Measuring propagation speed of Coulomb fields

• Published in: The European physical journal. C, Particles and fields Vol. 75; no. 3; pp. 1 - 10
• Main Authors: de Sangro, R., Finocchiaro, G., Patteri, P., Piccolo, M., Pizzella, G.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2015; Springer; Springer Nature B.V
• Subjects: Astronomy; Astrophysics and Cosmology; Electric fields; Electromagnetism; Electron beams; Elementary Particles; Gravitation; Hadrons; Heavy Ions; Measurement; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; Propagation; Propagation velocity; Quantum Field Theories; Quantum Field Theory; Regular Article - Experimental Physics; String Theory; Time lag; Transverse Distance; Beam Line; Coulomb Field; Transverse Position; Longitudinal Position
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-015-3355-3

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, planet 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 Liénard–Weichert retarded potential leads to the same formula as the one obtained assuming that the electric field propagate with infinite velocity. The Feynman 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 uniformly moving electron beam. The results we obtain, on a finite lifetime kinematical state, are compatible with an electric field rigidly carried by the beam itself.