I watched this Minute Physics video on how current produces a magnetic force on a moving charge because of relativity. In the video (timestamp is around 2 minutes), he explains that when the charge is moving, in the inertial reference frame of the charge, the protons are contracted and thus increase in density, repelling the charge via electric field. And when the charge does not move, there is no force because the charge densities remain the same, keeping the wire neutral.
However, my question is: when the charge is not moving, why don't the electrons contract in the reference frame of the charge?
I've seen some attempts at explaining this in the comments section, but it seems that none of those explanations were confirmed as being the correct one.
The different explanations were:
- In the case with the stationary charge, the electrons are being contracted, but not the space between the electrons, so the density remains the same. However, in the moving charge case, the space the protons are in is also moving, hence, the space between the proton also contracts.
- Or: there is actually length contraction of the space between the electrons, but, since these electrons can move freely in the conducting wire, they repel each other, and the end result is no change in charge density. Meanwhile, the protons in the frame of the moving charge cannot move freely in the wire, so their density increases when subjected to length contraction.
Which one of these explanations is right? Or is there another explanation altogether? By the way, I am a high school student learning physics, so if possible, please don't use too much advanced math!
