arXiv subjects

George E. A. Matsas

Publications and source records attributed to George E. A. Matsas.

At least 19 recordsLinked to original sources

arXiv2026

Will we ever quantize the centers of mass of heavy systems? A case for a Heisenberg cut in quantum mechanics

The quantum orthodoxy attests that all dynamical degrees of freedom should be quantized, including those associated with the centers of mass of composite/complex systems, such as protons/pebbles. By assuming that the centers of mass of protons/pebbles should be quantized, one implies the existence of a corresponding Fock space, since, according to the present lore, quantum mechanics is a consequence of quantum field theory. Despite the fabulous success of quantum mechanics, it is unreasonable to assume the existence of annihilation and creation operators for pebbles. Fortunately, there are strong reasons to doubt that wave mechanics can describe the centers of mass of systems at or above the Planck scale, thereby jeopardizing the construction of the corresponding Fock space. We argue that isolated (free) systems with masses exceeding the Planck mass would have their centers of mass governed by classical (rather than quantum) mechanics, despite harboring macroscopic quantum phenomena as observed in the laboratory. Here, we briefly revisit (i) the arguments for the need for a Heisenberg cut delimiting the boundary between the quantum and classical realms and (ii) the kind of new physics expected at (the uncharted region of) the Heisenberg cut.

quant-ph↗

arXiv2026

Nonperturbative Danielson-Satishchandran-Wald Decoherence with Unruh-DeWitt detectors

Recently, Danielson, Satishchandran, and Wald (DSW) have proposed a novel source of decoherence for uniformly accelerated charges and masses in spatial superposition in spacetimes containing a bifurcating Killing horizon. Such an effect can be traced back to the emission and absorption of soft photons and gravitons, which effectively act as "which-path'' information probes. This results in the decoherence of any such superposition in a finite proper time. With this in mind, we study the DSW mechanism using a gapless finite-time detector prepared in a spatial superposition of uniformly accelerated paths in Minkowski spacetime that interacts with a massive scalar field. The calculation is nonperturbative. Such a model will enable us to analyze the decoherence process in a more controlled manner, highlighting the main factors that give rise to this interesting mechanism.

gr-qc↗

arXiv2026

Larmor radiation as a witness to the Unruh effect

We discuss the emission of radiation from general sources in quantum scalar, electromagnetic and gravitational fields using the Rindler coordinate frame, which is suitable for a uniformly accelerated observer, in the Minkowski vacuum. In particular, we point out that, to recover the usual Larmor radiation in the interaction picture, it is necessary to incorporate the Unruh effect. Thus, the observation of classical Larmor radiation could be seen as vindicating the Unruh effect in the sense that it is not correctly reproduced in this context unless the Unruh effect is taken into account.

gr-qc↗

arXiv2026

Emission of pairs of Minkowski photons through the lens of the Unruh effect

We discuss the emission of pairs of photons by charges with generic worldlines in the Minkowski vacuum from the viewpoint of inertial observers and interpret them from the perspective of Rindler observers. We show that the emission of pairs of Minkowski photons corresponds, in general, to three distinct processes according to Rindler observers: scattering, and emission and absorption of pairs of Rindler photons. In the special case of uniformly accelerated charges, the radiation observed in the inertial frame can be fully described by the scattering channel in the Rindler frame. Therefore, the emission of pairs of Minkowski photons -- commonly referred to as Unruh radiation -- can be seen as further evidence supporting the Unruh effect.

gr-qc↗

arXiv2025

Quantum internal vibrations in macroscopic systems with classical centers of mass

Harmonizing classical and quantum worlds is a major challenge for modern physics. A significant portion of the scientific community supports the notion that classical mechanics is an effective theory that arises from quantum mechanics. Recently, the present authors have argued that this should not be the case, as quantum mechanics is not trustworthy for describing the center of mass of systems with masses $m$ much larger than the Planck mass $M_\text{P}$. In this vein, a simple gravitational self-decoherence model was proposed, describing how the center of mass of quantum systems would classicalize for $m \sim M_\text{P}$. Here, we show that our model does not prevent macroscopic systems (with classical centers of mass) from harboring quantum internal vibrations (as has been observed in the laboratory).

quant-ph↗

arXiv2025

A simple gravitational self-decoherence model

One of the most significant debates of our time is whether our macroscopic world (i) naturally emerges from quantum mechanics or (ii) requires new physics. We argue for the latter and propose a simple gravitational self-decoherence mechanism. For this purpose, we postulate the existence of a Heisenberg cut such that particles with masses $m$ much smaller and larger than a critical mass $M_{\rm C}$ (of the order of the Planck mass $M_{\rm P}$) would be necessarily treated according to quantum and classical rules, respectively. Our effective model is designed to capture the new physics that free quantum particles would experience as their masses approach $M_{\rm C}$. The purity loss for free quantum particles is evaluated and shown to be highly inefficient for quantum particles with $m \ll M_{\rm C}$ but very effective for those with $m \sim M_{\rm C}$. The physical picture behind it is that coherence would (easily) leak from heavy enough particles to (non-observable) spacetime quantum degrees of freedom. Finally, we contextualize our proposal with state-of-the-art experiments and show how it can be tested in a future Stern-Gerlach-like experiment.

quant-ph↗

arXiv2025

Globally hyperbolic evaporating black hole and the information loss issue

We discuss the information loss issue for completely evaporating black holes in the context of a globally hyperbolic spacetime that maintains unchanged the entire semiclassical picture except for the "last evaporation breath," which pertains to full quantum gravity. Even though observers outside the black hole cannot access information that enters the horizon, there is no actual loss of information imposed by the spacetime causal structure since it is carried over from one Cauchy surface to the next (provided the local evolution is unitary).

gr-qc↗

arXiv2024

The number of fundamental constants from a spacetime-based perspective

We revisit Duff, Okun, and Veneziano's divergent views on the number of fundamental constants and argue that the issue can be set to rest by having spacetime as the starting point. This procedure disentangles the resolution in what depends on the assumed spacetime (whether relativistic or not) from the theories built over it. By defining that the number of fundamental constants equals the minimal number of independent standards necessary to express all observables, as assumed by Duff, Okun, and Veneziano, it is shown that the same units fixed by the apparatuses used to construct the spacetimes are enough to express all observables of the physical laws defined over them. As a result, the number of fundamental constants equals two in Galilei spacetime and one in relativistic spacetimes.

gr-qc↗

arXiv2024

Probing the Schroedinger-Newton equation in a Stern-Gerlach interferometer

Explaining the behavior of macroscopic objects from the point of view of the quantum paradigm has challenged the scientific community for a century today. A mechanism of gravitational self-interaction, governed by the so-called Schroedinger-Newton equation, is among the proposals that aim to shed some light on it. Despite all efforts, this mechanism has been proven difficult to probe. Here, we consider a simple Stern-Gerlach-like experiment to try it out. The Schroedinger-Newton equation can be analytically solved under certain proper conditions, and a dephasing effect induced by the gravitational self-interacting potential can be calculated.

quant-ph↗

arXiv2023

Disfavoring the Schroedinger-Newton equation

The main goal of this brief report is to provide some new insight into how promising the Schroedinger-Newton equation would be to explain the emergence of classicality. Based on the similarity of the Newton and Coulomb potentials, we add an electric self-interacting term to the Schroedinger-Newton equation for the hydrogen atom. Our results rule out the possibility that single electrons self-interact through their electromagnetic field. Next, we use the hydrogen atom to get insight into the intrinsic difficulty of testing the Schroedinger-Newton equation itself and conclude that the Planck scale must be approached before sound constraints are established. Although our results cannot be used to rule out the Schroedinger-Newton equation at all, they might be seen as disfavoring it if we underpin on the resemblance between the gravitational and electromagnetic interactions at low energies.

quant-ph↗

arXiv2022

Black-hole analog in vehicular traffic

We propose here a simple black-hole analog in vehicular-traffic dynamics. The corresponding causal diagram is determined by the propagation of the tail light flashes emitted by a convoy of cars on a highway. In addition to being a new black-hole analog, this illustrates how causal diagrams, so common in general relativity, may be useful in areas as unexpected as vehicular-traffic dynamics.

gr-qc↗

arXiv2022

Can quantum mechanics breed negative masses?

The Casimir effect realizes the existence of static negative energy densities in quantum field theory. We establish physically reasonable conditions for the non-negativity of the total mass of a Casimir apparatus held in equilibrium in the Minkowski background, irrespective of any condensed matter consideration. Specifically, the dynamical equilibrium requires the presence of additional matter to hold the system apart. As long as this extra matter satisfies the dominant energy condition, the mass of the combined system is positive. Thus, the very same reason why energy cannot travel backwards in time could be the underlying mechanism behind the positivity of the mass. We discuss the takeaways from the Casimir setting to more general circumstances.

gr-qc↗

arXiv2020

Neutrino flavor oscillations without flavor states

We analyze the problem of neutrino oscillations via a fermionic particle detector model inspired by the physics of the Fermi theory of weak interactions. The model naturally leads to a description of emission and absorption of neutrinos in terms of localized two-level systems. By explicitly including source and detector as part of the dynamics, the formalism is shown to recover the standard results for neutrino oscillations without mention to "flavor states", which are ill defined in quantum field theory. This illustrates how particle detector models provide a powerful theoretical tool to approach the measurement issue in quantum field theory and emphasizes that the notion of flavor states, although sometimes useful, must not play any crucial role in neutrino phenomenology.

hep-ph↗

arXiv2020

Uniformly accelerated classical sources as limits of Unruh-DeWitt detectors

Although the thermal and radiative effects associated with a two-level quantum system undergoing acceleration are now widely understood and accepted, a surprising amount of controversy still surrounds the simpler and older problem of an accelerated classical charge. We argue that the analogy between these systems is more than superficial: There is a sense in which a "UD detector" in a quantized scalar field effectively acts as a classical source for that field if the splitting of its energy levels is so small as to be ignored. After showing explicitly that a detector with unresolved inner structure does behave as a structureless scalar source, we use that analysis to rederive the scalar version of a previous analysis of the accelerated electromagnetic charge, without appealing to the troublesome concept of "zero-energy particles." Then we recover these results when the detector energy gap is taken to be zero from the beginning. This vindicates the informal terminology "zero-frequency Rindler modes" as a shorthand for "Rindler modes with arbitrarily small energy." In an appendix, the mathematical behavior of the normal modes in the limit of small frequency is examined in more detail than before. The vexed (and somewhat ambiguous) question of whether coaccelerating observers detect the acceleration radiation can then be studied on a sound basis.

hep-th↗

arXiv2020

Traces of the Unruh effect in surface waves

We look for classical traces of the Unruh effect in gravity waves. For this purpose, we start considering a white noise state of gravity waves on the surface of a water basin and calculate the two- and four-point functions of the Fourier transform of the surface-height field with respect to accelerated observers. The influence of the basin boundaries and possible deviations from Gaussianity in the white noise state are considered in order to approximate conditions attainable in the laboratory. Eventually, we make the basin infinitely large in order to make contact between our classical results and quantum ones derived in free space. We hope that our results help to strengthen the bridge between the Unruh effect and this classical analog.

gr-qc↗

arXiv2019

Observer dependence of entanglement in "nonrelativistic" quantum mechanics

It was recently shown that, in general, the von Neumann spin entropy of fermionic particles is not invariant under Lorentz boosts. We show that an analogous result can be recovered (at the lowest order of $v^2 /c^2$) using plain nonrelativistic quantum mechanics provided one uses that energy weighs: $E=m c^2$. This should (i) help to moderate the skepticism on the observer-dependence of the spin entropy of fermionic particles, (ii) emphasize the soft relativistic nature of this result, and (iii) show that this is a particular case of a more general class of systems, since our calculation only assumes a nonrelativistic particle endowed with an internal degree of freedom.

quant-ph↗

arXiv2019

Classical and quantum aspects of the radiation emitted by a uniformly accelerated charge: Larmor--Unruh reconciliation and zero-frequency Rindler modes

The interplay between acceleration and radiation harbors remarkable and surprising consequences. One of the most striking is that the Larmor radiation emitted by a charge can be seen as a consequence of the Unruh thermal bath. Indeed, this connection between the Unruh effect and classical bremsstrahlung was used recently to propose an experiment to confirm (as directly as possible) the existence of the Unruh thermal bath. This situation may sound puzzling in two ways: first, because the Unruh effect is a strictly quantum effect while Larmor radiation is a classical one, and second, because of the crucial role played by zero-frequency Rindler photons in this context. In this paper we settle these two issues by showing how the quantum evolution leads naturally to all relevant aspects of Larmor radiation and, especially, how the corresponding classical radiation is entirely built from such zero-Rindler-energy modes.

gr-qc↗

arXiv2018

Relativistic spring-mass system

The harmonic oscillator plays a central role in physics describing the dynamics of a wide range of systems close to stable equilibrium points. The nonrelativistic one-dimensional spring-mass system is considered a prototype representative of it. It is usually assumed and galvanized in textbooks that the equation of motion of a relativistic harmonic oscillator is given by the same equation as the nonrelativistic one with the mass $M$ at the tip multiplied by the relativistic factor $1/(1 - v^2/c^2)^{1/2}$. Although the solution of such an equation may depict some physical systems, it does not describe, in general, one-dimensional relativistic spring-mass oscillators under the influence of elastic forces. In recognition to the importance of such a system to physics, we fill a gap in the literature and offer a full relativistic treatment for a system composed of a spring attached to an inertial wall, holding a mass $M$ at the end.

physics.class-ph↗