Magnetic monopoles

Magnets have a south and a north pole. Are there any physical theories that predict magnetic monopoles ?

That website mentions they have never been constructed. It seems a little hokey, though. So I kept looking.

That website is a little more interesting.

For what it’s worth, there was a brief flurry of excitement in the 70’s when some researchers announced that they had produced (or discovered) magnetic monopoles. As I understood from a college physics professor, it turned out to be a mistaken interpretation of the data; but apparently some quasi-reputable theories do predict that it “could be possible”.

That page seems to be a joke.

It is not a requirement for a magnet to have “a north and south pole.” Take ring magnets, for example. These permanent magnets are shaped like a donut, and the circular magnetic lines of force are contained within the steel. (You can picture the lines as “zooming around” inside the ring like cars around a circular racetrack.) A wire w/ electrical current running through it will also set up a circular magnetic field with - guess what - no north or south pole.

So a magnet can have zero poles or two poles, but not one pole.

Floater, I’ve seen some wacky sites out there that even our resident Hiyruu hasn’t touched upon. It wouldn’t suprise me in the least.

Some day I will release my study if “How to make UFO” websites. :smiley:

One reason many people don’t believe there will ever be a “naked” long lived magnetic monopole is that, if you send an electron in orbit around one of them, it will accelerate forever and accelerating electrons give off photons. I.e., you have a source of infinite energy.

Hence a lot of quack science is can get caught up in the topic. As for erislover’s two links: people have already commented on the first and the second is non-quack but relates to quark level/short term interactions.

While there’s no observational evidence in favour of them existing, magnetic monopoles have a perfectly respectable history within 20th century physics. The first classic paper on the subject was by Dirac in 1931. Within classical physics, you can think of a monopole as a very long, thin bar magnet. You have one end of it, but the other end is infinitely far away. In the lingo, you call the bit in between the “Dirac string”. That’s a pretty unsatisfying picture - a monopole with the rest of the magnet dangling from it. But Dirac pointed out that in quantum mechanics, due to the odd properties of something called the “phase”, you could arrange things so that you never see the string. In particular, moving an electric charge around the string would have no effects. However, for this to happen, the electric charge (e) had to be related to the “magnetic charge” of the monopole (g) as follows:

  g e = 2 pi n

where n is an arbitary integer. Bingo! - you have one magnetic monopole in the universe and you’ve “explained” why charges are always some multiple of a basic charge. It has to be this way, or you could see the string.

Dirac’s relationship between the two types of charges turns out to be more fundamental than that. Even divorced from his particular argument, it keeps cropping up again and again. In particular, in the 70s when people started to get really interested in gauge theories of quantum fields (as in the Standard Model of particle physics), 't Hooft and Polyakov (two very brilliant guys) independently realised that monopoles could occur in some of them. These 't Hooft-Polyakov monopoles are slightly bizarre. They’re fundamental manifestations of the theories, but they’re not like quarks or electrons: they’re extended objects with the sort of (topological) properties mathematicians love. And while they can’t occur in the Weinberg-Salam standard model, they do arise in many Grand Unified Theories. And they obey the Dirac formula above.

As a result, most physicists believe that monopoles are likely to exist. However, there are good observational reasons for believing that they’re rare. For a start, they eat up the magnetic fields of galaxies. Since galaxies are observed to have magnetic fields, that restricts them (the Parker limit). Nobody expects one to turn up soon, but theoretical physicists love them.

Haven’t heard this before.

Suppose you have a bunch of ordinary bar magnets, and shove them into a ball, so that the Norths are all inside and the Souths all stick out at the surface.

You couldn’t access the North’s field, only the South’s field on the outside.

Would this crude construct qualify as a Magnetic Monopole?

Nein. Putting magnets with the same pole in a ball wouldn’t make anything, because the magnet doesn’t care whether one of its poles is in a ball or not, the field is the same. The ball doesn’t have any effect at all on the manget: it still has a north and south pole whether one or both are in the ball or not.
I heard there was a very heavy beam balanced on something and its slightest movement would indicate that a magnetic monopole had flown past. But I don’t kow where this interesting equipment is.