Observable consequences of strong coupling in theories with large distance modified gravity

In this talk, we review theories that modify gravity at cosmological distances, and show that any such theory must exhibit a strong coupling phenomenon. We show that all consistent theories that modify the dynamics of the spin-2 graviton on asymptotically flat backgrounds, automatically have this property. Due to the strong coupling effect, modification of the gravitational force is source-dependent, and for lighter sources sets in at shorter distances. This universal feature makes modified gravity theories predictive and potentially testable by precision gravitational measurements at scales much shorter than the current cosmological horizon.