  We present a comparison between simulated dynamics of the unitary fermion gas
using the superfluid local density approximation (SLDA) and a simplified
bosonic model, the extended Thomas Fermi (ETF) with a unitary equation of
state. Small amplitude fluctuations have similar dynamics in both theories for
frequencies far below the pair breaking threshold and wave vectors much smaller
than the Fermi momentum, and the low frequency linear responses match well for
surprisingly large wave vectors, even up to the Fermi momentum. For non-linear
dynamics such as vortex generation, the ETF provides a semi-quantitative
description of SLDA dynamics as long as the fluctuations do not have
significant power near the pair breaking threshold, otherwise the dynamics of
the ETF cannot be trusted. Nonlinearities in the ETF tends to generate
high-frequency fluctuations, and with no normal component to remove this energy
from the superfluid, features like vortex lattices cannot relax and crystallize
as they do in the SLDA. We present a heuristic diagnostic for validating the
reliability of ETF dynamics by considering the approximate conservation of
square of the gap: $\int|\Delta|^2$.
