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Astrophysicists unveil glut of gravitational-wave detections

nature.com

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Re: Astrophysicists unveil glut of gravitational-wave detections

#91

Post by mr_sturd »

2bitencryption wrote: post #88

question: according to Wikipedia, LIGO was built between 1994-2002, and didn't detect gravitational waves until 2016. I never heard about LIGO until the discovery in 2016, so for almost 20 years it was off my radar, so to speak. What multi-decade experiments are being created today, which will be ready to produce amazing results in 20-30 years? What's currently under construction, but I'll never hear about it until 2…

My head instantly went to fusion experiments[0]. There are planned experiments in that space which, if they go ahead, won't produce results until the 2040s.

[0] - https://en.m.wikipedia.org/wiki/List_of_fusion_experiments

Re: Astrophysicists unveil glut of gravitational-wave detections

#92

Post by ww520 »

2bitencryption wrote: post #88

question: according to Wikipedia, LIGO was built between 1994-2002, and didn't detect gravitational waves until 2016. I never heard about LIGO until the discovery in 2016, so for almost 20 years it was off my radar, so to speak. What multi-decade experiments are being created today, which will be ready to produce amazing results in 20-30 years? What's currently under construction, but I'll never hear about it until 2…

From the talk by the Caltech professor leading LIGO, the theory was good on paper but the engineering problems were very tough. The platform to make measurement has to be absolutely still. But the Earth always has some movements due to seismic activities. For years they just couldn't get the passive vibration isolation tech stable enough for the measurement to work. The project was almost canceled. Finally they went back to the drawing board and partnered with some companies to build new active vibration isolation technologies. It took years to get it working.

Their active vibration isolation technology is insanely good. It basically detects tiny seismic movement of the Earth far away and actively compensates the stable platform. This is one instance of scientific project spawning off new technologies, which will have many other uses in the future.

Re: Astrophysicists unveil glut of gravitational-wave detections

#93

Post by aardvark179 »

baq wrote: post #80
foo92691 wrote: post #65

Earlier quoted context omitted.

So far all of the signals observed by LIGO are from sources that we expected would exist. The most exciting thing would be to observe an unexpected signal.

did you model how an alcubierre drive would look like on the waveform? (only half joking ;))

The original solution field equation is for a constant speed drive, which I believe does not emit any gravitational waves. I’m not sure how much work has been done on the formation of the bubble and what effects that would produce, or indeed how a ship could change its heading, which are events that I think should produce gravity waves.

Re: Astrophysicists unveil glut of gravitational-wave detections

#94

Post by PhantomGremlin »

dekhn wrote: post #31
pinko wrote: post #10

Earlier quoted context omitted.

Yes, we carefully explain the statistical confidence of our detections in each discovery paper, and there are dozens of methods papers that go into excruciating detail on those techniques. Prior to our first detection, the overwhelming prime directive of our collaboration was _not to make a false detection_ and we went to insane lengths to avoid one; e.g., we had a small team of people secretly injecting false signal…

Has LIGO ever responded to Sabine Hossenfelder's claims? http://backreaction.blogspot.com/2019/09/whats-up-with-ligo....

I have a basic problem with Sabine's claims. In a response comment she says: "No signal analysis can confirm that the signal was of astrophysical origin."

I know nothing about the actual hardware. But I can reasonably speculate that LIGO can afford to have local atomic clocks. So they can timestamp their observations to nanosecond precision.

Given the finite speed of light, the candidate astrophysical events are necessarily detected many milliseconds apart. There can only be two ways these potential events would correlate:

1) there are so many many possible false positives constantly happening that there is some reasonable probability of this correlation occurring by chance.

or 2) a highly sophisticated "goof" or fraud. Someone could presumably set up some local source near each detector and spoof a signal. E.g. carefully "wiggle" large masses, each only a few km away from each detector.

So, if it's not astrophysical, can Sabine tell us which it is? False positive? Goof?

Re: Astrophysicists unveil glut of gravitational-wave detections

#95

Post by jasonwatkinspdx »

im3w1l wrote: post #15
pinko wrote: post #10

Earlier quoted context omitted.

Yes, we carefully explain the statistical confidence of our detections in each discovery paper, and there are dozens of methods papers that go into excruciating detail on those techniques. Prior to our first detection, the overwhelming prime directive of our collaboration was _not to make a false detection_ and we went to insane lengths to avoid one; e.g., we had a small team of people secretly injecting false signal…

That sounds hilarious, but you must be quite unique in having this approach right? Or are the particule physics people playing similar games?

Not quite the same lengths, but AIRC LHC uses two detectors with substantial design differences, and partitions the teams from sharing information for some of what they target, as a way to reduce systemic errors.

Re: Astrophysicists unveil glut of gravitational-wave detections

#96

Post by hinkley »

mabbo wrote: post #20

The article mentions the new KAGRA detector in Japan joining the group. Does anyone know: how does the accuracy improve as more detectors come online? Will we see a day where we have 20, 50, 100 detectors around the globe and events are near-certain because so many detectors see them? Or is the diminishing returns, and 4 detectors is already too many?

When we have five or more detectors, will we be able to ‘see’ features of the earth’s interior using the discrepancies in the data?

Re: Astrophysicists unveil glut of gravitational-wave detections

#97

Post by mycall »

magicalhippo wrote: post #84
sleavey wrote: post #76

Earlier quoted context omitted.

Cavities. We trade off bandwidth for peak sensitivity by sending the same light back and forth between mirrors in the arms of the interferometer hundreds of times. As the gravitational wave passes, the same light samples it over and over and picks up additional phase shift, enhancing the signal. The downside is that we can't see gravitational waves at signals far above the cavity pole frequencies at a few 10s of kHz,…

In addition they've been using squeezed light[1] since 2019 to help increase the sensitivity. [1]: https://www.optica-opn.org/home/newsroom/2019/december/squee...

I wonder if twisting light is similar to this (now useful in fiber optics) or if this would be another dimension to explore.

Re: Astrophysicists unveil glut of gravitational-wave detections

#98

Post by jiggawatts »

mrfusion wrote: post #19

Could we be seeing warp drive signatures?

A simple "energy budget" analysis would immediately reveal that current detectors have no hope of detecting any artificial gravity wave sources.

What they're picking up now is events with titanic energies, things like black holes merging and neutron stars colliding.

These are many, many of orders of magnitude more energetic than even supernovae!

Re: Astrophysicists unveil glut of gravitational-wave detections

#99

Post by hinkley »

foo92691 wrote: post #58
SavantIdiot wrote: post #52

Do gravitational wave interferometers create a single pixel of data, or do they create an "image" of gravitational distortion in a 2D region? The first few Google/Wiki hits talk about the physics of interferometry, but not the actual resulting output from real hardware. I'm assuming there is no image, otherwise there would be some associated with the articles, rather than artistic renditions?

You can think of each individual detector producing a single-channel audio signal. By combining the signals from multiple detectors it's possible to determine where the signal is coming from. But the output is neither a picture nor a single pixel: it's a brief blip of a few seconds of audio-frequency time series. A decent analogy is to think of each LIGO detector not as a camera but a microphone.

There are devices that are arrays of microphones that can be used to detect what direction a noise comes from. The Army uses one to triangulate rifle fire, and Boeing started using one circa the 787 to locate cabin noises (planes have a sound insulation budget, and positively identifying the ingress points allows for better ambient noise levels).
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