Authors: James Overduin, Richard Conn Henry

Pythagoras’ theorem lies at the heart of physics as well as mathematics, yet its historical origins are obscure. We highlight a purely pictorial, gestalt-like proof that may have originated during the Zhou Dynasty. Generalizations of the Pythagorean theorem to three, four and more dimensions undergird fundamental laws including the energy-momentum relation of particle physics and the field equations of general relativity, and may hint at future unified theories. The intuitive, “pre-mathematical” nature of this theorem thus lends support to the Eddingtonian view that “the stuff of the world is mind-stuff.”

Publication date: Available online 18 May 2020

Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

Author(s): Feraz Azhar

Publication date: Available online 15 May 2020

Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

Author(s): William L. Harpere

Authors: Damiano Anselmi, Eugenio Bianchi, Marco Piva

We derive the predictions of quantum gravity with fakeons on the amplitudes and spectral indices of the scalar and tensor fluctuations in inflationary cosmology. The action is $R+R^{2}$ plus the Weyl-squared term. The ghost is eliminated by turning it into a fakeon, that is to say a purely virtual particle. We work to the next-to-leading order of the expansion around the de Sitter background. The consistency of the approach puts a lower bound ($ m_{\chi }>m_{\phi }/4$) on the mass $m_{\chi }$ of the fakeon with respect to the mass $m_{\phi }$ of the inflaton. The tensor-to-scalar ratio $r$ is predicted within less than an order of magnitude ($4/3<N^{2}r<12$ to the leading order in the number of $e$-foldings $N$). Moreover, the relation $r\simeq -8n_{T}$ is not affected by the Weyl-squared term. No vector and no other scalar/tensor degree of freedom is present.

Authors: F. Hammad, A. Landry, K. Mathieu

We study the quantum Hall effect inside a gravitational field. First, we review the influence of the gravitational field of the Earth on the quantum Hall effect. Taking the gravitational field of the Earth to be uniform along the vertical direction, we compute the affected quantized Hall resistivity. Then, we investigate how the gravitational field modifies the Landau levels of a particle moving between two massive hemispheres in the presence of a constant and uniform magnetic field perpendicular to the plane of motion. We find that the familiar degeneracy of the Landau levels is removed and the spacing between the latter becomes dependent on the mass density of the hemispheres and on the gravitational constant $G$. We use this result to show that the quantum Hall effect in a thin conductor, sandwiched between two massive hemispheres, should yield a slightly different variation of the Hall resistivity with the applied magnetic field. We then argue that the well-known problem of the gravitationally induced electric field, that might a priori be thought to hinder the effect of gravity, has actually a beneficial role as it amplifies the latter. We finally discuss whether there is a possibility of using the quantum Hall effect to probe the inverse-square law of gravity.

Authors: Chunlong Li, Sheng-Feng Yan, Lingqin Xue, Xin Ren, Yi-Fu Cai, Damien A. Easson, Ye-Fei Yuan, Hongsheng Zhao

We study the equivalence principle, regarded as the cornerstone of general relativity, by analyzing the deformation observable of black hole shadows. Such deformation can arise from new physics and may be expressed as a phenomenological violation of the equivalence principle. Specifically, we assume that there is an additional background vector field that couples to the photons around the supermassive black hole. This type of coupling yields impact on the way the system depends on initial conditions, and affects the black hole shadow at different wavelengths by a different amount, and therefore observations of the shadow in different wavelengths could constrain such couplings. This can be tested by future multi-band observations. Adopting a specific form of the vector field, we obtain constraints on model parameters from Event Horizon Telescope observations and measurements of gas/stellar orbits.

Authors: Andrea Addazi

We show that the formation/evaporation of Black Holes (BH) unitarizes quantum gravity at all the orders of the perturbation theory. Non-perturbative quantum effects save the scattering amplitudes from any polynomial divergences. Such a phenomena is intimately related to the dynamical emergence of an effective non-locality as well as emergent modifications of the Heisenberg’s uncertainty principle. The BH production de-localizes quantum gravity vertices and propagators as a consequence of its holographically stored entropy. In this sense, quantum gravity is a superrenormalizable theory, although non-locality is hidden in its action.

Wuthrich, Christian and Huggett, Nick (2020) Out of Nowhere: Spacetime from causality: causal set theory. [Preprint]

Huggett, Nick and Wuthrich, Christian (2020) Out of Nowhere: The ’emergence’ of spacetime in string theory. [Preprint]

Author(s): Lorenzo Maccone and Changliang Ren

An object’s distance and direction could be measured in a new radar scheme that uses entangled photons, something unachievable with previous quantum radar proposals.

[Phys. Rev. Lett. 124, 200503] Published Thu May 21, 2020

savelyev, Yasha (2020) Universal G\”odel statements and computability of intelligence. [Preprint]

Huggett, Nick and Wuthrich, Christian (2020) Out of Nowhere: The ’emergence’ of spacetime. [Preprint]

Abstract

QBism is one of the main candidates for an epistemic interpretation of quantum mechanics. According to QBism, the quantum state or the wavefunction represents the subjective degrees of belief of the agent assigning the state. But, although the quantum state is not part of the furniture of the world, quantum mechanics grasps the real via the Born rule which is a consistency condition for the probability assignments of the agent. In this paper, we evaluate the plausibility of recent criticism of QBism. We focus on the consequences of the subjective character of the quantum state, the issue of realism and the problem of the evolution of the quantum state in QBism. In particular, drawing upon Born’s notion of invariance as the mark of the real, it is argued that there is no essential difference between Einstein’s program of ‘the real’ and QBists’ realism. Also, it will be argued that QBism can account for the unitary evolution of the quantum state.

Linford, Daniel (2020) Big Bounce or Double Bang? A Reply to Craig & Sinclair on the Interpretation of Bounce Cosmologies. [Preprint]

Abstract

The Hilbert space formalism describes causality as a statistical relation between initial experimental conditions and final measurement outcomes, expressed by the inner products of state vectors representing these conditions. This representation of causality is in fundamental conflict with the classical notion that causality should be expressed in terms of the continuity of intermediate realities. Quantum mechanics essentially replaces this continuity of reality with phase sensitive superpositions, all of which need to interfere in order to produce the correct conditional probabilities for the observable input-output relations. In this paper, I investigate the relation between the classical notion of reality and quantum superpositions by identifying the conditions under which the intermediate states can have real external effects, as expressed by measurement operators inserted into the inner product. It is shown that classical reality emerges at the macroscopic level, where the relevant limit of the measurement resolution is given by the variance of the action around the classical solution. It is thus possible to demonstrate that the classical notion of objective reality emerges only at the macroscopic level, where observations are limited to low resolutions by a lack of sufficiently strong intermediate interactions. This result indicates that causality is more fundamental to physics than the notion of an objective reality, which means that the apparent contradictions between quantum physics and classical physics may be resolved by carefully distinguishing between observable causality and unobservable sequences of hypothetical realities “out there”.

Abstract

Distance, it is often argued, is the only coherent and empirically adequate world-making relation that can glue together the elements of the world. This paper offers entanglement as an alternative world-making relation. Entanglement is interesting since it is consistent even with quantum gravity theories that do not feature space at the fundamental level. The paper thereby defends the metaphysical salience of such non-spatial theories. An account of distance (space) is the predominant problem of empirical adequacy facing entanglement as a world-making relation. A resolution of this obstacle utilizes insights from the Ryu–Takayanagi formula (a holographic relation between entanglement and spacetime) and Susskind and Maldacena’s related ER = EPR conjecture (a relation between bell pairs and wormholes). Together these indicate how distance can be recovered from entanglement and thus carves the way for entanglement fundamentalism.

Martens, Niels C.M. and Read, James (2020) Sophistry about symmetries? Synthese. ISSN 1573-0964