### What did LIGO Actually See? (Gravitational waves discovery)

• I am trying to find an original video/image of what LIGO actually saw, but all I can find is artist renditions of gravitational waves.

As discussed in my answer below, LIGO is more like a microphone than a camera; so it makes more sense to talk about what we heard rather than what we saw. You can listen to the signal here: https://www.youtube.com/watch?v=TWqhUANNFXw

Wouldn't a better metaphor be a _seismometer_?

@user151841 Not really. Seismometers have three output data streams: acceleration in x, y , and z. Also, I think microphones are more intuitively familiar to the non-science public than seismometers. The LIGO detectors are also especially well suited to being compared to a microphone because the sensitive band of the detectors is completely within the range of human hearing.

If we want to get pedantic, technically LIGO's measurement is an actual video with an actual camera. All they do is take continual video feeds of the recombined laser's interference pattern. A lot of mathematical processing is necessary to produce the plots in the answers below. So really that video is what they actually "saw".

surely someone has "remixed" the *audio* in to human-hearable audio? where is that guys? it would be fantastic to listen to it, to get a sense of the attack/decay/length etc. surely this exists? all you'd have to do is modulate it up so many octaves right?

vvrrrooooop ! :) totally awesome. I assumed more of a flrrooowoooo. thanks again!

• The actual image isn't much. I was able to find it from Science, and this is all it is:

It's just a ripple, seen at slightly different times from two different observatories. The shift fits perfectly by shifting it by the speed of light difference in their locations. Thus is the proof of gravity waves.

It should be noted that the reason there are two instruments is to provide a cross check against other vibration sources. Each observatory works by detecting vibrations on a 4 km scale, down to a very small order of magnitude (1/10,000 the width of a proton). When the two are compared, then one can assume the signal must have come from a non-local source, which only Gravity Waves fit that definition.

"The actual image isn't much", "this is all it is." Your tone understates how awesome it actually is IMO ;). Of course, I'm a little bit biased.

How do the two observation locations coordinate their times relative to a shared or common clock? Are they referring to the same atomic clock and making adjustments for "latency", the time it takes to get the time?

They record them at the same time, but due to the speed of the wave, it took 7ms difference in time to recurve the signal.

How do they know they're recording at the same time?

Atomic clock, GPS, or others. There are a lorry of ways to record at that resolution

@TRomano We use GPS which is accurate to 10s of nanoseconds. You can read more about the aLIGO timing system here: http://authors.library.caltech.edu/20471/1/Bartos2010p11577Classical_Quant_Grav.pdf

@ChrisMueller: I suspected it was GPS, but didn't have time to look it up at that moment. Thanks!

Content dated before 7/24/2021 11:53 AM

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