The increasing interest of researchers in the basic properties of growth processes has provided the initiative for a number of experimental studies designed to check the applicability of various theoretical ideas to experimental systems. While many experimental studies have been inspired by the KPZ theory, most have failed to provide support for the KPZ prediction that α = ½. Instead, most data suggest that α > ½. These experimental results initiated a closer look at the theory, and led to the discovery that quenched noise affects the scaling exponents in unexpected ways. In this chapter, we discuss some of these key experiments, including fluid-flow experiments, paper wetting, propagation of burning fronts, growth of bacterial colonies and paper tearing. Atom deposition in molecular beam epitaxy, which is one important class of experiments on kinetic roughening of interfaces, will be discussed in Chapter 12. The new theoretical ideas needed to understand the effect of atomic diffusion on the roughening process will be developed at that time.

Fluid flow in a porous medium

Two-phase fluid flow experiments have long been used to study various growth phenomena. The Hele–Shaw cell, well-known from studies on growth instabilities in viscous fingering, has proved to be a useful experimental setup for the study of the growth of selfaffine interfaces. A trypical setup used in these experiments (Fig. 11.1) is a thin horizontal Hele–Shaw cell made from two transparent plates.