Electron in Earth Orbit: Does it Emit Radiation?

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Discussion Overview

The discussion centers on whether an electron in circular orbit around the Earth emits radiation, exploring both classical and relativistic perspectives. Participants consider implications of the equivalence principle and the nature of radiation emitted by charged particles in different frames of reference.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question if an electron in Earth orbit emits radiation, drawing parallels to an electron on a laboratory bench, which experiences upward acceleration due to gravity.
  • One participant asserts that an electron in orbit behaves classically and would emit Larmor radiation, providing a formula for the power radiated, but notes that this power is very small.
  • Another participant argues that the equivalence principle does not apply to radiation emitted by electric charges, suggesting a need for further exploration of this concept.
  • There is a suggestion that while an electron in freefall may radiate, an observer in the same frame would not detect this radiation, implying a distinction between local and global properties of radiation.
  • A proposal is made about detecting radio frequency signals from charged capacitors in orbit, raising questions about the nature of radiation in such scenarios.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether an electron in orbit emits radiation or the implications of the equivalence principle regarding radiation. Multiple competing views are presented, and the discussion remains unresolved.

Contextual Notes

Limitations include the dependence on classical versus quantum mechanical interpretations, the assumptions regarding the applicability of the equivalence principle, and the unresolved nature of the radiation detection in different frames of reference.

yogi
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Does an electron in circular Earth orbit emit radiation?
 
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A good question, similar to the question: "Does an electron 'sitting' on a laboratory bench emit radiation as by the equivalence principle it is accelerating upwards at an acceleration g?"

If the answer to the orbiting scenario is 'yes', then the electron might be expected to spiral inwards to conserve energy; however where does the energy of radiation of an emitting supported electron on a lab bench come from?

Garth
 
Last edited:
yogi: Yes. An e in Earth orbit behaves classically because its radial quantum number is so high. It would emit what is called Larmor radiation at the rate:
P=2e^2 R^2 \omega^2/3c^2. (This is in Gaussian units.)
You can put numbers into see that this radiated power is tiny.

Garth: The EP does not hold for radiation by electric charges.
There is another post about that today.
 
Meir Achuz said:
Garth: The EP does not hold for radiation by electric charges.
There is another post about that today.
Why not? It would seem logical to expect that all physical processes within this universe's space-time would be subject to the the geometric effects and principles of GR.

There has been dicsussion on this subject on these Forums some time ago.

Garth
 
Seems the references cited in the other thread support the notion that 1) an electron in freefall will radiate, and 2) an observer comoving in the freefalling frame does not see the radiation? So unless there is some identifiable local physics that tell the electron in free fall when and how to radiate - the radiation must be due to a global property. If we place a charged spherical capacitor in orbit we should expect to detect radio frequence signals? - what about a charged parallel plate capacitor?
 

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