# Causes/Make-up of a Charge

1. Apr 10, 2013

### x8xPTx8x

Hey guys, Im new to this forum. So I apologize if this question has been answered in a direct or indirect way on another forum.I'm extremely interested in physics, And Im a very deep thinker. Im currently reading up on String Theory in hope of understanding as much as I can. I really enjoy learning the actual makeup and framework of our universe, and that leads me to my question:

All through physics, you learn about atoms that are made up of protons, neutrons, and electrons. Furthermore, you learn that protons have a +1 charge, and electrons have a -1 charge. And obviously these charges allow the atom to be stable.

What I'm actually curious about, is what actually is a charge? Ive looked this up on google and have visited many websites without finding an actual answer. I know a charge is a "property" and can't be fully explained, much like a "color." But color is made up of a certain wavelength of light. But as far as what a charge actually is, or where it comes from still baffles me. It seems like you always hear about charges and how they affect the atom. But I'm so curious about what this "charge" actually is. Could someone shed some light on what a charge is? I know how they work and what they do, and I know its a form of electricity. But what is the different between a +1 charge and a -1 charge. If someone could provide an in-depth, detailed answer, I would sincerely and greatly appreciate it!

2. Apr 10, 2013

Staff Emeritus
There is no end to the cycle of "I know X is Y"...but what is it really?

A perfectly good answer to "what is a giraffe" is pointing to one and saying, "That's a giraffe". Likewise, charge is a particular property. There is no deeper level.

3. Apr 10, 2013

### x8xPTx8x

oh ok... thanks Vanadium 50 for your response. I was unaware of this. I know some things in science just simply exist. I guess its much like saying "whats smaller than a point particle?" Logically, you would expect an answer, but there simply isnt one. That must be why I could find an answer.

But I'm still having trouble wrapping my head around it... With the giraffe analogy, someone may not no what a giraffe is per say, but we could describe one to him.

It just seems like there really isnt a description of what a charge is, just what a charge does and how it allows certain theories to work. Furthermore, when it comes to point particles, though its elements are an invalid idea, we can still merely describe it. I could pick up a string and say "its similar to something like this."

Is there a way to describe a particle that has a charge from another particle that has no charge? Is there an idea of what may be a charge other than "it attracts the opposite, and repels the similar"? How does an idea such as "charge" come along, and there not ever be somewhat more of a definite description.

I apologize if I'm coming off as stubborn. I do understand that somethings are understood moreso by the idea of them than what they actually are. This one is just a tough one for me. With all the confirmation with how charges work in electromagnetism, I find it baffling that we're still unable to describe it more specifically. Like thats the only thing I can find about particles is about how they attract or repel: nothing else.

Maybe there is a more definitie answer in science, and I simply just have not come across it. If there is such information, I would appreciate any assistance.

4. Apr 10, 2013

### DrZoidberg

5. Apr 10, 2013

### DrewD

Be careful looking at these more sophisticated explanations of things like charge (Motl's description on stackX). Sometimes it may just be saying that you are looking at a Giraffa camelopardalis. The added details may help physicists understand how charge relates to other things, but in reality, it is still a giraffe.

Charge is the "thing" that causes the electric (and magnetic) field. Charge is a number, positive or negative, that describes the magnitude of attractive or repulsive forces between particles that interact with the electric field. You can get deeper, but I doubt there is a concise explanation of the "thing" that charge is.

you could, but after a very long detailed description you would end up describing charged particles. Somewhere it either stops or else we have a very daunting task ahead of us.

Then try this http://www.smbc-comics.com/index.php?db=comics&id=2942#comic. Charge is "like" that (well the first two before strong force takes over). You could say that particles are "like" stings, but giraffes are "like" clams: they both have long necks.

I'm being absurd and I hope it isn't coming off as rude. There are deep explanations about things, but usually the real explanations IS just a description of how something behaves and the "thing" is anything that behaves that way.

I have a lot of work that I'm putting off. You should keep looking for your answer, but I doubt you will find it in a simple phrase.

6. Apr 11, 2013

### x8xPTx8x

Thanks so much for the responses to my questions. I apologize if my deep curiousity came off as unwilling to accept a fact.

However, I found an answer that sufficed my general question.

For those who were also wondering: well, Im currently reading "The Elegant Universe" by Brian Greene. For those who dont know of this book, I would highly suggest it! It has in-depth explanations of the theoretical portions of physics with easy-to-understand analogies and descriptions.

While reading I found the answer. Its currently talking about how String theory actually works at the quantum and general level. And it stated that strings makeup particles, the forces, and a particle's CHARGE. So there it is in a nutshell. The superstrings not only are responsible for the makeup of a particle, but also the charge of that particle. Though its still an unclear representation of a charge, it sufficed my curiousity as to how/where this charge came from and what it s. Its simply created by the near-infinite ways these superstrings vibrate. It hasnt given an detailed specicity as to how a vibrating string HOW it makes a charge. And im unsure if it will. Nevertheless, the fact is that a CHARGE is described as how the strings vibrate to makeup matter and its properties.

Again, I highly suggest this book for those interested in general and quantum physics, as well as answers to the greatest answers of the Universe... Whether or not theyre absolutely true is, of course, not a definite... but it definitely provides some logical insight.

Thanks again Drew, Vanadium, Zoidberg for the responses.

7. Apr 11, 2013

### x8xPTx8x

DrZoidberg, thanks for your link. I just noticed that it describes a charge much like this book Im currently reading. So i apologize for not noticing your link till after posting. Your source was even more in-depth, so I greatly appreciate it.

8. Apr 11, 2013

### psmt

I think we should all bear in mind that there is a strong answer available from regular QFT, without having to resort to string theory. The Lagrangian for a Dirac field is invariant under a global rephasing of the field, from which a charge operator can be defined as the spatial integral of the timelike component of the corresponding conserved current. When the theory is quantized, states of definite particle number then turn out to be eigenstates of the charge operator, with definite multiples of a fundamental unit of charge, and this charge is still conserved because the charge operator commutes with the Hamiltonian. When the global phase symmetry is promoted to a local symmetry by the introduction of the electromagnetic field, the interaction term in the new theory is proportional to that unit of charge. From this theory, suitably quantized, things like Coulomb's law etc. can be recovered, as you would hope.

Of course, this answer invites lots of new questions/objections, but my point is that charge (and generalisations - e.g. colour charge, weak hypercharge) is well-defined within the standard model, even if it's not known why the charges of particular particles take the values they do.

String theory might be more fundamental, but on the other hand it might be completely wrong, in which case "fundamental" doesn't come into it.

9. Apr 11, 2013

### DrewD

Yup, we knew:-) Enjoy the book, but there is a long way to go.

Now the question is what is a field "made of". No matter what, there must be building blocks that can't be described as being made of something else. I felt like the OP was looking for that sort of answer, not a technical explanation of how one can define a charge operator. I also wouldn't have been able to explain it nearly as well as you did.

10. Apr 11, 2013

Staff Emeritus
It's interesting that you accept the answer "it's just a property of strings" but not "it's just a property of particles". The reason I think it's interesting is because we know there are particles, but we don't know there are strings. I don't want to argue with you, since different people find different arguments convincing. I just find it interesting.

As far as the "mathy" answer of psmt, I don't find that particularly compelling, since the people who were developing QM and QFT already knew about charge. If the equations didn't accommodate charge, they would have picked different equations. I could write down equations that suggest two different kinds of charge, with different strengths and different particles having it - it would be a perfectly fine theory, just not one that describes our universe. So I don't think this explains much - it was designed to match observation from the start.

11. Apr 12, 2013

### psmt

I don't find it very compelling either!

I don't know much at all about how this happened historically, but i think you could at least motivate the Dirac Lagrangian without any reference to charge, on the basis of trying to find out whether Nature might make use of the spinor representation of the Lorentz group. Once the quanta of that field turn out to have spin-1/2, require anticommutation relations to make the theory consistent, and have a conserved charge corresponding to particles minus antiparticles, i think you'd have to say you've got more out of the theory than you put in by hand. Of course, hindsight's a wonderful thing and all that.

But i agree that the whole Noether thing is not really an explanation, just one possible definition.

12. Apr 12, 2013

### Staff: Mentor

I find it compelling. It is true that they already knew about charge, but the mathy answer describes an important aspect of charge that isn't at all apparent from any other answer and that aspect ties in with the most fundamental principles of modern physics.

Basically, according to modern physics, the most fundamental aspects of the universe are the symmetries that the laws of the universe posses. Noether's theorem relates the symmetries of the laws to conserved quantites, one conserved quantity for each symmetry. Charge is the conserved quantity for one such symmetry.

13. Apr 12, 2013

### ZapperZ

Staff Emeritus
Unfortunately, and I hope you realize this, you are accepting an explanation that is based on principles that has no empirical verification at this moment. In the words of Greene himself, if there are no experimental evidence, then String theory is not physics, but philosophy.

So be careful on what you accept as valid. If you wish that this is based on accepted physics, then what you area already "comfortable" with as the explanation for charge is not something that is considered to be valid yet in physics.

This book, and the TV series that accompanied it, have been discussed at length, in several threads, in the Beyond The Standard Model forum here.

Zz.

Last edited: Apr 12, 2013