Weekly Papers on Quantum Foundations (36)

Authors: J. C. PearlE. G. Cavalcanti

In a recent work, it was shown by one of us (EGC) that Bell-Kochen-Specker inequality violations in phenomena satisfying the no-disturbance condition (a generalisation of the no-signalling condition) cannot in general be explained with a faithful classical causal model—that is, a classical causal model that satisfies the assumption of no fine-tuning. The proof of that claim however was restricted to Bell scenarios involving 2 parties or Kochen-Specker-contextuality scenarios involving 2 measurements per context. Here we show that the result holds in the general case of arbitrary numbers of parties or measurements per context; the connection between fine-tuning and Bell-KS inequality violations is generic and not an artefact of the simplest scenarios. This result unifies, in full generality, Bell nonlocality and Kochen-Specker contextuality as violations of a fundamental principle of classical causality.

Authors: Ángel Rivas

We analyze the validity of Bell and Kochen-Specker theorems under local (or noncontextual) realism but avoiding an assumption of the existence of a joint probability distribution for incompatible observables. We formulate a realist model which complies with this requirement. This is obtained by employing divergent sequences that nevertheless have marginals which are convergent. We find that under standard reasonable assumptions this possibility does not lead to a loophole of those theorems, by deriving a short of CHSH inequality valid for any finite size ensemble. Moreover, we analyze a Hardy’s paradox setting where noncontextual realism imposes the existence of joint probabilities for incompatible observables.

Authors: Alastair A. AbbottRalph SilvaJulian WechsNicolas BrunnerCyril Branciard

A weak measurement performed on a pre- and post-selected quantum system can result in an average value that lies outside of the observable’s spectrum. This effect, usually referred to as an “anomalous weak value”, is generally believed to be possible only when a non-trivial post-selection is performed, i.e., when only a particular subset of the data is considered. Here we show, however, that this is not the case in general: in scenarios in which several weak measurements are sequentially performed, an anomalous weak value can be obtained without post-selection, i.e., without discarding any data. We discuss several questions that this raises about the subtle relation between weak values and pointer positions for sequential weak measurements. Finally, we consider some implications of our results for the problem of distinguishing different causal structures.

Authors: Donald Salisbury

Peter Bergmann and his students embarked in 1949 on a mainly canonical quantization program whose aim was to take into account the underlying four-dimensional diffeomorphism symmetry in the transition from a Lagrangian to a Hamiltonian formulation of Einstein’s theory. They argued that even though one seemed to destroy the full covariance through the focus on a temporal foliation of spacetime, this loss was illusory. Early on they convinced themselves that only the construction of classical invariants could adequately reflect the fully relativistic absence of physical meaning of spacetime coordinates. Efforts were made by Bergmann students Newman and Janis to construct these classical invariants. Then in the late 1950’s Bergmann and Komar proposed a comprehensive program in which classical invariants could be constructed using the spacetime geometry itself to fix intrinsic spacetime landmarks. At roughly the same time Dirac formulated a new criterion for identifying initial phase space variables, one of whose consequences was that Bergmann himself abandoned the gravitational lapse and shift as canonical variables. Furthermore, Bergmann in 1962 interpreted the Dirac formalism as altering the very nature of diffeomorphism symmetry. One class of infinitesimal diffeomorphism was to be understood as depending on the perpendicular to the given temporal foliation. Thus even within the Bergmann school program the preservation of the full four-dimensional symmetry in the Hamiltonian program became problematic. Indeed, the ADM and associated Wheeler-DeWitt program that gained and has retained prominence since this time abandoned the full symmetry. There do remain dissenters – raising the question whether the field of quantum gravity has witnessed a Renaissance in the ensuing decades – or might the full four-dimensional symmetry yet be reborn?

Authors: S. Deser

I summarize, at its 41st–and what would have been Bruno’s 94th–birthday, the history of the discoveries of Supergravity and some of its structure and later developments.

下午12:56 | ScienceDirect Publication: Physics ReportsScienceDirect RSShttps://www.sciencedirect.com/journal/physics-reportsRSS for NodeTue, 23 Jul 2019 10:02:48 GMTCopyright © 2019 Elsevier B.V. All rights reservedRapid solidification as non-ergodic phenomenonPublication date: 20 July 2019Source: Physics Reports, Volume 818Author(s): P.K. Galenko, D. JouAbstractRapid solidification is a relevant physical phenomenon in material sciences, whose theoretical analysis requires going beyond the limits of local equilibrium statistical physics and thermodynamics and, in particular, taking account of ergodicity breaking and of generalized formulation of thermodynamics. The ergodicity breaking is related to the time symmetry breaking and to the presence of some kinds of fluxes and gradient flows making that an average of microscopic variables along time is different than an average over some chosen statistical ensemble. In fast processes, this is due, for instance, to the fact that the system has no time enough to explore the who

Publication date: Available online 10 September 2019

Source: Physics Reports

Author(s): Hamed Adami, Mohammad Reza Setare, Tahsin Çağrı Şişman, Bayram Tekin

Abstract

We give a detailed review of construction of conserved quantities in extended theories of gravity for asymptotically maximally symmetric spacetimes and carry out explicit computations for various solutions. Our construction is based on the Killing charge method, and a proper discussion of the conserved charges of extended gravity theories with this method requires studying the corresponding charges in Einstein’s theory with or without a cosmological constant. Hence we study the ADM charges (in the asymptotically flat case but in generic viable coordinates), the AD charges (in generic Einstein spaces, including the anti-de Sitter spacetimes) and the ADT charges in anti-de Sitter spacetimes. We also discuss the conformal properties and the behavior of these charges under large gauge transformations as well as the linearization instability issue which explains the vanishing charge problem for some particular extended theories. We devote a long discussion to the quasi-local and off-shell generalization of conserved charges in the 2+1 dimensional Chern–Simons like theories and suggest their possible relevance to the entropy of black holes.

下午12:56 | ScienceDirect Publication: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern PhysicsScienceDirect RSShttps://www.sciencedirect.com/journal/studies-in-history-and-philosophy-of-science-part-b-studies-in-history-and-philosophy-of-modern-physicsRSS for NodeWed, 24 Jul 2019 09:46:42 GMTCopyright © 2019 Elsevier Ltd. All rights reservedImprints of the underlying structure of physical theoriesPublication date: Available online 12 July 2019Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern PhysicsAuthor(s): Jorge ManeroAbstractIn the context of scientific realism, this paper intends to provide a formal and accurate description of the structural-based ontology posited by classical mechanics, quantum mechanics and special relativity, which is preserved across the empirical domains of these theories and explain their successful predictions. Along the lines of ontic structural realism, such a description is undertaken by

Publication date: Available online 12 September 2019

Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

Author(s): Elliott Sober

Abstract

A Markov process can be invariant under time reversal and it also can exhibit a failure of invariance that is “uniformly positive.” I show how each of these possibilities contributes to the project of deciding when a temporal sequence of states has a higher probability than its mirror image. Neither suffices, but a distinct property of the Markov process completes the project, namely the unconditional probabilities of two possible states of the system at the start of the process. The concept of forward time-translational invariance plays a role in the analysis, but I discuss backward time-translational invariance as well. I argue that the Markov framework helps clarify how the Past Hypothesis (the hypothesis that the universe began in a very low entropy state) is related to the Second Law of Thermodynamics, and how each is relevant to explaining why histories that exhibit entropy increase have higher probabilities than histories that exhibit entropy decline. I argue that the Past Hypothesis, if true, helps explain this fact about histories, but a far weaker hypothesis about the universe’s initial state suffices to do so.

Authors: T. P. Shestakova

The meaning of the wave function of the Universe was actively discussed in 1980s. In most works on quantum cosmology it is accepted that the wave function is a probability amplitude for the Universe to have some space geometry, or to be found in some point of the Wheeler superspace. It seems that the wave function gives maximally objective description compatible with quantum theory. However, the probability distribution does not depend on time and does not take into account the existing of our macroscopic evolving Universe. What we wish to know is how quantum processes in the Early Universe determined the state of the present Universe in which we are able to observe macroscopic consequences of these quantum processes. As an alternative to the Wheeler – DeWitt quantum geometrodynamics we consider the picture that can be obtained in the extended phase space approach to quantization of gravity. The wave function in this approach describes different states of the Universe which correspond to different stages of its evolution.

Authors: Emanuele AlesciSina BahramiDaniele Pranzetti

We construct a formalism for evolving spherically symmetric black hole initial data sets within a canonical approach to quantum gravity. This problem can be formulated precisely in quantum reduced loop gravity, a framework which has been successfully applied to give a full theory derivation of loop quantum cosmology. We extend this setting by implementing a particular choice of partial gauge which is then used to select a kinematical Hilbert space where the symmetry reduction is imposed through semiclassical states. The main result of this investigation is an effective Hamiltonian that can be used to solve for quantum black hole geometries by evolving classical black hole initial data sets.

Authors: Emanuele AlesciSina BahramiDaniele Pranzetti

In a previous work we derived an effective Hamiltonian constraint for the Schwarzschild geometry starting from the full loop quantum gravity Hamiltonian constraint and computing its expectation value on coherent states sharply peaked around a spherically symmetric geometry. We now use this effective Hamiltonian to study the interior region of a Schwarzschild black hole, where a homogeneous foliation is available. Descending from the full theory, our effective Hamiltonian, though still bearing the well known ambiguities of the quantum Hamiltonian operator, preserves all relevant information about the fundamental discreteness of quantum space. This allows us to have a uniform treatment for all quantum gravity holonomy corrections to spatially homogeneous geometries, unlike the minisuperspace loop quantization models in which the effective Hamiltonian is postulated. We show how, for several geometrically and physically well motivated choices of coherent states, the classical black hole singularity is replaced by a homogeneous expanding Universe. The resultant geometries have no significant deviations from the classical Schwarzschild geometry in the pre-bounce sub-Planckian curvature regime, evidencing the fact that large quantum effects are avoided in these models. In all cases, we find no evidence of a white hole horizon formation. However, various aspects of the post-bounce effective geometry depend on the choice of quantum states.

上午8:16 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Hermens, Ronnie (2019) Completely real? A critical note on the claims by Colbeck and Renner. In: UNSPECIFIED.
上午7:41 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Pitts, J. Brian (2016) Historical and Philosophical Insights about General Relativity and Space-time from Particle Physics. New Directions in Logic and the Philosophy of Science: SILFS volume 3. pp. 291-301.
上午7:37 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Rivat, Sébastien and Grinbaum, Alexei (2019) Philosophical Foundations of Effective Field Theories. [Preprint]
2019年9月12日 星期四 下午6:00 | Yoshihiko Hasegawa and Tan Van Vu | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Yoshihiko Hasegawa and Tan Van Vu

The fluctuation theorem is the fundamental equality in nonequilibrium thermodynamics that is used to derive many important thermodynamic relations, such as the second law of thermodynamics and the Jarzynski equality. Recently, the thermodynamic uncertainty relation was discovered, which states that …

[Phys. Rev. Lett. 123, 110602] Published Thu Sep 12, 2019

2019年9月12日 星期四 上午4:02 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Farr, Matt (2019) Explaining Temporal Qualia. [Preprint]
2019年9月12日 星期四 上午3:56 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Schneider, Mike D. (2019) Betting on future physics. [Preprint]
2019年9月10日 星期二 下午12:14 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Gambini, Rodolfo and Pullin, Jorge (2019) Physical requirements for models of consciousness. [Preprint]
2019年9月10日 星期二 上午2:30 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Goyal, Philip (2019) Persistence and nonpersistence as complementary models of identical quantum particles.

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