Lecture Questions - Day 1 (2023)

Questions for the Day 1 lectures (May 15, 2023) can be posted here


Can you please turn on the transcripts/subtitles for the Zoom meeting ?

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Do earthquakes cause strain in the x and y lengths?

Hi @rahul_e,

Yes, Earthquakes cause the motion of our apparatus and they introduce noise in our detectors. In fact, one of the most difficult tasks for us to isolate the detectors from the Earth’s motion, or the so-called “seismic noise”. The seismic noise is the motivation for which our sensitivities at lower frequency gravitational waves (<20 Hz) is not soo good.


Can you please tell me more about Quantum squeezing? If possible, please share refs or links to learn more about them. What is squeezing in general?

Is there any info available about the materials used to build the lasers and the detector?

I suggest you to start from here Squeezing quantum noise | Physics Today | AIP Publishing


Why are those vacuum tube so long?

What are the novel research topics recently in focus using this data?

Gravitational waves cause a very small variation of lenght of the arms. Having a 4km laser arm, forgetting all optics inside, permits to reduce this relative strenght (delta_L/L).

@niraj, that’s a very good question! Since gravitational-wave signal amplitude is very small it will create a very small change in the arm-lengths of the laser interferometers. So, you need a long vacuum tube (arm-length) to be able to measure the change in the in the arm-length when gravitational waves pass through it. I hope that answers your question!

Hi @Medha23, there are a lot of topics spanning from experimental development up to astrophysics. This book contains many chapters describing all these topics. If you don’t have access to the book with your university, you can search for the chapters’ titles on the arxiv.

Hi @Medha23, really really short summary about astrophysical topics. Gravitational wave (GW) data allow to perform many tasks, sometimes very different among them. First of all, GW gives many informations on the observed objects (up to now, black holes and binary neutron stars) which can be combined with other observations as well (electromagnetic etc., as it was for GW170817 [1710.05832] GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral) ; moreover, GW are a new channel to test General Relativity and many other things: for instance, GW allow to measure the Hubble constant https://iopscience.iop.org/article/10.3847/1538-4357/abdcb7 independently with respect to the way it has been estimated up to now

What is the difference between the (O3a & O3b) and O3GK data release ?

@niraj So for a given strain h = delta L / L, the larger the L is, the greater the delta_L will be, and hence easier for us to measure. Although the arm lengths of LIGO detectors is 4kms, their effective length is even higher than this (around 1800 Kms) as photons bounce back and forth several times in the two arms before combining.

Hello Eric et al., What is the data policy release for O4? Would public data be accessible through GWOSC right after the events or is there a waiting period to gather the entire O4a ? In addition, will we have publicly available data that didn’t lead to a GW events (in order to check if something is hidden inside the data :wink: ) ? Thank you again for this great overview !

@Anushka, O3a are the first 6 months of the LIGO, Virgo runs. O3b the second 6 months. While O3GK a run done by the GEO and KAGRA detectors.

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You can go through the paper if you are interested: [0903.0338] Physics, Astrophysics and Cosmology with Gravitational Waves

What determines the sampling rate? ARe 4kHz and 16 kHz arbitrary/ what’s the reason for these specific values?

Hi @Anushka , while O3a / O3b refers to the data taken by the LIGO-Virgo detectors, O3GK refers to the data taken by GEO and KAGRA detectors, which sensitivity was considerably lower than the other detectors and so their data has been considered separately; KAGRA is planned to join LIGO-Virgo detectors in O4, GEO is more kind of (very important) technology and development laboratory

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