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Spontaneous Symmetry breaking-weinberg's chair

  1. Sep 24, 2009 #1
    In Weinberg's book, Quantum theory of fields-II, he talks about a chair in the chapter on spontaneous symmetry breaking. He says that, for a chair, a state with a definite l value is not stable but a state with a definite orientation is.

    I do not understand what he means.

    An l state can be disturbed by a very small perturbation.

    But, for an isolated chair in vacuum, a small perturbation is enough to change its orientation.

    What is the meaning of Weinberg's statement?
  2. jcsd
  3. Sep 24, 2009 #2
    If you subject a definite-orientation chair to the action of a weak field, it will change its orientation in a proportionally weak manner.

    A definite-angular-momentum chair is a superposition of states with different orientations. All it takes is a tiny external field that couples differently to different orientations, to induce the variation in energies of this states on the order of several times [tex]\hbar^2/I[/tex], and the chair will cease to have definite angular-momentum. A tiny change in external fields leads to a drastic change in angular momentum spectrum.
  4. Sep 26, 2009 #3
    Yes..that does make it clearer..thanks!:smile:
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