still beyond experimental reach.
Instead, chiral molecules can offer promising candidates for testing collapse
models.Comment: accepted by NATURE Scientific Reports, 12 pages, 1 figures, 2 table
Consciousness and the Wigner's friend problem
It is generally agreed that decoherence theory is, if not a complete answer,
at least a great step forward towards a solution of the quantum measurement
problem. It is shown here however that in the cases in which a sentient being
is explicitly assumed to take cognizance of the outcome the reasons we have for
judging this way are not totally consistent, so that the question has to be
considered anew. It is pointed out that the way the Broglie-Bohm model solves
the riddle suggests a possible clue, consisting in assuming that even very
simple systems may have some sort of a proto-consciousness, but that their
``internal states of consciousness'' are not predictive. It is, next, easily
shown that if we imagine the systems get larger, in virtue of decoherence their
internal states of consciousness progressively gain in predictive value. So
that, for macro-systems, they may be identified (in practice) with the
predictive states of consciousness on which we ground our observational
predictions. The possibilities of carrying over this idea to standard quantum
mechanics are then investigated. Conditions of conceptual consistency are
considered and found rather strict, and, finally, two solutions emerge,
differing conceptually very much from one another but in both of which the,
possibly non-predictive, generalized internal states of consciousness play a
crucial role
On the measurement problem for a two-level quantum system
A geometric approach to quantum mechanics with unitary evolution and
non-unitary collapse processes is developed. In this approach the Schrodinger
evolution of a quantum system is a geodesic motion on the space of states of
the system furnished with an appropriate Riemannian metric. The measuring
device is modeled by a perturbation of the metric. The process of measurement
is identified with a geodesic motion of state of the system in the perturbed
metric. Under the assumption of random fluctuations of the perturbed metric,
the Born rule for probabilities of collapse is derived. The approach is applied
to a two-level quantum system to obtain a simple geometric interpretation of
quantum commutators, the uncertainty principle and Planck's constant. In light
of this, a lucid analysis of the double-slit experiment with collapse and an
experiment on a pair of entangled particles is presented.Comment: for related papers, see http://www.uwc.edu/dept/math/faculty/kryukov
Postcolonial Publics: Art and Citizen Media in Europe
Postcolonial Publics: Art and Citizen Media in Europe presents a collection of six- teen chapters that explore the themes of how migrants, refugees and citizens express and share their political and social causes and experiences through art and media. These expressions, which we term âcitizen mediaâ, arguably become a platform for postcolonial intellectuals as the studies pursued in this volume investigate the different ways in which previously excluded social groups regain public voice. The volume strives to understand the different articulations of mi- grantsâ, refugeesâ, and citizensâ struggle against increasingly harsh European pol- itics that allow them to achieve and empower political subjectivity in a mediated and creative space. In this way, the contributions in this volume present case studies of citizen media in the form of âactivistic artâ or âartivismâ (Trandafoiu, Ruffini, Cazzato & Taronna, Koobak & Tali, NegrĂłn-Muntaner), activism through different kinds of technological media (Chouliaraki and Al-Ghazzi, Jedlowski), such as documentaries and film (DeniÄ), podcasts, music and soundscapes (Ro- meo and Fabbri, Western, Lazzari, Huggan), and activisms through writings from journalism to fiction (Longhi, Concilio, Festa, De Capitani). The volume argues that citizen media go hand in hand with postcolonial critique because of their shared focus on the deconstruction and decolonisation of Western logics and narratives. Moreover, both question the concept of citizen and of citizenship as they relate to the nation-state and explores the power of media as a tool for participation as well as an instrument of political strength. The book forwards postcolonial artivism and citizen media as a critical framework to understand the refugee and migrant situations in contemporary Europe
An integrated approach to the monitoring of rising damp in historic brick masonry
Monitoring rising damp in historic masonry buildings requires an integrated approach, including not only the quantification of moisture in materials over time, but also the investigation of the supply of water from the ground, the evaporative capacity of the surrounding air, and the presence of potentially hygroscopic salts. However, this approach is seldom applied, hence our knowledge of the phenomenon of rising damp in real historic masonry structures is often only partial. In this paper, the proposed approach was applied to the church of Santa Croce in Ravenna, Italy, an outstanding example of masonry building affected by rising damp and related materialsâ deterioration. Santa Croce is a Byzantine church surrounded by an archaeological site and the whole area is presently located under the water table level, requiring a continuously operating pumping system to prevent the flooding of the entire zone. The testing and monitoring of moisture and salts in the church's materials started in September 2020 and is presently running. The data collected so far are presented and discussed in this paper, providing a contribution to a better understanding of this phenomenon. Moreover, during the monitoring period, a pumping system failure caused the flooding of the area in the period August-November 2021, allowing to investigate the impact of this event on the moisture in the materials. The protocol of testing described in this paper may provide a promising and effective method to investigate rising damp and is a starting point in view of its mitigation
Evolving Techniques in Pancreatic Surgery
Diseases of the pancreas and periampullary region form an important clinical group of malignant and also benign diseases which still carry relatively high morbidity and mortality rates. Pancreatic ductal adenocarcinoma, in particular, is associated with very poor outcome as the number of new cases per year is just slightly higher than the number of deaths from this disease. Therefore, treatment of these conditions should always be based on both the highest level of evidence and technical expertise
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