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Germano D'Abramo

Publications and source records attributed to Germano D'Abramo.

At least 19 recordsLinked to original sources
arXiv2024

Mass-energy equivalence and the gravitational redshift: Does energy always have mass?

One of the most widespread interpretations of the mass-energy equivalence establishes that not only can mass be transformed into energy (e.g., through nuclear fission, fusion, or annihilation) but that every type of energy also has mass (via the mass-energy equivalence formula). Here, we show that this is not always the case. With the help a few thought experiments, we show that, for instance, the electric potential energy of a charged capacitor should not contribute to the capacitor's gravitational rest mass (while still contributing to its linear momentum). That result is in agreement with the fact that light (ultimately, an electromagnetic phenomenon) has momentum but not rest mass.

physics.gen-ph↗
arXiv2023

A note on Purcell's basic explanation of magnetic forces

In the 1960s, E.M. Purcell presented a basic explanation of the magnetic force experienced by a test charge moving parallel to a stationary current-carrying wire. According to Purcell's derivation, this force results from the difference between the relativistic length contraction of the distance among the stationary positive charges of the wire and the relativistic length contraction of the distance among the negative charges moving in the wire when the charges are observed in the rest frame of the test charge. The contraction difference generates a charge density imbalance that, in the rest frame of the test charge, is experienced as an electrostatic force, while, in the lab frame, is perceived as the magnetic force. In the present paper, we show that Purcell's approach is problematic since it generates inconsistencies and paradoxes. We maintain that Purcell's derivation has only an illustrative and expository value and should not be taken literally as describing something that really and physically happens in the wire. Furthermore, we believe that the difficulties pointed out here should be explicitly presented and discussed when introducing Purcell's approach in physics courses at the undergraduate and graduate levels.

physics.gen-ph↗
arXiv2023

Photoelectric effect induced by blackbody radiation: a theoretical analysis of a potential heat energy harvesting mechanism

The photoelectric effect induced by blackbody radiation could be a mechanism to harvest ambient thermal energy at a uniform temperature. Here, I describe (without going too much into mathematical details) the theoretical model I developed starting from 2010 to study that phenomenon, and I summarize the results of the numerical simulations. Simulations tell us that the process must be there. Moreover, at least two experimental tests have been performed in the past years that seem to corroborate, although not definitely, the alleged functioning of the proposed mechanism. Unfortunately, at present, the obtainable power density is extremely low and inadequate for immediate practical applications.

physics.gen-ph↗
arXiv2022

Non-cosmological, Non-Doppler Relativistic Frequency Shift over Astronomical Distances

We investigate in detail an apparently unnoticed consequence of special relativity. It consists in time dilation/contraction and frequency shift for emitted light affecting accelerated reference frames at astronomical distances from an inertial observer. The frequency shift is non-cosmological and non-Doppler in nature. We derive the main formulae and compare their predictions with the astronomical data available for Proxima Centauri. We found no correspondence with observations. Since the implications of the new time dilation/contraction and frequency shift are blatantly paradoxical, we do not expect to find one. By all indications, we are dealing with a genuine, and not a merely apparent, relativity paradox.

physics.gen-ph↗
arXiv2022

Mass-energy connection without special relativity

In 1905, Einstein carried out his first derivation of the mass-energy equivalence by studying in different reference frames the energy balance of a body emitting electromagnetic radiation and assuming special relativity as a prerequisite. In this paper, we prove that a general mass-energy relationship can be derived solely from very basic assumptions, which are the same made in Einstein's first derivation but completely neglecting special relativity. The general mass-energy relationship turns to a mass-energy equivalence when is applied to the case of a body emitting energy in the form of electromagnetic waves. Our main result is that if the core logic behind Einstein's approach is sound, then the essence of the mass-energy equivalence can be derived without special relativity. We believe that our heuristic approach, although not capable of giving the exact mathematical formula for the mass-energy equivalence, may represent a useful addition to the general discussion on the matter at the graduate level. Our finding suggests that the connection between mass and energy is at a deeper level and comes before any full-fledged physical theory.

physics.gen-ph↗
arXiv2022

Astronomical distances and velocities and special relativity

We show that some primary special relativity effects, which are believed to be hardly detectable in everyday life, such as time dilation, relativistic Doppler effect, and length contraction, should tangibly and spectacularly show up here on the Earth. They should occur in ordinary observations of known astronomical phenomena, also when these phenomena involve astronomical systems that move with very low velocities relative to us but are very distant. We shall do that by providing a reanalysis of the so-called Andromeda paradox and by revisiting the standard explanation of the muon lifetime dilation given when this phenomenon is observed from muon's perspective. Ultimately, we shall show that if Lorentz transformations (and basically, special relativity) are meant to entail real physical consequences, then the observable Universe should appear very differently from what we see every clear night.

physics.gen-ph↗
arXiv2021

On apparent faster-than-light behavior of moving electric fields

For every observer, however distant, the electric field of a uniformly moving charge is always directed away from, or points towards, the instantaneous present position of the charge and not away from, or towards, the retarded position at which the observer sees it (due to the finite speed of light). This fact is a well-established consequence of, among others, the application of the Liénard-Wiechert potentials, and its significance for fundamental physics is probably not fully appreciated. Here we show how and why this property has non-negligible consequences for what we take for granted about the relativity of simultaneity and faster-than-light communication. In particular, if we consider two opposite electric charges whose distance shrinks to zero at a constant velocity (shrinking electric dipole), then the cancellation of the total field seems to be instantaneous everywhere in space and in every inertial reference frame. A simple variant of the shrinking electric dipole setup appears to allow a sort of faster-than-light communication of information. Our results provide simple theoretical support to the conclusions of recent experiments on the propagation speed of Coulomb and magnetic fields. It would also be interesting to explore any possible connection between our findings and quantum non-locality.

physics.gen-ph↗
arXiv2014

Zeno at the Steering Wheel

This paper collects some reflections about an apparent incongruity between the usual (third-person) understanding of the probability of an event calculated for an extended period of time in the future (e.g., the expected probability of a driver to meet with a car accident in the next $M$ years) and the subjective perception of the same probability/risk that the person involved in that event has, instant by instant during that period of time. Similarities with the classical Zeno's paradoxes come to mind.

math.HO↗
arXiv2013

The Demon in a vacuum tube

In the present paper, several issues concerning the second law of thermodynamics, Maxwell's demon and Landauer's principle are dealt with. I argue that if the demon and the system on which it operates without dissipation of external energy are made of atoms and molecules (gas, liquid or solid) in thermal equilibrium (whose behaviour is described by a canonical distribution), then the unavoidable reason why the demon cannot successfully operate resides in the ubiquity of thermal fluctuations and friction. Landauer's principle appears to be unnecessary. I also suggest that if the behaviour of the demon and the system on which it acts is not always describable by a canonical distribution, as would happen for instance with the ballistic motion of electrons at early stages of thermionic emission, then a successful working demon cannot be ruled out a priori. A critical review of two recent experiments on thermionic emission Maxwell's demons is also given.

physics.class-ph↗
arXiv2013

On the exploitability of thermo-charged capacitors

Recently [Physics Letters A, 374, (2010) 1801] the concept of vacuum capacitor spontaneously charged harnessing the heat from a single thermal reservoir at room temperature has been introduced, along with a mathematical description of its functioning and a discussion on the main paradoxical feature that seems to violate the Second Law of Thermodynamics. In the present paper we investigate the theoretical and practical possibility of exploiting a such thermo-charged capacitor as voltage/current generator: we show that if very weak provisos on the physical characteristics of the capacitor are fulfilled, then a non-zero current should flow across the device, allowing the generation of potentially usable voltage, current and electric power out of a single thermal source at room temperature. Preliminary results show that the power output is tiny but non-zero.

physics.gen-ph↗
arXiv2013

How to defuse Earth impact threat announcements

Summary: In the past decade both scientists and laymen have probably heard at least once through the newspapers, TV and Internet that a new asteroid has been discovered with non-zero (sometimes "high") probability of collision with the Earth in the near future. Since early 2000's, such probabilities are routinely calculated by two impact monitoring systems (one in the US, the other in Europe) on preliminary orbits of newly discovered Near Earth Asteroids (NEAs), and are regularly updated whenever additional new astrometric observations for each threatening object become available. A typical pattern is that as the orbit becomes more precisely determined, impact probability often increases initially, but then turns around and decreases until it falls to zero, or some very low number. In the present study we define a probability measure which provides a simple tool to evaluate from the very beginning the chance that the impact probability calculated by monitoring systems for a threatening object will reach unity at the end of the overall process of orbit refinement. We stress that this chance is independent of the specific (fluctuating) value of the probability calculated by the monitoring systems. In a precise sense, which should be clear throughout the paper, the concrete impact probability of a newly discovered asteroid is not that given by the monitoring systems.

physics.space-ph↗
arXiv2012

Thermo-charged capacitors and the Second Law of Thermodynamics

In this Letter we describe a vacuum spherical capacitor that generates a macroscopic voltage between its spheres harnessing the heat from a single thermal reservoir at room temperature. The basic idea is trivial and it makes use of two concentric spherical electrodes with different work functions. We provide a mathematical analysis of the underlying physical process and discuss its connections with the Second Law of Thermodynamics.

physics.gen-ph↗
arXiv2012

"Strange" occurrences in SuperEnalotto

In this paper a way is suggested for calculating the probability of consecutive number strings within a sequence of n numbers randomly drawn (without replacement) among the set of the first N consecutive numbers, with N>>n. An explicit derivation is carried out for the special case of SuperEnalotto, nowadays the most famous lottery in Italy, with N=90 and n=6. It turns out that, on average, one every three drawings presents one or more consecutive number strings inside.

math.HO↗
arXiv2012

The Peculiar Status of the Second Law of Thermodynamics and the Quest for its Violation

Even though the second law of thermodynamics holds the supreme position among the laws of nature, as stated by many distinguished scientists, notably Eddington and Einstein, its position appears to be also quite peculiar. Given the atomic nature of matter, whose behaviour is well described by statistical physics, the second law could not hold unconditionally, but only statistically. It is not an absolute law. As a result of this, in the present paper we try to argue that we have not yet any truly cogent argument (known fundamental physical laws) to exclude its possible macroscopic violation. Even Landauer's information-theoretic principle seems to fall short of the initial expectations of being the fundamental `physical' reason of all Maxwell's demons failure. Here we propose a modified Szilard engine which operates without any steps in the process resembling the creation or destruction of information. We argue that the information-based exorcisms must be wrong, or at the very least superfluous, and that the real physical reason why such engines cannot work lies in the ubiquity of thermal fluctuations (and friction). We see in the above peculiar features the main motivation and rationale for pursuing exploratory research to challenge the second law, which is still ongoing and probably richer than ever. A quite thorough (and critical) description of some of these challenges is also given.

physics.class-ph↗
arXiv2011

A Note on Solid-State Maxwell Demon

Starting from 2002, at least two kinds of laboratory-testable, solid-state Maxwell demons have been proposed that utilize the electric field energy of an open-gap n-p junction and that seem to challenge the validity of the Second Law of Thermodynamics. In the present paper we present some arguments against the alleged functioning of such devices.

physics.class-ph↗
arXiv2009

Is thermo-ionic emission at room temperature exploitable?

In this brief note we describe two devices, a sort of flat and spherical capacitor, with which one should be able to test the possibility of creating a macroscopic voltage, and thus exploitable current, out of a single thermal source at room temperature. The basic idea is trivial and it makes use of a thermo-emitting cathode with work function as low as 0.7eV. The idea is not completely new, but our approach is simpler and neat. When implemented, it should allow to assess if approaches based on thermo-ionic materials at room temperature really violate the Second Law of Thermodynamics macroscopically.

physics.gen-ph↗
arXiv2009

The Seven Messengers and the "Buzzati sequence"

A young Prince decides to explore the Father's Kingdom and aims to reach its furthermost boundaries. He starts from the City with a Caravan and seven fast and strong Messengers. They have the task to maintain the communications between the Caravan and the City during the exploration, going back and forth between the Caravan and the City while the Caravan inexorably goes away. Drawing inspiration from a fantasy tale by the Italian writer Dino Buzzati, I derive the geometric progression (named "Buzzati sequence" in his honor) which governs the duration of the Messenger's trips, renewing further the fascination of the tale. I also note with wonder how all this apparently hidden mathematical structure was already known to the author. An extension of the "Buzzati sequence" to relativistic velocities of the Caravan and the Messengers is finally presented as exercise.

math.HO↗