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

  1. Apr 12, 2013 #1
    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: Apr 12, 2013
  2. jcsd
  3. Apr 12, 2013 #2

    bcrowell

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    We have a FAQ about this: https://www.physicsforums.com/showthread.php?t=534862 [Broken]
     
    Last edited by a moderator: May 6, 2017
  4. Apr 12, 2013 #3
    Oh, I didn't notice, thanks! Will remove this thread.
     
  5. Apr 12, 2013 #4
    Hmm, can't find where to do this. Is it possible?
     
  6. Apr 12, 2013 #5

    phinds

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