There was around-the-globe celebration when LIGO scientists, including those from LSU and at the LIGO facility in Livingston Parish, announced the first detection of gravitational waves. But was the party premature? As Forbes reports, a group of Danish researchers say that might be the case.
A team of five researchers from the Niels Bohr Institute in Copenhagen, submitted a paper casting doubt on the discovery after analyzing the openly available LIGO data. Their verdict: The gravitational waves LIGO scientists detected might not be signals at all, but rather patterns in the noise that have hoodwinked even the best scientists working on this puzzle.
The LIGO gravitational wave observatory consists of two experimental sites—one in Livingston and one in Hanford, Washington—each featuring a laser interferometer with arms that are several kilometers in length.
Even for these super-sensitive detectors, however, gravitational waves are difficult to measure. The problem isn’t so much the absolute weakness of the waves, but that there are many other disturbances that also wiggle the interferometer. The challenge is distinguishing the waves from the noise. LIGO scientists rely on the combined signal from both detectors to identify a gravitational wave signal.
A gravitational wave will travel through each site at a different time, since the signal travels at the speed of light, but the two sites are separated by thousands of kilometers. Things get really technical from here, but gravitational waves, after mathematical calculations, should be correlated between the two sites, while routine noise will not.
At least, that’s the idea.
The Danish group, in a head scratcher, found noise at the two detector sites also correlated. And worse, the correlation time is similar to the time-lag between the recorded signals, for each of the three so-far confirmed events.
“If the correlation properties of signal and the noise are similar, how is one to know precisely what is signal and what is noise?” says Andrew Jackson, the leader of the Danish group.
