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 ?


closed as unclear what you're asking by ACuriousMind, user36790, CuriousOne, user10851, John Rennie Mar 7 '16 at 7:03

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    $\begingroup$ the nature of things is more philosophy than physics. What kind of answer do you expect ? what other theory than the classical EM theory ? I suggest you clarify what you seek for. $\endgroup$ – Fabrice NEYRET Mar 2 '16 at 21:16
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    $\begingroup$ "Is there any suggested theory?" really? what about Maxwell? what about physics in general? $\endgroup$ – AccidentalFourierTransform Mar 2 '16 at 21:22
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    $\begingroup$ There is nothing "hidden" about magnetic forces. Take two magnets in your hands. Can you feel the force? What's hidden about that? The complete classical theory of what you are feeling has been published in 1873 by Maxwell, the quantum field version was developed in the 1940s-1960 by Dirac, Feynman and others. One can pretty much state that all of this is about as well understood as it ever will be. $\endgroup$ – CuriousOne Mar 2 '16 at 21:38
  • $\begingroup$ I read in Beiser 'Modern physics' that a potential picture of the origin of the magnetic field was coming from relativistic effects due to the fact that electrons move to speed close enough to light speed. Somehow we see magnetism as the effect of electric field from a fix observer. $\endgroup$ – Ronan Tarik Drevon Mar 2 '16 at 23:49
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    $\begingroup$ Any magnetic field is as strong as the involved particles with their magnetic dipole moments. Normally their orientations are equally distributed in space. Under acceleration the magnetic dipole moments get aligned and produce a common magnetic field. More see here $\endgroup$ – HolgerFiedler Mar 3 '16 at 11:35

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.


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