What is charge?

[WingsOfTheNeophyte]

Im randomly hoping someone who knows this comes along



My main question is what is charge?

What is it that makes something positive, or something negative, what is it makes that opposites attract, and same charges repel?


What is it that makes an electron attracted to a proton, how?

 

[arunma]

Im randomly hoping someone who knows this comes along



My main question is what is charge?

What is it that makes something positive, or something negative, what is it makes that opposites attract, and same charges repel?


What is it that makes an electron attracted to a proton, how?

The exact words from one of my freshman physics professors: "I don't know what mass is." While your question pertained to charge, the inverse square relationships that govern both charge and mass indicates to me that the same applies to electric charge.

It turns out that according to the Standard Model, protons, neutrons, and electrons are each comprised of three quarks, and there are six quarks in existence. Each quark has a fractional charge of magnitude 1/3 or 2/3, up to a sign (a chart on the Wikipedia article gives the charge of each type of quark). The charges on these quarks add to give either +1 (protons), -1 (electrons), or 0 (neutrons). Charge is a property that causes electromagnetic forces between particles. It is different from mass in that while mass has the added effect of inhibiting force (Newton's Second Law), charge causes force but does not impede it. And obviously, charge has the peculiar effect that it can cause both attractive and repulsive forces. Finally, and this is just speculation on my part, I find it interesting that mass is a component in determining the Hamiltonian of any particle, while charge is not.

But that doesn't really answer your question, does it? To echo my freshman professor, I don't really know what charge is. If you have a good answer, let me know.

 

[arunma]

What is it that makes an electron attracted to a proton, how?

I'm sorry, I almost forgot about this question (which I can answer). In the days of Newton and the later classical physicists, people believed in the idea of "action at a distance." That is to say, physicists accepted that masses and charges simply produce something called a "field" that affects other objects. With the advent of the Standard Model, physicists have now made all interactions local. We now know that forces are transmitted by charge-carrier particles

Every electric charge emits particles called virtual photons. When these virtual photons are detected by another electric charge, that charge "knows" exactly where the first charge is, what its charge is, and with how much force it should attract that charge. This is essentially how charges attract each other.

 

[Frumious Bandersnatch]

The exact words from one of my freshman physics professors: "I don't know what mass is." While your question pertained to charge, the inverse square relationships that govern both charge and mass indicates to me that the same applies to electric charge.

It turns out that according to the Standard Model, protons, neutrons, and electrons are each comprised of three quarks, and there are six quarks in existence.

Slight correction here. Protons and Neutrons are baryons and thus are composed of quarks but electrons are leptons and are thus fundamental particles. There are six flavors of leptons; electrons, electron neutrinos, muons, muon neutrinos, taon and tau neutrinos.

Each quark has a fractional charge of magnitude 1/3 or 2/3, up to a sign (a chart on the Wikipedia article gives the charge of each type of quark). The charges on these quarks add to give either +1 (protons), -1 (electrons), or 0 (neutrons). Charge is a property that causes electromagnetic forces between particles. It is different from mass in that while mass has the added effect of inhibiting force (Newton's Second Law), charge causes force but does not impede it. And obviously, charge has the peculiar effect that it can cause both attractive and repulsive forces. Finally, and this is just speculation on my part, I find it interesting that mass is a component in determining the Hamiltonian of any particle, while charge is not.

But that doesn't really answer your question, does it? To echo my freshman professor, I don't really know what charge is. If you have a good answer, let me know.

"Charge" is fundamental property of quarks and leptons. We call the electon charge "negative" and the proton charge postive only by convention. The electomagnetic force is one of the 4 fundamental forces. Like charges repel and opposite charges attract by the mechanism you have described in your second post. I guess the answer is that is the way our particular universe works.

 

[arunma]

Slight correction here. Protons and Neutrons are baryons and thus are composed of quarks but electrons are leptons and are thus fundamental particles. There are six flavors of leptons; electrons, electron neutrinos, muons, muon neutrinos, taon and tau neutrinos.

Did I actually say electrons!? My mistake entirely. Thank you for the correction.

 

[Frumious Bandersnatch]

Did I actually say electrons!? My mistake entirely. Thank you for the correction.

No problem. I thought it a bit strange that you had everything else so right and had that wrong. Must have been a small brain cramp. It happens to me more often as I get older.

 

[arunma]

No problem. I thought it a bit strange that you had everything else so right and had that wrong. Must have been a small brain cramp. It happens to me more often as I get older.

Oh, it affects us youngins too. I am amazed that only during the physics GRE did I forget how to do simple arithmetic. And then there was the time last year when I allegedly thought that temperature was a vector (I say "allegedly" because everyone in my thermal class accuses me of saying this, despite that I have no recollection of the event). And I blame the unhappy phenomenon of brain cramps for the B+ I got in optics.

Alas, at least I fit the description of the absent-minded physicist. I just hope that pulls some weight with the fellowship committees!

Anyway, you're absolutely right to point out that one who wishes to answer the philosophical question of what charge is should certainly consider leptons, which have integral charge. Here's one issue that's come to my mind. Shortly after the Big Bang, baryons and leptons were created by means of baryogenesis and leptogenesis. I've studied both processes somewhat. But only now do I wonder why there was no "quarkogenesis."

 

[UVsaturated]

I wish someone could say why charges have reactions to other charges the way they do. I strongly feel, without evidence just gut feeling, that these particles react to some external force that makes them take on their charge. The characteristics determine what we call a particle, but the characteristics themselves are not a particle. It seems to me that physicists are working on that very thing of going beyond the observable realm to see what makes the fabric of the universe the fabric of the universe. In otherwords, I think science is either on the verge of finding the absolute truth of particles and what lies hidden, or this question will remain unanswered for a long long time.

 

[arunma]

I wish someone could say why charges have reactions to other charges the way they do. I strongly feel, without evidence just gut feeling, that these particles react to some external force that makes them take on their charge. The characteristics determine what we call a particle, but the characteristics themselves are not a particle. It seems to me that physicists are working on that very thing of going beyond the observable realm to see what makes the fabric of the universe the fabric of the universe. In otherwords, I think science is either on the verge of finding the absolute truth of particles and what lies hidden, or this question will remain unanswered for a long long time.

Have you read my post #3? I think the charge-carrier model does an excellent job of explaining why charges react to other charges.

 

[UVsaturated]

Have you read my post #3? I think the charge-carrier model does an excellent job of explaining why charges react to other charges.

Contrarily, it only explains what we observe charges doing from your wording. I already know that charges attract and repel depending on their sign, but this doesn't really explain why. Like magnetic attraction, why does it exhibit a polarization and what makes the field attract particles of the opposite sign and repel positive signs?

 

[arunma]

Contrarily, it only explains what we observe charges doing from your wording. I already know that charges attract and repel depending on their sign, but this doesn't really explain why. Like magnetic attraction, why does it exhibit a polarization and what makes the field attract particles of the opposite sign and repel positive signs?

Well, these are two different questions (at least they would have been two different questions if we were living in 1850). The reason charges do what they do is because they emit virtual photons. These photons essentially give instructions to other charges, instructing them whether to attract or to repel, and with precisely what force.

Now as for magnetic fields, this is a slightly different issue. It turns out that magnetism is actually just another manifestation of electric force. Magnetism is caused by moving electric charges. The reason magnetic fields always appear as dipoles is because there is no magnetic charge in the universe. The laws of physics permit the existence of individual magnetic charges. But as David Griffiths (easily my favorite textbook author) puts it, "apparently, God just didn't make any magnetic charge!" Magnetism in metals is the result of microscopic current loops in the metal, and current loops produce dipole fields. This is why magnets are often modeled as collections of tiny north and south pole pairs. I guess the answer to your question on magnets is that monopoles don't exist because they didn't come with the universe. And the only other way to produce a magnetic field is with a moving charge (which will never produce the same field as a monopole). That's why magnets always have a net polarization.

 

[UVsaturated]

Arunma, that was an interesting way you worded that. I think I will stick to what I do know, but I have never heard of "virtual protons". Sounds interesting.