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Thread: Is magnetism less fundamental then electricity?

  1. #1 Is magnetism less fundamental then electricity? 
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    you first read this. They'll explain it beater then me.
    They also derive the magnetic force from Coulomb law.
    Relativistic electromagnetism - Wikipedia, the free encyclopedia

    Magnetism is just a relativistic effect of electrostatics. Magnetism, is just the electrostatic force in different reference frames. As the objects move, they are different time/length contractions. In the reference frame of a charge that is moving, there is a net charge because of these different time/length contractions. That corresponds to very small lengths for our every day speeds, but we detect an important force, because the electric force is huge inside ordinary mass.


    So what you think? Is magnetism a fundamental force or not? Is magnetism just electricity in a different reference frame?


    I think yes. I expect to see certain people disagreeing. I'm baffled by that.


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  3. #2  
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    So what you think? Is magnetism a fundamental force or not? Is magnetism just electricity in a different reference frame?
    Magnetic and electric fields are just two aspects of the same underlying entity, the electromagnetic field, described by the Faraday tensor in relativistic electrodynamics. You can't separate the two in relativistic physics, and neither one is more "fundamental" than the other. What "mix" of aspects a specific observer measures depends on his state of relative motion.

    So in short - it is the electromagnetic field that is fundamental, not its electric or magnetic components.


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  4. #3  
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    Quote Originally Posted by Markus Hanke View Post
    So what you think? Is magnetism a fundamental force or not? Is magnetism just electricity in a different reference frame?
    Magnetic and electric fields are just two aspects of the same underlying entity, the electromagnetic field, described by the Faraday tensor in relativistic electrodynamics. You can't separate the two in relativistic physics, and neither one is more "fundamental" than the other. What "mix" of aspects a specific observer measures depends on his state of relative motion.

    So in short - it is the electromagnetic field that is fundamental, not its electric or magnetic components.
    Markus I understand what you say, in terms of the mathematics that describes EM. But QI's question remains a good one, it seems to me. I too have been shown that magnetism arises naturally from the effects of relativity on moving electric charge.

    Does the symmetrical relationship suggested by what you say imply that one can equally derive electrostatic force from applying relativity to magnetism, in some way?
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  5. #4  
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    Quote Originally Posted by exchemist View Post
    I too have been shown that magnetism arises naturally from the effects of relativity on moving electric charge.
    And that is absolutely correct, I didn't try to imply anything else.

    Does the symmetrical relationship suggested by what you say imply that one can equally derive electrostatic force from applying relativity to magnetism, in some way?
    No, because the Faraday 2-form F is closed, whereas its dual ( the Maxwell 2-form *F ) is not, in the presence of sources. What this means is that there is no such thing as magnetic charges ( we'll ignore GUTs here ), but on the other hand electric charges are relativistic invariants. You can not "transform away" an electric charge by going into another frame of reference, hence if one observer sees an electric field, all observers must necessarily see an electric field - the same is not true in the case of magnetism. All that changes between observers is the "mix" of E and B fields, but not the underlying 2-form F, which is a covariant tensor.

    This is what I meant to say - both E and B fields are observer-dependent and are necessarily symmetrical between one another, but the Faraday tensor F which combines the two is a covariant geometric object, and hence the same for all observers. That makes it more fundamental than either E or B fields, which is why it is the entity that is used in relativistic electrodynamics, as opposed to E and B fields.

    It should be noted here also that, unlike is the case for example for gravity, the Faraday 2-form itself arises from an even more fundamental entity, the electromagnetic 4-potential A, through exterior differentiation :

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  6. #5  
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    Quote Originally Posted by exchemist View Post
    Does the symmetrical relationship suggested by what you say imply that one can equally derive electrostatic force from applying relativity to magnetism, in some way?
    Yea, if you assume Magnetism is real , you can mathematically deduce electromagnetism.

    Quote Originally Posted by Markus Hanke View Post
    So what you think? Is magnetism a fundamental force or not? Is magnetism just electricity in a different reference frame?
    Magnetic and electric fields are just two aspects of the same underlying entity, the electromagnetic field, described by the Faraday tensor in relativistic electrodynamics. You can't separate the two in relativistic physics, and neither one is more "fundamental" than the other. What "mix" of aspects a specific observer measures depends on his state of relative motion.

    So in short - it is the electromagnetic field that is fundamental, not its electric or magnetic components.
    I expected you'll say something like that. Haha :P

    And i still messed up the question of the poll. I was expecting you'll say yes, its as fundamentall as electricity. Now it doesn't measure what i was expecting. Oh well
    Can you delete the poll?

    On the topic. What happened to reductionism? It doesn't sound very reductionist to me. If electromagnetism is fundamental, then why you can deduce half of it from the other half? There is too much redundancy

    Quote Originally Posted by exchemist View Post
    I understand what you say, in terms of the mathematics that describes EM. But QI's question remains a good one,
    This question exposes philosophical differences.
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    Quote Originally Posted by Quantum immortal View Post
    If electromagnetism is fundamental, then why you can deduce half of it from the other half?
    You can't. You can eliminate magnetic fields through a change in reference frames, but the same is not true for electric fields. The geometry of these is different, they are not symmetric. That is why you need both the Faraday 2-form and its dual to fully specify the laws of electromagnetism.

    Can you delete the poll?
    I'll have to check on this, I can't immediately find a way to delete it.
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  8. #7  
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Quantum immortal View Post
    If electromagnetism is fundamental, then why you can deduce half of it from the other half?
    You can't. You can eliminate magnetic fields through a change in reference frames, but the same is not true for electric fields. The geometry of these is different, they are not symmetric. That is why you need both the Faraday 2-form and its dual to fully specify the laws of electromagnetism.

    .
    I suppose someone might interpret this as meaning that electric charge is more "fundamental", in some sense, than magnetism. Though I'm not sure a great deal is to be gained by arguing about such a thing.

    For me, what this exchange flags up is actually something else: my personal queasiness about treating any mathematical formalism as a fundamental reality. I've always tended to the - possibly naive - view that the mathematics is a subservient, quantifying description of an underlying physical concept. If I can't visualise the concept I have difficulty taking the maths as physically real. But then, I am not a natural mathematician. There do seem to be physicists for whom the mathematics is itself the physical concept, or who at any rate don't see any distinction.
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  9. #8  
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Quantum immortal View Post
    If electromagnetism is fundamental, then why you can deduce half of it from the other half?
    You can't. [...]
    Here it deduces the magnetic force from relativity and coulomb law. How you interpret it?
    Relativistic electromagnetism - Wikipedia, the free encyclopedia


    Quote Originally Posted by exchemist View Post
    I suppose someone might interpret this as meaning that electric charge is more "fundamental", in some sense, than magnetism. Though I'm not sure a great deal is to be gained by arguing about such a thing.

    For me, what this exchange flags up is actually something else: my personal queasiness about treating any mathematical formalism as a fundamental reality. I've always tended to the - possibly naive - view that the mathematics is a subservient, quantifying description of an underlying physical concept. If I can't visualise the concept I have difficulty taking the maths as physically real. But then, I am not a natural mathematician. There do seem to be physicists for whom the mathematics is itself the physical concept, or who at any rate don't see any distinction.
    Have a look at the wikipedia article...

    I sure agree with you...

    One of those Physicists you are describing is Markus. Not meant to be offensive or anything...
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  10. #9  
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    Recently I found this amazing video. What a beautiful way to ilustrate relativity effects and magnetism. I never even though of it in such way. I always prefered calculation to ilustration.
    http://www.youtube.com/watch?v=1TKSfAkWWN0
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  11. #10  
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    Quote Originally Posted by Quantum immortal View Post
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Quantum immortal View Post
    If electromagnetism is fundamental, then why you can deduce half of it from the other half?
    You can't. [...]
    Here it deduces the magnetic force from relativity and coulomb law. How you interpret it?
    Relativistic electromagnetism - Wikipedia, the free encyclopedia


    Quote Originally Posted by exchemist View Post
    I suppose someone might interpret this as meaning that electric charge is more "fundamental", in some sense, than magnetism. Though I'm not sure a great deal is to be gained by arguing about such a thing.

    For me, what this exchange flags up is actually something else: my personal queasiness about treating any mathematical formalism as a fundamental reality. I've always tended to the - possibly naive - view that the mathematics is a subservient, quantifying description of an underlying physical concept. If I can't visualise the concept I have difficulty taking the maths as physically real. But then, I am not a natural mathematician. There do seem to be physicists for whom the mathematics is itself the physical concept, or who at any rate don't see any distinction.



    Have a look at the wikipedia article...

    I sure agree with you...

    One of those Physicists you are describing is Markus. Not meant to be offensive or anything...
    Well yes, though the article cautiously describes it as a simplified teaching strategy, I notice. And yes I know Markus is one of those physicists, but I respect his knowledge and have been careful to express myself neutrally, as I would hate to be seen as disparaging him.

    I dimly recall this argument - about the "reality" of what seem to be purely mathematical descriptions of the world - from Oxford. 40 years on, I am no longer sure whether it is a real philosophical distinction, or whether it may just be a matter of the cast of mind of the scientist concerned. Seeing as science is the business of constructing explanatory and predictive models of reality, one could make the case that a purely mathematical model is no less "real" than any other kind. It just makes me a bit……... queasy.
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  12. #11  
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    Quote Originally Posted by Quantum immortal View Post
    Here it deduces the magnetic force from relativity and coulomb law. How you interpret it?
    Relativistic electromagnetism - Wikipedia, the free encyclopedia
    I interpret it in precisely the way I was explaining it before - the presence of a magnetic field allows you to deduce the presence of an electric charge at some state of relative motion, and all other observers will agree ( charge is invariant ). However, the reverse is not true - the absence of a magnetic field in some frame does not mean there is no electric charge present, or alternatively, the presence of an electric field does not allow you to deduce the presence of magnetic fields, because both E and B fields are observer-dependent. The upshot is that you need relations for both fields to uniquely specify the laws of electromagnetism - as I have stated earlier. Magnetism alone isn't enough, but then neither is the electric field.

    If I can't visualise the concept I have difficulty taking the maths as physically real.
    Consider electromagnetism as formulated in the language of differential forms, and the associated plain text meanings :



    "No magnetic tubes ever end" = "Magnetic field lines form closed loops" = "There are no magnetic charges"



    "The number of electric tubes that end in an elementary volume is equal to the amount of charge enclosed in that volume"

    Maybe I have some special insight that others don't have ( which I sincerely doubt ! ), but to me the meaning of these expressions is so visual and intuitive that I really don't think one could formulate them any more clearly, or elegantly. Or am I missing something ?
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  13. #12  
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    Quote Originally Posted by Gere View Post
    Recently I found this amazing video. What a beautiful way to ilustrate relativity effects and magnetism. I never even though of it in such way. I always prefered calculation to ilustration.
    How Special Relativity Makes Magnets Work - YouTube
    Yes, it is a good illustration why in relativity one needs to leave behind the old Newtonian notions of forces and interactions, and instead consider the geometry of the problem. Once one realises that total charge is an invariant for all observers, and that the underlying geometric object is neither the electric nor the magnetic field but rather the Faraday 2-form F, the whole things ceases to be a mystery

    or who at any rate don't see any distinction.
    Actually, I do see a distinction. Mathematics to me is a language that describes things, but it isn't identical to the things themselves; that doesn't make the things it describes any less real though.
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  14. #13  
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    Quote Originally Posted by Markus Hanke View Post
    Yes, it is a good illustration why in relativity one needs to leave behind the old Newtonian notions of forces and interactions, and instead consider the geometry of the problem. Once one realises that total charge is an invariant for all observers, and that the underlying geometric object is neither the electric nor the magnetic field but rather the Faraday 2-form F, the whole things ceases to be a mystery
    Well said, as always, Markus. I think a lot of students fixate too soon on the differences, when perhaps they should first consider the invariants. Once they get in the habit of focusing on those, the rest tends to fall into place. It preps them nicely for relativity, as you point out.
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    Sometimes I come into these threads and thoughtfully stroke my chin and nod so that anyone who happens to be reading over my shoulder will think I'm not actually a bumbling half-wit.
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    "Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us." -Calvin
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  16. #15  
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    I should remark here that I am a very visual person myself - I taught myself the theory of differential forms precisely because I wanted to understand electromagnetism in a more visual way. It's a very powerful formalism because it is inherently covariant - both the exterior derivative and the hodge star are invariant under changes in coordinate basis ( though the hodge dual depends explicitly on the metric ). Hence, it is of great importance to the theory of gravitation.
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  17. #16  
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Quantum immortal View Post
    Here it deduces the magnetic force from relativity and coulomb law. How you interpret it?
    Relativistic electromagnetism - Wikipedia, the free encyclopedia
    I interpret it in precisely the way I was explaining it before - the presence of a magnetic field allows you to deduce the presence of an electric charge at some state of relative motion, and all other observers will agree ( charge is invariant ). However, the reverse is not true - the absence of a magnetic field in some frame does not mean there is no electric charge present, or alternatively, the presence of an electric field does not allow you to deduce the presence of magnetic fields, because both E and B fields are observer-dependent. The upshot is that you need relations for both fields to uniquely specify the laws of electromagnetism - as I have stated earlier. Magnetism alone isn't enough, but then neither is the electric field.

    If I can't visualise the concept I have difficulty taking the maths as physically real.
    Consider electromagnetism as formulated in the language of differential forms, and the associated plain text meanings :



    "No magnetic tubes ever end" = "Magnetic field lines form closed loops" = "There are no magnetic charges"



    "The number of electric tubes that end in an elementary volume is equal to the amount of charge enclosed in that volume"

    Maybe I have some special insight that others don't have ( which I sincerely doubt ! ), but to me the meaning of these expressions is so visual and intuitive that I really don't think one could formulate them any more clearly, or elegantly. Or am I missing something ?
    Nicely done. Now I have a picture. I suppose once upon a time, when I used the maths of QM every day, I was able to form a picture direct from the maths like that, but even then supporting text and/or diagrams were a big help. Maths is often a shorthand for a physical picture, I realise. Perhaps it always is, but if the subject is not one's speciality, that picture may not be obvious without some explanatory words - which in this instance you have just provided.

    But Markus, you must admit, not everyone has integrals as their signature. This strikes me as the equivalent of the putting at the foot of one's messages the family motto of that (fictitious) Scots family which reads: "I'll thank ye not to fuck aboot wi' me."
    Last edited by exchemist; March 12th, 2014 at 01:40 PM.
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  18. #17  
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    Quote Originally Posted by exchemist View Post
    But Markus, you must admit, not everyone has integrals as their signature.
    Ha ha, yes, I admit
    There is great beauty and meaning in what I have in my signature - it's the underlying principle that makes GR work the way it does, that provides the link between matter, energy, space-time, geometry and topology. It is one of these rare gems that few people are aware of, even among physicists and mathematicians. I couldn't resist putting it as my signature
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    Just quick question that just came to my mind. Maybe I`m tripping. Since charge is lorentz scalar why it doesn`t have Casimir operator in Lorentz/Poincare group?
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    Magnetism is the relativistic correction for the speed-of-light action of the EM force. That's why it acts at right angles and against the electric force.

    ETA: @Markus, from the EE's POV remember it's B, not E. And it's divergent. (Errr, well, either it is or H is, I always forget which.)
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  21. #20  
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    Quote Originally Posted by Markus Hanke View Post
    I taught myself the theory of differential forms
    Well done! And I suppose you had no help?
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    Quote Originally Posted by Flick Montana View Post
    Sometimes I come into these threads and thoughtfully stroke my chin and nod so that anyone who happens to be reading over my shoulder will think I'm not actually a bumbling half-wit.
    *nods thoughtfully*
    ei incumbit probatio qui dicit, non qui negat
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    Quote Originally Posted by Guitarist View Post
    Well done! And I suppose you had no help?
    Oh, I had plenty of help, both online and in real life; I haven't forgotten your own contribution ( for which I am grateful ) either, you have pointed me into the right direction. However, I must admit though that at that time the pure and abstract maths did little for me in terms of understanding and application of forms to physics ( which is, after all, my main focus ). What did it for me in the end was the excellent visual presentation in Misner/Thorne/Wheeler "Gravitation" - a text that has become the gold standard in gravitational physics for a very good reason. Highly recommended !
    Last edited by Markus Hanke; March 13th, 2014 at 05:35 AM.
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    Quote Originally Posted by Gere View Post
    Since charge is lorentz scalar why it doesn`t have Casimir operator in Lorentz/Poincare group?
    I'm afraid I am not well enough versed in group theory to answer this. Anyone else ?
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  25. #24  
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    Not me, I remember asking my physical chemistry tutor for a tutorial on group theory as an undergrad (it is used in vibrational spectroscopy), he looked me in the eye and said "At your level that's inorganic chemistry. Go and bother Dr <inorganic chem tutor>." The result of this is I know how to use it in this application but the maths behind it is a bit sketchy for me...
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    Well seems my question wasn`t valid after all. The point I was aiming at was this.

    Since infinitesimal generators of Lorentz group are these



    and Poincare group is semidirect product of Lorentz group and translations (semidirect because they do not commute with each other) whose generators are momenta



    one can construct Casimir operators in this group/algebra which commute with each other operator from Poincare group. These are squared momentum whose eigenvalue can be computed easily as



    and so called Pauli-Lublanski operator/vector (its square is Casimir)



    whose eigenvalue is



    where s is spin (for free particle). One can say that conservation of spin/angular momentum and mass are consequences of this but imho that would be overestimating group theory. From this hovewer it deduce that spin and mass are good labels for asymptotic field states (free particles) so my idea was that charge is good label too as it is Lorentz scalar why shouldn`t it have Casimir operator within relevant symmetry algebra.

    I think however that this has something to do with C-symmetry which is not part of Poincare group as well as P and T which are not in Poincare group as well.
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    The voltage is the electric field. It is pure potential until the positive and negative potentials get into a chemical circumstance where the electrons will get excited and moved (with the speed of light at that) -quick little guys. When the potential is in a circuit, there are resistances and this is how we use ohm's law to understand this and harness these energies. When the electrons flow like this the conductor of the flow will give off a magnetic field. The magnetic field is caused by current flow (the chemical reactions of the electrons moving fast. The magnetic field is always 90 degrees from the electric field (Transverse or perpendicular) -

    Note though that modern science and space telescope observances tell us that the chemical portion of the Universe may be only around 5% of the totality of existence
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