Speed of light vs speed of sound

Click For Summary

Discussion Overview

The discussion revolves around the comparison of the speed of light and the speed of sound, particularly focusing on how these speeds are affected by the motion of the source and the receiver. Participants explore theoretical implications, experimental observations, and the conditions under which these speeds are measured, addressing both conceptual and mathematical aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Aaron questions whether the speed of sound is dependent on the speed of the receiver, suggesting that it appears to be affected, unlike the speed of light.
  • Some participants assert that the speed of sound is determined by the medium's properties (temperature and density) and is independent of the source's speed.
  • Others introduce the concept of relativistic addition of velocities, noting that while the speed of light remains constant regardless of the observer's speed, the speed of sound can vary based on the observer's motion relative to the medium.
  • Aaron references a previous post claiming that neither the source nor the receiver affects the speed of sound until it reaches the receiver, which he challenges.
  • There is a discussion about the implications of frame of reference, with some participants suggesting that the speed of light is invariant in the observer's frame, while the speed of sound is fixed in the medium's frame.
  • One participant speculates about the possibility of overtaking a light pulse in a medium where light travels significantly slower than in vacuum, raising questions about the speed of light relative to a moving receiver.
  • Aaron expresses uncertainty about whether there is experimental evidence showing that the speed of light is independent of the receiver's speed, regardless of the medium.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus, as multiple competing views remain regarding the effects of the receiver's speed on the measured speeds of light and sound. The discussion reflects differing interpretations of experimental evidence and theoretical frameworks.

Contextual Notes

Participants note the importance of frame of reference and the conditions under which measurements are made, indicating that assumptions about the medium and the nature of the waves can significantly influence conclusions drawn from the discussion.

  • #31
@PeroK fine, light isn't fundamental to the theory we currently use under the name of SR - but I think we agree on that.

And "we can reformulate the theory without it " or "the theory works without it" is pretty much what I mean by "it is not fundamental to the theory"
 
Last edited:
Physics news on Phys.org
  • #32
The assumption that there exists some observable phenomenon (it doesn't have to be light) that propagates at the same speed relative to all inertial observers and without a medium is sufficient to derive the entire panoply of special relativity: Lorentz transforms, relativity of simultaneity, universal speed limit, relativistic velocity addition, length contraction, time dilation, Minkowski space-time, all that good stuff.

Hi Nugatory,that's a good point. Actually that is kind of why I was originally interested to know whether the fact that light travels at "c" for a moving receiver has been proven experimentally. With emphasis on, "propagates at the same speed relative to all inertial observers and without a medium".

Fizeau:
1) With a medium.
2) Medium is moving relative to observer.
3) Conclusion is that the observer is moving relative to the medium and therefore all inertial observers are taken into account.

De Sitter:
1) Moving source.
2) No medium (space).
3) Moving observer (the Earth), but irrelevant based on the experimental setup?
4) Conclusion is that a moving source has no effect on the speed of light.

Michelson Morley:
1) Source moving together with observer inside what was thought to be a fixed medium.
2) No fixed medium was detected so vacuum was hypothesized.

As I understand it, these three experiments could be used to prove SR. But in these three experiements, you don't explicitly fulfill the conditions in bold (above). We have a moving source in De Sitter, and a moving medium in Fizeau, but I'm not sure if its fair to extrapolate a "moving observer" from Fizeau.regards,
Aaron

EDIT: On the other hand, SR does correctly predict the observed speed in the Fizeau experiment which uses relativistic velocity addition... just confused :(
 
Last edited:
  • #33
wabbit said:
@PeroK fine, light isn't fundamental to the theory we currently use under the name of SR - but I think we agree on that.

And "we can reformulate the theory without it " or "the theory works without it" is pretty much what I mean by "it is not fundamental to the theory"

@wabbit

I think I see what you're saying now. That's beyond my knowledge of SR.
 

Similar threads

Undergrad Speed of Sound & Light: Is it True?
  • · Replies 1 ·
Replies
1
Views
1K
Graduate 1-Way Speed of Light
  • · Replies 42 ·
2
Replies
42
Views
3K
Undergrad Conventionality of the One-Way Speed of Light
  • · Replies 6 ·
Replies
6
Views
2K
High School Speed of Light & Sound: Revolutionary Phenomenon?
  • · Replies 22 ·
Replies
22
Views
2K
Undergrad Can we determine the one way speed of light by combined measurements?
  • · Replies 146 ·
5
Replies
146
Views
11K
Undergrad Speed of light and speed of sound both constant
  • · Replies 38 ·
2
Replies
38
Views
5K
Undergrad Bell's Spaceship Paradox, Born Rigidity, and the 1-Way Speed of Light
  • · Replies 47 ·
2
Replies
47
Views
4K
Undergrad A light wave and a sound wave travelling together
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad How Does the Twin Paradox Apply to Light and Sound Waves?
  • · Replies 48 ·
2
Replies
48
Views
6K
Undergrad A spaceship traveling close to the speed of light sending some data....
  • · Replies 94 ·
4
Replies
94
Views
10K