EM waves- self propagating in a vacuum?

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Discussion Overview

The discussion revolves around the propagation of electromagnetic (EM) waves in a vacuum, particularly questioning how these waves can self-propagate without a medium. Participants explore various explanations, including photon theory and Maxwell's equations, while grappling with the underlying mechanisms of EM wave propagation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that EM waves are created by moving charged particles but struggles to understand their self-propagation in a vacuum.
  • Another participant suggests that Maxwell's equations provide an explanation for EM wave propagation beyond photon theory.
  • A participant explains that the oscillating charge generates electric and magnetic fields that renew themselves as they propagate, effectively "forgetting" the source charge.
  • There is a discussion about the nature of the changing fields, with one participant questioning whether the source charge's movement is necessary for the fields to change.
  • It is proposed that once an initial disturbance is created by a moving charge, the wave will continue to propagate even if the charge remains stationary.
  • One participant emphasizes that physics often does not answer "why" questions, suggesting that the behavior of fields is simply a fundamental aspect of nature.
  • Another participant recommends looking at Faraday's ideas for a simpler understanding of how EM waves propagate compared to Maxwell's equations.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and acceptance of different explanations for EM wave propagation. There is no consensus on a single explanation, and multiple viewpoints remain regarding the mechanisms involved.

Contextual Notes

Some participants acknowledge the complexity of the topic and the limitations of their understanding, indicating that certain assumptions and definitions may not be fully addressed in the discussion.

kasap
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First of all, I understand that an EM wave is created by a charged particle that is moving.

What I don't understand is how it propagates itself when traveling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really can't wrap my head around the idea of self propagation.

Sorry in advance if this question is a load of rubbish, thanks.
 
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kasap said:
First of all, I understand that an EM wave is created by a charged particle that is moving.

What I don't understand is how it propagates itself when traveling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really can't wrap my head around the idea of self propagation.

Well, you must.

Close to the oscillating charge the field is dependent on the oscillating charge, but as the field expands it continually renews itself by alternately generating E and H fields. The cause of the field, the oscillating charge, is essentially "forgotten"!
 
Thanks to both of you for your replies,
rude man said:
Well, you must.

Close to the oscillating charge the field is dependent on the oscillating charge, but as the field expands it continually renews itself by alternately generating E and H fields. The cause of the field, the oscillating charge, is essentially "forgotten"!

Thank you this makes more sense now, I looked up Maxwell's equations and saw that a changing magnetic field gives rise to an electric field and vice versa. But what causes them to change, is it not that the source (the oscillating charge) is constantly changing position? Sorry in advance if this is a stupid question.
 
What causes them to change? That is just how they are. Is it any more mysterious than the fact that charges and current create the fields in the first place?

Physics isn't really in the habit of answering "why" questions.
 
kasap said:
But what causes them to change, is it not that the source (the oscillating charge) is constantly changing position?
The charge need not continue to change position. If it briefly changes position and then remains at rest then there will be a brief wave which will propagate at the speed of light forever (in principle).
 
kasap said:
But what causes them to change, is it not that the source (the oscillating charge) is constantly changing position? Sorry in advance if this is a stupid question.

The initial disturbance is created by the moving charge, but once created it will continue to propagate. Intuitively, it's not all that different from what happens when you toss a rock into a pool of still water - the ripples keep spreading long after the rock has quietly sunk to the bottom.
 
mikeph said:
What causes them to change? That is just how they are. Is it any more mysterious than the fact that charges and current create the fields in the first place?

Physics isn't really in the habit of answering "why" questions.

DaleSpam andf Nugatory have done well in answering 'why'. It's a really cool topic although I would look at Faradays basic ideas on Bf and how they are created by moving charges (from your 'static' frame of reference) as opposed to Maxwell's equations for more simplicity in understanding how these EM waves propagate through space.
 

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