Concerning Hidden Momentum
The fact that the author of an excellent textbook on electromagnetism could be duped by "hidden momentum" vividly illustrates the problematic nature of its use.
physics.class-ph↗
arXiv subjects
Timothy H. Boyer
Publications and source records attributed to Timothy H. Boyer.
Unresolved Classical Electromagnetic Aspects of the Aharonov-Bohm Phase Shift
The long-standing controversy regarding the Aharonov-Bohm phase shift is reviewed. The shifts of both optical and particle interference patterns are summarized. It is pointed out that a line of electric dipoles and a line of magnetic dipoles (a long solenoid) both produce experimentally observed phase shifts similar to that produced by introducing a rectangular block of glass behind one slit of a double-slit interference pattern; the double-slit pattern is shifted while the single-slit envelope remains undisplaced. The quantum explanation for the magnetic interference pattern shift introduced by Aharonov and Bohm in 1959 involves completely different ideas from those suggested by a semiclassical analysis. Experiments planned by Caprez, Barwick, and Batelaan should clarify the connections between classical and quantum theories in connection with the Ahronov-Bohm phase shift.
physics.atom-ph↗
Interaction of a Point Charge and a Magnet: Comments on "Hidden Mechanical Momentum Due to Hidden Nonelectromagnetic Forces"
The interaction of a point charge and a magnetic moment (and by extension a point charge and a solenoid) is explored within well-defined point-charge magnetic-moment models where full calculations are possible. It is shown explicitly how the "hidden mechanical momentum" is introduced by the "hidden" external forces of constraint, requiring a prescribed response (through order 1/c^2) of the system to electromagnetic forces. These external forces often go unmentioned in the textbook and research literature. The dependence of "hidden mechanical momentum" upon detailed external (nonelectromagnetic) forces may undermine the idea's usefulness in describing nature. Some statements of dubious validity in the textbook literature are noted.
physics.class-ph↗
Comment on Experiments Related to the Aharonov-Bohm Phase Shift
Recent experiments undertaken by Caprez, Barwick, and Batelaan should clarify the connections between classical and quantum theories in connection with the Aharonov-Bohm phase shift. It is pointed out that resistive aspects for the solenoid current carriers play a role in the classical but not the quantum analysis for the phase shift. The observed absence of a classical lag effect for a macroscopic solenoid does not yet rule out the possibility of a lag explanation of the observed phase shift for a microscopic solenoid.
physics.class-ph↗
Scaling Symmetries of Scatterers of Classical Zero-Point Radiation
Classical radiation equilibrium (the blackbody problem) is investigated by the use of an analogy. Scaling symmetries are noted for systems of classical charged particles moving in circular orbits in central potentials V(r)=-k/r^n when the particles are held in uniform circular motion against radiative collapse by a circularly polarized incident plane wave. Only in the case of a Coulomb potential n=1 with fixed charge e is there a unique scale-invariant spectrum of radiation versus frequency (analogous to zero-point radiation) obtained from the stable scattering arrangement. These results suggest that non-electromagnetic potentials are not appropriate for discussions of classical radiation equilibrium.
physics.class-ph↗
Connecting Blackbody Radiation, Relativity, and Discrete Charge in Classical Electrodynamics
It is suggested that an understanding of blackbody radiation within classical physics requires the presence of classical electromagnetic zero-point radiation, the restriction to relativistic (Coulomb) scattering systems, and the use of discrete charge. The contrasting scaling properties of nonrelativistic classical mechanics and classical electrodynamics are noted, and it is emphasized that the solutions of classical electrodynamics found in nature involve constants which connect together the scales of length, time, and energy. Indeed, there are analogies between the electrostatic forces for groups of particles of discrete charge and the van der Waals forces in equilibrium thermal radiation. The differing Lorentz- or Galilean-transformation properties of the zero-point radiation spectrum and the Rayleigh-Jeans spectrum are noted in connection with their scaling properties. Also, the thermal effects of acceleration within classical electromagnetism are related to the existence of thermal equilibrium within a gravitational field. The unique scaling and phase-space properties of a discrete charge in the Coulomb potential suggest the possibility of an equilibrium between the zero-point radiation spectrum and matter which is universal (independent of the particle mass), and an equilibrium between a universal thermal radiation spectrum and matter where the matter phase space depends only upon the ratio mc^2/kT. The observations and qualitative suggestions made here run counter to the ideas of currently accepted quantum physics.
physics.class-ph↗
The Paradoxical Forces for the Classical Electromagnetic Lag Associated with the Aharonov-Bohm Phase Shift
The classical electromagnetic lag assocated with the Aharonov-Bohm phase shift is obtained by using a Darwin-Lagrangian analysis similar to that given by Coleman and Van Vleck to identify the puzzling forces of the Shockley-James paradox. The classical forces cause changes in particle velocities and so produce a relative lag leading to the same phase shift as predicted by Aharonov and Bohm and observed in experiments. An experiment is proposed to test for this lag aspect implied by the classical analysis but not present in the currently-accepted quantum topological description of the phase shift.
physics.class-ph↗
Darwin-Lagrangian Analysis for the Interaction of a Point Charge and a Magnet: Considerations Related to the Controversy Regarding the Aharonov-Bohm and Aharonov-Casher Phase Shifts
The classical electromagnetic interaction of a point charge and a magnet is discussed by first calculating the interaction of point charge with a simple model magnetic moment and then suggesting a multiparticle limit. The Darwin Lagrangian is used to analyze the electromagnetic behavior of the model magnetic moment (composed of two oppositely charged particles of different mass in an initially circular orbit) interacting with a passing point charge. The changing mangetic moment is found to put a force back on a passing charge; this force is of order 1/c^2 and depends upon the magnitude of the magnetic moment. It is suggested that in the limit of a multiparticle magnetic toroid, the electric fields of the passing charge are screened out of the body of the magnet while the magnetic fields penetrate into the magnet. This is consistent with our understanding of the penetration of electromagnetic velocity fields into ohmic conductors. Conservation laws are discussed. The work corresponds to a classical electromagnetic analysis of the interaction which is basic to understanding the controversy over the Aharonov-Bohm and Aharonov-Casher phase shifts and represents a refutation of the suggestions of Aharonov, Pearle, and Vaidman.
physics.class-ph↗
Illustrations of the Relativistic Conservation Law for the Center of Energy
The relativistic conservation law involving the center of energy is reviewed and illustrated using simple examples from classical electromagnetic theory. It is emphasized that this conservation law is parallel to the conservation laws for energy, linear momentum, and energy, in arising from the generators of the Poincare group for electromagnetic theory; yet this relativistic law reflecting the continuous flow of energy goes virtually unmentioned in the text books. The illustrations here present situations both where external forces are present and are absent. The cases of a parallel plate capacitor, a flattened slip-joint solenoid, and two interacting charges are included.
physics.class-ph↗
Blackbody Radiation, Conformal Symmetry, and the Mismatch Between Classical Mechanics and Electromagnetism
The blackbody radiation problem within classical physics is reviewed. It is again suggested that conformal symmetry is the crucial unrecognized aspect, and that only scattering by classical electromagnetic systems will provide equilibrium at the Planck spectrum. It is pointed out that the several calculations of radiation scattering using nonlinear mechanical systems do not preserve the Boltzmann distribution under adiabatic change of parameter, and this fact seems at variance with our expectations in connection with derivations of Wien's displacement theorem. By contrast, the striking properties of charged particle motion in a Coulomb potential or in a uniform magnetic field suggest the possiblity that these systems will fit with classical thermal radiation. It may be possible to give a full scattering calculation in the case of cyclotron motion in order to provide the needed test of the connection between conformal symmetry and classical thermal radiation.
physics.class-ph↗
Unfamiliar trajectories for a relativistic particle in a Kepler or Coulomb potential
Relativistic particles in the Kepler and Coulomb potentials may have trajectories that are qualitatively different from the trajectories found in nonrelativistic mechanics. Spiral scattering trajectories were pointed out by C. G. Darwin in 1913 in connection with the relativistic Rutherford scattering of classical charged particles. Relativistic trajectories are of current interest in connection with Cole and Zou's computer simulation of the hydrogen ground state in classical physics.
physics.gen-ph↗
Casimir Forces and Boundary Conditions in One Dimension: Attraction, Repulsion, Planck Spectrum, and Entropy
Quantities associated with Casimir forces are calculated in a model wave system of one spatial dimension with Dirichlet or Neumann boundary conditions. 1)Due to zero-point fluctuations, a partition is attracted to the walls of a box if the wave boundary conditions are alike for the partition and the walls, but is repelled if the conditions are different. 2)The use of Casimir energies in the presence of zero-point radiation introduces a natural maximum-entropy principle which is satisfied only by the Planck spectrum for both like and unlike boundary conditions between the box and partition. 3)The Casimir forces are attractive and increasing with temperature for like boundary conditions, but are repulsive and decreasing with temperature for unlike conditions. 4)In the high-temperature limit, there is a temperature-independent Casimir entropy for like but not for unlike boundary conditions. These results have 3-dimensional electromagnetic counterparts.
quant-ph↗
Derivation of the Blackbody Radiation Spectrum from a Natural Maximum-Entropy Principle Involving Casimir Energies and Zero-Point Radiation
By numerical calculation, the Planck spectrum with zero-point radiation is shown to satisfy a natural maximum-entropy principle whereas alternative choices of spectra do not. Specifically, if we consider a set of conducting-walled boxes, each with a partition placed at a different location in the box, so that across the collection of boxes the partitions are uniformly spaced across the volume, then the Planck spectrum correspond to that spectrum of random radiation (having constant energy kT per normal mode at low frequencies and zero-point energy (1/2)hw per normal mode at high frequencies) which gives maximum uniformity across the collection of boxes for the radiation energy per box. The analysis involves Casimir energies and zero-point radiation which do not usually appear in thermodynamic analyses. For simplicity, the analysis is presented for waves in one space dimension.
physics.class-ph↗
Thermodynamics of the Harmonic Oscillator: Wien's Displacement Law and the Planck Spectrum
A thermodynamic analysis of the harmonic oscillator is presented. Motivation for the study is provided by the blackbody radiation spectrum; when blackbody radiation is regarded as a system of noninteracting harmonic oscillator modes, the thermodynamics follows from that of the harmonic oscillators. Using the behavior of a harmonic oscillator thermodynamic system under a quasi-static change of oscillator frequency w, we show that the thermodynamic functions can all be derived from a single function of w/T, analogous to Wien's displacement theorem. The high- and low-frequency energy limits allow asymptotic energy forms involving T alone or w alone, corresponding to energy equipartition and zero-point energy. It is noted that the Planck spectrum with zero-point radiation corresponds to the function satisfying the Wien displacement result which provides the smoothest possible interpolation between energy equipartition at low frequency and zero-point energy at high frequency.
physics.class-ph↗
Connecting blackbody radiation and zero-point radiation within classical physics: A new minimum principle and a status review
A new thermodynamic analysis is presented for the intimate connections between blackbody radiation and zero-point radiation within classical physics. First, using the thermodynamic behavior of an oscillator under an adiabatic change of frequency, we show that the thermodynamic functions can all be derived from a single function of w/T, analogous to Wien's displacement theorem. The high- and low-frequency limits allow asymptotic energy forms involving T alone or w alone, corresponding to energy equipartition and zero-point energy. It is then suggested that the actual thermodynamic behavior for a harmonic oscillator is given by the function satisfying the Wien displacement result which provides the smoothest possible interpolation between scale-decoupled energy equipartition at low frequency and scale-invariant zero-point energy at high frequency. This leads to the Planck spectrum. Second, we turn to radiation in a box with conducting walls and a conducting partition so that the discrete normal mode structure of the box becomes important. The contrasting Casimir energies are explored for the Rayleigh-Jeans and zero-point spectra. The Rayleigh-Jeans spectrum involves no change of energy with partition position, and the zero-point spectrum involves no change of entropy. It is suggested that the Planck spectrum with zero-point radiation satisfies a natural minimum principle which corresponds to greatest independence of the system energy from the position of the partition for a fixed temperature. Numerical calculation is used for confirmation. Third, we review the previous derivations of the Planck radiation spectrum in classical physics, all of which involve zero-point radiation.
physics.class-ph↗
Semiclassical Explanation of the Matteucci-Pozzi and Aharonov-Bohm Phase Shifts
Classical electromagnetic forces can account for the experimentally observed phase shifts seen in an electron interference pattern when a line of electric dipoles or a line of magnetic dipoles (a solenoid) is placed between the electron beams forming the interference pattern.
quant-ph↗
Classical Electromagnetic Interaction of a Point Charge and a Magnetic Moment: Considerations Related to the Aharonov-Bohm Phase Shift
A fundamentally new understanding of the classical electromagetic interaction of a point charge and a magnetic moment through order second order in 1/c is suggested. This relativistic analysis connects together hidden momentum in magnets, Solem's strange polarization of the classical hydrogen atom, and the Aharonov-Bohm Phase shift. We use a relativistic magnetic moment model consisting of many superimposed classical hydrogen atoms interacting through the Darwin Lagrangian with an external charge but not with each other. The analysis of Solem regarding the strange polarization of the classical hydrogen atom is seen to give a fundamentally different mechanism for the electric field of the passing charge to change the magnetic moment. The changing magnetic moment leads to an electric force back at the point charge which i)is second order in 1/c, ii)depends upon the magnetic dipole moment, changing sign with the dipole moment, iii)is odd in the charge q of the passing charge, and iv)reverses sign for charges passing on opposite sides of the magnetic moment. We suggest that a realistic multi-particle magnetic moment involves a changing magnetic moment which keeps the electromagnetic field momentum constant. This means also that the magnetic moment does not allow a significant shift in its internal center of energy. This criterion also implies that the Lorentz forces on the charged particle and on the point charge are equal and opposite and that the center of energy of each moves according to Newton's second law where the force is exactly the Lorentz force. Finally, we note that the results and suggestion given here are precisely what are needed to explain both the Aharonov-Bohm phase shift and the Aharonov-Casher phase shift as arising from classical electromagnetic forces.
physics.class-ph↗