Why does LIGO have observatories in both Hanford, Washington, and Livingston, Louisiana?

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gravitational lens — gravity A galactic cluster, about five billion light-years away, produces a tremendous gravitational field that “bends” light around it. This lens produces multiple copies of a blue galaxy about twice as distant. Four images are visible in a circle surrounding the lens; a fifth is visible near the center of the picture, which was taken by the Hubble Space Telescope.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) operates two separate installations in Hanford, Washington, and Livingston, Louisiana, to ensure the reliability of its data.1

Because LIGO is an incredibly sensitive instrument capable of detecting minute changes in distance, it is highly susceptible to "noise" from local sources, such as seismic disturbances, wind, thermal fluctuations, or electrical current variations. These environmental factors can produce spurious signals that mimic the appearance of a gravitational wave. By maintaining two widely separated detectors, scientists can cross-reference signals; a true gravitational wave will be detected by both observatories, while local noise will typically only affect one site. This dual-site configuration is essential for confirming the authenticity of a detection.1