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11th Dimention?

  1. Nov 22, 2003 #1
    In the TV show, Elegent Universe, Brian Greene explains that there are 11 dimentions of space and time, but why exactly 11?
    He also said that for string theory to work that there must be 6 additional dimentions, so what are the other 5 dimentions?

    11 dimentions....WHAT?
  2. jcsd
  3. Nov 22, 2003 #2
    The theory is only consistent in 11 dimensions, as far as people know. If you try to do string theory in other dimensions, you end up running into problems upon quantization: probabilities aren't conserved, or symmetries are broken, etc.

    Seven extra dimensions, in 11-dimensional M-theory: 1 time dimension, the usual 3 space dimensions, and 7 more space dimensions (usually taken to be curled up small to explain why we don't see them).
  4. Nov 23, 2003 #3
    Re: Re: 11th Dimention?

    i must confess, i am wholly ignorant of M-theory. i know the derivation that shows that the supersymmetric string lives in critical dimension 10, and i believe them when they tell me that this is the only possible choice.

    so i have always wondered what kind of fast trick witten pulled by moving to 11 dimensions... that is certainly not the critical dimension allowed in conformal supersymmetric field theory, and required for unitary.

    presumably, there is some construction in M-theory that produces a unitary model in 11D, but i guarantee you, it aint supersymmetric field theory on the world sheet. so what is it?
  5. Nov 23, 2003 #4
    So how do the other 6 or 7 dimentions work?
    Why are they needed?
  6. Nov 24, 2003 #5
    The seven extra dimensions are not seperate physical dimensions at all. We exist within these seven extra dimensions just as we do ours but can only view our dimension normally because of the way we function. These dimensions may be needed to allow for the formation of new more advanced processing forms but this would suggest that the dimensions are not set at seven but rather they will continue whenever a new form is created. Dimensions are what make evolution possible. When a new form of processing is created a new dimension must also be created to allow for the normal functioning of its kind. For example we would not be able to function within the dimension of an atom because our bodies and minds are a combination of atoms making us need to process at a quicker rate in order to keep up with atoms that make up our body. So these seperate dimensions are really just variations in processing which would explain why we cannot rapidly see the formation of our planet. In order to understand what changes our universe will go through or to see symmetry in our univers we would have to understand how processing ahead of ours has evanced and if we do this we could emulate and predict what fate lies for us as well.
    Last edited: Nov 24, 2003
  7. Nov 24, 2003 #6
    I have posted a theory on how the first ten of these dimensions work, and I'm begining to form my own concept of ten dimensions, but I have not found room for an eleventh dimension, could anyone explain how this works?
  8. Nov 28, 2003 #7
    I understand that the 7 'extra' dimensions (besides the 3 spatial and 1 time dimensions that we observe on a macroscopical scale) must be compactified somehow to make them invisible in a larger scale. What I don't understand is why people always claim that these 7 'extra' dimensions must be spatial dimentions. Does it somehow follow from the theory that none of these dimensions can be a second time-dimension [?]

    Kind regards,
    Freek Suyver.
  9. Nov 28, 2003 #8


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    Yes, at least in 26-dimensional bosonic string theory. The extrat dimensions come out as specifically spatial. I believe it's the same in superstring theory. The eleventh dimension in M-theory comes out of interpreting a degree of freedom as a dimension, and it would have to be spatial. There are some multitime theories around, but the main line of stringy physics doesn't have that feature in it.
  10. Nov 28, 2003 #9


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    Can you give a link or two for this?
  11. Nov 28, 2003 #10
  12. Nov 30, 2003 #11
    Last edited by a moderator: Nov 30, 2003
  13. Mar 22, 2005 #12
    In addressing the 7 extra dimensions as being spatial dimentions, can it be that conditions of what is spatial, are not as we understand them? Measures such as density, heat, Velocity , tempature, and frequency could also be conditions of spatial existance. I think any 3 dimentional object with a density of zero would not take up any space. Is this not a spatial demention that overlaps and in not seen? It seems to fit the conditions required for the 7 extra dimentions.
  14. Mar 22, 2005 #13


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    Density is merely a derived property, not an intrinisc property. It is nothing more than the mass divided by the volume. Volume is merely the extent of an object in the existing three dimensions. Mass, on the other hand, you could maybe make an argument about it as a dimension.
  15. Mar 22, 2005 #14
    What will it like if the universe has another extra time dimension???? Time, as I understand (or experience) it, can only has 1 dimension: there is past and there is future... so, how will an extra time dimension change the physics?
  16. Mar 23, 2005 #15
    Hi all.

    Well I am going off on my own here, and what I have to say has nothing to do with any branch of known physics which I have encountered. However.

    In space, we have length, and length times Length which is area, (LxL or LL or L^2 or [tex]L^2[/tex] and Length times Length times Length which is volume (LLL, L^3, [tex]L^3[/tex]and so on). We don't like to talk about LLLL, or any more L's than that. I am not sure why except that it is hard to think about and some famous people have said that it is impossible to think about. Oh well. For them maybe.

    And then we do have multiples of time in everyday physics, only the multiples occur in the denominator, the inverse side of the ratio, under the division sign. For example, L/T (T for time) is velocity, and L/TT or [tex]L/T^2[/tex] is acceleration, and L/TTT is a quantity known in ballistics as jerk. Sorry about that but that is what it is called. I am not sure why physicists use these formulas routinely and still insist there is only one dimension of time, but there it is.

    And then there is Einstein-Minkowski spacetime, in which our beloved uncle Albert and his math teacher agree that space and time are really the same thing. So we should have at least three dimensions of space and three dimensions of time, not?

    But that is only six dimensions, if you accept my logic, which I have to warn you is not advisable. Please do not pester your physics teacher with this stuff, because I know for a fact that they will be very irritable about it.

    Personally, I like the notion, which I have just now invented, that what we see around us and proclaim as real is actually the condensed spacetime dimensions described in Calabi-Yau maths. The other dimensions are the very large ones, open ended dimensions that, so far as we know, run out to infinity.

    Anyway, there are some formulas in physics which involve numbers like [tex]c^5[/tex], which in my clumsey notation would be LLLLL/TTTTT. Ahem. That would seem to be five dimensions of space and five dimensions of time, or, as we can all add, ten dimensions. This is strictly unorthodox and again, has nothing to do with mainstream physics, and students of physics would do well to ignore it, as has been done for a couple hundred years now by everybody of any importance whatsoever. But I do assure you that c^5 really is a number used by ordinary physicists, altho I don't know of any who would say comfortably that it represents ten dimensions.

    Now, then, I hope we are all satisfactorily tucked into wonderland, and that poor Micheal Jackson doesn't undergoe a horrific collapse in the courtroom. Too much imagination may not be a good thing after all. But as long as it keeps you studying physics and math, hey, why not? Only do take my advice on this, and keep your hands off of dimensions that do not belong to you.

  17. Mar 25, 2005 #16
    I mean, what make a dimension a time dimension rather than a space dimension? Is it the sign different in the Lorentz Invariant?

    With extra time dimension, the topology of the time dimensions will be very different, what is the physics like with extra time dimension? Had someone ever writen a consistent electrodynamics with an extra time dimension? What would the Maxwell Eq be like in that case?
  18. Mar 26, 2005 #17


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    Where would you put an extra time dimension that would not result in serious CPT violations? I don't think that is a good solution.
  19. Apr 3, 2005 #18
    If you think of time as you would spatial dimensions, then it would seem impossible to have another time dimension, but maybe perhaps we just can't comprehend it (just as we can't visualize the fourth spatial dimension very well).

    What I am getting to is that if there is a second (or even third or higher time dimensions), then it would be "perpendicular" to the first time dimension we are familiar with. Maybe it means nothing, or maybe it means the divergence to different possible futures.

    I am not a physics expert by any means, so some of this stuff may turn out to be impossible.
  20. Apr 3, 2005 #19


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    The two or more orthogonal time dimensions would span a "time vector space" so rather than just t1 and t2, you would have a*t1 + b*t2 as your time thingy, with a and b any two constants. Or of course higher dimensional equivalents if there were more time dimensions. So it's not divegence of two or three futures but a complex mix of infinitely many possible "paths through futurespace". Nice idea (and title!) for a science fiction story.
  21. Apr 3, 2005 #20
    have you been following the John Titor time travel thing SA ???

    Now it seems he is getting support from factions of the physics community and your paths through futurespace is not unlike him choosing to navigate different timelines of a possible future

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