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?

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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

This is the video where he talks about quantised charges.
https://youtu.be/S3xH97Su-KY?t=859

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.

I feel like this should be on r/physics or r/science. All these responses are hurting my brain and not hurting my brain in a Schroeder type situation. Where is Brian Greene? Or someone who can dumb this down way more? Examples with oranges and apple would be fine

Check out the [fractional Hall effect ](https://en.m.wikipedia.org/wiki/Fractional_quantum_Hall_effect) .

It turns out that in certain systems, we get particles that exhibit fractional charge.

First off all, fractional charges are still quantised charges. It just means fractional with respect to the electron charge. Quarks have a fractional charge of 1/3 or 2/3 (ignoring minus signs). So if you define the quantum of charge as 1/3e, where e is the electron charge, then there only exist particles with integer multiples of the quantum charge in nature (in terms of fundamental particles at least).

Now, the reason you’ll never physically measure a fractional charge is because of something called ‘quark confinement’. It basically means that quarks can’t freely exist on their own – only together with other quarks – always in such a way that the total charge is an integer multiple of the electron charge.