The phenomenon that a quantum particle propagating in a detector, such as a Wilson cloud chamber, leaves a track close to a classical trajectory is analyzed. We introduce an idealized quantum-mechanical model of a charged particle that is periodically illuminated by pulses of laser light resulting in repeated indirect measurements of the approximate position of the particle. For this model we present a mathematically rigorous analysis of the appearance of particle tracks, assuming that the Hamiltonian of the particle is quadratic in the position- and momentum operators, as for a freely moving particle or a harmonic oscillator.

Quantum information has shed new light on the black hole (BH) information paradox, revealing that, due to the information scrambling and entanglement, the information in a BH can be retrieved from the Hawking radiation far more quickly than expected. However, BHs in reality have symmetries, which hinders the information from being fully scrambled. Here, we study information leakage from a quantum uncharged rotating BH and clarify how symmetry affects the process of leakage. We especially show that symmetry induces a \emph{delay} in the onset of information leakage and \emph{information remnant} that lingers for. The delay turns out to be related to the thermodynamic properties of the underlying model of the BH, bridging the information problem to the BH thermodynamics, while the information remnant is dominated by the symmetry-breaking of the BH. Our analysis thus unveils non-trivial connections between the information leakage problem and the macroscopic BH physics.

In this work we attempt to confront the orthodox widespread claim present in the foundational literature of Quantum Mechanics (QM) according to which ‘superpositions are never actually observed in the lab’. In order to do so, we begin by providing a critical analysis of the famous measurement problem which, we will argue, was originated by the strict application of the empirical-positivist requirements to subsume the quantum formalism under their specific understanding of ‘theory’. In this context, the ad hoc introduction of the projection postulate (or measurement rule) can be understood as a necessary requirement coming from a naive empiricist standpoint which presupposes that observations are self evident givens of “common sense” experience –independent of metaphysical (categorical) presuppositions. We then turn our attention to two “non-collapse” interpretations of QM –namely, modal and many worlds– which even though deny that the “collapse” is a real physical process anyhow retain the measurement rule as a necessary element of the theory. In contraposition, following Einstein’s claim according to which “it is only the theory which decides what can be observed”, we propose a return to the realist representational understanding of ‘physical theories’ in which ‘observation’ is considered as derived from theoretical presuppositions. It is from this standpoint that we discuss a new non-classical conceptual representation which allows us to understand quantum phenomena in an intuitive (anschaulicht) manner. Leaving behind the projection postulate, we discuss the general physical conditions for measuring and observing quantum superpositions.

Quantum correlations which violate a Bell inequality are presumed to power better-than-classical protocols for solving communication complexity problems (CCPs). How general is this statement? We show that violations of correlation-type Bell inequalities allow advantages in CCPs, when communication protocols are tailored to emulate the Bell no-signaling constraint (by not communicating measurement settings). Abandonment of this restriction on classical models allows us to disprove the main result of, inter alia, [Brukner et. al., Phys Rev. Lett. 89, 197901 (2002)]; we show that quantum correlations obtained from these communication strategies assisted by a small quantum violation of the CGLMP Bell inequalities do not imply advantages in any CCP in the input/output scenario considered in the reference. More generally, we show that there exists quantum correlations, with nontrivial local marginal probabilities, which violate the $I_{3322}$ Bell inequality, but do not enable a quantum advantange in any CCP, regardless of the communication strategy employed in the quantum protocol, for a scenario with a fixed number of inputs and outputs

In this short survey article, I discuss Bell’s theorem and some strategies that attempt to avoid the conclusion of non-locality. I focus on two that intersect with the philosophy of probability: (1) quantum probabilities and (2) superdeterminism. The issues they raised not only apply to a wide class of no-go theorems about quantum mechanics but are also of general philosophical interest.

Authors: Beth Parks

Barriers to women’s education and employment in Europe and the U.S. in the nineteenth century made it unlikely that any women would be among the few physicists whose ideas are taught in high school and college courses. This paper explores the social settings in which three influential physicists worked–James Clerk Maxwell, Robert Millikan, and Albert Einstein–to better understand the limited opportunities available to women. By acknowledging and explaining why there weren’t more women among these founding physicists, instructors may help students understand the barriers that still exist and feel more empowered to overcome them and pursue physics as a career.

Publication date: Available online 29 June 2020

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

Author(s): Robert DiSalle

Authors: Tom Draper, Benjamin Knorr, Chris Ripken, Frank Saueressig

We study the gravity-mediated scattering of scalar fields based on a parameterisation of the Lorentzian quantum effective action. We demonstrate that the interplay of infinite towers of spin zero and spin two poles at imaginary squared momentum leads to scattering amplitudes that are compatible with unitarity bounds, causal, and scale-free at trans-Planckian energy. Our construction avoids introducing non-localities or the massive higher-spin particles that are characteristic in string theory.

Authors: Qi-Qi Fan, Cong Li, Hao-Ran Zhang, Peng-Zhang He, Jian-Bo Deng

We regard the background of space-time as a physical system composed of discrete volume elements at the Planck scale and get the internal energy of space-time by Debye model. A temperature-dependent minimum energy limit of the particles is proposed from the thermal motion part of the internal energy. As decreases of the temperature caused by the expansion of the universe, more and more particles would be”released” because of the change of the energy limit, we regard these new particles as a source of dark energy. The minimum energy limit also leads to a corrected number of particles in universe and a modified conservation equation. According to the modified conservation equation, an effective cosmological constant consistent with its observed value is obtained.

Authors: Mark P. Hertzberg, Jacob A. Litterer

It is well known that a theory of the (i) Lorentz invariant and (ii) locally interacting (iii) two degrees of freedom of a massless spin 1 particle, the photon, leads uniquely to electromagnetism at large distances. In this work, we remove the assumption of (i) Lorentz boost invariance, but we still demand (ii) and (iii). We consider several broad classes of theories of spin 1, which in general explicitly violate Lorentz symmetry. We restrict to the familiar two degrees of freedom of the photon. We find that most theories lead to non-locality and instantaneous signaling at a distance. By demanding a mild form of locality (ii), namely that the tree-level exchange action is manifestly local, we find that the photon must still be sourced by a conserved charge with an associated internal symmetry. This recovers the central features of electromagnetism, although it does not by itself impose Lorentz boost symmetry. The case of gravitation dramatically improves the final conclusion and is reported in detail in our accompanying paper Part 2.

Authors: G.E. Volovik

We discuss two scenarios of emergent gravity. In one of them the quantum vacuum is considered as superplastic crystal, and the effective gravity describes the dynamical elastic deformations of this crystal. In the other one the gravitational tetrads emerge as the bilinear form of the fermionic fields. In spite of the essentially different mechanisms of emergent gravity, these two scenarios have one important common property: the metric field has dimension of the inverse square of length $[g_{\mu\nu}]=1/[l]^2$, as distinct from the conventional dimensionless metric, $[g_{\mu\nu}]=1$, in general relativity. As a result the physical quantities, which obey diffeomorphism invariance, become dimensionless. This takes place for such quantities as Newton constant, the scalar curvature, the cosmological constant, particle masses, fermionic and scalar bosonic fields, etc. This may suggest that the dimensionless physics can be the natural consequence of the diffeomorphism invariance, and thus can be the general property of any gravity, which emerges in the quantum vacuum. One of the nontrivial consequences of the shift of dimensions is related to topology. Due to the shift of dimensions some operators become topological, and contain the integer or fractional prefactors in the action. This in particular concerns the intrinsic 3+1 quantum Hall effect and the Nieh-Yan quantum anomaly in terms of torsion.

Authors: Enrico Pajer, David Stefanyszyn, Jakub Supeł

Poincar\’e invariance is a well-tested symmetry of nature and sits at the core of our description of relativistic particles and gravity. At the same time, in most systems Poincar\’e invariance is not a symmetry of the ground state and is hence broken spontaneously. This phenomenon is ubiquitous in cosmology where Lorentz boosts are spontaneously broken by the existence of a preferred reference frame in which the universe is homogeneous and isotropic. This motivates us to study scattering amplitudes without requiring invariance of the interactions under Lorentz boosts. In particular, using on-shell methods and assuming massless, relativistic and luminal particles of any spin, we show that the allowed interactions around Minkowski spacetime are severely constrained by unitarity and locality in the form of consistent factorization. The existence of an interacting massless spin-2 particle enforces (analytically continued) three-particle amplitudes to be Lorentz invariant, even those that do not involve a graviton, such as cubic scalar couplings. We conjecture this to be true for all n-particle amplitudes. Also, particles of spin S > 2 cannot self-interact nor can be minimally coupled to gravity, while particles of spin S > 1 cannot have electric charge. Given the growing evidence that free gravitons are well described by massless, luminal relativistic particles, our results imply that cubic graviton interactions in Minkowski must be those of general relativity up to a unique Lorentz-invariant higher derivative correction of mass dimension 9. Finally, we discuss a surprising and general lesson revealed by applying our analysis to the sub-Hubble limit of inflation and Dark Energy models.

Coffey, Kevin (2020) On the Ontology of Particle Mass and Energy in Special Relativity. [Preprint]

This article does not provide any content.

Roush, Sherrilyn (2003) Copernicus, Kant, and the Anthropic Cosmological Principles. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, 34 (1). pp. 5-35.

Woodward, James (2020) Flagpoles Anyone? Causal and Explanatory Asymmetries. [Preprint]

Okon, Elias and Muciño, Ricardo (2020) Wigner’s convoluted friends. [Preprint]

Abstract

We propose a Quantum Field Theory description of beams on a Mach–Zehnder interferometer and apply the method to describe Interaction Free Measurements (IFMs), concluding that there is a change of momentum of the fields in IFMs. Analysing the factors involved in the probability of emission of low-energy photons, we argue that they do not yield meaningful contributions to the probabilities of the IFMs.

Abstract

Karim Thébault has argued that for ontic structural realism to be a viable ontology it should accommodate two principles: physico-mathematical structures it deploys must be firstly consistent and secondly substantial. He then contends that in geometric quantization, a transitional machinery from classical to quantum mechanics, the two principles are followed, showing that it is a guide to ontic structure. In this article, I will argue that geometric quantization violates the consistency principle. To compensate for this shortcoming, the deformation quantization procedure will be offered.

Author(s): A. Tononi, F. Cinti, and L. Salasnich

The recent developments of microgravity experiments with ultracold atoms have produced a relevant boost in the study of shell-shaped ellipsoidal Bose-Einstein condensates. For realistic bubble-trap parameters, here we calculate the critical temperature of Bose-Einstein condensation, which, if compar…

[Phys. Rev. Lett. 125, 010402] Published Mon Jun 29, 2020

Di Biagio, Andrea and ROVELLI, Carlo (2020) Stable Facts, Relative Facts. [Preprint]

Abstract

In the recent literature, it has been shown that the wave function in the de Broglie–Bohm theory can be regarded as a new kind of field, i.e., a “multi-field”, in three-dimensional space. In this paper, I argue that the natural framework for the multi-field is the original second-order Bohm’s theory. In this context, it is possible: (i) to construe the multi-field as a real-valued scalar field; (ii) to explain the physical interaction between the multi-field and the Bohmian particles; and (iii) to clarify the status of the energy–momentum conservation and the dynamics of the theory.