  Previously it has been shown that imposing a Petrov-like boundary condition
on a hypersurface may reduce the Einstein equation to the incompressible
Navier-Stokes equation, but all these correspondences are established in the
near horizon limit. In this note, we remark that this strategy can be extended
to an arbitrary finite cutoff surface which is spatially flat, and the
Navier-Stokes equation is obtained by employing a non-relativistic
long-wavelength limit.

General Relativity and Quantum Cosmology;High Energy Physics - Theory