81–90 of 108 posts
Earlier quoted context omitted.
I hope to live long enough to see the evolution of interferometers that will be to LIGO as HST was to Galileo's telescope.
I thought LIGO was the HST to Galileo's telescope.
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?
Additional detectors improve our ability to detect somewhat (assuming they're of similar sensitivity -- otherwise they can actually hurt our overall network sensitivity!). But the _real_ advantage is in source localization to guide multi-messenger (optical/gamma/neutrino) followup, which is where many of the most important discoveries will come from. It's like triangulation. Given that an observatory costs on the ord…
Seriously, impressive cutting edge technology!
How do they know it’s black holes colliding and not just large stars?
Extensive computer modeling is used to predict the expected waveforms, and then we fit the observed waveforms to the expected ones.
At least someone explained it like this to me.
Earlier quoted context omitted.
Speaking of which, I can understand how interferometry gets you to, say, 1/1000th of a wavelength, but the wavelength is 1000nm. How do they go from 1nm to 1/10000th the width of a proton? What's the trick? Is it an integral transform thing, like how spectrum analyzers can claim super low noise floors if you sort of gloss over the "noise is proportional to badwidth" part and look in a tiny bandwidth without normalizi…
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,…
[1]: https://www.optica-opn.org/home/newsroom/2019/december/squee...
Obviously, being able to detect amplitudes so small is key to this whole project, as the sources are so distant (and presumably the inverse square law applies).
This makes me wonder how these phenomena would appear much closer to the events - how close would we need to be to perceive with our senses the passing of a gravitational wave, and what would it look like? I'm guessing some kind of passing tidal forces would be felt — has anyone done modeling to figure out what that might be like?
How close and how much amplitude (or would frequency be the killer?) would be required to start damaging ordinary material objects? Is it so close to the source that you're already doomed in the black hole's grip anyway, or would an event at the center of our galaxy be perceptible here? Would the waves rip apart nearby stars (for what value of nearby), or be noticeable in their spectra as some kind of ripple? It'd be cool to get some kind of a sense of the scale of these events' affected zone.
LIGO is a huge milestone. Turning it on is like the moment Galileo pointed his telescope to the moon. This is a new class of instruments observing the universe in a medium that was never utilized before. Using gravitational waves can observe things that cannot be seen before, like stars behind the dust clouds. It opens a new window to the world. We might finally be able to “see” dark matter. May be able to see the gr…
Here's one (negative!) result on trying to detect dark matter with LIGO: https://www.ligo.org/science/Publication-O3DarkPhotons/
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 20 years from now, when it makes an amazing discovery?
Earlier quoted context omitted.
Speaking of which, I can understand how interferometry gets you to, say, 1/1000th of a wavelength, but the wavelength is 1000nm. How do they go from 1nm to 1/10000th the width of a proton? What's the trick? Is it an integral transform thing, like how spectrum analyzers can claim super low noise floors if you sort of gloss over the "noise is proportional to badwidth" part and look in a tiny bandwidth without normalizi…
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,…
Earlier quoted context omitted.
Speaking of which, I can understand how interferometry gets you to, say, 1/1000th of a wavelength, but the wavelength is 1000nm. How do they go from 1nm to 1/10000th the width of a proton? What's the trick? Is it an integral transform thing, like how spectrum analyzers can claim super low noise floors if you sort of gloss over the "noise is proportional to badwidth" part and look in a tiny bandwidth without normalizi…
Great question! The precision is not just better than the wavelength of the light. It's also way smaller than the surface roughness of the mirrors! How does it work?! Like you suggest, and adding to what sleavey mentioned above, I would say the answer is: averaging over time and space. The laser beam is pretty wide, so it averages over a significant area of mirror surface. (The optical system also selects one spatial…