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What gives a proton it's charge?

  1. Dec 31, 2012 #1
    It had been asked before on physics forums but the given answers didn't convince me .
     
  2. jcsd
  3. Jan 1, 2013 #2
    Well, there's kind of two questions you're asking there. The first one's easy to answer, the second one is, as of now, unanswerable.

    So, a proton gets its charge from the quarks that compose it, two up quarks at +2/3 charge, and one down quark at -1/3 charge. This equals a grand total of +1 charge (that's about the extent of my math skills, btw:{

    The real question I gander you're getting at, though, is what is charge itself, or what is the nature of charge? The answer to that is pretty much "it is what it is." Its a fundamental, first principle sort of thing. It's about as fundamental as why is there something rather than nothing or what happened before the big bang. Does that help?
     
  4. Jan 1, 2013 #3

    jtbell

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    Which answers are those? If you tell us, it will prevent us from wasting time by giving them again. :smile:
     
  5. Jan 1, 2013 #4
    Ya sort off but are they sure that quarks are indivisible ?? Charge has a relation to electromagnetism
    So what's the relationship between qurks and electromagnetism ?
     
  6. Jan 1, 2013 #5
  7. Jan 1, 2013 #6
    Not much. At least relative to the relation between EM and everthing else in the universe. The world of quarks is dominated by the strong and weak forces, EM and gravity play minor roles here, although there is a dynamic interplay between the strong force and the coulomb (EM) force. The strong force gathers the charged quarks tightly together within the nucleon while the repulsive coulomb (EM) force prevents them from annhiliating each other.
     
  8. Jan 1, 2013 #7
    There are theories that charge is a component of momentum in the fifth dimension. If we postulate existence of a compact fifth dimension, then we get Maxwell equations from Einstein equation and the U(1) gauge symmetry. Read about Kaluza-Klein theory.
     
  9. Jan 2, 2013 #8
    Now that's interesting. This whole idea of extra dimensions, though, is a bit heartbreaking. It is so appealing on so many levels, it is the Deus ex Machina of the tragedy of modern physics. However, in real life it seems as though Deus never comes, although we can fantasize about it. It's kind of like that supermodel poster on your wall, so near yet so far. Heartbreaking, but fun to fantasize about.
     
  10. Jan 2, 2013 #9
    sorry to say,but kaluza klein is a rejected theory also there is no five dimension of charge.
     
  11. Jan 2, 2013 #10
    There is no absolute answer....no completely satisfying answer yet.

    A simple classical view is that an electron has a 'negative charge', an observed characteristic with an observed strength and when combined with a proton, becomes a neutron. Now before you reject this as silly, consider the composition of neutron stars...where electrons have been forced to combine with protons!! It is a smidgen artificial since we have no theory to determine the strength of charge...not the mass of the electron....in the Standard Model...those are plugged in experimental results....


    Another superficial perspective is that some particles exhibit a certain force...we call that the electromagnetic force....and we have some math to describe observations. Other particles exhibit other forces....and we use different math, like for the strong force.


    Of course that begs the question 'what is charge'?

    Ultimately this all goes back to spontaneous symmetry breaking early in the universe and the accompanying mathematical theory insofar as it takes us. Before symmetry was broken, charge, mass, space, time, the forces, everything, were all apparently 'unified'....appeared as one.

    So far we don't have a complete theory.
     
  12. Jan 2, 2013 #11
    I wouldn't treat it quite so lightly...extra dimensions have proven to provide a wealth of theoretical insights....as in string theory.

    yet they may be 'mother nature head fakes'!!
     
  13. Jan 2, 2013 #12

    dextercioby

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    It may have been asked under <What gives a proton its charge?>. ;) :)
     
  14. Jan 2, 2013 #13
    Don't you mean theoretical evidence, Naty?:redface:
     
  15. Jan 3, 2013 #14
    Remember that a proton with a positive charge and an electron with a negative charge is arbitrary.If the electron were assigned a positive charge, the proton would be negative. We would then ask what does a proton lack that gives it a negative charge and what does an electron have that gives it a positive charge.
     
  16. Jan 3, 2013 #15

    bhobba

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    Exactly. It is sometimes (incorrectly) claimed that if you write GR in 5 dimensions you get EM as well as GR - that's the Kaluza-Klein miracle. But miracles rarely if ever occur in physics - there must be a reason. The answer is what I said before is not quite true - it only works if the metric does not depend on the 5th dimension which basically means it has the symmetry of a cylinder. That's the real key - it imposes the simplest gauge symmetry on the theory (the symmetry of a circle) and it is known, mathematically, that is the real basis of EM. So its basically EM in - EM out.

    The best answer that can be given right now for the existence of charges and fields, not just EM charge and field but weak and nuclear, is gauge symmetry.

    Exactly - it is generally accepted there is some fundamental symmetry lurking about from which all the other symmetries are merely low energy 'broken' symmetries.

    Thanks
    Bill
     
    Last edited: Jan 3, 2013
  17. Jan 3, 2013 #16
    So what? I've often wondered what this return to perfect symmetry quest was actually supposed to tell us, other than "when we heat up everything real good, everything looks the same!" Wow, thanks for that wondrous insight. Now I understand so much more about the atom and the universe to know that as we get closer to the big bang and higher temperatures, the weak and EM forces become one, then the strong at higher temp, and then gravity. Personally, it's interesting and important to know, but explaining fundamental forces and features of particulate matter such as electric charge using broken symmetries basically tells me nothing about the nature of these entities.
     
  18. Jan 3, 2013 #17
    Actually Kaluza-Klein is still a living theory and still some theorists publish papers on it. It is quite not mainstream, but that proves nothing about its validity.

    Yes, but the "machine" that produced the Maxwell equations was Einstein field equations and usual spacetime symmetries. What KK really proves is that any gauge theory can be formulated in fully geometric way by postulating new dimensions. The topology of the dimensions set the gauge group and the size of the dimensions set the theory constants.

    This is actually something more than just pushing EM in and getting the same. It's the promising way of unifying any gauge theory with gravity.

    And for philosophers, it's one of the nice answers for the question "why".

    The unification idea, provided it is valid, tells us a lot about the universe. It tells us what is possible, how the universe looks in very different condition than ours. It often guides us to discovery of some new phenomenons. And if we went advanced enough, then some day we would probably be able to heat universe back to the melting point, restore the initial symmetry and break it other way. We would be able to alter laws of physics. All provided that the unification is a valid way to describe physics. So it's worth a try.
     
    Last edited: Jan 3, 2013
  19. Jan 3, 2013 #18
    I was saying that with charges.you are misinterpreting it.With a degree of freedom you can associate a dimension type thing if you wish.
     
  20. Jan 3, 2013 #19

    bhobba

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    It's not the broken symmetries that explains anything - its the symmetries themselves. For example U(1) gauge symmetry explains EM when you work through the math - and in a very beautiful way. Broken symmetries unifies them - that's all.

    Of course like all explanations it leaves questions unanswered - but that is in the nature of explanation itself.

    Thanks
    Bill
     
  21. Jan 3, 2013 #20

    bhobba

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    Yes of course. This interplay between gauge theories and geometries is a powerful idea.

    Thanks
    Bill
     
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