Measuring Propagation Speed of Coulomb Fields

TL;DR

This paper investigates the propagation speed of Coulomb fields by experimentally measuring the electric field of a uniformly moving electron beam, aiming to clarify whether electromagnetic fields propagate at finite or infinite velocity.

Contribution

The study provides experimental evidence on the propagation characteristics of Coulomb fields for uniformly moving charges, addressing a longstanding theoretical paradox.

Findings

Results suggest the electric field is carried rigidly with the moving beam.

Experimental data are compatible with the electric field propagating at the same speed as the beam.

Findings contribute to understanding the fundamental nature of electromagnetic field propagation.

Abstract

The problem of gravity propagation has been subject of discussion for quite a long time: Newton, Laplace and, in relatively more modern times, Eddington pointed out that, if gravity propagated with finite velocity, planets motion around the sun would become unstable due to a torque originating from time lag of the gravitational interactions. Such an odd behavior can be found also in electromagnetism, when one computes the propagation of the electric fields generated by a set of uniformly moving charges. As a matter of fact the Li\'enard-Weichert retarded potential leads to a formula indistinguishable from the one obtained assuming that the electric field propagates with infinite velocity. Feyman explanation for this apparent paradox was based on the fact that uniform motions last indefinitely. To verify such an explanation, we performed an experiment to measure the time/space evolution of the electric field generated by an uniformely moving electron beam. The results we obtain on such a finite lifetime kinematical state seem compatible with an electric field rigidly carried by the beam itself.