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profloater
2014-Feb-01, 06:15 PM
In the beginning charge was an electron property and positive was an absence of electrons. Now quarks have e/3 and electrons have -e.
Is it mainstream now to see charge as two things, +e/3 and -e ? Or are those related as a single property plus its absence?

ShinAce
2014-Feb-01, 08:38 PM
Charge was actually defined as positive to begin with. So by definition, a proton is the basic unit of charge. The electron could be the anti-charge.

I recall a book on electromagnetism a long time ago that had a simple yet profound sentence in it. "The basic unit of free charge found in nature comes in integer multiples of the electron charge." Hidden in that sentence is the fact that the individual charges of quarks are not free. A collection of quarks(a proton) always adds up to integer charge.

For this reason, we can still say the fundamental charge is the electron(or proton).

trinitree88
2014-Feb-02, 12:48 AM
The quarks in a proton also have color charge, an assigned quantum number so that you don't have two identical fermions inside the proton violating Fermi Dirac statistics.

Shaula
2014-Feb-02, 05:43 AM
And weak isospin, the charge analogue for the weak force.

profloater
2014-Feb-02, 11:01 AM
But the proton attracts the electron, and repels other protons, so there seems to be a positive charge property and a negative charge property. The fact that early belief was electricity flowed from + to - and now we know electrons actually "flow" from - to + does not help in considering the hydrogen atom. In a transistor we talk of "holes" into which electrons flow and these are explained as absense of electrons, but a proton cannot be said to be missing its electron, surely, it has positive charge as a property. Is that so?

grapes
2014-Feb-02, 12:02 PM
In the beginning charge was an electron property and positive was an absence of electrons. Now quarks have e/3 and electrons have -e.

Quarks have 2e/3 or -e/3, I don't think any have e/3


Is it mainstream now to see charge as two things, +e/3 and -e ? Or are those related as a single property plus its absence?
It looks like you've answered your own question. :)


but a proton cannot be said to be missing its electron, surely, it has positive charge as a property. Is that so?

Glom
2014-Feb-02, 12:45 PM
Quarks have 2e/3 or -e/3, I don't think any have e/3

Anti-quark?

Strange
2014-Feb-02, 12:50 PM
But the proton attracts the electron, and repels other protons, so there seems to be a positive charge property and a negative charge property. The fact that early belief was electricity flowed from + to - and now we know electrons actually "flow" from - to + does not help in considering the hydrogen atom. In a transistor we talk of "holes" into which electrons flow and these are explained as absense of electrons, but a proton cannot be said to be missing its electron, surely, it has positive charge as a property. Is that so?

Yes, protons have a positive charge. Holes are the positive charges in semiconductors but they are quasi-particles created by a missing electron (the positive charge still comes from protons, though). So charge can be positive or negative (or zero).

Strange
2014-Feb-02, 12:52 PM
How do we know the charge distributed to quarks as we can never observe a free quark? Is it just based on the composition of particles with different net charge? Is there only a single solution to that? Or is there some more fundamental way of allocating the charges to quark?

profloater
2014-Feb-02, 12:58 PM
OK so charge is both positive and negative and for quarks comes in multiples of thirds according to the model, but we never see a lone quark.

profloater
2014-Feb-02, 01:11 PM
Is there a mainstream interpretation of charge as spin about x,y,z axes for a proton and about all axes for an electron spherical probability distribution? Since charge is an electrical property we know about at macro level, it is tempting to see it as literal spin or spins. If the proton were kind of fixed as in diagrams, the electron "orbits" or probability function would surely be distorted by the different charges on quarks?

grapes
2014-Feb-02, 04:10 PM
Quarks have 2e/3 or -e/3, I don't think any have e/3

Anti-quark?
Yes, anti-quarks have the opposite, -2e/3 or e/3

profloater
2014-Feb-02, 07:49 PM
I went back to the thread classical interpretation of the electron in which classical spin was discussed and was said to be classically orbiting charge, so that thread did deal with what I was wondering. So I am still not sure about the mainstream understanding of charge, + and - as applied to a proton electron pair, is it just a fundamental property without causal explanation?

ShinAce
2014-Feb-02, 08:33 PM
So I am still not sure about the mainstream understanding of charge, + and - as applied to a proton electron pair, is it just a fundamental property without causal explanation?

That is correct. It is considered fundamental because you always plug in a charge of -e to equations when dealing with electrons. Even when an atom has multiple electrons which screen the nucleus from each other, each electron has charge -e. The distribution of charges causes the skewed potential energies. Even when relativity is involved, the charge of an electron is still -e.

It's interesting that there's been talk lately(because of the Higgs) that mass is a an emergent property. Yet we still take for granted that charge is a fundamental property, without explanation. I can not, for the life of me, explain to anyone what charge 'is'.

Another fundamental property is the color charge of quarks. Red, green, and blue were 'picked' because it allows an easy rule to be obeyed. Combinations of quarks must always be white. So if you have two quarks and one is red, the other is anti-red. If you have three quarks, where one is red and the other blue, then the third is green. They don't literally have color.

In that sense, you could say that charge is a placeholder, like dark matter. We know it's there, but we don't know 'exactly' what it is.

profloater
2014-Feb-04, 09:06 AM
Thanks for that explanation, I was reading in scientific American about the anomalous proton diameter as measured by muon hydrogen and the way the electron prob enters the proton and a started wondering if the charge enters the proton too.

ShinAce
2014-Feb-04, 05:55 PM
The proton size anomaly does seem interesting, but I see no indication that charge can leave a muon by basic means. By basic I mean directly. A muon carries its charge, and that charge interacts with other charges. However, from QED, we know that there is a certain amount of self-interaction that a charge can perform. Virtual particles complicate our simple scenarion of 2 particles interacting. See vacuum polarization:
http://en.wikipedia.org/wiki/Vacuum_polarization

When you're dealing with charges, you're dealing with photons. While the photons control the push/pull of charged particles, the photons themselves carry no charge. But this doesn't have to be so. Quarks have a color charge, and that push/pull is mediated by the gluon. The gluon, while massless like the photon, DOES carry the color charge along with it.

Attempts to explore new models where the muon could couple in a new way(and not necessarily by 'lending' its charge) have not been fruitful. Here's one example:
http://arxiv.org/abs/1011.3519

We could say an electron has east charge while a proton has west charge and nothing would change. It's just a name for something that is well modeled, but not understood.

profloater
2014-Feb-06, 10:01 AM
Many thanks for that I will follow up references.