# Are magnetic monopoles expected?

1. Sep 25, 2012

### Decimator

Do physicists expect to find magnetic monopoles once a sufficiently obnoxious particle accelerator is built?

2. Sep 25, 2012

### Staff: Mentor

Some theories predict them, some do not. So "expected" is just guesswork, and depends on the physicist you ask.

3. Sep 25, 2012

### mikeph

I think most people would be very surprised, but who knows.

4. Sep 25, 2012

### Decimator

So the basic answer is: "No, unlike the Higgs boson, monopoles are not predicted with any degree of certainty." Correct?

5. Sep 25, 2012

### mrspeedybob

Once you understand the relationship between the electrostatic force and the magnetic force magnetic monopoles make no sense.

I suppose if you built a magnet so large that the opposite pole was in a causally disconnected part of the universe you could consider your local end to be a monopole, but even then you could model any part of the magnet, or the whole thing, as a collection of many dipole magnets fastened together.

6. Sep 25, 2012

### Staff: Mentor

The Higgs boson was expected - and compared to that, monopoles are not expected.

I come to the opposite conclusion: Magnetic monopoles would give symmetric Maxwell equations.

$$\vec\nabla\cdot\vec E=4\pi\rho_e$$
$$\vec\nabla\cdot\vec B=4\pi\rho_m$$
$$\vec\nabla\times\vec E=-\frac{4\pi}{c}\vec j_m-\frac{1}{c}\frac{\partial\vec B}{\partial t}$$
$$\vec\nabla\times\vec B=\frac{4\pi}{c}\vec j_e+\frac{1}{c}\frac{\partial\vec E}{\partial t}$$
Static electric charges produce electric fields.
Moving electric charges produce magnetic fields (in addition).
Static magnetic charges produce magnetic fields.
Moving magnetic charges produce electric fields (in addition).

7. Sep 25, 2012

### Born2bwire

I wouldn't say it like that as there isn't any certainty here. I would say that existence of monopoles does not affect the current batch of testable theories that we have. Monopoles could exist, but right now there isn't a theory that we can test that would demonstrate that the existence of magnetic monopoles would affect the results of the experiment. For now, testable aspects of theories that have magnetic monopoles will predict the same physics that theories without magnetic monopoles.

8. Sep 25, 2012

### Staff: Mentor

There are active searches for magnetic monopoles - so at least some theories predict detectable magnetic monopoles (or allow them within their parameter space). MoEDAL even got a part of its name from monopoles.

9. Sep 25, 2012

### dipole

As far as I'm aware in the standard model there's no reason why they can't or shouldn't exit - it's just a strange property of nature that they don't seem to. And some theories predict their existence, which is why people have spent a lot of money searching for them. To me it seems a very strange mystery that we have no explanation of why they don't exist, if truly they do not.

Maxwell's equations certainly hint that they should exist, because like mfb posted then you have a beautiful and total symmetry between electric and magnetic fields.

(Note that Gauss's law for magnetic monopoles is empirical and not derived from any other assumptions or postulates.)