  The scale-invariant glitch statistics observed in individual pulsars
(exponential waiting-time and power-law size distributions) are consistent with
a critical self-organization process, wherein superfluid vortices pin
metastably in macroscopic domains and unpin collectively via nearest-neighbor
avalanches. Macroscopic inhomogeneity emerges naturally if pinning occurs at
crustal faults. If, instead, pinning occurs at lattice sites and defects, which
are macroscopically homogeneous, we show that an alternative, noncritical
self-organization process operates, termed coherent noise, wherein the global
Magnus force acts uniformly on vortices trapped in a range of pinning
potentials and undergoing thermal creep. It is found that vortices again unpin
collectively, but not via nearest-neighbor avalanches, and that,
counterintuitively, the resulting glitch sizes are scale invariant, in accord
with observational data. A mean-field analytic theory of the coherent noise
process, supported by Monte-Carlo simulations, yields a power-law size
distribution, between the smallest and largest glitch, with exponent $a$ in the
range $-2\leq a \leq 0$. When the theory is fitted to data from the nine most
active pulsars, including the two quasiperiodic glitchers PSR J0537$-$6910 and
PSR J0835$-$4510, it directly constrains the distribution of pinning potentials
in the star, leading to two conclusions: (i) the potentials are broadly
distributed, with the mean comparable to the standard deviation; and (ii) the
mean potential decreases with characteristic age. An observational test is
proposed to discriminate between nearest-neighbor avalanches and coherent
noise.
