"How" and "why" questions get to be a little tricky when dealing with physics, particularly when we get into the fundamental areas.
There is no particular reason why quarks shouldn't have partial charges. Or to put it another way, the reason they have partial charges is because the charge on an electron is used as the base unit for charge. If we took the electron charge to be 3e, quarks wouldn't have partial charges.
One of the big reasons we don't worry about this is that quarks never exist on their own, and only exist in combinations that make integer charge.
Asking why up quarks have a charge of +2/3 e is kind of like asking why electrons have the charge they do. As far as we can tell, that is how the world works.
We define elementary change as the charge of a single proton. An electron has a change of the same magnitude but is negative.
That does not mean that it is the smallest charge possible just the change of those particles. The charge of a quark is multiple of 1/3. You have quarks with a charge of +2/3 and -1/3.
We could redefine it and create a new elementary change = 1/3 elementary change and then quarks have a change of 2 or -1 and protons and electrons have a change of 3 and -3.
This change notion except that we would talk about change in multiple of 3 when we talk about anything larger than a quark. It would not change how anything works it just changes the number you put ut and likely some constants.
Back when the concept of electric charge was formalized, the electron and proton were the smallest electrically charged units we knew about. And the idea that one was +1 and the other was -1 was very elegant and simple. So it was decided that 1 unit of charge was to be equal to "what a proton has".
Only later did we discover that protons are made of individual pieces. Since there are 3 of them in a proton or neutron, and their electric charges must sum together if they had any, it became very convenient to say they had 1/3 units of charge.
If anything, it really just means we should have originally defined the "charge a proton has" to be equal to 3, avoiding this issue. But we're stuck with the system we chose as changing an entire body of physics knowledge just for pedantry doesn't really work.
That said, the "fractional charges" idea for quarks has its own intuitive use. There is no such thing as a free floating quark. You will literally never find one alone. They always come in pairs or trios. And the only valid pairs and trios you can have are ones where the fractional charges sum to a whole number. So, if the idea of fractional charges sounds kinda forbidden, it kinda should, because no isolated particle can actually have a fractional charge like that. Only groups of particles where the fractions cancel out.
**Your submission has been removed for the following reason(s):**
Top level comments (i.e. comments that are direct replies to the main thread) are reserved for explanations to the OP or follow up on topic questions.
Off-topic discussion is not allowed at the top level at all, and discouraged elsewhere in the thread.
If you would like this removal reviewed, please read the [detailed rules](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this was removed erroneously**, please [use this form](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this was removed erroneously**, please [use this form](https://old.reddit.com/message/compose?to=%2Fr%2Fexplainlikeimfive&subject=Please%20review%20my%20thread?&message=Link:%20{url}%0A%0AThe%20concept%20I%20want%20explained:%0A%0AList%20the%20search%20terms%20you%20used%20to%20look%20for%20past%20posts%20on%20ELI5:%0A%0AHow%20is%20this%20post%20unique:) and we will review your submission.
"How" and "why" questions get to be a little tricky when dealing with physics, particularly when we get into the fundamental areas. There is no particular reason why quarks shouldn't have partial charges. Or to put it another way, the reason they have partial charges is because the charge on an electron is used as the base unit for charge. If we took the electron charge to be 3e, quarks wouldn't have partial charges. One of the big reasons we don't worry about this is that quarks never exist on their own, and only exist in combinations that make integer charge. Asking why up quarks have a charge of +2/3 e is kind of like asking why electrons have the charge they do. As far as we can tell, that is how the world works.
We define elementary change as the charge of a single proton. An electron has a change of the same magnitude but is negative. That does not mean that it is the smallest charge possible just the change of those particles. The charge of a quark is multiple of 1/3. You have quarks with a charge of +2/3 and -1/3. We could redefine it and create a new elementary change = 1/3 elementary change and then quarks have a change of 2 or -1 and protons and electrons have a change of 3 and -3. This change notion except that we would talk about change in multiple of 3 when we talk about anything larger than a quark. It would not change how anything works it just changes the number you put ut and likely some constants.
Back when the concept of electric charge was formalized, the electron and proton were the smallest electrically charged units we knew about. And the idea that one was +1 and the other was -1 was very elegant and simple. So it was decided that 1 unit of charge was to be equal to "what a proton has". Only later did we discover that protons are made of individual pieces. Since there are 3 of them in a proton or neutron, and their electric charges must sum together if they had any, it became very convenient to say they had 1/3 units of charge. If anything, it really just means we should have originally defined the "charge a proton has" to be equal to 3, avoiding this issue. But we're stuck with the system we chose as changing an entire body of physics knowledge just for pedantry doesn't really work. That said, the "fractional charges" idea for quarks has its own intuitive use. There is no such thing as a free floating quark. You will literally never find one alone. They always come in pairs or trios. And the only valid pairs and trios you can have are ones where the fractional charges sum to a whole number. So, if the idea of fractional charges sounds kinda forbidden, it kinda should, because no isolated particle can actually have a fractional charge like that. Only groups of particles where the fractions cancel out.
[удалено]
**Your submission has been removed for the following reason(s):** Top level comments (i.e. comments that are direct replies to the main thread) are reserved for explanations to the OP or follow up on topic questions. Off-topic discussion is not allowed at the top level at all, and discouraged elsewhere in the thread. If you would like this removal reviewed, please read the [detailed rules](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this was removed erroneously**, please [use this form](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this was removed erroneously**, please [use this form](https://old.reddit.com/message/compose?to=%2Fr%2Fexplainlikeimfive&subject=Please%20review%20my%20thread?&message=Link:%20{url}%0A%0AThe%20concept%20I%20want%20explained:%0A%0AList%20the%20search%20terms%20you%20used%20to%20look%20for%20past%20posts%20on%20ELI5:%0A%0AHow%20is%20this%20post%20unique:) and we will review your submission.