Spontaneous Symmetry breaking-weinberg's chair

[krishna mohan]

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?

[hamster143]

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 \hbar^2/I, 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.

[krishna mohan]

Yes..that does make it clearer..thanks!:smile: