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Propogation of Gravity vs Light

  1. Aug 21, 2008 #1
    Probably a really basic question but it bugs me:

    Gravity weakens as it propogates through space. So does light and all electromagnetic signals. Does anyone have an opinion on which of the two weakens proportionately more per unit of distance, and why?
     
  2. jcsd
  3. Aug 21, 2008 #2

    HallsofIvy

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    There does not seem to me to be any reason to think that they do not "weaken" at the same rate. Basically, the "weakening" is a matter of the same amount being spread out over a larger spherical surface.

    Back when I was in high school, my physics teacher had what he called a "butter gun". Basically it was a squirt gun with a pyramidal structure of rods attached. You put the toast between the rods and then squirted butter on it! The point was that, because area is proportional to the square of length, if you put the toast twice as far from the pistol, you could fit 4 pieces of toast where only one would fit before. Since you are firing the same amount of butter over 4 times the area, the thickness of butter is 1/4 as much on each slice of toast. Butter, light, or gravity, it's all 1/r2.
     
  4. Aug 21, 2008 #3
    Odd that both gravity and light travel at c, and both wane proportionate to 1/r^2. Coincidence? I wonder what else gravity and light have in common. Makes me think that gravity and light are just two aspects of one unified phenomenon.
     
  5. Aug 21, 2008 #4

    Chronos

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    They occupy exponentially larger volumes of space as distance increases. The relative force falls off proportionately. Energy is always conserved.
     
  6. Aug 22, 2008 #5
    if space were 4 dimensional then they would all follow an inverse cube law.
     
  7. Aug 22, 2008 #6
    Explain in laymans terms please?
     
  8. Aug 22, 2008 #7
    in x dimensional space long range forces would be expected to follow a 1/(x-1) law
     
  9. Aug 22, 2008 #8
    does that mean that since gravity etc. follows an invers squar law that the existence of a fourth spacial dimension can be ruled out?
     
  10. Aug 22, 2008 #9
    it means that gravity is confined to our 3 dimensions.
     
  11. Aug 22, 2008 #10

    Chronos

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    Gravity behaves poorly beyond 3 spatial dimensions.
     
  12. Aug 23, 2008 #11
    how so? poorly in what way?
     
  13. Aug 24, 2008 #12

    Chronos

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  14. Aug 25, 2008 #13
  15. Aug 25, 2008 #14

    Chronos

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    Of course if atoms are unstable in more than four dimensions, any discussion of higher order relationships is pointless. More than four dimensions are, however, apparently necessary [on local scales] to accomodate the zoo of exotic particles known to exist. This is a mathematical artifact, but, cannot be ignored.
     
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