Carbonated water is $H_2 0$ with $H_2 CO_3$ in it. $H_2 CO_3$, carbonic acid, decomposes into water and $CO_2$, carbon dioxide. When the cap is closed on a bottle of carbonated water, there is a certain amount of $CO_2$ in the top of the bottle, where there is no liquid, and this circulates back into the liquid to become more carbonic acid. This level of $CO_2$ in the air pocket at the top stays more or less in a constant equilibrium though. When the top is removed and the $CO_2$ is allowed to escape, more carbonic acid has to break down than is formed to maintain equilibrium of $CO_2$ levels with the surface. I understand this whole process, but there is one thing I can't wrap my head around.
When more carbonic acid is breaking down to form $CO_2$, why does that cause bubbles everywhere in the liquid? How is it that when the level of $CO_2$ on the surface drops, it immediately causes carbonic acid to decompose everywhere in the liquid? Is it a chain reaction emanating down from the surface or is there some other means of communicating this to everything below the top layer?