When the temperature is higher than the critical temperature , point is a local minimum. So when a particle is trapped at , it is in static equilibrium.
However, when the temperature is lowered, the system changes to the lowest curve in the figure shown. As we can see, at the new state, the location is no longer a minimum. Instead, it is a maximum.
So the particle is not in static equilibrium. Instead, it is in unstable equilibrium. In other words, even if the particle is displaced just a little bit, no matter how little, it falls to a state with a lower energy.
This process can be called symmetry-breaking.
This mechanical example is an analogy for illustrating the concepts of symmetry-breaking and phase transition.
— Me@2019-03-02 04:25:23 PM
2019.03.02 Saturday (c) All rights reserved by ACHK