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Is dark energy needed in a perturbed universe.

  1. Jan 21, 2005 #1

    wolram

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    http://arxiv.org/pdf/astro-ph/0501152
    Is dark energy needed in a perturbed universe.
    I came across this letter and thought it may be of interest.
     
  2. jcsd
  3. Jan 21, 2005 #2

    Garth

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    Is dark energy needed? See this paper by
    Blaschke & Dabrowski.

    Garth
     
    Last edited: Jan 21, 2005
  4. Jan 21, 2005 #3

    ohwilleke

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    A very interesting paper Wolram. The key points:

    (1) This does not propose any modification of GR. It simply proposed retaining GR and discarding an assumption behind the Friedman-Walker equation (homogenity) which almost all theorists using it recognize is there to make the math easier, not because anyone really thinks that the universe is homogeneous (indeed, the existence of large scale structure, an inhomogeneous feature of the universe, is a well established feature of modern cosmology).

    (2) Likewise, this does not propose any really new physical process. It just applies only theories with new assumptions.

    (3) The authors appear legitimate and the course of the paper is typical for a physics paper.

    (4) It points out that the dark energy proportion of current theory flowing out of observations and Friedman-Walker are far more sensitive to the infrared than to the blue end of the scale. This is the end of the scale where MOND and other proposed gravity modification take place as well.

    The biggest downside is that the ideas in this article are hard to prove affirmatively because they are sufficiently flexible that they make few predictions.
     
  5. Jan 21, 2005 #4

    Garth

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    The fluctuations seen in the WMAP data have now been confirmed to exist in later galaxy distribution. Surely if the requirement for homogeneity is dropped one would expect much greater anisotropies in WMAP?

    Garth
     
  6. Jan 21, 2005 #5

    jcsd

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    ohwilleke, actually most people do think the universe is very homogenous, sure everyone recognizes it's not totally homogenous, but the assumption of homogenity goes far beyond simple mathematical convience.
     
  7. Jan 24, 2005 #6

    ohwilleke

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    What about the large scale structure then? Stellar organization seems to have big "threads" of density and big "oceans" of emptiness. Moreover, it seems to be almost fractal (i.e. the gap-wall configuration seems to happen at multiple scale levels), wouldn't it be reasonable to suppose that such a structure produces significant imhomogeneity.

    And, whatever people have believed about the homogenity of the universe, I think it is definitely true that most people did not think the Friedman equations were as sensitive to this fact as it would appear that they are.
     
  8. Jan 24, 2005 #7

    hellfire

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    P.J.E. Peebles treats this issue with detail in "Principles of Physical Cosmology", pages 203 to 224. The observed fractal structure of the galaxy distribution under (few) hundred Mpc cannot be consistently extended to very large scales, where a (nearly) homogeneous distribution is observed.
     
  9. Jan 24, 2005 #8

    Chronos

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    I think the more important point is the inhomogenities observed in the post Big Bang universe are extremely consistent with what is predicted to emerge from an initial state that was as perfectly homogenous as permitted by quantum theory.
     
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