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String Theory and Absolute Zero

  1. Feb 7, 2006 #1
    Hi! Today I was reading this article in SciAm on a model that some string theorists were working on that had to do with the cosmic origin; it talked about how strings, when compressed - when losing energy - will only decrease in length to the Planck length, and its energy level would rebound as its length actually increases as one attempts to compress it or drain its energy further. I'm just wondering that, when the temperature of a string - theoretically - is lowered, approaching absolute-zero, wouldn't it reach the Planch length some temperature above absolute-zero? And if you still lower its temperature - assuming that it's not absolute-zero yet - wouldn't it actually increase in size, and not decrease in size to nothingness at absolute-zero - theoretically? Please tell me that I made a mistake in this reasoning or I misunderstood something; it's quite disturbing for me. If an answer is out there, great! Please tell me. Thank you very much!
     
  2. jcsd
  3. Feb 25, 2006 #2
    Let me take a stab at it.

    We have string points because you can’t construct a physical line with zero dimensional points that are zero distance apart. A lot of zeros equals zero. A physical universe can’t be made out of points that have a quantity of zero which are zero distance apart.

    In speaking here, I have used two concepts. The concept of a point, and the concept of distance between points. Those are two different things, and they really exist in a physical way. A point has a quantity and the distance between points is a quantity.

    If you were to reduce the distance between two points, the distance can reduce down to a Planck length, but at that length you bump up against the other point. It’s like taking two BBs (that you shoot from a BB gun). You can reduce the distance between two BBs until the BBs are against each other, and then they want to rebound away from each other. Mathematically speaking, the BB points are zero dimensional. Mathematically speaking the very center of each BB is the point itself. But the idea of string points (rather than zero dimensional points) implies you can’t reduce anything down to absolute zero.

    The point itself must have a string value, and the distance between two points is more clearly a string value.

    This has nothing to do with temperature. Absolute zero temperature is a random temperature. Its only definition is there isn’t a known temperature that is lower. And Planck length is the smallest distance we know of. There is no distance in the physical universe smaller than Planck Length.

    Planck Length is probably the literal diameter of a point. Think of the diameter of a BB. The very centers of two BBs side-by-side are one BB diameter apart. They can’t get any closer unless you compress them together, in which case they will want to rebound apart.
     
  4. Mar 2, 2006 #3
    I can't edit so here is another explanation.


    We have string points because you can’t construct a physical line with zero dimensional points that are zero distance apart. A lot of zeros equals zero. A physical universe can’t be made out of points that have a quantity of zero, zero distance apart.

    There are two concepts here, the concept of a point, and the concept of distance between points. Those are two different things, and they exist in a physical way. A point has a quantity and the distance between points is a quantity.

    If you were to bring two points closer together, the distance can reduce down to a Planck length, but at that length you bump up against the other physical point. It’s like taking two BBs. You can reduce the distance between two BBs until the BBs are against each other, then they want to rebound away from each other.

    That mysterious rebound effect is what the SciAm article was talking about.

    The point itself must have a value, a quantity, measured as a string value, and the distance between two points is a string.

    In pure math, the BB points are zero dimensional. The very center of each BB is the point itself. But the idea of string points (rather than zero dimensional points) implies you can’t reduce anything down to absolute zero, so the point itself has a size.

    Planck Length is probably the literal diameter of a point. Think of the diameter of a BB. The very centers of two BBs side-by-side are one BB diameter apart. They can’t get any closer unless you compress them together, in which case they will want to rebound apart.
     
    Last edited: Mar 2, 2006
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