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Charged particle、neutral particle will hit the ground simultaneously?

  1. Oct 29, 2013 #1
    If we drop a charged particle and a neutral particle at the same time(same hight) in a uniform gravitaional field, they will hit the ground simultaneously?

    on one hand:a freely falling charged particle will radiate according to a supported observer, so the radiation recoil (radiation damping) wil decelerate the charged particle,the neutral particle will hit ground first.

    on the other hand : a freely falling charged particle will not radiate according to a freely falling observer,so the two particles will hit the ground simultaneously.

    how to solve this paradox?
  2. jcsd
  3. Oct 29, 2013 #2


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    Well for starters, the back reaction on a charge involves the interaction of the charge with its own electromagnetic field so how could the charge be freely falling? In other words, a freely falling particle can only be under the influence of the "gravitational force" but the back reaction involves the Abraham-Lorentz force as well.
  4. Oct 29, 2013 #3


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    Same answer as for your previous thread, magnetar. The electromagnetic field surrounding a charged particle is extended. Although the particle itself falls freely in the gravitational field it sees locally, distant parts of it see a different gravitational field, in which they are not freely falling.

    The charged object therefore does emit electromagnetic radiation. producing a back reaction and causing the charged object to fall more slowly than the neutral one.
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