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What is the difference of positive and negative charge?

  1. Jun 24, 2012 #1

    I am aware of what generates the electric charge of each particle, the virtual fotons around it that the particle generates, and that when two particle interact with each other a foton is exchanged and so forth. My question is though, what generates the positive and negative charge, and what is the actual difference between them?
  2. jcsd
  3. Jun 24, 2012 #2
    There's not much to say here. Nothing "generates" the charges of particles; charge is merely a property of particles which, in the standard model, is fundamental and not explained in terms of anything else. Charge is a number, and the difference between positive and negative charges is the sign of this number (trivial, but true).

    Note that there is a symmetry between positive and negative charge in the following sense: if we all agreed from now on to call negative charge positive, and positive charge negative, nothing would change, and all our calculations would still work. There are two groups of charges. Charges from the same group will repel each other, and charges from different groups will attract each other. But which group we call "negative" and which group we call "positive" is a matter of convention.
  4. Jun 24, 2012 #3
    Defining definition. I would suggest that defining something means expressing it in more simple terms that are more understandable by the person asking. When the process is carried to the limit of the most simple terms you are stuck with what you have.

    An electron is a basic particle. That is as simple as it gets. It is the carrier of the negative charge which has a known measurable value related to force. Electrons repel each other to a degree related to that force. If you wished you could define force, but at some point definitions start to go in circles

    The carrier of the positive charge is not a basic particle. Present prevailing theory has it made up as quarks which have fractional charges. In this case the proton might as well be considered a basic particle. Protons are repelled by other protons and they are attracted to electrons by some force. That is the "bottom simple limit" of that definition.

    What it comes down to is that basic physical entities like charges can be only defined according to how they behave and we are stuck with that.

    Edit: As a social comment; while it is true that generally the Scientific World is pretty good at agreeing on definitions right down to the most basic terms, the general population is almost invariably ready to argue, fight, and slaughter each other over the most simple and shallow of definitions.

    Last edited: Jun 24, 2012
  5. Jun 24, 2012 #4
    I don't mean to offend either of you, but all of this sounds to me that we just haven't found out why yet, and the only explanation that we have so far is that "It just is that way, don't ask about it".
    You say that the electron has the negative charge, and that it's a basic part of nature. My question is then, what about anti-protons? They have a negative charge, and what is it that gives them that charge and what makes them different from matter-protons? Could it be that we just haven't discovered yet that both quarks and electrons are divisable? Maybe they are composed of even smaller parts that gives them their properties?
    I don't know, I'm just speculating. Please correct me if I'm wrong!
    Last edited: Jun 24, 2012
  6. Jun 24, 2012 #5
    That's certainly possible, even probable--almost no one believes that the standard model of particle physics is complete as it stands. For any given question, it's always possible to keep asking "why?" until you reach the boundary of our knowledge about the universe. That said, we have today a very nice predictive and self-consistent understanding of electricity and magnetism. While it may not be Ultimate Truth, there aren't currently any particular loose ends in this part of physics that you could pull on in the hope of unraveling something more fundamental. So our current theories postulate the existence of electric charge without explanation and leave it at that.

    Protons are made of two up quarks with charge +2/3 and one down quark with charge -1/3 for a total charge of 2/3 + 2/3 - 1/3 = +1 (in particle physicists' units of charge). Quantum field theory predicts, for any particle, the existence of an antiparticle which has opposite charge. This fact is well understood as a deep mathematical consequence of the union of quantum mechanics and special relativity. Thus there is an antiproton composed of two up antiquarks each with charge -2/3 and one down antiquark with charge +1/3, for a total charge of -1. So the charge of the antiproton, and its difference from the proton, is well understood.

    Certainly this is possible. Experiments are always testing this possibility. So far we have zero evidence that either quarks or electrons are composite particles as opposed to fundamental ones. That of course does not rule out compositeness, since our experiments can only probe down to a certain length scale. But in the absence of evidence otherwise, the theories we construct to explain our data postulate electrons and quarks as fundamental particles.

    Now, one may try to explain the otherwise inexplicable properties of the known particles by postulating that they are somehow composed of something more fundamental. This is a valid idea, but only useful if the new "deeper" theory explains more facts than it makes assumptions. As a trivial example, if a proposed theory explains why all electric charge comes in units of a fundamental charge, but assumes the existence of "supercharge," which only comes in units a fundamental supercharge, you haven't really gained much, especially if your theory makes no other testable predictions besides reproducing the known data, which is already explained by the standard model. And it turns out to be hard to explain the current data with a theory simpler than the standard model. So in particular we have no reason to believe that, say, electrons are composite.

    String theory is an example of a more fundamental theory that might explain things like the charges of the known particles in terms of more fundamental objects. Of course, string theory must itself make certain postulates about the existence and behavior of strings. The hope is that these postulates end up being more concise than the mess of particles we currently need to postulate in the standard model.
  7. Jun 24, 2012 #6
    Re: The Duck

    Thank you for the informative answer, it helped me a lot in understanding this issue.
    You explained very well how the anti-proton acquires its negative charge, but my question still remains if you take it one step further to why the anti-up quarks has their negative charge, but I guess this crosses the line to what we simply don't know.

    Just a question, are String Theorists working to explain this issue? Would an anti-up quark just be a higher vibration of its superstring compared to an electron's superstring?
    Last edited: Jun 24, 2012
  8. Jun 25, 2012 #7
    No offence taken. Perhaps I should have specified that these are what we are stuck with NOW; until we find otherwise.

    Duck you are a most excellent technical writer.

  9. Jul 24, 2012 #8
    I can answer this question in a very simple and easy manner. If something is negative then your reducing something from it and it just the opposite for positive. So for a negative charge if it was used in a work function if you put energy into it you would get less energy out then what you put in. Fortunately electrons generate energy for our applicances by motion within a circut and not by there charge.
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