Questions 1. How these detectors read distance of the event? In order to assert that the rate peaked 8*10^9 years ago, we'd need to know distance. Surely it's not based on amplitude 2. Galaxies collide. Is there reason to think that many galaxies contain a central supermassive (10^9 solar mass) black hole, and that such holes have collided as well? Perhaps too rare to be seen in five years?