On Thursday February 11 the LIGO Scientific Collaboration announced that they had directly detected gravitational waves using their Advanced LIGO device.
Gravitational waves are ripples in the spacetime curvature that move outward from a source. This phenomenon was predicted in 1916 by Albert Einstein as a consequence of his theory of general relativity.
Despite their early origins these waves have proved elusive to detect over the years.
LIGO stands for Laser Interferometer Gravitational-wave Observatory.
The signal they detected matches the prediction of a binary black hole collision by general relativity. This is enormously strong evidence in favor of general relativity.
The LIGO detection system works, in a basic sense, by a laser which is incident on a beam splitter, sending two beams off in parallel directions.
Each of those beams hits a mirror at the exact same distance and bounces back.
The beams travel up and down this distance hundreds of times and then are recombined and sent to a light detector.
Under normal circumstances the beams, which traveled the same distance, should be exactly in phase with each other.
Yet if a strong gravitational wave passes through the detector, one or both of the distances will be slightly stretched or shrunk.
This means the beams won’t be in phase with each other when they recombine.
This difference in phase is what is measured. The “arms” of the LIGO detector are 2.5 miles long.
There are actually 2 detectors, one in Louisiana and another in Washington.
This allows scientists to filter out background noise by comparing what each of the two detectors “hear.”
If both detectors detect the same disturbance around the same time, it’s probably a gravitational wave, which is exactly what happened on September 14, 2015.
Dr. Scott Noble, of the TU physics department, uses supercomputers to research systems of black holes. He describes the discovery as “A new realm of nature that was [previously] completely unexplored.”
In reference to the LIGO detectors he said it took “a whole revolution of engineering feats,” to get to a point where we could even measure gravitational waves.
It’s an exciting time to be a part of the physics community and the future of this technology looks full of more important physics discoveries.