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

Universal Limit on Communication. (arXiv:1611.05821v1 [hep-th])

on 2016-11-19 3:44am GMT

Authors: Raphael Bousso

I derive a universal upper bound on the capacity of any communication channel between two distant systems. The Holevo quantity, and hence the mutual information, is at most of order $E \Delta t / \hbar$, where $E$ the average energy of the signal, and $\Delta t$ is the amount of time for which detectors operate. The bound does not depend on the size or mass of the emitting and receiving systems, nor on the nature of the signal. No restrictions on preparing and processing the signal are imposed.

As an example, I consider the encoding of information in the transverse or angular position of a signal emitted and received by systems of arbitrarily large cross-section. In the limit of a large message space, quantum effects become important even if individual signals are classical, and the bound is upheld.

Hawking radiation inside a Schwarzschild black hole. (arXiv:1611.05524v1 [gr-qc])

on 2016-11-19 3:43am GMT

Authors: Andrew J. S. Hamilton

The boundary of any observer’s spacetime is the boundary that divides what the observer can see from what they cannot see. The boundary of an observer’s spacetime in the presence of a black hole is not the true (future event) horizon of the black hole, but rather the illusory horizon, the dimming, redshifting surface of the star that collapsed to the black hole long ago. The illusory horizon is the source of Hawking radiation seen by observers both outside and inside the true horizon. The perceived acceleration (gravity) on the illusory horizon sets the characteristic frequency scale of Hawking radiation, even if that acceleration varies dynamically, as it must do from the perspective of an infalling observer. The acceleration seen by a non-rotating free-faller both on the illusory horizon below and in the sky above is calculated for a Schwarzschild black hole. Remarkably, as an infaller approaches the singularity, the acceleration becomes isotropic, and diverging as a power law. The isotropic, power-law character of the Hawking radiation, coupled with conservation of energy-momentum, the trace anomaly, and the familiar behavior of Hawking radiation far from the black hole, leads to a complete description of the quantum energy-momentum inside a Schwarzschild black hole. The quantum energy-momentum near the singularity diverges as $r^{-6}$, and consists of relativistic Hawking radiation and negative energy vacuum in the ratio $3 : -2$. The classical back reaction of the quantum energy-momentum on the geometry, calculated using the Einstein equations, serves merely to exacerbate the singularity.

Quantum Estimation of Parameters of Classical Spacetimes. (arXiv:1611.05449v1 [quant-ph])

on 2016-11-19 3:43am GMT

Authors: T. G. Downes, J. R. van Meter, E. Knill, G. J. Milburn, C. M. Caves

We describe a quantum limit to measurement of classical spacetimes. Specifically, we formulate a quantum Cramer-Rao lower bound for estimating the single parameter in any one-parameter family of spacetime metrics. We employ the locally covariant formulation of quantum field theory in curved spacetime, which allows for a manifestly background-independent derivation. The result is an uncertainty relation that applies to all globally hyperbolic spacetimes. Among other examples, we apply our method to detection of gravitational waves using the electromagnetic field as a probe, as in laser-interferometric gravitational-wave detectors. Other applications are discussed, from terrestrial gravimetry to cosmology.

Proposed experiment to test fundamentally binary theories. (arXiv:1611.05761v1 [quant-ph])

on 2016-11-19 3:43am GMT

Authors: Matthias Kleinmann, Tamás Vértesi, Adán Cabello

Fundamentally binary theories are nonsignaling theories in which measurements of many outcomes are constructed by selecting from binary measurements. They constitute a sensible alternative to quantum theory and have never been directly falsified by any experiment. Here we solve two open problems related to them raised in Phys. Rev. Lett. 117, 150401 (2016). We first show that fundamentally binary theories are experimentally testable with current technology. For that, we identify a feasible Bell inequality-like experiment on pairs of entangled qutrits. In addition, we prove that, for any n, quantum n-ary correlations are not fundamentally (n-1)-ary. For that, we introduce a family of inequalities that hold for fundamentally (n-1)-ary theories but are violated by quantum n-ary correlations.

On the Fatal Mistake Made by John S. Bell in the Proof of His Famous Theorem

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

on 2016-11-19 12:45am GMT

Christian, Joy (2016) On the Fatal Mistake Made by John S. Bell in the Proof of His Famous Theorem. [Preprint]

The No Miracles Argument without the Base Rate Fallacy

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

on 2016-11-19 12:44am GMT

Dawid, Richard and Hartmann, Stephan (2016) The No Miracles Argument without the Base Rate Fallacy. [Preprint]

How to quantify coherence: Distinguishing speakable and unspeakable notions

on 2016-11-18 3:00pm GMT

Author(s): Iman Marvian and Robert W. Spekkens

A general framework for studying quantum coherence as a resource is presented, where coherence is classified as “speakable” or “unspeakable” based on whether or not the identity of the subspaces that appear in the coherent superposition is significant.

[Phys. Rev. A 94, 052324] Published Fri Nov 18, 2016

Dressed Hard States and Black Hole Soft Hair

on 2016-11-16 3:00pm GMT

Author(s): Mehrdad Mirbabayi and Massimo Porrati

A new analysis argues that soft black hole hair, introduced recently by Hawking, Perry, and Strominger, may not carry quantum information about the black hole relevant for the information loss paradox.

[Phys. Rev. Lett. 117, 211301] Published Wed Nov 16, 2016

Introduction to Special Issue on Dualities

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

on 2016-11-15 8:15pm GMT

Rickles, Dean and Castellani, Elena (2016) Introduction to Special Issue on Dualities. [Preprint]

Do We Really Understand the Cosmos?. (arXiv:1611.03505v1 [gr-qc])

on 2016-11-14 3:43am GMT

Authors: T. Padmanabhan

Our knowledge about the universe has increased tremendously in the last three decades or so — thanks to the progress in observations — but our understanding has improved very little. There are several fundamental questions about our universe for which we have no answers within the current, operationally very successful, approach to cosmology. Worse still, we do not even know how to address some of these issues within the conventional approach to cosmology. This fact suggests that we are missing some important theoretical ingredients in the overall description of the cosmos. I will argue that these issues — some of which are not fully appreciated or emphasized in the literature — demand a paradigm shift: We should not think of the universe as described by a specific solution to the gravitational field equations; instead, it should be treated as a special physical system governed by a different mathematical description, rooted in the quantum description of spacetime. I will outline how this can possibly be done.

Towards a Constructive Foundation of Quantum Mechanics

Latest Results for Foundations of Physics

on 2016-11-14 12:00am GMT

**Abstract**

I describe a constructive foundation for quantum mechanics, based on the discreteness of the degrees of freedom of quantum objects and on the Principle of Relativity. Taking Einstein’s historical construction of Special Relativity as a model, the construction is carried out in close contact with a simple quantum mechanical Gedanken experiment. This leads to the standard axioms of quantum mechanics. The quantum mechanical description is identified as a mathematical tool that allows describing objects, whose degree of freedom in space–time has a discrete spectrum, relative to classical observers in space–time. This description is covariant with respect to (continuous) coordinate transformations and meets the requirement that the spectrum is the same in every inertial system. The construction gives detailed answers to controversial questions, such as the measurement problem, the informational content of the wave function, and the completeness of quantum mechanics.