User:ShaoTang

Collective modes and Broken Symmetry

1,What is symmetry in physics? A symmetry transformation is a change in our point of view that does not change the result of possible experiments.In particular, a symmetry transformation that is infinitesimally close to being trivial can be represented by a linear unitary operator that is infinitesimally close to be trivial can be represented by a linear unitary operator that is infinitesimally close to the identity: $U=1+i\epsilon t$ with $epsilon$ a real infintesimal.For this to be unitary and linear,t must be Hermitian and linear, so it is a candidate for an observable.Indeed, most(and perhaps all) of the oberservables of physics, such as angular momentum or momentum, arise in this way from symmetry transformations.

2,Symmetry breaking: Explicit symmetry breaking Spontanous symmetry breaking

3,Why broken symmetry in low tempreture?