  In this work we investigate collective excitations at the boundary of a
recently constructed 4D quantum Hall state. Local bosonic operators for
creating these collective excitations can be constructed explicitly. Massless
relativistic wave equations with helicity $S$ can be derived exactly for these
operators from their Heisenberg equation of motion. For the S=1 and S=2 cases
these equations reduce to the free Maxwell and linearized Einstein equation
respectively. These collective excitations can be interpreted as hydrodynamical
modes at the boundary of the 4D QHE droplet. Outstanding issues are critically
discussed.
