Is it possible for a magnet to have only one pole? Or greater than two?
Magnetic monopoles exist according to some theories, but none have ever been found.
How the **** do they work?
I like the way my old advisor put it: “Magnetic monopoles certainly exist. But the number of them in the Universe might be very small, possibly zero”.
That is to say, the laws of physics allow for the existence of monopoles, and current theories predict that under the right conditions, one (well, two) could be made. But the right conditions are very extreme, and it’s likely that they have never occurred, or that if they have, it was before inflation scattered them extremely far and wide.
Oh, and the linked thread (which I didn’t see at the time, or I would have replied there) states that there is no observational evidence for monopoles. This isn’t quite correct: On February 14, 1982, an experiment set up by Stanford did in fact detect something which certainly seemed to have been a monopole. The detection has never been repeated, though, and nobody’s really sure what caused it, whether it was a genuine monopole that we were just lucky enough to detect, a weird quirky glitch in the apparatus that nobody’s yet explained, or an extremely elaborate hoax to which nobody has yet confessed. So it’s not strong evidence, but it’s still evidence.
You can certainly have more than two poles on a magnet. Stepper motor cores can have hundreds.
True, but those are each still one of the familiar two kinds of poles. It’s not like you introduce an east pole and a west pole, or anything.
If I allowed a monopole to stick to a conventional magnet, what would happen? Diminished field strength at that pole, but not the other one?
Probably.
Incidentally, this is part of the reason that you can’t get permanent electric dipoles, like you can with magnets: Free charges would accumulate at the poles and neutralize it.
Electrets are pretty close. Some molecules are permanent dipoles (like water).
True, I should have said “hard to get”, not “can’t get”. And I was leaving implicit that I meant on a macroscopic scale.
The Valentine’s day monopole was certainly not a hoax. The PI is a very highly respected physicist. They saw a flux jump in a superconducting loop. This is exactly what would happen if a monopole traversed the loop. Decades earlier, P.A.M. Dirac had predicted the existence of monopoles with a specific charge. The amplitude of the 1982 event was just what was expected for a “Dirac” monopole.
There are many things that can cause flux jumps in superconducting loops. The event was tantalizing, especially since the amplitude was the right size, but it was always a leap of faith to accept this single event as a monopole.
An earlier monopole “discovery” was made by Buford Price in a cosmic ray experiment. Luis Alvarez gave a pretty convincing argument that the event could be more easily explained in a conventional way.
If you have a classroom bar magnet, you can use a small Neo magnet to change its polarity.
Re-magnetize it so it has N poles at the two ends, and a big fuzzy S pole in the center.
Quoth JWT Kottekoe:
I didn’t say it was (or even might have been) a hoax by the PI. But for any given experiment (even a relatively simple one like this), there are always going to be many people involved in it, and many more who aren’t directly involved in it but who would have potentially had access to it. If it were a hoax, it could have been a grad student in the next lab over, whose keys open both lab rooms, for instance. Or an undergrad who talked the janitor into opening the door for them, or whatever.
And while there are many things that could cause a flux jump in a superconducting loop, are there any that could have caused a one-way jump, that didn’t jump back down?
Quoth wbeaty:
This is certainly possible (it’s called a linear quadrupole), but it’d probably be on the difficult side, in practice (and probably easier to do with electromagnets than with a fixed magnet). It’ll also weaken the magnet in the middle, since the souths will be trying to repel each other.
So if a monopole existed, would those lines of force used for illustration just reach out into the universe towards the nearest opposite pole?
I was under the impression that all magnetic effects could be explained with moving changes and taking relativity into account. Am I mistaken?
The lines of field (which should not be called lines of force) of a monopole would behave in the same manner as those of an electric charge: Radiating out uniformly in all directions near the source (i.e., much closer to the source than to other monopoles), eventually veering in to converge on another monopole or monopoles of the opposite charge.
All magnetic effects which have been repeatably observed can be explained in that way. The situation gets more complicated if there are monopoles (which, for practical purposes, have not been observed).
Doesn’t that make the whole idea of magnetic monopoles something left over from an older less complete understanding of electricity and magnetism. Sort of like looking for the crystal spheres that controlled the movement of the planets.
Yes, most practical superconductors are type II, meaning that the magnetic flux penetrates the superconductors. The flux vortices are pinned in place, but the pinning forces can be small and a tiny disturbance can cause flux to move.
I favor a different explanation: I would guess that the current in the loop was read out with a SQUID (superconducting quantum interference device). The response of a SQUID is periodic and is usually linearized by feedback. The feedback loop will have a maximum slew rate. If a transient exceeds the slew rate, the feedback will momentarily lose lock and will restabilize at a value offset by an integral number of flux quanta in the readout circuit. The signal will appear as a sudden flux jump, just as if a monopole had passed through the loop. It would take a coincidence for the magnitude of the jump to be correct for a Dirac monopole.
P.S. Sorry I misinterpreted your comment about a possible hoax.