  A new probabilistic representation is presented for solutions of the
incompressible Navier-Stokes equations in 3 dimensions with given forcing and
initial velocity. This representation expresses solutions as scaled conditional
expectations of functionals of a Markov process indexed by the nodes of a
binary tree. It gives existence and uniqueness of weak solutions for all time
under relatively simple conditions on the forcing and initial data. These
conditions involve comparison of the forcing and initial data with majorizing
kernels.
