Hexbyte – Tech News – Ars Technica |
LIGO + LHC =
Gravitational wave detector directly measures force imparted by collisions.
I always tell my students that LIGO (laser interferometer gravitational wave observatory) is one of humanity’s most stunning achievements. Basically, a group of people set out to measure the unmeasurable. They methodically overcame every source of noise that swamped the signal until gravitational waves were found. Along the way, LIGO scientists have created the most sensitive instrument in existence.
And once you’ve got a nice sensor, everyone wants to use it for their experiments. The latest bunch in the queue are the particle physicists, who think that the exquisite sensitivity of LIGO might make its equipment a good detector for particles.
Hexbyte – Tech News – Ars Technica | LIGO knows when you rock out
Before we get to how to turn LIGO into a particle physics detector, let’s quickly look at how LIGO works.
LIGO is a giant interferometer: a laser beam is split in two by a partially reflective mirror. The two light beams are sent to distant mirrors. The light beams reflect off the mirrors and return from whence they came. At the partially reflective mirror, the two light beams are recombined. Light is a wave, which means that it has an amplitude that oscillates between a positive and negative value. When the two waves are recombined, the outcome depends on their amplitudes at the moment they are recombined (this is called interference—hence “interferometry”).
If the two waves combine when they are in phase, then the waves always have the same amplitude value at the partially reflective mirror. The light wave that exits the interferometer in this case will be bright. We call this “constructive interference.” But if the two waves combine so that they are anti-phased, then the amplitudes of both waves are equal but opposite in sign. In this case, the result will be darkness: no light exits the interferometer.
The factor that determines how the waves add together is the difference in the distance they travelled. If the interferometer is set up so that no light exits the interferometer under normal conditions, a small movement of one mirror will result in a sudden light in the darknes