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What is charge?

  1. Oct 13, 2008 #1
    I know the question sounds ridiculously simple, but I haven't been able to form an answer. What is charge? Why do particles have an electrical charge and where does it come from? Is it just a basic property of particles or is there a mechanism?

    For your information: I'm a third year undergrad in physics, so I have a basic grasp of most branches of physics.
  2. jcsd
  3. Oct 13, 2008 #2
    It's a fluid.

    Not really though ;-) It's just an intrinsic property of a particle. Like mass or momentum. It's not an emergent property such as density or pressure. It's fundamental. You can't really define it in terms of simpler things.
  4. Oct 13, 2008 #3
    It's also a rather unique entity like dark energy (the cosmological constant) that is always measured at the same value regardless of reference frame....unlike, for example, all forms of energy.

    Oddly the charge of an electron, a fundamental particle, is opposite that of a proton which is composed of other particles...quarks....where some combination produces "charge"

    Charge in an electrical circuit is of course in coulombs...q = it....

    Maybe charge flows from the Higgs field (standard model theory) as does particle mass...nobody knows. (That's purse speculation)

    In string theory, charge flows from the vibrational pattern of the string...

    There is no theoretical foundation for why the fundamental value of charge is what it is...it's an experimentally determined constant...
  5. Oct 14, 2008 #4
    I dont know that we can ever say what something 'is'. we can only try to model it and say how it behaves. the question becomes 'what is it like'? it behaves 'as if what'?

    charge is the tendency of particles to produce electric fields. so the answer to your question will depend on what conceptual model you use to describe particles and fields.
    Last edited: Oct 14, 2008
  6. Oct 14, 2008 #5
    This is generally true currently, yet the unification of the strong/weak/electromagnetic forces can offer some mathematical insights... Weinberg/Salam/Glashow found a common source for the three in an electroweak unification...the three forces appear as one when energies are high enough...so the electromagnetic field and resulting "charge" is another result of symmetry breaking as the universe underwent a phase transition from high energy and instability to the lower energy more stable environment we now observe....yea, still rather vague, I know...

    "we know much, we understand little"
  7. Oct 14, 2008 #6
    It occurred to me there is yet another "weird" aspect of electric charge: if you observe a stationary electric charge and you are in the same coordinate system at rest, you'll observe an electric field only; if there is relative motion between you and the charge, the electric field disappears and all you see is a magnetic field!!!
  8. Oct 14, 2008 #7
    actually I dont think that the electric field of the charge will ever disappear.

    you will always see a charge and charges always have fields.
  9. Oct 14, 2008 #8
    Indeed, the electrical field doesn't dissapear. It will become weaker along the line of motion, and stronger in the plane perpendicular to it if you get to high enough velocities, but it won't go away.
  10. Oct 15, 2008 #9
    you guys are right...I must have gotten carried away....only the magnetic field pops in and out of "existence"..
  11. Oct 15, 2008 #10
    Actually, the electric field can disappear as well as the magnetic. In a rest frame with current in a superconducting loop, the is a magnetic field but no electric field.

    Either one can disappear and reappear with reference frames.

  12. Oct 15, 2008 #11
    soorry...this really has nothign to do with the question....but how the heck do you post a thread or a question to ask?? im soo confused..thanks in advance
  13. Oct 15, 2008 #12


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    When you're looking at the list of threads in a forum, click the "New Topic" button at the top or bottom of the list.

    By the way, I've deleted your other post with the same question, in the "Classical Physics" forum.

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  14. Oct 17, 2008 #13
    Naively, charge is the divergence of the electric field. The electric field can be expressed as the curl of an arbitrary, C^2 vector field over spacetime—curved or flat. That the divergence (charge) is conserved over time, is a direct result of the local Lorentz metric.

    Any vector field on spacetime has a conserved charge.

    (Edit: The charge minus the current out is conserved.)

    But experimentally, charge is always attached to mass. So the usually way of thinking about these things is significantly different. From an arrangement of charge and currents, you derive the associated fields, where the equal sign in Gauss’ law is not taken as a statment of equivalence but a directional assignment from charge to field.
    Last edited: Oct 18, 2008
  15. Oct 17, 2008 #14
    Charge is the source/sink of the photon.
  16. Oct 17, 2008 #15


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    Homework Helper

    ?? What photon?
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