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What are branes and LQG?

  1. Dec 1, 2003 #1
    I'm a very ignorant person. Could someone please explain to me what branes and LQG are? I know what a string is (or at least i think i do). I am a firm believer of K.I.S.S. so try to keep it simple for me because I'm just in 11th grade.
  2. jcsd
  3. Dec 1, 2003 #2


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    A brane is a feature of more advanced string theory, its a piece of spacetime of some number of dimensions (almost any number). The word brane comes from "membrane", and the idea is "Like that but in several dimensions" Originally branes and strings were more or less on an equal footing, and branes were where strings stuck their end points (if I may be so over colorful). In later work it's branes on branes, and crossed branes, and all sorts of variations.

    LQG stands for Loop Quantum Gravity. About 20 years ago it was found that you can do interesting things with "Wilson loops" that were sort of physics around a loop in space. Then it was found they didn't have to be loops (but the name stuck) and they started using networks. The idea is to use these networks to build quantum gravity of spacetime. The traditional way of quantizing gravity, they way they had quantized the other forces, didn't work.

    Now both advanced string physics, with branes, and Loop Quantum Gravity, without loops, are candidates for quantizing gravity. May the best theory win. And by "best" I mean the one that actually gets the job completely done. If they both do, even better.
    Last edited: Dec 1, 2003
  4. Dec 1, 2003 #3
    Thank you selfAdjoint.

    I still don't understand branes all that well but I now know what LQG is. A little more explination is needed on the whole branes thing.
    Does a single brane exist in just one dimension, exist on many dimensions or can it do both?
    ok, a lot more explination is needed on branes because in my mind I see them as the connector pieces in a K'nex set that the pegs fit into which I'm guessing is far from being correct. Keep in mind I know almost nothing about anything.

    Why do questions always lead to more questions?
  5. Dec 1, 2003 #4
    A zero-dimensional brane is a point, like a particle. A one-dimensional brane is a curve, like a string. A two-dimensional brane is a surface, like a membrane. You can keep adding dimensions branes as long as there are dimensions of space to accommodate them.
  6. Dec 1, 2003 #5


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    Michio Kaku has described branes as simply a way of slicing up an 11D bulk space. The same way in normal Euclidean geometry you can have lines, planes and solids, you can have branes of any dimension sliced from 11D space as a whole.
  7. Dec 2, 2003 #6
    I understand now, thank you :smile:
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