Editing Critical phenomena (section)

==Ergodicity breaking==

[[Ergodicity]] is the assumption that a system, at a given temperature, explores the full phase space, just each state takes different probabilities. In an Ising ferromagnet below <math>T_c</math> this does not happen. If <math>T<T_c</math>, never mind how close they are, the system has chosen a global magnetization, and the phase space is divided into two regions. From one of them it is impossible to reach the other, unless a magnetic field is applied, or temperature is raised above <math>T_c</math>.

See also [[superselection sector]]