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Just what we need, a finite dodecahedral universe

  1. Oct 16, 2003 #1


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    things seemed to be going along just fine and then a friend sent me


    this is a preprint of an article appearing in the current (9 October 2003) issue of Nature, which is also their cover article---a picture of a dodecahedron or something on the cover

    the gist is like this: you cant tile the plane with regular pentagons because the inner angle is 108 degrees

    but you can tile an ordinary 2-sphere with spherical regular pents that have the inner angle 120 degrees, because 3 angles of 120 degrees each will fit together

    Also JR Weeks is a freelance geometer Macartherfellow who does educational geometrical computer graphics----works at home (he is not institutionalized) and probably has more fun than a lot of other Math PhDs from Princeton

    And JR Weeks (never believe what geniuses tell you) says that since you can tile a 3-sphere with solid regular dodecahedra, well, obviously that must be what the universe is made of

    and he got this French Astronomer (Jean-Pierre Luminet) to believe him and they are fitting the bumps in the cosmic background (WMAP data) to this model.

    Luminet is at the "Observatoire de Paris" where, in 1675, a young Dane named Olaus Roemer first determined the speed of light---and got within roughly 10 percent of the right answer, which makes it holy ground, and JR Weeks is just running around loose in the town of Canton, NY.

    maybe this is all familiar to other people here but it took me by surprise this morning
    Last edited: Oct 16, 2003
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  3. Oct 16, 2003 #2


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    and he got this French Astronomer (Jean-Pierre Luminet) to believe him and they are fitting the bumps in the cosmic background (WMAP data) to this model.
    sometimes even the wrong bits fit in the wrong place.
    every one is doing this jigsaw and getting a different
  4. Oct 18, 2003 #3


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    I think it is now generally agreed that this model cannot be true as it would make certain predcitions which don't fit in with current observations.
  5. Oct 18, 2003 #4


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  6. Oct 27, 2003 #5
    Why such a model? It seams that it explains the 60° cut-off of the angular scale in the cuadrupole and octopole modes of the CMB.

    But how does the current model of an R^3 infinite euclidean space explain this cut off? Or does it ignore the cut off? It seams that this cut-off is not a widely accepted empirical fact, why?
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  7. Oct 27, 2003 #6


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    From what I hear currently, the team that is testing the viabilty of non-trivial topologies for the unievrse (given the observed flatness) using supercomputers has ruled out this model. Apparently they have tested most of these toplogies (though they are running out computer time) and it looks very likely that the universe is flat and infinite on a global scale.
  8. Oct 27, 2003 #7
    Because the statistics aren't good enough. It's right on the borderline between "definitely a real effect" and "probably not a real effect". Effects reported at this level of confidence have turned out to be non-existent before. So people are being cautious: it's significant enough to be worth considering explanations for it, but not significant enough to be sure that it's not just noise in the signal.

    (I know an astrophysicist who cynically remarked that it's the sort of result you include in your paper because it's flashy and suggests new physics, as opposed to being something you're sure is there.)

    Anyway, WMAP continues to collect statistics, and in a few years there will be Planck, so eventually we will know whether it's real or not.
  9. Oct 27, 2003 #8
    By the way, it's not really a cutoff in the power spectrum, it's just a dip.
  10. Oct 27, 2003 #9
    Could our universe be bordered by polygons with positive curvature such that angles fit seamlessly, or embedded with polyhedral spaces such that they fit positively curved spacetime seamlessly? Does the author refer to or imply cosmic strings or walls?
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