Authors: Tom Banks, Willy Fischler

We review arguments that the cosmological constant (c.c.) should not be thought of as a local contribution to the energy density, but rather as an infrared boundary condition specifying particular models of quantum gravity.

Author(s): Pavel Sekatski, Jean-Daniel Bancal, Sebastian Wagner, and Nicolas Sangouard

Bell’s theorem has been proposed to certify, in a device-independent and robust way, blocks either producing or measuring quantum states. In this Letter, we provide a method based on Bell’s theorem to certify coherent operations for the storage, processing, and transfer of quantum information. This …

[Phys. Rev. Lett. 121, 180505] Published Fri Nov 02, 2018

Egg, Matthias (2018) Dissolving the Measurement Problem Is Not an Option for the Realist. In: UNSPECIFIED.

The forgotten quantum pioneer who turned wartime spy

The forgotten quantum pioneer who turned wartime spy, Published online: 02 November 2018; doi:10.1038/d41586-018-07267-3

Davide Castelvecchi enjoys the extraordinary life of Sam Goudsmit, the atomic sleuth nominated for a Nobel prize 48 times.

Authors: John B. DeBrota, Blake C. Stacey

We answer several questions that have been Frequently Asked about QBism. These remarks (many of them lighthearted) should be considered supplements to more systematic treatments by the authors and others.

Authors: Philip Goyal

According to our understanding of the everyday physical world, observable phenomena are underpinned by persistent objects that can be reidentified (or tracked) across time by observation of their distinctive properties. This understanding is reflected in classical mechanics, which posits that matter consists of persistent, reidentifiable particles. However, the mathematical symmetrization procedures used to describe identical particles within the quantum formalism have led to the widespread belief that identical quantum particles lack either persistence or reidentifiability. However, it has proved difficult to reconcile these assertions with the fact that identical particles are routinely assumed to be reidentifiable in particular circumstances.

Moreover, neither of these assertions accounts for the mathematical form of the symmetrization procedures used to describe identical particles within the quantum framework, leaving open theoretical possibilities other than bosonic and fermionic behavior, such as paraparticles, which do not appear to be realized in nature. Here we propose the novel idea that both persistence and nonpersistence models must be employed in order to fully account for the behaviour of identical particles. Thus, identical particles are neither persistent nor nonpersistent. We prove the viability of this viewpoint by showing how Feynman’s and Dirac’s symmetrization procedures arise through a synthesis of a quantum treatment of these models, and by showing how reidentifiability emerges in a context-dependent manner. We further show that the persistence and nonpersistence models satisfy the key characteristics of Bohr’s concept of complementarity, and thereby propose that the behavior of identical particles is a manifestation of a persistence-nonpersistence complementarity, analogous to Bohr’s wave-particle complementarity for individual particles.

Abstract

Understanding the emergence of a tangible 4-dimensional space-time from a quantum theory of gravity promises to be a tremendously difficult task. This article makes the case that this task may not have to be carried. Space-time as we know it may be fundamental to begin with. I recall the common arguments against this possibility and review a class of recently discovered models bypassing the most serious objection. The generic solution of the measurement problem that is tied to semiclassical gravity as well as the difficulty of the alternative make it a reasonable default option in the absence of decisive experimental evidence.

Abstract

Complexified Liénard–Wiechert potentials simplify the mathematics of Kerr–Newman particles. Here we constrain them by fiat to move along Bohmian trajectories to see if anything interesting occurs, as their equations of motion are not known. A covariant theory due to Stueckelberg is used. This paper deviates from the traditional Bohmian interpretation of quantum mechanics since the electromagnetic interactions of Kerr–Newman particles are dictated by general relativity. A Gaussian wave function is used to produce the Bohmian trajectories, which are found to be multi-valued. A generalized analytic continuation is introduced which leads to an infinite number of trajectories. These include the entire set of Bohmian trajectories. This leads to multiple retarded times which come into play in complex space-time. If one weights these trajectories by their natural Bohmian weighting factors, then it is found that the particles do not radiate, that they are extended, and that they can have a finite electrostatic self energy, thus avoiding the usual divergence of the charged point particle. This effort does not in any way criticize or downplay the traditional Bohmian interpretation which does not assume the standard electromagnetic coupling to charged particles, but it suggests that a hybridization of Kerr–Newman particle theory with Bohmian mechanics might lead to interesting new physics, and maybe even the possibility of emergent quantum mechanics.

Le Bihan, Baptiste and Linnemann, Niels (2018) Have We Lost Spacetime on the Way? Narrowing the Gap Between General Relativity and Quantum Gravity. [Preprint]

In this paper, based on the discussion on what the real state of a coin at each point should be, we propose two basic assumptions. Then we point out the mathematical foundations that these two assumptions rely on and the familiar physical principles which these two assumptions, respectively, correspond to. These two assumptions, as required, do not seek help from the well-known formulation of quantum mechanics. They are self-consistent in a new presentation. Based on two basic assumptions, we derive the real state in a simple way and claim that the real state equals the quantum state totally after comparison from different aspects. We thus prove that the quantum state is the ontological object which obeys the redefinition of the reality rather than just a vague concept in quantum theory. We also consider the way in which Born’s rule arises naturally.

Abstract

The significance of the de Broglie/Bohm hidden-particle position in the relativistic regime is addressed, seeking connection to the (orthodox) single-particle Newton–Wigner position. The effect of non-positive excursions of the ensemble density for extreme cases of positive-energy waves is easily computed using an integral of the equations of motion developed here for free spin-0 particles in 1 + 1 dimensions and is interpreted in terms of virtual-like pair creation and annihilation beneath the Compton wavelength. A Bohm-theoretic description of the acausal explosion of a specific Newton–Wigner-localized state is presented in detail. The presence of virtual pairs found is interpreted as the Bohm picture of the spatial extension beyond single point particles proposed in the 1960s as to why space-like hyperplane dependence of the Newton–Wigner wavefunctions may be needed to achieve Lorentz covariance. For spin-1/2 particles the convective current is speculatively utilized for achieving parity with the spin-0 theory. The spin-0 improper quantum potential is generalized to an improper stress tensor for spin-1/2 particles.

Author(s): Dmitry V. Zhdanov, Denys I. Bondar, and Tamar Seideman

A quantum analog of friction (understood as a completely positive, Markovian, translation-invariant, phenomenological model of dissipation) is known to be at odds with detailed balance in the thermodynamic limit. We show that this is not the case for quantum systems with internal (e.g., spin) states…

[Phys. Rev. A 98, 042133] Published Mon Oct 29, 2018