Speed of Light Always The Same?

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Discussion Overview

The discussion centers around the concept of the speed of light in a vacuum and how it remains constant regardless of the observer's speed. Participants explore the implications of relativity, particularly in scenarios involving high-speed spaceships chasing photons. The conversation includes attempts to clarify the mathematical underpinnings and conceptual challenges associated with these ideas.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about how light can travel at the same speed for different observers, particularly when one observer is moving at 99% of the speed of light.
  • One participant mentions the classical physics perspective where speeds would add linearly, contrasting it with the relativistic formula that maintains the speed of light as constant at c.
  • Another participant highlights the effects of time dilation and length contraction, explaining that different observers measure distances and times differently, leading to the conclusion that light moves at c relative to all observers.
  • Some participants question the implications of the relativity of simultaneity, suggesting that it complicates the understanding of how different observers perceive the position of a photon.
  • There is a suggestion that visual aids, such as spacetime diagrams, could help clarify these concepts.
  • One participant raises the notion that it seems as if a photon could occupy multiple positions simultaneously depending on the observer's frame of reference, prompting further clarification on the nature of events and measurements in relativity.

Areas of Agreement / Disagreement

Participants generally agree on the principles of relativity and the constancy of the speed of light, but there remains significant confusion and disagreement regarding the implications and interpretations of these principles, particularly concerning the relativity of simultaneity and how different observers perceive the same photon.

Contextual Notes

Participants express limitations in understanding the mathematics involved and the conceptual challenges posed by relativistic effects. There is an acknowledgment that the discussion involves complex ideas that may not be easily visualized or understood without further study.

  • #31
Let's try again, keeping it simple.

Do you agree that when we are talking about an inertial observer, it does not make sense to use anything other than an inertial coordinate system?

Do you agree that by default we talk about inertial coordinate systems (for example in the second postulate, this is assumed)?

Can you give me an example where we would not use an inertial coordinate system (either by choice or as the result of coercion) in a scenario where we are discussing only inertial participants (participants in the scenario)?

cheers

neopolitan
 
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  • #32
neopolitan said:
Let's try again, keeping it simple.

Do you agree that when we are talking about an inertial observer, it does not make sense to use anything other than an inertial coordinate system?
It would be kind of pointless to use a non-inertial coordinate system in this situation, although there'd be nothing technically wrong with using one if you just wanted to see how things worked out in it.
neopolitan said:
Do you agree that by default we talk about inertial coordinate systems (for example in the second postulate, this is assumed)?
Well, it's not just assumed, it's specifically stated that the two postulates are meant to apply to inertial coordinate systems. But yes, I agree this is the default in SR.
neopolitan said:
Can you give me an example where we would not use an inertial coordinate system (either by choice or as the result of coercion) in a scenario where we are discussing only inertial participants (participants in the scenario)?
There isn't any specific reason why you'd normally make that choice, but it is your choice, if for whatever idiosyncratic reason you wanted to analyze this situation using a non-inertial system then again there'd be nothing physically incorrect about it.
 
  • #33
JesseM said:
It would be kind of pointless to use a non-inertial coordinate system in this situation, although there'd be nothing technically wrong with using one if you just wanted to see how things worked out in it.

Well, it's not just assumed, it's specifically stated that the two postulates are meant to apply to inertial coordinate systems. But yes, I agree this is the default in SR.

There isn't any specific reason why you'd normally make that choice, but it is your choice, if for whatever idiosyncratic reason you wanted to analyze this situation using a non-inertial system then again there'd be nothing physically incorrect about it.

In light of that, can you explain why it was sensible of you to say that the speed of light being c is a consequence of your (human invented) coordinate system?

cheers,

neopolitan
 

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