Authors: Steven B. Giddings

The impressive images from the Event Horizon Telescope sharpen the conflict between our observations of gravitational phenomena and the principles of quantum mechanics. Two related scenarios for reconciling quantum mechanics with the existence of black hole-like objects, with “minimal” departure from general relativity and local quantum field theory, have been explored; one of these could produce signatures visible to EHT observations. A specific target is temporal variability of images, with a characteristic time scale determined by the classical black hole radius. The absence of evidence for such variability in the initial observational span of seven days is not expected to strongly constrain such variability. Theoretical and observational next steps towards investigating such scenarios are outlined.

Authors: S. V. Mousavi, S. Miret-Artés

A Bohmian analysis of the so-called Schr\”{o}dinger-Langevin or Kostin nonlinear differential equation is provided to study how thermal fluctuations of the environment affects the dynamics of the wave packet from a quantum hydrodynamical point of view. In this way, after obtaining the Schr\”{o}dinger-Langevin-Bohm equation from the Kostin equation its application to simple but physically insightful systems such as the Brownian-Bohmian motion, motion in a gravity field and transmission through a parabolic repeller is studied. % If a time-dependent Gaussian ansatz for the probability density is assumed, the effect of thermal fluctuations together with thermal wave packets leads to Bohmian stochastic trajectories. From this trajectory based analysis, quantum and classical diffusion coefficients for free particles, thermal arrival times for a linear potential and transmission probabilities and characteristic times such as arrival and dwell times for a parabolic repeller are then presented and discussed.

Hobson, Art (2019) Entanglement, decoherence, and measurement. [Preprint]

In this paper we extend the WKB-like ‘non-relativistic’ expansion of the minimally coupled Klein–Gordon equation after (Kiefer and Singh 1991 Phys. Rev . D 44 1067–76; Lämmerzahl 1995 Phys. Lett . A 203 12–7; Giulini and Großardt 2012 Class. Quantum Grav . 29 215010) to arbitrary order in c −1 , leading to Schrödinger equations describing a quantum particle in a general gravitational field, and compare the results with canonical quantisation of a free particle in curved spacetime, following (Wajima et al 1997 Phys. Rev . D 55 1964–70). Furthermore, using a more operator-algebraic approach, the Klein–Gordon equation and the canonical quantisation method are shown to lead to the same results for some special terms in the Hamiltonian describing a single particle in a general stationary spacetime, without any ‘non-relativistic’ expansion.

Gryb, Sean and Palacios, Patricia and Thebault, Karim P Y (2019) On the Universality of Hawking Radiation. [Preprint]

Dardashti, Radin and Hartmann, Stephan (2019) Assessing Scientific Theories: The Bayesian Approach. [Preprint]

Bradley, Clara and Weatherall, James Owen (2019) On Representational Redundancy, Surplus Structure, and the Hole Argument. [Preprint]

Heartspring, William (2019) Reformulation of quantum mechanics and strong complementarity from Bayesian inference requirements. [Preprint]

Correlations detected in a quantum vacuum

Correlations detected in a quantum vacuum, Published online: 10 April 2019; doi:10.1038/d41586-019-01083-z

A vacuum as described by quantum mechanics is perhaps the most fundamental but mysterious state in physics. The discovery of correlations between electric-field fluctuations in such a vacuum represents a major advance.

A realist takes on quantum mechanics

A realist takes on quantum mechanics, Published online: 09 April 2019; doi:10.1038/d41586-019-01101-0

Graham Farmelo parses Lee Smolin’s takedown of the most successful physics theory ever.

Samaroo, Ryan (2019) Friedman and Some of his Critics on the Foundations of General Relativity. [Preprint]

van Dongen, Jeroen and De Haro, Sebastian and Visser, Manus and Butterfield, Jeremy (2019) Emergence and Correspondence for String Theory Black Holes. [Preprint]

De Haro, Sebastian and van Dongen, Jeroen and Visser, Manus and Butterfield, Jeremy (2019) Conceptual Analysis of Black Hole Entropy in String Theory. [Preprint]

Mulder, Ruward A. (2018) Emergence, Functionalism and Pragmatic Reality in Wallacian quantum mechanics. [Preprint]

Jaeger, Gregg (2019) A Realist View of the Quantum World. [Preprint]

Mulder, Ruward A. and Dieks, Dennis (2017) Is Time Travel Too Strange to Be Possible? – Determinism and Indeterminism on Closed Timelike Curves. Determinism and Indeterminism on Closed Timelike Curves. pp. 93-114.

Park, Seungbae (2019) The Descriptive and Normative Versions of Scientific Realism and Pessimism.

Author(s): Andrea Crespi, Francesco V. Pepe, Paolo Facchi, Fabio Sciarrino, Paolo Mataloni, Hiromichi Nakazato, Saverio Pascazio, and Roberto Osellame

The decay of an unstable system is usually described by an exponential law. Quantum mechanics predicts strong deviations of the survival probability from the exponential: Indeed, the decay is initially quadratic, while at very large times it follows a power law, with superimposed oscillations. The l…

[Phys. Rev. Lett. 122, 130401] Published Wed Apr 03, 2019

Volume 5, Issue 2, pages 80-97

Aurélien Drezet [Show Biography]

This is an analysis of the recently published article “Quantum theory cannot consistently describe the use of itself” by D. Frauchiger and R. Renner [1]. Here I decipher the paradox and analyze it from the point of view of de Broglie-Bohm hidden variable theory (i.e., Bohmian mechanics). I also analyze the problem from the perspective obtained by the Copenhagen interpretation (i.e., the Bohrian interpretation) and show that both views are self consistent and do not lead to any contradiction with a `single-world’ description of quantum theory.

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Volume 5, Issue 2, pages 69-79

Mohammed Sanduk [Show Biography]

The imaginary i in the formulation of the quantum mechanics is accepted within the axioms of the quantum mechanics theory, and, thus, there is no need for an explanation of its origin. Since 2012, in a non-quantum mechanics project, there has been an attempt to complexify a real function and build an analogy for relativistic quantum mechanics. In that theoretical attempt, a partial observation technique is proposed as one of the reasons behind the appearance of the imaginary i. The present article throws light on that attempt of complexification and tries to explain the logic of physics behind the complex phase factor. This physical process of partial observation acts as a process of physicalization of a virtual model. According to the positive results of analogy, the appeared imaginary i in quantum mechanics formulation may be related to a partial observation case as well.

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Volume 5, Issue 2, pages 51-68

Daniel Shanahan [Show Biography]

Effects associated in quantum mechanics with a divisible probability wave are
explained as physically real consequences of the equal but opposite reaction
of the apparatus as a particle is measured. Taking as illustration a
Mach-Zehnder interferometer operating by refraction, it is shown that this
reaction must comprise a fluctuation in the reradiation field of complementary
effect to the changes occurring in the photon as it is projected into one or
other path. The evolution of this fluctuation through the experiment will
explain the alternative states of the particle discerned in self interference,
while the maintenance of equilibrium in the face of such fluctuations becomes
the source of the Born probabilities. In this scheme, the probability wave
is a mathematical artifact, epistemic rather than ontic, and akin in this
respect to the simplifying constructions of geometrical optics.

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Volume 5, Issue 2, pages 16-50

Edward J. Gillis [Show Biography]

The assumption that wave function collapse is a real occurrence has very interesting consequences – both experimental and theoretical. Besides predicting observable deviations from linear evolution, it implies that these deviations must originate in nondeterministic effects at the elementary level in order to prevent superluminal signaling, as demonstrated by Gisin. This lack of determinism implies that information cannot be instantiated in a reproducible form in isolated microsystems (as illustrated by the No-cloning theorem). By stipulating that information is a reproducible and referential property of physical systems, one can formulate the no-signaling principle in strictly physical terms as a prohibition of the acquisition of information about spacelike-separated occurrences. This formulation provides a new perspective on the relationship between relativity and spacetime structure, and it imposes tight constraints on the way in which collapse effects are induced. These constraints indicate that wave function collapse results from (presumably small) nondeterministic deviations from linear evolution associated with nonlocally entangling interactions. This hypothesis can be formalized in a stochastic collapse equation and used to assess the feasibility of testing for collapse effects.
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