Astrophysicists unveil glut of gravitational-wave detections
1–10 of 108 posts
Re: Astrophysicists unveil glut of gravitational-wave detections
#2Interesting how, even with three LIGO observatories, there is still a 15% false positive rate. How many more observatories are needed to reduce this to a negligible number?
Re: Astrophysicists unveil glut of gravitational-wave detections
#3the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space!
But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned on a microphone and could hear things that were always happening but we could never observe before, and then we turn it off for a little while - the thought that there are events that are going on right now that we will never be able to detect because we arent listening gives me major FOMO.
Re: Astrophysicists unveil glut of gravitational-wave detections
#4the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
Why would you have FOMO? Why is any particular gravitational wave important enough that you'd worry about missing it? I'm not trying to hassle you here, I'm genuinely perplexed by this attitude.
Re: Astrophysicists unveil glut of gravitational-wave detections
#5Interesting how, even with three LIGO observatories, there is still a 15% false positive rate. How many more observatories are needed to reduce this to a negligible number?
LIGO collaboration member here: this is a tunable knob, independent of the number of detectors, that we've set very intentionally based on feedback from astronomers who want to follow up with optical/gamma/neutrino instruments following our BNS detections. We could reduce our false positive rate to a negligible number today, at the cost of _not_ reporting many likely discoveries.
Also, a minor point but there are only two LIGO detectors online at the moment, with a third sister detector in Italy (named Virgo), and a fourth coming online soon in Japan (named KAGRA). There does in fact exist a third LIGO instrument, but it's currently mothballed, awaiting construction in India.
Re: Astrophysicists unveil glut of gravitational-wave detections
#6Interesting how, even with three LIGO observatories, there is still a 15% false positive rate. How many more observatories are needed to reduce this to a negligible number?
LIGO collaboration member here: this is a tunable knob, independent of the number of detectors, that we've set very intentionally based on feedback from astronomers who want to follow up with optical/gamma/neutrino instruments following our BNS detections. We could reduce our false positive rate to a negligible number today, at the cost of _not_ reporting many likely discoveries. Also, a minor point but there are onl…
Do you publish some number about how sure you are?
Re: Astrophysicists unveil glut of gravitational-wave detections
#7the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
LIGO collaboration member here: we focus on maximizing the cumulative number of detections over time, and it turns out that by turning the detector off for a year to upgrade it, we can increase the sensitivity so much that a year after that we will have more total detections than if we had left it running continuous for two years. So you also have to think about all the distant/faint signals we would never be able to detect because we kept listening at too low a sensitivity...
(We do make sure that we have a dramatically less sensitive sister detector in Germany, called GEO, listening whenever we're not so that we'll see something really close and loud, like a galactic supernova, even when LIGO is offline.)
Re: Astrophysicists unveil glut of gravitational-wave detections
#8the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
LIGO collaboration member here: we focus on maximizing the cumulative number of detections over time, and it turns out that by turning the detector off for a year to upgrade it, we can increase the sensitivity so much that a year after that we will have more total detections than if we had left it running continuous for two years. So you also have to think about all the distant/faint signals we would never be able to…
I sincerely love that your reply to FOMO was to point out how his FOMO should be even worse. This is exactly how my brain works when I'm optimizing something: I have to balance one obsession with all the other things I need to obsess about.
Re: Astrophysicists unveil glut of gravitational-wave detections
#9the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
Why would you have FOMO? Why is any particular gravitational wave important enough that you'd worry about missing it? I'm not trying to hassle you here, I'm genuinely perplexed by this attitude.
I used to work in a library and we all had a similar feeling about books. They were all valuable and to be preserved! Objectively, that's not practical. But that base irrational feeling is still useful and important.
Re: Astrophysicists unveil glut of gravitational-wave detections
#10Earlier quoted context omitted.
LIGO collaboration member here: this is a tunable knob, independent of the number of detectors, that we've set very intentionally based on feedback from astronomers who want to follow up with optical/gamma/neutrino instruments following our BNS detections. We could reduce our false positive rate to a negligible number today, at the cost of _not_ reporting many likely discoveries. Also, a minor point but there are onl…
Do you publish some number about how sure you are?
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 signals -- "blind injections" -- into our data, so that we all expected to be regularly seeing them and wouldn't be tempted to gin the analysis to find a detection where there wasn't one. (Amusingly, because of this, it took weeks for many of us to believe the first detection was real, even after the blind injection team swore it wasn't one of theirs. In the end, we charged an independent team to do a forensic analysis of everything from the security cameras and seismometers in the observatories, to every computer and disk the data passed through, to convince ourselves this couldn't possibly have been maliciously injected by hand by a rogue scientist. It was a wild few weeks!)
Now that it's clear gravitational waves exist, however, we focus on optimizing the false alarm rate for astronomers (who want it well above zero so they don't miss anything) rather than optimizing for ~zero false detections.