The theory of strings predicts that the universe might occupy one random "valley" out of a virtually infinite selection of valleys in a vast landscape of possibilities
Quantum Effect, however allow a manifold to change state abruptly at some point-to tunnel through the intervening ridge to a nearby lower valley.
By Raphael Bousso and Joseph Polchinski, Scientific America, Beyond Einstein, September 2004
One has to keep in mind what these bubble universe stand for, and how they can existas bubbles within bubbles. Such topological formation would then seem strange wouldn't it, if, the tree analogy was taken to mean that each bubble could tunnel into one another as some relation is drawn "overtop" of Feynman's toy model?
Physically, the effect can be interpreted as an object moving from the "false vacuum" (where = 0) to the more stable "true vacuum" (where = v). Gravitationally, it is similar to the more familiar case of moving from the hilltop to the valley. In the case of Higgs field, the transformation is accompanied with a "phase change", which endows mass to some of the particles.
See Also: Unstable Universes: guest blog