Talk:Relativistic electromagnetism

message: I really wish Id not started this page now as it is too complex a subject to illustrate without diagrams that I cant draw! Suggestions on how to get out of this mess will be most welcome!--Light current 17:51, 30 April 2006 (UTC)
thread_title:  Regrets (I have a few!) 

message: I really need someone to help on improving my very basic (and not ver satisfactory) text based diagrams in this article. Any offers? You will be rewarded with thanks!!--Light current 00:30, 23 October 2005 (UTC)
thread_title:  Request for help 

message: A click on the "What links here" toolbox link shows that this article is well off the beaten track in Wikipedia. This could be a reason to consider it for AfD.  DFH 21:18, 21 November 2006 (UTC)
replies: text: As the person who started it, I tend to agree with you. It was a mistake. But maybe some bits of it might be saved for use in other articles.--Light current 22:59, 21 November 2006 (UTC)

text: OTOH, maybe it could be pruned down to the bare min to explain the concept only. Other more knowledgable editors may then wish to expand it properly in the fullness of time!--Light current 23:18, 21 November 2006 (UTC)
thread_title:  Off the beaten track in Wikipedia 

message: Are there any sources that show conclusively that this had never been done before Purcell ?
The reason I ask this is that I attended a brilliant lecture course in 1968 (yes - that's after Purcell) on electromagnetism & relativity in which the lecturer derived all of Maxwell's equations from just two postulates: the invarance of c (velocity of light) and e (charge of an electron) through all the standard transformations of special relativity. I don't recall any reference having been made to Purcell's work, though it's feasible that the lecturer had made use of some of his material. My suspicion is that the ideas go back a lot earlier than 1963. (Incidentally, I'm currently reading Subtle is the Lord by Abraham Pais – it was that which led me to browse Wikipedia for articles related to electromagnetism & relativity and hence find this one.) DFH 20:27, 23 November 2006 (UTC)
replies: text: Thats what Daniel V Schroeder said in his paper on this subject.--Light current 23:41, 23 November 2006 (UTC)
replies: text: In my 1956 edition of the "Encyclopaedia Britannica" (before Purcell) article on "electricty" v8, p159, it is shown how the "magnetic force" between two parallel wires of current is really an electrostatic attraction due to special relativity.  However, the math only went as far to show qualitatively that special relativity demands: A/R = (i/c)^2 where A=attraction due to i, R = repulsion between free electrons.  Understanding the connection is basic to a good theoretical understanding of special relativity.  Feynman in his famous 1964 physics course derives this relationship in v2 13-6.  Ywaz (talk) 17:45, 17 July 2010 (UTC)
thread_title:  How do we know that Purcell was the first to take this approach to electromagnetism & relativity ? 

message: Here  is the source material for this article. See if YOU can rewrite it--Light current 03:29, 1 January 2007 (UTC)
thread_title:  Source material 

message: I have a more simple explanation on "why" magnetic forces appear. However, I'm not sure whether it's correct or not:
Consider two identical charged objects with each with mass m moving at the same velocity v at a distance 2x from each other perpendicular to the velocity. Since their time slows down when they move, they repel each other less (slower) than we expect them to. Therefore, we say there's a magnetic force counteracting the repulsive electric force.
Mathematically: The objects' masses, charges and distance are the same in their reference frame as in the observer's. Due to time dilation, however, the acceleration - and therefore also the electric forces - observed in the observer's frame (primed) will be different:
:F' = m \cdot a' = m \cdot \frac{d^2x}{d(t')^2} = m \cdot \frac{d^2x}{dt^2} \cdot (t/t')^2 = m \cdot a \cdot \sqrt{1 - (v/c)^2}^2 = F \left(1 - (v/c)^2\right)
The observer concludes that there must be a magnetic force accounting for the difference:
:F_m = F' - F = F \left(1 - (v/c)^2\right) - F = -(v/c)^2 F
Pellishau (talk) 13:04, 18 January 2008 (UTC)
thread_title:  Another explanation on "The origin of magnetic forces" 

message: This article relates to the education and training of electrical and electronics engineers. The references show that in the 1960s there was a move to introduce special relativity into the teaching of electromagnetic fields. The textbook by Corson & Lorrain was perhaps the apex of this movement. Since the symmetries of relativity are exactly the symmetries of the EM field, there is good reason to treat the subjects together. However, at most, this program of study provides some intuition on how magnetic and electric fields are observer-dependent. Full derivation of the Maxwell equations is an overstatement. Some investigation is necessary to find why this initiative did not take hold. Edits to the page from today could expand from Purcell to the other sources, and explore engineering and physics education for traces of the movement.Rgdboer (talk) 01:53, 19 November 2009 (UTC)
thread_title:  Education and training 

message: I very doubt about the contraction of lenght that is exposed to talk about the origin of magnetic force, as it is described in most book. Why? First because the case is the one of an infinite wire, thus with an open finite wire, because of conservation of charges, if the whole negative lign, for example, contracts, then the tips will be positive, if you apply it to a closed loop, as there is speed of electron everywhere, and no motion of protons, you will have charge accumulations on some parts, very strange that charges are uniformly reparted in one frame and concentrated in another, this could be because of simultaneity, but simultaneity and time dilation could work in the opposite because charges have a certain pace, regular, to cross the wire section, and accelerate at each angle of the wire. Secondly does this contration is in addition to the transformation of electric field of each charge, that is also an outcome of lenght contration, then does both effects accumulate? This needs a simulation, because books have been written a long time ago.Klinfran (talk) 07:57, 1 September 2011 (UTC)
replies: text: Do you say that accelecation can decrease the density? Why? Relativity says only about speed and only about contraction. Furthermore, it does not matter in which direction the charges move. So, acceleration, which only changes the direction, should not change anything. The neutral wire should become negatively charged when current is created in it. --Javalenok (talk) 12:43, 7 May 2013 (UTC)
thread_title:  Origin of magnetic force 

message: When we analize the interaction between two current carying conductors we first represent the magnetic induction "B" following the right hand rule. But, if you look back at the origine of this representation you can find that it comes from Faraday and the orientation of the magnetic induction "B" was based on the pattern of iron filings formed around a magnet bar which resemble to " field of lines" conneting the two poles. 
If you look closer the iron piling particles also can be considered tini magnets and their orientation will always be that their internal atomic currents that creates their magnetic field will be aligned with the internal atomic currents of the large permanent magnet bar  so they will tend to have the same direction ! The independent "lines" are formed because the adjacent particles of iron will align their internal currents with the stronger current of the large permanent magnet bar while between the "lines" there will be repulsion, also particle of iron  from a "line" will form chains with the top and the bottom particle so that their internal currents will be aligned too.  So now from the two parallel electric current situation we arrive to another two parallel electric current situation!  There is no such a thing like magnetic induction "B" that is tangent to the conductors or circle the conductor...its just an illusion ! Can you see the error?  — Preceding unsigned comment added by 71.185.132.57 (talk) 01:00, 30 June 2013 (UTC)
replies: text: This is where we discuss format and content of the article, not (parts of) the subject — see wp:talk page guidelines. Questions like this might be welcome at the wp:reference desk/science. Good luck. - DVdm (talk) 11:23, 1 July 2013 (UTC)
thread_title:  Something is wrong with the magnetic induction B 

message: If the magnetic field is really an electric filed doesn't this mean that the electromagnetic propagation of radiation is invalid? — Preceding unsigned comment added by 71.185.132.57 (talk • contribs) 03:01, 7 July 2013 (UTC)
replies: text: DVdm has already indicated to you in the previous thread that this is not the forum for this kind of discussion; this question does not relate to editing the article.  Also do not remove talk page content as you did, and rmeber to sign your posts on talk ages with for tildes: (~~~~). Please follow the suggestions. — Quondum 03:14, 7 July 2013 (UTC)
thread_title:  Electromagnetic theory of radiation is still valid? 

message: "Relativistic electromagnetism is a modern teaching strategy for developing electromagnetic field theory from Coulomb’s law and Lorentz transformations."  This statement would be more rigorously complete if it included conservation (invariance) of charge as a premise.  Should it be changed?  — Quondum 20:15, 29 July 2013 (UTC)
replies: text: Yes, it is a good idea to get away from Coulomb’s law when doing relativity, even if the references use the electrostatic principle as a backdrop. Suggestion to focus on charge conservation is worthy. However, the topic is fraught with difficulties though well motivated. Caution should be taken regarding electro-mechanics as a deductive system.Rgdboer (talk) 22:36, 29 July 2013 (UTC)

text: Conservation of charge is not so much the point as relative charge density. On the topic of relativistic electromagnetism, I have suggested that the eddy current brake is instructive. On March 5,  someone logged in just to delete that suggestion, making no other contribution. At its best, this article may help students begin to appreciate EM field theory.Rgdboer (talk) 22:33, 30 July 2013 (UTC)
thread_title:  Introductory sentence 

message: In a frame of reference where length contractions of positive and negative charges in a neutral wire are non-zero and identical, it would seem that any charge whose frame deviates from this frame would receive a magnetic force. If the positive charges of the metal ions in a typical conductor are stationary in the lab frame (or "lab-stationary"), this would mean that in the lab frame the magnetic field "loops" propagate (or "drift") at half the drift velocity as the electron current (or approximately half as per the relativistic velocity addition formula). Therefore, even for a current flowing at a constant rate in a lab-stationary wire, the magnetic field produced is non-lab-stationary!
If, in the lab frame, you apply magnetic Lorentz force q(v x B) on a lab-stationary charge q via a magnetic field B traveling at this "midway" velocity v between that of the metal ions and that of the electron current, what you will find is that the otherwise neutral wire in the lab frame will have electric fields lines pointing to it (due to the negativity of conducting charge) which are proportional to (v x B) which, ceteris paribus, is proportional to v^2, or alternatively B^2.
Therefore, the distance between electrons in a wire does not have to decrease due to their relative motion with respect to the observer in order to explain this electric field. The increase of the electric field can be explained just as well by saying that the magnetic field of the wire is stationary only in the frame of reference between that of the metal ions and that of the electrons, and therefore an electric field is produced from an otherwise neutral wire via the magnetic Lorentz force on lab-stationary charges.
In the case of completely negative electron beam, the magnetic field of the beam travels at the velocity of the beam, and any lab-stationary charge would be subject to a magnetic Lorentz force based on an electric field that points toward the beam. The induced electric field complements the electric field of the charged particles of the beam, which in this special case are electrons.siNkarma86—Expert Sectioneer of Wikipedia86 = 19+9+14 + karma = 19+9+14 + talk 08:55, 15 March 2014 (UTC)
thread_title:  Opposite charges with opposite motions and matching length contraction 

message: After almost 5 years with no support with references, the following sections have been removed today:
=== Uniform electric field — simple analysis===
Consider the very simple situation of a charged parallel-plate capacitor, whose electric field (in its rest frame) is uniform (neglecting edge effects) between the plates and zero outside.
To calculate the electric field of this charge distribution in a reference frame where it is in motion, suppose that the motion is in a direction parallel to the plates as shown in figure 1. The plates will then be shorter by a factor of:
: \sqrt{1 - v^2/c^2} 
than they are in their rest frame, but the distance between them will be the same. Since charge is independent of the frame in which it is measured, the total charge on each plate is also the same. So the charge per unit area on the plates is therefore larger than in the rest frame by a factor of:
: 1\over\sqrt{1 - v^2/c^2} 
The field between the plates is therefore stronger by this factor.
=== More rigorous analysis ===
Consider the electric field of a single, infinite plate of positive charge, moving parallel to itself. The field must be uniform both above and below the plate, since it is uniform in its rest frame. We also assume that knowing the field in one frame is sufficient for calculating it in the other frame.
The plate however could have a non zero component of electric field in the direction of motion as in Fig 2a. Even in this case, the field of the infinite plane of negative charge must be equal and opposite to that of the positive plate (as in Fig 2b), since the combination of plates is neutral and cannot therefore produce any net fields. When the plates are separated, the horizontal components still cancel, and the resultant is a uniform vertical field as shown in Fig 1.
If Gauss's law is applied to pillbox as shown in Fig 1, it can be shown that the magnitude of the electric field between the plates is given by:
: |E'|= {\sigma' \over\epsilon_0}\  
where the prime (') indicates the value measured in the frame in which the plates are moving.  \sigma represents the surface charge density of the positive plate.  Since the plates are contracted in length by the factor
: \sqrt{1 - v^2/c^2} 
then the surface charge density in the primed frame is related to the value in the rest frame of the plates by:
:\sigma'\ = {\sigma\over\sqrt{1 - v^2/c^2}} 
But the electric field in the rest frame has value σ / ε0 and the field points in the same direction on both of the frames, so
:E' = {E\over\sqrt{1 - v^2/c^2}}\  
The E field in the primed frame is therefore stronger than in the unprimed frame. If the direction of motion is perpendicular to the plates, length contraction of the plates does not occur, but the distance between them is reduced. This closer spacing however does not affect the strength of the electric field. So for motion parallel to the electric field E,
:E' = E \ 
In the general case where motion is in a diagonal direction relative to the field the field is merely a superposition of the perpendicular and parallel fields., each generated by a set of plates at right angles to each other as shown in Fig 3. Since both sets of plates are length contracted, the two components of the E field are
:E'_y = {E_y\over\sqrt{1 - v^2/c^2}} 
and
: E'_x = E_x \  
where the y subscript denotes perpendicular, and the x subscript, parallel.
These transformation equations only apply if the source of the field is at rest in the unprimed frame.
=== The field of a moving point charge ===
A very important application of the electric field transformation equations is to the field of a single point charge moving with constant velocity. In its rest frame, the electric field of a positive point charge has the same strength in all directions and points directly away from the charge. In some other reference frame the field will appear differently.
 
In applying the transformation equations to a nonuniform electric field, it is important to record not only the value of the field, but also at what point in space it has this value.
In the rest frame of the particle, the point charge can be imagined to be surrounded by a spherical shell which is also at rest. In our reference frame, however, both the particle and its sphere are moving. Length contraction therefore states that the sphere is deformed into an oblate spheroid, as shown in cross section in Fig 4.
 
Consider the value of the electric field at any point on the surface of the sphere. Let x and y be the components of the displacement (in the rest frame of the charge), from the charge to a point on the sphere, measured parallel and perpendicular to the direction of motion as shown in the figure. Because the field in the rest frame of the charge points directly away from the charge, its components are in the same ratio as the components of the displacement:
:{E_y \over E_x} = {y \over x}
In our reference frame, where the charge is moving, the displacement x' in the direction of motion is length-contracted:
:x' = x\sqrt{1 - v^2/c^2} 
The electric field at any point on the sphere points directly away from the charge. (b) In a reference frame where the charge and the sphere are moving to the right, the sphere is length-contracted but the vertical component of the field is stronger. These two effects combine to make the field again point directly away from the current location of the charge. (While the y component of the displacement is the same in both frames).
However, according to the above results, the y component of the field is enhanced by a similar factor:
:E'_y = {E_y\over\sqrt{1 - v^2/c^2}} 
whilst the x component of the field is the same in both frames. The ratio of the field components is therefore
:{E'_y \over E'_x} = {E_y \over E_x\sqrt{1 - v^2/c^2}} = {y' \over x'}
So, the field in the primed frame points directly away from the charge, just as in the unprimed frame.
A view of the electric field of a point charge moving at constant velocity is shown in figure 4. The faster the charge is moving, the more noticeable the enhancement of the perpendicular component of the field becomes. If the speed of the charge is much less than the speed of light, this enhancement is often negligible. But under certain circumstances, it is crucially important even at low velocities.
=== The origin of magnetic forces ===
In the simple model of events in a wire stretched out horizontally, a current can be represented by the evenly spaced positive charges, moving to the right, whilst an equal number of negative charges remain at rest. If the wire is electrostatically neutral, the distance between adjacent positive charges must be the same as the distance between adjacent negative charges.
Assume that in our 'lab frame' (Figure 5), we have a positive test charge, Q, outside the wire,  traveling parallel to the current, at the speed, v, which is equal to the speed of the moving charges in the wire. It should experience a magnetic force, which can be easily confirmed by experiment.
Inside 'test charge frame'(Fig. 6), the only possible force is the electrostatic force Fe = Q · E because, although the magnetic field is the same, the test charge is at rest and, therefore, cannot feel it. In this frame, the negative charge density has Lorentz-contracted with respect to what we had in lab frame because of the increased speed. This means that spacing between charges has reduced by the Lorentz factor with respect to the lab frame spacing, l:
: l_- = {l\sqrt{1-v^2/c^2}} 
Thus, positive charges have Lorentz-expanded (because their speed has dropped):
: l_+ = l / \sqrt{1-v^2/c^2} 
Both of these effects combine to give the wire a net negative charge in the test charge frame. Since the negatively charged wire exerts an attractive force on a positively charged particle, the test charge will therefore be attracted and will move toward the wire.
For v \ll c, we can concretely compute both,
:: dead link: http://www.cartage.org.lb/en/themes/sciences/physics/electromagnetism/Magnetostatics/MagneticField/Magnetism/Magnetism1/MagnetismConsequence/MagnetismConsequence.htm 
the magnetic force sensed in the lab frame
: F_m = {Q v I \over 2 \pi \epsilon _0 c^2 R} 
and electrostatic force, sensed in the test charge frame, where we first compute the charge density with respect to the lab frame length, l:
: \lambda = {q \over l}_+ - {q \over l}_- = {q \over l}\bigl(\sqrt{1-v^2/c^2} - 1/\sqrt{1-v^2/c^2}\bigr) \approx {q \over l}\Bigl(1-\frac12{v^2\over c^2} \,-\, 1 - \frac12{v^2\over c^2}\Bigr) = -{q \over l}{v^2\over c^2}
and, keeping in mind that current I = {q\over t} = q{v\over l}, resulting electrostatic force
: F_e = Q E = Q  {\lambda \over 2 \pi \epsilon _0 R} = {Q q v^2 \over 2 \pi \epsilon _0 c^2 R l} = {Q v I\over 2 \pi \epsilon _0 c^2 R } 
which comes out exactly equal to the magnetic force sensed in the lab frame, F_e = F_m.
The lesson is that observers in different frames of reference see the same phenomena but disagree on their reasons.
If the currents are in opposite directions, consider the charge moving to the left. No charges are now at rest in the reference frame of the test charge. The negative charges are moving with speed v in the test charge frame so their spacing is again:
: l_{(-)} = {l\sqrt{1-v^2/c^2}} 
The distance between positive charges is more difficult to calculate. The relative velocity should be less than 2v due to special relativity. For simplicity, assume it is 2v. The positive charge spacing contraction is then:
: {\sqrt{1-(2v/c)^2}} 
relative to its value in their rest frame. Now its value in their rest frame was found to be
: l_{(+)} = {l\over\sqrt{1-v^2/c^2}} 
So the final spacing of positive charges is:
: l_{(+)} = {l\over\sqrt{1-v^2/c^2}}{\sqrt{1-(2v/c)^2}} 
To determine whether l(+) or l(-) is larger we assume that v << c and use the binomial approximation that
:(1+x)^p \approxeq 1+px\;\text{ when }\; x \ll 1
After some algebraic calculation it is found that l(+) < l(-), and so the wire is positively charged in the frame of the test charge.
:: citation: A. French (1968), no page given
One may think that the picture, presented here, is artificial because electrons, which accelerated in fact, must condense in the lab frame, making the wire charged. Naturally, however, all electrons feel the same accelerating force and, therefore, identically to the Bell's spaceships, the distance between them does not change in the lab frame (i.e. expands in their proper moving frame). Rigid bodies, like trains, don't expand however in their proper frame, and, therefore, really contract, when observed from the stationary frame.
=== Calculating the magnetic field  ===
==== The Lorentz force law ====
A moving test charge near a wire carrying current will experience a magnetic force dependent on the velocity of the moving charges in the wire. If the current is flowing to the right, and a positive test charge is moving below the wire, then there is a force in a direction 90° counterclockwise from the direction of motion.
==== The magnetic field of a wire ====
Calculation of the magnitude of the force exerted by a current-carrying wire on a moving charge is equivalent to calculating the magnetic field produced by the wire. Consider again the situation shown in figures. The latter figure, showing the situation in the reference frame of the test charge, is reproduced in the figure. The positive charges in the wire, each with charge q, are at rest in this frame, while the negative charges, each with charge −q, are moving to the left with speed v.  The average distance between the negative charges in this frame is length-contracted to:
: \sqrt{1 - v^2/c^2} 
where is the distance between them in the lab frame. Similarly, the distance between the positive charges is not length-contracted:
: \sqrt{1 - v^2/c^2} 
Both of these effects give the wire a net negative charge in the test charge frame, so that it exerts an attractive force on the test charge.
Electromechanics and relativistic electromagnetism has several sources now listed. — Rgdboer (talk) 01:42, 28 November 2015 (UTC)
replies: text: Well, as I recall, the Feynmann lectures in physics has a marvelous derivation of the magnetic field as the Lorentz-contracted electric field.  However, it is far more subtle and nuanced than the above deleted section (e.g. you need to work out the cross-products, to get B pointing in the correct direction).  Thus, yes, deleting the above seems appropriate: its somehow oversimplifying some very important details. 67.198.37.16 (talk) 19:20, 21 February 2016 (UTC)
thread_title:  Old content 

message: ==== The Lorentz force law ====
A moving test charge near a wire carrying current will experience a magnetic force dependent on the velocity of the moving charges in the wire. If the current is flowing to the right, and a positive test charge is moving below the wire, then there is a force in a direction 90° counterclockwise from the direction of motion.
==== The magnetic field of a wire ====
Calculation of the magnitude of the force exerted by a current-carrying wire on a moving charge is equivalent to calculating the magnetic field produced by the wire. Consider again the situation shown in figures. The latter figure, showing the situation in the reference frame of the test charge, is reproduced in the figure. The positive charges in the wire, each with charge q, are at rest in this frame, while the negative charges, each with charge −q, are moving to the left with speed v.  The average distance between the negative charges in this frame is length-contracted to:
: \sqrt{1 - v^2/c^2} 
where is the distance between them in the lab frame. Similarly, the distance between the positive charges is not length-contracted:
: \sqrt{1 - v^2/c^2} 
Both of these effects give the wire a net negative charge in the test charge frame, so that it exerts an attractive force on the test charge.
</div>
Electromechanics and relativistic electromagnetism has several sources now listed. — Rgdboer (talk) 01:42, 28 November 2015 (UTC)
replies: text: Well, as I recall, the Feynmann lectures in physics has a marvelous derivation of the magnetic field as the Lorentz-contracted electric field.  However, it is far more subtle and nuanced than the above deleted section (e.g. you need to work out the cross-products, to get B pointing in the correct direction).  Thus, yes, deleting the above seems appropriate: its somehow oversimplifying some very important details. 67.198.37.16 (talk) 19:20, 21 February 2016 (UTC)
thread_title:  Calculating the magnetic field  

message: Calculation of the magnitude of the force exerted by a current-carrying wire on a moving charge is equivalent to calculating the magnetic field produced by the wire. Consider again the situation shown in figures. The latter figure, showing the situation in the reference frame of the test charge, is reproduced in the figure. The positive charges in the wire, each with charge q, are at rest in this frame, while the negative charges, each with charge −q, are moving to the left with speed v.  The average distance between the negative charges in this frame is length-contracted to:
: \sqrt{1 - v^2/c^2} 
where is the distance between them in the lab frame. Similarly, the distance between the positive charges is not length-contracted:
: \sqrt{1 - v^2/c^2} 
Both of these effects give the wire a net negative charge in the test charge frame, so that it exerts an attractive force on the test charge.
</div>
Electromechanics and relativistic electromagnetism has several sources now listed. — Rgdboer (talk) 01:42, 28 November 2015 (UTC)
replies: text: Well, as I recall, the Feynmann lectures in physics has a marvelous derivation of the magnetic field as the Lorentz-contracted electric field.  However, it is far more subtle and nuanced than the above deleted section (e.g. you need to work out the cross-products, to get B pointing in the correct direction).  Thus, yes, deleting the above seems appropriate: its somehow oversimplifying some very important details. 67.198.37.16 (talk) 19:20, 21 February 2016 (UTC)
thread_title:  The magnetic field of a wire 

message: This page should really include some diagrams to illustrate Purcell's example.  Someone promised to add diagrams "ASAP" in 2005 but it's been 12 years.  — Preceding unsigned comment added by 69.29.109.118 (talk) 22:38, 22 November 2017 (UTC)
replies: text: Electromagnetism is inherently a four-dimensional phenomena; the science would have arisen earlier if planar diagrams sufficed. The spacetime diagrams are a place to start, but are insufficient. Above note that some attempts have been contributed, but detailing relative charge density is challenging. There may be recent publications that attempt the visualization, but field theory (physics) generally uses notation instead of diagrams. — Rgdboer (talk) 03:24, 23 November 2017 (UTC)
thread_title:  Suggested Addition 

message: It is very nice to look at electricity and SR and try to get magnetism out of it. But the scheme is doomed, for 2 reasons. The first reason is Bohr-van Leeuwen theorem, that you cannot sustain a permanent magnetic field in a classical system, so no permanent magnets for you. Concrete example below. 
The other reason is that there are constraints on how you can convert fields into each other. For example, you can convert a pure E field into up to an equal mix of E and B field, where the equal mix happens when you boost all the way to the speed of light. There is thus no way to convert a pure E field into a pure B field, and vice versa. 
This is the reason why Feynman would sometimes flip-flop between asserting that magnetism is coming from SR, v.s. actually coming from QM. 
A concrete example of a situation where no amount of SR will help explain a pure magnetic field is in the case of Stoner's ferromagnetism. In that situation, you have the same number of electrons going in every direction, i.e. all SR contributions to magnetism thus has to exactly cancel out. The magnetic field that is sustained is created by an imbalance in the density of spin up v.s. spin down electrons. The true source of the ferromagnetism of iron, hence, is purely quantum in origin, though not obvious how and I explain next. 
Recent developments means that we cannot say that it is due to quantum simply because of spin. Spin half is not a consequence of quantum theory + SR, as is almost universally claimed; it is purely geometrical in origin, and we only start to see it in classical spacetime once you start using sensible mathematics of Geometric Algebra. (Or rather, our failure to see it earlier, is a consequence of stupid maths blocking the way.) The true origin is the fermion's satisfaction of Pauli's Exclusion Principle, reaching through Coulomb's electric interaction (to produce exchange interaction) to create the imbalance of spin densities. Fermion behaviour is purely quantum, so (that particular, but really also generally) magnetism is purely quantum in origin. 
It could be quantum + SR in origin, but it has to be quantum, more than SR. I do not know if we could have the spin imbalance without SR, but SR AND gauge invariance tends to strongly suggest minimal coupling, which is then guaranteed correct. Of course, it is a mouthful to say that magnetism is purely quantum + electricity + SR + gauge invariance. 
I am not saying we should scrap the entire article. Nice pictures and clear exposition (that Feynman also tried) should be kept. After all, it is important for engineers to know the relationship between moving charges and magnetism. Just remove the offending final sentence asserting that all magnetism is coming from SR, and add a big bright caveat somewhere that really it is a quantum effect, hopefully stating that it is impossible to get a purely B field from a boosting a purely E field, which should be sufficient to convince people. 119.74.52.36 (talk) 07:01, 17 October 2019 (UTC)
thread_title:  Impossibility of Magnetism from Electricity + SR 

message: The article has a section titled Redundancy, claiming that the word "relativistic" in the article title is redundant, since all electromagnetic theories are relativistic.
I think differently. Previous to relativity, electromegnetism was associated with Luminiferous aether, which is not relativistic. 
Also, I don't see in this section any evidence to back up what it claims. The quote by Einstein can be understood to mean just that relativity builds upon earlier theories, not that earlier theories were relativistic too. Udirock (talk) 11:07, 16 July 2022 (UTC)
thread_title:  Redundancy?