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Effects of Electromagnetic mass indistinguishable from regular mass?

  1. Jan 15, 2012 #1
    An electrically charged particle has an electric field centred around itself that extends far into space.

    That field has an energy density proportional to the electric field squared.

    By Einstein's E=mc^2 that energy density is equivalent to a mass density.

    Thus, as a charged particle moves, it carries around with itself a "cloud" of mass in its electric field.

    If we assume the particle has a finite radius then the total mass in its electric field is finite.

    The centre of mass of this field mass/energy is located at the particle's postion and so moves with it.

    My question is this:

    Does this electromagnetic mass affect the particle's dynamics in exactly the same way as its "regular" mass even though it is spread diffusely throughout space?

    Thus is it true to say that:

    mass of charged particle = regular mass (localized at the particle position) + electromagnetic mass (extended throughout space)?
    Last edited: Jan 15, 2012
  2. jcsd
  3. Jan 15, 2012 #2
    I don't know how correct it is to say that any energy density is really a mass density, it's really more of a one way street (mass density is an energy density). However, ultimately your question comes down to the following: Does the electromagnetic FIELD (which carries energy) also participate in gravitational interactions. According to general relativity the answer is yes, EM fields DO curve spacetime just as any energy does.... However, the effect is also predicted to be so slight that I highly doubt it's ever been observed (and it is hardly a dominant effect).
  4. Jan 15, 2012 #3


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    A Rigorous Derivation of Electromagnetic Self-force
    Samuel E. Gralla, Abraham I. Harte, Robert M. Wald
    "Interestingly, we will also see that the electromagnetic self-energy of the body makes a non-zero, finite contribution to the particle’s mass."
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