Drop breakup is an accessible and simple example of singularity formation, where physical quantities, e.g. pressure in a liquid, in a mathematical model become infinite. Such infinities often have a very physical interpretation and is a common outcome of nonlinear interactions. They occurr in models for formation of black holes, patterns formed by bacterial colonies, and nuclear fission. Computers, which we use to simulate dynamics, do not know how to think about infinities. So we have to think harder and look harder at the problem ourselves.

Drop breakup represents a physical process which spontaneouly create a large range of length-scales: from angstroms to centimeters. How do dynamics on such disparate length-scales interact? Do they decouple completely? This question has a number of variants. It comes up in the theory of phase transitions, and (according to my string theorist friends) in theories on how the universe began.

Drop breakup is particularly tough on theorists. And I am a theorist. Everything you predict can be checked in a very detailed way against experimental results. There is no mystery ingredient for the theory. We know the equations exactly. In a sense, it is like looking through a kaleidascope. We see all the colored glass pieces. We also see the beautiful pattern these pieces make with every turn of the tube. But by and large we don't know how the two are connected, or what pattern the next turn of the tube will produce.