“Einstein’s gravitational theory, which is said to be the greatest single achievement of theoretical physics, resulted in beautiful relations connecting gravitational phenomena with the geometry of space; this was an exciting idea.” -Richard Feynman
There’s no doubt that LIGO has given us one of the most incredible breakthroughs of the 21st century: the direct detection of gravitational waves. But as wonderful as LIGO is, so far it’s only been able to detect the very final stages of mergers of stellar mass-scale black holes, and only every few months at that. The technique of laser interferometry is sound and powerful, but properties inherent to Earth itself fundamentally limit how good LIGO can potentially be.
But these restrictions go away if we go to space! Not only can we eliminate seismic noise, cease accounting for the curvature of the Earth, and get a better vacuum for free, but we can achieve much longer baselines. By sending a series of spacecraft up into orbit behind the Earth, we can detect more massive, more distant, and slower-period sources than LIGO could ever hope to see.