To Make the Perfect Mirror, Physicists Confront the Mystery of Glass Sometimes a mirror that reflects 99.9999% of light…

To Make the Perfect Mirror, Physicists Confront the Mystery of Glass

Sometimes a mirror that reflects 99.9999% of light isn’t good enough...

The Laser Interferometer Gravitational-Wave Observatory can sense movements thousands of times tinier than the width of an atom partly because of the instrument’s near-perfect mirrors. The mirrors bounce laser beams back and forth down the arms of LIGO’s L-shaped detectors. Changes in the relative lengths of the arms reveal when a gravitational wave flutters past Earth, stretching and squeezing space-time.

They’re nothing like regular mirrors. In your bathroom mirror, light reflects off metal, which has glass in front of it merely for protection. But LIGO’s 100-kilowatt laser would fry any metal. Instead, its mirrors are made entirely of glass.