Is Preacceleration of Particles in Dirac's Electrodynamics a Case of Backward Causation? The Myth of Retrocausation in Classical Electrodynamics

Abstract

Is it a “conceptual truth” or only a logically contingent fact that, in any given kind of case, an event x which asymmetrically causes (“produces”) an event y likewise temporally precedes y or at least does not temporally succeed y? A bona fide physical example in which the cause retroproduces the effect would show that backward causation is no less conceptually possible than forward causation. And it has been claimed ([9], p. 151; [4], p. 41) that in Dirac's classical electrodynamics (relativistic and non-relativistic), the preacceleration of charged particles before any forces are applied to them furnishes a genuine case of retrocausation by later forces.

An exposition of the pertinent physics furnishes the basis for arguing the following: Whereas the non-zero acceleration of a neutral NEWTONIAN mass particle is, of course, causally connected as such to the simultaneously applied non-zero force, the non-zero acceleration of a DIRACIAN charged particle is not causally connected at all as such to the applied forces. A fortiori, in Dirac's electrodynamics, the applied forces do not qualify asymmetrically as the causes of a non-zero acceleration as such; nor does a non-zero acceleration as such qualify as an effect produced by forces. This is shown by means of two considerations as follows: (1) In Dirac's theory, no functional dependence of the value of a non-zero acceleration on the weighted time-average of the forces is vouchsafed as a matter of physical LAW alone without any value of a constant of integration, just as no Newtonian law(s) alone can guarantee a functional dependence of the non-zero value of the velocity of a Newtonian mass particle on the applied forces. Instead, both functional dependencies alike are vouchsafed only with the crucial aid of some de facto boundary condition pertaining to either the past or to the future, so that (2) Non-zero preaccelerations of Diracian charged particles can no more be causally attributed as such to the retrocausal action of later forces than non-zero “prevelocities” of Newtonian mass particles can be held to be caused as such by later applied forces. The retrocausal interpretation of Dirac's preaccelerations is just as invalid as the retrocausal interpretation of Newtonian prevelocities.