Why does the speed of light have to be constant to all observers?

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Discussion Overview

The discussion centers around the necessity of the speed of light being constant for all observers, as posited by the principle of Special Relativity. Participants explore the implications of this constancy, including the concept of a cosmic speed limit and its potential effects on the logical consistency of the universe.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that if the speed of light were not constant, it would imply the absence of a cosmic speed limit, leading to questions about the logical consistency of the universe.
  • This participant also raises concerns about whether such a scenario would violate the law of conservation of energy.
  • Another participant references a FAQ that may address the question, indicating that there is existing material on the topic.
  • Subsequent posts express difficulty in removing the thread, indicating a procedural concern rather than a continuation of the discussion on the topic itself.

Areas of Agreement / Disagreement

The discussion remains unresolved, with one participant posing questions and concerns while others provide procedural responses without directly addressing the conceptual issues raised.

Contextual Notes

Limitations include the lack of detailed exploration into the implications of a non-constant speed of light and how it might affect physical laws, as well as the absence of responses that directly engage with the foundational questions posed.

Bobcent
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Hello!

I think I understand the principle of Special Relativity, that because the speed of light has to be constant to all observers, the only solution to the problem is that time slows down or speeds up for different observers who are traveling at different speeds.

But my question is: Why does the speed of light have to be constant to all observers?

If the speed of light wouldn't be constant to all observers, there wouldn't be a cosmic speed limit, right? Because then, if I travel at a certain speed and emit light in front of me, the speed of that light would be my speed + the speed of light.

So if there wouldn't be a cosmic speed limit, would the universe still be logically consistent? If not, in what way wouldn't it be? Would it somehow violate the law of conservation of energy?

Or would the universe actually be logically consistent even if there wouldn't be a cosmic speed limit, just that it turns out that that's not the way our universe works?
 
Last edited:
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We have a FAQ about this: https://www.physicsforums.com/showthread.php?t=534862
 
Last edited by a moderator:
Oh, I didn't notice, thanks! Will remove this thread.
 
Hmm, can't find where to do this. Is it possible?
 
Bobcent said:
Hmm, can't find where to do this. Is it possible?

Only by hitting "report" and asking a moderator to remove the thread, but thread removal is rarely done.
 

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