The model was proposed in part in order to reproduce the cosmic acceleration of dark energy without any need for a small but non-zero vacuum energy density. But critics argue that this branch of the theory is unstable. However, the theory remains interesting because of Dvali's claim that the unusual structure of the graviton propagator makes non-perturbative effects important in a seemingly linear regime, such as the solar system. Because there is no four-dimensional, linearized effective theory that reproduces the DGP model for weak-field gravity, the theory avoids the vDVZ discontinuity that otherwise plagues attempts to write down a theory of massive gravity.