File: 7 October 2026 · Source date: 7 October 2026 · LIGO
measured quantity
When a gravitational wave passes, the lengths of two perpendicular arms change at different rates. LIGO measures this very small relative change using laser interference. The detector does not directly capture an image of a black hole.
How to find signal?
Researchers monitor for noise, compare the timing of multiple detectors, and test the data against waveforms derived from general relativity. A brief vibration at a single facility is not considered a celestial source.
Limit of inference
Properties such as mass and distance are extracted probabilistically from the measured waveform. Results have error ranges and depend on model assumptions. This does not weaken the observation; It shows under what conditions the information is valid.
discussion question
Do you think knowing an event that we cannot see only from its effects is an indirect observation or a strong enough observation? What independent evidence would you look for?
Resources and further reading
LIGO — What are gravitational waves? ↗Share your answer
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