  We point out that a classical analog of the Sachdev-Ye-Kitaev model -- a
solvable model of quantum many-body chaos, was studied long ago in the
turbulence literature. Motivated by the Navier-Stokes equation in the turbulent
regime and the nonlinear Schr\"odinger equation describing plasma turbulence,
in which there is mixing between many different modes, the random coupling
model has a Gaussian-random coupling between any four of a large number $N$ of
modes. The model was solved in the 1960s, before the introduction of large $N$
path integral techniques, using a method referred to as the direct interaction
approximation. We use the path integral to derive the effective action for the
model. The large-$N$ saddle gives an integral equation for the two-point
function, which is very similar to the corresponding equation in the SYK model.
The connection between the SYK model and the random coupling model may, on the
one hand, provide new physical contexts in which to realize the SYK model and,
on the other hand, suggest new models of turbulence and techniques for studying
them.
