How LIGO Stays Still Enough to Feel a Ripple in Spacetime
Seismic Isolation
LIGO's gravitational-wave detectors must measure mirror movements of just 10^-19 meters—a thousandth the width of a proton—while Earth constantly shakes. To achieve this, the observatory layers two isolation strategies: passive quadruple pendulums that suspend each 40kg test mass on glass threads, and active seismic platforms that sense and cancel ground motion. Together, they reduce vibration by a factor of a trillion, letting LIGO feel the faint echo of colliding black holes.
Since gravitational waves make themselves known through changing distances between LIGO's mirrors, the only way to make gravitational waves detectable is to isolate LIGO's components from terrestrial vibrations to unprecedented levels.