“We listen for changes in the separation of mirrors over the 4-kilometer length of each laser-interferometric detector. But thermal energy in the 0.4 millimeter diameter glass strings that hold up 40-kilogram mirrors also causes ringing sounds that we call ‘violin modes.’ And a hiss comes from the quantum nature of the light: fluctuations in the nothingness of empty space that interfere with our pure laser beam.”
Rana Adhikari, professor of physics, talks about noises from the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors. The aim of LIGO is to measure the stretching and squeezing of space-time. Scientists listen to the detector outputs—which are sometimes disturbed by things from the earth, such as earthquakes or traffic—using headphones.