The velocity of light in the medium

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Discussion Overview

The discussion revolves around the behavior of light in a medium, specifically questioning whether a Lorentz transformation analogous to that in vacuum can be applied when light travels at a speed of c/n in a medium. Participants explore the implications of this transformation and the measurements of light speed by observers in different frames within the medium.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that light travels at a speed of c/n in a medium and question if Lorentz transformations can be modified to replace c with c/n.
  • Others clarify that c/n is the phase velocity of light in the medium, emphasizing that c remains the ultimate speed limit, as evidenced by phenomena like Cherenkov radiation.
  • There is a proposal that the speed measured by an observer in the medium would be the relativistic sum of velocities, rather than simply c/n.
  • A historical reference is made to Fizeau's experiment, which is noted as a significant step toward relativity, although it did not recognize the concept of relativistic velocity addition at the time.

Areas of Agreement / Disagreement

Participants express differing views on the application of Lorentz transformations in a medium, with some supporting the idea of a modified transformation and others arguing against it. The discussion remains unresolved regarding the implications of these transformations and the correct interpretation of light speed in a medium.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the nature of light in media and the definitions of speed in different frames. The historical context of Fizeau's experiment is also noted, but its implications for modern interpretations are not fully agreed upon.

ENDLESSYOU
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We know that light travels at the same speed in vacuum regardless of the observer.And light also travels at a speed of c/n in the medium.My question is since c/n is the limit speed in medium,then do we have the similar Lorentz transformation in the medium which just replace c with c/n?
For example, suppose space is filled with medium.And the observer is in S-frame in the medium. A light is traveling in S'-frame which is also in the medium and is moving at the speed of u respect to S.Then what's the speed of light that the observer measures in S? c/n?
 
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ENDLESSYOU said:
We know that light travels at the same speed in vacuum regardless of the observer.And light also travels at a speed of c/n in the medium.
c/n is the phase velocity of the light in the medium.
My question is since c/n is the limit speed in medium,then do we have the similar Lorentz transformation in the medium which just replace c with c/n?
c/n is not the limit speed, c is. (Check out: Cherenkov radiation) The Lorentz transformations remain as usual.
For example, suppose space is filled with medium.And the observer is in S-frame in the medium. A light is traveling in S'-frame which is also in the medium and is moving at the speed of u respect to S.Then what's the speed of light that the observer measures in S? c/n?
No. The speed measured by the observer will be the relativistic sum of those velocities (using the relativistic addition of velocity).
 
ENDLESSYOU said:
For example, suppose space is filled with medium.And the observer is in S-frame in the medium. A light is traveling in S'-frame which is also in the medium and is moving at the speed of u respect to S.Then what's the speed of light that the observer measures in S? c/n?

Doc Al said:
No. The speed measured by the observer will be the relativistic sum of those velocities (using the relativistic addition of velocity).

In fact, this was first observed by Fizeau in the 1850s. Of course, he didn't recognize it as relativistic velocity addition, but Einstein did, more than fifty years later!

http://en.wikipedia.org/wiki/Fizeau–Foucault_apparatus#Speed_of_light_in_moving_media
 
jtbell said:
Of course, he didn't recognize it as relativistic velocity addition, but Einstein did, more than fifty years later!

Nevertheless Fizeau's experiment was a major step toward to relativity because the experiments of Michelson and Morley can not be interpreted correctly without falsification of a complete aether drag.
 

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