According to the uncertainty principle each Planck sized region of space has a Planck scale amount of momentum associated with it. The energy in that momentum can be converted to particle-antiparticle pairs. According to the standard interpretation each pair has equal and opposite charges so that it can be argued that the charge density of space is zero. According to the Feynman-Stueckelberg interpretation these pairs can also be considered to have equal and opposite masses so that the mass density of space is zero. Would this explain why the Universe does not exponentially increase in size due to zero-point energy?