Was LIGO's gravitational wave detection a false signal from noise?

[Ibix]

Yes, but we are also moving at 627 km/s relative to the CMB. So how much would the signal be skewed?

Skewed in what sense? I think that the difference between Earth-centred and FLRW co-moving coordinates on the scales LIGO cares about is just a Lorentz transform, although I could be being overconfident there.

 

[auou]

Skewed in what sense?

That one detector runs into the wave head on and the other sideways.

 

[mfb]

That is just a relative motion of the source and the detectors. It has nothing to do with the CMB. And it is negligible at the current level of sensitivity. Redshift is relevant (~10%).

Again they show just a very small sample, and have probably used templates to get the match for the withened strain, the peaks in the SRN are still very different.

Of course they used templates. That's the analysis method.
The peaks in the SNR are not expected to be the same. The different detectors have different sensitivities and they have different orientations.

You are trying to make up issues that don't exist.

 

[Ibix]

That one detector runs into the wave head on and the other sideways.

Unless there's some reason you can't use standard aberration formulae, failing to distinguish between the Earth-centred inertial frame and the local FLRW co-moving frame will knock your angle estimates off by about 1/500 of a radian, or around a tenth of a degree (so says the back of an envelope).

I find it difficult to imagine people capable of planning on generating gravitational wave solutions for different source types forgetting about the possibility that the sources are in motion.

 

[auou]

It has nothing to do with the CMB.

Of course it has got nothing to do with the CMB itself, but the CMB acts like a reference frame.

The detectors could be moving away or running into the GW, or be hit from the side, skewing the signal. So it all depends on running into the wave at a particular time of day (orientation), a few hours later and we wouldn't notice a thing if the signal is perpendicular.

 

[auou]

I find it difficult to imagine people capable of planning on generating gravitational wave solutions for different source types forgetting about the possibility that the sources are in motion.

Imagine having a flag to define where the wind comes from, now start waving that flag around, and things become a lot more complicated.

 

[Nugatory]

Imagine having a flag to define where the wind comes from, now start waving that flag around, and things become a lot more complicated.

Yes, but is that a good analogy for this observational setup? If the flag were planted on a glacier, you wouldn't worry so much that the glacier's movement might mess up your measurements of wind speed and direction.
So do the calculation. What is an upper bound on the error introduced from the relative motion between different points on the surface of the rotating and orbiting earth? Can this effect be large enough toffee to the validity of the reported results?

 

[auou]

Yes, but is that a good analogy for this observational setup? If the flag were planted on a glacier …

No, it's not perfect. A flag has many 'points' that serve as a reference to define direction etc. LIGO and Virgo combined only 3.

 

[Nugatory]

No, it's not perfect. A flag has many 'points' that serve as a reference to define direction etc. LIGO and Virgo combined only 3.

Yes, so we have an example of why we do science with math instead of analogies.

Until you've quantitatively demonstrated an upper bound on the possible error produced because we only have three points and they are in relative motion you're just speculating idly.

 

[Dr. Courtney]

Yes, so we have an example of why we do science with math instead of analogies.

Until you've quantitatively demonstrated an upper bound on the possible error produced because we only have three points and they are in relative motion you're just speculating idly.

I don't consider that to be how confidence works in science if we apply the maxim that extraordinary claims require extraordinary evidence.

I tend to put the burden of proof that potential sources of error are smaller than their error bars on those publishing or defending extraordinary new experimental claims rather than on skeptics suggesting potential sources of error.

 

[websterling]

rather than on skeptics suggesting potential sources of error.

The problem is that many times the skeptics aren't bound by any burden of proof. Often the skeptic is ill informed (and possibly has their own agenda) and makes disparaging, derisive claims that add nothing and only cast doubt. The baseless claims receive unwarranted attention and must be defended. Much of this discussion seems to follow that model.

 

[Ibix]

I tend to put the burden of proof that potential sources of error are smaller than their error bars on those publishing or defending extraordinary new experimental claims rather than on skeptics suggesting potential sources of error.

True, but one presumes that a skeptic has some kind of response to "why on Earth would you think that's a relevant factor", which is all I think @Nugatory is asking. I don't think that it's unreasonable to ask a skeptic to provide some kind of order-of-magnitude calculation showing that the effect they're worried about is somewhere near a range that might affect the results. I can't even see why a linear speed relative to the CMB frame would be relevant unless the LIGO people were unaware that astronomical bodies move relative to the Earth, which seems slightly unlikely.

 

[auou]

Redshift is relevant (~10%).

Well if Redshift is relevant how much did the GW redshifted over time and loose energy?

For Galaxies moving away we can keep track about what's going on, the Hubble constant, but a GW is just one short single pulse.

Sure, we can know if it comes from one side or the other, 1 dimensional, but we know nothing about the 2nd dimension.

An other issue is how symmetric is the Gravity Wave, two spiralling-colliding objects are not 100% spherical.

Lots of unknowns!

 

[auou]

Often the skeptic is ill informed (and possibly has their own agenda) and makes disparaging, derisive claims that add nothing and only cast doubt.

That's how democracy works, people get to ask questions. The duty of the opposition is to oppose.

 

[PeterDonis]

That's how democracy works

Science is not a democracy.

 

[websterling]

Science is not a democracy.

And regardless of the field, generally the less knowledgeable the opposition, the louder their claims.

 

[Dr. Courtney]

Science is not a democracy.

No, not in the sense of truth or usefulness of scientific findings.

But lots of important projects are FUNDED by the democratic process, so it is wise to take questions and make the most advantage of "teachable moments." Taxpayers who fund these projects often do so not just for the advancement of science, but for the educational opportunities they afford both for students and the public at large. Good public relations means patiently answering a lot of questions that may be products of inadequate science education.

If scientists are not prepared and willing to answer ill-informed questions, we should not complain too loudly next time the funding gets cut. One great lesson I learned at the Air Force Academy is that we're always on parade. Scientists would do well to learn the same lesson.

 

[auou]

Science is not a democracy.

Perhaps not a 'democracy' an sich, but people are allowed to ask questions in contrast to a dictatorship. And isn't it the duty of peers to analyze critically? Otherwise anyone can just publish and claim whatever they want.

If it's not 'democracy' than what is the correct word for this 'interaction' to find the right consensus? I'm not sure if 'scientific method' fits the bill.

 

[PeterDonis]

isn't it the duty of peers to analyze critically?

Yes. But who are "peers"? The proper definition of that term is not "anyone who has a question, no matter how ill-informed". The proper definition is "those who have sufficient understanding of the field to make informed criticisms".

 

[Nugatory]

but people are allowed to ask questions

Of course people are allowed to ask questions. You asked, and your question was answered in posts 89, 91, 93, and 94: "No, we have the mathematical tools to show that the relative motion between the various sites will not introduce the sort of error that you're considering".

What's not allowed is to argue because you don't understand or don't like the answer.

 

[mfb]

Of course it has got nothing to do with the CMB itself, but the CMB acts like a reference frame.

The detectors could be moving away or running into the GW, or be hit from the side, skewing the signal. So it all depends on running into the wave at a particular time of day (orientation), a few hours later and we wouldn't notice a thing if the signal is perpendicular.

The CMB is an arbitrary reference frame without relevance here.
The sensitivity depends a bit on the direction - so what? I can't detect the Sun at night either. Is that an issue? Does that impact my observations of the Sun during the day?

Well if Redshift is relevant how much did the GW redshifted over time and loose energy?

About 10%. Read the paper?

For Galaxies moving away we can keep track about what's going on, the Hubble constant, but a GW is just one short single pulse.

For galaxies we don't rely on long-term observations of their distances either. The length of the measurement is irrelevant (apart from reducing statistical uncertainties).

Sure, we can know if it comes from one side or the other, 1 dimensional, but we know nothing about the 2nd dimension.

What does that even mean?

An other issue is how symmetric is the Gravity Wave, two spiralling-colliding objects are not 100% spherical.

There are no gravity waves. You mean gravitational waves. The emission is not spherically symmetric. So what?

I don't consider that to be how confidence works in science if we apply the maxim that extraordinary claims require extraordinary evidence.

I tend to put the burden of proof that potential sources of error are smaller than their error bars on those publishing or defending extraordinary new experimental claims rather than on skeptics suggesting potential sources of error.

With that argument, you could stop all scientific progress by making up hundreds of nonsense suggestions and then watch the scientists refuting all of them while you simply make up hundreds of new ones.

 

[vanhees71]

Science is not a democracy.

Indeed! Still some politicians don't get the idea that they cannot change the fundamental laws of nature by 2/3 majorities .

 

[Auto-Didact]

Science is not a democracy.

"Science is a democracy, in that every scientist has a voice, but it is nothing like majority rule. Indeed, what ground can I stand on when the majority of my profession embraces a research program I can not accept even though accepting it would be to my benefit? The answer is that democracy is much more than rule by majority. There is a system of ideals that transcends majority rule."

Excerpt from the chapter 'What is Science?' (The Trouble With Physics, Lee Smolin). I highly recommend reading the entire chapter, in it Smolin probably gives the most accurate definition of science given yet opposed to Popper, Kuhn, Lakatos and Feyerabend. In fact, I would probably make this chapter and the following compulsary literature for all science degrees.

 

[websterling]

This paper was placed on the arXiv last month. The authors are researchers at the Perimeter Institute. They used techniques different from those used by both LIGO and the Danish group. They conclude that LIGO observed gravitational waves from black hole mergers, that there is no cross-correlation between noise in the detectors, and that the Danish group's apparent failure to use appropriate window functions casts doubt on their conclusions.

Extraction of black hole coalescence waveforms from noisy data

Abstract: We describe independent analysis of LIGO data for black hole coalescence events. Gravitational wave strain waveforms are extracted directly from the data using a filtering method that exploits the observed or expected time-dependent frequency content. Statistical analysis demonstrates that residual noise, after filtering out spectral peaks, is nearly Gaussian, with no anomalous causal correlation between the Hanford and Livingston sites. The extracted waveforms and time offsets differ only slightly from the published LIGO results. Simulated events, with known signals injected into real noise, are used to determine uncertainties due to residual noise and demonstrate that our results are unbiased. While the extracted waveforms are clearly indicative of black hole coalescence, we find signal-to-noise ratios (SNRs) much smaller than the published matched-filter detection SNRs.

 

[mfb]

I'm not surprised, but it is nice to see that an independent analysis reproduces the results.
Now we have this analysis, we have a binary black hole merger seen by LIGO and Virgo at the same time, and we have the neutron star merger with an optical counterpart. I think the question in the title has an absolutely clear answer.

I wonder what the Danish group will do next...

 

[websterling]

and we have the neutron star merger with an optical counterpart. I think the question in the title has an absolutely clear answer.

One would hope so, but

I wonder what the Danish group will do next...

According to this post from October 20 by 4gravitons (who is now at NBI), A LIGO in the Darkness, they also have problems with the neutron star observation. The last paragraph of the post-

A few posts back, I mentioned a group at NBI who had been critical of LIGO’s data analysis and raised doubts of whether they detected gravitational waves at all. There’s not much I can say about this until they’ve commented publicly, but do keep an eye on the arXiv in the next week or two. Despite the optimistic stance I take in the rest of this post, the impression I get from folks here is that things are far from fully resolved.

The 5th comment to the post, by 4gravitons, is especially problematic-

The short answer is, they think glitches that look like neutron star collisions should be common in LIGO’s data, and they only published that one because the gamma ray telescopes were seeing something. But I don’t really want to say more about this until they’ve published or said something publicly, for one because I don’t know their full argument.

 

[mfb]

Oh come on...
That is basically accusing LIGO of active fraud. And if they do that, they could make their life much easier and claim LIGO didn't even record the published data.

I think I'll just ignore them, that was the healthiest choice the whole time.

 

[websterling]

Back in June when this all started I found this video of a talk given by Jackson- Understanding the LIGO gravitational wave event (GW150914)

Regardless of his/their analysis, from the start of the video he seems to want to plant seeds of doubt and discredit LIGO as much as possible. At times it felt like I was watching a negative political attack ad. Anyone wanting perspective on this whole affair should listen to the talk.