© David Kaplan.
This shape represents the energy of the fields A and B for every possible value of A and B. If the fields both have zero value, the energy is represented by the top of the central hump. Physical systems tend to evolve towards their lowest energy state, so the values of the fields want to be greater than zero—i.e., they want to roll down the hill. The lowest energy the fields can have is at the bottom of the ring. The energy anywhere around the ring is the same, but A and B take on different values. One example of this is when the A field has a non-zero value (of the ring's radius) and the B field is zero. That represents the point on the ring which is on the A arrow in the right-hand diagram. (Unit: 2)