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More Q's on Strings, Branes and parrallel Universe's

  1. May 10, 2005 #1
    I probably won't be able to ask this question as well as I envision it in my mind. So please bear with me and try and decipher my babbling gibberish as best you can. :smile:

    According to my very limited knowledge of Strings and Branes.......(theory)

    Strings are the smallest things in the Universe, and can sometimes stretch into membranes that basically are an entirely different universe. So are strings also the smallest things in those universes, and can sometimes stretch into Branes which are entirely different universes....etc...etc...etc...?

    So does this mean the "infinity" actually does exhist?

    If this makes any sense at all to you, please help as best as you feel like.

    Thanks a ton!
  2. jcsd
  3. May 10, 2005 #2


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    First off, infinity does exist. It is a concept. I use it all the time. I represent it by taking a number eight and laying it on its side. You can't do calculus without it. There are also many common place examples of infinity. For example, the number of counting numbers is infinite.

    Second, generally string theorists describe that universe as one or more membranes (Brane is just short for membrane although "Brane" is generally used in the specialized context of a fundamental underlying structure in space-time) in which live some strings. Maybe true dreamers would like Branes to be made out of strings, but mostly they are just "put in by hand".

    These strings do cool stuff. Under different conditions strings can act like different particles, say electrons or photons. In the string theory world, everything in the standard model is simply a different category of string behavior. To take an inaccurate and made up example, a string with a two hump standing wave might be a muon. The rules goving how this single kind of particle called strings act, defines all the laws of physics -- forces, particle masses, coupling constants, etc. If you knew the rules of string behavior (and true dreamers hope are simple enough to put on a t-shirt), then bam -- you suddenly can figure out everything there is to know about physics. You know all the rules of the game. This game seems likely to involve more dimensions than the three in space and one in time with which we are familiar.

    Well, except that, in brane theory, you might also need to know about branes. String theory leaves open the characteristics of empty space. LQG people like to talk about spin foams. Stingy people like to talk about branes.

    The main reasons that stringy people like to talk about Branes are two fold. First, Branes are a device that allows us to explain why the world seems four dimensional when physics seems to have more dimensions. If everything we know is clinging to a brain in the context of a larger dimensional universe, then the problem is solved. It also solves problems with gravity. One way to make gravity behave as it does is to allow gravitons to slip off the brane, thus we know why it is so weak. It isn't really weak, it just mostly doesn't arrive at a destination on our brane.

    I'll close by noting a key point. No body has made an useful testable predictions using string or brane theory. It is untried by experiment. We aren't even sure that it actually reproduces obvserved physics although we have some pretty suggestive lines of reasoning to think that it does or comes close. The brane part of the story is even more speculative than the string part.
  4. May 10, 2005 #3
    Hi ohwilleke

    What's interesting is that spin foams and D-brane charge appear to have the same construction in K-homology, through equivalence classes of Fredholm modules. So mathematically, spin foams and D-brane charge are equivalent. :surprised


    Last edited: May 10, 2005
  5. May 10, 2005 #4


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    Mike - who knew? Any online citation for Fredholm modules?
  6. May 10, 2005 #5
    First off: I am familiar with the symbol for infinity. I'm not the most edumicated feller 'round these parts, but I'm up to speed on that. Just don't know how to make one on my new fangled puter thingy. I don't have the infinity key on my keyboard nowheres. :-)

    Also, before I learned about string theory. I always thought that "infinity" didn't really exhist on a physical level. I thought that there was an absolute top # to the count of all of everything in the universe. In other words, if you add up the total # of eveyrhing, there would be an actual number. And it wouldn't be "infinity."

    But back to my original post.

    What String or Brane theory says to me, is this. If strings/branes are the smallest things in our universe, and branes are universe's unto themselves. Then wouldn't the smallest things in those universes be strings/branes. And those branes being universes unto themselves....etc..etc...etc.

    Also, supposing that that were true. Then IF we have been visited by ET's, which I don't believe that I've seen tangable evidence of, then for some reason, I think that that would be where they came from. Not from the outer reaches of our own universe, but from a parrallel universe. I have no idea how or why I would think that. And I CERTAINLY am not interested in any UFO discussions/debates. But I was just saying that for some unexplainable reason, that makes sense to me.

    Yep, I'm a kook. ;-)
    Last edited: May 10, 2005
  7. May 10, 2005 #6
    Hi selfAdjoint

    To be more precise, the spin foam is more like D-brane charge in Matrix theory. This is because a 3-brane in Matrix theory is more like a triangulation of a 3-manifold, with D0-branes as nodes and fundamental strings as edges, so is akin to a spin-network. The configurations of the 3-brane in Matrix theory are described by equivalence classes of the Fredholm modules, with each module giving you a "freeze-frame" picture of the 3-brane evolution.

    Fredholm modules can be found in noncommutative geometry literature, but is more penetrable in physics literature. See hep-th/0209210 for starters.


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