Thanks, glad you enjoyed it. Definitely agree on the sound. "h values" in this video is referring to gravitational wave "strain", and is unitless. We usually think about it as dL/L, where L is some length, and dL is how that length changes with the GW passing through. r and tau can in general be complex numbers (and they are complex for real mirrors). In this video all mirrors are considered simple thin mirrors, and so reflection and transmission are real in this case. I had to balance the length of the video with more explanation (and honestly this video went a lot longer than intended). If you're an undergrad apply to our LIGO SURF: labcit.ligo.caltech.edu/LIGO_web/students/SURF/

1) The three mirrors on the left form the input mode cleaner cavity. It's purpose is to stabilize the laser light before being input into the main interferometer. Without it, most of the input laser light would be rejected by the main interferometer, because it would not be stable enough to enter. 2) This is true, a GW modulates both space and time. The short answer to your question is the interferometer truly acts as a *timer*, since we are always firing lasers off in two directions, and measuring how long it takes for that laser to come back. If there is a difference in that time, we will detect it as a phase shift in the laser light, since the phase shift produces real light at the antisymmetric port. Maybe I can do an animation of this concept later.

@@craigcahillane1063 thanks

​@@craigcahillane1063 waitibg for new videos on this topic, Im phd students and I need more videos of you in topic.

Good question!

To answer you question, it needs a better understanding of GR that I do: you need to know the difference between local coordinates and proper distance, and how a GW can let local coordinates invariant while affecting proper distances. Look for this article (should be in open access): "The basics of gravitational wave theory", by Anna Flanagan and Scott A Hughes, sept 2005 in "New Journal of Physics", Volume 7, 2005. It's explained page 15 and 16.

From the photos it looks like LIGO has suspended their mirrors in a motion-dampening device. Still seems like there is a lot of noise relative to the size of the signal they are looking for.

manim

Mostly because the gravitational-wave signal has a very distinct signature. According to numerical relativity simulations, we expect the gravitational-wave emission to increase in frequency and amplitude, producing a chirp effect that increases from very low frequency to around 100 Hz or so (depending on the black hole masses). An earthquake is certaintly detected, but looks more like a low frequency rumbling that shakes the detectors around. A bird strike would look like an impulse with some slow decay, same as a lightening strike. Our black hole merger signals actually *increase* in frequency and amplitude, until they merger with a huge energy emission in GWs, then the final black hole wobbles as it decays to it's smooth final form. If we could hear it, the GW signal would probably sound something like this: kzfaq.info/get/bejne/q81ila50rJrLio0.html Also, we have two detectors that are a thousand miles apart, and if they see the same chirping signal within a couple of milliseconds we can be really, really sure it came from an astrophysical source.

Because they would say it if they would do it.

@@ThomasKundera It all depends who are "they".

@@peterkiedron8949 : "they" are the scientists operating the system. I doubt anybody else could do anyway.

I agree with your two first results. However, I got dP_trans/dh=2.76*10^5Watt/strain and h(dP_trans/dh)=2.76*10^(-16) Watt. Hope it helps!

They didn't what? Please don't say 'detect gravitation waves'