A group of Danish scientists has suggested that the historic first observations of gravitational waves may have been false readings. Several scientists have quashed this idea, however.
First, a bit of history. In February 2016, it was announced that gravitational waves had been found for the first time – ripples in space-time caused by colliding black holes. In June 2016, we found some more. And then we found more again in February 2017.
The detections were made using the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in Hanford, Washington, and Livingston, Louisiana. They both work by firing a laser along L-shaped tubes, measuring 4 kilometers (2.5 miles) on each side. By measuring really, really tiny perturbations in this laser, it’s possible to detect gravitational waves passing over our planet.
Or is it? Probably yes. But still, this Danish team led by James Cresswell from the Niels Bohr Institute & Discovery Centre in Copenhagen suggests otherwise. They say the small perturbations may have been the result of noise (interference in the signal, in other words) at both sites, with coincidentally the same time it would have taken for a gravitational wave to pass from one site to the other. It seems unlikely, but it's apparently not completely impossible.
“The residual noise for the two more recent events, GW151226 and GW170104, exhibits equivalent behavior with respect to each of their time lags,” the paper, which has not been peer-reviewed but is available on arXiv, states. “A clear distinction between signal and noise therefore remains to be established in order to determine the contribution of gravitational waves to the detected signals.”
It’s safe to say that the suggestion hasn’t gone down too well, however. A number of scientists have spoken out about the Danish team's paper and cast doubt on it.
Ian Harry from the Max Planck Institute for Gravitational Physics, Potsdam-Golm, laid out a number of his own criticisms in a blog post. “We are also in touch with the authors of the article to raise these concerns directly,” he wrote.
Sabine Hossenfelder, meanwhile, a theoretical physicist and science blogger, raised some concerns of her own in an article on Forbes. “Making sense of somebody else’s data is tricky, as I can confirm from my own experience,” she said. “Therefore, I think it is likely the Danish group made a mistake.”
A false reading is not unprecedented. In January 2015, the groundbreaking BICEP2 reading of the early universe was found to be wrong. Later that year, microwave ovens were found to be the result of a signal believed to be coming from space.
But this time around, all signs suggest this discovery is concrete. So don’t go sharpening your gravitational pitchforks just yet.