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Can light exist without space time?

  1. Oct 22, 2014 #1
    Since the medium in which light propagates is space time, would light be able to exist if spacetime did not exist? Is this like one of those chicken/egg problems, or can light be thought of as a legitimately independent entity?
     
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  3. Oct 22, 2014 #2

    A.T.

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    Does the way you think of it affect any quantitative predictions? If not, it's not a physics question.
     
  4. Oct 22, 2014 #3

    Vanadium 50

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    How can one answer the question "how would physical objects behave in a non-physical world?"
     
  5. Oct 23, 2014 #4

    ghwellsjr

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    The old idea that light propagates in a medium implies that there is just one particular Inertial Reference Frame (IRF) in which light propagates at a constant speed called "c". If that were true then we wouldn't call it spacetime, it would just be space, and time would be independent of space. But theories based on those ideas end up being rather cumbersome and confusing. On the other hand, Special Relativity asserts that light propagates at c in any and every IRF, no matter what the relative speeds are between those IRF's and that is a much simpler concept and still comports with everything we can measure about light, space and time.

    Rather than thinking of Special Relativity as a problem, it is a simple solution to what would otherwise be an intractable problem in thinking about light, space and time.
     
  6. Oct 23, 2014 #5

    HallsofIvy

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    I can't imagine how anything could exist without space-time?
     
  7. Oct 24, 2014 #6
    Isn't the speed of light constant in non-inertial frameoo)
     
  8. Oct 24, 2014 #7

    ghwellsjr

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    The speed of light is constant in the non-inertial frames I make using the radar method but other people make non-inertial frames in which the speed of light is not constant. There's no standard way (no rules) to make a non-inertial frame so you can do it any way you like. For example, in the coordinate system defined by GPS, the speed of light is not constant.
     
  9. Oct 24, 2014 #8

    Dale

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    Not in general, no.
     
  10. Oct 25, 2014 #9

    Vanadium 50

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    In general, if the speed of something is constant in an inertial frame, it is not constant in a non-inertial frame. Light, sound, cars, bulldozers, baseballs, etc. This goes back to Newtonian mechanics.
     
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