This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
LIGO's detectors are, at heart, the same instrument Albert Michelson first built alone in 1881 to look for the Earth's motion through a hypothesized aether, then refined with Edward Morley by 1887, scaled up by a factor of roughly a million and aimed at a different question. Michelson split a beam of light down two perpendicular paths, bounced each half off a mirror, and recombined them, reasoning that if the Earth moved through a stationary aether, light traveling with that motion and light traveling across it would take very slightly different times to return, shifting the interference pattern the recombined beams produced. He and Morley found nothing in 1887, a null result so clean it helped clear the way for special relativity instead of confirming the aether it was built to detect. LIGO uses the identical geometry, a beam split down two arms at right angles and recombined, but looks for a different kind of disturbance: not the observatory's motion through space, but a passing gravitational wave stretching one arm and compressing the other by an amount smaller than the width of a proton, over arms four kilometers long rather than Michelson's few meters. Where the Michelson-Morley experiment is remembered for a beautifully executed absence, LIGO's version of the same instrument was built to wait, for decades if necessary, for the one difference in that interference pattern that would mean something had actually happened. In September 2015 it did.