  We apply linear perturbation theory to the study of the universality and
criticality first observed by Choptuik in gravitational collapse. Since these
are essentially nonlinear phenomena our attempt is only a rough approximation.
In spite of this, universal behavior of the final black hole mass is observed
with an exponent of 1/2, slightly higher than the observed value of 0.367. The
universal behavior is rooted in the universal form that in-falling
perturbations on black holes have at the horizon.
