  In a two-dimensional toy model, motivated from five-dimensional heterotic
M-theory, we study the collision of scalar field kinks with boundaries. By
numerical simulation of the full two-dimensional theory, we find that the kink
is always inelastically reflected with a model-independent fraction of its
kinetic energy converted into radiation. We show that the reflection can be
analytically understood as a fluctuation around the scalar field vacuum. This
picture suggests the possibility of spontaneous emission of kinks from the
boundary due to small perturbations in the bulk. We verify this picture
numerically by showing that the radiation emitted from the collision of an
initial single kink eventually leads to a bulk populated by many kinks.
Consequently, processes changing the boundary charges are practically
unavoidable in this system. We speculate that the system has a universal final
state consisting of a stack of kinks, their number being determined by the
initial energy.
