electromagnetism - What is the nature of the magnetic fields?

In this question, I am hoping to find out if there is an explanation to the magnetic hidden forces. In other words, what causes these fields?

Is there any suggested theory, or any confirmed ones ?

What is the nature of this force ?

Answer

To see, what the reason for a phenomenon is, sometimes we have to read the historical facts backwards. Maxwell's explanation about the magnetic field as the result of moving charges was developed in the 1860th. Maxwell used Ampère's circuital law, discovered by André-Marie Ampère in 1823. According to Wikipedia, the law "relates the integrated magnetic field around a closed loop to the electric current passing through the loop."

The reason for the induction of a magnetic field couldn't be explained in this years. Only in 1907 it was predicted that electrons have a magnetic dipole moments: "The idea of elementary magnets is due to Walter Ritz (1907) and Pierre Weiss.".

On what for a phenomenon this prediction was based? It was based on the observation, that a charged body under rotation induces a magnetic field. Wikipedia about the electrons magnetic dipole moment: "From classical electrodynamics, a rotating electrically charged body creates a magnetic dipole with magnetic poles of equal magnitude but opposite polarity." About the magnetic dipole moment Wikipedia says: "... the electron magnetic dipole moment ... is the magnetic moment of an electron caused by its intrinsic properties of spin and electric charge." (The statement about electric charge is a little bit misleading because a neutron has a magnetic dipole moment too).

What we have to underline is the known now fact that the intrinsic spin and the (also intrinsic) magnetic dipole moment are "two sides of a coin". The spin axis and the north-south direction of the magnetic dipole moment of an electron are always parallel AND pointing always in the same directions. To label the directions is arbitrary (clockwise or anticlockwise, north-south or south-north), but once labeled, the relation is for all electrons the same. And all positrons have the "anti"-relation of intrinsic spin and magnetic dipole moment.

It is this relation between intrinsic spin and magnetic dipole moment that causes Lorentz force and Ampere's law. About the deflection of electrons in a non-parallel to the moving electrons magnetic field see my explanations here: "The magnetic dipole moment of a moving electron will be aligned by an external magnetic field. It should be recalled, that the magnetic dipole moment and the axis of intrinsic spin of an electron are parallel. And it should be recalled, that the (really performed) Einstein-de-Haas experiment has shown, that the intrinsic spin has the properties of a momentum. Furthermore, it is known from classical mechanics, that an external force, that tries to change the direction of a spinning gyroscope, causes that the axis evades perpendicular to the direction of this force. The analogy is obvious. That is the reason, why in a magnetic field the electron moves in a spiral path and comes to rest in the center of the spiral. ... Any deflection, caused by the alignment of the magnetic moment of the rotating electron, is also an acceleration process. Furthermore, the electron's acceleration is associated with the emission of photons. This, the electron's photon emission in a magnetic field, causes a deceleration of the electron's velocity. This time the photon emission causes the electron’s magnetic dipole moment axis to falls back from its alignment to the magnetic field."

All discoveries about electric and magnetic induction were made with accelerated electrons (or non-static to the charges magnetic fields). Even the repealing of attraction of two parallel wires was developed with varying electric currents. Coils are the devices to induce magnetic fields, in the coil the electrons flow in loops and by this naturally are accelerated (a circular motion is always an acceleration). To say it shorter, any induced magnetic field from the flow of electrons is due to the alignment of the electrons magnetic dipole moments during their accelerations.

The answer will be not complete without electromagnetic radiation. It was observed that a periodically changed electric current (in an antenna rod) lead not only to a induced time varying magnetic field but - if the power of the antenna generator is high enough - to a remarkable electromagnetic radiation. Accelerating electrons, this electrons emitting a part of their energy as electromagnetic radiation. It was observed that this radiation has an electric and a magnetic field component. In the near field of the antenna the electric field bears (induces) a magnetic field. The magnetic field induces an electric field and so on and this happens with a propagation velocity of - naturally - the speed of light. Electromagnetic radiation is caused by electrons (or other particles) but once emitted the periodical occurring electric and magnetic fields are self-propagating and not more related to any particle.