  The primary quantum mechanical equation of motion entails that measurements
typically do not have determinate outcomes, but result in superpositions of all
possible outcomes. Dynamical collapse theories (e.g. GRW) supplement this
equation with a stochastic Gaussian collapse function, intended to collapse the
superposition of outcomes into one outcome. But the Gaussian collapses are
imperfect in a way that leaves the superpositions intact. This is the tails
problem. There are several ways of making this problem more precise. But many
authors dismiss the problem without considering the more severe formulations.
Here I distinguish four distinct tails problems. The first (bare tails problem)
and second (structured tails problem) exist in the literature. I argue that
while the first is a pseudo-problem, the second has not been adequately
addressed. The third (multiverse tails problem) reformulates the second to
account for recently discovered dynamical consequences of collapse. Finally the
fourth (tails problem dilemma) shows that solving the third by replacing the
Gaussian with a non-Gaussian collapse function introduces new conflict with
relativity theory.
