Why does refraction of light involve a difference in speed?

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Discussion Overview

The discussion revolves around the phenomenon of light refraction and its relationship with the speed of light in different media. Participants explore the apparent contradiction between the constant speed of light as stated in the theory of relativity and the observed change in speed when light passes through various materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that refraction is explained by a difference in the speed of light between two media, referencing Snell's Law.
  • Another participant clarifies that the speed of light in a vacuum is a constant, aligning with the principles of relativity.
  • A further contribution explains that in relativity, the constant speed of light applies specifically to a vacuum, and that in a medium, the apparent reduction in speed is due to the absorption and re-emission of light by atoms, which introduces delays.
  • A later reply expresses appreciation for the explanations provided, indicating a level of understanding achieved.

Areas of Agreement / Disagreement

Participants present multiple views on the nature of light speed in different contexts, with some agreeing on the constant speed of light in a vacuum while others focus on the effects of media on light's apparent speed. The discussion does not reach a consensus on the compatibility of these concepts.

Contextual Notes

The discussion highlights the dependence on definitions of speed in different contexts and the unresolved nature of how these concepts interact within the framework of relativity and refraction.

Evans of Sprot
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As I understand it, refraction of light works because of a difference in the speed of light between the two medums involved (Snell's Law?).

However according to the theory of relativity the speed of light is a constant.

These two statements seem incompatible and I would like to know if there is a simple explanation.
 
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The speed of light in vacuum is a constant.
 
In Relativity, it is the speed of light in a vacuum that is constant. Also, in a medium the reason the apparent speed of light is lower is that the light is being absorbed and re-emitted by the atoms of the medium. It is the delay between the absorption and emission that seems to "slow" the light down. While the light is traveling from atom to atom it still travels at the constant speed it does in a vacuum.
 
Many thanks to you both!

Very simple really!
 

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