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Usefulness of a 4th spatial dimension

  1. Sep 10, 2008 #1
    Are the any thoughts on this paper (which I copied the first part of as a reference)? They seem to be saying the existance of a 4th spatial dimension would help resolve questions. But, I think I've read other places that speculation of this type is meaningless.

    Hierarchy Problem in the Shell-Universe Model
    Merab Gogberashvili
    Institute of Physics, Tamarashvili st. 6, 380077 Tbilisi, Georgia
    E-mail: gogber@hotmail.com
    (February 7, 2008)
    In the model where the Universe is considered as a thin shell expanding in 5-dimensional hyper-space there is a possibility to obtain one scale for particle theory corresponding to the 5-dimensional cosmological constant and Universe thickness.

    Several authors in the physics literature speculated about the possibility that our Universe may be a thin membrane in a large dimensional hyper-Universe (for simplicity here we consider the case of five dimensions). This approach is an alternative to the conventional Kaluza-Klein picture that extra dimensions are curled up to an unobservable
    size. In this paper we want to consider Universe as a bubble expanding in five dimensional space-time. This model of shell-Universe does not contradict the present time experiments and are supported by at least two observed facts. First is the isotropic runaway of galaxies, which for close universe model is usually explained as an expansion of a bubble
    in five dimensions. Second is existence of preferred frame in the Universe where the relict background radiation is isotropic. In the framework of the close-Universe model without boundaries this can also be explained if the universe is 3-dimensional sphere and the mean velocity of the background radiation is zero with respect to its center in the fifth
    dimension. In shell-Universe models the expansion rate of the Universe should depend not only on the matter density on the shell, but also on the properties of matter in inner-outer regions. This can give rise to the effect similar to the hypothetical dark matter. Also some authors want to introduce action at a distance without ultrafast communication
    as a possible connection of matter through the fifth dimension.
  2. jcsd
  3. Sep 10, 2008 #2


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    Thanks for beginning a thread with reference to a paper by a professional physicist, Pjpic.
    It makes it easier for the rest of us to understand what you have in mind, because we can see the paper.

    I don't always want to comment. Maybe I will comment, or maybe someone else will. But at least we see something definite. You should give a link which allows the whole paper to be downloaded, if the reader wishes.

    Here are the other papers by Gogberashvili

    If you want to discuss an idea, you should give accesss to the whole paper, so someone can read it if they want.

    In this case, I will give the link for you, here it is:

    It is an old (1998) paper. To read the whole thing, go to that link and click on PDF. This will download the PDF file. It is usually better to give people the link to the one-page abstract like this
    and then let them click on PDF if they decide they want to.
    This is more polite than giving them the direct PDF link which gives them no choice.

    I hope other people comment on this paper, and discuss it with you. I am not so interested in extra dimensions. I want to keep my world simple. Anything which is not absolutely necessary, I throw out. It might be convenient for some purposes to have a fourth spatial dimension in the analysis, but so far I do not recognize any strongly compelling argument why there must be any extra spatial dimension in nature.

    But other people will probably comment because they like extra dimensions.

    If you live in the same part of the world as Gogberashvili, then I hope that you and your family are safe and comfortable----in peaceful surroundings.
  4. Sep 11, 2008 #3
    so our 3 dimensional universe is the surface of a 4 dimensional hypersphere in a 4 dimensional space which is itself the surface of a 5 dimensional hypersphere in a 5 dimensional space? so there would be 2 different manifolds. a 3 dimensional one and a 4 dimensional one. since electromagnetism only works in 3 dimensions I assume that it is confined to the 3 dimensional manifold. but what is the advantage of a second manifold?
  5. Sep 11, 2008 #4
    The author of the article seems think it has some advantage. But his concepts are beyond my understanding. To a lay person, like me, it seems to have the advantage of removing the issues of 'boundry" and "expansion".
  6. Sep 11, 2008 #5
    I dont know if it was his main point but, if I'm not mistaken, he seems to be saying that below a distance equal to the thickness of the universe gravity would no longer follow an inverse square law. presumably it would follow an inverse fourth power law. (hence the possibility, I suppose, of combining gravity with the strong force)

    "The only parameter of the model Λ can be measured, for example, in the planned sub-millimeter measurements of gravity, since at distances of the shell thickness size Newton’s law must change."
    Last edited: Sep 11, 2008
  7. Sep 11, 2008 #6


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    Pjpic, you may have put your finger on the source of a trouble. You seem to have conceptual problems connected with expansion. And also the idea of a finite volume being boundaryless.

    It would help us explain things better, perhaps, if we knew more about you. Could you tell me something about yourself? What are your main interests? How did you come to be interested in cosmology? Any scrap of information that you think might help the rest of us understand where you are coming from and how best to explain stuff.
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