Hello all and welcome to the topic on Gravitational Wave physics! The idea is to have a space for discussion about gravitational waves, the people working in the field, and ways you all can be part of the effort to make a new kind of astronomy.
The idea is to get some introductions and get to know each other a little more before and after we talk on Tuesday Dec 5th.
I’ll go first: My name is Edgard Bonilla, I grew up in some remote town in Venezuela and have moved quite a bit to get here. Nowadays I am a postdoctoral researcher at Stanford University working to support the mechanical isolation for the LIGO detectors. I wear many (metaphorical) hats: I do theoretical and experimental work and whatever else is needed to ensure the detectors work as intended (electromechanics, cryogenics, earthquake early warning, vacuum hardware, and more). I have a few hobbies, but the memorable three are walking long distances, cooking, and videogames.
Thank you again for such a great and informative presentation! I have a few questions, and if you are able to answer them, I would be most appreciative.
What would the impacts of quantum optics be on LIGO measurements?
What kind of data is returned by these detectors, and how is that data analyzed?
Is the possible existence of graviton disproved by gravitational waves? Is there a framework to tie these two things together?
What would happen if there were two major collisions happening at the same time? Does LIGO have the ability to make these kind of distinctions?
Is the study of the gravitational wave memory effect currently something that LIGO is used for?
The field of Quantum optics already impacts the LIGO measurements in a big way. There is a whole team that works on using squeezed light states to change the state of the vacuum fluctuations on the output of the interferometer so it has lower noise. They even did some filter cavity ‘trickery’ to ‘beat’ the so-called standard quantum limit imposed by Heisenberg’s uncertainty principle. It’s pretty amazing stuff.
The data comes from a photodiode signal at the output of the interferometer. The data needs to be ‘calibrated’ so it can be interpreted as gravitational-wave strain. The calibrated signals are proportional to the motion of the two arms. Here’s an example for how the data looks like 1. Filtering a TimeSeries to detect gravitational waves - GWpy 3.0.7 documentation.
+The calibration is an involved process. But the basic idea is illustrated with this example: there are two ways you can measure something moving, one is by measuring how much it moved, the other is by measuring how much you have to correct its position so it doesn’t move. At LIGO we do a complicated combination of both, which needs to be correctly interpreted from the raw photodiode output.
+To find the ‘interesting’ bits of data, people do many things. One of them is to look for large spikes (like in the link above). Another way is to scan the data to match it with simulated gravitational wave signals, as predicted by numerical relativity calculations (we call these ‘template-based searches’).
No, in the same way that photons cannot be proven/disproven by the observations of electromagnetic waves, gravitons are not proven/disproven by gravitational waves. We have the wave/particle duality of Quantum mechanics to thank for that ambiguity. There are a few frameworks people have postulated for quantum gravity, but yet nothing close to experimental verification, What LIGO can do is to put constraints on some of these theories. As an extreme example, if we see that the speed of gravitational waves is different from the speed of light that would be a huge deal! (this doesn’t seem to be the case so far)
Two collisions happening at the same time would be a great problem to have! . We could probably distinguish them with template-based searches, plus the fact that they will arrive at the two detectors at different times from different regions of space.
Gravitational Wave memory effect! Wow I just learned something new. LIGO is not the best instrument to observe static motion/offsets of masses, it is more suited for high-frequency motion. One could believe that with enough data there might be something to be said, but I’m sure the systematic errors from noise sources will be hard to beat.
Thank you for such a detailed reply! It is all very clear and interesting. Thank you for providing the link to GWpy documentation, as well. I do have one clarification question. When you said that you compare the data to simulated gravitational wave signals, as predicted by numerical relativity calculations, do you mean that researchers have complied a list of astrological situations and done calculations to determine what they would look like if measured by LIGO?
That is correct! There are giant template banks with how the signals from gravitational waves might look like. You can find some information on them by searching for ‘gravitational wave template banks’. Sadly, I don’t know what’s the most up to date database, or even if it is public access, but you can find a few pictures on the internet. Maybe GWpy has access to a few of the templates, it would be a matter of searching.
Wow, that’s super interesting! From what I can see, there are a bunch of papers about it, but I have yet to find a database unfortunately. It looks like it’s a pretty complicated and time consuming task. Very cool, though! Thank you for the response.
. We could probably distinguish them with template-based searches, plus the fact that they will arrive at the two detectors at different times from different regions of space.