Far out cosmology: gravitational waves doubted (Introduction)

by David Turell , Saturday, November 03, 2018, 15:19 (2000 days ago) @ David Turell

A Danish group has disputed the findings saying background noise is not fully accounted for:

https://www.sott.net/article/399642-An-illusion-Grave-doubts-over-LIGOs-discovery-of-gr...

"The Danish group's independent checks, published in three peer-reviewed papers, found there was little evidence for the presence of gravitational waves in the September 2015 signal. On a scale from certain at 1 to definitely not there at 0, Jackson says the analysis puts the probability of the first detection being from an event involving black holes with the properties claimed by LIGO at 0.000004. That is roughly the same as the odds that your eventual cause of death will be a comet or asteroid strike - or, as Jackson puts it,"consistent with zero". The probability of the signal being due to a merger of any sort of black holes is not huge either. Jackson and his colleagues calculate it as 0.008.

"There is other evidence to suggest that at least one of the later detections came from a gravitational wave. On 17 August 2017, the orbiting Fermi telescope saw a burst of electromagnetic radiation at the same time as the LIGO and Virgo detectors picked up a signal. Analysis of all the evidence suggests that both signals came from the brutal collision of two neutron stars.

"The double whammy makes LIGO's detection seem unequivocal. Even here, though, the Danish group is dissenting. They point out that the collaboration initially registered the event as a false alarm because it coincided with what's known as a "glitch". The detectors are plagued by these short, inexplicable bursts of noise, sometimes several every hour. They seem to be something to do with the hardware with which the interferometers are built, the suspension wires and seismic isolation devices. Cornish says that LIGO analysts eventually succeeded in removing the glitch and revealing the signal, but Jackson and his collaborators are again unconvinced by the methods used, and the fact there is no way to check them.

"What are we to make of all this? Nothing, apparently. "The Danish analysis is just wrong," insists Cornish. "There were very basic mistakes." Those "mistakes" boil down to decisions about how best to analyse the raw data (see "How to catch a wave").

"Not everyone agrees the Danish choices were wrong. "I think their paper is a good one and it's a shame that some of the LIGO team have been so churlish in response," says Peter Coles, a cosmologist at Maynooth University in Ireland. Mukhanov concurs. "Right now, this is not the Danish group's responsibility. The ball is in LIGO's court," he says. "There are questions that should be answered."

"Brown thinks the Danish group's analysis is wrong, but worth engaging with. And Cornish admits the scrutiny may not be a bad thing. He and his colleagues plan to put out a paper describing the detailed properties of the LIGO noise. "It's the kind of paper we didn't really want to write because it's boring and we've got more exciting things to do." But, he adds, it is important, and increased scrutiny and criticism may in the end be no bad thing. "You do have to understand your noise.'"

Comment: It is good to have battles like this. We shall follow the battle.