Author(s): Yu Guo, Xiao-Min Hu, Zhi-Bo Hou, Huan Cao, Jin-Ming Cui, Bi-Heng Liu, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, and Giulio Chiribella

Communication in a network generally takes place through a sequence of intermediate nodes connected by communication channels. In the standard theory of communication, it is assumed that the communication network is embedded in a classical spacetime, where the relative order of different nodes is we…

[Phys. Rev. Lett. 124, 030502] Published Fri Jan 24, 2020

Despite the success of neural networks at solving concrete physics problems, their use as a general-purpose tool for scientific discovery is still in its infancy. Here, we approach this problem by modelling a neural network architecture after the human physical reasoning process, which has similarities to representation learning. This allows us to make progress towards the long-term goal of machine-assisted scientific discovery from experimental data without making prior assumptions about the system. We apply this method to toy examples and show that the network finds the physically relevant parameters, exploits conservation laws to make predictions, and can help to gain conceptual insights, e.g. Copernicus’ conclusion that the solar system is heliocentric.

There are two types of fluctuations in the quantum vacuum: type 1 vacuum fluctuations are on shell and can interact with matter in specific, limited ways that have observable consequences; type 2 vacuum fluctuations are off shell and cannot interact with matter. A photon will polarize a type 1, bound, charged lepton-antilepton vacuum fluctuation in much the same manner that it would polarize a dielectric, suggesting the method used here for calculating the permittivity $\epsilon_0$ of the vacuum. In a model that retains only leading terms, $\epsilon_0 \cong (6\mu_0/\pi)(8e^2/\hbar)^2= 9.10\times 10^{-12}$ C/(Vm). The calculated value for $\epsilon_0$ is 2.7\% more than the accepted value. The permittivity of the vacuum, in turn, determines the speed $c$ of light in the vacuum. Since the vacuum is at rest with respect to every inertial frame of reference, $c$ is the same in every inertial reference frame.

Authors: Neta Bahcall, Adam Burrows

The 2019 Nobel Prize in Physics honors three pioneering scientists for their fundamental contributions to basic cosmic questions – Professor James Peebles (Princeton University), Michel Mayor (University of Geneva), and Didier Queloz (University of Geneva and the University of Cambridge) – “for contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos,” with one half to James Peebles “for theoretical discoveries in physical cosmology,” and the other half jointly to Michel Mayor and Didier Queloz “for the discovery of an exoplanet orbiting a solar-type star.” We summarize the historical and scientific backdrop to this year’s Physics Nobel.

Authors: Mauro Dorato

I begin by examining the question of the quantum limits of knowledge by briefly presenting the constraints of the theory that derive from its mathematical structure (in particular the no-go theorems formulated by von Neumann and Kochen and Specker). I then argue that these theorems reflect on a formal level those practical and experimental settings that are needed to come to know the properties of physical systems. In particular, I discuss some aspects of this relationist and contextualist conception of reality by comparing, in their apparent diversity, Bohr holistic and Rovelli relationist interpretation of the formalism, that deep down share a unifying metaphysics of dispositions and propensities. Both interpretations are based on the widely shared fact that quantum mechanics does not describe previously definite quantities. In the final part I show that, as a consequence of a relationist and perspectival approach to quantum mechanics, the quantum state of the universe regarded as an isolated system cannot be known in principle, so that the universe must be described from within by dividing it into two arbitrary parts. This is in fact the only way in which any two systems can exchange information by being physically correlated.

Authors: I.N. Sibgatullin

The theorem given by R.I. Nigmatulin in “Equations of Hydro-and Thermodynamics of the Atmosphere when Inertial Forces Are Small in Comparison with Gravity” (2018) is wrong. The scales given in the paper are not suitable for application of hydrostatic (quasistatic) approximation suggested by the author. The modification of Richardson’s equation for vertical velocity neglecting horizontal advection of pressure results in violation of symmetry of equations and incorrect uncompensated additional vertical velocity.

Authors: M.A. Natiello, H.G. Solari

We examine the construction of electromagnetism in its current form, and in an alternative form, from a point of view that combines a minimal realism with strict demands of reason that we first introduce. We follow the historical development as presented in the record of original publications, the underlying epistemology (often explained by the authors) and the mathematical constructions. The historical construction develops along socio-political disputes (mainly, the reunification of Germany and the second industrial revolution), epistemic disputes (at least two demarcations of science in conflict) and several theories of electromagnetism. Such disputes resulted in the militant adoption of the ether by some, a position that expanded in parallel with the expansion of Prussia, but was facilitated by the earlier adoption of a standpoint that required physical hypothesis in the form of analogies as condition for understanding, antithetic to Newton’s “\emph{hypotheses non fingo}”. …

Authors: M.A. Zubkov

We discuss emergent gravity in the superplastic crystals. We restrict ourselves by the consideration of the gapped (massive) fermions coupled to gravity. In this approach the total stress – energy tensor $\langle t_{ij} \rangle$ is the topological invariant if the background metric does not depend on coordinates. In equilibrium its value is not changed if the system is modified smoothly. On the other hand, the response of $\langle t_{ij} \rangle$ to the variation of metric is proportional to the cosmological constant. Therefore, we arrive at the vanishing contribution of the fermionic fields to the cosmological constant.

Authors: Bala Iyer, Wei-Tou Ni

This article is a foreword for the special issue on Gravitational Wave Detection and Fundamental Physics in Space for International Journal of Physics D. In the foreword, we review briefly the history of the development of mission concepts and projects for the gravitational wave detection in space together with fundamental physics missions. We summarize briefly the gravitational-wave detection-in-space science goals and the current progress in the experimental & technological developments presented in the articles of this special issue, and list the articles with publication information and arXiv numbers.

Authors: Sylvain Carrozza, Steffen Gielen, Daniele Oriti

This Editorial introduces the Special Issue “Progress in Group Field Theory and Related Quantum Gravity Formalisms” which includes a number of research and review articles covering results in the group field theory (GFT) formalism for quantum gravity and in various neighbouring areas of quantum gravity research. We give a brief overview of the basic ideas of the GFT formalism, list some of its connections to other fields, and then summarise all contributions to the Special Issue.

Authors: David Benisty, Eduardo I. Guendelman

A correspondence between the Equivalence principle and the homogeneity of the universe is discussed. In Newtonian gravity, translation of co-moving coordinates in a uniformly expanding universe defines an accelerated frame. A consistency condition for the invariance of this transformation which requires a well defined transformation for the Newtonian potential, yields the Friedmann equations. All these symmetries are lost when we modify NSL (Newton’s Second Law) or the Poisson equation. For example by replacing NSL with non-linear function of the acceleration the concept of relative acceleration is lost and the homogeneity of the universe breaks.

Weatherall, James Owen (2018) Why Not Categorical Equivalence? [Preprint]

It has been debated whether protective measurement implies the reality of the wave function. In this article, I present a new analysis of the relationship between protective measurements and the reality of the wave function. First, I briefly introduce protective measurements and the ontological models framework for them. Second, I give a simple proof of Hardy’s theorem in terms of protective measurements. Third, I analyse two suggested ψ-epistemic models of a protective measurement. It is shown that although these models can explain the appearance of expectation values of observables in a single measurement, their predictions about the variance of the result of a non-ideal protective measurement are different from those of quantum mechanics. Finally, I argue that under an auxiliary finiteness assumption about the dynamics of the ontic state, protective measurement implies the reality of the wave function in the ontological models framework.

According to the orthodox interpretation of bounce cosmologies, the universe was born from an entropy-reducing phase in a previous universe. To defend the thesis that the whole of physical reality was caused to exist a finite time ago, Craig and Sinclair have argued the low-entropy interface between universes should instead be understood as the beginning of two universes. Here, I present Craig and Sinclair with a dilemma. On the one hand, if the direction of time is reducible, as friends of the Mentaculus—for example, Albert, Loewer, and Papineau—maintain, then there is reason to think that the direction of time and the entropic arrow of time align. But on that account, efficient causation is likely reducible to non-causal phenomena. In consequence, contrary to Craig and Sinclair’s theological aims, things can begin to exist without causes. On the other hand, if the direction of time is not reducible, Craig and Sinclair’s interpretation of bounce cosmologies is unjustified. Lastly, a reply to a potential objection motivates a discussion of how to interpret bounce cosmologies on the tensed theory of absolute time favoured by Craig and Sinclair. I offer two interpretations of bounce cosmologies that, given a tensed theory of absolute time, are preferable to those Craig and Sinclair offer, yet inconsistent with their project in natural theology; on one interpretation, the universe does not require a supernatural cause and, on the other, bounce cosmologies represent the universe as never having begun to exist.

Dolega, Krzysztof and Dewhurst, Joe (2020) Fame in the Predictive Brain: A deflationary approach to explaining consciousness in the prediction error minimization framework. [Preprint]

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

Abstract

We call attention to different formulations of how physical laws relate to what is physically possible in the philosophical literature, and argue that it may be the case that determinism fails under one formulation but reigns under the other. Whether this is so depends on our view on the nature of laws, and may also depend on the inter-theoretical relationships among our best physical theories, or so shall we argue.

Abstract

We analyze the interrelation of quantum and classical entanglement. The latter notion is widely used in classical optic simulation of some quantum-like features of light. We criticize the common interpretation that “quantum nonlocality” is the basic factor differing quantum and classical realizations of entanglement. Instead, we point to the breakthrough Grangier et al. experiment on coincidence detection which was done in 1986 and played the crucial role in rejection of (semi-)classical field models in favor of quantum mechanics. Classical entanglement sources produce light beams with the coefficient of second order coherence \(g^{(2)}(0) \ge 1.\) This feature of classical entanglement is obscured by using intensities of signals in different channels, instead of counting clicks of photo-detectors. The interplay between intensity and clicks counting is not just a technicality. We elevate this issue to the high foundational level.

Abstract

Hardy’s paradox was originally presented as a demonstration, without inequalities, of the incompatibility between quantum mechanics and the hypothesis of local causality. Equipped with newly developed tools that allow for a quantitative assessment of realism, here we revisit Hardy’s paradox and argue that nonlocal causality is not mandatory for its solution; quantum irrealism suffices.

Chen, Lu (2019) Intrinsic local distances: a mixed solution to Weyl’s tile argument. [Preprint]

Giovanelli, Marco (2018) Lorentz Contraction vs. Einstein Contraction. Reichenbach and the Philosophical Reception of Miller’s Ether-Drift Experiments. Proceeding of the Fourth International Conference on the Nature and Ontology of Spacetime. pp. 125-155.

Giovanelli, Marco (2019) ‘Geometrization of Physics’ vs. ‘Physicalization of Geometry.’ The Untranslated Appendix to Reichenbach’s Philosophie der Raum-Zeit-Lehre. [Preprint]

Giovanelli, Marco (2019) Nothing but Coincidences: The Point-Coincidence Argument and Einstein’s Struggle with the Meaning of Coordinates in Physics. [Preprint]

Giovanelli, Marco (2020) Like Thermodynamics before Boltzmann. On the Emergence of Einstein’s Distinction between Constructive and Principle Theories. [Preprint]

Chen, Lu (2019) Infinitesimal Gunk. [Preprint]

Chen, Lu (2019) Do Simple Infinitesimal Parts Solve Zeno’s Paradox of Measure? [Preprint]