The experiment would never have been done without the theory, and a long line of experiments suggesting that Nature and the theory had a lot to do with one anot

The experiment would never have been done without the theory, and a long line of experiments suggesting that Nature and the theory had a lot to do with one another, first. We knew that gravitational waves, or something very much like them, happened due to the binary pulsar work by Hulse and Taylor in 1974. Einstein's advance was quite spectacular, and early. Source: Am gravitational experimentalist.