Explore the cutting-edge hunt for merging supermassive black holes in this Presidential Lecture that reveals how astronomers use pulsar stars as cosmic clocks to create a galaxy-sized detector. Discover how recent evidence of surprisingly massive black holes in the distant universe suggests that giant binary black holes should exist in our cosmic neighborhood, and learn about the sophisticated techniques used to search for their distinct gravitational wave signatures while filtering out the background "hum" of the universe. Examine what current search limits tell us about galaxy formation and growth throughout cosmic history, and understand how pulsar timing arrays represent one of the most ambitious astronomical detection methods ever conceived. Gain insights into the intersection of gravitational wave astronomy, black hole physics, and cosmology as researchers work to detect these elusive cosmic giants before they merge.