  For a dense and strongly interacting system, such as a nucleus or a
strongly-coupled quark-gluon plasma, the foundation of hydrodynamics can be
better found in the quantum description of constituents moving in the strong
mean fields generated by all other particles. Using the result that the
Schroedinger equation and the Klein-Gordon equation can be written in
hydrodynamical forms, we find that the probability currents of the many-body
system in the mean-field description obey a hydrodynamical equation with stress
tensors arising from many contributions: quantum effects, mean-field
interactions, and thermal fluctuations. The influence of various contributions
to the hydrodynamical motion is expected to vary with the temperature, as the
quantum and mean-field stress tensors playing more important roles at low and
moderate temperatures.
