  The properties of an hyperbolically-expanding wormhole are studied. Using a
particular equation of state for the fluid on the wormhole throat, we reached
an equation of motion for the throat that leads to a constant surface energy
density $\sigma$. The Lagrangean leading to the above equation of motion
contains the "rest mass" of the expanding particle as a potential energy. The
associated Hamiltonian corresponds to a relativistic free particle of a total
Planck energy $E_{P}$. When the wormhole is embedded in de Sitter space, we
found that the cosmological constant is of Planck order of magnitude but hidden
at very tiny scales, in accordance with Carlip's recipe.
