The last i heard, nobody has seriously searched for MMPs since the 1970’s. of course, there is no proff that they exist. My question: if there was such a thing as a unit of magnetic “charge”-would our present view of the universe change very much?
Wiki on magnetic monopole searches. Apparently few, if any, research groups are still searching. FYI, a proton or a neutron masses about 1 Gev/c[sup]2[/sup], so the mass limits the Wiki article mentions for monopoles are greater than 600 proton masses, and less than 10[sup]17[/sup]. Quite a range!
Well timed post, by the way. I remember the excitement in 1982 with Blas Cabrera’s “Valentine’s Day” announcement. I’m sorry no more monopole candidates were found.
If Cabrera’s event was really a magnetic monopole, even if it were the only one in the universe, charge quantization would be explained. How cool would that be? If it were the only monopole in the universe, then experimental replication would be, um, problematic.
I seem to remember one theorectical interpretation that there HAD to be one in the universe and ONLY one would be good enough…
Anyone care to expand on that?
There is a unit of magnetic charge; the question is just whether there exist any objects which actually have that magnetic charge. The short form of the argument is that, given some relatively basic electrodynamics and quantum mechanics, if you had at least one magnetic charge and at least one electric charge in the Universe, then the product of their magnitudes has to be an integer multiple of some constants. The only way this can happen, in turn, is if electric charge and magnetic charge are both also quantized, each being an integer multiple of some fixed fundamental constant. We know that electric charges exist, and that they’re quantized, and so if there existed any magnetic monopoles at all, no matter how rare they are, we could explain why that must be so. Which doesn’t mean that they have to exist: It could be that there’s no inherent explanation for why charge is quantized.
As far as searches for them go, there are two primary ways it’s done. First, you can set out superconducting loops and monitor the current through them. If a monopole happens to pass through one of the loops, then the current will jump up to some value and stay there. This is the type of experiment which resulted in the 1982 event (which nobody can really adequately explain). Second, there are astronomical searches: In most grand unified models, protons can decay, and the decay is greatly catalyzed by the presence of a magnetic monopole. So you could in principle have a star-like object containing a monopole, which shines not as a result of fusion, but through proton decay.
Both of these searches are still ongoing, mostly because they’re both very easy. The superconducting loops are about the simplest elementary particle detector you’ll ever hear of, and the astronomical searches generally use scavenged data from other observations.
Meanwhile, my advisor is fond of saying that we know that monopoles exist, but there might be a very small number of them, such as zero. That is to say, if nothing else, it should be possible for a black hole to have a magnetic charge, and if it’s possible, then it probably happened (certainly, in fact, if the Universe is infinite), some time in the very early Universe. However, that would have been before the time of inflation, and the general expectation is that particles which were only formed before inflation would be so sparse now that you’d expect an average of about one of each of them in a volume the size of the observable Universe. And an average of about one is quite consistent with the possibility that the observable Universe contains zero of them.
Those monopoles sound dangerous! Hope the LHC doesnt produce any of those “either”
If they did, they probably wouldn’t get far. Individual monopoles are stable, but they can only be produced in pairs, and they would probably re-annihilate very quickly.
On the other hand, if we can produce them, then we could probably design an experiment explicitly for separating them, and use them for the ultimate long-lasting energy source. That’s one of the possibilities I like to trot out when people insist on asking for a practical use for CERN research.
Again, by the way, a reminder: We know that the LHC won’t produce anything that would destroy the Earth, since the upper end of cosmic rays are significantly more energetic, and the Earth has survived being bombarded by those for billions of years. Maybe you could argue that the Tunguska event was caused by something like that, so conceivably a small region around the lab could be at risk, but outside of Geneva, you’d certainly be safe.