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My first question

  1. Sep 1, 2004 #1
    My first question:)

    i've been read the <the elegant universe>. and it has mentioned several times the contradiction between principle of relativity and the quantum mechanics. but i still don't understand. so could somebody give me a hand.
    thank you very much :laughing: :smile:
  2. jcsd
  3. Sep 1, 2004 #2
    Be specific Dude!!

    Be specific Dude!!
    Ask exactly what you didn't understand.
    Be specific

    There are many contradictions between quantum mechanics and classical mechanics(of which principle of relativity is a part) as quantum mechanics
    denies the right of absolute measurement

    Last edited: Sep 1, 2004
  4. Sep 1, 2004 #3
    Tianwei, don't pay too much attention to this poolwin-guy...he suffers from complete lack of courtesy.

    There are two main contradictions between GTR (General Theory of Relativity) and QM. First there is the Heisenberg uncertainty priciple in QM that states that position and momentum, as well as energy and time are always uncertain when measurements are performed. In GTR there is never any uncertainty concerning the position of an object.

    Secondly, in QM there is no relation or connection if you will between space and time, like in GTR where we have the space-time-continuum. In QM time evolves independently from space. So curvature of spacetime does not occur in QM

  5. Sep 1, 2004 #4
    Besides, if you are interested in a model that tries to combine QM and GTR, please consult the strings, branes and LQG thread. In this department, just click on the LQG-thread and go to the last page. You will find a worddoc there that explains Loop Quantum Gravity (LQG) on an introductory level, at least that is the intention.

    If you have any comments, please pm me...

  6. Sep 1, 2004 #5


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    Are string theories and brane theories the same basicly, except for the diffrence in branes instead of strings?
  7. Sep 1, 2004 #6


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    Welcome to physicsforums as well! Have fun! I've learned much much much from it. : )
  8. Sep 1, 2004 #7

    branes are the manifolds on which strings can live. One could view our 4D-spacetime-manifold as a brane. The open strings are fotons that can only live on this brane. More specifically their endpoints of these strings is bound to the brane. Closed strings like gravitons can live anywhere. Each point of our brane is not really a point but a sphere with circular dimensions curled up like macaroni. why don't we see these dimensions ??? Well our photons only live on the brane, not on the other dimensions. So we never see them.

    Offcourse things would be quite spectacular once the graviton is found, because then we should be able to probe these other dimensions. Remember that the graviton is not confined to the brane, it can also exist in the other curled up dimensions. It can go from the brane to the other dimensions and the other way around.

    Last edited: Sep 1, 2004
  9. Sep 1, 2004 #8
    To Marlon: thank you so much for your very clear answers, and i think i am understand now. and i will read the LQG-thread, cos i am really interest in this part.

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