I saw a video on magnetic monopoles. In it the presenter spoke about quantised charges and said there is no reason we can’t have fractional charges. Can I ask why did he make that statement?

Question

Given electrons and protons are what we consider fundamental particles and both have a charge of -1 or 1 does it not just make sense we can only have charges in integer multiples of that?

I understand quarks have a 1/3 charge but for the purpose of this discussion I think we can ignore that. We can also ignore magnetic monopoles really that was just a lead in to my question.

(copied from my response to mcgato)

In: Physics

Answer 1

It’s been a while, but I believe that quantum theory dictates that angular momentum is quantized (don’t remember why). If a magnetic monopole exists anywhere in the universe, it follows from quantized angular momentum that electric charge is quantized. (This is left as a homework problem, but a magnetic monopole will cause a moving electric charge to have angular momentum. Quantized angular momentum ergo quantized electric charge.)

Since electric charge has only been observed as quantized, the belief is that a magnetic monopole should exist (or did exist at some point). Without the magnetic monopole, there is no theoretical reason for electric charge to be quantized. Thus 1.2 electron charge should be possible.

In undergrad, I worked on a magnetic monopole detection experiment. We did not find any magnetic monopoles.