The Foldy-Wouthuysen transformation

The Foldy-Wouthuysen transformation of the Dirac Hamiltonian is generally taught as simply a mathematical trick that allows one to obtain a two-component theory in the low-energy limit. It is not often emphasized that the transformed representation is the only one in which one can take a meaningful *classical limit*, in terms of particles and antiparticles. We briefly review the history and physics of this transformation.Comment: Standard LaTeX, 6 page

Electromagnetic Deflection of Spinning Particles

We show that it is possible to obtain self-consistent and physically acceptable relativistic classical equations of motion for a point-like spin-half particle possessing an electric charge and a magnetic dipole moment, directly from a manifestly covariant Lagrangian, if the classical degrees of freedom are appropriately chosen. It is shown that the equations obtained encompass the well-tested Lorentz force and Thomas--Bargmann--Michel--Telegdi spin equations, as well as providing a definite specification of the classical _magnetic_dipole_ force_, whose exact form has been the subject of recent debate. Radiation reaction---the force and torque on an accelerated particle due to its self-interaction---is neglected at this stage.Comment: 18 pp. (latex, uses revtex 3), UM-P-92/9

Adaptive Preferences, Self-expression and Preference-based Freedom Rankings

If preference-based freedom rankings are based on all-things-considered preferences, they risk judging phenomena of adaptive preferences as freedom enhancing. As a remedy, it has been suggested to base preference-based freedom rankings on reasonable preferences. But this approach is also problematic. This article argues that the quest for a remedy is unnecessary. All-things-considered preferences retain information on whether the availability of an option contributes to the value that freedom has for a person’s self-expression. If preference-based freedom rankings use all-things-considered preferences to evaluate whether an option contributes to a person’s self-expression, they are immune to the problem posed by adaptive preferences