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What would the universe be like if c were not uniform

  1. Aug 10, 2011 #1
    I sort of understand Einstein's theory of relativity. I'm trying to visualize what the universe would be like if the speed of light were added on to moving objects. objects are moving in so many directions that it's hard to understand how one would even add the speed of light on to a motion. for example, our galaxy is moving in a direction, our sun is moving around the galaxy's center, and we're moving around the sun and moving around our earth's axis. i suppose if visual light were added on to movement it might just be too confusing, but i cannot exactly imagine how.
     
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  3. Aug 10, 2011 #2

    Pengwuino

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    Are you asking what would happen if basically, the universe had a minimum speed, the speed of light?

    Well, for one, physics wouldn't exist because interactions would be impossible.
     
  4. Aug 10, 2011 #3
    No, I'm asking what would happen if the speed of life depended on how fast observer is going.
     
  5. Aug 10, 2011 #4

    Pengwuino

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    Do you mean speed of light?

    Well, you'd basically go back to classical mechanics/classical electrodynamics. At our human scale, nothing would really change.
     
  6. Aug 10, 2011 #5
    how about on a non-human scale?
     
  7. Aug 10, 2011 #6

    Pengwuino

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    Well, there would exist no "relativistic context" so far high energy and massive objects at the planetary/solar/galactic scale, the world would be just like Newtonian physics would predict.

    Then again, it makes a difference if you say "what if the speed of light was not invariant for all observers" vs. "what if there was no maximum speed limit". The former still allows you to have general relativity and all that. The latter wouldn't allow you to have relativity.

    Non-relativistic quantum mechanics would stay the same. Depending on whether or not you picked the former or latter choice above, you may or may not be able to keep most of relativistic quantum mechanics unchanged.
     
  8. Aug 10, 2011 #7
    even now i think our universe doesn't add up everything to 'c' it jus appear that way. sorry i am a non believer. :)
     
  9. Aug 10, 2011 #8

    Pengwuino

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    What does "add up everything to 'c'" even mean?
     
  10. Aug 11, 2011 #9
    The non local speed of light, i.e. the speed of light between two points, in a gravitational field is NOT uniform. Only the local speed of light, i.e. the speed of light at a point, is always the same.
     
  11. Aug 11, 2011 #10
    If the speed of light was not uniform , the relation between time and space which was constructed in the relativity theory will be destroyed and we will get an absolute space and absolute time.

    This constant value of the speed of light is the real deep link between Time "t" and Position "x" for any body , and without it we return back to the old ages of classical physics.
     
  12. Aug 16, 2011 #11
    This thread is confusing.

    As I understand bobsmith's question, he means, what would happen if Einstein's postulate about the speed of light were wrong.
    I am far from being able to answer that.

    However - I do understand the guy's question. It's a good approach, I think. It's sometimes very hard to understand Einsteins postulate "c is constant in every inertial frame". It might make sense then to ask: what would happen if it weren't the case? I think that's what he means.

    in a similar way, one could ask: How come the gravitational force is proportional to r^-2. Why not r^-2.00....1?
    Because - apparently, nothing would be able to exist as we know it, were it the case. (that's at least what I understood).

    Still haven't understood the answer though.
     
  13. Aug 16, 2011 #12

    HallsofIvy

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    The simple answer is that if light's velocity depended on the speed of the observor, the universe would be "Newtonian" rather than "Einsteinian". That is, classical physics would apply.
     
  14. Aug 16, 2011 #13

    pervect

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    As far as cosmology goes nobody seriously tries to do Newtonian cosmology anymore. I imagine a few old problems, such as Olber's paradox, would arise again if you tried.

    You'd probably wind up with a finite sized universe like a large version of our solar system. One which would have a center, maybe you could arrange to have the Earth at the center of it:).

    You'd have to throw out a bunch of actual observations and measurements though, including pretty much all of modern cosmology (and the associated observations), but if you shut your eyes to all these contradictory measurements that are trying to wake you up and telling you "it's not really like that", I suppose it could be peaceful.
     
  15. Aug 16, 2011 #14
    And what about the possibility of one catching his own emitted light? Doesn't that lead to a crazy paradox? :-)
     
  16. Aug 19, 2011 #15
    There are a few documented cases from the early days of jet aircraft where a pilot fired a forward facing machine gun, then out-distanced his bullets and turned into their path, thus shooting his own aircraft. If light speed were not invariant then the same thing would be possible and no more paradoxical
     
  17. Aug 20, 2011 #16

    pervect

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    Well, it's true that assuming that something that is impossible happens (like catching up with a light beam in a vacuum while at the same time using the rules of relativity) does lead to crazy results, the problem is that a false assumption can be used to prove anything.

    Other than that, I'm not quite sure what the question is, or why.
     
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