There are lots of (stupid) youtubes re the (stupid) STR cause of the mmf near a wire. They all briefly & quietly assert or infer that the electron spacings stay the same, ie before & after the current is switched on. A disaster for STR. I called it STRIKE-1, but that makes it look as if u are allowed a number of strikes – NO – one strike & the STR cause of mmf is out, that game is over.
And, if u think about it, STR is also out, that makes it two lost games, each has been struck out with the one pitch, its a case of killing two birds with one stone. When i say STR is also out (falsified), i mean the length contraction part of STR (not the time dilation part).
Aetherists believe in length contraction due to velocity, the velocity of the aetherwind (not due to some stupid STR relative velocity). In the case of a wire conducting an electric current, the aetherwind or length contraction are not needed to explain anything (eg electric current, emf, mmf etc). However, the aetherwind will of course affect the electric fields etc, eg the aetherwind can (we know) slow electricity (if a headwind), or can fast electricity (if a tailwind)(as shown by DeWitte)(& Torr & Kolen).
The cause of mmf near a wire remains a mystery. Indeed emf remains a mystery. But electricity is no longer a mystery, it is due to (my) elektons (photons that hug the wire).
So, lets look again at what Purcell wrote….
In the lab frame of Fig. 5.22(a), with spatial coordinates x, y, z, there is a line of positive charges, at rest and extending to infinity in both directions. We shall call them ions for short. Indeed, they might represent the copper ions that constitute the solid substance of a copper wire. There is also a line of negative charges that we shall call electrons. These are all moving to the right with speed v0. In a real wire the electrons would be intermingled with the ions; we’ve separated them in the diagram for clarity. The linear density of positive charge is λ0.
It happens that the linear density of negative charge along the line of electrons is exactly equal in magnitude.
That is, any given length of “wire” contains at a given instant the same number of electrons and protons.
[9] [9 It doesn’t have to, but that equality can always be established, if we choose, by adjusting the number of electrons per unit length. In our idealized setup, we assume this has been done.]
The net charge on the wire is zero. Gauss’s law tells us there can be no flux from a cylinder that contains no charge, so the electric field must be zero everywhere outside the wire. A test charge q at rest near this wire experiences no force whatsoever.
How can Purcell & Co justify [9]? They can't. A disaster for the STR cause of mmf, & a disaster for STR, both killed with one stone.