How do electromagnetic waves exist?

Question

So if magnetic fields are made by the shrinking of the different particles in a conductor when there is a current how can magnetic fields be created just by the changing electric fields? In the normal case current flows through a wire and a charged object moves next to the wire the moving electrons shrink less than the stationary protons so the wire is now positively charged from the point of view of the outside charge. What shrinking happens when an electromagnetic wave is created? I couldn't find a convincing explanation and could think of one so I would appreciate if someone can help me.

Answer 1

if magnetic fields are made by the shrinking of the different particles in a conductor when there is a current how can magnetic fields be created just by the changing electric fields?

Magnetic fields cannot generally be described as an effect of length contraction for currents. What can be described that way are magnetic forces, not magnetic fields. A magnetic force acts on a moving charge, and a moving charge has a rest frame, and in the rest frame it is stationary, so the force is purely electric. That chain of logic fails without a charge.

What shrinking happens when an electromagnetic wave is created? I couldn't find a convincing explanation

Indeed, as far as I know there is no such explanation. It will be difficult even just to construct an explanation for the force on a charge due to the EM wave.

The chain of logic used above starts in a frame where there is no E field, so the force is purely magnetic. This is a dramatic simplification for the analysis. However, for an EM wave no such frame exists. There are both E and B fields in all frames. So if the analysis is even possible, it will certainly be much more difficult.

Purcell’s approach is a fun exercise that shows the close relationship between relativity and electromagnetism. However, it is not the basis of a sound understanding of EM. There isn’t an actual way around Maxwell’s equations for someone wanting to understand EM.

Answer 2

Consider that the speed of light, $c$, is not specifically about light or E&M. It's really the speed of causality. In the Universe, the "instantaneous" interactions are not instantaneous at all where the cause and effect of the interaction are separated by a distance in space.

Now imagine that I am holding a big positive charge and you are existing some fixed distance away from me and facing me and holding a big negative charge. Our charges are unlike, so they attract, but we're both restricting them from moving along the line connecting us. However they are free to move up and down and left and right, just not toward each other.

Now let's say that I move my charge up and you're allowing your charge to move freely (but not along the line that connects us). What is your charge, which is attracted to my charge, going to do? It will also move up.

Then I move my charge down, your charge follows it down. I move my charge to my left (your right), your charge follows it to your right. I move my charge to your left and your charge follows it to your left.

Now, if there is an astronomer that is situated at an equal distance from both you and me and watching these charges move, they will see my charge move, and then they will see your charge follow at a later time, in which the time difference is the distance we are from each other divided by $c$, the speed of any instantaneous interaction.

If I move my charge left-and-right 10 times per second, your charge will vibrate left-and-right 10 times per second. I am, effectively, a transmitting antenna and you are, effectively, a receiving antenna. That's what happens in antennae: electric charge sloshes back and forth along the conducting elements of the antenna.

If I were to move it back-and-forth 1 million times per second, you could tune it in with your AM radio. If I were to do that 100 million times per second, you could tune it in with your FM radio (except the station would be halfway between 99.9 and 100.1 MHz). If I were to do that 500 trillion times per second, you would see it as a blur of orange light.

Them's are E&M waves.

Now consider that, instead of you and I holding two electric charges, we're big as gods in space somewhere and we're both holding planets. Like masses attract each other. Now, if I do the same thing, perturb my mass by moving it back and forth, your planet will also want to follow and move in the same way. But for some observer, who is equidistant to us both, they will see the same delay in time between the cause (from me forcing my planet to move) and your effect (the disturbance of the planet you're holding). It will be the distance between us divided by the same $c$.

Them's are gravitational waves, essentially what were detected by LIGO.

Answer 3

How do electromagnetic waves exist?

Basically they exist as waves in the electromagnetic field: a changing electrical field induces a changing magnetic field which induces a changing electrical field and so on.

The changing electrical field is usually initiated by an alternating current in a wire, aka an antenna.

Answer 4

TL;DR
Please bear in mind that the magnetic field in a permanent magnet is not created by the acceleration of electrons but by the mutual alignment of the magnetic dipoles of electrons. During the time of Oerstedt, Faraday and Maxwell, it was not known that electrons are not only electric charges but also magnetic dipoles. This gradually led to the view that it is the acceleration of charged particles that partially converts the electric field of the particles into a magnetic field. It was until 1925 that the electron spin was discovered on the basis of atomic spectra, which led to the introduction of the spin quantum number beside the magnetic quantum number.

It is now possible to imagine a model in which the alignment of these magnetic dipoles in electron currents leads to electro—magnetic induction. Even if one cannot accept this idea, the existing theory must take into account the permanent existence of magnetic dipoles of the electrons in the calculation of the strength of the induced magnetic fields. Which the theory does not currently do. It is paradoxical that in the NIST database the magnetic moment of the electron has a fixed value (is a constant) just like the unit electric charge, but is not included in the consideration of electro—magnetic induction. This is an omission in physics since the times of Ehrenfels, Pauli and Dirac.
TL;DR

Phillip Stanev: What shrinking happens when an electromagnetic wave is created?

An EM wave is created when the surface electrons on a conductor are synchronously accelerated back and forth. In the process, the applied and periodically changing electric field of the wave generator creates an aligned magnetic field of the electrons from the individual magnetic dipoles of the electrons. This combination of two fields leaves the conductor in the form of quanta, which at the electron level are emissions of photons from excited states - more precisely the relaxation of the electrons. The shrinking of something is not necessary.

Phillip Stanev: How do electromagnetic waves exist?

EM waves exist thanks to the synchronized emission of polarized photons. The rising and falling intensity of the EM wave is caused by the periodic acceleration of the electrons in the conductor.

Light, or more broadly EM radiation in general, consists of photons from the relaxation of excited subatomic particles, where photons are indivisible units that exist exactly between emission and absorption by subatomic particles. Photons inherit the electric and magnetic field components from the emitting particles and self-induce them periodically during their forward motion (with c). In the case of antenna radiation, the polarized emission of the photons leads to the macroscopic electro—magnetic field of the wave.