It is often described, that virtual photons are mere mathematical constructs, that can turn to real photons if there is enough time and space. And also, that virtual photons can mediate longitudinal field components of an E-field, especially from resting charges.

1.) Suppose a charge appears at the end of a rod like conductor by a shift of charges along the rod (let the charge rest at the end of the rod and not distribute over the rods surface). Suppose the rod is extremely long, so we don’t have to care about the counter-charge at the other end of the rod. From the moment of appearance, a longitudinal oriented front of an E-field will propagate from this charge with light speed (computable by retarded potentials). Will this front consist of real photons after some distance?

2.) Suppose the charge shift in the rod follows a sine movement. Then a longitudinal wave will propagate. Is there a possibility to slow down the speed of this propagation?

Wave propagation of real photons can be slowed down by dielectric material, superpositioning induced deflections of the oscillations of the materials electrons. But this requires a normal TEM-wave with orthogonal E- and B- components with respect to the propagation direction.

If real photons are given, slowing down a longitudinal wave could be done with superposition of some induced TE or TM waves? Real photons can be converted to phonons, excitons, polarons … - does this offer a possibility for a delaying superposition?

  • $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    Nov 25, 2022 at 23:12
  • $\begingroup$ photons are quantum mechanical particles and obey quantum mechanical equations. The collective waves in rod you are describing are modeled well with the E and B fields of classical electrodynamics. There is a connection in the limits between the quantum mechanical mathematics and the classical, but not in the way you are describing it. physics.stackexchange.com/questions/3580/… , $\endgroup$
    – anna v
    Nov 26, 2022 at 7:59
  • $\begingroup$ I should have emphasize, that I am not interested in electrodynamical processes in the rod. The rod is just a tool to let a charge pop up in space. I’m interested in the fields emerging from this point and the spherical propagation in space. 1) Will this (longitudinal) wave front consist of real photons after some distance? 2) Is there a way to slow the propagation down (when the charge appears in sine style)? $\endgroup$
    – barfotix
    Dec 1, 2022 at 11:46

1 Answer 1


2.) Suppose the charge shift in the rod follows a sine movement. Then a longitudinal wave will propagate. Is there a possibility to slow down the speed of this propagation?

How is a radio wave generated?

  • First, the wave generator is crucial. This determines the frequency with which surface atoms are accelerated and emit photons synchronously and polarized. Since the time of a free path of the electron exceeds by far the time of the half wavelength of the generator, a lot of photons are generated per half wave by each electron.

  • Depending on the material of the rod, the resistance that the electrons have to overcome is highly variable. As the free path length decreases, more and more IR photons are produced (at the expense of shorter wavelengths), and the antenna becomes warm or begins to glow. Not different from any other conductor. Not affected is the synchronous generation of the photons itself. You still get the radio wavelength given by the generator.

  • If you want to change the radio frequency (-wavelength), you have to change the frequency of the generator or put a resistor against the generator, which exceeds its power output, so that it becomes slower. This is not only possible via the electrical resistance. You can apply an external magnetic field, which causes the Hall effect and increases the internal resistance of the conductor.

I'm curious if you have an experimental setup behind the question.

  • $\begingroup$ A classical radio wave emerges from an open capacitor (antenna) and is able to propagate if the antenna fit the wavelength as you mentioned. E- and B-field are perpendicular to the propagation direction. A longitudinal wave emerges from a charge appearing in space (therefore the extremely long rod) and propagates with light speed (as it can be modeled by retarded potentials). There is only a longitudinal E-field component and presumably rotating B-fields around the E-components changing in time. Classical radio waves can be slowed down. Is there a way to slow down the longitudinal wave? $\endgroup$
    – barfotix
    Dec 1, 2022 at 11:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.