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Doughnut-Shaped Universe Back In the Race

Posted by kdawson on from the mmmmm-universe dept.

SpaceAdmiral writes "The once-popular idea that the universe could be small and finite is making a comeback. Many researchers thought that a 'wraparound' universe would mean that distant objects would be seen multiple times in the sky, but new research suggests that a '3-torus' (or 'doughnut universe'), as well as other shapes, could fit our actual observations, particularly the WMAP data."

7 of 124 comments (clear)

  1. Re:That's silly. by wass · · Score: 5, Informative

    It's primarily the boundary conditions that are leading to the 3-torus idea.

    A torus gives periodic boundary conditions in two dimensions. Periodic boundarty conditions for one axis can be thought of as curling a piece of paper around to make a cylinder. For someone on this paper, picture running on a soccer field, and if you run out of bounds on the left side you pop back in in the right side, aka pacman's tunnel. To make a torus, you'd need to wrap the top exposed circular edge to the bottom circular edge, in a donut way. You'd need to bend the paper to do this, so you'd really need something like a rubber membrane. But once you connect this, then you have a soccer field where when you kick a ball behind your opponent's goal, it comes out from behind your goal. That is 2-D boundary conditions. The simplest shape that can manifest these boundary conditions of a two-dimensional system is a torus, which exists in 3-D.

    Now extend this one step further. Take a 3-D space, and add periodic boundary conditions for left/right, back/front, and also top/down. This is the 3-torus that is discussed in the article. Someone confined to this 3-D surface has a full three independent degrees of freedom for movement, but the manifestation of this shape would look more complicated in four or five dimensions. But that is what is being talked about here.

    Of course in quantum cosmology there are other dimensions, such as the warped 5th dimension of the Randall-Sundrum model , which may or may not be periodic, and add to very peculiar topologies of the universe.

    --

    make world, not war

  2. Re:suggestion /. stop advertisementing for pay sit by Anonymous Coward · · Score: 3, Informative

    FWIW, here's the preprint.

  3. Re:That's silly. by docbrody · · Score: 2, Informative

    Though it's possible, how many other things in the universe are naturally doughnut shaped? uh, possibly almost everything (at least at the quantum level). -string theory. google strings vs. loops, or strings meet loops.
  4. Re:I Don't Think So by abigor · · Score: 2, Informative

    Haha, I can't believe this kooky bullshit got modded up. Note to mods: the link is to a crackpot site where the author, who is not a physicist or a mathematician, provides "proofs" showing Einstein was wrong, modern physics is wrong, etc.

  5. Here it is! by spun · · Score: 3, Informative
    I just looked it up and you are correct. Here's what I found:

    "There is no way of taking a man and moving him about in space, as ordinary people understand space, that will result in our changing his sides. Whatever you do, his right is still his right, his left his left. You can do that with a perfectly thin and flat thing, of course. If you were to cut a figure out of paper, any figure with a right and left side, you could change its sides simply by lifting it up and turning it over. But with a solid it is different. Mathematical theorists tell us that the only way in which the right and left sides of a solid body can be changed is by taking that body clean out of space as we know it,--taking it out of ordinary existence, that is, and turning it somewhere outside space. This is a little abstruse, no doubt, but any one with any knowledge of mathematical theory will assure the reader of its truth. To put the thing in technical language, the curious inversion of Plattner's right and left sides is proof that he has moved out of our space into what is called the Fourth Dimension, and that he has returned again to our world." The Plattner Story

    That was written in 1896, putting it 12 years after Flatland which I think was the first treatment of the theme of the consequences of differing numbers of dimensions. Nothing new under the sun, eh?
    --
    - None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
  6. Re:The Problem With Curvature by Tangent128 · · Score: 3, Informative

    Nonsense. Look at the faces of a geodesic dome. Each face is discrete, but the structure as a whole is curved for all practical purposes.

  7. Re:suggestion /. stop advertisementing for pay sit by Anonymous Coward · · Score: 2, Informative

    More than a decade has passed since I was in school and I live in the sticks; so no, I don't know _any_ current students or recent graduates.

    Additionally _every_ slashdot reader I know in person, all five of them, are either in the same position as myself, or are pre-collegiate children.

    If I was _really_ interested I could pay the eight bucks, or find some student online to give me a proxy or something. I'm not however, but your post annoys me.

    Not everyone here fits in your little world, sorry.