Potential delay (field lag)

  Potential delay (field lag) is the effect of distortion of the Coulomb symmetry of the field of a moving electric (or gravitational) charge in comparison with rest.  For the first time theoretically for electric charges, this effect was considered by A. Lienar (1898) and E. Wiechert (1900).  In their view, this effect consisted in the fact that the surfaces of equal potentials of the field of a moving charge (equipotential), when it moves due to the finiteness of the propagation velocity of electromagnetic waves, shift (relative to the current position of the charge) in the direction opposite to the direction of the charge velocity (“delay”).  This is expressed in an increase in the field strength in front of a moving charge and a decrease behind.  After the creation of the theory of relativity, this phenomenon (also called “potential delay” and also under the names of A. Lenard and E. Wiechert) was assigned to 4-dimensional space-time, which in the projection onto three-dimensional space gives the field “deformation” not in the form lag equipotentials, but in the form of compression of the field (decrease in the field strength in front and behind the charge and increase in the transverse directions).
    The proof of the first (classical) representation of IMMEDIATELY follows from the well-known phenomenon - the Doppler effect, which occurs when a source of electromagnetic waves (light and radio) moves and consists in a decrease in the wavelength in front of the source and an increase behind the corresponding inverse difference of the amplitudes of the tension waves.  Specifically, for a source of radio waves, you can put an alternating potential on a whip antenna in motion.  In this case, it is obvious that, reducing the frequency of the variable potential at the antenna down to zero, we arrive at a stationary (classical) picture of the "lagging" field.   
    It was found that the classical idea of ​​the deformation of the field of moving charges (both electric and gravitational) turned out to be richer in heuristic consequences.  So it made it possible to explain such fundamental (but discovered only as experimental) postulates of physics such as Ampere's law (interaction of currents), Faraday's law (electromagnetic induction).  It was also discovered (by integration of the field) that the “deformation” addition of the field energy of a moving charge in comparison with the rest in the classical representation turned out to be equal to the kinetic energy of the charge motion (the same for the gravitational charge-mass and its gravitational field), which explained the essence of the kinetic accumulation energy during the movement of these charges and, therefore, the essence of the 2nd (previously only experienced) Newton's Law.
     
 Kirsanov Yu.Ya "Lagging fields (retarded potentials) and the postulates of physics."