The quadrupole formula: a hundred years later

Einstein’s celebrated quadrupole formula lies at the foundation of the first indirect evidence for gravitational waves: it explains with high precision the shrinking of the orbital radius of the Hulse-Taylor system. The formula expresses the power radiated in the form of gravitational radiation in terms of the source quadrupole moments. However, the derivation assumes a flat spacetime background, but there is strong observational evidence for a positive cosmological constant. To account for this, the quadrupole formula is generalized by replacing the flat spacetime background with a de Sitter spacetime. In this talk, I will focus on the conceptual subtleties that arise and comment on physical implications.