Gravitational Waves: How LIGO Detects Cosmic Signals

3-Second Blueprint (English)

1. LIGO fires coherent laser beams simultaneously down two multi-kilometer vacuum tunnels with end mirrors to detect cosmic ripples.
2. In undisturbed spacetime, both perpendicular laser beams travel identical path lengths and return to the detector locked in phase.
3. Passing gravitational waves stretch or compress one arm slightly, shifting relative travel distance so returning waves fall out of phase.