Weekly Papers on Quantum Foundations (31)

This is a list of this week’s papers on quantum foundations published in the various journals or uploaded to the preprint servers such as arxiv.org and PhilSci Archive.

Inflation Due to Quantum Potential

Latest Results for Foundations of Physics

on 2015-8-01 12:00am GMT

Abstract

In the framework of a cosmological model of the Universe filled with a nonrelativistic particle soup, we easily reproduce inflation due to the quantum potential. The lightest particles in the soup serve as a driving force of this simple, natural and promising mechanism. It is explicitly demonstrated that the appropriate choice of their mass and fraction leads to reasonable numbers of e-folds. Thus, the direct introduction of the quantum potential into cosmology of the earliest Universe gives ample opportunities of successful reconsideration of the modern inflationary theory.

Gravity: Wanna be quantum

Nature Physics – Issue – nature.com science feeds

on 2015-7-31 12:00am GMT

Nature Physics 11, 626 (2015). doi:10.1038/nphys3390

Author: Angelo Bassi

Superpositions of massive objects would be hard to spot on Earth even in well-isolated environments because of the decoherence induced by gravitational time dilation.

Probing a gravitational cat state

Classical and Quantum Gravity – latest papers

on 2015-7-30 12:00am GMT

We investigate the nature of a gravitational two-state system (G2S) in the simplest setup in Newtonian gravity. In a quantum description of matter a single motionless massive particle can in principle be in a superposition state of two spatially separated locations. This superposition state in gravity, or gravitational cat state, would lead to fluctuations in the Newtonian force exerted on a nearby test particle. The central quantity of importance for this inquiry is the energy density correlation. This corresponds to the noise kernel in stochastic gravity theory , evaluated in the weak field nonrelativistic limit. In this limit quantum fluctuations of the stress–energy tensor manifest as the fluctuations of the Newtonian force. We describe the properties of such a G2S system and present two ways of measuring the cat state for the Newtonian force, one by way of a classical probe, the other a quantum harmonic oscillator. Our findings include: (i) mass density fluctuations pe…

How many quanta are there in a quantum spacetime?

Classical and Quantum Gravity – latest papers

on 2015-7-30 12:00am GMT

Following earlier insights by Livine and Terno, we develop a technique for describing quantum states of the gravitational field in terms of coarse grained spin networks. We show that the number of nodes and links and the values of the spin depend on the observables chosen for the description of the state. Hence the question in the title of this paper is ill posed, unless further information about what is been measured is given.

The quantum, the geon, and the crystal. (arXiv:1507.07777v1 [hep-th])

gr-qc updates on arXiv.org

on 2015-7-29 7:54am GMT

Authors: Gonzalo J. OlmoD. Rubiera-Garcia

Effective geometries arising from a hypothetical discrete structure of space-time can play an important role in the understanding of the gravitational physics beyond General Relativity. To discuss this question, we make use of lessons from crystalline systems within solid state physics, where the presence of defects in the discrete microstructure of the crystal determine the kind of effective geometry needed to properly describe the system in the macroscopic continuum limit. In this work we study metric-affine theories with non-metricity and torsion, which are the gravitational analog of crystalline structures with point defects and dislocations. We consider a crystal-motivated gravitational action and show the presence of topologically non-trivial structures (wormholes) supported by an electromagnetic field. Their existence has important implications for the quantum foam picture and the effective gravitational geometries. We discuss how the dialogue between solid state physics systems and modified gravitational theories can provide useful insights on both sides.

Discrete Hamiltonian for General Relativity. (arXiv:1507.07591v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-7-29 7:54am GMT

Authors: Jonathan ZiprickJack Gegenberg

Beginning from canonical general relativity written in terms of Ashtekar variables, we derive a discrete phase space with a physical Hamiltonian for gravity. The key idea is to define the gravitational fields within a complex of three-dimensional cells such that the dynamics is completely described by discrete boundary variables, and the full theory is recovered in the continuum limit. Canonical quantization is attainable within the loop quantum gravity framework, and we believe this will lead to a promising candidate for quantum gravity.

Operational formulation of time reversal in quantum theory: reconsidering Wigner’s theorem. (arXiv:1507.07745v1 [quant-ph])

gr-qc updates on arXiv.org

on 2015-7-29 7:54am GMT

Authors: Ognyan OreshkovNicolas J. Cerf

The symmetry of quantum theory under time reversal has long been a subject of controversy because the transition probabilities given by Born’s rule do not apply backward in time. Here, we resolve this problem within a rigorous operational probabilistic framework. We argue that reconciling time reversal with the probabilistic rules of the theory requires a notion of operation that permits realizations via both pre- and post-selection. We develop the generalized formulation of quantum theory that stems from this approach and give a precise definition of time-reversal symmetry, emphasizing a previously overlooked distinction between states and effects. We prove an analogue of Wigner’s theorem, which characterizes all allowed symmetry transformations in this operationally time-symmetric quantum theory. Remarkably, we find larger classes of symmetry transformations than those assumed before. This suggests a possible direction for search of extensions of known physics.

The quantum formulation derived from assumptions of epistemic processes. (arXiv:1507.07701v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-7-29 7:53am GMT

Authors: Inge S. Helland

Motivated by Quantum Bayesianism I give background for a general epistemic approach to quantum mechanics, where complementarity and symmetry are the only essential features. A general definition of a symmetric epistemic setting is introduced, and for this setting the basic Hilbert space formalism is arrived at under certain technical assumptions. Other aspects of ordinary quantum mechanics will be developed from the same basis elsewhere.

Quantum Theory is an Information Theory

Latest Results for Foundations of Physics

on 2015-7-28 12:00am GMT

Abstract

In this paper we review the general framework of operational probabilistic theories (OPT), along with the six axioms from which quantum theory can be derived. We argue that the OPT framework along with a relaxed version of five of the axioms, define a general information theory. We close the paper with considerations about the role of the observer in an OPT, and the interpretation of the von Neumann postulate and the Schrödinger-cat paradox.

Operational formulation of time reversal in quantum theory

Nature Physics – AOP – nature.com science feeds

on 2015-7-27 12:00am GMT

Nature Physics. doi:10.1038/nphys3414

Authors: Ognyan Oreshkov & Nicolas J. Cerf

Nonlocality and the Epistemic Interpretation of Quantum Mechanics

PhilSci-Archive: No conditions. Results ordered -Date Deposited.

on 2015-7-26 7:17pm GMT

Ben-Menahem, Yemima (2015) Nonlocality and the Epistemic Interpretation of Quantum Mechanics. UNSPECIFIED.

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