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I Hubble red shifts could be gravitational red shifts rather than space-expansion red shifts?

  1. Nov 27, 2017 #21


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    Staff: Mentor

    And indeed it is.
    Actually, I think @phinds understands very well what you are suggesting. The problem is that it has implications that don't match observations. Namely if the universe was a sphere, redshifts would not be uniform and would point toward its center. In addition, the density of galaxies would decreade with increasing distance from the center.

    So it isn't that he doesn't want to try to understand your scenario, it's that he already has (A lot of people ask similar questions) and we already know that it conflicts with what is observed.

    ....you've also mixed together gravitational and cosmological redshift in an odd way. That one's new.
  2. Nov 27, 2017 #22


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    That surprises me. Do you have any references that explain this? Because grammatically it seems like "unbounded" and "without boundary" should be synonymous.

    Googling, it looks to me like that's even the name of a chapter in Einstein's book, which would explain why that definition has so much traction. So was the definition changed?
  3. Nov 27, 2017 #23


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  4. Nov 27, 2017 #24


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    I just read this and it seems wrong. A loop of string is finite but is not bounded because there are no ends. Likewise, the surface of a sphere is finite but there are no 'bounds'. Just introduce some more dimensions and the same can apply to our 3D space.
    The phrase "finite but boundless" can be found in a lot of the popular science literature (no citation but I'd bet I could find one if you press me) and it could apply to any finite universe, whatever the geometry.
  5. Dec 8, 2017 #25
    Personally, I thought the poster had raised an intriguing question, one that hadn't occurred to me before. The answer (when it came) was worth the wait. . .
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