Violate the principle of relativity?

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Homework Help Overview

The original poster is exploring a scenario involving the speed of light in a medium, specifically within a water pipe where the light moves in the same direction as the water flow. The question raised is whether this situation violates the principle of relativity.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between the speed of light in different media and the principle of relativity. There is an attempt to clarify the distinction between the speed of light in a vacuum and in a medium. Some participants suggest the need for understanding velocity addition formulas to address the original poster's concerns.

Discussion Status

The discussion is ongoing, with participants providing insights and references to relevant concepts such as the Fizeau experiment and the velocity addition formula. There is a mix of interpretations being explored, and some guidance has been offered regarding the relationship between the speed of light and the flow of water.

Contextual Notes

Participants are navigating assumptions about the nature of light speed in different contexts and how it relates to established principles of relativity. There is an acknowledgment of the complexity of the topic, with references to external resources for further exploration.

tkm2002
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Homework Statement


In a water pipe, the light moves in the same direction of the water flow. It is
determined that the speed of light is dependent on the speed of water flow. Does
that violate the principle of relativity?


Homework Equations





The Attempt at a Solution


why the speed of light is dependent?
I know it should not be violate the principle of relativity but I don't know how to explain.
 
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You are looking at a famous relativity example.

A distinction must be made between "speed of light (in a given medium)" and "speed of light in a vacuum (the speed limit of the universe)". I call the latter the "information speed limit".

I can suggest some more if you want, but that nugget of info above may be useful to you :).

EDIT: Actually, that is a downright awful attempt at being helpful, let's see if I can do better. You need to know about velocity addition formulae to answer the question. If you have tried all of that to no avail, then the water stuff is known as the fizeau experiment (books and interwebs know all about it)
 
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tkm2002 said:
In a water pipe, the light moves in the same direction of the water flow. It is determined that the speed of light is dependent on the speed of water flow. Does that violate the principle of relativity?

Hi tkm2002! :smile:

No, it confirms the principle of relativity …

the v(1 ± 1/n2) formula is what special relativity predicts (by adding or subtracting v, the speed of the water, to c/n, the speed of light in the water) …

see http://en.wikipedia.org/wiki/Fizeau_experiment#Derivation_in_special_relativity" :wink:
 
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Last edited by a moderator:
Special Relativity has a formula for "adding" velocities.

That formula is different from ordinary adding, but it agrees with the results of Fizeau's experiment …

so Fizeau's experiment does not violate Special Relativity, but confirms it.

See that link for details. :smile:
 

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