Implications of a positive cosmological constant for general relativity

Most of the literature on general relativity over the last century assumes that the cosmological constant A is zero. However, by now independent observations have led to a consensus that the dynamics of the universe is best described by Einsteins equations with a small but positive A. Interestingly, this requires a drastic revision of conceptual frameworks commonly used in general relativity, no matter how small A is. We first explain why, and then summarize the current status of generalizations of these frameworks to include a positive A, focusing on gravitational waves.