Does the equivalence principle hold for charged particles?

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Discussion Overview

The discussion centers on the equivalence principle (EP) and its implications for charged particles, particularly whether the principle holds in the context of electromagnetic radiation. Participants explore the theoretical and conceptual challenges posed by the interaction of charged particles with gravitational fields and acceleration, questioning the frame dependence of radiation detection.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that the EP fails for charged particles, suggesting it is intended only for gravitational effects without electromagnetic considerations.
  • Others propose that radiation is frame independent, although they acknowledge the complexity of the issue and the potential for differing interpretations based on the observer's frame of reference.
  • A participant highlights that while an accelerating charge is said to radiate, the situation becomes problematic when considering stationary charges in a gravitational field, which do not radiate from the perspective of co-stationary observers.
  • There is a discussion about the relativity of concepts such as work and energy, suggesting that electromagnetic radiation may also be a relative concept, dependent on the observer's frame.
  • Some participants express uncertainty about the implications of current theories of electromagnetism and whether they adequately address the question of radiation from accelerating charges.
  • A later reply questions the assumption that accelerating charges necessarily radiate, indicating that this remains an open question in classical electrodynamics.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the equivalence principle holds for charged particles, with multiple competing views presented regarding the frame dependence of radiation and the implications for electromagnetic theory.

Contextual Notes

The discussion reveals limitations in current understanding, particularly regarding the definitions of radiation and the influence of acceleration on electromagnetic interactions. The complexity of the relationship between charged particles and gravitational fields is emphasized, with unresolved mathematical and conceptual challenges noted.

  • #31
pianoplayer said:
I'm inclined to go along with you guys (e.g., Qoo and Chronos) who argue that no radiation is seen by an observer accelerating with the charge. Here's a question: from a purely classical perspective, could one look at the problem as follows. The observer who's accelerating with the charge will see a static electric field -- no time dependence, no retarded potentials, and thus no radiation. Now a guy floating in space sees this accelerating charge move past. From his point of view, the electric field is not static. Could one sit down and do the calculation to show that he sees time-varying (transverse) components of an electric and magnetic field with a non-zero Poynting vector, i.e., EM radiation. If this can be demonstrated, it seems this would settle the argument without resorting to arguments about "fuzzy" particles, etc. Or perhaps it's not this simple.

http://xxx.lanl.gov/abs/gr-qc/0006037

goes through this calculation, though I really have only glanced at it.

To write the Poynting vector at Rindler instant \mbox{\omega_0} for the local observer who is
seated at (Xo, Yo,Zo), we can write everything in the instantaneous rest frame of the
source S at the retarded time and then use the Lorentz boost that transforms this frame
to the instantaneous rest frame of O (at the moment of observation).

They find that an accelerating observer sees only a pure electric field, and hence no Poynting vector.
 

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