arXiv subjects

Rodrigo Medina

Publications and source records attributed to Rodrigo Medina.

12 recordsLinked to original sources

arXiv2018

Momentum exchange between an electromagnetic wave and a dispersive medium

We present an elementary discussion of the momentum transferred by an electromagnetic wave propagating in a dispersive medium. Our analysis is based on Minkowski's electromagnetic momentum density which have been recently seen to be consistent with a fully covariant expression of the energy-momentum tensor of the electromagnetic field in a dispersive medium and with all the experimental evidence. We show that the medium may be either pulled or pushed as the electromagnetic pulse enters in it depending on the value of the frequency.

physics.class-ph↗

arXiv2017

The energy-momentum tensor of electromagnetic fields in matter

We present a complete resolution of the Abraham-Minkowski controversy . This is done by considering several new aspects which invalidate previous discussions. We show that: 1)For polarized matter the center of mass theorem is no longer valid in its usual form. A contribution related to microscopic spin should be considered. 2)The electromagnetic dipolar energy density contributes to the inertia of matter and should be incorporated covariantly to the the energy-momentum tensor of matter. Then there is an electromagnetic component in matter's momentum density whose variation explains the results of the only experiment which supports Abraham's force. 3)Averaging the microscopic Lorentz's force results in the unambiguos expression for the force density exerted by the field. This force density is consistent with all the experimental evidence. 4)Momentum conservation determines the electromagnetic energy-momentum tensor. This tensor is different from Abraham's and Minkowski's tensors, but one recovers Minkowski's expression for the momentum density. The energy density is different from Poynting's expression but Poynting's vector remains the same. Our tensor is non-symmetric which allows the field to exert a distributed torque on matter. We use our results to discuss momentum and angular momentum exchange in various situations of physical interest. We find complete consistency of our equations in the description of the systems considered. We also show that several alternative expressions of the field energy-momentum tensor and force-density cannot be successfully used in all our examples. In particular we verify in two of these examples that the center of mass and spin introduced by us moves with constant velocity, but that the standard center of mass does not.

physics.class-ph↗

arXiv2016

An elementary approach to electromagnetic momentum in matter

We present an elementary discussion of the momentum transferred to a conducting sheet by an electromagnetic wave propagating in a polarizable medium. We show that conservation of momentum is consistent with Minkowski's expression for the momentum density.

physics.class-ph↗

arXiv2014

Electromagnetic fields in matter revisited

The force density on matter and the kinetic energy-momentum tensor of the electromagnetic field in matter are obtained starting from Maxwell equations and Lorentz force at microscopic level and averaging over a small region of space-time. The macroscopic force density is taken to depend linearly on the average fields and their first derivatives and is shown to be determined by two phenomenological fields which are subsequently identified with the free current density and the polarization density tensor. It is shown that as expected, the average current density is the sum of the free current density and a dipolar contribution and that the average field satisfy the Maxwell equations. The macroscopic energy-momentum tensor of the field is shown to be equal to the standard empty-space energy-momentum tensor built with the macroscopic fields plus a dipolar correction. The density of momentum of the field is confirmed to be given by Minkowski's expression. The energy-momentum tensor of macroscopic matter is equal to the average of the microscopic energy-momentum tensor of matter plus the difference between the average tensor of microscopic fields and the macroscopic tensor of fields.

physics.class-ph↗

arXiv2014

Belinfante-Rosenfeld tensor and the inertia principle

In a recent letter we show that for an isolated system with a non symmetric energy momentum tensor the usual forms of the center of mass motion theorem are not valid. This was illustrated with a particular configuration of a magnet and a point charge for which it was shown that what is usually regarded as the center of mass of the system does not remain stationary even if the system is isolated. In a subsequent work we demonstrated that the violation of the center of mass motion theorem for isolated systems with spin is a direct consequence of the conservation of total angular momentum. We also show that there exists a generalized center of mass and spin which moves with constant velocity. In this letter we show that this center of mass and spin corresponds to the center of mass defined by the Belinfante-Rosenfeld tensor. We also show that, if the spin density instead of being of microscopic origin appears by a scaling process, the macroscopic Belinfante-Rosenfeld tensor emerges from the average of the microscopic energy-momentum tensor as the true macroscopic energy momentum tensor. This implies that in general spin has to be considered as a source of the gravitational field in general relativity.

hep-th↗

arXiv2014

An Improved Inertia Principle

We show that for isolated relativistic systems with spin the conservation of total angular momentum implies that, instead of the center of mass, it is a modified center of mass and spin which behaves inertially. This requires a change in the the statement of the Principle of Inertia.

physics.class-ph↗

arXiv2014

The force density and the kinetic energy-momentum tensor of electromagnetic fields in matter

We determine the invariant expression of the force density that the electromagnetic field exerts on dipolar matter and construct the non-symmetric energy-momentum tensor of the electromagnetic field in matter which is consistent with that force and with Maxwell equations. We recover Minkowski's expression for the momentum density. We use our results to discuss momentum exchange of an electromagnetic wave-packet which falls into a dielectric block. In particular we show that the wave-packet pulls the block when it enters and drags it when it leaves. The usual form of the center of mass motion theorem does not hold for this system but a modified version of the theorem which includes a spin contribution is shown to be satisfied.

physics.class-ph↗

arXiv2014

Violation of the center of mass theorem for systems with electromagnetic interaction

In this letter we show that for isolated systems for which the energy current density is not equal to the momentum density, that means for systems with non-symmetric energy-momentum, the usual statements of the center of mass motion theorem are not valid. We also discuss the modified version of the theorem that is always valid. Then we present a simple and exactly workable example of an electromagnetic interacting system which illustrates the violation of those standard versions of the center of mass motion theorem. We show that for this system Minkowski's density of linear momentum which yields a non-symmetric electromagnetic energy-momentum tensor, but not Abraham's, is compatible with total momentum conservation.

physics.class-ph↗

arXiv2007

Lagrangian of the quasi-rigid extended charge

It is proposed a Lagrangian for the quasi-rigid extended charged particle, which consists of a bare point particle term plus the standard electromagnetic minimal coupling. The quasi-rigid motion is imposed as a constraint. The extension of the particle and the quasi-rigid motion appear inside the current density. The Lorentz contraction of the extended particle makes the interaction term dependent on the acceleration. This dependence produces the additional terms in the equations of motion that are necessary for the proper energy and momentum conservation, and that were previously identified as the inertial effects of stress. The momentum of stress is obtained as an explicit function of the electromagnetic field.

hep-th↗

arXiv2006

The inertia of stress

We present a simple example in which the importance of the inertial effects of stress is evident. The system is an insulating solid narrow disc whose faces are uniformly charged with charges of equal magnitude and opposite signs. The motion of the system in two different directions is considered. It is shown how the contributions to energy and momentum of the stress that develops inside the body to balance the electrostatic forces have to be added to the electromagnetic contributions to obtain the results predicted by the relativistic equivalence of mass and energy.

physics.class-ph↗

arXiv2006

Radiation reaction of a classical quasi-rigid extended particle

The problem of the self-interaction of a quasi-rigid classical particle with an arbitrary spherically symmetric charge distribution is completely solved up to the first order in the acceleration. No ad hoc assumptions are made. It is shown that most of the puzzles that this problem has aroused are due to the inertia of the negative pressure that equilibrates the electrostatic repulsion inside the particle. When the inertia of pressure is taken into account the dressed mass turns out to be the bare mass plus the electrostatic mass m=m_0 + m_e. It is shown that a proper mechanical behaviour requires that m_0 > m_e/3. This condition poses a lower bound on the radius that a particle of a given bare mass and charge may have. The violation of this condition is the reason why the Lorentz-Abraham-Dirac formula for the radiation reaction of a point charge predicts unphysical motions that run away or violate causality. Provided the mass condition is met the solutions of the exact equation of motion never run away and conform to causality and energy and momentum conservation. When the radius is much smaller than the wave-length of the radiated fields, but the mass condition is still met, the exact expression reduces to the formula that was advocated recently by Rohrlich.

physics.class-ph↗

arXiv2005

Orthodox Quantum Mechanics Free from Paradoxes

A formulation of quantum mechanics based on an operational definition of state is presented. This formulation, which includes explicitly the macroscopic systems, assumes the probabilistic interpretation and is nevertheless objective. The classical paradoxes of quantum mechanics are analyzed and their origin is found to be the fictitious properties that are usually attributed to quantum-mechanical states. The hypothesis that any mixed state can always be considered as an incoherent superposition of pure states is found to contradict quantum mechanics. A solution of EPR paradox is proposed. It is shown that entanglement of quantum states is compatible with realism and locality of events, but implies non-local encoding of information.

quant-ph↗