Comment by aap_
2 years ago
Charge is quantized. You cannot have just any amount of electric charge. An electron has three elementary units of negative charge, quarks have -1 and 2. Whether it's a coincidence that proton and electron charge are of the same magnitude (and the neutron is neutral) is another question, but at the elementary level you don't have that much choice for what the charge of a particle is.
But why is charge quantised?
In the Standard Model properties are defined as relationships within/between symmetry groups. There are only so many things you can do to/with/in a symmetry group, and that's where the quantisation comes from.
But... that's a mathematical metaphor applied to observations. It's a good fit, but it doesn't explain why it's those symmetry groups and not others, or why symmetry groups are a good fit at all.
There's likely some kind of fundamental mechanism that generates these symmetries, and no one knows what that is.
Resonance seems a candidate.
Information compression (edit sorry you said no one knows why the need to symmetry groups and I provided the answer).
> quarks have -1 and 2.
Wikipedia suggests the quarks that make up the proton have charge ⅔e and -⅓e
https://en.wikipedia.org/wiki/Up_quark
https://en.wikipedia.org/wiki/Down_quark
The post you’re replying to seems to be taking ⅓e as the basic unit of charge.
Is it true that the quarks themselves, in isolation, have that charge? Or is it that combining quarks into a baryon or meson gives the resultant particle a charge according to a fixed ratio of the constituent quarks?
Gemini advanced says it’s the latter, because of color confinement. But I’d defer to a human expert
Quarks can not be alone, because of this confinement. What we see experimentally is that when we add energy to particles at some point they split into new particles and we never see a naked quarks.
We explain this by saying the quarks have a color charge and it must always be neutral. A single quark would be lets say red, but that's for some reason not possible. If we try to rip the quark out, it takes so much energy that this energy can be used to create another quark that results in a color neutral particle (red, antired)=meson, (red,green,blue)=baryon.
NB: this is a bit simplistic and other comments explain this quite in detail NB2: this color charge is just a name, its not an actual color
OP assigned -3 units of charge to the electron, so all works out.
Of course, the quarks had to go and be 1/3 or 2/3 of an e in charge. But they can never be observed isolated, so nature allows it.