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Expanding Universe (an interestin mind experiment)

  1. Sep 29, 2006 #1
    Try thinking about measuring the expansion of the universe based on relativity. That is to say that depending on where you are located in the universe you might measure expansion or you might measure contraction!
    Think about this.
    The observer is placed anywhere inside of a giant ball of yellow "play dough". throughout the inside of the yellow ball are many little balls of different colored "play dough" representing galaxies.
    Now something starts to squeeze the yellow ball.
    Now depending on where the observer is located. He will percieve the colored "play dough" (the galaxies) expanding or he we percieve the galaxies contracting.
    Can it be that our universe is being sqeezed by other dimensions (other universes?

    I would appreciate any comments
    Thank You
    Pat Fontecchio
  2. jcsd
  3. Sep 30, 2006 #2
    If the universe is being squeezed, then it would have to be squeezed by gravity. But observation indicate a homogenous, isotropic universe at large scales. So there does not seem to be any mechanism for squeezing.
  4. Sep 30, 2006 #3
    Let us assume that the yellow ball is being sqeezed equally from all directions.
    And let us assume that the yellow ball is compressing.
    There is at the exact center of our ball a infinitesimally small point at which there can be no compression, just like the epicenter of an earth quake.
    from the exact moment that compression starts ,there is, at that exact moment, expansion away from the epicenter equal in all directions.
    So if the observer were closer to the epicenter what would he observe?
  5. Oct 2, 2006 #4
    Don´t think of it as play dough, think of it as a raisin muffin in an oven. As the muffin itself expands, the raisins expand with the muffin giving all the raisins a expansion movement from what ever raisin you are standing on.
  6. Oct 3, 2006 #5


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    But in a universe with a finite speed of light [wrt local reference frames], cosmological expansion will be apparent to all observers. It is difficult to explain redshifts > 1.66 without cosmological expansion.
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