In the question: Special relativity and electromagnetism, the question was in reference to a Veritasium video where he describes how magnetic fields are caused by special relativity. He describes how if a current is flowing through a wire, and a positively charged cat is moving at the same speed as the negative charge, then from its reference frame, the positive charge contracts in an otherwise neutral wire and causes a net positive charge, therefore repelling the cat.
The questioner asks why the same effects relating to the length contraction don't occur when electrons are flowing and everything else is stationary.
Here is the part that confused me: The top answer replied:
If each pair of neighboring electrons had been separated by a little rigid rod, the electrons would have to come closer together when the current starts flowing. But there are no such rods, and the row of electrons is free to stretch when the current begins to flow, and this stretching is exactly canceled out by the length contraction, such that in the lab it looks like the distance between the moving electrons is the same as the distance between the stationary protons.
What? Why would electrons have to come closer together when they start flowing (when not in reference to the relativistic length contraction)? That would make one side of the wire charged? It's not possible for all of the electrons to compress in a closed loop without bunching up in packs!
Why do the electrons stretch when they start flowing? Would that not make one side of the wire charged? Once again, it's not possible for all the electrons in a closed loop to stretch without bunching up at some point.
What I think I understand from this picture of relativistic charge distribution is that while the positive charges on the squirrel (or cat's) side of the wire are now contracted since the electrons are stationary relative to the squirrel, on the opposing side, the electrons are now moving at twice the speed of the positive charge in the opposing direction, resulting in ... a net negative charge, right? But if the positive charge is contracting due to moving at the speed of 1x, and the electrons are contracting due to moving at the speed of 2x, (with x being the speed of squirrel), then are we not back to where we started with a neutral wire if we subtract 1x from each??? (Am I assuming that length contraction is linear? Did I just change reference frames? Is it both?)
And lastly, assuming that the electrons do stretch for some reason when current flows through them, isn't it incredibly convenient that "this stretching is exactly canceled out by the length contraction"? What is the basis of this claim?
I might be misunderstanding everything here. I really appreciate any answers.