Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relationship between electricity, magnetism, and relativity

  1. Dec 22, 2013 #1
    I know that magnetism can be explained as the relativistic interaction between say a current, and a moving charge. My question however is twofold, is magnetism nothing but electric forces when relativity is taken into account? If the answer is yes, does that make magnetism a sort of psuedo-force?
  2. jcsd
  3. Dec 22, 2013 #2


    User Avatar
    2017 Award

    Staff: Mentor

    As long as there are no magnetic monopoles, I think you can see it in this way, but you don't have to. That's probably a philosophic question.

    If there are magnetic monopoles (and we just did not find them so far), this is certainly not true.

  4. Dec 22, 2013 #3
  5. Dec 22, 2013 #4


    Staff: Mentor

    The electromagnetic force is a real force. You can split the real electromagnetic force into an electric component and a magnetic component. These are components of a real force, not independent forces in their own right. Thus they are not pseudo forces, but they are frame dependent.
  6. Dec 22, 2013 #5
    Thanks to everyone for responding. Just to clarify, this is not two separate forces, not one force and a psuedo force, but one force seen from two different frames of reference?
  7. Dec 22, 2013 #6


    User Avatar
    Science Advisor

    Yes. There is one and only one electromagnetic field, which is a covariant object, and the Lorentz force law can be written in terms of the electromagnetic field. In order to split the electromagnetic field and the Lorentz force law into electric and magnetic components you must choose an inertial frame and the split depends on the choice of frame. I can go into the mathematical details if you wish.
  8. Dec 22, 2013 #7
    I don't think relativity necessarily implies that you should see electric phenomena as more "fundamental" than magnetic phenomena. Rather, it seems to show that while an "electromagnetic" effect is definitely real, it doesn't make much sense to say that something is fundamentally "electric" or "magnetic" because that distinction is observer-dependent. So I would think that "electromagnetism" is the fundamental thing because even though not everyone agrees on whether something is "electric" or "magnetic," they can all agree that it's electromagnetic.

    Note that in the mathematical formulation of relativistic electromagnetics, there's no preference given to the electric field over the magnetic field. The more important object is the electromagnetic field tensor, which includes both the electric and magnetic field.
  9. Dec 22, 2013 #8


    Staff: Mentor

    Yes. Perhaps you recall doing inclined plane problems where you would break the force of gravity into a normal component and a sliding component. The one force is gravity, the normal and sliding forces are just components of that one force. How you split gravity up into normal and sliding forces depends on the angle of your "frame". It is a similar concept about how you split the EM force into E and M components.
  10. Dec 22, 2013 #9
    Here is an interesting perspective:


  11. Dec 22, 2013 #10


    User Avatar
    Science Advisor

    In a limited sense it does. There are two invariant (frame independent) quantities that can be formed from the electromagnetic field, namely E·B and E2 - B2. Depending on whether the latter quantity is positive or negative, you can say that (at a particular point) an electromagnetic field is "mostly electric" or "mostly magnetic".
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook