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A comment on Why Doesn’t Gravity Happen Instantly?.

Re:Why Doesn’t Gravity Happen Instantly? by vaidhy on Friday December 18, 2020 @01:52PM (#25470492)
For me, the more amazing thing is that we are able to detect 2 neutron stars merging from 130 million light years away. Just curious how sensitive these instruments need to be and our ability pick signals from the noise.
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Re:Why Doesn’t Gravity Happen Instantly? by magicalhippo on Friday December 18, 2020 @04:06PM (#25472025)
Sensitive enough that the randomness in the photon pressure on the 40kg mirrors is a source of noise they have to contend with[1]:

First, we observe that [quantum radiation pressure noise] contributes to the motion of the kilogram-scale mirrors of LIGO. This observation is also made in the Advanced Virgo GW detector. It is remarkable that quantum vacuum fluctuations can influence the motion of these macroscopic, human-scale objects, and that the effect is measured. This is quantum mechanics at its experimentally most macroscopic scale.

There's some great info in this[2] paper about the detector, sensitivity and performance of Advanced LIGO. And yeah it blows my mind every time I think about it.

[1]: https://arxiv.org/abs/2002.01519

[2]: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.102.0...

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Re:Why Doesn’t Gravity Happen Instantly? by pinko on Friday December 18, 2020 @02:44PM (#25471056)
Sensitive enough to detect a change in the relative length of two 4km-long arms equivalent to less than 1/10,000th the width of a proton.

And we distinguish signals from noise via a few different approaches, but our flagship search relies on matched filtering against simulated waveforms, and requiring the same signal to be coincident in time across multiple, geographically-distant detectors for which very few noise sources are correlated.

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Re:Why Doesn’t Gravity Happen Instantly? by gbh444g on Friday December 18, 2020 @09:09PM (#25474339)
A somewhat unrelated note: the proportion between Earth and Milky Way diameters is (100 trillions) the same as the proportion between a human body and a large atom nucleus. We are galaxy sized objects in some sense.
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