How Does Light's Speed Remain Constant in Moving Reference Frames?

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Homework Help Overview

The discussion revolves around the behavior of light's speed in different reference frames, specifically addressing a scenario where a beam of light is sent towards a receding galaxy. The original poster is uncertain about the principles governing the speed of light as perceived by observers in the galaxy.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants express their thoughts on the constancy of the speed of light across different reference frames, with some referencing Einstein's theory of special relativity. There is also mention of the Doppler effect in relation to frequency, though its relevance to the speed of light is questioned.

Discussion Status

Several participants agree on the notion that the speed of light remains constant at "c" regardless of the observer's motion. However, there is a lack of detailed exploration into the underlying principles, and the conversation appears to be open for further input and clarification.

Contextual Notes

Participants are navigating the implications of special relativity and the assumptions about inertial frames of reference, particularly in relation to the speed of light and its perception by different observers.

gmsss
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Homework Statement



We send a beam of light, traveling at the speed of light c, toward a distant galaxy, which is receding from us with a speed of 0.90 c. Observers in the galaxy see the light coming toward them with a speed of ?


Homework Equations


cant say


The Attempt at a Solution


i think answer is "c" but don't know exact principle behind it
i tried "Doppler's effect in light" but that tell us about apparent frequency
and i don't know how to start now
 
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Well, I won't pretend to be an expert in this but I believe you are right it should be "c" and I think it has to do with the idea that the speed of light is constant in all reference frames. I think Einstein came up with the idea as the basis for special relativity but someone else might like to come on here and correct me
 
I agree with Cherrybawls. I'm still no expert but I'm pretty sure of the answer. It's a postulate of Special Relativity.
More interesting would have been the question if they asked for the frequency of light, in which case you'd have to apply the relativistic Doppler effect.
 
gmsss said:

Homework Statement



We send a beam of light, traveling at the speed of light c, toward a distant galaxy, which is receding from us with a speed of 0.90 c. Observers in the galaxy see the light coming toward them with a speed of ?

This is what I think-
The galaxy is moving at a constant speed of 0.90c w.r.t earth. So it is an inertial frame of reference. Whatever is the speed of light on Earth will be the same in that galaxy too.
 

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