Constance of speed of light and refraction index question

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Discussion Overview

The discussion revolves around the apparent contradiction between the constancy of the speed of light in vacuum, as stated in the special theory of relativity, and the observation that light slows down when passing through materials with a refractive index greater than one. Participants seek to clarify these concepts and explore the implications of light's speed in different mediums.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the speed of light in vacuum is constant across reference frames but questions how this applies to light traveling through materials.
  • Another participant explains that while the speed of light in vacuum is constant, it can appear to slow down in materials due to atomic interactions, suggesting that light travels at speed "c" between atoms but is globally slower due to absorption and re-emission processes.
  • A participant asks whether the constancy of light's speed holds true in non-vacuum conditions and within the same material reference frames.
  • A later reply asserts that the constancy does not apply in non-vacuum conditions.

Areas of Agreement / Disagreement

Participants express differing views on the implications of light's speed in various mediums, indicating that the discussion remains unresolved regarding the relationship between the speed of light in vacuum and in materials.

Contextual Notes

There are unresolved assumptions regarding the definitions of speed in different contexts and the implications of atomic interactions on light's propagation in materials.

Taturana
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I'm new to the forum, so, hi =D

Special theory of relativity tell us that the speed of light is the same, independently of the reference frame.

But we know that, while light travels through some materials (with refraction index larger than one), it speeds slows down.

These two "things" seems to have a contradiction to me. What's the explanation for that? (I think I'm making some confusion with these concepts)

If someone can help me with that, I would be grateful.

Thanks all
 
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The speed of light in vacuum is the same no matter what the frame of reference. That does not say that the speed is not reduced when it is moving through something.

(You can argue that, since all substances consist of a few atoms with vacuum between them, the speed of light is "c" between the atoms but it is "globally" slower than c because of the time required for the atoms to absorb and re-emit the light.)
 
HallsofIvy said:
The speed of light in vacuum is the same no matter what the frame of reference.

Is that also true assuming light not in vacuum (and the reference frames in the same material too)?
 
Taturana said:
I'm new to the forum, so, hi =D

Special theory of relativity tell us that the speed of light is the same, independently of the reference frame.

But we know that, while light travels through some materials (with refraction index larger than one), it speeds slows down.

These two "things" seems to have a contradiction to me. What's the explanation for that? (I think I'm making some confusion with these concepts)

If someone can help me with that, I would be grateful.

Thanks all

Please start by reading the FAQ thread in the General Physics forum.

Zz.
 
Taturana said:
Is that also true assuming light not in vacuum (and the reference frames in the same material too)?

No!
 

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