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Proof of extra dimension from primordial BHs

  1. Feb 5, 2008 #1
  2. jcsd
  3. Feb 5, 2008 #2
  4. Feb 5, 2008 #3
    That's an interesting article, heres something I don't understand in the article:

    How does a dimension have size?! A dimension is a degree of freedom of movement - it's not exactly a measurable quantity is it?
  5. Feb 5, 2008 #4
    Think about an ant crawling on an infinitely long garden hose. It has two degrees of movement, X and Y. If it walks along the X dimension, it can keep walking forever. But if it walks along the Y dimension, it can only go about an inch or so before it comes back to its starting point. We can think of the Y dimension as having a "size", or being "small", because although the ant has freedom of movement in that direction, it doesn't have much.

    String theory people think of the universe as being ten-dimensional, but they (usually) think that six of the dimensions are "curled up", like the surface of the garden hose. This is how they explain that we don't observe those dimensions-- they are curled up VERY small, like the distance you can travel in that dimension is on the planck scale and thus undetectable. Sometimes string theorists talk about specialized versions of string theory with "large extra dimensions". When they say "large" in this case they mean, like, a millimeter.
  6. Feb 5, 2008 #5
    If you look at a piece of paper, it seems to be completely two-dimensional. In reality, it's just really thin and if you zoom in on it, you can tell that it obviously has thickness.

    So even if it looks like it only has an X and Y dimension, it also has a Z dimension. The idea is that if you zoom up on space-time, you will be able to see other dimensions that are too small for us to normally notice.

    This obviously isn't a great analogy, since a piece of paper is an object, not a degree of freedom like you said, but then again humans don't have the capacity to visualize these extra dimensions, so this is the best I can give you. :tongue:
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