The original version of this story appeared in Quanta Magazine.
There are precision measurements, and then there’s the Laser Interferometer Gravitational-Wave Observatory. In each of LIGO’s twin gravitational wave detectors (one in Hanford, Washington, and the other in Livingston, Louisiana), laser beams bounce back and forth down the four-kilometer arms of a giant L. When a gravitational wave passes through, the length of one arm changes relative to the other by less than the width of a proton. It’s by measuring these minuscule differences—a sensitivity akin to sensing the distance to the star Alpha Centauri down to the width of a human hair—that discoveries are made.
The design of the machine