Final answer:
LIGO detects gravitational waves by using the destructive interference of laser light, which is disturbed when a gravitational wave passes through, causing a measurable change in the light's interference pattern. The Michelson interferometer can demonstrate similar principles on a smaller scale in an educational or laboratory setting.
Step-by-step explanation:
How LIGO Uses Interference to Detect Gravitational Waves
The Laser Interferometer Gravitational-Wave Observatory (LIGO) utilizes a phenomenon known as constructive and destructive interference to detect the incredibly subtle presence of gravitational waves, as predicted by Einstein's theory of general relativity. In LIGO, laser light is split into two beams that travel along two perpendicular arms of the interferometer. If the lengths of the arms are exactly equal, the light waves will return in sync and interfere constructively or destructively. Ideally, they are carefully calibrated so that when they recombine, they do so in such a way that they cancel each other out perfectly—resulting in destructive interference.
When a gravitational wave passes through the detector, it distorts space-time in such a way that the lengths of the two arms are momentarily unbalanced. This slight change in length alters the interference pattern, causing a small but detectable amount of light to reach the photodetector, which otherwise would not detect light due to the aforementioned destructive interference. This subtle shift indicates the passing of a gravitational wave. The key to LIGO's sensitivity is that it can detect these minuscule changes in arm length, on the order of one-ten-thousandth the diameter of a proton.
On a smaller scale, similar principles can be used in a laboratory setting using the Michelson interferometer. This device can produce and measure interference patterns with high precision, providing a tabletop demonstration of the principles underlying LIGO's more complex and sensitive setup. Students can learn about wave interference by conducting experiments with such an interferometer, which, although it won't detect gravitational waves, still showcases the fundamental physics of light interference.